Targeted dendrimer conjugates

Abstract

Provided herein are targeted dendrimer conjugates comprising a topoisomerase inhibitor. Also provided herein are pharmaceutical compositions comprising the conjugates, and therapeutic methods and uses using the conjugates, particularly in relation to cancer therapy.

Description

[0001] TARGETED DENDRIMER CONJUGATES Field The present disclosure generally relates to targeted dendrimer conjugates comprising a topoisomerase inhibitor. The disclosure also relates to pharmaceutical compositions comprising the 5 conjugates, and to therapeutic methods and uses using the conjugates, particularly in relation to cancer therapy. Background According to the World Health Organization (WHO), cancer is the leading cause of death worldwide, 10 being responsible for nearly 10 million deaths in 2020, which equates to approximately one in six deaths globally. Despite many decades of research efforts and the delivery of a range of therapies and diagnostics to aid in the treatment and care of cancer patients, the WHO predict over 35 million new cancer cases by 2050, an increase of 77% from the estimated 20 million cases in 2022. Oncology agents are an important class of pharmaceuticals, and there have been significant advances 15 in the treatment of cancer in recent decades. Various approaches to cancer therapy have been investigated, including small molecule therapeutics, antibody therapies, and antibody-drug conjugates (ADCs). However, a number of oncology agents are associated with severe side effects due to their cytotoxic properties, providing a narrow therapeutic window, and limiting the dosage regimen that can be used and potentially also limiting the efficacy of the treatment. Further, while advances have been made in surgical, 20 chemotherapy, radiotherapy, and biological therapy for the treatment of a range of cancers, the incidence of cancer is still increasing. Ongoing challenges to the development of improved safe and efficacious oncology therapies include effective delivery of the therapeutic to the site of the tumour, potency of therapeutic agents, duration of activity, side effects and toxicity, development of anti-cancer drug resistance, patient compliance, and early 25 detection. Developments in oncology therapies are technically extremely difficult, costly and time consuming. One class of oncology drugs are topoisomerase inhibitors. For example, camptothecin and structurally related compounds such as SN-38, irinotecan and exatecan are topoisomerase 1 inhibitors. An example of an approved topoisomerase inhibitor therapy is trastuzumab deruxtecan (Enhertu®), which 30 contains the monoclonal HER2-selective antibody trastuzumab conjugated to exatecan. Enhertu® is approved for the therapy of breast cancer or gastric or gastroesophageal adenocarcinoma. However, there are also side effects associated with Enhertu® therapy, such as nausea, vomiting, decreased appetite, neutrophilia and diarrhea. More serious side effects include left ventricular dysfunction, embryo-fetal toxicity, and interstitial lung disease / pneumonitis, with cases resulting in death having been reported. 35 Looking at other topoisomerase inhibitors, a known issue with SN-38 is that, whilst the compound has high topoisomerase 1 inhibitory activity, formulation is hampered by poor aqueous solubility, and

[0002] 1 20778549_1 (GHMatters) P122809.PCT clinical use would be limited by high toxicity and rapid clearance. Irinotecan is a prodrug, containing a dipiperidylcarbamate group at the C-10 position, and when used in vivo, irinotecan is metabolised in the liver and plasma to release the active compound SN-38. Irinotecan has been approved for clinical use as a therapy for treatment of several cancers. Irinotecan has shown activity in leukemia, lymphoma, colorectal, 5 lung, ovarian, cervical, pancreatic, stomach, and breast cancers. However, irinotecan still has rapid clearance and significant side effects, most notably gastrointestinal toxicities, causing diarrhoea, vomiting, abdominal pain, anorexia, and haematological toxicities such as neutropenia, leukopenia, and thrombocytopenia. Marketed irinotecan carries a black box warning for diarrhoea and myelosuppression. In addition, irinotecan is metabolised in the liver to the active metabolite SN-38 by carboxylesterases, and 10 then glucuronidated to the inactive SN-38G, however, the conversion and enzyme activity is highly variable amongst patients. Research has also been carried out into identifying improved formulations of irinotecan, in order to further address some of the shortcomings of that active agent. For example, Onivyde® is an injectable liposomal irinotecan product containing liposomes of approximately 110nm diameter dispersed in a 15 formulation buffer, which is critical to control lipid degradation. This liposomal formulation also carries a black box warning for neutropenia and severe diarrhoea. Many solubilisation strategies have also been applied to attempt to overcome these issues. For example, conjugation to polyethylene glycol) by Nektar (NKTR-102) (which failed its phase 3 study in metastatic breast cancer), Enzon (EZN2208) and Prolynx (PL038) (PEG) provides a relatively aqueous- 20 soluble conjugate. Another approach is the use of small micelles or liposomes such as NK-012 (Nippon Kayaku), SN2310 emulsion (Oncogenex), and Irinophore (Champions Oncology), with and without conjugation to a lipophilic carrier. Other approaches have been SN-38 triblock co-polymers (Mahidol University, Thailand), a DSPC / cholesterol nanoparticle, Hyaluranon- Irinotecan (Alchemia, failed its phase 3 study in colorectal 25 cancer), CRLXIOI, a cyclodextrin-conjugated CPT-11 (Cerulean) and poly-1- hydroxymethylethylene hydroxymethyl-formaI XMT1001 (Mersana) which failed in multiple phase 2 studies. These approaches have largely been unsuccessful in the clinic due to lack of efficacy or grade 3 and 4 neutropenia. PAMAM-SN-38 dendrimers have been studied in vitro for oral delivery (Goldberg et al, J Control Release, 2011, 150(3), p318-325). England et al (J Control Release, 2017, 247, p73-85) generated 30 dendrimers conjugated via random sites on the dendrimer to the C10- position of SN-38, and only with about 8% drug loading. Fox et al (Mol. Pharm., 2009, 6(5), pi 562- 1572) describe irinotecan conjugated via carboxylate on glycine or alanine to an aspartic or glutamic acid surface dendrimer with 4-6% irinotecan loading. WO2020 / 102852 also describes dendrimers comprising SN38 moieties attached to the dendrimer 35 periphery using a diglycolic acid or thiodiacetic acid linker.

[0003] 2 20778549_1 (GHMatters) P122809.PCT There remains a need for alternative and / or improved oncology therapies which provide effective therapeutic effects, preferably over a prolonged period of time, with low levels of side effects and good therapeutic window. 5 Summary The present inventors have now identified certain HER2-targeted dendrimer conjugates containing topoisomerase inhibitors, specifically DXd or SN-38, which are particularly effective for the therapy of cancers, and provide therapeutic effects over an extended period of time. Example conjugates according to the present disclosure provide efficacy profiles in xenograft studies which are comparable with or, in 10 some cases, better than the marketed product Enhertu®. Accordingly, in a first aspect, there is provided a dendrimer-targeting agent conjugate, or a pharmaceutically acceptable salt thereof, the conjugate comprising: a) a dendrimer comprising i) a core unit; and 15 ii) building units; wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is covalently attached to at least two building units; b) a topoisomerase inhibitor which is attached through a linker to an outer building unit of the dendrimer, the linker having the formula 20 wherein S is a spacer group; and Cl is an enzymatically cleavable group comprising a peptide having at least 2 amino acid residues; c) pharmacokinetic-modifying moieties which are attached to outer building units, the pharmacokinetic-modifying moieties comprising a hydrophilic polymer; and 25 d) a HER2 targeting agent which is attached through a connector to the core unit of the dendrimer. In some embodiments, the topoisomerase inhibitor is DXd, optionally wherein the DXd is attached via an oxygen atom as shown below

[0004] 3 20778549_1 (GHMatters) P122809.PCT . In some embodiments, the topoisomerase inhibitor is SN-38, optionally wherein the SN-38 is attached via an oxygen atom as shown below: 5 In some embodiments, the hydrophilic polymer group is a polyethylene glycol (PEG), polyethyloxazoline (PEOX), poly-(2)-methyl-(2)-oxazolamine (POZ), polysarcosine or a poly (2- hydroxypropyl)methacrylamide polymer, optionally a polyethylene glycol (PEG) polymer. In some embodiments, the hydrophilic polymer group is a polyethylene glycol (PEG) polymer having an average molecular weight in the range of from 750 to 1500 Da. 10 In some embodiments, the core unit comprises at least 3 nitrogen atoms, with at least one nitrogen atom being for attachment of a spacer group, and at least two nitrogen atoms being for attachment of building units. In some embodiments, the core unit is . 15 In some embodiments, the building units are lysine residues or analogues thereof having two nitrogen atoms and one acyl group, optionally wherein the building units are lysine residues. In some embodiments, the building units are . In some embodiments, the dendrimer has 2 or 3 generations of building units.

[0005] 4 20778549_1 (GHMatters) P122809.PCT In some embodiments, the HER2 targeting agent is selected from the group consisting of an antibody, an antigen-binding fragment thereof, a fusion protein, and an antibody mimetic. In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) 5 comprises the amino acid sequence set out in SEQ ID NO: 1, CDR-H2 comprises the amino acid sequence set out in SEQ ID NO: 2, CDR-H3 comprises the amino acid sequence set out in SEQ ID NO: 3, CDR light chain 1 (CDR-L1) comprises the amino acid sequence set out in SEQ ID NO: 4, CDR-L2 comprises the amino acid sequence set out in SEQ ID NO: 5, and CDR-L3 comprises the amino acid sequence set out in SEQ ID NO: 6. 10 In some embodiments, the HER2 targeting agent is a single domain antibody, optionally a VHHcomprising three complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence set out in SEQ ID NO: 42, CDR-H2 comprises the amino acid sequence set out in SEQ ID NO: 43, and CDR-H3 comprises the amino acid sequence set out in SEQ ID NO: 44. In some embodiments, the connector comprises a polyethylene glycol moiety having an average 15 molecular weight in the range of from 100 to 1500 Da, optionally wherein the connector group comprises 2 polyethylene glycol moieties. In some embodiments, the connector comprises a cyclic moiety, and wherein the connector group is formable from first and second connector precursors; the first connector precursor comprising the dendrimer, a part-connector group, and a first cyclisable group; and the second connector precursor 20 comprising the HER2 targeting agent, a further part-connector group, and a second cyclisable group which is capable of reaction with the first cyclisable group, to form the cyclic moiety. In some embodiments, the cyclic moiety is . In some embodiments, the connector is 25

[0006] 5 20778549_1 (GHMatters) P122809.PCT , wherein m is an integer of from 3 to 30, and n is an integer of from 20 to 30. In some embodiments, Cl is a cathepsin-cleavable group. In some embodiments, Cl comprises a Val-Cit group, or a Gly-Gly-Phe-Gly group. 5 In some embodiments, Cl is In some embodiments, S is 10 . 3 to 20. In some embodiments, the linker is

[0007] 6 20778549_1 (GHMatters) P122809.PCT , , 5 wherein p is an integer of from 2 to 20, and q is an integer of from 3 to 20. In some embodiments, the conjugate is one of the example conjugates. In another aspect there is provided a pharmaceutical composition, comprising a conjugate or salt as defined herein; and a pharmaceutically acceptable excipient. In another aspect, there is provided a conjugate or salt as defined herein, or a pharmaceutical 10 composition as defined herein, for use in therapy. In another aspect, there is provided a conjugate or salt as defined herein, or a pharmaceutical composition as defined herein, for use in the treatment of cancer. In another aspect, there is provided a method of treating cancer in a subject, comprising administering an effective amount of a conjugate or salt as defined herein, or of a pharmaceutical composition as defined 15 herein, to the subject. In another aspect, there is provided use of a conjugate or salt as defined herein for the manufacture of a medicament for the treatment of cancer.

[0008] 7 20778549_1 (GHMatters) P122809.PCT In some embodiments, the cancer is selected from the group consisting of ovarian cancer, breast cancer, non-small cell lung cancer, stomach cancer, gastric or gastroesophageal junction adenocarcinoma and uterine cancer. In some embodiments, the cancer is a HER2-positive cancer. 5 Brief Description of the Drawings Figures 1A-1L show Surface Plasmon Resonance sensorgrams showing results of experiments to determine binding kinetics of example anti-HER2 conjugates of the disclosure. Figure 2 shows A) a graph of tumour volume versus days since first dose for mice containing SKOV- 10 3 tumour xenografts who were administered either vehicle, a control dendrimer lacking a HER2 targeting group, Enhertu®, or an example conjugate; and B) Kaplan-Meier plots showing probability of survival against time for the different treatment groups in the mouse SKOV-3 xenograft study. Figure 3 shows A) a graph of tumour volume versus days since first dose for mice containing JIMT- 1 xenografts who were administered either vehicle, control dendrimers, Enhertu®, or an example conjugate; 15 and B) a graph of change in mouse body weight over time for the different treatment groups in the mouse JIMT-1 xenograft study. Detailed Description Definitions 20 Unless specifically defined otherwise, all technical and scientific terms used herein shall be taken to have the same meaning as commonly understood by one of ordinary skill in the art (e.g. chemistry, medicinal chemistry, polymer chemistry, and the like). The present disclosure refers to the contents of certain documents being incorporated herein by reference. In the event of any inconsistent teaching between the teaching of the present disclosure and the 25 contents of those documents, the teaching of the present disclosure takes precedence. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure. As used herein, the term “and / or”, e.g., “X and / or Y” shall be understood to mean either "X and Y" 30 or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning. As used herein, the term “about”, unless stated to the contrary, refers to + / - 20%, more preferably + / - 10%, of the designated value. For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as 35 ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite

[0009] 8 20778549_1 (GHMatters) P122809.PCT a range not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the subranges 1 to 4, 1.5 to 4.5, 1 to 2, among other subranges. As another example, the recitation of the numerical ranges 1 to 5, such as 2 to 4, includes the subranges 1 to 4 and 2 to 5, among other subranges. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. For example, the recitation of the numerical range 1 to 5 includes the numbers 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, among other numbers. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited. Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. As used herein, the terms "a", "an" and "the" include both singular and plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth. Unless otherwise indicated, terms such as "first," "second," etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower- numbered item (e.g., a “first” item) and / or a higher-numbered item (e.g., a “third” item). As used herein, the word “comprise” and other forms of the word, such as “comprising” and “comprises,” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the disclosure. The disclosure also includes all of the steps, features, compositions, layers and components thereof referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features. Each embodiment of the present disclosure described herein is to be applied mutatis mutandis to each and every other embodiment unless specifically stated otherwise or required otherwise by context. As used herein, “Ca to Cb” or “Ca-b” in which “a” and “b” are integers refer to the number of carbon atoms in the specified group. That is, the group can contain from “a” to “b”, inclusive, carbon atoms. Thus, for example, a “C1 to C4 alkyl”, or “C1-4-alkyl” group includes alkyl groups having from 1 to 4 carbons, e.g. CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CH-, CH3CH2CH2CH2-, CH3CH2CH(CH3)- and (CH3)3C-. As used herein, the term “alkyl” refers to a straight or branched hydrocarbon chain that is fully saturated (i.e., contains no double or triple bonds). The alkyl group may for example have from 1 to 20 carbon atoms (whenever it appears herein, a numerical range such as “1 to 20” refers to each integer in the given range; e.g., “1 to 20 carbon atoms” means that the alkyl group may consist of 1 carbon atom, 2 carbon

[0010] 9 20778549_1 (GHMatters) P122809.PCT atoms, 3 carbon atoms, etc., up to and including 20 carbon atoms, although the present definition also covers the occurrence of the term “alkyl” where no numerical range is designated). The alkyl group may for example be a medium size alkyl having 1 to 9 carbon atoms. The alkyl group could also be a lower alkyl having 1 to 4 carbon atoms. The alkyl group of the compounds may be designated as “C1-4-alkyl” or similar designations. By way of example only, “C1-4-alkyl” indicates that there are one to four carbon atoms in the alkyl chain, i.e., the alkyl chain is selected from the group consisting of methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, and t-butyl. Typical alkyl groups include, but are in no way limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl, hexyl, and the like. Where specified, an alkyl group may be optionally substituted by one or more optional substituents as herein defined. As used herein, the term “alkenyl” refers to an unsaturated linear or branched hydrocarbon, having for example from 2 to 20 carbon atoms and having at least one double bond. Where appropriate, the alkenyl group may have a specified number of carbon atoms, for example, C2-C6alkenyl which includes alkenyl groups having 2, 3, 4, 5 or 6 carbon atoms in linear or branched arrangements. Non-limiting examples of alkenyl groups include, ethenyl, propenyl, isopropenyl, butenyl, s- and t-butenyl, hex-1,3 -diene, non-1,3,5- triene and the like. As used herein, the term “alkynyl” refers to an unsaturated linear or branched hydrocarbon, having for example from 2 to 20 carbon atoms, having at least one triple bond. Where appropriate, the alkynyl group may have a specified number of carbon atoms, for example, C2-C6 alkynyl which includes alkynyl groups having 2, 3, 4, 5 or 6 carbon atoms in linear or branched arrangements. Non-limiting examples include ethynyl, propynyl, butynyl, pentynyl and hexynyl. As used herein, the term “alkylene” refers to a divalent straight-chain (i.e. linear) or branched saturated hydrocarbon group. In one example, an alkylene group contains from 2 to 10 carbon atoms ((i.e. C2-10 alkylene). In one example, an alkylene group contains from 2 to 6 carbon atoms (i.e. C2-6 alkylene). Examples of alkylene groups include, for example, -CH2CH2-, -CH2CH2CH2-, -CH2CH(CH3)-, - CH2CH2CH2CH2-, -CH2CH(CH3)CH2-, and the like. As used herein, the terms “halo” or “halogen,” mean, in the context of the compounds defined herein, a fluorine, chlorine, bromine, or iodine atom, unless otherwise dictated by context. Additionally, terms such as “haloalkyl” may include monohaloalkyl and polyhaloalkyl. For example, the term “halo-C1-C4- alkyl” may include, but is not limited to, fluoromethyl, difluoromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 4-chlorobutyl, 3-bromopropyl, 1-fluoro-2-bromoethyl, and the like. As used herein, the term “carbocyclyl” or “carbocyclic” means a cyclic ring or ring system containing only carbon atoms in the ring system backbone. When the carbocyclyl is a ring system, two or more rings may be joined together in a fused, bridged or spiro-connected fashion. Carbocyclyls may have any degree of saturation. Thus, carbocyclyls include cycloalkyls, cycloalkenyls, cycloalkynyls, and carbocyclic aromatic groups. The carbocyclyl group may have 3 to 20 carbon atoms, although the present definition also covers the occurrence of the term “carbocyclyl” where no numerical range is designated. The

[0011] 10 20778549_1 (GHMatters) P122809.PCT carbocyclyl group may also be a medium size carbocyclyl having 3 to 10 carbon atoms or 3 to 6 carbon atoms. The carbocyclyl group may be designated as “C5-10 carbocyclyl or 5-10-membered carbocyclic group” or similar designations. Examples of carbocyclyl rings include, but are not limited to, cyclohexyl, cyclohexenyl, 2,3-dihydro-indene, bicycle[2.2.2]octanyl, adamantyl, and spiro[4.4]nonanyl, phenyl and naphthyl. As used herein, the term “aliphatic carbocyclic” or ‘aliphatic carbocycle” means any of a non- aromatic monocyclic, bicyclic and polycyclic, (including fused, bridged or conjugated) hydrocarbon ring system, e.g. C3-20(such as C3-10or C3-8). The ring or rings may be saturated, for example cycloalkyl, or may possess one or more double bonds (cycloalkenyl) and / or one or more triple bonds (cycloalkynyl). Examples of aliphatic carbocyclic groups are monocyclic 5-6-membered or bicyclic 9-10 membered ring systems. Suitable examples include cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cyclopentenyl, cyclohexenyl, cyclooctenyl, cyclopentadienyl, cyclohexadienyl, cyclooctatetraenyl and decalinyl. Where indicated, a carbocyclyl group may be optionally substituted by one or more optional substituents as herein defined. As used herein, the term “aromatic carbocyclic”, “aromatic carbocycle”, “aromatic” or “aryl” means an aromatic ring system containing only carbon atoms in the ring backbone. Typically, an aromatic group has from 5 to 18 carbon atoms, or from 5 to 10 carbon atoms. The aromatic group may for example be designated as “C5-10 aromatic”. Examples of aromatic groups include, but are not limited to, phenyl and naphthyl. As used herein, the term “heterocyclic” means an aromatic or non-aromatic ring system containing 3 or more ring atoms, that contain(s) one or more heteroatoms, that is, an element other than carbon, such as N, O and / or S, in the ring backbone. The remaining ring atoms are typically carbon atoms. In some embodiments, a heterocyclic group contains 1, 2, or 3 heteroatoms. A heterocyclic ring can for example be a heterocycloalkyl ring or can for example be a heterocyclic aromatic (also known as heteroaryl) group, or if polycyclic, any combination thereof. In some embodiments, a heterocyclic group has from 5 to 20 ring atoms. The number of carbon atoms plus the number of heteroatoms sums up to equal the total number of ring atoms. A heterocyclic ring can also include one or more double bonds, e.g. it may be a heterocycloalkenyl group. The phrase “heterocyclic group” includes fused ring species including those comprising fused aromatic and non-aromatic groups. For example, a dioxolanyl ring and a benzdioxolanyl ring system (methylenedioxyphenyl ring system) are both heterocyclic groups within the meaning herein. The phrase also includes polycyclic ring systems containing a heteroatom such as, but not limited to, quinuclidyl. Heterocyclic groups include, but are not limited to, pyrrolidinyl, piperidinyl, homopiperidinyl, piperazinyl, homo piperazinyl, morpholinyl, homomorpholinyl, pyrrolyl, pyrazolyl, triazolyl, tetrazolyl, oxazolyl, isoxazolyl, thiazolyl, pyridinyl, thiophenyl, benzothiophenyl, benzofuranyl, dihydrobenzofuranyl, indolyl, dihydroindolyl, azaindolyl, indazolyl, benzimidazolyl, azabenzimidazolyl, benzoxazolyl, benzothiazolyl, benzothiadiazolyl, imidazopyridinyl, isoxazolopyridinyl, thianaphthalenyl,

[0012] 11 20778549_1 (GHMatters) P122809.PCT purinyl, xanthinyl, adeninyl, guaninyl, quinolinyl, isoquinolinyl, tetrahydroquinolinyl, quinoxalinyl, and quinazolinyl groups. As used herein, the term “heteroaryl”, “heteroaromatic” or “aromatic heterocycle” means an aromatic ring system that contain(s) one or more heteroatoms, that is, an element other than carbon, such as N, O 5 and / or S, in the ring backbone. The remaining ring atoms are typically carbon atoms. The heteroaromatic group may for example have 5-18 ring members (i.e. the number of atoms making up the ring backbone, including carbon atoms and heteroatoms). In some embodiments, the heteroaromatic group has from 5 to 10 ring atoms or from 5 to 7 ring atoms. A heteroaromatic group may for example be designated as “5-7 membered heteroaryl,” “5-10 membered heterocycle,” or similar designations. Examples of heteroaromatic 10 rings include, but are not limited to, furyl, thienyl, phthalazinyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl, pyrazolyl, isoxazolyl, isothiazolyl, triazolyl, thiadiazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, thiophenyl, benzothiophenyl, quinolinyl, isoquinolinyl, benzimidazolyl, benzoxazolyl, benzothiazolyl, indolyl, isoindolyl, and benzothienyl. As used herein, the term “optionally substituted” unless otherwise specified means that a group may 15 be unsubstituted or substituted by one or more (e.g., 0, 1, 2, 3, 4, or 5 or more) substituents. In an embodiment, an optionally substituted group has 1 substituent. In another embodiment an optionally substituted group has 2 substituents. In another embodiment, an optionally substituted group has 3 substituents. In another embodiment, an optionally substituted group has 4 substituents. In another embodiment, an optionally substituted group has 5 substituents. 20 It is to be understood that certain radical naming conventions can include either a mono-radical or a di-radical, depending on the context. For example, where a substituent requires two points of attachment to the rest of the molecule, it is understood that the substituent is a di-radical. For example, a substituent identified as alkyl that requires two points of attachment includes di-radicals such as –CH2–, –CH2CH2–, – CH2CH(CH3)CH2–, and the like. Other radical naming conventions clearly indicate that the radical is a di- 25 radical such as “alkylene”. Where the conjugates disclosed herein have at least one chiral center, they may exist as individual enantiomers and diastereomers or as mixtures of such isomers, including racemates. Other forms of isomerism include double bond isomerism in which compounds containing a carbon-carbon double bond may exist as Z or E isomers, conformational isomerism, and atropisomerism. Unless otherwise indicated, 30 all such isomers and mixtures thereof are included in the scope of the compounds disclosed herein. Separation of individual isomers or selective synthesis of individual isomers is accomplished by application of various methods which are known to practitioners in the art. Dendrimer-Targeting Agent Conjugates 35 In a first aspect, there is provided a dendrimer-targeting agent conjugate, or a pharmaceutically acceptable salt thereof, the conjugate comprising:

[0013] 12 20778549_1 (GHMatters) P122809.PCT a) a dendrimer comprising i) a core unit; and ii) building units; wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is 5 covalently attached to at least two building units; b) a topoisomerase inhibitor which is attached through a linker to an outer building unit of the dendrimer, the linker having the formula wherein S is a spacer group; and Cl is an enzymatically cleavable group comprising a peptide 10 having at least 2 amino acid residues; c) pharmacokinetic-modifying moieties which are attached to outer building units, the pharmacokinetic-modifying moieties comprising a hydrophilic polymer; and d) a HER2 targeting agent which is attached through a connector to the core unit of the dendrimer. 15 Dendrimer The conjugates of the disclosure comprise a dendrimer comprising i) a core unit; and ii) building units. Core Unit 20 The core unit of the dendrimer provides an attachment point for at least two building units, and for the targeting agent which is attached through a connector. Any suitable core unit which contains functional groups that can form suitable covalent linkages may be utilised. In some embodiments, the core unit is covalently attached to 2, 3 or 4 building units. In some embodiments, the core unit is covalently attached to 2 building units. 25 In some embodiments, the core unit is derivable from a precursor having three reactive groups, for example using a suitable protecting group strategy. For example, two of the reactive groups may be used for attachment of building units, and one may be used for attachment of a targeting agent via a connector. In some embodiments, the core unit is derivable from a precursor having four reactive groups, for example using a suitable protecting group strategy. For example, three of the reactive groups may be used 30 for attachment of building units, and one may be used for attachment of a targeting agent via a connector. The core unit may for example be formed from a core unit precursor comprising amino groups. As another example, the core unit may be formed from a core unit precursor comprising carboxylic acid groups.

[0014] 13 20778549_1 (GHMatters) P122809.PCT In some embodiments, the core unit comprises at least three nitrogen atoms, with at least one nitrogen atom being for attachment of a connector, and at least two nitrogen atoms being for attachment of building units. In some embodiments, the core unit is covalently attached to at least two building units via amide 5 linkages. In some embodiments, each amide linkage is formed between a nitrogen atom present in the core unit and the carbon atom of an acyl group present in a building unit. In other embodiments, each amide linkage is formed between the carbon atom of an acyl group present in the core unit and a nitrogen atom present in a building unit. In some embodiments, the core unit is covalently attached to the connector group via an amide 10 linkage. In some embodiments, the amide linkage is formed between a nitrogen atom present in the core unit and the carbon atom of an acyl group present in a connector precursor. In other embodiments, the amide linkage is formed between the carbon atom of an acyl group present in the core unit and a nitrogen atom present in a connector precursor. In some embodiments, the core unit has the formula: 15 wherein Alk1 and Alk2 are groups, e.g. groups. In some embodiments, the core unit is: . With such core units, by use of a suitable protecting group strategy, the terminal nitrogens may be 20 functionalised with different groups from the central nitrogen, e.g. building units may be attached to the terminal nitrogens, and the central nitrogen functionalised with a connector. In some embodiments, the core unit is any suitable core unit used in the examples. Building Units 25 Any suitable building unit (BU) may be used to produce the dendrimers in the conjugates, as long as it contains a first functional group which is capable of forming a linkage with a functional group present on another building unit or a core unit, and contains at least two further functional groups which (e.g. following deprotection, if a protecting group strategy is used during synthesis) are capable of forming a linkage with a functional group present on another building unit. 30 In some preferred embodiments, building units of different generations are covalently attached to one another via amide linkages formed between a nitrogen atom present in one building unit and the carbon atom of an acyl group present in another building unit. For example, in some embodiments, the building

[0015] 14 20778549_1 (GHMatters) P122809.PCT units are lysine residues or analogues thereof, and may be formed from suitable building unit precursors, e.g. lysine or lysine analogues containing appropriate protecting groups. Lysine analogues have two amino nitrogen atoms, e.g. for bonding to a subsequent generation of building units, and an acyl group, e.g. for bonding to a previous generation of building units or a core. Examples of suitable building units include: 5 group a to the core or to a previous generation building unit; and wherein each nitrogen atom provides a covalent attachment point which may be used for covalent attachment to a subsequent generation building unit, or 10 to one of the groups comprising either a topoisomerase inhibitor or a pharmacokinetic-modifying moiety. In some preferred embodiments, the building units are: . In some preferred embodiments, the building units are: . 15 In some other embodiments, the building units are aspartic acid residues, glutamic acid residues or analogues thereof, i.e. formed from suitable precursors e.g. aspartic acid, glutamic acid or analogues thereof, containing suitable protecting groups. In such embodiments, the core unit may be formed from a core unit precursor comprising carboxylic acid groups (i.e. which can react with amino groups present in the aspartic acid / glutamic acid / analogues). 20 The outer generation of building units may be formed for example by building units as used in the other generations of building units as described above, for example lysine or lysine analogue building units. The outer generation of building units is the generation of building units that is furthest from the core of the dendrimer, i.e., no further generations of building units are attached. It will be appreciated that the dendrons of the dendrimer may for example be synthesised to the 25 required number of generations through the attachment of building units accordingly. In some embodiments each generation of building units may be formed of the same building unit, for example all of the

[0016] 15 20778549_1 (GHMatters) P122809.PCT generations of building units may be lysine building units. In some other embodiments, one or more generations of building units may be formed of different building units to other generations of building units. The dendrimer has from two to four generations of building units, i.e.2, 3 or 4 generations of building 5 units. In some embodiments, the dendrimer has 2 generations of building units. In some embodiments, the dendrimer has 3 generations of building units. In some embodiments, the dendrimer has two generations of building units. For example in the case where the building units are lysines, the dendrimer may comprise the substructure: . 10 In some embodiments, the dendrimer has three generations of building units. For example in the case where the building units are lysines, the dendrimer may comprise the substructure: . In some embodiments, the generations of building units are complete generations. For example, where the dendrimer has three generations of building units, in some embodiments the dendrimer has three 15 complete generations of building units. With a core unit having two reactive amine groups, such a dendrimer will comprise 14 building units (i.e. core unit + 2 BU + 4 BU + 8 BU). Similarly, for example, where the dendrimer has two generations of building units, in some embodiments the dendrimer has two complete generations of building units. With a core having two reactive amine groups, such a dendrimer will comprise 6 building units (i.e. core unit + 2 BU + 4 BU).

[0017] 16 20778549_1 (GHMatters) P122809.PCT However, it will be appreciated that, due to the nature of the synthetic process for producing the dendrimers, one or more reactions carried out to produce the dendrimers may not go fully to completion. Accordingly, in some embodiments, the dendrimer may comprise incomplete generations of building units. For example, a population of dendrimers may be obtained, in which the dendrimers have a distribution of numbers of building units per dendrimer. In some embodiments, where the dendrimer has three generations of building units, a population of dendrimers is obtained which has a mean number of building units per dendrimer of at least 8, or at least 9, or at least 10, or at least 11, or at least 12, or at least 13. In some embodiments, a population of dendrimers is obtained in which at least 60%, at least 70%, at least 80%, at least 90% or at least 95% of the dendrimers have 10 or more building units. In some embodiments, a population of dendrimers is obtained in which at least 60%, at least 70%, at least 80%, at least 90% or at least 95% of the dendrimers have 12 or more building units. In some embodiments, where the dendrimer has four generations of building units, a population of dendrimers is obtained which has a mean number of building units per dendrimer of at least 25, or at least 26, or at least 27, or at least 28, or at least 29. In some embodiments, a population of dendrimers is obtained in which at least 60%, at least 70%, at least 80%, at least 90% or at least 95% of the dendrimers have 25 or more building units. In some embodiments, a population of dendrimers is obtained in which at least 60%, at least 70%, at least 80%, at least 90% or at least 95% of the dendrimers have 29 or more building units. In some embodiments, each generation of building units in each dendron (X) may be represented by the formula [BU]2(b-1), wherein b is the generation number. A dendron (X) having three complete generations of building units may be represented as [BU]1-[BU]2-[BU]4. A dendron (X) having four complete generations of building units may be represented as [BU]1-[BU]2-[BU]4-[BU]8. In some embodiments, the dendrimer portion of the conjugate may have the building units represented solely by the number of building units in the outer generation of building units. For example, a dendrimer having two dendrons and three generations of building units may be characterised using the following nomenclature [BU]8, since the outer generation will contain 8 building units (and the subsurface layer will contain 4 building units, and the inner layer will contain 2 building units). Similarly, a dendron having two dendrons and four generations of building units may be characterised using the following nomenclature [BU]16. In some embodiments, dendrons are the same. In some embodiments, the dendrons are different. In some embodiments, the building units are any of the building units used in the examples. Topoisomerase Inhibitor The conjugate of the present disclosure comprises a topoisomerase inhibitor which is attached through a linker to an outer building unit of the dendrimer.

[0018] 17 20778549_1 (GHMatters) P122809.PCT Topoisomerase inhibitors are substances that block the action of topoisomerases, which can be divided into two subtypes, topoisomerase I and topoisomerase II. In some embodiments, the topoisomerase inhibitor is a topoisomerase I inhibitor. In some embodiments, the topoisomerase inhibitor is a camptothecin active. Camptothecin is a 5 topoisomerase 1 inhibitor having the structure: A family of structurally-related compounds also having topoisomerase inhibitory activity has also been identified. Examples of camptothecin actives (the residue of which may form part of the first terminal group) include SN-38, irinotecan (CPT-11), topotecan, silatecan, cositecan, exatecan, DXd, lurtotecan, 10 gimatecan, belotecan and rubitecan. In some embodiments, a camptothecin active is a compound having the substructure: In some embodiments, the topoisomerase inhibitor comprises a hydroxyl group, and the topoisomerase inhibitor is attached via an oxygen atom. 15 In some embodiments, the topoisomerase inhibitor is DXd. DXd has the structure: . In some embodiments, the topoisomerase inhibitor is D w herein the DXd is attached via an oxygen atom as shown below:

[0019] 18 20778549_1 (GHMatters) P122809.PCT . In some embodiments, the topoisomerase inhibitor is exatecan. Exatecan has the structure: . In some embodiments, the topoisomerase inhibitor is SN-38. SN-38 has the structure: 5 . In some embodiments, the topoisomerase inhibitor is SN-38, wherein the SN-38 is attached via an oxygen atom as shown below: . In some embodiments, the topoisomerase inhibitor is SN-38, wherein the SN-38 is attached via an 10 oxygen atom as shown below:

[0020] 19 20778549_1 (GHMatters) P122809.PCT . In some embodiments, the topoisomerase inhibitor is any of the topoisomerase inhibitors present in the examples. Whilst in some embodiments the conjugate has only a single topoisomerase inhibitor, more 5 commonly the conjugate will comprise multiple topoisomerase inhibitors. The number of topoisomerase inhibitors present in the conjugate will depend on various factors, including the number of generations of building units and the number of available sites on outer building units. In some embodiments, the conjugate has 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, 13, or 14, or 15, or 16 topoisomerase inhibitors. Providing multiple topoisomerase inhibitors on the dendrimer surface attached through a linker 10 comprising a spacer group and an enzymatically cleavable group, facilitates the provision of a particularly therapeutically effective conjugate, wherein a high concentration of topoisomerase inhibitor can be delivered to the site of interest within the body. Linker 15 The conjugate comprises a topoisomerase inhibitor which is attached through a linker to an outer building unit of the dendrimer, the linker having the formula wherein S is a spacer group; and Cl is an enzymatically cleavable group comprising a peptide having at least 2 amino acid residues . 20 Typically, group S is attached to the core unit of the dendrimer, and group Cl is attached to the topoisomerase inhibitor. Where the conjugate comprises multiple topoisomerase inhibitors, in some embodiments the conjugate also comprises multiple linkers, for example one for each topoisomerase inhibitor. 25 Spacer Group The linker comprise a spacer group S. The spacer group serves to connect the topoisomerase inhibitor to the outer building unit, and to space it therefrom, facilitating tailoring of properties. The In some embodiments, the spacer group comprises a backbone having a length in the range of from 4 to 65 atoms.

[0021] 20 20778549_1 (GHMatters) P122809.PCT In some embodiments, the spacer group comprises a backbone having a length in the range of from 4 to 10 atoms, or from 4 to 6 atoms, or 5 atoms. In some embodiments, the spacer group comprises a backbone having a length in the range of from 20 to 40 atoms, or from 25 to 37 atoms, or 31 atoms. 5 Examples of suitable backbones include alkylene and PEG groups. Where an alkylene group is used, it may be substituted or optionally substituted, for example with substituents such as C1-4alkyl groups, or C1-4alkoxy groups. In some embodiments, S is: , wherein p is an integer of from 2 to 20. In some embodiments, p is an integer of 10 from 2 to 10, or from 2 to 5. In some embodiments, p is 3. In some embodiments, S is: , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. In some embodiments, the spacer group is any of the spacer groups used in the examples. 15 Enzymatically cleavable group The linker comprises group Cl, an enzymatically-cleavable group comprising a peptide having at least 2 amino acid residues. In some embodiments, Cl is a group which is cleavable by a lysosomal protease. In some 20 embodiments, Cl is a group which is cleavable by a cathepsin. Enzymatically cleavable groups include, but are not limited to, peptide linkers such as those containing Val-Cit, Val-Ala, or Phe-Lys groups. Peptide linkers, and their peptide bonds, are advantageously expected to have good serum stability, as lysosomal proteolytic enzymes have very low activities in blood. Val-Cit, Val-Ala and Phe-Lys linkers are rapidly hydrolysed by cathepsin B. 25 In some embodiments, Cl is a cathepsin-cleavable group. In some embodiments, Cl is a cathepsin B-cleavable group. In some embodiments, Cl comprises a Val-Cit group. In some embodiments, Cl comprises a Val-Ala group. In some embodiments, Cl comprises a paraaminobenzyl-containing group (PAB), e.g.:

[0022] 21 20778549_1 (GHMatters) P122809.PCT . In some embodiments, Cl is a valine-citrulline-paraaminobenzyl-containing group (Val-Cit-PAB), e.g. having the structure: . 5 For example, the PAB group may be covalently attached to an amine group present on a topoisomerase inhibitor via the carbonyl group, forming a carbamate linkage. In some embodiments Cl is a valine-alanine-paraaminobenzyl-containing group (Val-Ala-PAB), e.g. having the structure: 10 In some embodiments, Cl comprises a pyrrolidine-containing group, e.g.: In some embodiments, Cl is

[0023] 22 20778549_1 (GHMatters) P122809.PCT

[0024] . In some embodiments, Cl is Further examples of enzymatically-cleavable groups include Gly-Gly-Phe-Gly (SEQ ID NO 56): 5 motifs. Linkers containing a Gly-Gly-Phe-Gly motif may undergo degradation in the lysozyme. In some embodiments, Cl comprises a glycine-glycine-phenylalanine-glycine group (Gly-Gly-Phe- Gly), e.g. having the structure: . In some embodiments, Cl comprises a methylene group. 10 In some embodiments, Cl is: . For example, the methylene group in the above structure may be covalently attached to an oxygen atom present on a topoisomerase inhibitor. In such embodiments, where the cleavable group is attached to the topoisomerase inhibitor via an 15 oxygen atom, degradation of the Gly-Gly-Phe-Gly group may result in release of a species containing the

[0025] 23 20778549_1 (GHMatters) P122809.PCT chemotherapeutic agent and a hemi-aminal, which is self-immolative, and generates the topoisomerase inhibitor containing a hydroxyl group. In some embodiments, the enzymatically-cleavable group is any of the enzymatically-cleavable groups used in the examples. 5 In some embodiments, the linker has the structure: , wherein p is an integer of from 2 to 20. In some embodiments, p is an integer of from 2 to 10, or from 2 to 5. In some embodiments, p is 3. In some embodiments, the linker has the structure: 10 , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. In some embodiments, the linker has the structure: 15 , wherein p is an integer of from 2 to 20. In some embodiments, p is an integer of from 2 to 10, or from 2 to 5. In some embodiments, p is 3. In some embodiments, the linker has the structure:

[0026] 24 20778549_1 (GHMatters) P122809.PCT , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. In some embodiments, the linker is any of the linkers used in the examples. 5 In some embodiments, the group comprising the topoisomerase inhibitor and the linker is , wherein p is an integer of from 2 to 20. In some embodiments, p is an integer of from 2 to 10, or from 2 to 5. In some embodiments, p is 3. In some embodiments, the group comprising the topoisomerase inhibitor and the linker is 10 , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. In some embodiments, the group comprising the topoisomerase inhibitor and the linker is

[0027] 25 20778549_1 (GHMatters) P122809.PCT

[0028] , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. In some embodiments, the group comprising the topoisomerase inhibitor and the linker is 5 , wherein q is an integer of from 3 to 20. In some embodiments, q is an integer of from 5 to 15, or from 7 to 11. In some embodiments, q is 9. Pharmacokinetic-Modifying Moieties 10 The conjugates comprise pharmacokinetic-modifying moieties which are attached to outer building units. A pharmacokinetic-modifying moiety is a moiety that can modify or modulate the pharmacokinetic profile of the conjugate. The pharmacokinetic modifying moiety may modulate the absorption, distribution, metabolism, excretion and / or toxicity of the conjugate. The pharmacokinetic modifying moiety (T2) may change the solubility profile. The pharmacokinetic modifying moiety (T2) may for example reduce 15 clearance of the conjugate. The pharmacokinetic-modifying moiety may for example comprise an oligomeric or polymeric group, e.g. which is hydrophilic, biocompatible and / or water-soluble. In some embodiments, the pharmacokinetic-modifying moiety is a water-soluble oligomer or polymer having a molecular weight in the range of from 300 to 5000 Daltons. 20 In some embodiments, the pharmacokinetic-modifying moiety comprises a hydrophilic polymeric group.

[0029] 26 20778549_1 (GHMatters) P122809.PCT In some embodiments, the term “hydrophilic polymeric group” refers to a polymeric group that has a solubility in water at 25 °C of at least 5 mg / ml, or at least 10 mg / ml, or at least 25 mg / ml, more preferably at least 50 mg / ml, and still more preferably at least 100 mg / ml. In some embodiments, the pharmacokinetic-modifying moiety comprises a polyethylene glycol (PEG) group, or a polyethyloxazoline (PEOX) group, or a poly-(2) methyl-(2)-oxazolamine (POZ), or a polysarcosine (poly (n-methylated glycine)), or a poly(2-hydroxypropyl)methacrylamide (pHPMA) group. In some embodiments, the hydrophilic polymer group is a polyethylene glycol (PEG) polymer. In some embodiments, the pharmacokinetic-modifying moiety comprises a PEG group. A PEG group is a polyethylene glycol group, i.e. a group comprising repeat units of the formula -CH2CH2O-. PEG materials used to produce the dendrimer of the present disclosure typically contain a mixture of PEGs having some variance in molecular weight (i.e., ± 10%), and therefore, where a molecular weight is specified, it is typically an approximation of the average molecular weight of the PEG composition. For example, the term “PEG~2100” refers to polyethylene glycol having an average molecular weight of approximately 2100 Daltons, i.e. ± approximately 10% (PEG1890 to PEG2310). The term “PEG~2300” refers to polyethylene glycol having an average molecular weight of approximately 2300 Daltons, i.e. ± approximately 10% (PEG2070to PEG2530). Three methods are commonly used to calculate MW averages: number average, weight average, and z-average molecular weights. As used herein, the phrase "molecular weight" is intended to refer to the weight-average molecular weight which can be measured using techniques well-known in the art including, but not limited to, NMR, mass spectrometry, matrix-assisted laser desorption ionization time of flight (MALDI-TOF), gel permeation chromatography or other liquid chromatography techniques, light scattering techniques, ultracentrifugation and viscometry. In some embodiments, the pharmacokinetic-modifying moieties comprise PEG groups having an average molecular weight of between about 200 and 5000 Daltons, or from 200 to 4000 Daltons, or from 300 to 3000 Daltons, or from 300 to 2000 Daltons, or from 400 to 1500 Daltons, or from 400 to 1200 Daltons, or from 400 to 1000 Daltons, or from 400 to 800 Daltons, or from 400 to 600 Daltons. In some embodiments, the hydrophilic polymer group is a polyethylene glycol (PEG) polymer having an average molecular weight in the range of from 750 to 1500 Da. In some embodiments, the pharmacokinetic-modifying moieties comprise PEG groups having an average molecular weight of about 400, about 450, about 500, about 550, about 600, about 650, about 700, about 750, about 800, about 900, about 1000, about 1100, about 1200, about 1300, about 1400 or about 1500 Daltons. In some embodiments, the PEG group has a polydispersity index (PDI) of between about 1.00 and about 1.50, between about 1.00 and about 1.25, or between about 1.00 and about 1.10. In some embodiments, the PEG group has a polydispersity index (PDI) of about 1.05. The term “polydispersity index” refers to a measure of the distribution of molecular mass in a given polymer sample. The

[0030] 27 20778549_1 (GHMatters) P122809.PCT polydispersity index (PDI) is equal to the weight average molecular weight (Mw) divided by the number average molecular weight (Mn) and indicates the distribution of individual molecular masses in a batch of polymers. The polydispersity index (PDI) has a value equal to or greater than one, but as the polymer approaches uniform change length and average molecular weight, the polydispersity index (PDI) will be 5 closer to one. Where the pharmacokinetic-modifying moieties comprise PEG groups, the PEG groups may be linear or branched. If desired, an end-capped PEG group may be used. In some embodiments, the PEG group is a methoxy-terminated PEG. In some embodiments, the pharmacokinetic-modifying moieties comprise polysarcosine groups, 10 i.e. a group comprising repeat units of the formula . In some embodiments, the pharmacokinetic-modifying moieties comprise polysarcosine groups having an average molecular weight of at least 750 Daltons, at least 1000 Daltons, or at least 1500 Daltons. In some embodiments, pharmacokinetic-modifying moieties comprise polysarcosine groups having an 15 average molecular weight in the range of from 750 Daltons to 2500 Daltons, or from 1000 Daltons to 2500 Daltons. In some embodiments, the pharmacokinetic-modifying moieties comprise PEOX groups. A PEOX group is a polyethyloxazoline group, i.e. a group comprising repeat units of the formula . 20 PEOX groups are so named since they can be produced by polymerisation of ethyloxazoline. PEOX materials used to produce the dendrimer of the present disclosure typically contain a mixture of PEOXs having some variance in molecular weight (i.e., ± 10%), and therefore, where a molecular weight is specified, it is typically an approximation of the average molecular weight of the PEOX composition. In some embodiments, the pharmacokinetic-modifying moieties comprise PEOX groups having an average 25 molecular weight of at least 750 Daltons, at least 1000 Daltons, or at least 1500 Daltons. In some embodiments, the pharmacokinetic-modifying moieties comprise PEOX groups having an average molecular weight in the range of from 750 Daltons to 2500 Daltons, or from 1000 Daltons to 2000 Daltons. If desired, an end-capped PEOX group may be used. In some embodiments, the PEOX group is a methoxy- terminated PEOX. 30 The pharmacokinetic-modifying moieties may for example be attached via use of a precursor which contains a reactive group that is reactive with an amine group, such as a reactive acyl group (which can

[0031] 28 20778549_1 (GHMatters) P122809.PCT form an amide bond), or an aldehyde (which can form an amine group under reductive amination conditions). In some embodiments, the pharmacokinetic-modifying moieties each comprise a PEG group covalently attached to a PEG linking group (L1) via an ether linkage formed between a carbon atom present 5 in the PEG group and an oxygen atom present in the PEG linking group, and each pharmacokinetic- modifying moiety is covalently attached to a building unit via an amide linkage formed between a nitrogen atom present in a building unit and the carbon atom of an acyl group present in the PEG linking group. In some embodiments, the pharmacokinetic-modifying moieties are each and wherein the PEG group is a methoxy-terminated PEG having an average molecular weight in the range of 10 from about 500 to 3000 Daltons, or from 2000 to 2700 Daltons, or from 750 to 1500 Daltons. HER2 Targeting Agent The conjugates comprise a HER2 targeting agent, i.e. the targeting agent is capable of binding to human epidermal growth factor receptor 2 (HER2, also known as ERBB2; Gene ID No .2064, NCBI).The 15 HER2 / ERBB2 receptor is over-expressed in some forms of cancer, and targeting that receptor blocks signals that stimulate cancer cell growth. The HER2 targeting agents described herein are useful for targeting of the disclosed dendrimer conjugates to tumors and cancer cells. The targeting agent is for localisation and concentration of the conjugate at the site or target of interest in the body. Targeting agents include antibodies, fusion proteins, antibody fragments, antibody 20 mimetics, peptide sequences, small molecules, and other motifs capable of selective binding to the target of interest. The interaction may occur through any type of bonding or association including, for example, covalent, ionic bonding, hydrogen bonding, and Van der Waals forces. As used herein, the term “binds” or “binding” in reference to the interaction of a targeting agent 25 (e.g. protein or an antigen binding domain thereof) with an antigen means that the interaction is dependent upon the presence of a particular structure (e.g., an antigenic determinant or epitope) on the antigen. For example, an antibody recognizes and binds to a specific protein structure rather than to proteins generally. If an antibody binds to epitope “A”, the presence of a molecule containing epitope “A” (or free, unlabeled “A”), in a reaction containing labeled “A” and the antibody, will reduce the amount of labeled “A” bound 30 to the antibody. As used herein, the term “specifically binds”, “binds specifically”, or similar phrases shall be taken to mean a protein of the disclosure reacts or associates more frequently, more rapidly, with greater duration and / or with greater affinity with a particular antigen (e.g. HER2) or cell expressing same than it does with alternative antigens or cells. For example, a protein that specifically binds to an antigen binds that antigen

[0032] 29 20778549_1 (GHMatters) P122809.PCT with greater affinity (e.g., 20 fold, or 40 fold, or 60 fold, or 80 fold, or 100 fold, or 150 fold, or 200 fold greater affinity), avidity, more readily, and / or with greater duration than it binds to other antigens. It is also understood by reading this definition that, for example, a protein that specifically binds to a first antigen may or may not specifically bind to a second antigen. As such “specific binding” does not necessarily require exclusive binding or non-detectable binding of another antigen, this is meant by the term “selective binding”. As used herein, “peptidic” refers to a molecule comprising two or more amino acids linked by peptide bonds. The targeting agents as described herein are useful for targeting the dendrimer-targeting agent conjugate to a desired target, such as tumours, cancer cells, and / or the tumour microenvironment. Any desired number of targeting agents may be readily incorporated into the conjugate in a controlled manner by use of the targeting agent presentation group. In some embodiments, the conjugate has a single (i.e.1) targeting agent. In some other embodiments, the conjugate contains multiple targeting agents, for example 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, or 13, or 14, or 15, or 16 targeting agents. In some embodiments, the HER2 targeting agent is selected from the group consisting of an antibody, an antigen-binding fragment thereof, a fusion protein, and an antibody mimetic. In some embodiments, the targeting agent is an antibody. For the purposes of the present disclosure, the term “antibody” includes four chain protein comprising e.g., two light chains and two heavy chains including recombinant or modified antibodies (e.g., chimeric antibodies, humanized antibodies, primatized antibodies, de-immunized antibodies and half antibodies, bispecific antibodies) capable of specifically binding to one or a few closely related antigens by virtue of a Fv. An antibody generally comprises constant domains, which can be arranged into a constant region or constant fragment or fragment crystallizable (Fc). Exemplary forms of antibodies comprise a four-chain structure as their basic unit. Full-length antibodies comprise two heavy chains (~50-70 kDa) covalently linked and two light chains (~23 kDa each). A light chain generally comprises a variable region and a constant domain and in mammals is either a κ light chain or a λ light chain. A heavy chain generally comprises a variable region and one or two constant domain(s) linked by a hinge region to additional constant domain(s). Heavy chains of mammals are of one of the following types α, δ, ε, γ, or μ. Each light chain is also covalently linked to one of the heavy chains. For example, the two heavy chains and the heavy and light chains are held together by inter-chain disulfide bonds and by non-covalent interactions. The number of inter-chain disulfide bonds can vary among different types of antibodies. Each chain has an N- terminal variable region (VH or VL wherein each are ~110 amino acids in length) and one or more constant domains at the C- terminus. The constant domain of the light chain (CL which is ~110 amino acids in length) is aligned with and disulfide bonded to the first constant domain of the heavy chain (CH which is -330-440

[0033] 30 20778549_1 (GHMatters) P122809.PCT amino acids in length). The light chain variable region is aligned with the variable region of the heavy chain. The antibody heavy chain can comprise 2 or more additional CH domains (such as, CH2, CH3 and the like) and can comprise a hinge region between the CH1 and CH2 constant domains. Antibodies can be of any type (e.g., IgG, IgE, IgM, IgD, IgA, and IgY), class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2) or subclass. In some embodiments, the antibody is a human antibody or a deimmunized or germlined version thereof, or an affinity matured version thereof. The terms "full-length antibody," or "whole antibody" are used interchangeably to refer to an antibody in its substantially intact form, as opposed to an antigen binding fragment of an antibody. Specifically, whole antibodies include those with heavy and light chains including a constant region. The constant region may be wild-type sequence constant regions (e.g., human wild-type sequence constant regions) or amino acid sequence variants thereof. As used herein, the term “variable region" refers to the portions of the light and / or heavy chains of an antibody as defined herein that is capable of specifically binding to an antigen and includes amino acid sequences of complementary determining regions “CDRs”; i.e., CDRl, CDR2, and CDR3, and framework regions “FRs”. FR are those variable region residues other than the CDR residues. For example, the variable region comprises three or four FRs (e.g., FR1, FR2, FR3 and optionally FR4) together with three CDRs. VH refers to the variable region of the heavy chain. VL refers to the variable region of the light chain. As used herein, the term “complementarity determining regions” (syn. CDRs; i.e., CDRl, CDR2, and CDR3) refers to the amino acid residues of an antibody variable region the presence of which are major contributors to specific antigen binding. Each variable region typically has three CDR regions identified as CDRl, CDR2 and CDR3. Each complementarity determining region may comprise amino acid residues from a "complementarity determining region" as defined by Kabat et al., (1987 and / or 1991). For example, in a heavy chain variable region CDRH1 is between residues 31-35, CDRH2 is between residues 50-65, and CDRH3 is between residues 95-102. In a light chain, CDRL1 is between residues 24-34, CDRL2 is between residues 50-56, and CDRL3 is between residues 89-97. These CDRs can also comprise numerous insertions, e.g., as described in Kabat (1987 and / or 1991). The present disclosure is not limited to FRs and CDRs as defined by the Kabat numbering system, but includes all numbering systems, including the canonical numbering system or of Chothia and Lesk (1987); Chothia et al. (1989); and / or Al-Lazikani et al., (1997); the numbering system of Honnegher and Plükthun (2001); the IMGT system discussed in Giudicelli et al., (1997); or the Enhanced Chothia Numbering Scheme (http: / / www.bioinfo.org.uk / mdex.html). In one example, the CDRs and / or FRs are defined according to the Kabat numbering system. Optionally, heavy chain CDR2 according to the Kabat numbering system does not comprise the five C-terminal amino acids listed herein or any one or more of those amino acids are substituted with another naturally-occurring amino acid. In an additional, or alternative, option, light chain CDR1 does not comprise the four N-terminal amino acids listed herein or any one or more of those

[0034] 31 20778549_1 (GHMatters) P122809.PCT amino acids are substituted with another naturally-occurring amino acid. In this regard, Padlan et al., 1995 established that the five C-terminal amino acids of heavy chain CDR2 and / or the four N-terminal amino acids of light chain CDR1 are not generally involved in antigen binding. In some embodiments, the CDRs and / or FRs are defined according to the Chothia numbering system. 5 As used herein, the term “Kabat numbering system” refers to the scheme for numbering antibody variable regions and identifying CDRs (hypervariable regions) as set out in Kabat et al. (1987 and / or 1991). As used herein, the term “Chothia numbering system” refers to the scheme for numbering antibody variable regions and identifying CDRs (structural loops) as set out in Chothia and Lesk (1987) or Al- Lazikani et al. (1997). 10 As used herein, the term “antigen binding domain” shall be taken to mean the region of a targeting agent such as an antibody that is capable of specifically binding to an antigen (i.e. HER2). In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFNIKDTYIH (SEQ ID NO: 1), CDR-H2 comprises the amino acid 15 sequence RIYPTNGYTRYADSVKG (SEQ ID NO: 2), CDR-H3 comprises the amino acid sequence WGGDGFY (SEQ ID NO: 3), CDR light chain 1 (CDR-L1) comprises the amino acid sequence RASQDVNTAVA (SEQ ID NO: 4), CDR-L2 comprises the amino acid sequence SASFLYS (SEQ ID NO: 5), and CDR-L3 comprises the amino acid sequence QQHYTTPPT (SEQ ID NO: 6). In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof 20 comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFTFTDYTMD (SEQ ID NO: 7), CDR-H2 comprises the amino acid sequence DVNPNSGGSIYNQRFK (SEQ ID NO: 8), CDR-H3 comprises the amino acid sequence GPSFYFDY (SEQ ID NO: 9), CDR light chain 1 (CDR-L1) comprises the amino acid sequence KASQDVSIGVA (SEQ ID NO: 10), CDR-L2 comprises the amino acid sequence ASYRYT 25 (SEQ ID NO:11), and CDR-L3 comprises the amino acid sequence QQYYIYPYT (SEQ ID NO: 12). In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence TASGFNIK DTYIH (SEQ ID NO: 13), CDR-H2 comprises the amino acid sequence RIYPTNGYTR (SEQ ID NO: 14), CDR-H3 comprises the amino acid sequence 30 SRWGGDGFYAMDY (SEQ ID NO: 15), CDR light chain 1 (CDR-L1) comprises the amino acid sequence KASQDVNTAVA (SEQ ID NO: 16), CDR-L2 comprises the amino acid sequence YSASFRYT (SEQ ID NO: 17), and CDR-L3 comprises the amino acid sequence QQHYTTPPT (SEQ ID NO: 18). In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) 35 comprises the amino acid sequence DYYIH (SEQ ID NO: 19), CDR-H2 comprises the amino acid sequence RVNPDHGDSYYNQKFKD (SEQ ID NO: 20), CDR-H3 comprises the amino acid sequence

[0035] 32 20778549_1 (GHMatters) P122809.PCT ARNYLFDHW (SEQ ID NO: 21), CDR light chain 1 (CDR-L1) comprises the amino acid sequence KASQDWGTAVA (SEQ ID NO: 22), CDR-L2 comprises the amino acid sequence WASIRHT (SEQ ID NO: 23), and CDR-L3 comprises the amino acid sequence HQFATYT (SEQ ID NO: 24). In some embodiments, the HER2 targeting agent is an antibody or antigen-binding fragment thereof 5 comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence SYYMY (SEQ ID NO: 25), CDR-H2 comprises the amino acid sequence YISSGSEIYYSDSVKG (SEQ ID NO: 26), CDR-H3 comprises the amino acid sequence LGDDGMDV (SEQ ID NO: 27), CDR light chain 1 (CDR-L1) comprises the amino acid sequence RASQNVRTAVA (SEQ ID NO: 28), CDR-L2 comprises the amino acid sequence LASNRHT 10 (SEQ ID NO: 29), and CDR-L3 comprises the amino acid sequence LQHNSYPLT (SEQ ID NO: 30). In some embodiments, the antibody or antigen-binding fragment thereof comprises a heavy chain comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGGLVQPGGSLRLSCAASGFNIKDTYIHWVRQAPGKGLEWVARIYPTNGYTRYADSV 15 KGRFTISADTSKNTAYLQMNSLRAEDTAVYYCSRWGGDGFYAMDYWGQGTLVTVSSASTKGP SVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTV PSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMIS RTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNG KEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEW 20 ESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSP G (SEQ ID NO: 31). In some embodiments, the antibody or antigen-binding fragment thereof comprises a light chain comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence 25 DIQMTQSPSSLSASVGDRVTITCRASQDVNTAVAWYQQKPGKAPKLLIYSASFLYSGVPSRFSGS RSGTDFTLTISSLQPEDFATYYCQQHYTTPPTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASV VCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 32). In some embodiments, the antibody or antigen-binding fragment thereof comprises a heavy chain 30 comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGGLVQPGGSLRLSCAASGFTFTDYTMDWVRQAPGKGLEWVADVNPNSGGSIYNQR FKGRFTLSVDRSKNTLYLQMNSLRAEDTAVYYCARNLGPSFYFDYWGQGTLVTVSSASTKGPS VFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVP 35 SSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISR TPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGK

[0036] 33 20778549_1 (GHMatters) P122809.PCT EYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWE SNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG (SEQ ID NO: 33). In some embodiments, the antibody or antigen-binding fragment thereof comprises a light chain 5 comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence DIQMTQSPSSLSASVGDRVTITCKASQDVSIGVAWYQQKPGKAPKLLIYSASYRYTGVPSRFSGS GSGTDFTLTISSLQPEDFATYYCQQYYIYPYTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASV VCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE 10 VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 34). In some embodiments, the antibody or antigen-binding fragment thereof comprises a heavy chain comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence QVQLQQSGPELVKPGASLKLSCTASGFNIKDTYIHWVKQRPEQGLEWIGRIYPTNGYTRYDPKFQ 15 DKATITADTSSNTAYLQVSRLTSEDTAVYYCSRWGGDGFYAMDYWGQGASVTVSSASTKGPSV FPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKRVEPKSCDKTHTCPPCPAPELVGGPSVFLLPPKPKDTLMISRTP EVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPPEEQYNSTLRVVSVLTVLHQDWLNGKEY KCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESN 20 GQPENNYKTTPLVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO:35). In some embodiments, the antibody or antigen-binding fragment thereof comprises a light chain comprising at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence 25 DIVMTQSHKFMSTSVGDRVSITCKASQDVNTAVAWYQQKPGHSPKLLIYSASFRYTGVPDRFTG SRSGTDFTFTISSVQAEDLAVYYCQQHYTTPPTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC EVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 36). In some embodiments, the HER2 targeting agent has any of the amino acid sequences set out in US 30 11,325,981 B2, the entire contents of which are incorporated herein by reference. In some embodiments, the HER2 targeting agent has any of the amino acid sequences set out in US2017 / 0066829 A1, the entire contents of which are incorporated herein by reference. In some embodiments, the antibody comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence35 EVQLVESGGGLVQPGGSLRLSCAASGFNIKDTYIHWVRQAPGKGLEWVARIYPTNGYTRYADSV KGRFTISADTSKNTAYLQMNSLRAEDTAVYYCSRWGGDGFYAMDYWGQGTLVTVSSASTKGP

[0037] 34 20778549_1 (GHMatters) P122809.PCT SVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTV PSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMIS RTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNG KEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEW 5 ESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSP GDIQMTQSPSSLSASVGDRVTITCRASQDVNTAVAWYQQKPGKAPKLLIYSASFLYSGVPSRFSG SRSGTDFTLTISSLQPEDFATYYCQQHYTTPPTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC EVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 37). 10 In some embodiments, the antibody is trastuzumab. In some embodiments, the antibody is deglycosylated trastuzumab. In some embodiments, the antibody comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGGLVQPGGSLRLSCAASGFNIKDTYIHWVRQAPGKGLEWVARIYPTNGYTRYADSV 15 KGRFTISADTSKNTAYLQMNSLRAEDTAVYYCSRWGGDGFYAMDYWGQGTLVTVSSASTKGP SVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTV PSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMIS RTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNG KEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEW 20 ESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSP GDIQMTQSPSSLSASVGDRVTITCRASQDVNTAVAWYQQKPGKAPKLLIYSASFLYSGVPSRFSG SRSGTDFTLTISSLQPEDFATYYCQQHYTTPPTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC EVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 38). 25 In some embodiments, the antibody is inetetamab. In some embodiments, the antibody comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGGLVQPGGSLRLSCAASGFTFTDYTMDWVRQAPGKGLEWVADVNPNSGGSIYNQR FKGRFTLSVDRSKNTLYLQMNSLRAEDTAVYYCARNLGPSFYFDYWGQGTLVTVSSASTKGPS 30 VFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVP SSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISR TPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGK EYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWE SNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG 35 DIQMTQSPSSLSASVGDRVTITCKASQDVSIGVAWYQQKPGKAPKLLIYSASYRYTGVPSRFSGS GSGTDFTLTISSLQPEDFATYYCQQYYIYPYTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASV

[0038] 35 20778549_1 (GHMatters) P122809.PCT VCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC (SEQ ID NO: 39). In some embodiments, the antibody is pertuzumab. In some embodiments, the antibody comprises at least 80 %, at least 85 %, at least 90 %, at least 95 5 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence QVQLQQSGPELVKPGASLKLSCTASGFNIKDTYIHWVKQRPEQGLEWIGRIYPTNGYTRYDPKFQ DKATITADTSSNTAYLQVSRLTSEDTAVYYCSRWGGDGFYAMDYWGQGASVTVSSASTKGPSV FPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSS SLGTQTYICNVNHKPSNTKVDKRVEPKSCDKTHTCPPCPAPELVGGPSVFLLPPKPKDTLMISRTP 10 EVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPPEEQYNSTLRVVSVLTVLHQDWLNGKEY KCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESN GQPENNYKTTPLVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK DIVMTQSHKFMSTSVGDRVSITCKASQDVNTAVAWYQQKPGHSPKLLIYSASFRYTGVPDRFTG SRSGTDFTFTISSVQAEDLAVYYCQQHYTTPPTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS 15 VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC EVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 40). In some embodiments, the antibody is margetuximab. In some embodiments, the antibody is 19H6-Hu. In some embodiments, the HER2 targeting agent is a bispecific antibody having at least 80 %, 20 at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence GEVQLVESGGGLVQPGGSLRLSCAASGFTFADYTMDWVRQAPGKGLEWVGDVNPNSGGSIYN QRFKGRFTFSVDRSKNTLYLQMNSLRAEDTAVYYCARNLGPSFYFDYWGQGTLVTVSSASTKG PSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVT 25 VPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMI SRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLN GKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYVYPPSRDELTKNQVSLTCLVKGFYPSDIAVE WESNGQPENNYKTTPPVLDSDGSFALVSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSL SPG 30 GDIQMTQSPSSLSASVGDRVTITCKASQDVSIGVAWYQQKPGKAPKLLIYSASYRYTGVPSRFSG SGSGTDFTLTISSLQPEDFATYYCQQYYIYPATFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTAS VVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYAC EVTHQGLSSPVTKSFNRGEC GDIQMTQSPSSLSASVGDRVTITCRASQDVNTAVAWYQQKPGKAPKLLIYSASFLYSGVPSRFSG 35 SRSGTDFTLTISSLQPEDFATYYCQQHYTTPPTFGQGTKVEIKGGSGGGSGGGSGGGSGGGSGEV QLVESGGGLVQPGGSLRLSCAASGFNIKDTYIHWVRQAPGKGLEWVARIYPTNGYTRYADSVK

[0039] 36 20778549_1 (GHMatters) P122809.PCT GRFTISADTSKNTAYLQMNSLRAEDTAVYYCSRWGGDGFYAMDYWGQGTLVTVSSAAEPKSS DKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVH NAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVY VLPPSRDELTKNQVSLLCLVKGFYPSDIAVEWESNGQPENNYLTWPPVLDSDGSFFLYSKLTVDK SRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG (SEQ ID NO: 41). In some embodiments, the antibody comprises or consists of an amino acid sequence as disclosed in the examples. In some embodiments, the targeting agent is a fusion protein. As used herein, a “fusion protein” is a protein created by the joining of two or more nucleic acid sequences that originally coded for separate proteins or part thereof (e.g. fusion of a portion of a protein receptor with a portion of an antibody (such as in etanercept)). In some embodiments, the targeting agent is an antibody fragment. As used herein, the term “antibody fragment” shall be taken to mean a portion of or a fragment of an antibody capable of specifically binding to an antigen, including for example, a FV, VH, VL or a variable region as defined herein. This term shall be understood to encompass fragments directly derived from an antibody as well as proteins produced using recombinant means. In an embodiment, the antibody fragment is selected from a Fab, Fab2, Fv, scFv, heavy chain antibody, domain antibody, heavy chain antibody, diabody, or triabody. As used herein, the term “Fv” shall be taken to mean any protein, whether comprised of multiple polypeptides or a single polypeptide (scFV), in which a VL and a VH associate and form a complex having an antigen binding domain, i.e., capable of specifically binding to an antigen. The VH and the VL which form the antigen binding domain can be in a single polypeptide chain or in different polypeptide chains. In an embodiment, an Fv of the disclosure (as well as any protein of the disclosure) may have multiple antigen binding sites which may or may not bind the same antigen. This term shall be understood to encompass fragments directly derived from an antibody as well as proteins produced using recombinant means. In some examples, the VH is not linked to a heavy chain constant domain CH1 and / or the VL is not linked to a light chain constant domain (CL), e.g., a domain antibody. Exemplary Fv containing polypeptides or proteins include a Fab fragment, a Fab’ fragment, a F(ab’) fragment, a scFv, a diabody, a triabody, A “Fab fragment” consists of a monovalent antigen-binding fragment of an immunoglobulin, and can be produced by digestion of a whole antibody with the enzyme papain, to yield a fragment consisting of an intact light chain and a portion of a heavy chain or can be produced using recombinant means. A Fab fragment generally comprises or consists of a VH and CH1 and a VL and CL. A “Fab' fragment” of an antibody can be obtained by treating a whole antibody with pepsin, followed by reduction, to yield a molecule consisting of an intact light chain and a portion of a heavy chain comprising a VH and a single constant domain. Two Fab' fragments are obtained per antibody treated in this manner. A Fab’ fragment can also be produced by recombinant means. A “single chain Fv” or “scFv” is a recombinant molecule containing the variable region

[0040] 37 20778549_1 (GHMatters) P122809.PCT fragment (Fv) of an antibody in which the variable region of the light chain and the variable region of the heavy chain are covalently linked by a suitable, flexible polypeptide linker. In some embodiments, the antibody fragment is selected from: a heavy chain antibody, Fab, Fab2, Fv, scFv or a single domain antibody. As used herein, the “single-domain antibodies (sdAbs)”, also referred to as a “domain antibodies (dAb)” or “nanobodies” comprises a single variable region of a heavy chain VHor light chain VL.In an embodiment, the variable region is camelid-derived. In an embodiment, the variable region is derived from sharks. In an embodiment, the VHis a camelid-derived VH. In some embodiments, the targeting agent is a single domain antibody. In some embodiments, the targeting agent is a VHsingle domain antibody. In some embodiments, the targeting agent is a VLsingle domain antibody. In some embodiments, the targeting agent has a molecular weight of about 4 kDa to about 80 kDa, or about 5 kDa to about 80 kDa, or about 5 kDa to about 60 kDa, or about 5 kDa to about 50 kDa, or about 5 kDa to about 40 kDa, or about 5 kDa to about 30 kDa, or about 5 kDa to about 20 kDa, or about 5 kDa to about 16 kDa, or about 5 kDa to about 15 kDa, or about 5 kDa to about 12 kDa, or about 10 kDa to about 16 kDa or about 15kDa to 20 kDa. As described herein “kDA” or “kilodalton” refers to a unit of molecular mass consisting of 1000 daltons. In some embodiments, the HER2 targeting agent is a single domain antibody, In some embodiments, the single domain antibody comprises a single domain amino acid sequence as described in for example, EP2215125A1, US20110028695, Hussack et al. (2018) or. Arezumand et al. (2017), the entire contents of each of which are incorporated herein by reference. In some embodiments, the single domain antibody comprises a single domain amino acid sequence as described US20110028695, the entire contents of which are incorporated herein by reference. In some embodiments, the single domain antibody is 2D3 comprising the amino acid sequence as shown in SEQ ID NO: 1986 of US20110028695. In some embodiments, the HER2 targeting agent is a single domain antibody. In some embodiments, the targeting agent is a VHH or antigen-binding fragment thereof. In some embodiments the targeting agent is a VHH or antigen-binding fragment thereof comprising three complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFTFDDYAMS (SEQ ID NO: 42), CDR-H2 comprises the amino acid sequence SINWSGTHTD (SEQ ID NO: 43), and CDR-H3 comprises the amino acid sequence NWRDAGTTWFEKSGS (SEQ ID NO: 44). In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence

[0041] 38 20778549_1 (GHMatters) P122809.PCT EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSS (SEQ ID NO: 45). In some embodiments, the targeting agent is a VHHwhich comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence MEVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYA DSVKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSS C (SEQ ID NO: 46). In some embodiments, the targeting agent is a VHHwhich comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSX ENLYFQGHHHHHH (SEQ ID NO: 47), wherein X is an unnatural amino acid, preferably a 4- azidophenylalanine residue. In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSX (SEQ ID NO: 48), wherein X is an unnatural amino acid, preferably a 4-azidophenylalanine residue. In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence GGSHHHHHHGMASMTGGQQMGRDLYENLYFQGEVQLVESGGSLVQPGGSLRLSCAASGFTFD DYAMSWVRQVPGKGLEWVSSINWSGTHTDYADSVKGRFTISRNNANNTLYLQMNSLKSEDTA VYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSS (SEQ ID NO: 49). In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence GGSHHHHHHGMASMTGGQQMGRDLYENLYFQGEVQLVESGGSLVQPGGSLRLSCAASGFTFD DYAMSWVRQVPGKGLEWVSSINWSGTHTDYADSVKGRFTISRNNANNTLYLQMNSLKSEDTA VYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSX (SEQ ID NO: 50), wherein X is an unnatural amino acid, preferably a 4-azidophenylalanine residue.

[0042] 39 20778549_1 (GHMatters) P122809.PCT In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSX C (SEQ ID NO: 51), wherein X is any amino acid and is 0 to 20 residues in length (e.g.0, 1, 2, 3, 4 or 5 residues in length). In one embodiment X is 4 residues in length. In some embodiments, the targeting agent is a VHHwhich comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence CXEVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYA DSVKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSS (SEQ ID NO: 52), wherein X is any amino acid and is 0 to 20 residues in length (e.g.0, 1, 2, 3, 4 or 5 residues in length). In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSX CX (SEQ ID NO: 53), wherein X is any amino acid and is 0 to 20 residues in length (e.g.0, 1, 2, 3, 4 or 5 residues in length). In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence XCXEVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDY ADSVKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTV SS (SEQ ID NO: 54), wherein X is any amino acid and is 0 to 20 residues in length (e.g.0, 1, 2, 3, 4 or 5 residues in length). In some embodiments, the targeting agent is a VHH which comprises at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 97 %, at least 98 %, at least 99 %, or 100% sequence identity with the amino acid sequence EVQLVESGGSLVQPGGSLRLSCAASGFTFDDYAMSWVRQVPGKGLEWVSSINWSGTHTDYADS VKGRFTISRNNANNTLYLQMNSLKSEDTAVYYCAKNWRDAGTTWFEKSGSAGQGTQVTVSSL GTLCTPSRENLYFQGHHHHHH (SEQ ID NO: 55). In some embodiments, the targeting agent comprises or consists of a single domain amino acid sequence as disclosed in the examples.

[0043] 40 20778549_1 (GHMatters) P122809.PCT In some embodiments, the HER2 targeting agent is a mimetic of an antibody or an antibody fragment. As used herein, the term “mimetic” or “mimetics” refers to compounds that like antibodies or antibody fragments, can bind antigens, but are not structurally related to antibodies. This term shall be understood to not encompass antibodies or antibody fragments as described herein. This term shall be understood to 5 encompass synthetic mimetics (produced in vitro) and mimetics produced using recombinant means. This term shall be understood to encompass protein mimetics. In an embodiment, the mimetic is selected from an: affibody, aptamer, affilins, affimer, affitins, anticalins, avimers, alpha bodies, monobodies, DARPins, aptamer, Fyomers, fibronectin type III-derived protein scaffold, phytocystatin-derived protein scaffold and a paratope mimetic peptide. Like antibodies, 10 mimetics can be used as targeting moieties. In an embodiment, the mimetic is derived from one of the following protein scaffolds: z domain of protein A, gamma-B crystallin, ubiquitin, cystatin, sac7d, triple helix, coiled coil, lipocalin , cyclotides, A domains of a membrane receptor, ankyrin repeat motif, sh3 domain of Fym, Kunits domains of a protease inhibitor, type III domain of fibronectin and IgG-like, thermostable carbohydrate binding module family 15 32 (CBM32) from a Clostridium perfringens. In some embodiments, the targeting agent is an affibody. As used herein, the term “affibody” refers to any of a class of very small (approximately 6 kDa) polypeptide antibody mimetics based on a three alpha helix bundle domain of about 58 amino acids in length known as a “Z domain”. Typically, the scaffold for affibodies is based on a modified version of the B-domain of Protein A. Affibodies are characterized by 20 very high stability (withstanding temperatures as high as 90 ºC) and target affinities ranging from nanomolar to picomolar. See, e.g., Nord et al. (1995), Protein Eng., 8:601-608, the entire contents of which are incorporated herein by reference. Examples of known affibodies include, for example, affibodies against HER2 (e.g., the Anti-HER2 Affibody®, AFFIBODY AB, Bromma, Sweden; U.S. Patent No.7,993,650), the entire contents of which 25 are incorporated herein by reference. In some embodiments, the targeting agent is a small molecule. As used herein, a small molecule refers toa molecule having a molecular weight of less than about 1,000 Da. In some embodiments, the small molecule has a molecular weight of less than about 750 Da, or less than about 500 Da. In some embodiments, the targeting agent is competitive for binding with other targeting agents, such 30 as those commercially available. In one example, the targeting agent is competitive for binding with a commercially available antibody therapy. In some embodiments, the targeting agent is an antibody, antibody fragment or peptide sequence, and is covalently linked via the C-terminus of the targeting agent. The covalent attachment site of the targeting agent precursor can for example be cysteine, lysine, N- 35 terminal amines, tyrosine, carbohydrates, non-natural amino acids or transaminase or recognition

[0044] 41 20778549_1 (GHMatters) P122809.PCT sequences. Binding sites for covalent attachment to proteins are known in the art, (for example, Milla P., et al, Current Drug Metabolism (2012) V13, 1:105-119.) In some embodiments, an intermediate comprising the targeting agent comprises an unnatural amino acid residue for attachment. The unnatural amino acid residue may have a side chain that has a reactive 5 functional group that is complementary to a reactive functional group which may be present on a targeting agent presentation group precursor or on a connector group precursor. In some embodiments, the unnatural amino acid residue is one containing an azide group, e.g. it may be a 4-azidophenylalanine residue, e.g. . Azide groups are capable of undergoing cycloaddition reactions with alkyne groups which may be present in a targeting agent presentation group precursor or connector group 10 precursor. In some embodiments, the unnatural amino acid is a diene-containing amino acid, e.g. a spirocyclopentadiene-containing amino acid such as: . Diene groups are capable of undergoing cycloaddition (e.g. Diels-Alder) reactions with alkene groups, such as those present on maleimide. Further examples of unnatural amino acids which may be used for attachment include those containing a carbonyl group, such as a ketone, and 15 those containing a methylcyclopropylene group. Additional examples of unnatural amino acids include: some agent or any amino acid sequences defined herein.

[0045] 42 20778549_1 (GHMatters) P122809.PCT In some embodiments, the HER2 targeting agent is any of the HER2 targeting agents set out in Swain et al, Nature Reviews Drug Discovery, 2023, Vol.22, 101-126), the entire contents of which are incorporated herein by reference. In some embodiments, the targeting agent is any of the targeting agents used in the examples. 5 Connector The HER2 targeting agent is attached through a connector to the core unit of the dendrimer. Any suitable connector may be used. The use of a connector may, for example, assist in spacing the targeting agent from the dendrimer, and may facilitate improved binding of the targeting agent to its target. 10 In some embodiments, the connector comprises a backbone having a length in the range of from 50 to 150 atoms, optionally from 75 to 125 atoms. As used herein, the term ‘backbone’ refers to the continuous chain of atoms in the connector from the attachment point to the core to the attachment point to the targeting agent via the shortest path. In some embodiments, the connector comprises a hydrophilic polymeric group, which serves to space 15 the targeting from the dendrimer. In some embodiments, the term “hydrophilic polymeric group” refers to a polymeric group that has a solubility in water at 25 °C of at least 5 mg / ml, or at least 10 mg / ml, or at least 25 mg / ml, more preferably at least 50 mg / ml, and still more preferably at least 100 mg / ml. In some embodiments, the hydrophilic polymer is a polyethylene glycol (PEG), polyethyloxazoline20 (PEOX), poly-(2)-methyl-(2)-oxazolamine (POZ), polysarcosine or a poly (2- hydroxypropyl)methacrylamide (pHPMA) polymer. In some embodiments, the hydrophilic polymer comprises at least 3 monomer units. In some embodiments, the hydrophilic polymer comprises up to 50 monomer units. In some embodiments, the hydrophilic polymer comprises from 3 to 30, or from 20 to 30 monomer units. 25 In some embodiments, the connector comprises a PEG moiety. In some embodiments, the connector comprises a polyethylene glycol moiety having an average molecular weight in the range of from 100 to 1500 Da. In some embodiments, the polyethylene glycol moiety has an average molecular weight in the range of from 100 to 400 Da, or from 100 to 300 Da, or about 150, about 200, or about 250 Da. In some embodiments, the polyethylene glycol moiety has an average molecular weight in the range of from 750 to 30 1500 Da, or from 800 to 1200 Da, or about 800, about 900, about 1000, about 1100, or about 1200 Da. Any suitable means of attachment to the HER2 targeting agent may be utilised. In some embodiments, the connector is attached to the HER2 targeting agent via amide bond formation, for example by forming an amide bond between a carboxylic acid group present on the targeting agent and an amine group present at one end of the connector. In some embodiments, the connector is attached to the HER2 35 targeting agent via conjugate addition of a suitable nucleophilic group present in the HER2 targeting agent, such as a thiol group, to a group containing an α,β-unsaturated carbonyl moiety, such as a maleimide group.

[0046] 43 20778549_1 (GHMatters) P122809.PCT Any suitable means of attachment to the core unit of the dendrimer may be utilised. In some embodiments, the connector is attached to the core unit of the dendrimer via amide bond formation, for example by forming an amide bond between a carboxylic acid group present at one end of the connector and an amine group present in the core unit. 5 In some embodiments, the connector may be formed from precursors having complementary reactive groups. Such an approach allows loading of the targeting agent onto a part-connector precursor group, assembly of a dendrimer intermediate containing another part-connector precursor group, and then incorporation of the targeting agent into the conjugate and formation of the complete connector, for example using chemical reactions which proceed under mild conditions, and which are well tolerated by the various 10 moieties present. For example, the connector may comprise an amide group, and may for example be formed from appropriate precursors containing i) an acid or active ester, and ii) an amine respectively. Alternatively, the connector may for example be formed from appropriate precursors containing i) a suitable nucleophilic group, such as a thiol group, and ii) a group containing an α,β-unsaturated carbonyl moiety, such as a maleimide group. As another example, the connector may comprise a cycloaddition reaction 15 product, and may for example be formed from appropriate precursors containing i) an azide, and ii) an alkene or alkyne moiety. In some embodiments the connector comprises a cyclic moiety, wherein the connector group is formable from first and second connector precursors; the first connector precursor comprising the dendrimer, a part-connector group, and a first cyclisable group; and the second connector precursor 20 comprising the HER2 targeting agent, a further part-connector group, and a second cyclisable group which is capable of reaction with the first cyclisable group, to form the cyclic moiety. In some embodiments, the cyclic moiety is . Such a cyclic moiety may be formed, for example, by reaction of precursors comprising the groups: 25 In some embodiments, the first connector precursor has the structure:

[0047] 44 20778549_1 (GHMatters) P122809.PCT wherein n is an integer of from 20 to 30. In some embodiments, n is an integer of from 22 to 26. In some embodiments, n is 24. In some embodiments, the connector comprises the structure: 5 wherein n is an integer of from 20 to 30. In some embodiments, n is an integer of from 22 to 26. In some embodiments, n is 24. In some embodiments, the second connector precursor has the structure: , 10 wherein m is an integer of from 3 to 30. In some embodiments, m is an integer of from 3 to 10, or from 3 to 5. In some embodiments, m is 4. In some embodiments, the connector comprises the structure: wherein m is an integer of from 3 to 30. In some embodiments, m is an integer of from 3 to 10, or from 3 15 to 5. In some embodiments, m is 4. In some embodiments, the second connector precursor has the structure:

[0048] 45 20778549_1 (GHMatters) P122809.PCT , wherein m is an integer of from 3 to 30. In some embodiments, m is an integer of from 22 to 26. In some embodiments, m is 24. In some embodiments, the connector comprises the structure: 5 , wherein m is an integer of from 3 to 30. In some embodiments, m is an integer of from 22 to 26. In some embodiments, m is 24. In some embodiments, the connector comprises 2 polyethylene glycol moieties. For example, in the case where the connector is formed by reaction of a first connector precursor and a second connector 10 precursor having complementary reactive groups, each of the first connector precursor and second connector precursor may in some embodiments contain a polyethylene glycol moiety. In some embodiments, the connector is

[0049] 46 20778549_1 (GHMatters) P122809.PCT wherein m is an integer of from 3 to 30, and n is an integer of from 20 to 30. In some embodiments, m is an integer of from 22 to 26. In some embodiments, m is 24. In some embodiments, m is an integer of from 3 to 10, or from 3 to 5. In some embodiments, m is 4. In some embodiments, n is an integer of from 22 to 26. In some embodiments, n is 24. In some embodiments, the connector is any of the connectors used in the examples. In some embodiments, the core unit has the formula: wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; and the dendrimer has 2 generations of building units. In some embodiments, the core unit has the formula: wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; and the dendrimer has 3 generations of building units. In some embodiments, the core unit has the formula: wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; the dendrimer has 2 or 3 generations of building units; and the topoisomerase inhibitor is DXd. In some embodiments, the core unit has the formula: wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; the dendrimer has 2 or 3 generations of building units; and the topoisomerase inhibitor is SN-38. In some embodiments, the core unit has the formula:

[0050] 47 20778549_1 (GHMatters) P122809.PCT wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; the dendrimer has 2 or 3 generations of building 5 units; the topoisomerase inhibitor is DXd or SN-38; 20; and 10 In some embodiments, the core unit has the formula: 15 wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; the dendrimer has 2 or 3 generations of building units; the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence 20 GFNIKDTYIH (SEQ ID NO: 1), CDR-H2 comprises the amino acid sequence RIYPTNGYTRYADSVKG (SEQ ID NO: 2), CDR-H3 comprises the amino acid sequence WGGDGFY

[0051] 48 20778549_1 (GHMatters) P122809.PCT (SEQ ID NO: 3), CDR light chain 1 (CDR-L1) comprises the amino acid sequence RASQDVNTAVA (SEQ ID NO: 4), CDR-L2 comprises the amino acid sequence SASFLYS (SEQ ID NO: 5), and CDR-L3 comprises the amino acid sequence QQHYTTPPT (SEQ ID NO: 6); or the HER2 targeting agent is a VHHor antigen-binding fragment thereof comprising three complimentary 5 determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFTFDDYAMS (SEQ ID NO: 42), CDR-H2 comprises the amino acid sequence SINWSGTHTD (SEQ ID NO: 43), and CDR-H3 comprises the amino acid sequence NWRDAGTTWFEKSGS (SEQ ID NO: 44); and the connector is 10 wherein m is an integer of from 3 to 30, and n is an integer of from 20 to 30. In some embodiments, the core unit has the formula: 15 wherein Alk1 and Alk2 are alkylene groups, e.g. C2-6alkylene groups; the building units are lysines; the pharmacokinetic modifying groups comprise a PEG group; the dendrimer has 2 or 3 generations of building units; 20 the topoisomerase inhibitor is DXd or SN-38; , wherein p is an integer of from 2 to 20; or S is:

[0052] 49 20778549_1 (GHMatters) P122809.PCT , wherein q is an integer of from 3 to 20; and 5 the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFNIKDTYIH (SEQ ID NO: 1), CDR-H2 comprises the amino acid sequence RIYPTNGYTRYADSVKG (SEQ ID NO: 2), CDR-H3 comprises the amino acid sequence WGGDGFY (SEQ ID NO: 3), CDR light chain 1 (CDR-L1) comprises the amino acid sequence RASQDVNTAVA 10 (SEQ ID NO: 4), CDR-L2 comprises the amino acid sequence SASFLYS (SEQ ID NO: 5), and CDR-L3 comprises the amino acid sequence QQHYTTPPT (SEQ ID NO: 6); or the HER2 targeting agent is a VHHor antigen-binding fragment thereof comprising three complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence GFTFDDYAMS (SEQ ID NO: 42), CDR-H2 comprises the amino acid sequence SINWSGTHTD 15 (SEQ ID NO: 43), and CDR-H3 comprises the amino acid sequence NWRDAGTTWFEKSGS (SEQ ID NO: 44); and the connector is

[0053] 50 20778549_1 (GHMatters) P122809.PCT , wherein m is an integer of from 3 to 30, and n is an integer of from 20 to 30. In some embodiments, the conjugate is one of the example conjugates. The skilled person will appreciate that the conjugates may be produced in a variety of forms, 5 including salt forms (e.g. where there are ionisable groups present in the conjugate), as well as different solvates, for example. It will be understood that the present disclosure relates to all such forms of the dendrimer-targeting moiety conjugates. Suitable salts of the conjugates include those formed with organic or inorganic acids or bases. As used herein, the phrase “pharmaceutically acceptable salt” refers to pharmaceutically acceptable organic or 10 inorganic salts. Exemplary acid addition salts include, but are not limited to, sulfate, citrate, acetate, oxalate, chloride, bromide, iodide, nitrate, bisulfate, phosphate, acid phosphate, isonicotinate, lactate, salicylate, acid citrate, tartrate, oleate, tannate, pantothenate, bitartrate, ascorbate, succinate, maleate, gentisinate, fumarate, gluconate, glucuronate, saccharate, formate, benzoate, glutamate, methanesulfonate, ethanesulfonate, benzenesulfonate, p-toluenesulfonate, and pamoate (i.e., 1,1′-methylene-bis-(2-hydroxy- 15 3-naphthoate)) salts. Exemplary base addition salts include, but are not limited to, ammonium salts, alkali metal salts, for example those of potassium and sodium, alkaline earth metal salts, for example those of calcium and magnesium, and salts with organic bases, for example dicyclohexylamine, N-methyl-D- glucomine, morpholine, thiomorpholine, piperidine, pyrrolidine, a mono-, di- or tri-lower alkylamine, for example ethyl-, tert-butyl-, diethyl-, diisopropyl-, triethyl-, tributyl- or dimethyl-propylamine, or a mono-, 20 di- or trihydroxy lower alkylamine, for example mono-, di- or triethanolamine. A pharmaceutically acceptable salt may involve the inclusion of another molecule such as an acetate ion, a succinate ion or other counterion. The counterion may be any organic or inorganic moiety that stabilizes the charge on the parent compound. Furthermore, a pharmaceutically acceptable salt may have more than one charged atom in its structure. Instances where multiple charged atoms are part of the pharmaceutically acceptable salt can 25 have multiple counter ions. Hence, a pharmaceutically acceptable salt can have one or more charged atoms and / or one or more counterion. It will also be appreciated that non-pharmaceutically acceptable salts also fall within the scope of the present disclosure since these may be useful as intermediates in the preparation of pharmaceutically acceptable salts or may be useful during storage or transport. Those skilled in the art of organic and / or medicinal chemistry will appreciate that many organic 30 compounds can form complexes with solvents in which they are reacted or from which they are precipitated or crystallized. These complexes are known as “solvates”. For example, a complex with water is known as

[0054] 51 20778549_1 (GHMatters) P122809.PCT a “hydrate”. As used herein, the phrase “pharmaceutically acceptable solvate” or “solvate” refer to an association of one or more solvent molecules and a compound of the present disclosure. Examples of solvents that form pharmaceutically acceptable solvates include, but are not limited to, water, isopropanol, ethanol, methanol, DMSO, ethyl acetate, acetic acid, and ethanolamine. 5 The skilled person will also recognize that some structures described herein may be resonance forms or tautomers of compounds that may be fairly represented by other chemical structures. For example, the term “tautomers” may refer to a set of compounds that have the same number and type of atoms but differ in bond connectivity and are in equilibrium with one another. A “tautomer” is a single member of this set of compounds. Typically, a single tautomer is drawn but it may be understood that this single structure 10 may represent all possible tautomers that might exist. Examples may include enol-ketone tautomerism. When a ketone is drawn it may be understood that both the enol and ketone forms are part of the disclosure. Resonance forms and tautomers are within the scope of the present disclosure. Isotopically-labeled conjugates are also within the scope of the present disclosure. As used herein, an “isotopically-labeled conjugate” refers to a presently disclosed conjugate. including pharmaceutically 15 acceptable salts thereof, in which one or more atoms are replaced by an atom having an atomic mass or mass number different from the atomic mass or mass number usually found in nature. Examples of isotopes that can be incorporated into compounds presently disclosed include isotopes of hydrogen, carbon, nitrogen, oxygen, phosphorous, fluorine and chlorine, such as2H,3H,13C,14C,15N,18O,170,31P,32P,35S,18F, and36CI, respectively. 20 Pharmaceutical Compositions In some embodiments, the conjugates are presented as a pharmaceutical composition. Accordingly, there is also provided a pharmaceutical composition comprising a dendrimer-targeting agent conjugate as described herein and a pharmaceutically acceptable excipient. 25 Any suitable route of administration may be used. In some embodiments, the composition is formulated for parenteral delivery. In some embodiments, the composition is formulated for intravenous delivery. In some embodiments, the composition is formulated for subcutaneous delivery. In some embodiments, the composition is formulated for intramuscular injection. The excipient(s) must be pharmaceutically acceptable in the sense of being compatible with the other 30 ingredients of the composition and not unduly deleterious to the recipient thereof. In some embodiments, the composition comprises a pharmaceutically acceptable solvent, such as water for injection and / or a pharmaceutically acceptable organic solvent. The compositions of the present disclosure may for example include polymeric excipients / additives or carriers, e.g., polyvinylpyrrolidones, derivatised celluloses such as hydroxymethylcellulose, 35 hydroxyethylcellulose, and hydroxypropylmethylcellulose, Ficolls (a polymeric sugar), hydroxyethylstarch

[0055] 52 20778549_1 (GHMatters) P122809.PCT (HES), dextrates (e.g., cyclodextrins, such as 2-hydroxypropyl-β-cyclodextrin and sulfobutylether-β- cyclodextrin), polyethylene glycols, and pectin. The compositions may further include diluents, buffers, citrate, trehalose, binders, disintegrants, thickeners, lubricants, preservatives (including antioxidants), inorganic salts (e.g., sodium chloride), 5 antimicrobial agents (e.g., benzalkonium chloride), sweeteners, antistatic agents, sorbitan esters, lipids (e.g., phospholipids such as lecithin and other phosphatidylcholines, phosphatidylethanolamines, fatty acids and fatty esters, steroids (e.g., cholesterol)), and chelating agents (e.g., EDTA, zinc and other such suitable cations). Other pharmaceutical excipients and / or additives suitable for use in the compositions according to the present disclosure are listed in "Remington: The Science & Practice of Pharmacy", 19.sup.th ed., 10 Williams & Williams, (1995), and in the "Physician's Desk Reference", 52.sup.nd ed., Medical Economics, Montvale, N.J. (1998), and in "Handbook of Pharmaceutical Excipients", Third Ed., Ed. A. H. Kibbe, Pharmaceutical Press, 2000. The conjugates may for example be formulated in compositions including those suitable for parenteral (including intraperitoneal, intravenous, subcutaneous, or intramuscular injection) administration. 15 The compositions may conveniently be presented in unit dosage form and may be prepared by any of the methods well known in the art of pharmacy. All methods include the step of bringing the conjugate into association with a carrier that constitutes one or more accessory ingredients. In general, the compositions are prepared by bringing the conjugate into association with a liquid carrier to form a solution or a suspension, or alternatively, bring the conjugate into association with formulation components suitable for 20 forming a solid, optionally a particulate product, and then, if warranted, shaping the product into a desired delivery form. In some preferred embodiments, the composition is formulated for parenteral delivery. For example, in one embodiment, the formulation may be a sterile, lyophilized composition that is suitable for reconstitution in an aqueous vehicle prior to injection. In some embodiments, a composition suitable for 25 parenteral administration conveniently comprises a sterile aqueous preparation of the conjugate, which may for example be formulated to be isotonic with the blood of the recipient. In some embodiments, the composition is formulated for parenteral infusion, for example as part of a chemotherapy regimen. In some embodiments, the composition is formulated for intraperitoneal delivery. Any suitable means of delivery may be used. For example, in some embodiments delivery may be by lavage or aerosol. 30 In one embodiment the composition is formulated for intraperitoneal delivery, and is for treatment of cancers in the peritoneal cavity, which include malignant epithelial tumors (e.g., ovarian cancer), and peritoneal carcinomatosis (eg gastrointestinal especially colorectal, gastric, gynecologic cancers, and primary peritoneal neoplasms). As discussed below, the conjugates may for example be administered in combination with one or 35 more additional pharmaceutically active agents. For example, the conjugate may be administered in a composition together with a further pharmaceutical active agent.

[0056] 53 20778549_1 (GHMatters) P122809.PCT Examples of further pharmaceutically active agents include chemotherapeutic and cytotoxic agents, small molecule cytotoxics, tyrosine kinase inhibitors, checkpoint inhibitors, EGFR inhibitors, and antibody therapies. Not only can the conjugates be administered with other chemotherapy or radiotherapy drugs but may 5 also be administered in a composition together with other medications as appropriate. Uses of Dendrimer-Targeting Agent Conjugates Example conjugates of the present disclosure have been demonstrated to have excellent properties making them suitable as anticancer agents. For example, example conjugates according to the present 10 disclosure have been shown to display strong binding to HER2 antigen. Example conjugates have also been demonstrated to provide good selective release properties, in respect of the topoisomerase inhibitor. Moreover, example conjugates have been shown to have excellent unexpected activity in xenograft studies in mice. For example, in a breast cancer model, an example conjugate was found to have comparable activity to the approved product Enhertu®. In an ovarian cancer model, an example conjugate was found 15 to outperform Enhertu®. Accordingly, the conjugates and compositions as described herein can be used in various applications in the field of medicine. For example, the conjugates find use in the treatment of various conditions depending on the nature of the targeting agent. For example, the conjugates as described herein may be useful in treating cancers. 20 Accordingly, there is provided a conjugate or pharmaceutical composition as described herein for use in therapy, and more specifically for use in therapy of cancer. In some embodiments, the conjugate is used in a method of treating or preventing cancer, for example for suppressing the growth of a tumour. In some embodiments the conjugate is for use in the treatment of cancer. There is also provided a method of treating cancer comprising administering to a subject in need thereof a therapeutically effective amount of 25 a conjugate or pharmaceutical composition as defined herein. There is also provided use of a conjugate as defined herein, or of a composition as defined herein, in the manufacture of a medicament for the treatment of cancer. In some embodiments, the cancer is a solid tumour. The cancer may be a primary or metastatic tumour. In some embodiments the cancer is a primary tumour. In some embodiments the cancer is a 30 metastatic tumour. In some embodiments, the cancer is a HER2-positive cancer. In some embodiments, the cancer is selected from the group consisting of ovarian cancer, breast cancer, non-small cell lung cancer, stomach cancer, gastric or gastroesophageal junction adenocarcinoma, uterine cancer, melanoma, hepatocellular carcinoma, prostate cancer, cholangiocarcinoma, pancreatic 35 adenocarcinoma, intestinal cancer, head and neck carcinoma, colorectal cancer, cervical cancer, gallbladder cancer, esophageal cancer, and bladder cancer.

[0057] 54 20778549_1 (GHMatters) P122809.PCT In some embodiments, the cancer is selected from the group consisting of breast cancer, HER2- positive breast cancer, metastatic HER2-positive breast cancer, metastatic HER2-low breast cancer, gastric cancer, HER2-positive gastric cancer, HER2-positive advanced gastric cancer, gastro-oesophageal junction cancer, and HER2-positive gastro-oesophageal junction cancer. 5 In some embodiments, the cancer is selected from the group consisting of colorectal cancer and metastatic colorectal cancer. A therapeutically effective amount of the conjugate or composition is used in the therapeutic methods and uses. It will be appreciated that the term “therapeutically effective amount” refers to a conjugate, or composition comprising the conjugate, being administered in an amount sufficient to alleviate or prevent 10 to some extent one or more of the symptoms of the disorder or condition being treated. The conjugate may be administered by any suitable route, including for example, intravenously (IV). In some embodiments, the conjugate is delivered as an IV bolus. In some embodiments the conjugate is administered IV over a time a period in the range of from 0.5 to 60 minutes, or in the range of from 0.5 to 30 minutes, or in the range of from 0.5 to 15 minutes. In another example, the conjugate may be 15 administered intraperitoneally. The route of administration may for example be targeted to the disease or disorder which the subject has. For example, in some embodiments the disease or disorder may be an intra-abdominal malignancy such as a gynecological or gastrointestinal cancer, and the conjugate may be administered intraperitoneally. In some embodiments the conjugate may be for treatment of a cancer of the peritoneal cavity, such as a 20 malignant epithelial tumors (e.g., ovarian cancer) or peritoneal carcinomatosis (e.g. gastrointestinal especially colorectal, gastric, gynecologic cancers, and primary peritoneal neoplasms), and the conjugate is administered intraperitoneally. When used for chemotherapy treatment purposes, the conjugate will be administered in an amount sufficient to deliver a therapeutically effective dose of chemotherapy to the target (e.g. tumour), whilst at 25 the same time avoiding unacceptable exposure of other parts of the body (e.g. other organs) to cytotoxicity. The precise dosage may be dependent on the nature of the chemotherapeutic (e.g. an ultracytotoxic agent), and the condition to be treated. In some embodiments, a therapeutically effective amount of the conjugate is administered to a subject in need thereof at a predetermined frequency. In some embodiments, the conjugate is administered to a 30 subject in need thereof according to a dosage regimen in which the conjugate is administered once per one to four weeks. In some embodiments, the conjugate is administered to a subject in need thereof according to a dosage regimen in which the conjugate is administered once per three to four weeks. In some embodiments, a dosing regimen involving administration once per three to four weeks for a total of 2, 3, 4, 5, 6, 7, 8, 8, 9 or 10 doses is used. In some embodiments, the conjugate is administered to a subject according 35 to a quad-shot regimen, for example the conjugate is administered over consecutive days for up to a week

[0058] 55 20778549_1 (GHMatters) P122809.PCT with 3 to 4 weeks break between administration rounds. In some embodiments, the quad-shot regimen includes two administrations per day over two consecutive days at 3 to 4 week intervals. Combinations 5 Drugs are often administered in combination with other drugs, especially during chemotherapy. Accordingly, in some embodiments the conjugate is administered in combination with one or more further pharmaceutically active agents, for example one or more further anti-cancer agents / drugs. The conjugate and the one or more further pharmaceutically active agents may be administered simultaneously, subsequently or separately. For example, they may be administered as part of the same composition, or by 10 administration of separate compositions. The one or more further pharmaceutically active agents may for example be anti-cancer agents for therapy of a cancer selected from the group consisting of ovarian cancer, breast cancer, non-small cell lung cancer, stomach cancer, gastric or gastroesophageal junction adenocarcinoma, uterine cancer, melanoma, hepatocellular carcinoma, prostate cancer, cholangiocarcinoma, pancreatic adenocarcinoma, intestinal 15 cancer, head and neck carcinoma, colorectal cancer, cervical cancer, gallbladder cancer, esophageal cancer, and bladder cancer. The one or more further pharmaceutically active agents may for example be anti-cancer agents for therapy of a cancer selected from the group consisting of breast cancer, HER2-positive breast cancer, metastatic HER2-positive breast cancer, metastatic HER2-low breast cancer, gastric cancer, HER2-positive20 gastric cancer, HER2-positive advanced gastric cancer, gastro-oesophageal junction cancer, and HER2- positive gastro-oesophageal junction cancer. The one or more further pharmaceutically active agents may for example be anti-cancer agents for therapy of a cancer selected from the group consisting of colorectal cancer and metastatic colorectal cancer. Examples of further pharmaceutically active agents include chemotherapeutic and cytotoxic agents, 25 small molecule cytotoxics, tyrosine kinase inhibitors, checkpoint inhibitors, EGFR inhibitors, and antibody therapies. Examples of further pharmaceutically active agents include leucovorin and 5-fluorouracil. Preparation of Dendrimer-Targeting Agent Conjugates 30 The dendrimer-targeting agent conjugates of the present disclosure may be prepared by any suitable methods, such as those described in the examples. A skilled person will be familiar with typical methods and processes used in the synthesis and purification of organic compounds and polymers. In some embodiments, protecting group chemistry may be used in the synthesis of the conjugates, 35 for example to allow selective reaction of desired groups to build up part of the conjugate structure, and

[0059] 56 20778549_1 (GHMatters) P122809.PCT then unveiling other functionality as desired to allow other parts of the conjugate structure to be incorporated. The use of protecting groups. e.g. amine protecting groups such as Boc, Fmoc, Cbz; alcohol protecting groups such as TBDMS, TBDPS, benzyl ethers, PMB ethers; acid protecting groups such as 5 methyl esters, ethyl esters, t-butyl esters, benzyl esters and the like are known to a skilled person. Suitable protecting groups, methods for their introduction and removal are for example described in Greene & Wuts, Protecting Groups in Organic Synthesis, Third Edition, 1999. In some embodiments, the conjugates are prepared by reacting a first intermediate comprising: a) a dendrimer comprising 10 i) a core unit; and ii) building units; wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is covalently attached to at least two building units; b) a topoisomerase inhibitor which is attached through a linker to an outer building unit of the 15 dendrimer, the linker having the formula wherein S is a spacer group; and Cl is an enzymatically cleavable group comprising a peptide having at least 2 amino acid residues; c) pharmacokinetic-modifying moieties which are attached to outer building units, the 20 pharmacokinetic-modifying moieties comprising a hydrophilic polymer; and d) a part-connector and a first reactive group (e.g. a cyclisable group, such as an azide; or a group capable of forming an amide bond, such as an amine or acid; or a group capable of undergoing a conjugate addition reaction, such as a thiol or a maleimide group) attached to the core unit of the dendrimer; with a second intermediate comprising: 25 a HER2 targeting agent, a part-connector and a second reactive group which is complementary to the first reactive group (e.g. the other partner in a cycloaddition reaction, such as a cyclisable group containing an alkene or alkyne; or the other partner in an amidation reaction, i.e. an amine or an acid; or the other partner in a conjugate addition reaction, i.e. a thiol or maleimide group). The first intermediate may be prepared by any suitable route. For example, an intermediate 30 comprising a topoisomerase inhibitor attached to the linker, which linker contains a reactive group that is complementary to a reactive group on a surface building unit of the dendrimer, may be reacted with a further intermediate comprising: a dendrimer comprising i) a core unit; and

[0060] 57 20778549_1 (GHMatters) P122809.PCT ii) building units; wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is covalently attached to at least two building units; pharmacokinetic-modifying moieties which are attached to outer building units, the 5 pharmacokinetic-modifying moieties comprising a hydrophilic polymer; the outer building units having reactive groups which are complementary to the linker reactive group and a part connector group attached to the core unit of the dendrimer, comprising a reactive group which is orthogonal to (i.e. which does not react with) the linker reactive group or outer building unit reactive groups. 10 For example, the linker reactive group may be a carboxylic acid, which can undergo an amide coupling reaction with amine groups present on outer building units (e.g. in the case of lysine dendrimers). Typical reaction conditions may for example include the use of an amide coupling reagent, such as EDCI, BOP, HATU, TBTU, pentafluorophenyl phosphinate, and a suitable solvent. A base, such as triethylamine, or NMM may be used. The reaction may for example be carried out at room temperature, 15 or with cooling. The intermediate comprising: a dendrimer comprising i) a core unit; and ii) building units; 20 wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is covalently attached to at least two building units; pharmacokinetic-modifying moieties which are attached to outer building units, the pharmacokinetic-modifying moieties comprising a hydrophilic polymer; the outer building units having reactive groups which are complementary to the linker reactive group, 25 and a part connector group comprising a reactive group, which is attached to the core of the dendrimer, may again be prepared by any suitable route. For example, it may be prepared by i) assembly of generations of building blocks on the dendrimer; ii) incorporation of pharmacokinetic-modifying moieties onto the outer building units, and iii) deprotection to unveil reactive groups (e.g. amine groups in the case of lysine dendrimers) on the outer building units of 30 the dendrimer. Stage i) may for example include iterative assembly of generations of building units. For example, in the case of a dendrimer containing lysine building units, the core unit may be reacted with di-amine- protected lysine to form amide bonds. The amine protecting groups (e.g. Boc groups) may then be removed (e.g. by treatment with a 35 suitable acid). Those steps may be repeated as desired to build up generations of building units.

[0061] 58 20778549_1 (GHMatters) P122809.PCT Stage ii) involves incorporation of pharmacokinetic-modifying moieties onto the outer building units. For example, when incorporating the outer generation of building units, an orthogonal protecting group strategy may be utilised, such as in the case of a lysine dendrimer, utilising α-N-Boc-ε-N-Fmoc-lysine. This then allows incorporation of an outer layer of building units with different protecting groups present. 5 Selective deprotection of one set of protecting groups (e.g. removal of the Boc groups under acidic conditions, or removal of Fmoc groups with piperidine) provides the free amine (or the salt form thereof), which can then be reacted. A precursor comprising the pharmacokinetic modifying moiety and comprising a reactive group can then be reacted with a complementary group on the dendrimer (e.g. reacting a carboxylic acid or active 10 ester group with an amine group present on an outer building unit in the case of a dendrimer containing lysine building units). Stage iii) involves deprotection of the other set of protecting groups under suitable deprotection conditions. The second intermediate may also be prepared by any suitable route. For example, a part-connector 15 group may be attached to the HER2 targeting agent via amide bond formation, for example by forming an amide bond between a carboxylic acid group present on the targeting agent and an amine group present at one end of the connector. As another example, a part-connector group may be attached to the HER2 targeting agent via conjugate addition of a suitable nucleophilic group present in the HER2 targeting agent, such as a thiol group (e.g. in a cysteine residue), to a group containing an α,β-unsaturated carbonyl moiety, 20 such as a maleimide group. Any suitable technique may be used to obtain the HER2 targeting agent. For example, in some embodiments, the HER2 targeting agent may be available commercially. A skilled person will also be familiar with typical methods for producing antibodies and other proteins. Methods also include providing a cell line expressing a peptide or antibody (for example a 25 mammalian expression system such as NS0 murine myeloma cells, PER.C6 human cells, and Chinese hamster ovary (CHO) cells), culturing the cells under suitable conditions and in appropriate media to produce the peptide or antibody, and then isolating and purifying the product. Some peptidic agents may for example be produced by techniques including resin-based synthesis. Small molecule targeting agents may be produced by chemical synthesis. 30 Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. Examples 35 The present disclosure is further exemplified by the following non-limiting examples.

[0062] 59 20778549_1 (GHMatters) P122809.PCT Abbreviations Abbreviation approx. Approximately BME Beta(ß)-Mercaptoethanol °C degrees Celsius Calc calculated CV Column Volume D doublet Dd doublet of doublet DCM Dichloromethane DIPEA N,N-Diisopropylethylamine DMF N,N-Dimethylformamide DMSO Dimethylsulfoxide ESI Electrospray Ionization EtOAc Ethyl Acetate FPLC Fast Protein Liquid Chromatography H hour(s) HPLC High Pressure Liquid Chromatography Hz Hertz IPTG Isopropyl β-D-1-thiogalactopyranoside LB Lysogeny broth m multiplet μL microlitre μm Micron μmol Micromole MeCN Acetonitrile mL millilitres min minute(s) nM nanomole MTBE Methyl-tert-butyl ether MTD Maximum Tolerated Dose NMM N-Methyl Morpholine NMP N-Methyl Pyrrolidine NMR Nuclear Magnetic Resonance NSG NOD-Skid-Gamma PyBOP benzotriazol-1-yloxytripyrrolidinophosphonium hexafluorophosphate Rt retention time rt room temperature sec second(s) SPR Surface Plasmon Resonance t triplet TB Terrific broth TCEP Tris(2-carboxyethyl)phosphine TLC Thin Layer Chromatography UPLC Ultra-Performance Liquid Chromatography UV Ultra Violet

[0063] 60 20778549_1 (GHMatters) P122809.PCT General Methods Automated Chromatography Automated flash chromatography was performed on Büchi Pure Chromatography System with a 5 binary solvent system consisting of solvent A (water) and solvent B (MeCN) with / without a modifier. The components were detected using an ELSD detector and a UV detector at l = 270 nm. Automated Chromatography Methods: [AutoFlash Method 10-20-63-68-100 CV, 120g C18]: 120g Velocity UltraPure spherical C18, 40- 10 60 μm cartridge, 120 Å; gradient was (%B) 0-2.5 CV 10%, 2.5-20.6 CV 10-20%, 20.6-26.5 CV 20-63%, 26.5-28.3 CV 63%, 28.3-37.1 CV 63-68%, 37.1-37.4 CV 68%, 37.4-41.1 CV 68-100%, 41.1-41.4 CV 100%, 41.4-43.9 CV 100-50%; at a flow rate of 80 mL / min. [AutoFlash Method 10-35-55-100 min (+ 0.05% TFA modifier), 80 g C18], 80g Velocity UltraPure spherical C18, 40-60 μm cartridge; gradient was (%B) 0-5.3 min 10%, 5.3-5.4 min 10%, 5.4-23 min 10- 15 35%, 23-28 min 35-55%, 28-28.3 min 55%, 28.3-33.6 min 55-100%, 33.6-33.8 min 100%, 33.8-39.1 min 100-70%, 39.1-41.6 min 70%; at a flow rate of 55 mL / min. [AutoFlash Method 10-60-100 min (+ 0.05% TFA modifier), 80g C18]: 80g Velocity UltraPure spherical C18, 40-60 μm cartridge; gradient was (%B); gradient was 0-1.4 CV 10%, 1.4-11.4 CV 10%, 11.4-12.4 CV 10-60%, 12.4-12.5 CV 60%, 12.5-13.9 CV 60-100%, 13.9-14.2 CV 100%; at a flow rate of 20 45 mL / min. [AutoFlash Method 10-60-100 min (+ 0.05% TFA modifier), 40g C18]: 40g Velocity UltraPure spherical C18, 40-60 μm cartridge; gradient was (%B); Gradient was 0-3 CV 10%, 3-18 CV 10%, 18-20 CV 10-60%, 20-20.2 CV 60%, 20.2-23.2 CV 60-100%, 23.2-23.5 CV 100%; at a flow rate of 45 mL / min. [AutoFlash Method 5-20-35-50-90 min (+ 0.05% TFA modifier), 30 g C18]: 35g C18 Biotage® 25 Sfär column; gradient was 0-2 CV 5%, 2-2.5 CV 5%, 2.5-5.5 CV 5-20%, 5.5-21.3 CV 20-35%, 21.3-21.8 CV 35-50%, 21.8-24.8 CV 50-90%, 24.8-25.3 CV 90%, 25.3-27.3 CV 90-50%, at a flow rate of 25 mL / min. [AutoFlash Method 5-20-40-60-90 min (+ 0.05% TFA modifier), 30 g C18]: 30g C18 Biotage® Sfär column; gradient was Gradient was 0-1 CV 5%, 1-3 CV 5-20%, 3-10 CV 20-40%, 10-11 CV 40-60%, 30 11-14 CV 60%, 14-15 CV 60-90%, 15-21 CV 90%; at a flow rate of 25 mL / min. Analytical HPLC 1 HPLC data was recorded on a Waters 2695 separation module with 2996 PDA detector using a Kinetex®2.6 µm 2.1 x 75 mm C18 column. The instrument control software was Waters Empower 3. The 35 three mobile phases used were a) 1% v / v TFA buffer or 1% v / v formic acid buffer or 100 mM ammonium formate, b) water and c) acetonitrile. The flow rate was typically 0.4 mL / min and injection volumes were

[0064] 61 20778549_1 (GHMatters) P122809.PCT typically 5-10 µL. The peaks were detected using UV detector at λ = 243 nm, 280 nm or 360 nm (unless otherwise specified). HPLC-Method 5-70, 15 min, TFA: The gradient was: 0-2 min, 5% B; 2-8 min, 5-70% B; 8-10 min, 70% B; 10-12 min, 70-5% B; 12-15 min, 5% B; at a flow rate of 0.40 mL / min. The peaks were detected using UV detector at wavelength, 243 and 280 nm. HPLC-Method 15-75, 40oC, 15 min, TFA: The gradient was: 0-2 min, 15% B; 2-8 min, 15-75% B; 8-10 min, 75% B; 10-12 min, 75-15% B; 12-15 min, 15% B; at a flow rate of 0.40 mL / min. The peaks were detected using UV detector at wavelength, 280 and 360 nm. Analytical HPLC 2 HPLC data was recorded on a Waters Acquity Arc Separation Module with 2998 PDA detector using an Agilent Zorbax 300 SB-C8, RRHD, 1.8µm, 2.1 x 100 mm column. The two mobile phases used were a) 0.1% v / v TFA in water b) 0.1% v / v TFA in acetonitrile. The flow rate was typically 0.8 mL / min and the injection volume was 2 µL. The peaks were detected using UV detector at λ = 359 nm with the column temperature 80oC. HPLC-Method 15-80, 9.5 min, TFA: The gradient was: 0-0.6 min, 15% B; 0.6-8 min, 15-80% B; 6- 6.3 min, 80% B; 6.3-6.6 min, 80-15% B; 6.6-9.5 min, 15% B; at a flow rate of 0.80 mL / min. The peaks were detected using UV detector at wavelength, 359 nm at 80 °C. Preparative HPLC Preparative HPLC was performed on Gilson HPLC system using Waters XBridgeTMBEH300 Prep C185µm OBDTM30 x150 mm column using a binary solvent system consisting of solvent A and solvent B. The flow rate was 8.0 mL / min. The components were detected using a UV detector at λ = 214, 243 and 256 nm. Preparative HPLC Methods: Prep-HPLC Method 10-60, TFA: Solvent A, Water + 0.05% TFA (v / v); Solvent B, MeCN 0.05% TFA (v / v); gradient: 0-10 min, 10% B; 10-37 min, 10-60% B; 37-48 min, 60% B; 48-53 min, 60-10% B, 53-60 min 10% B. Prep-HPLC Method 30-60, TFA: Solvent A, Water + 0.05% TFA (v / v); Solvent B, MeCN 0.05% TFA (v / v); gradient: 0-5 min, 30% B; 5-55 min, 10-60% B; 55-61 min, 60-30% B. FPLC Fast Protein Liquid Chromatography (FPLC) was performed on a GE AKTA Purifier 10. FPLC Methods:

[0065] 62 20778549_1 (GHMatters) P122809.PCT FPLC Method Protein A-1: Column = Cytiva HiTrap MabSelect PrismA™ column 5 mL; Buffer A (wash) = 10 mM PBS, pH 7.4; Buffer B (elution) = 0.1 M citrate buffer, pH 3.0; Loading rate = 1-1.5 mL / min; Elution rate = 2-2.5 mL / min; Injection volume up to 5mL. Stepwise gradient elution from 0% B (wash), then up to 100% B depending on the extent of retention on the column. UV detection at 280 nm. 5 UV detection at 280 nm. FPLC Method SEC-1: Column = Sepax SRT-10C SEC 300 Å; Buffer = 50 mM phosphate, pH 7.0; Running rate = 0.75 mL / min; injection volume up to 0.5 mL. UV detection at 280 nm. FPLC Method SEC-2: Column = Cytiva Superdex 200 Increase 10 / 300 GL 24 mL; Buffer = 10 mM PBS, pH 7.4; Running rate = 0.5 mL / min; Injection volume up to 0.5 mL. UV detection at 280 nm. 10 FPLC Method HIC-1: Column = Cytiva HiTrap Butyl HP, 1 mL; Buffer A (wash) = 0.5 M ammonium sulfate, 50 mM phosphate buffer, pH 7.; Buffer B (elution buffer) deionised water, pH 7.0; Running rate = 1 mL / min (loading); 2 mL / min (wash and elution); Injection volume up to 1 mL. UV detection at 280 nm. FPLC Method CEX-1: Column = Cytiva HiTrap SP XL, 5 mL; Buffer A (wash) = 20 mM acetate 15 buffer, pH 4.; Buffer B (elution buffer) = 20 mM acetate buffer, 1 M NaCl, pH 4; Running rate = 1 mL / min (loading); 2-2.5 mL / min (wash and elution); Injection volume up to 5 mL. Stepwise gradient elution from 0% B (wash), then up to 100% B depending on the extent of retention on the column. UV detection at 280 nm. 20 Analytical UPLC UPLC-SQD was recorded on Waters ACQUITY H-Class UPLC coupled to a SQ Detector 2 single quad mass spectrometer with Phenomenex Kinetex EVO C181.7µm, 2.1 x 100 mm, 100Å (with EVO C18 guard column) using a ternary solvent system consisting of solvent A (Water), solvent B (MeCN), solvent C (0.2% v / v TFA in water). Throughout the analysis, the composition of solvent C remained constant at 25 5%, resulting in a TFA concentration of 0.01% in the gradient method. The column temperature was 40 °C. The flow rate was typically 0.4 mL / min and the injection volume was typically 0.2-0.5 µL. The peaks were detected within λ = 200 – 400 nm (unless otherwise specified). UPLC Methods: 30 UPLC-SQD Method 5-80, 9 min: Gradient was 0-0.5 min, 5% B; 0.5-5 min, 5-80% B; 5-6 min, 80% B; 6.0-6.2 min, 80-95% B, 6.2-7.2 min 95% B, 7.2-7.5 min 95-5% B, 7.5-9 min 5% B.

[0066] 63 20778549_1 (GHMatters) P122809.PCT UPLC-SQD Method 5-60, 9 min: Gradient was 0-0.5 min, 5% B; 0.5-5 min, 5-60% B; 5-6 min, 60% B; 6.0-6.2 min, 60-95% B, 6.2-7.2 min 95% B, 7.2-7.5 min 95-5% B, 7.5-9.0 min 5% B. UPLC-SQD Method 5-10-35, 9 min: Gradient was 0-0.5 min, 5% B; 0.5-1 min, 5-10% B; 1-5 min, 10-35% B; 5-6 min, 35% B, 6-6.2 min 35-95% B, 6.2-7.2 min 95% B, 7.2-7.5 min 95-5% B, 7.5-9 % B. UPLC-SQD Method 5-20-80, 9 min: Gradient was 0-0.5 min, 5% B; 0.5-1 min, 5-20% B; 1-5 min, 20-80% B; 5-6 min, 80% B, 6-6.2 min 80-95% B, 6.2-7.2 min 95% B, 7.2-7.5 min 95-5% B, 7.5-9 % B. Analytical UPLC-ToF (Ultra-High Pressure Liquid Chromatography- Time of Flight) UPLC-ToF data was recorded with a Waters Aquity UPLC binary separation module with Waters Aquity PDA detector and Waters LCT Premiere (ToF) Mass Spectrometer. The column used was Phenomenex Kinetex EVO C182.6µm 2.1x100mm column or Sepax Proteomix RP-1000, 1000 Å, 5µm 2.1x100mm for protein or conjugate analysis. The instrument control software was Waters Masslynx Version 4.2. The two mobile phases used were a) 0.01% v / v TFA in water and b) 0.01% v / v TFA in acetonitrile. The flow rate was typically 0.2 mL / min or 0.4 mL / min and injection volumes were typically 0.5-1 µL. The peaks were detected within λ = 200 nm – 400 nm (unless otherwise specified). UPLC-ToF Methods: UPLC-ToF Method 20-80-Protein, 15 min: The gradient was 20% MeCN / H2O (0-1 min), 20-80% MeCN / H2O (1-10 min), 80% MeCN / H2O (10-11 min), 80-20% MeCN / H2O (11-13 min), 20% MeCN / H2O (13-15 min), 0.01% TFA v / v buffer in both mobile phases), UV detection at 216 nm, column temperature = 90 °C. UPLC-ToF Method 5-70-Protein, 65 °C, 15 min: The gradient was 5% MeCN / H2O (0-1 min), 5- 70% MeCN / H2O (1-10 min), 70% MeCN / H2O (10-11 min), 70-95% MeCN / H2O (11.0-11.2 min), 95%% MeCN / H2O (11.2-13 min), 95-5% MeCN / H2O (13-13.2 min), 5% MeCN / H2O (15 min) 0.1% TFA v / v buffer in both mobile phases), UV detection at 216 nm, column temperature = 65 °C. UPLC-ToF Method 5-70, 40 ºC, 15 min: The gradient was 5% MeCN / H2O (0-1 min), 5-70% MeCN / H2O (1-11 min), 70% MeCN / H2O (11-11.2 min), 70 to 95% MeCN / H2O (11.2 to 13 min), 95% MeCN / H2O (13 to 13.2 min), 95 to 5% MeCN / H2O (13.2 to 15 min), 0.1% TFA v / v in both mobile phases), UV detection at 216 nm, column temparature = 40°C. Size Exclusion Chromatography SEC Method: SEC was performed on SephadexTMLH-20 column under gravity using MeCN or MeOH as the eluent at a flow rate of ~40-50 drops / min. Each fraction size comprised of 400-600 drops. Fractions containing PEGylated compounds were detected by TLC [TLC plates were developed in aq 5% (w / v) BaCl2followed by a solution of I2in ethanol] and / or were analyzed by HPLC. Fractions containing the

[0067] 64 20778549_1 (GHMatters) P122809.PCT desired products were pooled, concentrated in vacuo and the residue was dissolved in the minimum amount of de-ionised water, filtered (0.45 m filter disc) and lyophilized without delay (unless otherwise specified). Centrifugal Ultrafiltration Centrifugal ultrafiltration was carried out either on Eppendorf centrifuge 5810R at 4000 rpm or 5415R at 14000 rpm using Amicon® Ultra centrifugal filters with specified molecular weight cut-off (MWCO) Ultracel®regenerated cellulose membrane. NMR NMR spectra were recorded in CD3OD, CDCl3,D2O, CD3CN or otherwise stated on a Brucker Avance Neo 400MHz NMR instrument.1H NMR Loading Method (qNMR): The quantity of linker loaded onto the dendrimer was determined by NMR spectroscopy using an internal standard (3,4,5-trichloropyridine). Accurately weighed quantities of both the dendrimer-linker construct and the internal standard were dissolved in CD3OD and the NMR spectrum of the solution recorded. By comparing the integrated areas of the internal standard and selected regions of the dendrimer- linker construct (i.e., areas of the NMR spectrum attributable only to resonances of the linker), the number of moles of linker could be calculated per mole of construct. Endotoxin assessment Endotoxin assessment method: Endotoxin assessment was performed according to manufacturer’s protocol (Genscript ToxinSensor™ Chromogenic LAL Endotoxin Assay Kit). Final values were determined by measurement of the absorbance at 542 nm via a plate reader and extrapolated using a standard curve. SPR Surface Plasmon Resonance (SPR) experiments were used to determine the binding kinetics (on- rates, off-rates and equilibrium dissociation constant (affinity)) of anti-HER2 mAb bioconjugates. Experiments were conducted on a Biacore™ 8K+ unit (Cytiva) using Series S CM5 sensor chips (Cytiva). The recombinant antigens (Table 5.1) were obtained from a commercial source (Sino Biological) and were reconstituted according to the manufacturer’s instructions and aliquoted prior to freezing at -20 °C. The recombinant antigens were typically immobilized onto the surface of the chip using the following method: The stock solution of the antigen was diluted to 1 µg / mL in acetate buffer, pH 4 (immobilization buffer). The flow cells were activated using the amine coupling kit (Cytiva, Cat. No. BR100050) using the

[0068] 65 20778549_1 (GHMatters) P122809.PCT manufacturer’s protocol, and then the antigen was injected for between 5-7 min at a flow rate of 10 µL / min. The flow cells were then blocked with ethanolamine. The kinetics assay consisted of two start-up cycles to prime the chip surface followed by injection of various concentrations of the test article in HBS-P+ buffer (Cytiva) at 25 °C for 300 sec at 30 µL / min 5 over the flow cell followed by a dissociation phase of 1800 sec at 30 µL / min in separate cycles. Test article concentrations were typically run at 20nM, 10 nM, 5 nM, 2.5 nM, 1.25 nM and 0 nM. Regeneration of the chip surface between cycles was performed using 3.0M aq. MgCl2for 30 sec. Biacore Insight Evaluation software was used to evaluate the binding kinetics. The sensorgrams were double reference subtracted before fitting to a one-step or two-step 1:1 binding model of the data. 10 Due to the slow dissociation rate of the bioconjugates 48, 49 and 58, the data was fit first to a 1:1 dissociation only model to calculate the dissociation rate constant independently of the association phase. Once the dissociation rate constant was determined, this was set as a constant to fit a 1:1 binding model.

[0069] 66 20778549_1 (GHMatters) P122809.PCT Table of Compounds

[0070] 67 20778549_1 (GHMatters) P122809.PCT

[0071] 68 20778549_1 (GHMatters) P122809.PCT

[0072] 69 20778549_1 (GHMatters) P122809.PCT

[0073] 70 20778549_1 (GHMatters) P122809.PCT

[0074] 71 20778549_1 (GHMatters) P122809.PCT

[0075] 72 20778549_1 (GHMatters) P122809.PCT

[0076] 73 20778549_1 (GHMatters) P122809.PCT

[0077] 74 20778549_1 (GHMatters) P122809.PCT

[0078] 75 20778549_1 (GHMatters) P122809.PCT Example 1: Intermediates 1.1 Dendrimer Scaffolds 1.1.1 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NH2.TFA)4(ε-PEG25)4] 1 Synthesised and characterised according to analogous procedures described in WO2021 / 035310 A1 and WO02 / 00079299. 1.1.2 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NH2.TFA)8(ε-PEG25)8] 2 Synthesised and characterised according to analogous procedures described in WO2021 / 035310 A1 and WO02 / 00079299. 1.2 Linkers and Common Intermediates containing DXd 1.2.1 Fmoc-GGFG-C(O)NH-CH2-DXd 7 To a stirred solution of Fmoc-GGFG-C(O)NH-CH2-O-CH2-CO2H 6 (CAS: 2264011-98-3, 727 mg, 1.13 mmol), exatecan mesylate 3 (CAS: 169869-90-3, 500 mg, 0.94 mmol) and NMM (204 µL, 1.86 mmol) in DMF (15 mL) at room temperature was added PyBOP (586 mg, 1.13 mmol). After stirring for 18 h, the volatiles were removed in vacuo and the residue was dissolved in DMSO (4 mL) and purified by automated flash purification [AutoFlash Method 10-20-63-68-100 CV, 120g C18] eluting with acetonitrile:water. Fractions eluting between 18-26 CV were collected and concentrated in vacuo to give Fmoc-GGFG- C(O)NH-CH2-DXd 7 as a yellow solid (820 mg, 82%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.95 min. ESI MS (+ve) 1063 [M]+; calc. m / z for C57H55F1N8O12 [M]+= 1063.11. 1.2.2 H2N-GGFG-C(O)NH-CH2-DXd 8 Fmoc-GGFG-C(O)NH-CH2-DXd 7 (90 mg, 85 µmol mmol) was dissolved in piperidine:DMF (1:9 v / v, 5 mL) with stirring at rt. After 2 h, the reaction mixture was concentrated to dryness and the residue was triturated with diethyl ether (2 x 5 mL). The residual solid was then dissolved in deionised water (3.0 mL) and the resulting solution then lyophilised to give H2N-GGFG-C(O)NH-CH2-DXd 8 (62 mg, 87 %), which was used without further purification. LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 3.43 min. ESI MS (+ve) 841 [M]+; calc. m / z for C42H45FN8O10[M]+= 840.87. 1.2.3 HO2C-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd 9 To a stirred solution of H2N-GGFG-C(O)NH-CH2-DXd 5 (25 mg, 29 µmol) in DMF (5 mL) was added NMM (4.8 µL, 45 µmol) followed by glutaric anhydride (4 mg, 35 µmol). The reaction mixture was 76 20778549_1 (GHMatters) P122809.PCT stirred for 18 h whereupon the volatiles were removed in vacuo. The residue was purified by preparative HPLC (Prep HPLC Method 10-60, TFA, Rt = 37 min) to give HO2C-(CH2)3-C(O)NH-GGFG-C(O)NH- CH2-DXd 9 as yellow solid (18.0 mg, 63%) LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 3.91 min. ESI MS (+ve) 955 [M]+; calc. m / z for C47H51FN8O13 [M]+= 955. 1H NMR (400 MHz, DMSO-d6): δ (ppm): 0.87 (t, J 4.0 Hz, 3H), 1.67-1.89 (m, 4H); 2.05-2.37 (m, 9H); 2.71-2.84 (m, 1H), 2.86-2.97 (m, 1H); 2.97-3.12 (m, 1H), 3.49-3.85 (m, 6H), 4.12 (dd, J 19.2 and 15.4 Hz, 2H), 4.29 (dd, J 6.8 and 2.8 Hz, 1H), 4.52-4.75 (m, 2H), 4.90 (d, J 18.7 Hz, 1H), 5.11-5.26 (m, 2H), 5.47 (d, J 16.3 Hz, 1H), 5.53-5.67 (m, 1H), 6.98-7.27 (m, 5H) and 7.35-7.56 (m, 2H). 1.2.4 HO2C-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd 11 To a stirred solution of H2N-GGFG-C(O)NH-CH2-DXd 8 (220 mg, 0.26 mmol) in DMF (10 mL) was added NMM (167 µL, 1.52 mmol) followed by HO2C-PEG9-NHS Ester 10 (104 mg, 0.91 mol). The reaction mixture was stirred for 3 days whereupon the volatiles were removed in vacuo and the residue was purified by preparative HPLC (Prep-HPLC Method 10-60, TFA, Rt= 35 min to 42 min) to give HO2C-PEG9- C(O)NH-GGFG-C(O)NH-CH2-DXd 11 as a yellow solid (180 mg, 65 %). LCMS (UPLC-SQD Method 5-60, 9 min): Rt = 4.68 min. ESI MS (+ve) 1337 [M]+; calc. m / z for C64H85FN8O22[M]+= 1337. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.78-0.97 (m, 3H), 1.65-1.92 (m, 2H), 1.98-2.17 (m, 1H), 2.16-2.33 (m, 4H), 2.33-2.53 (m, 4H), 2.70-2.84 (m, 1H), 2.86-3.08 (m, 2H), 3.25-3.41 (m, 1H), 3.43-3.56 (m, 30H), 3.56-3.67 (m, 6H), 3.67-3.84 (m, 4H), 3.97-4.22 (m, 2H), 4.22-4.37 (m, 1H), 4.52-4.89 (m, 21H), 5.01-5.28 (m, 2H), 5.33-5.49 (m, 1H), 5.49-5.67 (m, 1H), 6.95-7.23 (m, 5H) and 7.32-7.53 (m, 2H). 1.2.5 tert-BuO2C-CH2-O-C(O)-OPNP 14 To a stirred solution of tert-butyl-2-hydroxyacetate 12 (CAS: 50595-15-8, 400 mg, 3.01 mmol) and bis(4-nitrophenyl) carbonate 13 (CAS: 5070-13-3, 997 mg, 3.01 mmol) in DMF (15 mL) at 0 ºC was added triethylamine (2.01 mL, 7.52 mmol). The reaction was allowed to warm to rt and stirred for 2 h which gave a yellow solution of tert-BuO2C-CH2-O-C(O)-OPNP 14 (893 mg, 100%), which was used without further purification. LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.90 min. ESI MS (+ve) 313 [M+H2O]+; calc. m / z for C13H17NO8 [M+H2O]+= 313. 1.2.6 Fmoc-Val-Cit-PAB-Pyr-NBoc(Me) 17 To a solution of Fmoc-Val-Cit-PAB-O-C(O)-OPNP 15 (3.86 g, 5.03 mmol) in DMF (40 mL) at rt was added a solution of H-Pyr-NBoc(Me) 16 (CAS: 863971-53-3, 1.08 g, 5.03 mmol) in DMF (4 mL). The reaction mixture was stirred for 5 h and then concentrated in vacuo. The residue was suspended in diethyl 77 20778549_1 (GHMatters) P122809.PCT ether (50 mL) and the suspension stirred for 18 h. The solids were separated by filtration and dried in a stream of air to give Fmoc-Val-Cit-PAB-Pyr-NBoc(Me) 17 as a pale yellow solid (3.81 g, 90 %). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 5.32 min. ESI MS (+ve) 865 [M+Na]+; calc. m / z for C45H59N7 NaO9 [M+Na]+= 865. 1H NMR (400 MHz, DMSO-d6): δ (ppm): 0.75-0.97 (m, 6H), 1.26-1.50 (m, 11H), 1.52-1.63 (m, 1H), 1.64-1.75 (m, 2H), 1.76-1.89 (m, 3H), 1.90-2.02 (m, 1H), 2.58-2.86 (m, 3H), 2.86-3.23 (m, 6H), 3.84-4.04 (m, 2H), 4.15-4.58 (m, 4H), 4.85-5.09 (m, 2H) 5.29-5.47 (m, 2H), 5.84-6.04 (m, 1H), 7.10-7.47 (m, 7H), 7.47-7.63 (m, 2H), 7.63-7.80 (m, 2H), 7.80-7.98 (m, 2H), 7.98-8.18 (m, 1H) and 9.99-10.13 (m, 1H). 1.2.7 Fmoc-Val-Cit-PAB-Pyr-NH(Me).TFA 18 To a chilled (ice-water) suspension of Fmoc-Val-Cit-PAB-Pyr-NBoc(Me) 17 (3.81 g, 4.53 mmol) in DCM (28 mL) was added TFA (6.92 mL, 90.5 mmol) dropwise over 5 min. The reaction mixture was stirred for 1 h, removed from the cooling bath and the volatiles were removed in vacuo. The residue was dissolved in MeCN (30 mL) and the resulting solution concentrated in vacuo to remove residual TFA. The residue was dissolved in de-ionised water (30 mL) and the solution lyophilised to give Fmoc-Val-Cit-PAB- Pyr-NH(Me).TFA 18 as an off-white solid (4.23 g, 91%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 3.87 min. ESI MS (+ve) 743 [M+H]+; calc. m / z for C40H52N7O7[M+H]+= 743. 1H NMR (400 MHz, DMSO-d6): δ (ppm): 0.66-1.06 (m, 6H), 1.28-2.08 (m, 9H), 2.55-2.71 (m, 2H), 2.76-3.13 (m, 4H), 3.13-3.50 (m, 4H), 3.86-4.11 (m, 6H), 4.17-4.47 (m, 4H), 4.90-5.15 (m, 2H), 5.87-6.17 (m, 1H), 7.19-7.50 (m, 6H), 7.50-7.66 (m, 2H), 7.66-7.98 (m, 3H), 8.06-8.19 (m, 1H), 8.21-8.42 (m, 1H) and 10.00-10.13 (m, 1H). 1.2.8 Fmoc-Val-Cit-PAB-Pyr-N(Me)-CO2-CH2-CO2-t-Bu 19 To a stirred solution of tert-BuO2C-CH2-O-C(O)-OPNP 14 (893 mg from previous step, 3.01 mmol) and triethylamine (2.01 mL, 7.52 mmol) in DMF (15 mL) was added Fmoc-Val-Cit-PAB-Pyr-NH(Me).TFA 18 (1.98 g,2.31 mmol). After 2 h, the volatiles were removed in vacuo and the solid residue was triturated with diethyl ether (2 x 50 mL) and then dried under high vacuum to give Fmoc-Val-Cit-PAB-Pyr-N(Me)- CO2-CH2-CO2-t-Bu 19 as an off-white solid (1.42 g, 68%) which was used in the subsequent step (tert- butyl ester deprotection) without further purification. LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 5.28 min. ESI MS (+ve) 901 [M+H]+; calc. m / z for C47H62N7O11 [M+H]+= 901 1.2.9 Fmoc-Val-Cit-PAB-Pyr-N(Me)-CO2-CH2-CO2H 20 A solution of Fmoc-Val-Cit-PAB-Pyr-N(Me)-CO2-CH2-CO2-t-Bu 19 (520 mg from previous step, assumes 0.59 mmol) in DCM:TFA (4:1 v / v, 0.4 mL) was stirred for 4 h whereupon an additional portion 78 20778549_1 (GHMatters) P122809.PCT of TFA was added (45 µL). After stirring for 16 h in total, the volatiles were removed in vacuo and the residue was purified by automated flash purification [AutoFlash Method 10-35-55-100 min (+ 0.05% TFA modifier), 80g C18] eluting with acetonitrile:water. Fractions eluting between 18-20 mins were collected and concentrated in vacuo to give Fmoc-Val-Cit-PAB-Pyr-N(Me)-CO2-CH2-CO2H 20 as a white solid (60 mg, 11%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.62 min. ESI MS (+ve) 867 [M+Na]+; calc. m / z for C43H53N7O11Na [M+Na]+= 867. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.85-1.04 (m, 6H), 1.47-2.16 (m, 9H), 2.71-3.03 (m, 3H), 3.03-3.27 (m, 2H), 3.34-3.53 (m, 4H), 3.89-3.99 (m, 1H), 4.05-4.19 (m, 1H), 4.19-4.28 (m, 1H), 4.33-4.61 (m, 5H), 4.97-5.12 (m, 2H) and 7.12-7.88 (m, 12H). 1.2.10 H2N-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 21 To a solution of exatecan mesylate 3 (243 mg, 0.46 mmol) in DMF: DMSO (1:1 v / v, 40 mL) was added Fmoc-Val-Cit-PAB-Pyr-N(Me)-CO2-CH2-CO2H 20 (387 mg, 0.46 mmol) followed by PyBOP (286 mg, 0.55 mmol) and NMM (151 µL, 1.37 mmol). The reaction was stirred for 1 h after which time compound 19 was consumed (LCMS). The volatiles were removed in vacuo and the residue was dissolved in deionized water (120 mL) and the solution was lyophilised to give a yellow oil. The oil was dissolved in dry DMF to give a total volume of 15 mL and piperidine (905 µL, 9.18 mmol) added. After 1 h, the reaction mixture was purified directly by automated flash chromatography [AutoFlash Method 10-60-100 min (+ 0.05% TFA modifier), 80 g C18] eluting with acetonitrile:water. Fractions eluting between 6-8 CV were collected and concentrated in vacuo to give H2N-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 21 as a yellow solid (488 mg, 85%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt= 3.59 min. ESI MS (+ve) 1040 [M+H]+; calc. m / z for C52H63FN10O12[M+H]+= 1040. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.84-1.56 (m, 6H); 1.32-2.00 (m, 14H), 2.15-2.48 (m, 4H), 2.67-2.94 (m, 2H), 2.94-3.06 (m, 2H), 3.06-3.27 (m, 4H), 3.37-3.49 (m, 3H), 3.83 (d, J 5.5 Hz, 2H), 4.42- 4.64 (m, 3H), 7.36-7.52 (m, 6H), 7.66-7.75 (m, 2H), 7.81-7.95 and (m, 2H). 1.2.11 H2OC-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 22 To a solution of H2N-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 21 (50 mg, 48 µmol) and HO2C-PEG9-NHS ester 7 (35 mg, 48 µmol) in DMF (2 mL) was added triethylamine (40 mg, 144 µmol). After stirring for 18 h, the reaction mixture was purified directly by automated flash chromatography [AutoFlash Method 10- 60-100 min (+ 0.05% TFA modifier), 40 g C18]. Fractions eluting at 13 CV were collected and concentrated in vacuo to give H2OC-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 22 as a yellow solid (36 mg, 85%). 79 20778549_1 (GHMatters) P122809.PCT LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.26 min. ESI MS (+ve) 1537 [M+H]+; calc. m / z for C74H104FN10O24 [M+H]+= 1537. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.74-1.03 (m, 9H), 1.25-2.09 (m, 15H), 2.09-2.37 (m, 6H), 2.37-2.53 (m, 4H), 2.55-2.89 (m, 5H), 2.89-3.17 (m, 8H), 3.24-3.45 (m, 4H), 3.58-3.77 (m, 4H), 3.82-4.23 (m, 5H), 4.31-4.66 (m, 22H), 4.99-5.69 (m, 7H), 6.65-6.75 (m, 1H), 6.91-7.03 (m, 1H), 7.03-7.26 (m, 2H) and 7.28-7.63 (m, 5H). 1.3 Linkers and Common Intermediates containing SN-38 1.3.1 SN-38C-10-O(CO)-PNP 24 To a chilled (ice-water bath) and stirred solution of SN-3823 (2.0 g, 5.10 mmol) in anhydrous DMSO (75 mL) and THF (75 mL) was added triethylamine (2.03 mL14.5 mmol) and bis-4-nitrophenyl carbonate 13 (2.64 g, 8.67 mmol). After 1 h, the reaction mixture was lyophilised overnight to remove the majority of DMSO and the resulting semi solid was suspended in MTBE (125 mL) and stirred. After 20 min, the suspension was filtered and the residue was washed with MTBE (2 x 125 mL) and dried in a stream of air to give SN-38C-10-O(CO)-PNP 24 (3.45 g, >100%, contains residual DMSO and 4-nitrophenol but deemed suitable for use in subsequent steps). LCMS (UPLC-SQD Method 5-20-80, 9 min): Rt= 4.69 min. ESI MS (+ve) 558 [M+H]+; calc. m / z for C29H23N3O9[M+H]+= 558. 1H NMR (400 MHz, DMSO-d6): δ (ppm): 0.79-1.00 (m, 3H), 1.10 (s, 6H), 1.22-1.39 (m, 3H), 1.78- 1.96 (m, 2H), 2.51-2.57 (m, 13H), 3.07 (s, 2H), 3.13-3.26 (m, 3H), 5.32 (s, 2H), 5.45 (s, 2H), 6.53 (s, 1H), 6.82-6.92 (m, 0H), 7.34 (s, 1H), 7.67-7.81 (m, 2H), 7.90-8.02 (m, 1H), 8.04-8.12 (m, 0H) and 8.23-8.43 (m, 4H) 1.3.2 H2N-Val-Cit-PAB-Pyr-NBoc(Me) 25 To a stirred solution of Fmoc-Val-Cit-PAB-O-C(O)-OPNP 15 (1.0 g, 1.3 mmol) in DMF (10 mL) was added H-Pyr-NBoc(Me) 16 (3.07 g, 1.4 mmol) at room temperature. After 1 h, the volatiles were removed in vacuo and to the residual organics was added diethyl ether (50 mL). The resulting suspension was stirred for 1 h and the pale yellow solid was separated by filtration and washed with diethyl ether (50 mL). The solid (Fmoc-Val-Cit-PAB-Pyr-NBoc(Me) 17, not weighed) was dissolved in piperidine:DMF (1:9 v / v, 10 mL) and the resulting solution was stirred at room temperature. After 30 min, the volatiles were removed in vacuo and the residue was triturated with diethyl ether (3 x 50 mL) to eventually give a pale yellow solid. The solid was separated by filtration and dried in vacuo to give H2N-Val-Cit-PAB-Pyr- NBoc(Me) 25 (550 mg, 68%, 2 steps). LCMS (UPLC-ToF Method 5-70, 15 min): Rt = 5.08 min. ESI MS (+ve) 620 [M+H]+; calc. m / z for C30H49N7O7 [M+H]+= 620. 80 20778549_1 (GHMatters) P122809.PCT 1.3.3 HO2C-PEG9-Val-Cit-PAB-Pyr-NBoc(Me) 26 To a stirred solution of H2N-Val-Cit-PAB-Pyr-NBoc(Me) 25 (1.50 g, 2.42 mmol) in acetonitrile was added a solution of HO2C-PEG9-NHS ester 10 (1.48 g, 2.42 mmol) in acetonitrile (3 mL). The reaction mixture was stirred for 18 h whereupon the volatiles were removed in vacuo. The residue was dissolved in DMSO (6 mL) and purified in portions (~2 mL of DMSO solution per run) by automated flash chromatography [AutoFlash Method 5-20-40-60-90 min (+ 0.05% TFA modifier), 30 g C18] eluting with acetonitrile:water. Fractions from the various runs were analysed by LCMS and those containing the desired product were combined and concentrated in vacuo to give HO2C-PEG9-Val-Cit-PAB-Pyr-NBoc(Me) 26 as a yellow solid (900 mg, 33%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 5.42 min. ESI MS (+ve) 1117 [M+H]+; calc. m / z for C52H90N7O19 [M+H]+= 1117. 1.3.4 HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me) 27 To a chilled (ice-water bath) solution of HO2C-PEG9-Val-Cit-PAB-Pyr-NBoc(Me) 26 (900 mg, 0.82 mmol) in DCM (9 mL) was added TFA (1.6 mL, 21.5 mmol) with stirring. After 20 mins, the ice-water bath was removed, and the reaction mixture was allowed to warm to room temperature. After stirring for 4 h, the volatiles were concentrated in vacuo and the residue was dissolved in water and the resulting solution then lyophilised to give HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me) 27 as a brown oil (806 mg, 87% was used in subsequent steps without further purification). LCMS (UPLC-SQD Method 5-80, 9 min): Rt= 4.53 min. ESI MS (+ve) 1017 [MH]+; calc. m / z for C47H82N7O17[MH]+= 1017. 1.3.5 HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me)C(O)-SN-38C-1028 To a stirred solution of HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me) 27 (902 mg, 0.80 mmol) in DMF (18 mL) at room temperature was added SN-38C-10-O(CO)-PNP 24 (690 mg, 1.20 mmol). After stirring for 5 min, triethylamine (333 µL, 2.40 mmol) was added. After stirring for 10 min, the reaction mixture was concentrated in vacuo and the residue was dissolved in DMSO (5 mL) and purified in portions (1 mL of DMSO solution per run) by automated flash chromatography [AutoFlash Method 5-20-35-50-90 min (+ 0.05% TFA modifier), 35 g C18] eluting with acetonitrile:water. Fractions from the various runs were analysed by LCMS and those containing the desired product were combined and concentrated in vacuo to give HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me)C(O)-SN-38C-1028 as a yellow solid (460 mg, 40%). LCMS (UPLC-SQD Method 5-60, 9 min): Rt = 5.19 min. ESI MS (+ve) 1436 [MH]+; calc. m / z for C70H100N9O23 [MH]+= 1436. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.90-1.12 (m, 7H), 1.23-1.47 (m, 3H), 1.47-1.66 (m, 2H), 1.66-1.80 (m, 1H), 1.80-2.20 (m, 7H), 2.46-2.63 (m, 3H), 2.89-3.29 (m, 6H), 3.36-3.69 (m, 26H), 3.69-3.85 81 20778549_1 (GHMatters) P122809.PCT (m, 4H), 4.14-4.25 (m, 1H), 4.26-4.63 (m, 2H), 4.93-5.24 (m, 2H), 5.26-5.49 (m, 2H), 5.51-5.71 (m, 1H) and 7.10-8.35 (m, 8H). 1.4 Synthesis of HER-2-Targeted VHH 1.4.1 HER2-VHH-(Terminal Cys) 29 Sequence: MEVQLVESGG SLVQPGGSLR LSCAASGFTF DDYAMSWVRQ VPGKGLEWVS SINWSGTHTD YADSVKGRFT ISRNNANNTL YLQMNSLKSE DTAVYYCAKN WRDAGTTWFE KSGSAGQGTQ VTVSSC Predicted MW (Average):13,709.15 Da Number of amino acids: 126 Theoretical pI: 5.71 Plasmid name: pET-2D3-cys-tagless (features kanamycin selection, IPTG inducible) Culture Method: Shake flask, batch expression. Materials: Terrific broth (24 g / L yeast extract, 20 g / L tryptone, 4 ml / L glycerol, 0.017 M KH2PO4, 0.72 M K2HPO4), 30 µg / mL Kanamycin sulfate. 1. Transform chemically competent BL21(DE3) Star with pET-2D3-cys-tagless 2. Plate out on LB agar overnight. 3. Pick single colony and inoculate 250 mL overnight culture (TB Kanamycin, 37 °C with shaking). 4. Spin down overnight culture and resuspend cells in 250 mL fresh media with 1 mM IPTG. Incubate with shaking for 4 h at 37 °C. 5. Harvest cells by centrifugation at 2,000 x g. 6. Store cell pellets at -20 °C until processed. Purification 1. Resuspend frozen wet cell pellet in BugBuster® reagent (Merck) and further disrupt cells using mechanical lysis. Perform two passes through an Emulsiflex C3 (Avestin) at 10,000-15,000 psi. 2. Recover insoluble material by centrifugation at 12,000 x g for 15 mins. 3. Wash insoluble pellet thrice with 50 mM Tris, 1% v / v Triton-X 100, pH 8 by resuspending in buffer and re-pelleting by centrifugation. Pellet will be an off-white colour with a wax-like consistency. 4. Dissolve pellet in 6 M guanidine HCl, 50 mM NaH2PO4, 300 mM NaCl, 20 mM Imidazole, pH 8.0 (30-50 mL), incubate overnight with stirring to completely solubilize. Solution will become light brown and slightly turbid. 82 20778549_1 (GHMatters) P122809.PCT 5. Centrifuge at 12,000 x g for 15 minutes to separate remaining solids, filter supernatant through a 0.45 µm syringe filter. 6. Snap-dilute by slowly adding filtered sample to 1 L of vigorously stirring 50 mM Tris pH 8.0, 0.05% v / v 2-mercaptoethanol. A fine white precipitate will form. Stir overnight at room temperature. 5 7. Clarify solution by centrifugation at 12000 x g for 10 minutes or by vacuum filtration (0.45 µm). Discard white precipitate. Nanobody will be in clear supernatant / filtrate. 8. Concentrate solution and buffer exchange to remove remaining guanidine HCl using a 10 kDa MWCO Amicon® ultrafiltration device or tangential flow filtration capsule. Exchanging into 50 mM Tris, 0.05%v / v β-mercaptoethanol can limit formation of nanobody-nanobody dimers which can sometimes10 precipitate at high protein concentration. Nanobodies are stored in 50 mM Tris, 0.05% v / v β- mercaptoethanol, pH 8.0. 9. (Optional) Perform anion exchange chromatography using HiTrap Q HP 5mL (Cytiva), Buffer A (50 mM Tris, pH 8.0) using gradient elution with buffer B (1 M NaCl, 50 mM Tris, pH 8.0) or size exclusion chromatography using Superdex 75 Increase 10 / 300 GL (Cytiva) in 50 mM Sodium 15 Phosphate, 150 mM Sodium Chloride, pH 7.0. UPLC-ToF (UPLC-ToF Method 20-80-Protein, 15 min) HER2-VHH (Terminal Cys) 29 (monomer), Rt = 4.25 min with m / z 13,703 amu (following reduction with BME). SDS Page gel of cell lysate fractions and refolding (not shown), showed nanobody to be present in the insoluble fraction. A 15 kDa sized protein in the soluble fraction was found not to be nanobody 20 following purification. The refolded nanobody remained soluble. 1.5. Trastuzumab Intermediates 1.5.1 Deglycosylated Trastuzumab 31 25 Adapted from the procedure described by Anami, Y., Tsuchikama, K. (2020). Transglutaminase- Mediated Conjugations. In: Tumey, L. (eds) Antibody-Drug Conjugates. Methods in Molecular Biology, vol 2078. Humana, New York, NY. https: / / doi.org / 10.1007 / 978-1-4939-9929-3_5 A solution of Trastuzumab 30 for SC injection (2 mL of 120 mg / mL Herceptin®) was buffer exchanged via Amicon® Ultra-15 centrifugal filter unit 50 kDa MWCO (Merck Millipore) into 10 mM 30 PBS, pH 7.4. The concentration was adjusted to 10 mg / mL with 10 mM PBS, pH 7.4. PNGase F (New England Biolabs, 500,000 units / mL, 30 µL) was added to the solution and incubated at 37 °C for 12-24 h and the reaction was monitored by UPLC. For the reduction of 48, TCEP, 0.5 M (tris(2- carboxyethyl)phosphine), 1% v / v (Sigma-Aldrich) was used. UPLC-ToF analysis of TCEP reduced product (UPLC-ToF Method 5-70-Protein, 65 °C, 15 min): Heavy chain: Rt= 5.08 min; m / z 49,150 Da (changed 35 from m / z 50,594 Da before reaction); Light chain: Rt = 4.94 min; m / z 23,441 Da (no change during reaction). After 24 h, the PNGase F was removed using centrifugation (Amicon® Ultra-15 centrifugal filter unit 50 kDa MWCO), samples were run at 5,000x g for 15 min with a total of 5 washes. 83 20778549_1 (GHMatters) P122809.PCT 1.5.2 Trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 To a solution of deglycosylated trastuzumab 31 in PBS buffer pH 7.4 (10 mL, 2.4 mg / mL) was added a solution of sulfo-DBCO-PEG4-amine 5 (CAS: 2055198-05-3, 86.3 mg, 0.128 mmol) in 10 mM PBS (5 mL) at rt. The reaction mixture was left at rt followed by the addition of microbial transglutaminase (Activa® TI Transglutaminase, 3,000 units, Ajinomoto), resuspended in 10 mM PBS, pH 7.4 (100 mL). The final concentration is 13 units of microbial transglutaminase per 1 mg of 31. The sample was incubated at room temperature for 72 h or until completion of the modification [Reaction monitored via UPLC-ToF (UPLC-ToF Method 5-70-Protein, 65 °C, 15 min)]. An increase in heavy chain mass vs 31 can be observed by UPLC-ToF analysis with a peak at Rt = 5.22 min; m / z at 49,808 Da (m / z 49,150 Da before reaction). Upon completion, MTGase and unreacted linker were removed by affinity chromatography using HiTrap™ MabSelect™ PrismA 5 ml column (Cytiva, Buffer A: 10 mM PBS, pH 7.4; Buffer B: 0.1 M citrate buffer, pH 3.0). Eluted fractions were immediately neutralised to pH 7.0 with 1.0 M Tris, pH 9.0. Purification runs were monitored at 280 nm. Fractions of interest were collected and buffered exchanged with Amicon® Ultra-15 centrifugal filter unit 50 kDa MWCO and concentrated to 100 mL final volume (2 mg / mL in 10 mM PBS, pH 7.4). 1.6. Bioconjugation Linkers 1.6.1 MAL-CH2-CyHexyl-CO2H 35 A stirred solution of maleic anhydride 33 (3.04 g, 31.0 mmol) and trans-4- (aminomethyl)cyclohexanecarboxylic acid 34 (4g, 25.4 mmol) in glacial acetic acid (50 mL) was heated at 120 °C for 6 h. Upon cooling to room temperature, the reaction mixture was stirred for 18 h and concentrated in vacuo. EtOAc (50 mL) was poured onto the residue and the resulting suspended solids were separated by filtration. The filtrate was washed with water (3 x 30 mL), dried (MgSO4) and concentrated to ~30 mL volume in vacuo. The solution was placed in the freezer at -20 °C for 18 h and the resulting crystalline solid was separated by filtration and dried in vacuo to give MAL-CH2-CyHexyl-CO2H 35 (2.3 g, 39%). 1H NMR (400 MHz, CD3OD): δ (ppm): 0.80-1.02 (m, 2H), 1.20-1.32 (m, 2H), 1.45-1.71 (m, 3H), 1.81-1.90 (m, 2H), 2.02-2.19 (m, 2H), 2.44-2.56 (m, 2H), 3.19-3.28 (m, 2H) and 7.00 (s, 2H). 1.6.2 MAL-CH2-CyHexyl-NHS Ester 36 To a stirred solution of MAL-CH2-CyHexyl-CO2H 35 (2.3 g, 9.7 mmol) in DCM (30 mL) at rt was added DCC (2.19 g, 10.7 mmol) and N-hydroxysuccinamide (1.23 g, 10.8 mmol). After 18 h, the resulting suspension was filtered, and the filtrate was concentrated in vacuo. The residue was triturated with MeCN (2 x ~10 mL) and any solids were separated by filtration. The filtrate was concentrated in vacuo to give MAL-CH2-CyHexyl-NHS Ester 36 (3.3 g, quant.) 84 20778549_1 (GHMatters) P122809.PCT1H NMR (400 MHz, CD3OD): δ (ppm): 0.96-1.12 (m, 2H), 1.31-1.46 (m, 2H), 1.47-1.83 (m, 4H), 1.92-2.06 (m, 2H), 2.64-2.74 (m, 1H), 2.76-2.85 (m, 4H), 3.22-3.30 (m, 2H) and 7.03 (s, 2H). 1.6.3 MAL-CH2-CyHexyl-C(O)NH-PEG24-CO2H 38 To a stirred solution of amino-dPEG®₂₄-acid 37 (CAS: 756526-07-4, 700 mg, 0.62 mmol) and NMM (204 µL, 1.86 mmol) in DMF (5 mL) at rt was added MAL-CH2-CyHexyl-NHS Ester 36 (245 mg, 0.73 mmol). After stirring for 18 h, more MAL-CH2-CyHexyl-NHS Ester 36 (41 mg, 0.12 mmol) was added to the reaction mixture and stirring continued. After 18 h, the volatiles were removed in vacuo and the residue was dissolved in deionised water and extracted with EtOAc (2 x 25 mL). The aqueous layer was concentrated in vacuo to give MAL-CH2-CyHexyl-C(O)NH-PEG24-CO2H 38 as a clear colourless oil (930 mg, wet), which was used in subsequent steps without further purification. LCMS (UPLC-SQD Method 5-10-35, 9 min): Rt = 6,49 min. ESI MS (+ve) 1366 [M+H]+; calc. m / z for C63H117N2O29 [M+H]+= 1366. 1.6.4 MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO 40 To a stirred solution of MAL-CH2-CyHexyl-C(O)NH-PEG24-CO2H 38850 mg, 0.62 mmol) in DMF (5 mL) at room temperature was added NMM (205µL, 1.86 mmol) and NH2-(CH2)2-DBCO 39 (CAS: 1255942-06- 3, 206 mg, 0.75 mmol) and PyBOP (390 mg, 0.75 mmol). The reaction mixture was stirred for 18 h whereupon the volatiles were removed in vacuo. The residue was dissolved in water (25 mL) and extracted with ethyl acetate (3 x 25 mL). The aqueous phase was concentrated in vacuo to a volume of ~6 mL and filtered (0.2 µm filter disc). The filtrate was collected and purified by preparative HPLC over several runs [Prep-HPLC Method 30-60, TFA; Product elutes at 36-38 min] to give MAL-CH2-CyHexyl-C(O)NH- PEG24-C(O)NH-(CH2)2-DBCO 40 as a light brown oil (425 mg, 43%). LCMS (UPLC-SQD Method 5-20-80, 9 min): Rt= 4.38 min. ESI MS (+ve) 1625 [M+H]+; calc. m / z for C81H131N4O29[M+H]+= 1625. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.93-1.11 (m, 2H), 1.31-1.52 (m, 2H), 1.57-1.92 (m, 5H), 1.99-2.25 (m, 14H), 2.25-2.35 (m, 2H), 2.44-2.64 (m, 1H), 3.08-3.22 (m, 1H), 3.24-3.41 (m, 10H), 3.42- 3.69 (m, 94H), 3.69-3.85 (m, 2H), 5.11-5.24 (m, 1H), 6.84 (s , 2H), 7.24-7.33 (m, 1H), 7.33-7.44 (m, 2H), 7.44-7.56 (m, 4H) and 7.61-7.74 (m, 1H). Example 2: DXd Loaded Dendrimers 2.1 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd)4(ε- PEG25)4] 41 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NH2.TFA)4(ε-PEG25)4] 1(100 mg, 14.1 µmol), HO2C-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd 9 (89 mg, 93.2 µmol) and NMM (50 µL, 85 20778549_1 (GHMatters) P122809.PCT 451 µmol) in DMF (5 mL) at room temperature was added PyBOP (44 mg, 84.6 µmol). The reaction mixture was stirred for 18h whereupon the volatiles were removed in vacuo. The residue was dissolved in methanol (2 mL) and the resulting solution filtered (0.45 µM filter disc). The filtrate was purified by size exclusion chromatography (SEC method, eluent = methanol) to give N3-PEG24- C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd)4(ε-PEG25)4] 41 as a light yellow solid (137 mg, 94%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.83 min. ESI MS (+ve) 10376 [M]+; calc. m / z for C489H792F4N50O183 [M]+= 10376 1H NMR (400 MHz, CD3OD): δ (ppm): 0.74-0.95 (m, 11H), 1.08-1.93 (m, 57H), 1.94-2.42 (m, 42H), 2.46-2.61 (m, 3H), 2.70-2.86 (m, 4H), 2.86-3.18 (m, 27H), 3.23-3.26 (m, 2H), 3.27 (m, 12H), 3.28- 3.32 (m, 3H), 3.33-3.99 (m, 517H), 3.99-4.26 (m, 14H), 4.26-4.42 (m, 5H), 4.55-4.76 (m, 18H), 4.94-5.28 (m, 9H), 5.32-5.65 (m, 8H), 6.95-7.22 (m, 19H) and 7.22-7.45 (m, 7H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.27 ppm (12H, s) with integrals of aromatic region at δ (ppm) = 6.95-7.22 (m, 19H) and 7.22-7.45 (m, 7H) shows 93% capping (3.7 drug-linkers per molecule of dendrimer). 2.2 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd)4(ε- PEG25)4] 42 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NH2.TFA)4(ε-PEG25)4] 1 (65 mg, 9.1 µmol), HO2C-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd 11 (79 mg, 59 µmol) and NMM (35 µL, 316 µmol) in DMF (5 mL) at room temperature was added PyBOP (31 mg, 59 µmol). The reaction mixture was stirred for 18h whereupon the volatiles were removed in vacuo. The residue was dissolved in methanol (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, eluent = methanol) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH- CH2-DXd)4(ε-PEG25)4] 42 as a yellow solid (80 mg, 73%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt= 4.86 min. ESI MS (+ve) 11906 [M+H]+; calc. m / z for C557H929F4N50O219[M+H]+= 11906. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.91-1.05 (m, 11H), 1.21-2.02 (m, 53H), 2.07-2.73 (m, 48H), 2.84-2.98 (m, 5H), 3.00-3.29 (m, 28H), 3.35-3.37 (m, 3H), 3.38 (s, 12H), 3.39-3.43 (m, 4H), 3.44- 3.53 (m, 5H), 3.53-3.97 (m, 578H), 4.13-4.48 (m, 22H), 4.67-4.87 (m, 55H), 5.13-5.37 (m, 11H), 5.46-5.59 (m, 5H), 5.64-5.77 (m, 5H), 7.12-7.36 (m, 20H) and 7.41-7.58 (m, 8H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.38 ppm (s, 12H) with integrals of aromatic region at δ (ppm) = 7.12-7.36 (m, 20H) and 7.41-7.58 (m, 8H) shows full capping (4 drug-linkers per molecule of dendrimer). 86 20778549_1 (GHMatters) P122809.PCT 2.3 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH-CH2- DXd)8(ε-PEG25)8] 43 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NH2.TFA)8(ε-PEG25)8] 2 (100 mg, 7.6 µmol), HO2C-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd 11 (122 mg, 91 µmol) and NMM (53 µL, 486 µmol) in DMF (5 mL) at room temperature was added PyBOP (47 mg, 91 µmol). The reaction mixture was stirred for 18h whereupon the volatiles were removed in vacuo. The residue was dissolved in methanol (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, eluent = methanol) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-PEG9-C(O)NH- GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8] 43 as a yellow solid (147 mg, 85%). LCMS (UPLC-SQD Method 5-80, 9 min): Rt = 4.99 min. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.86-1.08 (m, 23H), 1.19-2.06 (m, 109H), 2.06-2.74 (m, 91H), 2.79-2.99 (m, 10H), 2.99-3.29 (m, 55H), 3.38 (s, 24H), 3.39-3.43 (m, 4H), 3.44-3.53 (m, 9H), 3.53- 3.70 (m, 1078H), 3.70-4.01 (m, 115H), 4.14-4.38 (m, 31H), 4.38-4.49 (m, 9H), 4.66-4.86 (m, 35H), 5.07- 5.34 (m, 19H), 5.43-5.59 (m, 10H), 5.60-5.75 (m, 9H), 7.13-7.33 (m, 41H) and 7.36-7.52 (m, 15H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.38 ppm (s, 24H) with integrals of aromatic region at δ (ppm) = 7.13-7.33 (m, 41H) and 7.36-7.52 (m, 15H) shows full capping (8 drug-linkers per molecule of dendrimer). 2.4 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2- DXd)8(ε-PEG25)8] 44 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NH2.TFA)8(ε-PEG25)8] 2 (150 mg, 11.4 µmol), HO2C-(CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd 9 (105 mg, 110 µmol) and NMM (120 µL, 1.09 mmol) in DMF (5 mL) at room temperature was added PyBOP (57 mg, 110 µmol). The reaction mixture was stirred for 18h whereupon the volatiles were removed in vacuo. The residue was dissolved in methanol (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, eluent = methanol) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-(CH2)3- C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8] 44 as a yellow solid (155 mg, 69%). LCMS (UPLC-SQD Method 5-70, 15 mins): Rt = 8.63 min. ESI MS (+ve) 19244 [M-DXd]+; calc. m / z for C907H1469F7N95O337 [M-DXd]+= 19244 1H NMR (400 MHz, CD3OD): δ (ppm): 0.70-0.96 (m, 22H), 0.99-1.92 (m, 127H), 1.92-2.44 (m, 83H), 2.45-2.59 (m, 5H), 2.69-3.20 (m, 65H), 3.26 (m, 24H), 3.27-3.31 (m, 4H), 3.31-3.41 (m, 8H), 3.41- 4.00 (m, 878H), 4.01-4.41 (m, 39H), 4.53-4.75 (m, 29H), 4.89-5.68 (m, 37H), 6.91-7.21 (m, 41H) and 7.21- 7.44 (m, 15H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.26 ppm (s, 24H) with integrals of aromatic region at δ (ppm) = 6.91-7.21 (m, 41H) and 7.21-7.44 (m, 15H) shows full capping (8 drug-linkers per molecule of dendrimer). 87 20778549_1 (GHMatters) P122809.PCT 2.5 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-PEG9-C(O)NH-Val-Cit-PAB-Pyr- N(Me)C(O)-DXd)8(ε-PEG25)8] 45 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NH2.TFA)8(ε-PEG25)8] 2 (100 mg, 7.6 µmol), HO2C-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 22 (140 mg, 91 µmol) and NMM (53 µL, 486 µmol) in DMF (5 mL) at room temperature was added PyBOP (47 mg, 91 µmol). The reaction mixture was stirred for 18 h whereupon additional quantities of PyBOP (47 mg, 91 µmol) and NMM (107 µL, 974 µmol) were added. The reaction mixture was stirred for 2 days whereupon an additional quantity of HO2C-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd 22 (23 mg, 15 µmol) was added together with triethylamine (13 µL, 91 µmol). After stirring for 18 h, the volatiles were removed in vacuo. The residue was dissolved in methanol (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, eluent = methanol) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd)8(ε-PEG25)8] 45 as a yellow solid (127 mg, 69%). LCMS (UPLC-SQD Method 5-80, 9 mins): Rt= 5.34 min. ESI MS (+ve) 24372 [M]+; calc. m / z for C1150H1910F8N114O431 [M]+= 24374. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.66-1.00 (m, 54H), 1.05-1.91 (m, 138H), 1.93-2.09 (m, 13H), 2.09-2.29 (m, 28H), 2.29-2.38 (m, 15H), 2.38-2.58 (m, 27H), 2.58-2.85 (m, 23H), 2.89-3.17 (m, 62H), 3.25 (m, 24H), 3.27-3.31 (m, 6H), 3.31-3.40 (m, 11H), 3.41-3.46 (m, 18H), 3.46-3.75 (m, 957H), 3.75-4.31 (m, 41H), 4.35-4.53 (m, 13H), 4.55-4.71 (m, 13H), 5.15-5.28 (m, 8H), 5.32-5.49 (m, 8H), 5.49- 5.71 (m, 8H), 6.47-6.72 (m, 7H), 6.88-7.02 (m, 4H), 7.02-7.14 (m, 3H), 7.14-7.25 (m, 4H), 7.25-7.41 (m, 18H), 7.41-7.54 (m, 7H) and 8.00-8.17 (m, 4H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.25 ppm (s, 24H) with integrals of aromatic region at δ (ppm) = 6.47-6.72 (m, 7H), 6.88-7.02 (m, 4H), 7.02-7.14 (m, 3H), 7.14- 7.25 (m, 4H), 7.25-7.41 (m, 18H), 7.41-7.54 (m, 7H) and 8.00-8.17 (m, 4H) shows approximately 7.2 drug- linkers per molecule of dendrimer. Example 3: SN-38 Loaded Dendrimers 3.1 N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)4(ε-PEG25)4] 46 To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NH2.TFA)4(ε-PEG25)4] 1 (50 mg, 7.1 µmol), HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me)C(O)-SN-38C-1028 (50 mg, 7.1 µmol) and NMM (19 µL, 212 µmol) in DMF (2 mL) at room temperature was added PyBOP (22 mg, 42 µmol). The reaction mixture was stirred for 18 h whereupon the volatiles were removed in vacuo. The residue was dissolved in acetonitrile (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, 88 20778549_1 (GHMatters) P122809.PCT eluent = acetonitrile) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α- NHC(O)-PEG9-Val-Cit-PAB-Pyr- N(Me)-C(O)-SN-38C-10)4(ε-PEG25)4] 46 as a yellow waxy solid (77 mg, 88%). LCMS (UPLC-ToF Method 5-80, 15 mins): Rt = 5.03 min. ESI MS (+ve) 12294 [M]+; calc. m / z for C581H984N54O223 [M]+= 12294. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.85-1.07 (m, 29H), 1.08-2.18 (m, 89H), 2.37-2.72 (m, 23H), 2.87-3.27 (m, 39H), 3.35 (m, 12H), 3.37-3.41 (m, 4H), 3.41-3.52 (m, 12H), 3.51-3.87 (m, 542H), 4.02-4.58 (m, 23H), 4.95-5.72 (m, 28H) and 7.10-8.19 (m, 35H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.35 ppm (s, 12H) with integrals of aromatic region at δ (ppm) = 7.10-8.19 (m, 35H) shows full capping (8 drug-linkers per molecule of dendrimer). To a stirred solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NH2.TFA)8(ε-PEG25)8] 2 (70 mg, 49 µmol), HO2C-PEG9-Val-Cit-PAB-Pyr-NH(Me)C(O)-SN-38C-1028 (50 mg, 38 µmol) and NMM (29 µL, 262 µmol) in DMF (3 mL) at room temperature was added PyBOP (26 mg, 49 µmol). The reaction mixture was stirred for 18 h whereupon additional portions of PyBOP (26 mg, 50 µmol) and NMM (2 µL, 16 µmol) were added. After stirring for 18 h, the volatiles were removed in vacuo. The residue was dissolved in acetonitrile (1 mL) and the resulting solution was purified by size exclusion chromatography (SEC method, eluent = acetonitrile) to give N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)- PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)8(ε-PEG25)8] 47 as a yellow solid (85 mg, 88%). LCMS (UPLC-ToF Method 5-70, 15 mins): Rt= 9.04 min. ESI MS (+ve) 23559 [M]+; calc. m / z for C1117H1876N106O423[M]+= 23559. 1H NMR (400 MHz, CD3OD): δ (ppm): 0.88-1.09 (m, 61H), 1.09-2.23 (m, 193H), 2.32-2.76 (m, 50H), 2.88-3.27 (m, 80H), 3.38 (m, 24H), 3.39-3.42 (m, 5H), 3.43-3.52 (m, 22H), 3.52-3.68 (m, 1032H), 3.68-3.87 (m, 72H), 4.08-4.55 (m, 44H), 5.01-5.70 (m, 50H) and 7.17-8.15 (m, 67H). Comparison of integral for MeO terminus of PEG groups at δ (ppm) = 3.38 ppm (s, 24H) with integrals of aromatic region at δ (ppm) = 7.17-8.15 (m, 67H) shows full capping (8 drug-linkers per molecule of dendrimer). Example 4: Bioconjugates 4.1 DXd-Dendrimer HER-2 Antibody-Conjugates 4.1.1 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-PEG9- C(O)NH-GGFG-C(O)NH-CH2-DXd)4(ε-PEG25)4]}248 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (100 mg of a 11.3 mg / mL solution in PBS, pH 7.4) was added a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-PEG9-C(O)NH- GGFG-C(O)NH-CH2-DXd)4(ε-PEG25)4] 42 (32.5 mg) in de-ionized water (1 mL) at room temperature. The 89 20778549_1 (GHMatters) P122809.PCT progress of the reaction was followed by UPLC-ToF analysis using the following process: An aliquot (20 µL) of the reaction mixture was removed and 3 µL 0.5M TCEP solution in water was added. The resulting solution was left at room temperature for 5 min, filtered (0.22 µm filter disc) and analysed directly by UPLC-ToF [Method: UPLC-ToF Method 5-70-Protein, 65 °C, 15 min]. The reduced bioconjugate 48 (heavy chain) was present as a broad signal at Rt = 7.50 min. Unreacted dendrimer 42 and the light chain of the bioconjugate were present at Rt = 9.69 min and 6.80 min respectively. After 3d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method Protein A-1]. Wash buffer ran from 0 min to 24 ml. Elution buffer ran from 23 min to 40 min. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 to a final concentration of 4.68 mg / mL. Step 2: [FPLC Method SEC-1]. Fractions collected between Rt = 8-10 mL from multiple runs were pooled and concentrated (Amicon® Ultra Centrifugal Filter, 10 kDa MWCO) and finally buffer exchanged / concentrated to give a stock solution of the bioconjugate 48 in 10 mM PBS, pH 7.4 (3 mL). The final concentration of the stock solution was calculated as follows: A known aliquot (volume) of the stock was buffer exchanged into deionised water, lyophilised to dryness and accurately weighed. In doing so, the stock solution was determined to have a concentration of 2.33 mg / mL of bioconjugate 48 (refer to Table 2 for characterization data). The conjugate was then sterile filtered (0.22 µm filter disc) and checked for endotoxin (see Endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 48 (Lane A = Intact; Lane B = Reduced) LCMS (Sample reduced with TCEP) [Method = UPLC-ToF Method 5-70-Protein, 65 °C, 15 min]; Rt(light chain) = 4.96 min; Rt(heavy chain + dendrimer) = 5.24 min 4.1.2 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4 [Lys]8[(α- NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8]}249 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (65 mg of a 11.3 mg / mL solution in PBS, pH 7.4) was added a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9- C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8] 43 (40.2 mg) in deionized water (1 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 49 (heavy chain) was present as a broad signal at Rt = 7.97 min. Unreacted dendrimer 43 and the light chain of the bioconjugate were present at Rt = 10.03 min and 6.79 min respectively. After 3d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method Protein A-1]. Wash buffer ran from 0 min to 24 mL. Elution buffer ran from 24 min to 35 min. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 30 kDa MWCO) and buffer exchanged into 0.5 M ammonium sulfate, 50 mM phosphate buffer, pH 7.0 to a final volume of ~ 10 mL. 90 20778549_1 (GHMatters) P122809.PCT Step 2: [FPLC Method HIC-1]. Fractions collected during the elution phase (between Rt ~ 6-11 mL from multiple runs) were pooled, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO), buffer exchanged into 10 mM PBS, pH 7.4 and concentrated to give the stock solution (3 mL). The concentration of the stock solution was determined using the method described above for bioconjugate 48 (1.84 mg / mL). The stock solution of bioconjugate 49 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 49 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt (light chain) = 4.97 min; Rt (heavy chain + dendrimer) = 6.95 min. 4.1.3 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)- (CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd)4(ε-PEG25)4}250 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (100 mg of a 16.4 mg / mL solution in PBS, pH 7.4) was added a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α-NHC(O)-(CH2)3-C(O)NH- GGFG-C(O)NH-CH2-DXd)4(ε-PEG25)4] 41 (28 mg) in 10 mM PBS, pH 7.4 (3 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 50 (heavy chain) was present as a broad signal at Rt= 5.87 min. Unreacted dendrimer 41 and the light chain of the bioconjugate were present at Rt= 8.70 min and 5.43 min respectively. After 2 d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method Protein A-1]. Wash buffer ran from 0 min to 13 mL. Elution buffer ran from 13 min to 27 min. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 0.5 M ammonium sulfate, 50 mM phosphate buffer, pH 7.0 to a final volume of ~ 7 mL. Step 2: [FPLC Method HIC-1]. Fractions collected during the elution phase (between Rt~ 8-12 mL from multiple runs) were pooled, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO), buffer exchanged into 10 mM PBS, pH 7.4 and concentrated to give the stock solution of biconjugate 50 (8 mL). The stock solution was passed through PierceTMhigh capacity endotoxin removal resin according to the manufacturer’s instructions and the filtrate was sterile filtered (0.22 µm filter disc) and checked for endotoxin (see endotoxin assessment method). The concentration of the stock solution was determined using the method described above for conjugate 48 (8 mL, concentration = 5.50 mg / mL). SDS Page Gel (not shown) of Bioconjugate 50 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt (light chain) = 5.72 min; Rt (heavy chain + dendrimer) = 6.43 min. 91 20778549_1 (GHMatters) P122809.PCT 4.1.4 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)- (CH2)3-C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8]}251 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (93 mg of a 16.4 mg / mL solution in PBS, pH 7.4) was added a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-(CH2)3- C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε-PEG25)8] 44 (50 mg) in 10 mM PBS, pH 7.4 (2 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 51 (heavy chain) was present as a very broad signal at Rt = 6.56 min. Unreacted dendrimer 44 and the light chain of the bioconjugate were present at Rt = 8.88 min and 5.20 min respectively. After 4 d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method Protein A-1]. Wash buffer ran from 0 min to 5 mL. Elution buffer ran from 5 min to 10 min. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 0.5 M ammonium sulfate, 50 mM phosphate buffer, pH 7.0 to a final volume of ~ 5 mL. Step 2: [FPLC Method HIC-1]. Fractions collected during the elution phase (between Rt ~ 32.5-53 mL from multiple runs) were pooled, concentrated (Amicon® Ultra Centrifugal Filter, 100 kDa MWCO), buffer exchanged into deionised water and concentrated to give the stock solution of biconjugate 51 (5 mL). The stock solution was passed through PierceTMhigh capacity endotoxin removal resin according to the manufacturer’s instructions and the filtrate was sterile filtered (0.22 µm filter disc) and checked for endotoxin (see endotoxin assessment method). The concentration of the stock solution was determined using the method described above for conjugate 48 (5 ml, concentration = 8.0 mg / mL). SDS Page Gel (not shown) of Bioconjugate 51 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt(light chain) = 6.43 min; Rt(heavy chain + dendrimer) = 6.88 min. 4.1.5 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)- PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd)8(ε-PEG25)8]}252 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (44 mg of a 1.46 mg / mL solution in PBS, pH 7.4) was added a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9- C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd)8(ε-PEG25)8] 45 (29.1 mg) in 10 mM PBS, pH 7.4 (1.72 mL) at 37 °C. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 52 (heavy chain) was present as a broad signal at Rt = 6.72 min. Unreacted dendrimer 45 and the light chain of the bioconjugate were present at Rt = 9.01 min and 5.02 min respectively. After 6 d, the reaction mixture was purified by FPLC as follows: 92 20778549_1 (GHMatters) P122809.PCT Step 1: [FPLC Method Protein A-1]. Wash buffer ran from 0 min to 4.5 mL. Elution buffer ran from 4.5 mL to 11.2 mL. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 to a final volume of ~ 4 mL. Step 2: [FPLC Method SEC-2]. Fractions typically collected between Rt = 8-11 mL from multiple runs were pooled and concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and finally buffer exchanged / concentrated to give a stock solution of the bioconjugate 52 in 10 mM PBS, pH 7.4 (1.9 mL). The concentration of the stock solution was determined using the method described above for conjugate 48 (5 mg / mL). The stock solution of bioconjugate 52 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 52 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt (light chain) = 5.04 min; Rt (heavy chain + dendrimer) = 6.72 min. 4.2 DXd-Dendrimer HER-2 VHH-Conjugates 4.2.1 HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO 53 A solution of the HER2-VHH-(Terminal Cys) 29 (100 mg) in 10 mM PBS, pH 7.4 + 0.05% BME (14.4 mL) was washed with 10 mM PBS, pH 7.4 (4 x 10 mL) using Amicon® Ultra Centrifugal Filters (15 kDa MWCO) to remove BME and the resulting solution concentrated to approx.15 mL total volume. To the solution of the HER2-VHH-(Terminal Cys) 29 was added a 0.5M TCEP.HCl (102 µL, 51 µmol) and the resulting solution was left to stand at room temperature. After 1 h, the solution was washed with 10 mM PBS, pH 7.4 (4 x 30 mL) using Amicon® Ultra Centrifugal Filters (15 kDa MWCO) to remove the excess TCEP and concentrated to approx.15 mL total volume. To the resulting solution was added a solution of MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO 40 (16.1 mg, 10.0 µmol) in 10 mM PBS, pH 7.4 (1.6 mL) and the reaction mixture was left to stand at room temperature for 18 h. The reaction mixture was washed with 10 mM PBS, pH 7.4 (4 x 30 mL) using Amicon® Ultra Centrifugal Filters (10 kDa MWCO) to remove the excess linker and concentrated approx.14 mL total volume to give HER2-VHH- (Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO 53 (7.88 mg / mL as determined by nanodrop, 110 mg). LCMS (UPLC-ToF 5-70-Protein, 65 °C, 15 min): Rt = 7.91 min. ESI MS (+ve) 15327 [M]+; calc. m / z for intermediate 53 [M]+= 15,333. 93 20778549_1 (GHMatters) P122809.PCT 4.2.2 HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO / N3- PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε- PEG25)8] 54 To a freshly prepared solution of HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24- C(O)NH-(CH2)2-DBCO 53 in 10 mM PBS, pH 7.4 (40.3 mg, 7.88 mg / mL) was added a solution of N3- PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α- NHC(O)-PEG9-C(O)NH-GGFG-C(O)NH-CH2-DXd)8(ε- PEG25)8] 43 (50 mg, 2.1 µmol) in 10 mM PBS, pH 7.4 (2 mL). The reaction mixture was diluted with 10 mM PBS, pH 7.4 to a total volume of 12 mL and left to stand at 4 °C for 3 d. The progress of the reaction was followed by UPLC-ToF by removing an aliquot (20 µL) and analysed directly by UPLC-ToF. Bioconjugate 54 was present as a sharp peak at Rt = 9.44 min. Unreacted dendrimer 43 was present at Rt = 10.56 min. After 3 d, the reaction was purified by FPLC as follows: FPLC Method Protein A-1: Wash buffer ran from 0 min to 30 mL. Elution buffer ran from 30 mL to 55 mL. Fractions from the elution phase from multiple runs were checked by UPLC-ToF analysis. Those containing the desired product were combined, concentrated (Amicon® Ultra Centrifugal Filter, 30 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 to give the stock solution of the bioconjugate 54 (3 mL). The concentration of the stock solution was determined using the method described above for bioconjugate 48 (12.26 mg / mL). The stock solution of bioconjugate 54 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 54 (intact) LCMS (UPLC-ToF Method 5-70-Protein, 65 °C, 15 min); Rt= 7.57 min. ESI MS (+ve) 38114 [M]+; calc. m / z for bioconjugate 54 [M]+= 38113. 4.2.3 HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO / N3- PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)- DXd)8(ε-PEG25)8] 55 To a freshly prepared solution of HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24- C(O)NH-(CH2)2-DBCO 53 in 10 mM PBS, pH 7.4 (36 mg, 2.4 mg / mL) was added a N3-PEG24- C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9-C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd)8(ε- PEG25)8] 45 (57 mg, 2.3 µmol). The progress of the reaction was followed by UPLC-ToF by removing an aliquot (20 µL) and analysed directly by UPLC-ToF. Bioconjugate 55 was present as a sharp peak at Rt =7.51 min. Unreacted dendrimer 45 was present at Rt = 8.76 min After standing at room temperature for 3 days the reaction mixture was buffer exchanged (Amicon® Ultra Centrifugal Filter, 10 kDa MWCO) into 20 mM acetate, pH 4.0 and concentrated (2 mL final volume) and purified by FPLC as follows: Step 1: FPLC Method CEX-1: Wash buffer ran from 0 min to 20.0 mL. Elution buffer ran from 20 mL to 60 mL. Fractions from the wash phase contained the unbound dendrimer. Fractions from the elution 94 20778549_1 (GHMatters) P122809.PCT phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 10 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 to a final volume of 2 mL. Step 2: FPLC Method Protein A-1: Wash buffer ran from 0 min to 12.0 mL. Product eluted at 100% elution buffer (from 35.0 mL to 50 mL). Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 30 kDa MWCO) and buffer exchanged into de-ionised water to remove all salts and lyophilised. HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl- C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9- C(O)NH-Val-Cit-PAB-Pyr-N(Me)C(O)-DXd)8(ε-PEG25)8] 55 was obtained as white powder (4.0 mg), which was re-dissolved in 10 mM PBS, pH 7.4 (400 µL or 10 mg / mL stock solution). HPLC-Analytical (HPLC Method 5-70, 65°C, 15 min); Rt = 9.53 min. 4.3 SN-38-Dendrimer HER-2 Antibody-Conjugates 4.3.1 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α- NHC(O)-PEG9- Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)4(ε-PEG25)4]}256 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}232 (150 mg of a 12.43 mg / mL solution in 10 mM PBS, pH 7.4) was added to a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[(α- NHC(O)- PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)4(ε-PEG25)4] 46 (31.4 mg) in 10 mM PBS, pH 7.4 (2.0 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 56 (heavy chain) was present as a broad signal at Rt = 6.53 min. Unreacted dendrimer 46 and the light chain of the bioconjugate were present at Rt = 8.42 min and 5.21 min respectively. After 6 d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method HIC-1]. Wash buffer ran from 0 min to 10.0 mL. Elution buffer ran from 10.0 mL to 25.0 mL. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 water to a final volume of ~ 5 mL. Step 2: [FPLC Method Protein A-1]. Fractions typically collected between Rt = 40-50 mL from multiple runs were pooled and concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and finally buffer exchanged / concentrated to give a stock solution of the bioconjugate 56 in 10 mM PBS, pH 7.4 (~5.0 mL). The concentration of the stock solution was determined using the method described above for conjugate 48. The stock solution of bioconjugate 56 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see Endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 56 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt(light chain) = 5.20 min; Rt(heavy chain + dendrimer) = 6.50 min. 95 20778549_1 (GHMatters) P122809.PCT 4.3.2 Trastuzumab-{CONH-PEG4-Sulfo-DBCO / N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)- PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)8(ε-PEG25)8]}257 To a solution of trastuzumab-{CONH-PEG4-Sulfo-DBCO}250 (100 mg of a 12.43 mg / mL solution in PBS, pH 7.4) was added to a solution of N3-PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9- Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)8(ε-PEG25)8]}247 (40.2 mg) in 10 mM PBS, pH 7.4 (2.0 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF analysis using the process described above for the synthesis of bioconjugate 48. The reduced bioconjugate 57 (heavy chain) was present as a broad signal at Rt = 7.17 min. Unreacted dendrimer 47 and the light chain of the bioconjugate were present at Rt = 9.08 min and 5.21 min respectively. After 8 d, the reaction mixture was purified by FPLC as follows: Step 1: [FPLC Method HIC-1]. Wash buffer ran from 0 min to 8.0 mL. Elution buffer ran from 8.0 mL to 25.0 mL. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 water to a final volume of ~ 5 mL. Step 2: [FPLC Method Protein A-1]. Fractions typically collected between Rt= 15-30 mL from multiple runs were pooled and concentrated (Amicon® Ultra Centrifugal Filter, 50 kDa MWCO) and finally buffer exchanged / concentrated to give a stock solution of the bioconjugate 57 in 10 mM PBS, pH 7.4 (4.5 mL). Fractions from the wash phase contained the unbound dendrimer. The concentration of the stock solution was determined using the method described above for conjugate 56 (3.5 mg / mL). The stock solution of bioconjugate 57 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see Endotoxin assessment method). SDS Page Gel (not shown of Bioconjugate 57 (Lane A = intact; Lane B = reduced) LCMS (Sample reduced with TCEP, UPLC-ToF Method 5-70-Protein, 65 °C, 15 min, no MS); Rt(light chain) = 5.02 min; Rt(heavy chain + dendrimer) = 6.87 min. 4.4 SN-38-Dendrimer HER-2 VHH-Conjugates 4.4.1 HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24-C(O)NH-(CH2)2-DBCO / N3- PEG24-C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)8(ε- PEG25)8] 58 To a freshly prepared solution of HER2-VHH-(Terminal Cys) / MAL-CH2-CyHexyl-C(O)NH-PEG24- C(O)NH-(CH2)2-DBCO 53 in 10 mM PBS, pH 7.4 (91 mg, 2 mg / mL) was added a solution of N3-PEG24- C(O)[N(PN)2][Lys]2[Lys]4[Lys]8[(α-NHC(O)-PEG9-Val-Cit-PAB-Pyr-N(Me)-C(O)-SN-38C-10)8(ε-PEG25)847 (125 mg) in 10 mM PBS, pH 7.4 (6.3 mL) at room temperature. The progress of the reaction was followed by UPLC-ToF by removing an aliquot (20 µL) and analysed directly by UPLC-ToF. Bioconjugate 58 was present as a sharp peak at Rt = 7.83 min. Unreacted dendrimer 47 was present at Rt = 9.12 min. After 3 d, the reaction was purified by FPLC as follows: 96 20778549_1 (GHMatters) P122809.PCT [FPLC Method CEX-1]: Wash buffer ran from 0 min to 20.0 mL. Stepwise elution buffer (30%) ran from 20.0 mL to 115.0 mL. Product elution at 40% elution buffer from 115.0 mL to 150 mL. Fractions from the elution phase from multiple runs were combined, concentrated (Amicon® Ultra Centrifugal Filter, 30 kDa MWCO) and buffer exchanged into 10 mM PBS, pH 7.4 to a final volume of ~ 7 mL. The concentration of the stock solution was determined using the method described above for conjugate 48 (13.0 mg / mL). The stock solution of bioconjugate 58 was sterile filtered (0.22 µm filter disc), checked for endotoxin (see endotoxin assessment method). SDS Page Gel (not shown) of Bioconjugate 58 LCMS (UPLC-ToF Method 5-70-Protein, 65 °C, 15 min); Rt = 7.75 min. ESI MS (+ve) 39020 [M]+; calc. m / z for bioconjugate 58 [M]+= 38892. 4.5 Determination of Drug Loading and Drug Release 4.5.1. Forced Release of Payload with Papain: General Procedure An aliquot of an aqueous solution of the dendrimer or the bioconjugate solution stock (50 µL) was diluted to a final volume of 1.5 mL using 0.1 M acetate buffer, pH 5.0. Papain (15 mg, Sigma-Aldrich, 10 units / mg) was added to the resulting solution and the reaction mixture left to stand at 37 °C for a minimum of 1 h. A portion of the reaction mixture (20 µL) was diluted with DMSO (20 µL) and the resulting solution mixed thoroughly and analysed by HPLC [HPLC-Method 15-75, 40oC, 15 min, TFA; 5.0 µL injection, UV detection at 360 nm]. The amount of DXd 4 released (Rt = 6.19 min) was quantified using a standard concentration curve of a freshly prepared solution of DXd. All the SN-38 bioconjugates were analysed using UPLC-Tof (UPLC-ToF Method 5-70, 40 ºC, 15 min). The amount of SN-3823 released (Rt = 4.69 min) from SN-38 bioconjugates was quantified using standard curve of a freshly prepared solution of SN- 38. See Table 4.5 for results (% Wt Drug (Papain Release)). 4.5.2. Quantification of the Payload by HPLC: General Procedure The bioconjugate sample diluted to suitable concentration and then analysed by HPLC [ HPLC- Method 15-80, 9.5 min, TFA, 2.0 µL injection, UV detection at 359 nm]. The amount of DXd 4 on the bioconjugate was quantified by comparing the peak area under the bioconjugate peak with a standard curve for exatecan peak at (λAbsorbance=359 nm). See Table 4.5 for results (% Wt Drug (HPLC)). 4.5.3. Determination of Payload Release by cathepsin B over 24 h. Cathepsin B solution (>1715 units / mg, 385 µg / mL, 1.6 µL) was added to a solution of the dendrimer or bioconjugates (30 µM in citrate buffer, pH 5.5). The resulting solution was then diluted with citrate buffer to give final dendrimer concentration of 15 µM. The reaction mixture was left to stand at 37 °C for 24 h and analysed by HPLC [HPLC-Method 15-75, 40oC, 15 min, TFA ; 5.0 µL injection, UV detection at 97 20778549_1 (GHMatters) P122809.PCT 360 nm]. The amount of DXd 4 released (Rt = 6.19 min) was quantified using a standard concentration curve of a freshly prepared solution of DXd. See Table 4.5 for results (% Wt Drug (Cathepsin B Release, 24 h)). 5 Table 4.5 Drug release and drug quantification of the bioconjugates and dendrimers. Example 5: Binding to Immobilised Human and Canine HER-2 (SPR) Table 5.1 shows the results of Surface Plasmon Resonance binding studies which determined the 10 binding kinetics of example conjugates of the disclosure. The sensorgrams are also provided in Figures 1A to 5L. Table 5.1: SPR binding to immobilised human and canine HER-2 receptors. 98 20778549_1 (GHMatters) P122809.PCT Example 6: Efficacy Study in SKOV-3 Xenograft A SKOV-3 (a human ovarian cancer cell line) mouse xenograft ovarian cancer model study was carried out to assess the anti-tumour efficacy properties of the bioconjugate 57. The study was carried out in NSG mice approximately 5-8 weeks old. Animals induced with 5 x 106SKOV-3 cells in PBS:Matrigel via SC injection into the flank. Mice were weighed and tumours measured twice weekly using electronic callipers. Doses were administered via IV tail vein injection (volume was between 50 µL-150 µL) once weekly for three weeks. Tumours were grown to approximately 120-150 mm3prior to randomisation into dosing groups of 8 mice per group. Dosing groups (and doses) were as follows: 1) Vehicle (saline) 2) Dendrimer 47 (3.28 mg / kg SN-38 equivalents) 3) Enhertu 59 (5 mg / kg) 4) Bioconjugate 57 (3.28 mg / kg SN-38 equivalentsError! Bookmark not defined.) Maximum tolerated dose was determined separately using compound 60 (for the synthesis of 60, see: WO2020102852A1). Tumours were measured with a calliper every 2-3 days and tumour volume was calculated with ^^ = ½ (x(y2) where x represents the longest length measured and y represents shortest length measured. For the last data point at day 35 post dosing, n=7 unless annotated. Monitoring was continued until terminal endpoint was reached, which included i) tumour / tail ulceration, ii) acute weight loss (>10% over 3 days) and iii) tumours exceeding 1000 mm3. Figure 2A shows the anti-tumour efficacy of the treatments against the SKOV-3 tumour xenografts. Tumour volumes are expressed as mean tumour volume (± SEM). As shown in Figure 2A, the example bioconjugate 57 achieved statistically significantly enhanced tumour growth inhibition compared with Enhertu® or the control dendrimer that lacked the HER2-targeting antibody (p<0.0001 for both comparisons). Points and error bars show means ± standard error of the mean (SEM). Statistical analyses used the Mixed Effects Model (GraphPad Prism v9.4.1). As shown in Figure 2B, analysis of survival curves showed significantly enhanced probability of survival of the example bioconjugate 57 group versus all other groups (p<0.0002). Probability of survival in the example bioconjugate 57 group was 100% (at end-of-study, 45 days). Median survival, or the time at which probability of survival dropped to 50%, was 40 days for Enhertu®, 28 days for the control 99 20778549_1 (GHMatters) P122809.PCT dendrimer, and 13 days for the vehicle control. Survival analyses used tumour volume (≥ 1000 mm3), tumour-site ulceration, or end-of-study as endpoints. Survival analyses used the logrank (Mantel-Cox) test (GraphPad Prism v9.4.1). All treatments were well tolerated, as measured by change in body weight over time. Example 7: Efficacy Study in JIMT-1 Xenograft – Targeted DXd A JIMT-1 (a human breast cancer cell line) mouse xenograft cancer model study was carried out to assess the anti-tumour efficacy properties of HER2-targeted DXd bioconjugates in a trastuzumab resistant tumour model. The study was carried out in NSG female mice approximately 6-8 weeks old. Animals were implanted subcutaneously with 5 x 106JIMT1 cells in PBS:Matrigel into the flank. Mice were weighed and tumours measured twice weekly using electronic callipers. Doses were administered via IV tail vein injection (volume was between 200 µL) once weekly for three weeks. Tumours were grown to approximately 100-250 mm3prior to randomisation into dosing groups of 10 mice per group. Dosing groups were as follows (dosed with 0.257 mg / kg DXd- the DXd equivalent for 10 mg / kg Enhertu): 1) Vehicle (saline) 2) Compound 54 3) Compound 42 4) Compound 43 5) Compound 49 6) Compound 48 7) Compound 52 8) Compound 59 (10 mg / kg) 9) Compound 61 (10 mg / kg) Tumours were measured with a calliper every 2-3 days and tumour volume was calculated with ^^ = ½ (x(y2) where x represents the longest length measured and y represents shortest length measured. Monitoring was continued until terminal endpoint was reached, which included i) tumour / tail ulceration, ii) acute weight loss (>10% over 3 days) and iii) tumours exceeding 1200 mm3. As shown in Figure 3A, after 21 days, the example bioconjugate (SPL9530) achieved strong tumour growth inhibition, which was comparable to Enhertu®, and which was improved compared to control dendrimers. Figure 3B also shows that there was no significant change in mouse body weight over the time period, indicating that the treatments were well tolerated. 100 20778549_1 (GHMatters) P122809.PCT

Claims

CLAIMS 1. A dendrimer-targeting agent conjugate, or a pharmaceutically acceptable salt thereof, the conjugate comprising: 5 a) a dendrimer comprising i) a core unit; and ii) building units; wherein the dendrimer has from 2 to 4 generations of building units and wherein the core unit is covalently attached to at least two building units; b) a topoisomerase inhibitor which is attached through a linker to an outer building unit of the dendrimer, the linker having the formulawherein S is a spacer group; and Cl is an enzymatically cleavable group comprising a peptide having at least 2 amino acid residues; c) pharmacokinetic-modifying moieties which are attached to outer building units, the pharmacokinetic-modifying moieties comprising a hydrophilic polymer; and d) a HER2 targeting agent which is attached through a connector to the core unit of the dendrimer.

2. A conjugate or salt as claimed in claim 1, wherein the topoisomerase inhibitor is DXd, optionally wherein the DXd is attached via an oxygen atom as shown below.

3. A conjugate or salt as claimed in claim 1, wherein the topoisomerase inhibitor is SN-38, optionally wherein the SN-38 is attached via an oxygen atom as shown below: 101 20778549_1 (GHMatters) P122809.PCT.

4. A conjugate or salt as claimed in any of claims 1 to 3, wherein the hydrophilic polymer group is a polyethylene glycol (PEG), polyethyloxazoline (PEOX), poly-(2)-methyl-(2)-oxazolamine (POZ), polysarcosine or a poly (2-hydroxypropyl)methacrylamide polymer, optionally a polyethylene glycol (PEG) polymer.

5. A conjugate or salt as claimed in claim 4, wherein the hydrophilic polymer group is a polyethylene glycol (PEG) polymer having an average molecular weight in the range of from 750 to 1500 Da.

6. A conjugate or salt as claimed in any of claims 1 to 5, wherein the core unit comprises at least 3 nitrogen atoms, with at least one nitrogen atom being for attachment of a spacer group, and at least two nitrogen atoms being for attachment of building units.

7. A conjugate or salt as claimed in claim 6, wherein the core unit is.

8. A conjugate or salt as claimed in any of claims 1 to 7, wherein the building units are lysine residues or analogues thereof having two nitrogen atoms and one acyl group, optionally wherein the building units are lysine residues.

9. A conjugate or salt as claimed in claim 8, wherein the building units are.

10. A conjugate or salt as claimed in any one of claims 1 to 9, wherein the dendrimer has 2 or 3 generations of building units. 102 20778549_1 (GHMatters) P122809.PCT11. A conjugate or salt as claimed in any of claims 1 to 10, wherein the HER2 targeting agent is selected from the group consisting of an antibody, an antigen-binding fragment thereof, a fusion protein, an antibody mimetic, and a small molecule. 5 12. A conjugate or salt as claimed in any of claims 1 to 11, wherein the HER2 targeting agent is an antibody or antigen-binding fragment thereof comprising six complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence set out in SEQ ID NO: 1, CDR- H2 comprises the amino acid sequence set out in SEQ ID NO: 2, CDR-H3 comprises the amino acid sequence set out in SEQ ID NO: 3, CDR light chain 1 (CDR-L1) comprises the amino acid sequence set out in SEQ ID NO: 4, CDR-L2 comprises the amino acid sequence set out in SEQ ID NO: 5, and CDR-L3 comprises the amino acid sequence set out in SEQ ID NO:

6.

13. A conjugate or salt as claimed in any of claims 1 to 11, wherein the HER2 targeting agent is a single domain antibody, optionally a VHH comprising three complimentary determining regions (CDRs), wherein CDR heavy chain 1 (CDR-H1) comprises the amino acid sequence set out in SEQ ID NO: 42, CDR-H2 comprises the amino acid sequence set out in SEQ ID NO: 43, and CDR-H3 comprises the amino acid sequence set out in SEQ ID NO:

44.

14. A conjugate or salt as claimed in any of claims 1 to 13, wherein the connector comprises a polyethylene glycol moiety having an average molecular weight in the range of from 100 to 1500 Da, optionally wherein the connector group comprises 2 polyethylene glycol moieties.

15. A conjugate or salt as claimed in any of claims 1 to 14, wherein the connector comprises a cyclic moiety, and wherein the connector group is formable from first and second connector precursors; the first connector precursor comprising the dendrimer, a part-connector group, and a first cyclisable group; and the second connector precursor comprising the HER2 targeting agent, a further part-connector group, and a second cyclisable group which is capable of reaction with the first cyclisable group, to form the cyclic moiety.

16. A conjugate or salt as claimed in claim 15, wherein the cyclic moiety is. 103 20778549_1 (GHMatters) P122809.PCT17. A conjugate or salt as claimed in any of claims 1 to 16, wherein the connector iswherein m is an integer of from 3 to 30, and n is an integer of from 20 to 30.

18. A conjugate or salt as claimed in any of claims 1 to 17 wherein Cl is a cathepsin-cleavable group.

19. A conjugate or salt as claimed in any of claims 1 to 18, wherein Cl comprises a Val-Cit group, or a Gly-Gly-Phe-Gly group. A conjugate or salt as claimed in any of claims 1 to 19, wherein Cl is21. A conjugate or salt as claimed in any of claims 1 to 20, wherein S is 104 20778549_1 (GHMatters) P122809.PCT. wherein q is an integer of from 3 to 20.

22. A conjugate or salt as claimed in any of claims 1 to 21, wherein the linker is ,wherein p is an integer of from 2 to 20, and q is an integer of from 3 to 20.

23. A conjugate or salt as claimed in any of claims 1 to 22, which is one of the example conjugates. 105 20778549_1 (GHMatters) P122809.PCT24. A pharmaceutical composition, comprising a conjugate or salt as claimed in any of claims 1 to 23; and a pharmaceutically acceptable excipient.

25. A conjugate or salt as claimed in any of claims 1 to 23, or a pharmaceutical composition as 5 claimed in claim 24, for use in therapy.

26. A conjugate or salt as claimed in any of claims 1 to 23, or a pharmaceutical composition as claimed in claim 24, for use in the treatment of cancer.

27. A method of treating cancer in a subject, comprising administering an effective amount of a conjugate or salt as claimed in any of claims 1 to 23, or of a pharmaceutical composition as claimed in claim 24, to the subject.

28. Use of a conjugate or salt as claimed in any of claims 1 to 27 for the manufacture of a medicament for the treatment of cancer.

29. A method, use, or conjugate, salt or composition for use, as claimed in any of claims 26 to 28, wherein the cancer is selected from the group consisting of ovarian cancer, breast cancer, non-small cell lung cancer, stomach cancer, gastric or gastroesophageal junction adenocarcinoma, uterine cancer, melanoma, hepatocellular carcinoma, prostate cancer, cholangiocarcinoma, pancreatic adenocarcinoma, intestinal cancer, head and neck carcinoma, colorectal cancer, cervical cancer, gallbladder cancer, esophageal cancer, and bladder cancer.

30. A method, use, or conjugate, salt or composition for use, as claimed in any of claims 26 to 28, wherein the cancer is a HER2-positive cancer. 106 20778549_1 (GHMatters) P122809.PCT

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