Bicyclic peptide ligands specific for nk cells

Abstract

The present invention relates to polypeptides which are covalently bound to molecular scaffolds such that two or more peptide loops are subtended between attachment points to the scaffold. In particular, the invention describes peptides which bind to natural killer (NK) cells. The invention also includes multimeric binding complexes comprising at least two of said bicyclic peptide ligands. The invention also includes pharmaceutical compositions comprising said peptide ligands or said multimeric binding complexes and the use of said peptide ligands, multimeric binding complexes and pharmaceutical compositions in detecting diseases and disorders mediated by natural killer (NK) cells, and in preventing, suppressing or treating a disease or disorder mediated by natural killer (NK) cells, such as inflammatory disorders, autoimmune disease and cancer.

Description

[0001] BICYCLIC PEPTIDE LIGANDS SPECIFIC FOR NK CELLS FIELD OF THE INVENTION The present invention relates to polypeptides which are covalently bound to molecular scaffolds such that two or more peptide loops are subtended between attachment points to the scaffold. In particular, the invention describes peptides which bind to natural killer (NK) cells. The invention also includes multimeric binding complexes comprising at least two of said bicyclic peptide ligands. The invention also includes pharmaceutical compositions comprising said peptide ligands or said multimeric binding complexes and the use of said peptide ligands, multimeric binding complexes and pharmaceutical compositions in detecting diseases and disorders mediated by natural killer (NK) cells, and in preventing, suppressing or treating a disease or disorder mediated by natural killer (NK) cells, such as inflammatory disorders, autoimmune disease and cancer. BACKGROUND OF THE INVENTION Cyclic peptides are able to bind with high affinity and specificity to protein targets and hence are an attractive molecule class for the development of therapeutics. In fact, several cyclic peptides are already successfully used in the clinic, as for example the antibacterial peptide vancomycin, the immunosuppressant drug cyclosporine or the anti-cancer drug octreotide (Driggers et al. (2008), Nat. Rev. Drug. Discov.7(7), 608-24). Good binding properties result from a relatively large interaction surface formed between the peptide and the target as well as the reduced conformational flexibility of the cyclic structures. Typically, macrocycles bind to surfaces of several hundred square angstrom, as for example the cyclic peptide CXCR4 antagonist CVX15 (400 Å2; Wu et al. (2007), Science 330, 1066-71), a cyclic peptide with the Arg-Gly-Asp motif binding to integrin αVb3 (355 Å2) (Xiong et al. (2002), Science 296(5565), 151-5) or the cyclic peptide inhibitor upain-1 binding to urokinase-type plasminogen activator (603 Å2; Zhao et al. (2007), J. Struct. Biol.160(1), 1-10). Due to their cyclic configuration, peptide macrocycles are less flexible than linear peptides, leading to a smaller loss of entropy upon binding to targets and resulting in a higher binding affinity. The reduced flexibility also leads to locking target-specific conformations, increasing binding specificity compared to linear peptides. This effect has been exemplified by a potent and selective inhibitor of matrix metalloproteinase 8 (MMP-8) which lost its selectivity over other MMPs when its ring was opened (Cherney et al. (1998), J. Med. Chem.41(11), 1749- 51). The favourable binding properties achieved through macrocyclization are even more pronounced in multicyclic peptides having more than one peptide ring as for example in vancomycin, nisin and actinomycin. Different research teams have previously tethered polypeptides with cysteine residues to a synthetic molecular structure (Kemp and McNamara (1985), J. Org. Chem; Timmerman et al. (2005), ChemBioChem). Meloen and co-workers had used tris(bromomethyl)benzene and related molecules for rapid and quantitative cyclisation of multiple peptide loops onto synthetic scaffolds for structural mimicry of protein surfaces (Timmerman et al. (2005), ChemBioChem). Methods for the generation of candidate drug compounds wherein said compounds are generated by linking cysteine containing polypeptides to a molecular scaffold as for example 1,1',1''-(1,3,5-triazinane-1,3,5-triyl)triprop-2-en-1-one (TATA) (Heinis et al.(2014) Angewandte Chemie, International Edition 53(6) 1602-1606). Phage display-based combinatorial approaches have been developed to generate and screen large libraries of bicyclic peptides to targets of interest (Heinis et al. (2009), Nat. Chem. Biol. 5(7), 502-7 and WO 2009 / 098450). Briefly, combinatorial libraries of linear peptides containing three cysteine residues and two regions of six random amino acids (Cys-(Xaa)6-Cys-(Xaa)6- Cys) were displayed on phage and cyclised by covalently linking the cysteine side chains to a small molecule scaffold. Natural killer (NK) cells are members of the innate immune system. Multiple reports have provided evidence for a central role of NK cell receptors in natural cytotoxicity and usefulness in the treatment of cancer. There is a need for new agents capable of binding to NK cells, particularly to direct NK cell activity in the context of mediating an immune response to combat disorders such as cancer, inflammatory diseases and autoimmune diseases. SUMMARY OF THE INVENTION Provided herein is a peptide ligand, comprising a polypeptide having an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1); or a modified derivative thereof, wherein wherein X represents dNva or dA; wherein dNva represents D-norvaline, dA represents D- alanine, dC represents D-cysteine, and Cba represents cyclobutylalanine; or a pharmaceutically acceptable salt thereof. In some embodiments the peptide ligand or pharmaceutically acceptable salt thereof comprises a polypeptide of SEQ ID NO: 2 or SEQ ID NO:3. In some embodiments the polypeptide ligand or pharmaceutically acceptable salt thereof comprises one or more N- and / or C-terminal additions. In some embodiments the peptide ligand or pharmaceutically acceptable salt thereof comprises a polypeptide of SEQ ID NO: 4 or SEQ ID NO:5. In some embodiments the C-terminus is amidated. In some embodiments the polypeptide of the peptide ligand is attached to a molecular scaffold, such as TATA or a derivative thereof as defined herein. In some embodiments the peptide ligand is specific for natural killer (NK) cells. According to another aspect of the invention, there is provided a peptide ligand specific for natural killer (NK) cells which comprises an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1); wherein X represents dNva or dA, and wherein Cba represents cyclobutylalanine and Nva represents norvaline, or a pharmaceutically acceptable salt thereof. According to a further aspect of the invention, there is provided a bicyclic peptide ligand which comprises a peptide ligand as defined herein and a molecular scaffold, wherein the three cysteine residues of said peptide ligand form covalent bonds with the molecular scaffold to form two loop sequences. According to a further aspect of the invention, there is provided a multimeric binding complex which comprises at least two bicyclic peptide ligands wherein at least one bicyclic peptide ligand is as defined herein, wherein said peptide ligands may be the same or different. According to a further aspect of the invention, there is provided a multimeric binding complex which comprises at least two bicyclic peptide ligands as defined herein, wherein said peptide ligands may be the same or different. In some embodiments the multimeric binding complex additional comprises one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators or chromophores. In one embodiment, the multimeric binding complex comprises a fluorophore. According to a further aspect of the invention, there is provided a heterotandem bicyclic peptide complex comprising: (a) a first bicyclic peptide ligand capable of binding to a component present on a cancer cell; attached to (b) one or more second bicyclic peptide ligands as defined herein, wherein said one or more second bicyclic peptide ligands may be the same or different. According to a further aspect of the invention, there is provided a heterotandem bicyclic peptide complex comprising: (a) a first bicyclic peptide ligand which binds to a component present on a cancer cell; conjugated via a linker to (b) one or more second bicyclic peptide ligands specific for natural killer (NK) cells as defined herein. In some embodiments the linker is a linear linker or a branched linker. In some embodiments the linker comprises three or four branches and is capable of binding to three of four bicyclic peptide ligands. In some embodiments the linker comprises one or more PEG groups, such as one or more PEGngroups where each n is independently an integer from about 2 to about 25. In some embodiments the linker comprises one or more azide groups capable of reacting with one or more alkyne groups of the one or more peptide ligands; and / or one or more carboxylic acid groups or activated derivatives thereof capable of reacting with one or more amine groups of one or more peptide ligands. In some embodiments the first bicyclic peptide ligand binds to EphA2, Nectin-4, PD-L1, MT1, or PSMA. In some embodiments the first bicyclic peptide ligand binds to EphA2 and comprises a polypeptide of SEQ ID NO: 6 or 7. In some embodiments the polypeptide is attached to a molecular scaffold, such as TATA or a derivative thereof as defined herein. In some embodiments the heterotandem bicyclic peptide complex is BCY27047 or a pharmaceutically acceptable salt thereof or is BCY26129 or a pharmaceutically acceptable salt thereof. According to a further aspect of the invention, there is provided a pharmaceutical composition comprising a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein in combination with one or more pharmaceutically acceptable excipients. According to a further aspect of the invention, there is provided a peptide ligand, bicyclic peptide ligand, multimeric binding complex, heterotandem binding complex or pharmaceutical composition as defined herein for use in preventing, suppressing or treating a disease or disorder mediated by natural killer (NK) cells. BRIEF DESCRIPTION OF THE FIGURES Figure 1: Binding of AF647-labeled NKp46 Bicycle dimer (BCY28671) to isolated NK cells. Figure 2: Binding of AF647-labeled NKp46 Bicycle dimer (BCY28672) to isolated NK cells. Figure 3: Binding of AF647-labeled NKp46 Bicycle dimer (BCY28671) to CD56+ cells in PBMC preparation. Figure 4: Binding of AF647-labeled NKp46 Bicycle dimer (BCY28672) to CD56+ cells in PBMC preparation. Figure 5: NK:A431-luc Cytotoxicity Assay Results for BCY27047. Figure 6: NK:A431-luc Cytotoxicity Assay Results for BCY26129. Figure 7: NK:HT1080-luc Cytotoxicity Assay Results for BCY27047. Figure 8: NK:HT1080-luc Cytotoxicity Assay Results for BCY26129. Figure 9: IFNƔ Secretion Assay Results for BCY27047. Figure 10: IFNƔ Secretion Assay Results for BCY26129. Figure 11: TNFa Secretion Assay Results for BCY27047. Figure 12: TNFa Secretion Assay Results for BCY26129 DETAILED DESCRIPTION OF THE INVENTION The present invention provides peptides which are capable of binding to natural killer (NK) cells. A peptide capable of binding to NK cells as provided herein may be comprised, for example, in a peptide ligand comprising said peptide covalently bound to a molecular scaffold (e.g. a molecular scaffold as described in more detail herein) such that two or more peptide loops are subtended between attachment points to the scaffold. A peptide ligand may be attached directly or indirectly (e.g. via a linker) to another peptide ligand (i.e. two or more peptide ligands, which may be the same or different, may be attached together) thereby forming a complex as described in more detail herein. For example, one or more peptide ligands comprising a peptide capable of binding to NK cells as described herein may be attached to one or more further peptide ligands which bind to another biological target, such as EphA2, Nectin-4, PD-L1, MT1 or PSAM (particularly EphA2). A peptide, peptide ligand or complex comprising multiple peptide ligands may be attached directly or indirectly (e.g. via a linker) to one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators or chromophores. In one embodiment, therefore, provided herein is a peptide ligand comprising a polypeptide having an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1) or a modified derivative thereof, wherein X represents dNva or dA; wherein dNva represents D-norvaline, dA represents D-alanine, dC represents D-cysteine, and Cba represents cyclobutylalanine; or a pharmaceutically acceptable salt thereof. In some embodiments the peptide is capable of binding to NK cells. In some embodiments the peptide is specific for NK cells. Natural killer (NK) cells are members of the innate immune system representing a small fraction of peripheral blood mononuclear cells. As frontline responders, these immune cells detect and eliminate unhealthy cells and bridge the innate immune response to the adaptive immune response. Due to their inherent properties, NK cells are an excellent candidate to enhance the therapeutic tools in immune oncology and autoimmunity. NK cells are responsible for immune surveillance conducted through a variety of inhibitory and activating receptors. These activating and inhibitory receptors on the NK cellular surface are a complex means through which the activity of NK cells is kept in balance in healthy individuals. NK cells recognize the MHC class I molecules on the surface of healthy cells and are restrained through inhibitory receptors from eliminating these healthy cells. In times of stress, infection, or transformation, NK cells recognize the unhealthy cells through the loss of MHC class I on the cell surface and the induction of NK cell receptor ligands which bind to activating receptors. The recognition of non-self by the NK cells elicits a cytotoxic response, a release of cytokines and cytotoxic molecules for the elimination of the unhealthy cells. NK cell activity is by a complex mechanism that involves both activating and inhibitory signals. Multiple reports have provided evidence for a central role of NK cell receptors in natural cytotoxicity and usefulness in the treatment of cancer. There is an unmet need for further understanding and enhancement of NK cell mediated recognition and killing of tumor cells. Reports suggest tumor cells utilize many mechanisms to reduce NK activity, and that NK cell presence and efficacy is associated with favorable prognosis in patients (Pasero et al. (2015) Oncotarget 6(16), 14360-14373, Stringaris et al. (2014) Haematologica 99(5), 836-847). It is through therapeutic intervention that one may harness the potential NK cells may play in mediating an immune response to combat cancer and autoimmune diseases. NKp46 Binding Bicyclic Peptides In one embodiment, the bicyclic peptide is specific for (i.e. binds to) a natural cytotoxicity receptor present on the NK cell surface. Such a receptor may in some embodiments comprise or define an epitope capable of being selectively bound by the provided peptides and ligands comprising them. In a further embodiment, the bicyclic peptide is specific for (i.e. binds to) a natural cytotoxicity receptor selected from NKp30, NKp44 and NKp46. In a yet further embodiment, the bicyclic peptide is specific for (i.e. binds to) NKp46. The natural cytotoxicity receptors (NCR) are a family of stimulatory receptors expressed on the NK cell surface that elicit NK activation and cell-mediated cytotoxicity. The NCR family consists of three members, NKp30, NKp44, and NKp46. Although the cellular ligand for NKp46 is unknown, a role for NKp46 in antitumor immunity has been shown. Viral antigen-mediated NKp46 activation of NK cells results in tumor rejection (Chinnery et al. 2012). Upon interaction with its ligand, the NKp46 receptor triggers NK cells to induce directed cytotoxicity, illustrated by the use of anti-NKp46 blocking antibodies inhibiting the ability of NK cells to lyse targets (Arnon et al.2004). The amount of NCR expression on the NK cell surface also increases NK cytotoxicity. A strong correlation between the density of NCR expression and the ability of NK cells to kill target cells, including a wide variety of tumor cells, has been identified (Moretta et al.2006). In AML and in cervical cancer and precursor lesions, the insufficient amount of NCR or NCR ligands rendered tumor cells resistant to NK cytotoxicity (Costello et al.2002, Garcia-Iglesias et al.2009). In many solid tumors, NK cells are downregulated by the tumor microenvironment, among which include the tumor shedding of NCR ligands and immune editing, which prevent NK cells’ ability to recognize, infiltrate, and kill the tumor cells (Nayyar 2019, Stojanovic et al.2011, Sordo- Bahamonde et al.2020, Watanabe et al.2010, Izawa et al.2011, Koo et al.2013, Sun et al. 2015, Hasmim et al.2015, Han et al.2018). Stringaris et al. (2014) reported downregulation of NKp46, upregulation of NK cell inhibitory receptor NKG2A and low cytotoxic capacity of NK cells from AML patients. Furthermore, in solid cancer such as prostate cancer, there was reported a decreased expression of several activating receptors (CD16, NKp30, NKp46, NKG2D and DNAM-1), and an increase in the inhibitory receptor CD85j (Pesaro et al.2016). In contrast, Gautheir et al. (2019) has identified NKp46 as a good candidate for the targeting of an activating receptor on NK cells in cancer, demonstrating no statistically significant downregulation of NKp46 in the periphery in SCCHN, breast, liver, lung, kidney, and metastatic melanoma cancer patients. Additionally, in multiple solid tumors sustained NKp46 expression, associated with the downregulation of other activating receptors, such as NKG2D, NKp30, and NKp44, and low CD16 expression on tumor infiltrating lymphocytes has been reported for cancers, such as acute myeloid leukemia, breast cancer, and lung carcinoma (Fauriat et al.2007, Mamessier et al.2011, Platonova et al.2011, Levi et al. 2015, Kim et al.2010, MacFarlane et al.2017). Therefore, NKp46 has shown to be a specific NK surface marker suitable for therapeutic application to identify and target NK cells to tumors. Accordingly, in some embodiments the provided peptides and ligands comprising such (described in more detail herein) bind to one or more of NKp30, NKp44, NKp46, e.g. NKp46. In some embodiments the provided peptides and ligands comprising such (described in more detail herein) are specific for one or more of NKp30, NKp44, NKp46, e.g. NKp46. As set out above, provided herein is a peptide ligand comprising a polypeptide having an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1) or a modified derivative thereof, wherein X represents dNva or dA, wherein dNva represents D-norvaline, dA represents D-alanine, dC represents D-cysteine, and Cba represents cyclobutylalanine; or a pharmaceutically acceptable salt thereof. In some embodiments X is dNva and the peptide thus comprises the amino acid sequence: [dC]Y[Cba]PDYLC[dNva]DEYC (SEQ ID NO: 2). or a modified derivative thereof, or a salt thereof. In some embodiments X is dA and the peptide thus comprises the amino acid sequence [dC]Y[Cba]PDYLC[dA]DEYC (SEQ ID NO: 3) or a modified derivative thereof, or a salt thereof. According to a first aspect of the invention, there is provided a peptide ligand specific for natural killer (NK) cells which comprises an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1); wherein X represents dNva or dA, and wherein Cba represents cyclobutylalanine and Nva represents norvaline, or a pharmaceutically acceptable salt thereof. In one embodiment, X represents dNva and the peptide ligand comprises the sequence: [dC]Y[Cba]PDYLC[dNva]DEYC (SEQ ID NO: 2); wherein Nva represents norvaline, or a pharmaceutically acceptable salt thereof. In an alternative embodiment, X represents [dA] and the peptide ligand comprises the sequence: [dC]Y[Cba]PDYLC[dA]DEYC (SEQ ID NO: 3); wherein Cba represents cyclobutylalanine, or a pharmaceutically acceptable salt thereof. In some embodiments the peptide comprising an amino acid sequence which is: [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1) or a modified derivative thereof, or a salt thereof, is extended at the N-terminus. In some embodiments the peptide is extended at the N-terminus with one or more (e.g. from 1 to about 10, e.g. from 1 to about 5, e.g.1, 2, 3, 4 or 5) additional amino acids or analogs thereof. In some embodiments the peptide is extended at the C-terminus. In some embodiments the peptide is extended at the C-terminus with one or more (e.g. from 1 to about 10, e.g. from 1 to about 5, e.g. 1, 2, 3, 4 or 5) additional amino acids or analogs thereof. In some embodiments the peptide is extended at the N-terminus and the C-terminus. In some embodiments the peptide is extended at the N-terminus and the C-terminus with one or more (e.g. from 1 to about 10, e.g. from 1 to about 5, e.g.1, 2, 3, 4 or 5) additional amino acids or analogs thereof. In some embodiments the peptide is modified at the N- and / or C-terminus. In some embodiments the peptide is modified at the N- and C- terminus. Examples of N-terminal modifications include N-terminal acetylation, represented by “Ac”. Examples of C-terminal modifications include extension of the peptide by one or more amino acids or amino acid analogs such as lysine (K) or a variant thereof. An example of a variant of lysine is K(PYA) wherein PYA represents pentynoic acid (e.g. 4-pentynoic acid). In some embodiments K(PYA) has the structure (e.g. prior to attachment to e.g. a linker such as an azide group comprised in a linker): An example of a C-terminal modification is amidation; i.e. the conversion of a C- terminal carboxylic acid group (-C(O)OH or -C(O)O- to an amide -C(O)NH2). In some embodiments the C-terminus of the peptide is amidated. An example of a peptide of SEQ ID NO: 2 which is modified at the N- and C- terminus is SEQ ID NO: 4; and an example of a peptide of SEQ ID NO: 3 which is modified at the N- and C- terminus is SEQ ID NO: 5. In one embodiment, the peptide ligand additionally comprises N- and / or C-terminal additions and comprises an amino acid sequence which is selected from: Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4), and Ac-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof. In a further embodiment, the peptide ligand additionally comprises N- and / or C-terminal additions and comprises an amino acid sequence which is: Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof. In some embodiments a peptide ligand as provided herein comprises a peptide as provided herein attached to a molecular scaffold. The molecular scaffold can be any molecular scaffold as described in more detail herein. In some embodiments the molecular scaffold is attached to one or more reactive groups in the peptide. In some embodiments the molecular scaffold is attached to one or more reactive groups e.g. to one or more cysteines groups (e.g. to the thiol group comprised in the cysteine side chain) in the peptide. In some embodiments the peptide comprises three cysteine residues (L-cysteine and / or D-cysteine) and the molecular scaffold is attached to the three cystine groups. According to a further aspect of the invention, there is provided a bicyclic peptide ligand which comprises a peptide ligand as defined herein and a molecular scaffold, wherein the three cysteine residues of said peptide ligand form covalent bonds with the molecular scaffold to form two loop sequences. One example of a molecule suitable for use as a molecular scaffold in the peptide ligands and complexes comprising them as provided herein is TATA (1,3,5-Triacryloylhexahydro-1,3,5- triazine, available from Sigma Aldrich). TATA has the structure: In some embodiments TATA reacts with cysteinyl-thiol groups of peptides as described herein to form a peptide ligand comprising a scaffold which is a derivative of TATA of form: wherein each Cys-S represents a cysteine residue (e.g. L-cysteine or D-cysteine). Accordingly, in one embodiment, the molecular scaffold is a derivative of TATA which has the following structure: , which can also be depicted as wherein * denotes the point of attachment of the three cysteine residues. In one embodiment, provided herein is a bicycle peptide ligand comprising a peptide of SEQ ID NO: 1, or a modified derivative thereof, optionally extended at the N- and / or C- terminus, or a pharmaceutically acceptable salt thereof, bonded at each of three reactive residues (e.g. at each of the three cysteine residues (e.g. L-cysteine or D-cysteine)) to a molecular scaffold which is a derivative of TATA as described herein. In one embodiment said bicycle ligand comprises a peptide sequence of SEQ ID NO: 2, 3, 4, or 5. When the bicycle ligand comprises SEQ ID NO: 4 the ligand may be referred to as BCY26631. When the bicycle ligand comprises SEQ ID NO: 5 the ligand may be referred to as BCY24188. In one embodiment, the bicyclic peptide comprises a molecular scaffold which is a derivative of TATA which has the following structure: , wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises an amino acid sequence which is selected from: Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (the bicyclic peptide of which is herein referred to as BCY26631), and Ac-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5) (the bicyclic peptide of which is herein referred to as BCY24188), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof. In a further embodiment, the bicyclic peptide comprises a molecular scaffold which is a derivative of TATA which has the following structure: , wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises an amino acid sequence which is: Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (the bicyclic peptide of which is herein referred to as BCY26631), and wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof. In a further embodiment, the pharmaceutically acceptable salt is selected from the free acid or the sodium, potassium, calcium or ammonium salt. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art, such as in the arts of peptide chemistry, cell culture and phage display, nucleic acid chemistry and biochemistry. Standard techniques are used for molecular biology, genetic and biochemical methods (see Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., 2001, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Ausubel et al., Short Protocols in Molecular Biology (1999) 4thed., John Wiley & Sons, Inc.), which are incorporated herein by reference. Multimeric Binding Complexes According to a further aspect of the invention, there is provided a multimeric binding complex which comprises at least two bicyclic peptide ligands (for example, 2, 3, or 4 bicyclic peptide ligands), which may be the same or different, wherein at least one bicyclic peptide ligand is a peptide ligand as defined herein. According to a further aspect of the invention, there is provided a multimeric binding complex which comprises at least two bicyclic peptide ligands as defined herein, wherein said peptide ligands may be the same or different. In some embodiments the multimeric binding complex comprises for example, 2, 3, or 4 bicyclic peptide ligands as defined herein, wherein said peptide ligands may be the same or different. In one embodiment, the multimeric binding complexes comprise more than one bicyclic peptide which are the same (i.e. homomultimers). In an alternative embodiment, the multimeric binding complexes comprise bicyclic peptides which are different (i.e. heteromultimers). In one embodiment the multimeric binding complex comprises at least two bicycle peptide ligands which are the same and at least one different bicycle peptide. In some embodiments the multimeric binding complex comprises (a) two bicycle peptide ligands which are the same and (b) one or two further bicycle peptide ligands which may be the same or different, and wherein the two further bicycle peptide ligands of (b) may be the same or different to the two bicycle peptide ligands of (a). In one embodiment the multimeric binding complex additional comprises one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators or chromophores. In one embodiment, the multimeric binding complex additionally comprises a fluorophore. In one embodiment, the multimeric binding complex comprises two bicyclic peptides which are the same (i.e. homodimers). Effector groups As will be apparent from the discussion herein, in some embodiments a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein may comprise one or more effector groups and / or functional groups, such as one or more cytotoxic agents, chelators (e.g. radiochelators), chromophores and / or fluorophores. In some embodiments a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein may comprise one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators, chromophores and / or fluorophores attached to said ligand or complex by a linker moiety. Any suitable linker moiety may be used. In some embodiments a linker for attaching a one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators, chromophores and / or fluorophores may be a linker as described herein. In some embodiments the one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators or chromophores are directly attached to a peptide ligand as described herein. In some embodiments the one or more effector groups and / or functional groups, such as one or more cytotoxic agents, radiochelators or chromophores are attached to a complex comprising at least two peptide ligands as described herein and are attached to a linker attaching the two or more peptide ligands together. In some embodiments the one or more effector groups and / or functional groups comprise one or more chelators, e.g. one or more metal ion chelators. Any suitable metal ion chelators can be used. In some embodiments a chelator is a chelator for a radioisotope (i.e. is a radiochelator). In some embodiments a fluorophore is attached to a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein. In some embodiments a fluorophore is a fluorescent dye. In some embodiments the fluorescent dye comprises a reactive group (e.g. a carboxylic acid group or an activated derivative thereof) for reaction with a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein; e.g. for reaction with a linker comprised in a complex herein. In some embodiments a fluorophore is selected from: Alexa Fluor (AF) dyes (Alexa Fluor 350, Alexa Fluor 488, Alexa Fluor 532, Alexa Fluor 546, Alexa Fluor 568, Alexa Fluor 594, Alexa Fluor 633, Alexa Fluor 647, Alexa Fluor 660 and Alexa Fluor 680), AMCA, AMCA-S, BODIPY dyes (BODIPY FL, BODIPY R6G, BODIPY TMR, BODIPY TR, BODIPY 530 / 550, BODIPY 558 / 568, BODIPY 564 / 570, BODIPY 576 / 589, BODIPY 581 / 591, BODIPY 630 / 650, BODIPY 650 / 665), Carboxyrhodamine 6G, carboxy-X- rhodamine (ROX), Cascade Blue, Cascade Yellow, Coumarin 343, Cyanine dyes (Cy3, Cy5, Cy3.5, Cy5.5, Cy7, Cy7.5), Dansyl, Dapoxyl, Dialkylaminocoumarin, 4',5'-Dichloro-2',7'- dimethoxy-fluorescein, DM-NERF, Eosin, Erythrosin, Fluorescein, FAM, Hydroxycoumarin, IRDyes (IRD40, IRD 700, IRD 800), JOE, Lissamine rhodamine B, Marina Blue, Methoxy coumarin, Naphthofluorescein, Oregon Green 488, Oregon Green 500, Oregon Green 514, Pacific Blue, PyMPO, Pyrene, Rhodamine B, Rhodamine 6G, Rhodamine Green, Rhodamine Red, Rhodol Green, 2',4',5',7'-Tetra-bromosulfone-fluorescein, Tetramethyl-rhodamine (TMR), Carboxytetramethylrhodamine (TAMRA), Texas Red, and Texas Red-X. In some embodiments a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein comprising one or more effector groups and / or functional groups, such as a fluorophore, e.g. a fluorophore as described herein, is useful in detecting a diseases and disorder in a subject, such as a disease or disorder mediated by natural killer (NK) cells. Exemplary disorders are described in more detail herein. In some embodiments the ligand or complex binds to a target e.g. an NK cell or binding site thereon in a subject having or suspected of having a disease or disorder as described herein. In some embodiments the binding of the ligand or complex is detectable, e.g. due via detection of the effector group (e.g. the fluorophore). In some embodiments provided herein is a compound which is a peptide ligand, a bicyclic peptide ligand, a multimeric binding complex or a heterotandem binding complex as described herein comprising one or more effector groups and / or functional groups, such as a fluorophore, e.g. a fluorophore as described herein, for use in a method of diagnosing a pathology in a subject; in some embodiments the pathology is a disease or disorder associated with NK cells (e.g. a disease or disorder described herein). In some embodiments the method comprises contacting the compound or a composition comprising the compound with a sample (e.g. an in vitro, ex vivo or in vivo sample) and detecting a change characteristic of the pathology in the sample in the presence of the compound or composition. The method may for example comprise detecting the fluorescence of a fluorescently-labelled compound as described herein. Thus the provided compounds may be useful in developing and performing assay procedures, immunofluorescent stainings and the like. Heterotandem Binding Complexes According to a further aspect of the invention, provided herein is a heterotandem bicyclic peptide complex comprising (i) one or more first bicyclic peptide ligands; attached to (ii) one or more second bicyclic peptide ligands, wherein said one or more second bicyclic peptide ligands are one or more bicyclic peptide ligands as provided herein. The or each second bicyclic peptide ligand provided herein is typically specific for natural killer (NK) cells. The one or more first bicyclic peptide ligands typically bind to one or more further biological targets and are typically not specific for NK cells. For example, the one or more first bicyclic peptide ligands may bind to one or more cancer cells (e.g. to one or more components (e.g. epitopes) present on or expressed by a one or more cancer cells). When the heterotandem bicyclic peptide complex comprises two or more first bicyclic peptide ligands, the two or more first bicyclic peptide ligands may be the same or different. The two or more first bicyclic peptide ligands may be specific for the same biological target or for different targets. The heterotandem bicyclic peptide complex may comprise one or more linkers. A linker may link (i) one or more first bicyclic peptide ligands to one or more second bicyclic peptide ligands as provided herein. Any suitable linker can be used. Some exemplary linkers are described in more detail herein. Accordingly, in some embodiments provided herein is a heterotandem bicyclic peptide complex comprising (i) one or more first bicyclic peptide ligands; linked via a linker to (ii) one or more second bicyclic peptide ligands as provided herein. According to a further aspect of the invention, there is provided a heterotandem bicyclic peptide complex comprising: (a) a first bicyclic peptide ligand which binds to a component present on a cancer cell; conjugated via a linker to (b) one or more second bicyclic peptide ligands specific for natural killer (NK) cells as defined herein. First References herein to the term “cancer cell” includes any cell which is known to be involved in cancer. Cancer cells are created when the genes responsible for regulating cell division are damaged. Carcinogenesis is caused by mutation and epimutation of the genetic material of normal cells, which upsets the normal balance between proliferation and cell death. This results in uncontrolled cell division and the evolution of those cells by natural selection in the body. The uncontrolled and often rapid proliferation of cells can lead to benign or malignant tumors (cancer). Benign tumors do not spread to other parts of the body or invade other tissues. Malignant tumors can invade other organs, spread to distant locations (metastasis) and become life-threatening. In one embodiment the cancer cell is a fibrosarcoma cell, a lung cancer cell, an ovarian cancer cell, a prostate cancer cell, a bladder cancer cell, a colon cancer cell, or a breast cancer cell. In one embodiment, the cancer cell is selected from an HT1080, A549, SC-OV-3, PC3, HT1376, NCI-H292, LnCap, MC38, MC38 #13, 4T1-D02, H322, HT29, T47D and RKO tumor cell. In one embodiment the first bicyclic peptide ligand comprises a polypeptide attached to a molecular scaffold. In some embodiments the molecular scaffold is a derivative of TATA which has the following structure: wherein * denotes the point of attachment to the polypeptide, e.g. to three cysteine residues of the polypeptide. In one embodiment, the component present on a cancer cell is EphA2. Eph receptor tyrosine kinases (Ephs) belong to a large group of receptor tyrosine kinases (RTKs), kinases that phosphorylate proteins on tyrosine residues. Ephs and their membrane bound ephrin ligands (ephrins) control cell positioning and tissue organization (Poliakov et al. (2004) Dev Cell 7, 465-80). Functional and biochemical Eph responses occur at higher ligand oligomerization states (Stein et al. (1998) Genes Dev 12, 667-678). Among other patterning functions, various Ephs and ephrins have been shown to play a role in vascular development. Knockout of EphB4 and ephrin-B2 results in a lack of the ability to remodel capillary beds into blood vessels (Poliakov et al., supra) and embryonic lethality. Persistent expression of some Eph receptors and ephrins has also been observed in newly- formed, adult micro-vessels (Brantley-Sieders et al. (2004) Curr Pharm Des 10, 3431-42; Adams (2003) J Anat 202, 105-12). The de-regulated re-emergence of some ephrins and their receptors in adults also has been observed to contribute to tumor invasion, metastasis and neo-angiogenesis (Nakamoto et al. (2002) Microsc Res Tech 59, 58-67; Brantley-Sieders et al., supra). Furthermore, some Eph family members have been found to be over-expressed on tumor cells from a variety of human tumors (Brantley-Sieders et al., supra); Marme (2002) Ann Hematol 81 Suppl 2, S66; Booth et al. (2002) Nat Med 8, 1360-1). EPH receptor A2 (ephrin type-A receptor 2) is a protein that in humans is encoded by the EPHA2 gene. EphA2 is upregulated in multiple cancers in man, often correlating with disease progression, metastasis and poor prognosis e.g.: breast (Zelinski et al (2001) Cancer Res.61, 2301–2306; Zhuang et al (2010) Cancer Res. 70, 299–308; Brantley-Sieders et al (2011) PLoS One 6, e24426), lung (Brannan et al (2009) Cancer Prev Res (Phila) 2, 1039–1049; Kinch et al (2003) Clin Cancer Res.9, 613-618; Guo et al (2013) J Thorac Oncol.8, 301-308), gastric (Nakamura et al (2005) Cancer Sci.96, 42-47; Yuan et al (2009) Dig Dis Sci 54, 2410-2417), pancreatic (Mudali et al (2006) Clin Exp Metastasis 23, 357-365), prostate (Walker-Daniels et al (1999) Prostate 41, 275–280), liver (Yang et al (2009) Hepatol Res.39, 1169–1177) and glioblastoma (Wykosky et al (2005) Mol Cancer Res.3, 541–551; Li et al (2010) Tumor Biol.31, 477–488). The full role of EphA2 in cancer progression is still not defined although there is evidence for interaction at numerous stages of cancer progression including tumor cell growth, survival, invasion and angiogenesis. Downregulation of EphA2 expression suppresses tumor cancer cell propagation (Binda et al (2012) Cancer Cell 22, 765-780), whilst EphA2 blockade inhibits VEGF induced cell migration (Hess et al (2001) Cancer Res.61, 3250–3255), sprouting and angiogenesis (Cheng et al (2002) Mol Cancer Res.1, 2–11; Lin et al (2007) Cancer 109, 332- 40) and metastatic progression (Brantley-Sieders et al (2005) FASEB J.19, 1884–1886). An antibody drug conjugate to EphA2 has been shown to significantly diminish tumor growth in rat and mouse xenograft models (Jackson et al (2008) Cancer Research 68, 9367-9374) and a similar approach has been tried in man although treatment had to be discontinued for treatment related adverse events (Annunziata et al (2013) Invest New drugs 31, 77-84). In one embodiment, the first bicyclic peptide ligand comprises an EphA2 binding bicyclic peptide ligand. Suitable examples of EphA2 binding bicyclic peptide ligands are disclosed in WO 2019 / 122860, WO 2019 / 122861 and WO 2019 / 122863, the peptides of which are incorporated herein by reference. In one embodiment, the EphA2 binding bicyclic peptide ligand comprises an amino acid sequence which is: C[HyP]LVNPLCLEP[d1Nal]WTC (SEQ ID NO: 6); or a modified derivative thereof; wherein HyP represents trans-4-hydroxy-L-proline and d1Nal represents D-1-naphthylalanine, or a pharmaceutically acceptable salt thereof. In one embodiment, the EphA2 binding bicyclic peptide ligand comprises an amino acid sequence which is: C[HyP]LVNPLCLEP[d1Nal]WTC (SEQ ID NO: 6). In some embodiments the EphA2 binding bicyclic peptide ligand comprises one or more N-terminal and / or C-terminal modifications. In some embodiments the EphA2 binding ligand comprises: A[HArg]DC[HyP]LVNPLCLEP[d1Nal]WTC (SEQ ID NO: 7) or a modified derivative thereof. In some embodiments the EphA2 binding ligand comprises: A[HArg]DC[HyP]LVNPLCLEP[d1Nal]WTC (SEQ ID NO: 7). In some embodiments the polypeptide of the EphA2 binding bicyclic peptide ligand is attached to a molecular scaffold as disclosed herein. Thus in some embodiments the EphA2 binding bicyclic peptide ligand comprises a polypeptide of SEQ ID NO: 7 (or a modified derivative therof0 attached (e.g. via the three cysteine residues) to a molecular scaffold which is a derivative of TATA as defined herein. In a further embodiment, the molecular scaffold is a derivative of TATA which has the following structure: , wherein * denotes the point of attachment of the three cysteine residues, and the EphA2 binding bicyclic peptide ligand optionally comprises N-terminal and / or C-terminal modifications and comprises: A[HArg]DC[HyP]LVNPLCLEP[d1Nal]WTC (SEQ ID NO: 7) (the bicyclic peptide of which is herein referred to as BCY13118), wherein HArg represents homoarginine, HyP represents trans-4-hydroxy-L-proline and 1Nal represents 1-naphthylalanine, or a pharmaceutically acceptable salt thereof. In an alternative embodiment, the component present on a cancer cell is Nectin-4. Nectin-4 is a surface molecule that belongs to the nectin family of proteins, which comprises 4 members. Nectins are cell adhesion molecules that play a key role in various biological processes such as polarity, proliferation, differentiation and migration, for epithelial, endothelial, immune and neuronal cells, during development and adult life. They are involved in several pathological processes in humans. They are the main receptors for poliovirus, herpes simplex virus and measles virus. Mutations in the genes encoding Nectin-1 (PVRL1) or Nectin-4 (PVRL4) cause ectodermal dysplasia syndromes associated with other abnormalities. Nectin-4 is expressed during foetal development. In adult tissues its expression is more restricted than that of other members of the family. Nectin-4 is a tumor-associated antigen in 50%, 49% and 86% of breast, ovarian and lung carcinomas, respectively, mostly on tumors of bad prognosis. Its expression is not detected in the corresponding normal tissues. In breast tumors, Nectin-4 is expressed mainly in triple-negative and ERBB2+ carcinomas. In the serum of patients with these cancers, the detection of soluble forms of Nectin-4 is associated with a poor prognosis. Levels of serum Nectin-4 increase during metastatic progression and decrease after treatment. These results suggest that Nectin-4 could be a reliable target for the treatment of cancer. Accordingly, several anti-Nectin-4 antibodies have been described in the prior art. In particular, Enfortumab Vedotin (ASG-22ME) is an antibody- drug conjugate (ADC) targeting Nectin-4 and is currently clinically investigated for the treatment of patients suffering from solid tumors. In one embodiment, the first peptide ligand comprises a Nectin-4 binding bicyclic peptide ligand. Suitable examples of Nectin-4 binding bicyclic peptide ligands are disclosed in WO 2019 / 243832, the peptides of which are incorporated herein by reference. In an alternative embodiment, the component present on a cancer cell is PD-L1. Programmed cell death 1 ligand 1 (PD-L1) is a 290 amino acid type I transmembrane protein encoded by the CD274 gene on mouse chromosome 19 and human chromosome 9. PD-L1 expression is involved in evasion of immune responses involved in chronic infection, e.g., chronic viral infection (including, for example, HIV, HBV, HCV and HTLV, among others), chronic bacterial infection (including, for example, Helicobacter pylori, among others), and chronic parasitic infection (including, for example, Schistosoma mansoni). PD-L1 expression has been detected in a number of tissues and cell types including T-cells, B-cells, macrophages, dendritic cells, and nonhaematopoietic cells including endothelial cells, hepatocytes, muscle cells, and placenta. PD-L1 expression is also involved in suppression of anti-tumor immune activity. Tumors express antigens that can be recognised by host T-cells, but immunologic clearance of tumors is rare. Part of this failure is due to immune suppression by the tumor microenvironment. PD- L1 expression on many tumors is a component of this suppressive milieu and acts in concert with other immunosuppressive signals. PD-L1 expression has been shown in situ on a wide variety of solid tumors including breast, lung, colon, ovarian, melanoma, bladder, liver, salivary, stomach, gliomas, thyroid, thymic epithelial, head, and neck (Brown JA et al.2003 Immunol. 170:1257-66; Dong H et al. 2002 Nat. Med. 8:793-800; Hamanishi J, et al. 2007 Proc. Natl. Acad. Sci. USA 104:3360-65; Strome SE et al.2003 Cancer Res.63:6501-5; Inman BA et al.2007 Cancer 109:1499-505; Konishi J et al.2004 Clin. Cancer Res.10:5094-100; Nakanishi J et al.2007 Cancer Immunol. Immunother.56:1173-82; Nomi T et al.2007 Clin. Cancer Res.13:2151-57; Thompson RH et al.2004 Proc. Natl. Acad. Sci. USA 101: 17174- 79; Wu C et al.2006 Acta Histochem.108:19-24). In addition, the expression of the receptor for PD-L1, Programmed cell death protein 1 (also known as PD-1 and CD279) is upregulated on tumor infiltrating lymphocytes, and this also contributes to tumor immunosuppression (Blank C et al. 2003 Immunol. 171:4574-81). Most importantly, studies relating PD-L1 expression on tumors to disease outcome show that PD-L1 expression strongly correlates with unfavourable prognosis in kidney, ovarian, bladder, breast, gastric, and pancreatic cancer (Hamanishi J et al.2007 Proc. Natl. Acad. Sci. USA 104:3360-65; Inman BA et al.2007 Cancer 109:1499-505; Konishi J et al.2004 Clin. Cancer Res.10:5094-100; Nakanishi J et al.2007 Cancer Immunol. Immunother.56:1173-82; Nomi T et al.2007 Clin. Cancer Res.13:2151-57; Thompson RH et al.2004 Proc. Natl. Acad. Sci. USA 101:17174-79; Wu C et al.2006 Acta Histochem. 108:19-24). In addition, these studies suggest that higher levels of PD-L1 expression on tumors may facilitate advancement of tumor stage and invasion into deeper tissue structures. The PD-1 pathway can also play a role in haematologic malignancies. PD-L1 is expressed on multiple myeloma cells but not on normal plasma cells (Liu J et al.2007 Blood 110:296-304). PD-L1 is expressed on some primary T-cell lymphomas, particularly anaplastic large cell T lymphomas (Brown JA et al, 2003 Immunol.170:1257-66). PD-1 is highly expressed on the T-cells of angioimmunoblastic lymphomas, and PD-L1 is expressed on the associated follicular dendritic cell network (Dorfman DM et al.2006 Am. J. Surg. Pathol.30:802-10). In nodular lymphocyte-predominant Hodgkin lymphoma, the T-cells associated with lymphocytic or histiocytic (L&H) cells express PD-1. Microarray analysis using a readout of genes induced by PD-1 ligation suggests that tumor-associated T-cells are responding to PD-1 signals in situ in Hodgkin lymphoma (Chemnitz JM et al. 2007 Blood 110:3226-33). PD-1 and PD-L1 are expressed on CD4 T-cells in HTLV-1 -mediated adult T-cell leukaemia and lymphoma (Shimauchi T et al.2007 Int. J. Cancer 121: 2585-90). These tumor cells are hyporesponsive to TCR signals. Studies in animal models demonstrate that PD-L1 on tumors inhibits T-cell activation and lysis of tumor cells and in some cases leads to increased tumor-specific T-cell death (Dong H et al. 2002 Nat. Med.8:793-800; Hirano F et al.2005 Cancer Res.65:1089-96). Tumor-associated APCs can also utilise the PD-1:PD-L1 pathway to control antitumor T-cell responses. PD-L1 expression on a population of tumor-associated myeloid DCs is upregulated by tumor environmental factors (Curiel TJ et al.2003 Nat. Med.9:562-67). Plasmacytoid dendritic cells (DCs) in the tumor-draining lymph node of B16 melanoma express IDO, which strongly activates the suppressive activity of regulatory T-cells. The suppressive activity of IDO-treated regulatory T-cells required cell contact with IDO- expressing DCs (Sharma MD et al. 2007 Clin. Invest.117:2570-82). In one embodiment, the first peptide ligand comprises a PD-L1 binding bicyclic peptide ligand. Suitable examples of PD-L1 binding bicyclic peptide ligands are disclosed in WO 2020 / 128526 and WO 2020 / 128527, the peptides of which are incorporated herein by reference. In an alternative embodiment, the component present on a cancer cell is membrane type 1 matrix metallopeptidase 14 (MT1, also known as MMP14). MT1-MMP is a transmembrane metalloprotease that plays a major role in the extracellular matrix remodeling, directly by degrading several of its components and indirectly by activating pro-MMP2. MT1-MMP is crucial for tumor angiogenesis (Sounni et al (2002) FASEB J. 16(6), 555-564) and is over- expressed on a variety of solid tumours, therefore the MT1-MMP –binding bicycle peptides of the present invention have particular utility in the targeted treatment of cancer, in particular solid tumours such as non-small cell lung carcinomas. In one embodiment, the bicyclic peptide of the invention is specific for human MT1-MMP. In a further embodiment, the bicyclic peptide of the invention is specific for mouse MT1-MMP. In a yet further embodiment, the bicyclic peptide of the invention is specific for human and mouse MT1-MMP. In a yet further embodiment, the bicyclic peptide of the invention is specific for human, mouse and dog MT1- MMP. Suitable examples of MT1 binding bicyclic peptide ligands are disclosed in WO 2016 / 067035, the peptides of which are incorporated herein by reference. In an alternative embodiment, the component present on a cancer cell is prostate-specific membrane antigen (PSMA). Prostate-specific membrane antigen (PSMA) (also known as Glutamate carboxypeptidase II (GCPII), N-acetyl-L-aspartyl-L-glutamate peptidase I (NAALADase I) and NAAG peptidase) is an enzyme that in humans is encoded by the FOLH1 (folate hydrolase 1) gene. Human GCPII contains 750 amino acids and weighs approximately 84 kDa. Human PSMA is highly expressed in the prostate, roughly a hundred times greater than in most other tissues. In some prostate cancers, PSMA is the second-most upregulated gene product, with an 8- to 12-fold increase over levels in noncancerous prostate cells. Because of this high expression, PSMA is being developed as potential biomarker for therapy and imaging of some cancers. In human prostate cancer, the higher expressing tumors are associated with quicker time to progression and a greater percentage of patients suffering relapse. In one embodiment, the first peptide ligand comprises a PSMA binding bicyclic peptide ligand. Suitable examples of PSMA binding bicyclic peptide ligands are disclosed in WO 2019 / 243455 and WO 2020 / 120980, the peptides of which are incorporated herein by reference. Second Peptide Ligands It will be appreciated that in some embodiments the one or more second peptide ligands are required to bind to one or more components present on a natural killer (NK) cell. It will also be appreciated that when there is more than one second peptide ligand present, said second peptide ligands may bind to the same or differing targets within NK cells. Thus, in one embodiment, said second bicyclic peptide ligands are specific for the same target within the NK cell. In a further embodiment, the heterotandem bicyclic peptide complex comprises at least two identical second bicyclic peptide ligands. By “identical” it is meant second bicyclic peptides having the same amino acid sequence, most critically the same amino acid sequence refers to the binding portion of said second bicyclic peptide (for example, the sequence may vary in attachment position). In this embodiment, each of the second bicyclic peptides within the heterotandem bicyclic peptide complex will bind exactly the same epitope upon the same target of the NK cell – the resultant target bound complex will therefore create a homodimer (if the heterotandem bicyclic peptide complex comprises two identical second bicyclic peptides), homotrimer (if the heterotandem bicyclic peptide complex comprises three identical second bicyclic peptides) or homotetramer (if the heterotandem bicyclic peptide complex comprises four identical second bicyclic peptides), etc. In an alternative embodiment, the heterotandem bicyclic peptide complex comprises at least two differing second bicyclic peptide ligands. By “differing” it is meant second bicyclic peptides having a different amino acid sequence. In this embodiment, the differing second bicyclic peptide ligands within the heterotandem bicyclic peptide complex will typically bind to different epitopes on NK cells - in some embodiments the resultant target bound complex will therefore create a biparatopic (if the heterotandem bicyclic peptide complex comprises two differing second bicyclic peptides), triparatopic (if the heterotandem bicyclic peptide complex comprises three differing second bicyclic peptides) or tetraparatopic (if the heterotandem bicyclic peptide complex comprises four differing second bicyclic peptides), etc. Without being bound by theory it is believed that the resultant heterotandem bicyclic peptide complexes are able to activate receptors by hetero-crosslinking differing targets, such as differing target receptors on NK cells. Thus, in one embodiment, said second bicyclic peptide ligands are specific for different targets on NK cells. It will be appreciated that in this embodiment, the heterotandem bicyclic peptide complex comprises at least two differing second bicyclic peptide ligands (i.e. second bicyclic peptide ligands having differing amino acid sequences). In this embodiment, each of the second bicyclic peptides within the heterotandem bicyclic peptide complex will typically bind a differing epitope upon NK cells – the resultant target bound complex will therefore create a bispecific heterotandem bicyclic peptide complex (if the heterotandem bicyclic peptide complex comprises two differing second bicyclic peptides), trispecific multimeric binding complex (if the heterotandem bicyclic peptide complex comprises three differing second bicyclic peptides), tetraspecific heterotandem bicyclic peptide complex (if the heterotandem bicyclic peptide complex comprises four differing second bicyclic peptides), etc. NKp46 Binding Bicyclic Peptides Examples of such NKp46 binding bicyclic peptides are as described hereinbefore. Linkers It will be appreciated that the first peptide ligand may be conjugated to the one or more second peptide ligands via any suitable linker. Typically, the design of said linker will be such that the two or more total Bicyclic peptides are presented in such a manner that they can bind unencumbered to their respective targets either alone or while simultaneously binding to both target receptors. Additionally, the linker should permit binding to both targets simultaneously while maintaining an appropriate distance between the target cells that would lead to the desired functional outcome. The properties of the linker may be modulated to increase length, rigidity or solubility to optimise the desired functional outcome. The linker may also be designed to permit the attachment of more than one Bicycle to the same target. Increasing the valency of either binding peptide may serve to increase the affinity of the heterotandem for the target cells or may help to induce oligomerisation of one or both of the target receptors. In one embodiment the linker is a linear linker or a branched linker. In some embodiments the linker is a branched linker and comprises three or four branches. In some embodiments the linker is capable of binding to three or four bicyclic peptide ligands. In some embodiments the linker comprises three branches and is capable of binding to three bicyclic peptide ligands. In some embodiments the linker comprises four branches and is capable of binding to four bicyclic peptide ligands. In some embodiments the linker comprises one or more repeating monomer groups. In some embodiments, the linker is a bidentate or polydentate group having a length of from about 0.3 nm to about 300 nm. In some embodiments the linker has a length of from about 0.5 nm to about 200 nm, such as from about 1 nm to about 100 nm, e.g. from about 1.5 nm to about 50 nm, e.g. from about 2 nm to about 20 nm, such as from about 3 nm to about 10 nm. In some embodiments the linker length is the persistence length. In some embodiments the length is determined when linker is in aqueous solution under physiological conditions, (e.g. phosphate buffered saline, pH 7.4 at 37 °C) and in some embodiments can be determined using atomic force microscopy. In some embodiments, the linker comprises one or more linking moieties such as one or more poly(alkyleneglycol) groups such as poly(ethyleneglycol) or poly(propyleneglycol). In some embodiments the linker may comprise one or more groups such as an amine group, an amide group; an alkylene group; a carbamate group; an ether group; an ester group; a disulphide bond; a hydrazone group; a sulfonamide group; a thioether group; or a cyclic group, preferably a 4-12 membered carbocyclic or heterocyclic group, a 5-12 membered heteroaryl group or a C6-12aryl group; wherein said alkylene, alkenylene, alkynylene, poly(alkyleneglycol), amine and cyclic group is each independently optionally substituted. In some embodiments the linker comprises one or more amino acids or amino acid analogs. In some embodiments the linker comprises from about 1 to about 5 amino acids or amino acid analogs. In some embodiments the side chains of two amino acids or amino acid analogs in the linker are attached together. In some embodiments the linker comprises a moiety of form wherein each R1is H or C1-4alkyl; each R2is selected from the side chain of an amino acid (e.g. a canonical amino acid) or is C1-4alkyl which may be substituted e.g. with OH, SH, SC1-4alkyl, aryl (which may be substituted with OH), heteroaryl, C(O)OH, C(O)NH2, N+H3, NH(C=N+H2)NH2, for example, R2may comprise the side chain of arginine or homo-arginine; and wherein LINK is a linker, wherein LINK is optionally a C2-8hydrocarbylene (e.g. alkylene) linker optionally terminated by or substituted with one or more groups such as an amine group, an amide group; an alkylene group; a carbamate group; an ether group; an ester group; a disulphide bond; a hydrazone group; a sulfonamide group; a thioether group; or a cyclic group as defined herein; for example, LINK may comprise a C3-6alkylene group which terminates in or is interrupted by an amide group; e.g. LINK may comprise a moiety of form -C1-4alkylene-NHC(O)-C1-4alkylene-, e.g. -C4alkylene-NHC(O)-C1alkylene-. In some embodiments said moiety is attached to a polypeptide comprised in a peptide ligand or bicyclic peptide ligand as defined herein, e.g. at the N- or C- terminus of a polypeptide comprised in a peptide ligand or bicyclic peptide ligand as defined herein. In some embodiments the linker comprises one or more reactive groups for reaction with a bicyclic peptide ligand as described herein. Exemplary reactive groups include azide goups (which may react with alkyne groups on a bicyclic peptide ligand as described herein, e.g. in the presence of suitable conditions, for example in the presence of an azide-alkyne cycloaddition catalyst, e.g. thereby forming a 1,2,3-triazole group); carboxylic acids and activated derivatives thereof (such as NHS-esters) (which may react with amine groups on a bicyclic peptide ligand as described herein, e.g. in the presence of suitable conditions, e.g. thereby forming an amide bond), and the like. In some embodiments when the linker comprises a poly(alkyleneglycol), the poly(alkyleneglycol) is poly(ethyleneglycol) (PEG) or poly(propyleneglycol) (PPG). In some embodiments the linker comprises one or more group PEGn, wherein n represents the number of contiguous ethyleneglycol units in each said PEG group. In some embodiments n is an integer from about 2 to about 25, such as about 3 to about 10. In some embodiments the linker comprises one or more branches e.g. three branches and each branch comprises a PEGngroup. In some embodiments when the linker comprises an amide group, said amide group is of formula -NHC(O)- or -C(O)NH-. In some embodiments when the linker comprises an amine group, the amine group is of formula N(R)3, wherein each R may be the same or different. In some embodiments each R comprises a bicyclic peptide ligand as described herein, for example attached to the amine nitrogen via a linking moiety comprising one or more group PEGnas described herein. In some embodiments when the linker comprises a cyclic group the cyclic group is a C6aryl group. In some embodiments when the linker comprises an alkylene group the alkylene group is a C1-3alkylene group. In one embodiment, the linker is a linear linker. Without being bound by theory it is believed that the linear linker has the advantage of allowing the presence of one first peptide at one end and one second peptide at the other end. In some embodiments the linear linker is a group of formula N3—(Alk)m—PEGn—(Alk)m—Q wherein each Alk is independently a C1-3alkylene group; each m is independently 0 or 1; n is an integer from about 2 to about 25; and Q is a carboxylic acid (C(O)OH) or activated derivative thereof (e.g. an NHS-ester group). In a further embodiment, the linear linker is selected from: azide-PEG5-acid; and azide-PEG24-acid. Those skilled in the art will appreciate that when conjugated with bicyclic peptide ligands as described herein, the azide group will typically react with an alkyne group on one bicyclic peptide ligand (e.g. to an alkyne group comprised in a K(PYA) moiety as described herein) and the carboxylic acid or NHS-ester will typically react with an amine group on another bicyclic peptide ligand (e.g. to the N-terminal amino group of an polypeptide as described herein). In one embodiment, the linker is a branched linker. Without being bound by theory it is believed that the branched linker has the advantage of allowing the presence of one first peptide at one end and the two or more second peptides at the other end. In some embodiments the branched linker is a group of formula [N3—(Alk)m—PEGn—(Alk)m-]x-W-[-(Alk)m—PEGn—(Alk)m—Q]ywherein each Alk is independently a C1-3alkylene group which independently optionally terminates in an amide group or an -O- group; each m is independently 0, 1 or 2; n is an integer from about 2 to about 25; Q is a carboxylic acid or activated derivative thereof (e.g. an NHS-ester group); W is N or a benzene ring; and x and y are each independently 0 or an integer from 1 to about 4; wherein x + y is equal to the number of branches in the branched linker; for example a linker comprising three branches may have x = 2 and y = 1. For avoidance of doubt, when a linker comprises a plurality of groups [N3—(Alk)m—PEGn—(Alk)m- ] and / or [-(Alk)m—PEGn—(Alk)m—Q], said groups may be the same or different. In a further embodiment, the branched linker is selected from: N-(acid-PEG3)-N-bis(PEG3-azide);

[0002] Trimesic-[Peg10]3;

[0003]

[0004] TCA-[Peg23]3;

[0005] Methane-N-(PEG5-acid)-Tri(MeOPr-amide-PEG4-azide);

[0006] Methane-N-(PEG10-acid)-Tri(MeOPr-amide-PEG10-azide); and Bis-N-aminopropyl-glycine-(PEG5)2. In one particular embodiment, the branched linker is: N-(acid-PEG3)-N-bis(PEG3-azide). As explained above, those skilled in the art will appreciate that when conjugated with bicyclic peptide ligands as described herein, the or each azide group will typically react with an alkyne group on one bicyclic peptide ligand (e.g. to an alkyne group comprised in a K(PYA) moiety as described herein) and the or each carboxylic acid or NHS-ester will typically react with an amine group on another bicyclic peptide ligand (e.g. to the N-terminal amino group of an polypeptide as described herein). For example, when the branched linker is: the linker in the heterotandem bicyclic peptide complex may have the form: wherein NH-Bic1 represents a reacted amino group (e.g. the N-terminal amino group) of a first bicyclic peptide ligand and each Bic2—— represents a reacted alkyne group (e.g. a K(PYA) group) of a second bicyclic peptide ligand; other linkers behave analogously. Multimeric binding Complexes As described above, in some embodiments a multimeric binding complex comprises at least one bicyclic peptide ligand as described herein. In some embodiments a multimeric binding complex comprises at least two bicyclic peptide ligands as described herein. In some embodiments the bicyclic peptide ligands are attached together via a linker, such as a linker described herein. In some embodiments such a multimeric binding complex further comprises one or more effector groups and / or functional groups, such as one or more cytotoxic agents, chelators (e.g. radiochelators), chromophores and / or fluorophores. In some embodiments the one or more effector groups and / or functional groups, such as one or more cytotoxic agents, chelators (e.g. radiochelators), chromophores and / or fluorophores are attached directly to one of the two or more bicyclic peptide ligands. In some embodiments the one or more effector groups and / or functional groups, such as one or more cytotoxic agents, chelators (e.g. radiochelators), chromophores and / or fluorophores are attached to a linker between the two or more bicyclic peptide ligands. In some embodiments a multimeric binding complex comprises at least one bicyclic peptide ligand selected from BCY24188 and BCY26631. In some embodiments a multimeric binding complex comprises at least two bicyclic peptide ligands each selected from BCY24188 and BCY26631. In some embodiments a multimeric binding complex comprises two BCY24188 bicyclic peptide ligands, attached together via a linker. In some embodiments a multimeric binding complex comprises two BCY26631 bicyclic peptide ligands, attached together via a linker. In some embodiments two bicyclic peptide ligands moieties are attached together via reaction with a N-(amino-PEG2)-N-bis(PEG3-azide) linker. In some embodiments the linker may be: The linker in the multimeric binding complex may therefore have the form wherein EF is an effector and / or functional group as described herein, such as a cytotoxic agent, chelator (e.g. radiochelator), chromophore or fluorophore as described herein (e.g. a fluorophore as described herein), e.g. wherein prior to reaction with the linker the effector group comprises a carboxylic acid or activated derivative thereof which reacts with the NH2group of the linker thereby forming a moiety -NH-C(O)-EF; and each Bic2—— represents a reacted alkyne group (e.g. a K(PYA) group) of a bicyclic peptide ligand as described herein. In other words, the linker when comprised in the multimeric binding complex comprises a N- (amido-PEG2)-N-bis(PEG3-azide) linker. In some embodiments a multimeric binding complex comprises two BCY24188 bicyclic peptide ligands, attached together via a N-(amido-PEG2)-N-bis(PEG3-azide) linker. In some embodiments a multimeric binding complex comprises two BCY24188 bicyclic peptide ligands, each attached via the C-terminal K(PYA), to a N-(amido-PEG2)-N-bis(PEG3-azide) linker attached to a fluorophore as described herein. In some embodiments the fluorophore is AF647. An example of such a multimeric binding complex is BCY28671. In some embodiments a multimeric binding complex comprises two BCY26631 bicyclic peptide ligands, attached together via a N-(amido-PEG2)-N-bis(PEG3-azide) linker. In some embodiments a multimeric binding complex comprises two BCY26631 bicyclic peptide ligands, each attached via the C-terminal K(PYA), to a N-(amido-PEG2)-N-bis(PEG3-azide) linker attached to a fluorophore as described herein. In some embodiments the fluorophore is AF647. An example of such a multimeric binding complex is BCY28672. Accordingly, provided herein is a fluorescent bicyclic peptide dimer complex comprising a fluorophore as described herein linked to two NKp46 specific peptides (both of which are BCY24188) via an N-(amido-PEG2)-N-bis(PEG3-azide) linker. In some embodiments the fluorophore is AF647 and the complex is BCY28671. Also provided herein is a fluorescent bicyclic peptide dimer complex comprising a fluorophore as described herein linked to two NKp46 specific peptides (both of which are BCY26631) via an N-(amido-PEG2)- N-bis(PEG3-azide) linker. In some embodiments the fluorophore is AF647 and the complex is BCY28672. Such complexes are therapeutically useful, for example as clinical reagents for PD readout: Accordingly provided herein is a multimeric binding complex

[0007] or a salt thereof, wherein fluorophore is a fluorophore as described herein; for example when the flurophore is AF647 the complex may be BCY28671:

[0008] or a salt thereof. Also provided is a multimeric binding complex

[0009] or a salt thereof, wherein fluorophore is a fluorophore as described herein; for example when the flurophore is AF647 the complex may be BCY28672:

[0010] or a salt thereof. Heterotandem Complexes In one specific embodiment, the first peptide ligand comprises an EphA2 binding bicyclic peptide ligand attached to a TATA scaffold, the one or more second peptide ligands comprise two NKp46 binding bicyclic peptide ligands attached to a TATA scaffold and said heterotandem complex is the complex listed in Table A or a pharmaceutically acceptable salt thereof: Table A (EphA2 : NKp46; 1:2)

[0011] The heterotandem bicyclic peptide complex BCY27047 consists of an EphA2 specific peptide BCY13118 linked to two NKp46 specific peptides (both of which are BCY26631) via an N- (acid-PEG3)-N-bis(PEG3-azide) linker, shown pictorially as:

[0012] For avoidance of doubt, the structure of BCY27047 may be represented as: wherein L1is L2is L3is

[0013] BCY27047 may be provided in the form of a pharmaceutically acceptable salt, also provided herein. The heterotandem bicyclic peptide complex BCY26129 consists of an EphA2 specific peptide BCY13118 linked to two NKp46 specific peptides (both of which are BCY24188) via an N- (acid-PEG3)-N-bis(PEG3-azide) linker, shown pictorially as:

[0014] BCY26129

[0015] For avoidance of doubt, the structure of BCY26129 may be represented as: wherein L1is L2is

[0016] L3is BCY26129 may be provided in the form of a pharmaceutically acceptable salt, also provided herein. Numbering When referring to amino acid residue positions within the peptides of the invention, reactive groups, i.e. cysteine are omitted from the numbering as they are invariant, therefore, the numbering of amino acid residues within the peptides of the invention is referred to as below: -[dC]-Y1-[Cba]2-P3-D4-Y5-L6-C-X7-D8-E9-Y10-C- (SEQ ID NO: 1). For the purpose of this description, unless specified otherwise all bicyclic peptides are assumed to be cyclised with TATA and yielding a tri-substituted structure. Cyclisation with TATA occurs on the first, second and third cysteine groups. As used herein, the term “cysteine groups” in relation to cyclisation with a molecular scaffold as described herein may refer to both D-cysteine ([dC]) and L-cysteine (C) residues that may be present in a polypeptide comprised in a peptide ligand. Molecular Format N- or C-terminal extensions to the bicycle core sequence are added to the left or right side of the sequence, separated by a hyphen. For example, an N-terminal biotin-G-Sar5tail would be denoted as: [Biot]-G-[Sar5]-A-(SEQ ID NO: X). wherein [Biot] represents Biotin and [Sar] represents sarcosine. Inversed Peptide Sequences In light of the disclosure in Nair et al. (2003) J. Immunol.170(3), 1362-1373, it is envisaged that the peptide sequences disclosed herein would also find utility in their retro-inverso form. For example, the sequence is reversed (i.e. N-terminus become C-terminus and vice versa) and their stereochemistry is likewise also reversed (i.e. D-amino acids become L-amino acids and vice versa). Peptide Ligand Definition A peptide ligand, as referred to herein, refers to a peptide, peptidic or peptidomimetic covalently bound to a molecular scaffold. Typically, such peptides, peptidics or peptidomimetics comprise a peptide having natural or non-natural amino acids, two or more reactive groups (e.g. cysteine, homocysteine (hCys, (S)-2-Amino-4-sulfanylbutanoic acid), βCys ((R)-3-amino-3-mercaptopropanoic acid), penicillamine (Pen, (R)-2-amino-3-mercapto- 3-methylbutanoic acid), Dap ((S)-2,3-diaminopropanoic acid) or N-alkyl-Dap (e.g. N-methyl- Dap, (S)-2-amino-3-(methylamino)propanoic acid) which are capable of forming covalent bonds to the scaffold, and a sequence subtended between said reactive groups which is referred to as the loop sequence, since it forms a loop when the peptide, peptidic or peptidomimetic is bound to the scaffold. In the present case, the peptides, peptidics or peptidomimetics typically comprise three cysteine residues, and form two loops on the scaffold. Accordingly, in some embodiments the present disclosure provides a peptide ligand, bicyclic peptide ligand or a complex comprising a peptide ligand or bicyclic peptide ligand as provided herein, wherein one or more of the cysteine residues of one or more of the polypeptides comprised in said peptide ligand, bicyclic peptide ligand or complex is replaced with homocysteine (hCys), βCys, penicillamine (Pen), Dap or N-methyl-Dap. In some embodiments one or more (e.g.1, 2 or 3) of the cysteine residues (e.g. L-cysteine and / or D- cysteine) in any one of SEQ ID NOs: 1 to 5 is replaced with homo-cysteine (hCys), βCys, penicillamine (Pen), Dap or N-methyl-Dap. In some embodiments one or more (e.g.1, 2 or 3) of the cysteine residues (e.g. L-cysteine and / or D-cysteine) in any one of SEQ ID NOs: 6 or 7 is replaced with homocysteine (hCys), βCys, penicillamine (Pen), Dap or N-methyl-Dap. For avoidance of doubt, in the complexes provided herein which comprise two or more peptide ligands (e.g. two or more bicyclic peptide ligands), each said ligand is independently optionally modified in this way, such that different ligands may be modified or not and different modified ligands may comprise different modifications. Peptide specificity As explained above, in some embodiments the provided peptides and ligands comprising such (described in more detail herein) are specific for NK cells. In some embodiments the provided complexes (e.g. heterotandem binding complexes) contain peptides and ligands comprising such (described in more detail herein) that are specific for EphA2, Nectin-4, PD-L1, MT1 or PSAM. In some embodiments the provided complexes (e.g. heterotandem binding complexes) contain one or more first peptides or ligands comprising such (described in more detail herein) that are specific for EphA2 and one or more second peptides or ligands comprising such (described in more detail herein) that are specific for NK cells. As used herein, the term “specific” (“specific binding”, etc) refers in its broadest sense to a peptide or peptide ligand which binds to its biological target. In some embodiments the peptide or peptide ligand binds to its biological target in a specific manner; that is, the binding to the biological target is not non-specific. In some embodiments a peptide which exhibits non-specific binding is promiscuous; that is the peptide is capable of binding to multiple different biological species, typically including the target of interest and off-target binding sites, such as binding sites on cell types other than a target cell type. Accordingly, in some embodiments a peptide or peptide ligand which is chosen or designed to bind specifically to its intended target does not exhibit promiscuous binding to off-target binding sites. In some embodiments the binding to the target is a binding to a particular epitope on the target. A peptide or peptide ligand may be designed to be specific for a particular epitope or may be identified by suitable screening methods, such as display techniques (e.g. phage display) which can be used to develop high-affinity binders against given targets (e.g. epitopes). Alternatively, a peptide or peptide ligand can be identified with specific binding to a biological target (such as a cellular target) without knowledge of the specific epitope to which it binds. In some embodiments a peptide or peptide ligand which specifically binds to a target or epitope has a high affinity for the target or epitope. In some embodiments the binding affinity of a peptide or peptide ligand to its epitope may be expressed in terms of its dissociation constant (KD, also written as Kd). Typically, a peptide or peptide ligand which specifically binds to a biological target will have a KDagainst that target of less than 10 μM, e.g. less than 1 μM. Often, a peptide or peptide ligand which specifically binds to a biological target will have a nanomolar KDagainst that target, such as less than 100 nM, less than 20 nM, less than 10 nM or even less than 1 nM. Binding affinities can be determined by methods known in the art, such as SPR and competition assays. Some suitable assays are described in the examples. In some embodiments a peptide or peptide ligand which specifically binds to a biological target will have a higher affinity (lower KD) for the specific biological target than for other biological binding epitopes. For example, a peptide or peptide ligand which specifically binds to NK cells will typically bind to NK cells (e.g. to one or more epitopes expressed by NK cells, such as NKp30, NKp44, NKp46, e.g. NKp46) with a higher affinity than to other cell types. Similarly, a peptide or peptide ligand which specifically binds to EphA2 will typically bind to EphA2 with a higher affinity than to other epitopes. In some embodiments a peptide or peptide ligand which specifically binds to a biological target will bind to the target with an affinity at least twice as strong, e.g. at least 5 times, e.g. at least 10 times, e.g. at least 20 time, e.g. at least 50 times, e.g. at least 100 times, e.g. at least 1000 times or more as strong as the binding of the peptide to any other off-target binding partners. Advantages of the Peptide Ligands Certain bicyclic peptides of the present invention have a number of advantageous properties which enable them to be considered as suitable drug-like molecules for injection, inhalation, nasal, ocular, oral or topical administration. Such advantageous properties include: - Species cross-reactivity. This is a typical requirement for preclinical pharmacodynamics and pharmacokinetic evaluation; - Protease stability. Bicyclic peptide ligands should in most circumstances demonstrate stability to plasma proteases, epithelial ("membrane-anchored") proteases, gastric and intestinal proteases, lung surface proteases, intracellular proteases and the like. Protease stability should be maintained between different species such that a bicyclic peptide lead candidate can be developed in animal models as well as administered with confidence to humans; - Desirable solubility profile. This is a function of the proportion of charged and hydrophilic versus hydrophobic residues and intra / inter-molecular H-bonding, which is important for formulation and absorption purposes; and - An optimal plasma half-life in the circulation. Depending upon the clinical indication and treatment regimen, it may be required to develop a bicyclic peptide with short or prolonged in vivo exposure times for the management of either chronic or acute disease states. The optimal exposure time will be governed by the requirement for sustained exposure (for maximal therapeutic efficiency) versus the requirement for short exposure times to minimise toxicological effects arising from sustained exposure to the agent. Pharmaceutically Acceptable Salts It will be appreciated that salt forms are within the scope of this invention, and references to peptide ligands and complexes comprising such peptide ligands include the salt forms of said ligands and complexes. The salts of the present invention can be synthesized from the parent compound that contains a basic or acidic moiety by conventional chemical methods such as methods described in Pharmaceutical Salts: Properties, Selection, and Use, P. Heinrich Stahl (Editor), Camille G. Wermuth (Editor), ISBN: 3-90639-026-8, Hardcover, 388 pages, August 2002. Generally, such salts can be prepared by reacting the free acid or base forms of these compounds with the appropriate base or acid in water or in an organic solvent, or in a mixture of the two. Acid addition salts (mono- or di-salts) may be formed with a wide variety of acids, both inorganic and organic. Examples of acid addition salts include mono- or di-salts formed with an acid selected from the group consisting of acetic, 2,2-dichloroacetic, adipic, alginic, ascorbic (e.g. L-ascorbic), L-aspartic, benzenesulfonic, benzoic, 4-acetamidobenzoic, butanoic, (+) camphoric, camphor-sulfonic, (+)-(1S)-camphor-10-sulfonic, capric, caproic, caprylic, cinnamic, citric, cyclamic, dodecylsulfuric, ethane-1,2-disulfonic, ethanesulfonic, 2- hydroxyethanesulfonic, formic, fumaric, galactaric, gentisic, glucoheptonic, D-gluconic, glucuronic (e.g. D-glucuronic), glutamic (e.g. L-glutamic), α-oxoglutaric, glycolic, hippuric, hydrohalic acids (e.g. hydrobromic, hydrochloric, hydriodic), isethionic, lactic (e.g. (+)-L-lactic, (±)-DL-lactic), lactobionic, maleic, malic, (-)-L-malic, malonic, (±)-DL-mandelic, methanesulfonic, naphthalene-2-sulfonic, naphthalene-1,5-disulfonic, 1-hydroxy-2-naphthoic, nicotinic, nitric, oleic, orotic, oxalic, palmitic, pamoic, phosphoric, propionic, pyruvic, L- pyroglutamic, salicylic, 4-amino-salicylic, sebacic, stearic, succinic, sulfuric, tannic, (+)-L- tartaric, thiocyanic, p-toluenesulfonic, undecylenic and valeric acids, as well as acylated amino acids and cation exchange resins. One particular group of salts consists of salts formed from acetic, hydrochloric, hydriodic, phosphoric, nitric, sulfuric, citric, lactic, succinic, maleic, malic, isethionic, fumaric, benzenesulfonic, toluenesulfonic, sulfuric, methanesulfonic (mesylate), ethanesulfonic, naphthalenesulfonic, valeric, propanoic, butanoic, malonic, glucuronic and lactobionic acids. One particular salt is the hydrochloride salt. Another particular salt is the acetate salt. If the compound is anionic, or has a functional group which may be anionic (e.g. -COOH may be -COO-), then a salt may be formed with an organic or inorganic base, generating a suitable cation. Examples of suitable inorganic cations include, but are not limited to, alkali metal ions such as Li+, Na+and K+, alkaline earth metal cations such as Ca2+and Mg2+, and other cations such as Al3+or Zn+. Examples of suitable organic cations include, but are not limited to, ammonium ion (i.e. NH4+) and substituted ammonium ions (e.g. NH3R+, NH2R2+, NHR3+, NR4+). Examples of some suitable substituted ammonium ions are those derived from: methylamine, ethylamine, diethylamine, propylamine, dicyclohexylamine, triethylamine, butylamine, ethylenediamine, ethanolamine, diethanolamine, piperazine, benzylamine, phenylbenzylamine, choline, meglumine, and tromethamine, as well as amino acids, such as lysine and arginine. An example of a common quaternary ammonium ion is N(CH3)4+. Where the peptides of the invention contain an amine function, these may form quaternary ammonium salts, for example by reaction with an alkylating agent according to methods well known to the skilled person. Such quaternary ammonium compounds are within the scope of the peptides of the invention. The peptides (including peptide ligands and complexes thereof) of the invention may exist as a zwitterion. Such compounds may also be provided in the form of a pharmaceutically acceptable salt. Suitable salts include those formed with pharmaceutically acceptable acids, which provide a proton to a negatively charged group such as a COO- group, and a counter- ion to balance the positive charge on a positively charged group such as a quaternary nitrogen atom. Suitable pharmaceutically acceptable acids include hydrochloric acid, sulphonic acids including methanesulphonic acid and toluene sulphonic acid, ascorbic acid and citric acid. Hydrochloric acid and sulphonic acids are preferred, in particular hydrochloric acid. Alternatively, zwitterions can be combined with pharmaceutically acceptable bases, for example, alkali metal (e.g. sodium or potassium) and alkali earth metal (e.g. calcium or magnesium) hydroxides. Modified Derivatives It will be appreciated that modified derivatives of the peptide ligands as defined herein are within the scope of the present invention. In some embodiments, modified derivatives include functional fragments, derivatives and variants of sequences provided herein. As those skilled in the art will appreciate, fragments of amino acid sequences include deletion variants of such sequences wherein one or more, such as at least 1, 2, 3, 4 or 5 amino acids are deleted. Deletion may occur at the C- terminus or N-terminus of the reference sequence or within the reference sequence. Derivatives of amino acid sequences include modified sequences including sequences which are modified in vivo or ex vivo. Many different protein modifications are known to those skilled in the art and include modifications to introduce new functionalities to amino acid residues, modifications to protect reactive amino acid residues or modifications to couple amino acid residues to chemical moieties such as reactive functional groups on linkers for attachment to such amino acid residues. Exemplary modifications that can be made to the provided peptides, ligands and related complexes are described in more detail herein. Derivatives of amino acid sequences include addition variants of such sequences wherein one or more, such as at least 1, 2, 3, 4, or 5 amino acids are added or introduced into the reference sequence. Addition may occur at the C- terminus or N-terminus of the reference sequence or within the reference sequence. Some examples of peptides of SEQ ID NO 1 having further amino acids added thereto are provided in more detail herein. Variants of amino acid sequences include sequences wherein one or more amino acid such as at least 1, 2, 3, 4, or 5 amino acid residues in the reference sequence are exchanged for one or more alternative residues. Variants of amino acid sequences include sequences carrying naturally occurring amino acids and / or unnatural amino acids. Variants, derivatives and fragments of the aforementioned amino acid sequences typically retain at least some of the activity / functionality of the reference sequence. In a preferred embodiment, the variants, derivatives and fragments substantially retain their biological function(s) as described herein. Thus, in one embodiment the variants, derivatives and fragments retain the binding specificity of the reference sequence i.e. the ability to specifically bind to a biological target such as NKp30, NKp44, NKp46, e.g. NKp46. In one such embodiment, the variants, derivatives and fragments bind to the same epitope as the reference sequence. In another embodiment, the variants, derivatives and fragments retain the binding affinity of the reference sequence. Preferably, variants, derivatives and fragments of a reference sequence have increased / improved activity / functionality when compared to the reference sequence. In some embodiments a variant, derivative or fragment of an amino acid sequence is expressed in terms of its percentage identity to the reference sequence. Protocols to determine percent identity are routine procedures within the scope of those skilled in the art. Suitable methods include CLUSTAL W (Thompson et al., Nucleic Acids Research, 22(22) 4673-4680 (1994)) and iterative refinement (Gotoh, J. Mol. Biol.264(4) 823-838 (1996)); and methods described by Altschul et al., Bull. Math. Bio. 48: 603-16, 1986 and Henikoff and Henikoff, Proc. Natl. Acad. Sci. USA 89:10915-19, 1992. In an exemplary method, two amino acid sequences are aligned to optimize the alignment scores using a gap opening penalty of 10, a gap extension penalty of 1, and the "blosum 62" scoring matrix of Henikoff and Henikoff (ibid.), with percentage identity then calculated as: [100 x (T / L)]; wherein T = total number of identical matches and L = length of the longer sequence plus the number of gaps introduced into the longer sequence in order to align the two sequences. In some embodiments a variant, derivative or fragment of a reference sequence has at least at least 60% identity to the reference sequence, such as at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99% or more identity to the reference sequence. Examples of such suitable modified derivatives include one or more modifications selected from: N-terminal and / or C-terminal modifications; replacement of one or more amino acid residues with one or more non-natural amino acid residues (such as replacement of one or more polar amino acid residues with one or more isosteric or isoelectronic amino acids; replacement of one or more non-polar amino acid residues with other non-natural isosteric or isoelectronic amino acids); addition of a spacer group; replacement of one or more oxidation sensitive amino acid residues with one or more oxidation resistant amino acid residues; replacement of one or more amino acid residues with one or more replacement amino acids, such as an alanine, replacement of one or more L-amino acid residues with one or more D- amino acid residues; N-alkylation of one or more amide bonds within the bicyclic peptide ligand; replacement of one or more peptide bonds with a surrogate bond; peptide backbone length modification; substitution of the hydrogen on the alpha-carbon of one or more amino acid residues with another chemical group; modification of amino acids such as cysteine, lysine, glutamate / aspartate and tyrosine with suitable amine, thiol, carboxylic acid and phenol- reactive reagents so as to functionalise said amino acids; and introduction or replacement of amino acids that introduce orthogonal reactivities that are suitable for functionalisation, for example azide or alkyne-group bearing amino acids that allow functionalisation with alkyne or azide-bearing moieties, respectively. In one embodiment, the modified derivative comprises an N-terminal and / or C-terminal modification. In a further embodiment, wherein the modified derivative comprises an N- terminal modification using suitable amino-reactive chemistry, and / or C-terminal modification using suitable carboxy-reactive chemistry. In a further embodiment, said N-terminal or C- terminal modification comprises addition of an effector group, including but not limited to a cytotoxic agent, a radiochelator or a chromophore. In a further embodiment, the modified derivative comprises an N-terminal modification. In a further embodiment, the N-terminal modification comprises an N-terminal acetyl group. In this embodiment, the N-terminal residue is capped with acetic anhydride or other appropriate reagents during peptide synthesis leading to a molecule which is N-terminally acetylated. This embodiment provides the advantage of removing a potential recognition point for aminopeptidases and avoids the potential for degradation of the bicyclic peptide. In an alternative embodiment, the N-terminal modification comprises the addition of a molecular spacer group which facilitates the conjugation of effector groups and retention of potency of the bicyclic peptide to its target. In a further embodiment, the modified derivative comprises a C-terminal modification. In a further embodiment, the C-terminal modification comprises an amide group. In this embodiment, the C-terminal residue is synthesized as an amide during peptide synthesis leading to a molecule which is C-terminally amidated. This embodiment provides the advantage of removing a potential recognition point for carboxypeptidase and reduces the potential for proteolytic degradation of the bicyclic peptide. In one embodiment, the modified derivative comprises replacement of one or more amino acid residues with one or more non-natural amino acid residues. In this embodiment, non-natural amino acids may be selected having isosteric / isoelectronic side chains which are neither recognised by degradative proteases nor have any adverse effect upon target potency. Alternatively, non-natural amino acids may be used having constrained amino acid side chains, such that proteolytic hydrolysis of the nearby peptide bond is conformationally and sterically impeded. In particular, these concern proline analogues, bulky sidechains, Cα- disubstituted derivatives (for example, aminoisobutyric acid, Aib), and cyclo amino acids, a simple derivative being amino-cyclopropylcarboxylic acid. In one embodiment, the modified derivative comprises the addition of a spacer group. In a further embodiment, the modified derivative comprises the addition of a spacer group to the N-terminal cysteine and / or the C-terminal cysteine. In one embodiment, the modified derivative comprises replacement of one or more oxidation sensitive amino acid residues with one or more oxidation resistant amino acid residues. In a further embodiment, the modified derivative comprises replacement of a tryptophan residue with a naphthylalanine or alanine residue. This embodiment provides the advantage of improving the pharmaceutical stability profile of the resultant bicyclic peptide ligand. In one embodiment, the modified derivative comprises replacement of one or more charged amino acid residues with one or more hydrophobic amino acid residues. In an alternative embodiment, the modified derivative comprises replacement of one or more hydrophobic amino acid residues with one or more charged amino acid residues. The correct balance of charged versus hydrophobic amino acid residues is an important characteristic of the bicyclic peptide ligands. For example, hydrophobic amino acid residues influence the degree of plasma protein binding and thus the concentration of the free available fraction in plasma, while charged amino acid residues (in particular arginine) may influence the interaction of the peptide with the phospholipid membranes on cell surfaces. The two in combination may influence half-life, volume of distribution and exposure of the peptide drug, and can be tailored according to the clinical endpoint. In addition, the correct combination and number of charged versus hydrophobic amino acid residues may reduce irritation at the injection site (if the peptide drug has been administered subcutaneously). In one embodiment, the modified derivative comprises replacement of one or more L-amino acid residues with one or more D-amino acid residues. This embodiment is believed to increase proteolytic stability by steric hindrance and by a propensity of D-amino acids to stabilise β-turn conformations (Tugyi et al. (2005) PNAS, 102(2), 413–418). In one embodiment, the modified derivative comprises removal of any amino acid residues and substitution with alanines, such as D-alanines. This embodiment provides the advantage of identifying key binding residues and removing potential proteolytic attack site(s). It should be noted that each of the above mentioned modifications serve to deliberately improve the potency or stability of the peptide. Further potency improvements based on modifications may be achieved through the following mechanisms: - Incorporating hydrophobic moieties that exploit the hydrophobic effect and lead to lower off rates, such that higher affinities are achieved; - Incorporating charged groups that exploit long-range ionic interactions, leading to faster on rates and to higher affinities (see for example Schreiber et al., Rapid, electrostatically assisted association of proteins (1996), Nature Struct. Biol.3, 427-31); and - Incorporating additional constraint into the peptide, by for example constraining side chains of amino acids correctly such that loss in entropy is minimal upon target binding, constraining the torsional angles of the backbone such that loss in entropy is minimal upon target binding and introducing additional cyclisations in the molecule for identical reasons. (for reviews see Gentilucci et al., Curr. Pharmaceutical Design, (2010), 16, 3185-203, and Nestor et al., Curr. Medicinal Chem (2009), 16, 4399-418). Isotopic Variations The present invention includes all pharmaceutically acceptable (radio)isotope-labelled peptide ligands of the invention, wherein one or more atoms are replaced by atoms having the same atomic number, but an atomic mass or mass number different from the atomic mass or mass number usually found in nature, and peptide ligands of the invention, wherein metal chelating groups are attached (termed “effector”) that are capable of holding relevant (radio)isotopes, and peptide ligands of the invention, wherein certain functional groups are covalently replaced with relevant (radio)isotopes or isotopically labelled functional groups. Examples of isotopes suitable for inclusion in the peptide ligands of the invention comprise isotopes of hydrogen, such as2H (D) and3H (T), carbon, such as11C,13C and14C, chlorine, such as36Cl, fluorine, such as18F, iodine, such as123I,125I and131I, nitrogen, such as13N and15N, oxygen, such as15O,17O and18O, phosphorus, such as32P, sulphur, such as35S, copper, such as64Cu, gallium, such as67Ga or68Ga, yttrium, such as90Y and lutetium, such as177Lu, and Bismuth, such as213Bi. Certain isotopically-labelled peptide ligands of the invention, for example, those incorporating a radioactive isotope, are useful in drug and / or substrate tissue distribution studies, and to clinically assess the presence and / or absence of the target on diseased tissues. The peptide ligands of the invention can further have valuable diagnostic properties in that they can be used for detecting or identifying the formation of a complex between a labelled compound and other molecules, peptides, proteins, enzymes or receptors. The detecting or identifying methods can use compounds that are labelled with labelling agents such as radioisotopes, enzymes, fluorescent substances, luminous substances (for example, luminol, luminol derivatives, luciferin, aequorin and luciferase), etc. The radioactive isotopes tritium, i.e.3H (T), and carbon-14, i.e.14C, are particularly useful for this purpose in view of their ease of incorporation and ready means of detection. Substitution with heavier isotopes such as deuterium, i.e.2H (D), may afford certain therapeutic advantages resulting from greater metabolic stability, for example, increased in vivo half-life or reduced dosage requirements, and hence may be preferred in some circumstances. Substitution with positron emitting isotopes, such as11C,18F,15O and13N, can be useful in Positron Emission Topography (PET) studies for examining target occupancy. Isotopically-labelled compounds of peptide ligands of the invention can generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described in the accompanying Examples using an appropriate isotopically-labelled reagent in place of the non-labelled reagent previously employed. Molecular Scaffold In some embodiments a polypeptide disclosed herein is attached to a molecular scaffold. In one embodiment, the molecular scaffold comprises a non-aromatic molecular scaffold. References herein to “non-aromatic molecular scaffold” refers to any molecular scaffold as defined herein which does not contain an aromatic (i.e. unsaturated) carbocyclic or heterocyclic ring system. Accordingly, in some embodiments the polypeptide is attached to a non-aromatic molecular scaffold. In other embodiments the polypeptide is attached to an aromatic molecular scaffold. Suitable examples of non-aromatic molecular scaffolds are described in Heinis et al. (2014) Angewandte Chemie, International Edition 53(6) 1602-1606. As noted in the foregoing documents, the molecular scaffold may be a small molecule, such as a small organic molecule. In one embodiment the molecular scaffold may be a macromolecule. In one embodiment the molecular scaffold is a macromolecule composed of amino acids, nucleotides or carbohydrates. In one embodiment the molecular scaffold comprises reactive groups that are capable of reacting with functional group(s) of the polypeptide to form covalent bonds.

[0017] The molecular scaffold may comprise chemical groups which form the linkage with a peptide, such as amines, thiols, alcohols, ketones, aldehydes, nitriles, carboxylic acids, esters, alkenes, alkynes, azides, anhydrides, succinimides, maleimides, alkyl halides and acyl halides.

[0018] In one embodiment, the molecular scaffold is 1 ,T,1"-(1 ,3,5-triazinane-1 ,3,5-triyl)triprop-2-en- 1-one (also known as triacryloylhexahydro-s-triazine (TATA):

[0019] Thus, following cyclisation with the bicyclic peptides of the invention (e,g, on the cysteine residues), the molecular scaffold forms a tri-substituted 1 ,1',1"-(1 ,3,5-triazinane-1 ,3,5- triyl)tripropan-1-one derivative of TATA having the following structure: which may also be depicted as wherein * denotes the point of attachment of the three cysteine residues.

[0020] In an alternative embodiment, the molecular scaffold is 2,4,6-tris(bromomethyl)-s-triazine (TBMT):

[0021] TBMT.

[0022] Thus, following cyclisation with the bicyclic peptides of the invention on the cysteine residues, the molecular scaffold forms a tri-substituted derivative of TBMT having the following structure: which may also be depicted as wherein * denotes the point of attachment of the three cysteine residues. In an alternative embodiment, the molecular scaffold is 1 ,3,5-tris(bromoacetyl) hexahydro-1 , 3,5-triazine (TATB):

[0023] Thus, following cyclisation with the bicyclic peptides of the invention on the cysteine residues, the molecular scaffold forms a tri-substituted 1 ,3,5-tris(bromoacetyl) hexahydro-1 , 3,5-triazine derivative of TATB having the following structure: which may also be depicted as wherein * denotes the point of attachment of the three cysteine residues.

[0024] Synthesis

[0025] The peptides of the present invention may be manufactured synthetically by standard techniques followed by reaction with a molecular scaffold in vitro. When this is performed, standard chemistry may be used. This enables the rapid large scale preparation of soluble material for further downstream experiments or validation. Such methods could be accomplished using conventional chemistry such as that disclosed in Timmerman et al. (supra). Thus, the invention also relates to the manufacture of polypeptides or conjugates selected as set out herein, wherein the manufacture comprises optional further steps as explained below. In one embodiment, these steps are carried out on the end product polypeptide / conjugate made by chemical synthesis.

[0026] Optionally amino acid residues in the polypeptide of interest may be substituted when manufacturing a conjugate or complex.

[0027] Peptides can also be extended, to incorporate for example another loop and therefore introduce multiple specificities.

[0028] To extend the peptide, it may simply be extended chemically at its N-terminus or C-terminus or within the loops using orthogonally protected lysines (and analogues) using standard solid phase or solution phase chemistry. Standard (bio)conjugation techniques may be used to introduce an activated or activatable N- or C-terminus. Alternatively additions may be made by fragment condensation or native chemical ligation e.g. as described in (Dawson et al. 1994. Synthesis of Proteins by Native Chemical Ligation. Science 266:776-779), or by enzymes, for example using subtiligase as described in (Chang et al. Proc Natl Acad Sci U S A. 1994 Dec 20; 91 (26): 12544-8 or in Hikari et al. Bioorganic & Medicinal Chemistry Letters Volume 18, Issue 22, 15 November 2008, Pages 6000-6003).

[0029] Alternatively, the peptides may be extended or modified by further conjugation through disulphide bonds. This has the additional advantage of allowing the first and second peptide to dissociate from each other once within the reducing environment of the cell. In this case, the molecular scaffold (e.g. TATA, TATB or TBMT) could be added during the chemical synthesis of the first peptide so as to react with the three cysteine groups; a further cysteine or thiol could then be appended to the N- or C-terminus of the first peptide, so that this cysteine or thiol only reacted with a free cysteine or thiol of the second peptide, forming a disulphide- linked bicyclic peptide-peptide conjugate.

[0030] Furthermore, addition of other functional groups or effector groups may be accomplished in the same manner, using appropriate chemistry, coupling at the N- or C-termini or via side chains. In one embodiment, the coupling is conducted in such a manner that it does not block the activity of either entity.

[0031] In some embodiments synthesis of a peptide ligand as provided herein may comprise solidphase synthesis of a polypeptide as described herein. In some embodiments the solid-phase synthesis comprises Fmoc solid-phase peptide synthesis (e.g. as described in more detail herein). In some embodiments the synthesized polypeptide is cyclised with a molecular scaffold as described herein. In some embodiments the cyclised scaffold is purified e.g. by lyophilisation. In some embodiments synthesis of a complex as described herein comprises reaction of a cyclised polypeptide as described herein with a linker. In some embodiments reaction of a cyclised polypeptide with a linker involves reaction of an azide group (e.g. on the linker) with an alkyne group (e.g. on the polypeptide). In some embodiments reaction of an azide group with an alkyne group takes place in the presence of a suitable azide-alkyne cycloaddition catalyst. In some embodiments a suitable catalyst comprises CuSC In some embodiments reaction of an azide group with an alkyne group takes place under an inert atmosphere (e.g. N2). In some embodiments reaction of a cyclised polypeptide with a linker involves reaction of an amine group (e.g. on the polypeptide) with a carboxylic acid group or activated derivative thereof (e.g. an NHS-ester group) (e.g. on the linker). In some embodiments reaction of an amine group and a carboxylic acid group or activated derivative thereof takes place in the presence of a suitable coupling agent. In some embodiments a suitable coupling agent comprises a base.

[0032] In some embodiments synthesizing BCY27047 comprises reacting BCY13118 as defined herein or a salt thereof with a N-(acid-PEG3)-N-bis(PEG3-azide) linker to yield a product. In some embodiments the product is BCY14964 as defined herein. In some embodiments the synthesis comprises reacting the product of the reaction of BCY13118 or a salt thereof with a N-(acid-PEG3)-N-bis(PEG3-azide) linker (e.g. BCY14964) with BCY 26631 thereby forming BCY27047.

[0033] In some embodiments synthesizing BCY26129 comprises reacting BCY13118 as defined herein or a salt thereof with a N-(acid-PEG3)-N-bis(PEG3-azide) linker to yield a product. In some embodiments the product is BCY14964 as defined herein. In some embodiments the synthesis comprises reacting the product of the reaction of BCY13118 or a salt thereof with a N-(acid-PEG3)-N-bis(PEG3-azide) linker (e.g. BCY14964) with BCY 24188 thereby forming BCY26129.

[0034] Pharmaceutical Compositions

[0035] According to a further aspect of the invention, there is provided a pharmaceutical composition comprising a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein in combination with one or more pharmaceutically acceptable excipients. In some embodiments provided herein is a pharmaceutical composition comprising BCY27047 and one or more pharmaceutically acceptable excipients. In some embodiments provided herein is a pharmaceutical composition comprising BCY26129 and one or more pharmaceutically acceptable excipients. In some embodiments provided herein is a pharmaceutical composition comprising BCY28671 or BCY28672 and one or more pharmaceutically acceptable excipients. Generally, the present peptide ligands will be utilised in purified form together with pharmacologically appropriate excipients or carriers. Typically, these excipients or carriers include aqueous or alcoholic / aqueous solutions, emulsions or suspensions, including saline and / or buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride and lactated Ringer's. Suitable physiologically- acceptable adjuvants, if necessary to keep a polypeptide complex in suspension, may be chosen from thickeners such as carboxymethylcellulose, polyvinylpyrrolidone, gelatin and alginates. Intravenous vehicles include fluid and nutrient replenishers and electrolyte replenishers, such as those based on Ringer's dextrose. Preservatives and other additives, such as antimicrobials, antioxidants, chelating agents and inert gases, may also be present (Mack (1982) Remington's Pharmaceutical Sciences, 16th Edition). The peptide ligands of the present invention may be used as separately administered compositions or in conjunction with other agents. These can include antibodies, antibody fragments and various immunotherapeutic drugs, such as cyclosporine, methotrexate, adriamycin or cisplatinum and immunotoxins. Further examples of other agents which may be administered separately or in conjunction with the peptide ligands of the invention include cytokines, lymphokines, other hematopoietic factors, thrombolytic and anti-thrombotic factors. Pharmaceutical compositions can include "cocktails" of various cytotoxic or other agents in conjunction with the protein ligands of the present invention, or even combinations of selected polypeptides according to the present invention having different specificities, such as polypeptides selected using different target ligands, whether or not they are pooled prior to administration. The route of administration of pharmaceutical compositions according to the invention may be any of those commonly known to those of ordinary skill in the art. For therapy, the peptide ligands of the invention can be administered to any patient in accordance with standard techniques. The administration can be by any appropriate mode, including parenterally, intravenously, intramuscularly, intraperitoneally, transdermally, via the pulmonary route, or also, appropriately, by direct infusion with a catheter. Preferably, the pharmaceutical compositions according to the invention will be administered intravenously. The dosage and frequency of administration will depend on the age, sex and condition of the patient, concurrent administration of other drugs, counterindications and other parameters to be taken into account by the clinician.

[0036] The peptide ligands of this invention can be lyophilised for storage and reconstituted in a suitable carrier prior to use. This technique has been shown to be effective and art-known lyophilisation and reconstitution techniques can be employed. It will be appreciated by those skilled in the art that lyophilisation and reconstitution can lead to varying degrees of activity loss and that levels may have to be adjusted upward to compensate.

[0037] The compositions containing the present peptide ligands or a cocktail thereof can be administered for prophylactic and / or therapeutic treatments. In certain therapeutic applications, an adequate amount to accomplish at least partial inhibition, suppression, modulation, killing, or some other measurable parameter, of a population of selected cells is defined as a "therapeutically-effective dose". Amounts needed to achieve this dosage will depend upon the severity of the disease, but generally range from 0.005 to 5.0 mg of selected peptide ligand per kilogram of body weight, with doses of 0.05 to 2.0 mg / kg / dose being more commonly used. For prophylactic applications, compositions containing the present peptide ligands or cocktails thereof may also be administered in similar or slightly lower dosages.

[0038] A composition containing a peptide ligand according to the present invention may be utilised in prophylactic and therapeutic settings to aid in the alteration, inactivation, killing or removal of a select target cell population in a mammal. In addition, the peptide ligands described herein may be used extracorporeally or in vitro selectively to kill, deplete or otherwise effectively remove a target cell population from a heterogeneous collection of cells. Blood from a mammal may be combined extracorporeally with the selected peptide ligands whereby the undesired cells are killed or otherwise removed from the blood for return to the mammal in accordance with standard techniques.

[0039] Therapeutic Uses

[0040] Polypeptide ligands and complexes comprising such selected according to the method of the present invention may be employed in in vivo therapeutic and prophylactic applications, in vitro and in vivo diagnostic applications, in vitro assay and reagent applications, and the like. Ligands having selected levels of specificity are useful in applications which involve testing in non-human animals, where cross-reactivity is desirable, or in diagnostic applications, where cross-reactivity with homologues or paralogues needs to be carefully controlled. In some applications, such as vaccine applications, the ability to elicit an immune response to predetermined ranges of antigens can be exploited to tailor a vaccine to specific diseases and pathogens.

[0041] Substantially pure peptide ligands of at least 90 to 95% homogeneity are preferred for administration to a mammal, and 98 to 99% or more homogeneity is most preferred for pharmaceutical uses, especially when the mammal is a human. Once purified, partially or to homogeneity as desired, the selected polypeptides may be used diagnostically or therapeutically (including extracorporeally) or in developing and performing assay procedures, immunofluorescent stainings and the like (Lefkovite and Pernis, (1979 and 1981 ) Immunological Methods, Volumes I and II, Academic Press, NY).

[0042] According to a further aspect of the invention, there is provided a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein, for use in preventing, suppressing or treating a disease or disorder mediated by NK cells.

[0043] According to a further aspect of the invention, there is provided a method of preventing, suppressing or treating a disease or disorder mediated by NK cells, which comprises administering to a patient in need thereof the peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein.

[0044] According to a further aspect of the invention, there is provided the use of a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein, in the manufacture of a medicament for preventing, suppressing or treating a disease or disorder mediated by NK cells.

[0045] In one embodiment, the disease or disorder mediated by NK cells is selected from inflammatory disorders, autoimmune disease and cancer. In a further embodiment, the disease or disorder mediated by NK cells is selected from: rheumatoid arthritis (RA), bone erosion, intraperitoneal abscesses, inflammatory bowel disease, allograft rejection, psoriasis, angiogenesis, atherosclerosis, asthma, multiple sclerosis, systemic lupus erythematosus (SLE), ocular surface disorders (such as dry eye), ankylosing spondylitis, psoriatic arthritis, cancer (such as multiple myeloma and breast cancer).

[0046] In a further embodiment, the disease or disorder mediated by NK cells is selected from cancer. According to a further aspect, there is provided a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein for use in preventing, suppressing or treating a disease or disorder selected from inflammatory disorders, autoimmune disease and cancer. According to a further aspect, there is provided a method of preventing, suppressing or treating a disease or disorder selected from inflammatory disorders, autoimmune disease and cancer, which comprises administering to a patient in need thereof the peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein. According to a further aspect, there is provided use of a peptide ligand, bicyclic peptide ligand, multimeric binding complex or heterotandem binding complex as defined herein in the manufacture of a medicament for preventing, suppressing or treating a disease or disorder selected from inflammatory disorders, autoimmune disease and cancer.

[0047] Examples of cancers (and their benign counterparts) which may be treated (or inhibited) include, but are not limited to tumours of epithelial origin (adenomas and carcinomas of various types including adenocarcinomas, squamous carcinomas, transitional cell carcinomas and other carcinomas) such as carcinomas of the bladder and urinary tract, breast, gastrointestinal tract (including the esophagus, stomach (gastric), small intestine, colon, rectum and anus), liver (hepatocellular carcinoma), gall bladder and biliary system, exocrine pancreas, kidney, lung (for example adenocarcinomas, small cell lung carcinomas, non-small cell lung carcinomas, bronchioalveolar carcinomas and mesotheliomas), head and neck (for example cancers of the tongue, buccal cavity, larynx, pharynx, nasopharynx, tonsil, salivary glands, nasal cavity and paranasal sinuses), ovary, fallopian tubes, peritoneum, vagina, vulva, penis, cervix, myometrium, endometrium, thyroid (for example thyroid follicular carcinoma), adrenal, prostate, skin and adnexae (for example melanoma, basal cell carcinoma, squamous cell carcinoma, keratoacanthoma, dysplastic naevus); haematological malignancies (i.e. leukemias, lymphomas) and premalignant haematological disorders and disorders of borderline malignancy including haematological malignancies and related conditions of lymphoid lineage (for example acute lymphocytic leukemia [ALL], chronic lymphocytic leukemia [CLL], B-cell lymphomas such as diffuse large B-cell lymphoma [DLBCL], follicular lymphoma, Burkitt’s lymphoma, mantle cell lymphoma, T-cell lymphomas and leukaemias, natural killer [NK] cell lymphomas, Hodgkin’s lymphomas, hairy cell leukaemia, monoclonal gammopathy of uncertain significance, plasmacytoma, multiple myeloma, and post-transplant lymphoproliferative disorders), and haematological malignancies and related conditions of myeloid lineage (for example acute myelogenousleukemia [AML], chronic myelogenousleukemia [CML], chronic myelomonocyticleukemia [CMML], hypereosinophilic syndrome, myeloproliferative disorders such as polycythaemia vera, essential thrombocythaemia and primary myelofibrosis, myeloproliferative syndrome, myelodysplastic syndrome, and promyelocyticleukemia); tumours of mesenchymal origin, for example sarcomas of soft tissue, bone or cartilage such as osteosarcomas, fibrosarcomas, chondrosarcomas, rhabdomyosarcomas, leiomyosarcomas, liposarcomas, angiosarcomas, Kaposi’s sarcoma, Ewing’s sarcoma, synovial sarcomas, epithelioid sarcomas, gastrointestinal stromal tumours, benign and malignant histiocytomas, and dermatofibrosarcomaprotuberans; tumours of the central or peripheral nervous system (for example astrocytomas, gliomas and glioblastomas, meningiomas, ependymomas, pineal tumours and schwannomas); endocrine tumours (for example pituitary tumours, adrenal tumours, islet cell tumours, parathyroid tumours, carcinoid tumours and medullary carcinoma of the thyroid); ocular and adnexal tumours (for example retinoblastoma); germ cell and trophoblastic tumours (for example teratomas, seminomas, dysgerminomas, hydatidiform moles and choriocarcinomas); and paediatric and embryonal tumours (for example medulloblastoma, neuroblastoma, Wilms tumour, and primitive neuroectodermal tumours); or syndromes, congenital or otherwise, which leave the patient susceptible to malignancy (for example Xeroderma Pigmentosum).

[0048] References herein to the term "prevention" involves administration of the protective composition prior to the induction of the disease. "Suppression" refers to administration of the composition after an inductive event, but prior to the clinical appearance of the disease. "Treatment" involves administration of the protective composition after disease symptoms become manifest.

[0049] Animal model systems which can be used to screen the effectiveness of the peptide ligands in protecting against or treating the disease are available. The use of animal model systems is facilitated by the present invention, which allows the development of polypeptide ligands which can cross react with human and animal targets, to allow the use of animal models.

[0050] The invention is further described below with reference to the following examples.

[0051] EXAMPLES

[0052] Materials and Methods

[0053] Preparation of Bicyclic Peptide Ligands (General Method)

[0054] Bicyclic peptides were synthesized on Rink amide resin using standard Fmoc (9- fluorenylmethyloxycarbonyl) solid-phase peptide synthesis, either by manual coupling (for large scale) or using a Biotage Syroll automated peptide synthesizer (for small scale). Following TFA-based cleavage from the resin, peptides were precipitated with diethyl ether and dissolved in 50:50 acetonitrile / water. The crude peptides (at ~1 mM concentration) were then cyclized with 1.3 equiv. of the scaffold, using ammonium bicarbonate (100 mM) as a base. Completion of cyclization was determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) or LC-MS. Once complete, the cyclization reaction was quenched using N-acetyl cysteine (10 equiv. with respect to the peptide), and the solutions were lyophilized. The residue was dissolved in an appropriate solvent and purified by RP-HPLC. Peptide fractions of sufficient purity and the correct molecular weight (verified by either MALDI- TOF and HPLC or LC-MS) were pooled and lyophilized. Concentrations were determined by UV absorption using the extinction coefficient at 280 nm, which was based on Trp / Tyr content.

[0055] All amino acids, unless noted otherwise, were used in the L-configurations. References herein to amino acids with a “d” prefix (i.e. dC or dA) refer to amino acids in the D-configurations.

[0056] EXAMPLES

[0057] Example 1: Preparation of Heterotandem Bicyclic Peptide Complex BCY27047

[0058] BCY14964

[0059] A mixture of BP-23825 (155.5 mg, 249.40 pmol, 1.2 eq), and HATU (95.0 mg, 249.92 pmol, 1.2 eq) was dissolved in NMP (1.0 mL), then the pH of this solution was adjusted to 8 by dropwise addition of DIEA (64.6 mg, 499.83 pmol, 87.0 pL, 2.4 eq), and then the solution was allowed to stir at 25 °C for 5 min. BCY13118 (500.0 mg, 207.83 pmol, 1.0 eq) was dissolved in NMP (5.0 mL), and then added to the reaction solution, the pH of the resulting solution was adjusted to 8 by dropwise addition of DIEA. The reaction mixture was stirred at 25 °C for 45 min. LC-MS showed BCY13118 was consumed completely and one main peak with desired m / z was detected. The reaction mixture was concentrated under reduced pressure to remove solvent and produced a residue. The residue was then purified by preparative-HPLC to give BCY14964 (1.35 g, 403.46 pmol, 64.7% yield, 90% purity) as a white solid. Calculated MW: 3011.53, observed m / z: 1506.8 ([M+2H]2+), 1005.0 ([M+3H]3+).

[0060] Procedure for preparation of BCY27047

[0061] To a solution of compound 1 (BCY14964, 41.2 mg, 13.2 pmol, 1.00 eq, TFA) and compound 2 (BCY26631 , 60.1 mg, 27.0 pmol, 2.05 eq, TFA) in DMF (0.50 mL) (predegassed and purged with N2 for 3 times) was added THPTA (11.4 mg, 26.4 pmol, 2.00 eq). Then CuSO4-5H2O (4.00 M, 6.60 pL, 2.00 eq) and VcNa (4.00 M, 19.8 pL, 6.00 eq) were added under N2. The reaction mixture was stirred at 20 °C for 0.5 hrs under N2 atmosphere. LC-MS showed compound 1 (BCY14964) was consumed completely, and one main peak with desired m / z (calculated MW: 7230.3, observed m / z 1447.1 ([M / 5+H]+)) was detected. The crude product was purified by prep-HPLC and BCY27047 (31.2 mg, 3.97 pmol, 30.1 % yield, 93.48% purity, TFA) was obtained as a white solid.

[0062] Example 2: Preparation of Heterotandem Bicyclic Peptide Complex BCY26129

[0063] Procedure for preparation of BCY26129

[0064] To a solution of compound 1 (BCY14964, 97.9% purity, 29.7 mg, 9.31 pmol, 1.00 eq, TFA, which may be prepared as described in Example 1 ) and compound 2 (BCY24188, 41.1 mg, 19.1 pmol, 2.05 eq) in DMF (0.30 mL) (pre-degassed and purged with N2 for 3 times) was added THPTA (8.09 mg, 18.6 pmol, 2.00 eq). Then CUSO4-5H2O (4.00 M, 4.66 pL, 2.00 eq) and VcNa (4.00 M, 13.9 pL, 6.00 eq) were added under N2. The reaction mixture was stirred at 20 °C for 0.5 h under N2 atmosphere. LC-MS showed compound 1 was consumed completely, and one main peak with the desired m / z (calculated MW: 7174.2, observed m / z: 1435.8 ([M / 5+H]+)) was detected. The crude product was purified by prep-HPLC and BCY26129 (31.6 mg, 4.17 umol, 44.8% yield, 96.21% purity, TFA) was obtained as a white solid. BIOLOGICAL DATA

[0065] 1. NKp46 SPR Assay

[0066] Peptides were tested against Fc-tagged human NKp46 (ACROBiosystems, cat no. NC1- H5257).

[0067] For analysis of peptide binding, a Biacore 8k+ instrument was used with a CM5 chip (Cytiva). All experiments were carried out at 25°C. Anti-human IgG (Fc) antibody (Cytiva) was immobilized on all flow cells by standard amine coupling chemistry. The running buffer was HBS-N (Cytiva, 10 mM HEPES, 0.15 M NaCI, pH 7.4) and the flow rate was 10 pL / min. The carboxymethyl dextran surface was activated with a 1 :1 ratio of 0.4 M 1 - ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) / 0.1 M N-hydroxy succinimide (NHS) (Cytiva) for 420s. Anti-human IgG (Fc) antibody was diluted to 12.5 pg / mL in 10 mM sodium acetate pH 5.0 and injected onto the chip surface for 360 s. Residual activated groups were blocked with a 420 s injection of 1 M ethanolamine (pH 8.5). The final surface density was 3000 - 5000 RU. Fc-tagged human NKp46 was diluted to 0.1 pM in HBS-N and was captured on flow cell 2 only of the sensor chip at a flow rate of 10 pL / min to 500 - 1000 RU. The buffer was then changed to PBS-P+

[0068] (Cytiva) supplemented with 2 % DMSO. Peptide dilutions were prepared in this buffer to give a final concentration of 2 % DMSO. The flow rate was 50 pL / min with 60 s association and 400 s dissociation. Data were corrected for DMSO volume exclusion effects. All data were double-referenced against blank injections and reference surface response using standard processing procedures. Data processing and kinetic fitting was performed using Biacore Insight Evaluation Software with Extended Screening and Characterization Extension (Cytiva). Data were fitted using steady state affinity 1 :1 binding model to determine KD. Data were fitted using kinetic 1 :1 binding model to determine kinetic constants where appropriate.

[0069] Selected peptides of the invention were tested in this assay and the results are shown in Table 1.

[0070] Table 1 : SPR Assay Data for Selected Bicyclic Peptides of the Invention 2. Binding to purified NK

[0071] The affinity of NKp46 dimeric bicyclic peptides conjugated to AF 647 (available from Lumiprobe) to NK cells negatively selected from healthy peripheral blood and cryopreserved or from fresh peripheral blood was evaluated using a flow cytometry assay.

[0072] On the day of the experiment, medium was prepared by supplementing RPMI-1640 (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1 % Penicillin Streptomycin (Corning™ 30-002-CI), herein referred to as working medium. Previously isolated human NK cells ((AllCells, LP-CR-CD56+-NS-10M), were quick thawed in a water bath and washed once at 500 rpm for 5 minutes in 10 mL of prewarmed working medium. Cellular pellet was then resuspended to concentration of 5x106cells / mL in working medium. Subsequently, 100 pL of cell suspension was plated in a 96-well V-bottom polypropylene plate (Greiner Bio-One 651201 ). Preparation of samples for flow cytometry: Fixable Viability Dye (eBioscience™ Cat# 65-0865-18) was prepared as a 1 :1000 dilution in PBS and 100 pL of viability dye was added to each well and incubated in the dark at 4°C for 30 minutes. Subsequently, wells were washed with 100 pL of PBS for 5 minutes at 500 rpm and supernatant was discarded. Next, Bicyclic peptides were diluted in working medium and added to the corresponding cell plate at a starting concentration of 50 nM titrated in a 1 :5 dilution series to perform a 8-point serial dilution. Plates were then incubated 1 hour at 37°C, 5% CO2. Postincubation, plate was centrifuged at 500 rpm for 5 minutes and supernatant discarded. Samples were then washed once in 200 pL of 1X phosphate buffer saline (PBS; Gibco™ 10-010-023) at 500 rpm for 5 minutes and supernatant was discarded.

[0073] Cells were resuspended in 200 pL of stain buffer and kept at 4°C in the dark until read by BD FACSSymphony™ flow cytometer.

[0074] Flow cytometry results were analyzed in FlowJo™ software with a gating strategy to evaluate the lymphocyte population then exclude debris, gate on single and live cells only, and determining the geometric mean of the AF 647 in the live NK population. The binding affinities were calculated using a four-parameter logistic regression using Prism GraphPad™ 8.0.2 software.

[0075] The data shown in Figure 1 illustrates dose-dependent binding of BCY28671 on NK cell surface. Data from a single representative NK donor (n=3). The data shown in Figure 2 illustrates dose-dependent binding of BCY28672 on NK cell surface. Data from a single representative NK donor (n=3).

[0076] The data shown in Table 2 demonstrates that AF 647-tagged NKp46 BCY28671 and BCY28672 elicits a dose-dependent binding to NK cells.

[0077] Table 2: Binding affinities (Kd,app) for the AF 647 NKp46 dimers binding to NK cells

[0078] 3. Binding to PBMC

[0079] The affinity of NKp46 dimeric bicyclic peptides conjugated to AF 647 to NK cells in primary healthy peripheral blood mononuclear cells (PBMCs) was evaluated using a flow cytometry assay.

[0080] On the day of the experiment, medium was prepared by supplementing RPMI-1640 (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1 % Penicillin Streptomycin (Corning™ 30-002-CI), herein referred to as working medium. Previously isolated human PBMCs from whole blood were quick thawed in a water bath and washed once at 500 rpm for 5 minutes in 10 mL of prewarmed working medium. Cellular pellet was then resuspended to concentration of 5x106cells / mL in working medium. Subsequently, 100 pL of cell suspension was plated in a 96-well V-bottom polypropylene plate (Greiner Bio-One 651201 ).

[0081] Preparation of samples for flow cytometry: Fixable Viability Dye (eBioscience™ Cat# 65- 0865-18) was prepared as a 1 :1000 dilution in PBS and 100 pL of viability dye was added to each well and incubated in the dark at 4°C for 30 minutes. Subsequently, wells were washed with 100 pL of PBS for 5 minutes at 500 rpm and supernatant was discarded. Next, human TruStain FcX™ block (BioLegend® 422302) was prepared by diluting 1.5 pL of FcX in 25 pL of stain buffer (1X PBS supplemented with 2% FBS). Fc block solution (25 pL / well) was incubated at room temperature (RT) for 10 minutes in the dark. Antibody master mix cocktail was prepared by diluting 1.5 pL the following antibodies per 100 pL of stain buffer: BUV737™ anti-human CD3 (BD biosciences® 612750; clone UCHT1 ), and BUV395 anti-human CD56 (BD biosciences® 612750;clone NCAM16.2). Cells were resuspended in master mix cocktail (100 pL) and incubated at 4°C for 30 minutes in the dark. Subsequently, cells were washed 3 times in 100 pL of stain buffer for 5 minutes at 500 rpm and supernatant was discarded.

[0082] Bicyclic peptides were diluted in working medium and added to the corresponding cell plate at a starting concentration of 50 nM titrated in a 1 :5 dilution series to perform a 8-point serial dilution. Plates were then incubated 1 hour at 37°C, 5% CO2. Post-incubation, plate was centrifuged at 500 rpm for 5 minutes and supernatant discarded. Samples were then washed once in 200 pL of 1X phosphate buffer saline (PBS; Gibco™ 10-010-023) at 500 rpm for 5 minutes and supernatant was discarded.

[0083] Cells were resuspended in 200 pL of stain buffer and kept at 4°C in the dark until read by BD FACSFortessa™ flow cytometer.

[0084] Flow cytometry results were analyzed in FlowJo™ software with a gating strategy to evaluate the lymphocyte population then exclude debris, gate on single and live cells only, and determining the geometric mean of the AF 647 in the CD3+ and CD3- / CD56+ populations. The binding affinities were calculated using a four-parameter logistic regression using Prism Graph Pad™ 8.0.2 software.

[0085] The data shown in Figure 3 illustrates dose-dependent binding of AF-647 labelled NKp46 bicyclic peptide dimer BCY28671 to CD56+ (NK cells) from human PBMCs. Data from a single representative PBMC donor (n=4). BCY18807 is a non-binding bicyclic peptide dimer, comprised of all D-amino acids.

[0086] The data shown in Figure 4 illustrates dose-dependent binding of AF-647 labelled NKp46 bicyclic peptide dimer BCY28672 to CD56+ (NK cells) from human PBMCs. Data from a single representative PBMC donor (n=4). BCY18807 is a non-binding bicyclic peptide dimer, comprised of all D-amino acids.

[0087] The data shown in Table 3 demonstrates that AF 647-tagged NKp46 BCY28671 and BCY28672 elicits a dose-dependent binding to NK cells only (CD56+ isolated). Comparatively, non-binding AF 647-tagged NKp46 BCY18807 elicits no binding in any PBMC population. Table 3: Binding affinities (Kd,app) for the AF 647 NKp46 dimers binding to subpopulations in PBMC cells

[0088] 4. NK Cytotoxicity Assay

[0089] Heterotandem bicyclic peptide complexes were evaluated for NK functional readouts (i.e. cytotoxicity) in NK-tumor cell line co-cultures.

[0090] NK cells were isolated using a negative isolation kit (STEMCELL™ Technologies 17955) from the total PBMC population purified from whole blood. Alternatively, CD56+ NK cells were also harvested from peripheral blood, negatively selected, and cryopreserved (AllCells, LP,CR,CD56+, NS, 10M, Custom). NK cells pellet was then resuspended in RPMI-1640 (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1 % Penicillin Streptomycin (Corning™ 30-002-CI) and 50 ILI / mL human IL-2 (Miltenyi Biotec® 130-097- 748), at a concentration of 4x105cells / mL. For the NK cell cytotoxicity assays, 50 pL (2x104) of cell suspension was plated in the 96-well plate (Grenier® Bio One ™ 655090) containing 50 pl (1x103) A431-luc cells (ATCC® CRL-1555-LUC2) or HT1080-luc cells (ATCC® CCL- 121-luc2) in DMEM (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1 % Penicillin Streptomycin (Corning™ 30-002-CI). Test articles were diluted in DMEM medium (Corning™ 10-013-CV) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35- 011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1 % Penicillin Streptomycin (Corning™ 30-002-CI)) and added to the corresponding cell plate (50 pl) at a suggested starting concentration of 30 or 10 nM titrated in a 1 :4 dilution series to perform an 10-point serial dilution. The plates were then incubated for 24 hours at 37°C, 5% CO2. Post-incubation, plates was centrifuged at 250 xg for 5 minutes and 100 pl supernatant discarded. Samples were then incubated 10 minutes with 50 pl Bright-Glo™ Luciferase Assay system (Promega™ E2620). Luminescence upon excitation at 570 nm was read using a CLARIOstar® plate-reader with MARS Data Analysis Software™. Data was fit to a four- parameter non-linear regression in GraphPad Prism™ 8.0.2 to generate an EC50 value.

[0091] Selected heterotandem bicyclic peptide complexes of the invention were tested in this assay and the results are shown in Figures 5-8.

[0092] Figure 5 illustrates that BCY27047 elicits a dose-dependent NK cell response to kill EphA2+ve A431-luc tumor cell line. No enhanced, dose-dependent effect in tumor cell killing is observed with non-binding heterotandem bicyclic peptide complex (BCY15666) in comparison to NK:A431-luc coculture without addition of a heterotandem bicyclic peptide complex. Average luminescence for No NK-TICA (referring to “No BCY”) is arbitrarily shown at 2.9 pM for reference. The EC50 =5.3 nM of BCY27047 was calculated using a four-parameter logistic regression using GraphPad Prism™ 8.0.2.

[0093] Figure 6 illustrates that BCY26129 elicits a dose-dependent NK cell response to kill EphA2+ve A431-luc tumor cell line. No enhanced, dose-dependent effect in tumor cell killing is observed with non-binding heterotandem bicyclic peptide complex (BCY15666) in comparison to NK:A431-luc coculture without addition of a heterotandem bicyclic peptide complex. Average luminescence for No NK-TICA (referring to “No BCY”) is arbitrarily shown at 2.9 pM for reference. The EC50 =7.6 nM of BCY26129 was calculated using a four-parameter logistic regression using GraphPad Prism™ 8.0.2.

[0094] Figure 7 illustrates that BCY27047 elicits a dose-dependent NK cell response to kill EphA2+ve HT1080-luc tumor cell line. No enhanced, dose-dependent effect in tumor cell killing is observed with non-binding heterotandem bicyclic peptide complex (BCY15667) in comparison to NK:HT1080-luc coculture without addition of a heterotandem bicyclic peptide complex. Average luminescence for No NK-TICA (referring to “No BCY”) is arbitrarily shown at 5e-16 M for reference. The EC50 = 2.1 pM of BCY27047 was calculated using a four-parameter logistic regression using GraphPad Prism™ 8.0.2.

[0095] Figure 8 illustrates that BCY26129 elicits a dose-dependent NK cell response to kill EphA2+ve HT1080-luc tumor cell line. No enhanced, dose-dependent effect in tumor cell killing is observed with non-binding heterotandem bicyclic peptide complex (BCY15667) in comparison to NK:HT1080-luc coculture without addition of a heterotandem bicyclic peptide complex. Average luminescence for No NK-TICA (referring to “0 BCY”) is arbitrarily shown at 5e-16 M for reference. The EC50 =22.9 pM of BCY26129 was calculated using a four-parameter logistic regression using GraphPad Prism™ 8.0.2. 5. Cytokine Secretion Assay

[0096] Heterotandem bicyclic peptide complexes were evaluated for NK functional readouts (i.e. cytokine secretion) in NK-tumor cell line co-cultures.

[0097] NK cells were isolated using a negative isolation kit (STEMCELL™ Technologies 17955) from the total PBMC population purified from whole blood. Alternatively, CD56+ NK cells were also obtained from peripheral blood, negatively selected, and cryopreserved (Allcells, LP,CR,CD56+, NS, 10M, Custom). NK cells pellet was then resuspended in RPMI-1640 (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1% Penicillin Streptomycin (Corning™ 30-002-CI) and 50 ILI / mL human IL-2 (Miltenyi Biotec® 130-097- 748), at a concentration of 4x105cells / mL. For the NK cell cytokine secretion assay, 2x105NK cell in 50 pl cell suspension were plated in the 96-well U-bottom plate (Grenier Bio One™ 650180) containing 50 pl (4x104) HT1080-luc cells (ATCC® CCL-121-luc2) in DMEM (Gibco™ 11875-093; with L-glutamine) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1% Penicillin Streptomycin (Corning™ 30-002-CI). Test articles were diluted in DMEM medium (Corning™ 10-013-CV) with 10% heat-inactivated fetal bovine serum (FBS; Corning® 35-011-CV), 10 mM HEPES (Gibco™ 15-630-080), and 1% Penicillin Streptomycin (Corning™ 30-002-CI) and added to the corresponding cell plate (50 pl) at a suggested starting concentration of 10 nM titrated in a 1 :5 dilution series to perform an 8-point serial dilution. The plates were then incubated for 4-6 hours at 37°C, 5% CO2. Post-incubation, plates was centrifuged at 250 xg for 5 minutes and 100 pl supernatant harvested. Samples were immediately stored at -70°C or assessed for cytokine levels. Interferon-gamma (IFNg) or TNF-alpha (TNFa) levels were measured in 25 pl of collected supernatants through the V-Plex Kits (2plex with IFNg and TNFa) Proinflammatory Panel (Mesoscale Diagnostics K151QOD, K151QWD). Data was gathered on MESO® QuickPlex SQ 120MM reader, with TeamLink™, ProductLink™, and InstrumentLink™ connectivity 1 .0.38 and was fit and analyzed to a four-parameter non-linear regression in GraphPad Prism™ 8.0.2 software to quantify to cytokine levels.

[0098] Selected heterotandem bicyclic peptide complexes of the invention were tested in this assay and the results are shown in Figures 9-12.

[0099] Figure 9 demonstrates that NK cells co-cultured with the HT1080-luc tumor cell line in the presence of BCY27047, or non-binding heterotandem bicyclic peptide complex BCY15667. Cytokine released (IFNY) was measured by V-Plex Kit (IFNg) Proinflammatory Panel (Mesoscale Diagnostics K151QOD). Data was gathered on MESO® QuickPlex SQ 120MM reader, with TeamLink™, ProductLink™, and InstrumentLink™ connectivity 1.0.38 and was fit and analyzed to a four-parameter non-linear regression in GraphPad Prism™ 8.0.2 software to quantify to cytokine levels. The EC50 = 8.4 pM of BCY27047.

[0100] Figure 10 demonstrates that NK cells co-cultured with the HT1080-luc tumor cell line in the presence of BCY26129, or non-binding heterotandem bicyclic peptide complex BCY15667. Cytokine released (IFNY) was measured by V-Plex Kit (IFNg) Proinflammatory Panel (Mesoscale Diagnostics K151QOD). Data was gathered on MESO® QuickPlex SQ 120MM reader, with TeamLink™, ProductLink™, and InstrumentLink™ connectivity 1.0.38 and was fit and analyzed to a four-parameter non-linear regression in GraphPad Prism™ 8.0.2 software to quantify to cytokine levels. The EC50 = 7.6 pM of BCY26129.

[0101] Figure 11 illustrates NK cells produce TNF-alpha when co-cultured with the HT1080-luc tumor cell line in presence of BCY27047, or non-binding heterotandem bicyclic peptide complex BCY15667. Cytokine released (TNF-alpha) was measured by MSD Assay: V-Plex Kit (TNFa) Proinflammatory Panel (Mesoscale Diagnostics K151 QWD). Data was gathered on MESO® QuickPlex SQ 120MM reader, with TeamLink™, ProductLink™, and InstrumentLink™ connectivity 1.0.38 and was fit and analyzed to a four-parameter non-linear regression in GraphPad Prism™ 8.0.2 software to quantify to cytokine levels. The EC50 = 8.8 pM of BCY27047.

[0102] Figure 12 illustrates NK cells produce TNF-alpha when co-cultured with the HT1080-luc tumor cell line in presence of BCY26129, or non-binding heterotandem bicyclic peptide complex BCY15667. Cytokine released (TNF-alpha) was measured by MSD Assay: V-Plex Kit (TNFa) Proinflammatory Panel (Mesoscale Diagnostics K151QWD). Data was gathered on MESO® QuickPlex SQ 120MM reader, with TeamLink™, ProductLink™, and InstrumentLink™ connectivity 1.0.38 and was fit and analyzed to a four-parameter non-linear regression in GraphPad Prism™ 8.0.2 software to quantify to cytokine levels. The EC50 = 9.5 pM of BCY26129.

[0103] LIST OF REFERENCES

[0104] Muta T et al, Nature. 1994 Mar 3;368(6466):70-3. doi: 10.1038 / 368070a0. Erratum in: Nature. 1994 May 26;369(6478):340. PMID: 8107887.

[0105] Ravetch JV, Bolland S. IgG Fc receptors. Annu Rev Immunol. 2001 ;19:275-90. doi: 10.1146 / annurev.immunol.19.1.275. PMID: 11244038. Arnould L et al, Br J Cancer. 2006 Jan 30;94(2):259-67. doi: 10.1038 / sj.bjc.6602930. PMID: 16404427; PMCID: PMC2361112.

[0106] Zhang W et al, J Clin Oncol. 2007 Aug 20;25(24):3712-8. doi: 10.1200 / JC0.2006.08.8021.

[0107] PMID: 17704420.,

[0108] Zhang X et al, Mol Immunol. 2020 Mar; 119:48-58. doi: 10.1016 / j.molimm.2020.01.009. Epub 2020 Jan 21. PMID: 31978707.,

[0109] Wu SY et al, Mol Cancer. 2020 Aug 6;19(1):120. doi: 10.1186 / s12943-020-01238-x. PMID: 32762681 ; PMCID: PMC7409673.

[0110] Manches O et al, Blood. 2003 Feb 1;101(3):949-54. doi: 10.1182 / blood-2002-02-

[0111] 0469. Epub 2002 Oct 3. PMID: 12393572.

[0112] Clynes RA et al, Nat Med. 2000 Apr;6(4):443-6. doi: 10.1038 / 74704. PMID: 10742152.

[0113] Riddle DS et al, Hum Gene Ther. 2005 Jul;16(7):830-44. doi: 10.1089 / hum.2005.16.830.

[0114] PMID: 16000065.

[0115] Rataj F et al, Br J Cancer. 2019 Jan;120(1):79-87. doi: 10.1038 / s41416-018-0341-

[0116] 1. Epub 2018 Nov 15. PMID: 30429531 ; PMCID: PMC6325122.

[0117] Caratelli S et al, Front Immunol. 2017 Apr 27;8:457. doi: 10.3389 / fimmu.2017.00457. PMID: 28496440; PMCID: PMC5406408.

[0118] Salmon JE et al, Arthritis Rheum. 2001 Apr;44(4):739-50. doi: 10.1002 / 1529- 0131 (200104)44:4<739::AID-ANR129>3.0.CO;2-0. PMID: 11315912.

[0119] Morgan AW et al, Rheumatology (Oxford). 2003 Apr;42(4):528-33. doi: 10.1093 / rheumatology / keg169. PMID: 12649399.

[0120] Wu J et al, J Clin Invest. 1997 Sep 1 ;100(5):1059-70. doi: 10.1172 / JCI119616. PMID: 9276722; PMCID: PMC508280.

[0121] Nabbe KC et al, Arthritis Rheum. 2003 Jan;48(1):255-65. doi: 10.1002 / art.10721 . PMID: 12528127.

[0122] Kleinau S et al, J Exp Med. 2000 May 1 ;191(9):1611-6. doi: 10.1084 / jem.191.9.1611. PMID: 10790435; PMCID: PMC2213438.

[0123] Bolland S et al, Immunity. 2000 Aug;13(2):277-85. doi: 10.1016 / s1074-7613(00)00027-3.

[0124] PMID: 10981970.

[0125] Salmon JE et al, Arthritis Rheum. 2001 Apr;44(4):739-50. doi: 10.1002 / 1529-

[0126] 0131 (200104)44:4<739::AID-ANR129>3.0.CO;2-0. PMID: 11315912.

[0127] Boruchov AM et al, J Clin Invest. 2005 Oct; 115(10):2914-23. doi:

[0128] 10.1172 / JCI24772. Epub 2005 Sep 15. PMID: 16167082; PMCID: PMC1201664.

[0129] Chen JY et al, Arthritis Rheumatol. 2014 Nov;66(11 ):3113-21 . doi: 10.1002 / art.38813. PMID: 25154742; PMCID: PMC4232894.

[0130] Henriques A et a / , Rheumatol Int. 2012 Apr;32(4):863-9. doi: 10.1007 / s00296-010-1709-

[0131] 6. Epub 2011 Jan 8. PMID: 21221593. Chen JY et al, Arthritis Rheumatol. 2014 Nov;66(11 ):3113-21 . doi: 10.1002 / art.38813. PMID: 25154742; PMCID: PMC4232894.

[0132] Clarkson SB et al, N Engl J Med. 1986 May 8;314(19):1236-9. doi: 10.1056 / NEJM198605083141907. PMID: 2939345.

[0133] Flaherty MM et al, Toxicol Sci. 2012 Jan;125(1 ):299-309. doi: 10.1093 / toxsci / kfr278. Epub 2011 Oct 24. PMID: 22025730.

[0134] Anthony RM et al, Science. 2008 Apr 18;320(5874):373-6. doi: 10.1126 / science.1154315.

[0135] PMID: 18420934; PMCID: PMC2409116.

[0136] Debre M et al, Lancet. 1993 Oct 16;342(8877):945-9. doi: 10.1016 / 0140-6736(93)92000-j.

[0137] PMID: 8105212.,

[0138] Hsu CH et al, Pediatr Infect Dis J. 1993 Jun;12(6):509-12. doi: 10.1097 / 00006454- 199306000-00010. PMID: 8345983.

[0139] Ortiz DF et al, Sci Transl Med. 2016 Nov 16;8(365):365ra158. doi: 10.1126 / scitranslmed.aaf9418. PMID: 27856797.

[0140] Li X et al, Expert Opin Ther Targets. 2014 Mar;18(3):335-50. doi:

[0141] 10.1517 / 14728222.2014.877891. PMID: 24521454; PMCID: PMC4019044.

[0142] Pasero C et al, Oncotarget. 2015 Jun 10;6(16):14360-73. doi: 10.18632 / oncotarget.3965.

[0143] PMID: 25961317; PMCID: PMC4546472.

[0144] Stringaris K et al, Haematologica. 2014 May;99(5):836-47. doi:

[0145] 10.3324 / haematol.2013.087536. Epub 2014 Jan 31. PMID: 24488563; PMCID: PMC4008119.

[0146] Chinnery F et al, Oncoimmunology. 2012 Sep 1 ;1(6):874-883. doi: 10.4161 / onci.20636.

[0147] PMID: 23162755; PMCID: PMC3489743.

[0148] Arnon Tl et al, Blood. 2004 Jan 15;103(2):664-72. doi: 10.1182 / blood-2003-05-

[0149] 1716. Epub 2003 Sep 22. PMID: 14504081.

[0150] Moretta L et al, Semin Immunol. 2006 Jun;18(3):151-8. doi:

[0151] 10.1016 / j.smim.2006.03.002. Epub 2006 May 26. PMID: 16730454.

[0152] Costello RT et al, Blood. 2002 May 15;99(10):3661-7. doi: 10.1182 / blood.v99.10.3661.

[0153] PMID: 11986221.

[0154] Garcia-Iglesias T et al, BMC Cancer. 2009 Jun 16;9:186. doi: 10.1186 / 1471-2407-9-186.

[0155] PMID: 19531227; PMCID: PMC2704222.

[0156] Nayyar G et al, Front Oncol. 2019 Feb 11;9:51. doi: 10.3389 / fonc.2019.00051 . PMID: 30805309; PMCID: PMC6378304.

[0157] Stojanovic A et a / , J Innate Immun. 2011 ;3(4):355-64. doi: 10.1159 / 000325465. Epub 2011

[0158] Apr 18. PMID: 21502747.

[0159] Sordo-Bahamonde C et al, Cancers (Basel). 2020 Apr 7;12(4):893. doi: 10.3390 / cancers12040893. PMID: 32272610; PMCID: PMC7226138. Watanabe M et al, Dis Esophagus. 2010 Nov;23(8):675-81. doi: 10.1111 / j.1442- 2050.2010.01073.x. PMID: 20545975.

[0160] Izawa S et al, Cancer Immunol Immunother. 2011 Dec;60(12):1801-10. doi: 10.1007 / S00262-011-1082-7. Epub 2011 Aug 3. PMID: 21811786.

[0161] Koo KC et al, PLoS One. 2013 Nov 4;8(11):e78049. doi: 10.1371 / journal.pone.0078049.

[0162] PMID: 24223759; PMCID: PMC3817174.

[0163] Sun C et al, Cell Mol Immunol. 2015 May;12(3):292-302. doi: 10.1038 / cmi.2014.91. Epub 2014 Oct 13. PMID: 25308752; PMCID: PMC4654321.

[0164] Hasmim M et al, Front Immunol. 2015 Sep 23;6:482. doi: 10.3389 / fimmu.2015.00482. PMID: 26441986; PMCID: PMC4585210.

[0165] Han B et a / , J Immunol Res. 2018 Sep 3;2018:6248590. doi: 10.1155 / 2018 / 6248590. PMID: 30255106; PMCID: PMC6140275.

[0166] Stringaris K et al, Haematologica. 2014 May;99(5):836-47. doi:

[0167] 10.3324 / haematol.2013.087536. Epub 2014 Jan 31. PMID: 24488563; PMCID: PMC4008119.

[0168] Rocca YS et al, Front Immunol. 2016 Oct 10;7:413. doi: 10.3389 / fimmu.2016.00413. PMID: 27777574; PMCID: PMC5056190.

[0169] Gauthier L et al, Cell. 2019 Jun 13; 177(7): 1701 -1713. e16. doi: 10.1016 / j.cell.2019.04.041. Epub 2019 May 30. PMID: 31155232.

[0170] Fauriat C et a / , Blood. 2007 Jan 1 ;109(1 ):323-30. doi: 10.1182 / blood-2005-08-

[0171] 027979. Epub 2006 Aug 29. PMID: 16940427.

[0172] Mamessier E et al, Cancer Res. 2011 Nov 1 ;71 (21 ):6621 -32. doi: 10.1158 / 0008-5472. CAN- 11-0792. Epub 2011 Sep 21. PMID: 21937679.

[0173] Platonova S et a / , Cancer Res. 2011 Aug 15;71(16):5412-22. doi: 10.1158 / 0008-5472. CAN- 10-4179. Epub 2011 Jun 27. PMID: 21708957.

[0174] Levi I et al, Oncotarget. 2015 May 30;6(15):13835-43. doi: 10.18632 / oncotarget.3453. PMID: 26079948; PMCID: PMC4537053.

[0175] Kim HS et al, Immunity. 2010 Feb 26;32(2):175-86. doi: 10.1016 / j.immuni.2010.02.004.

[0176] PMID: 20189481 ; PMCID: PMC2843589.

[0177] MacFarlane AW 4th et al, Oncoimmunology. 2017 May 19;6(7):e1330235. doi: 10.1080 / 2162402X.2017.1330235. PMID: 28811973; PMCID: PMC5543845.

[0178] Pasero C et al, Oncotarget. 2015 Jun 10;6(16):14360-73. doi: 10.18632 / oncotarget.3965.

[0179] PMID: 25961317; PMCID: PMC4546472.

[0180] Stringaris K et al, Haematologica. 2014 May;99(5):836-47. doi: 10.3324 / haematol.2013.087536. Epub 2014 Jan 31. PMID: 24488563; PMCID: PMC4008119. The following are numbered aspects of the invention:

[0181] 1. A peptide ligand specific for natural killer (NK) cells which comprises an amino acid sequence which is:

[0182] [dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1 ); wherein X represents dNva or dA, and wherein Cba represents cyclobutylalanine and Nva represents norvaline, or a pharmaceutically acceptable salt thereof.

[0183] 2. The peptide ligand according to aspect 1 , wherein X represents dNva and the peptide ligand comprises the sequence:

[0184] [dC]Y[Cba]PDYLC[dNva]DEYC (SEQ ID NO: 2); wherein Nva represents norvaline, or a pharmaceutically acceptable salt thereof.

[0185] 3. The peptide ligand according to aspect 1 , wherein X represents [dA] and the peptide ligand comprises the sequence:

[0186] [dC]Y[Cba]PDYLC[dA]DEYC (SEQ ID NO: 3); wherein Cba represents cyclobutylalanine, or a pharmaceutically acceptable salt thereof.

[0187] 4. The peptide ligand according to any of aspects 1 to 3, wherein the peptide ligand additionally comprises N- and / or C-terminal additions and comprises an amino acid sequence which is selected from:

[0188] Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4), and Ac-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

[0189] 5. The peptide ligand according to any of aspects 1 to 3, wherein the peptide ligand additionally comprises N- and / or C-terminal additions and comprises an amino acid sequence which is:

[0190] Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

[0191] 6. A bicyclic peptide ligand which comprises a peptide ligand according to any of aspects 1 to 5, and a molecular scaffold, wherein the three cysteine residues of said peptide ligand form covalent bonds with the molecular scaffold to form two loop sequences.

[0192] 7. The bicyclic peptide ligand according to aspect 6, wherein the molecular scaffold is a derivative of TATA which has the following structure: wherein * denotes the point of attachment of the three cysteine residues.

[0193] 8. The bicyclic peptide ligand according to aspect 6 or aspect 7, wherein the bicyclic peptide comprises a molecular scaffold which is a derivative of TATA which has the following structure: wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises an amino acid sequence which is selected from:

[0194] Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (the bicyclic peptide of which is herein referred to as BCY26631), and

[0195] Ac-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5) (the bicyclic peptide of which is herein referred to as BCY24188), wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof. 9. The bicyclic peptide ligand according to aspect 6 or aspect 7, wherein the bicyclic peptide comprises a molecular scaffold which is a derivative of TATA which has the following structure: wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises an amino acid sequence which is:

[0196] Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (the bicyclic peptide of which is herein referred to as BCY26631 ), and wherein Cba represents cyclobutylalanine, Nva represents norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

[0197] 10. The peptide ligand of any of aspects 1 to 5 or the bicyclic peptide ligand of any of aspects 6 to 9, wherein the pharmaceutically acceptable salt is selected from the free acid or the sodium, potassium, calcium or ammonium salt.

[0198] 11. A multimeric binding complex which comprises at least two bicyclic peptide ligands according to any of aspects 6 to 9, wherein said peptide ligands may be the same or different.

[0199] 12. A heterotandem bicyclic peptide complex comprising:

[0200] (a) a first bicyclic peptide ligand which binds to a component present on a cancer cell; conjugated via a linker to

[0201] (b) one or more second bicyclic peptide ligands specific for natural killer (NK) cells according to any of aspects 6 to 9.

[0202] 13. The heterotandem bicyclic peptide complex according to aspect 12, wherein the first bicyclic peptide ligand comprises an EphA2 binding bicyclic peptide ligand.

[0203] 14. The heterotandem bicyclic peptide complex according to aspect 13, wherein the EphA2 binding bicyclic peptide ligand comprises an amino acid sequence which is:

[0204] C[HyP]LVNPLCLEP[d1 Nal]WTC (SEQ ID NO: 6); wherein HyP represents trans-4-hydroxy-L-proline and 1 Nal represents 1 -naphthylalanine, or a pharmaceutically acceptable salt thereof.

[0205] 15. The heterotandem bicyclic peptide complex according to aspect 13 or aspect 14, wherein the molecular scaffold is a derivative of TATA which has the following structure: wherein * denotes the point of attachment of the three cysteine residues, and the EphA2 binding bicyclic peptide ligand optionally comprises N-terminal and / or C-terminal modifications and comprises:

[0206] A[HArg]DC[HyP]LVNPLCLEP[d1 Nal]WTC (SEQ ID NO: 7) (the bicyclic peptide of which is herein referred to as BCY13118), wherein HArg represents homoarginine, HyP represents trans-4-hydroxy-L-proline and 1 Nal represents 1 -naphthylalanine, or a pharmaceutically acceptable salt thereof.

[0207] 16. The heterotandem bicyclic peptide complex according to any of aspects 12 to 15, wherein the linker is:

[0208] (a) a linear linker selected from: azide-PEG24-acid; or

[0209] (b) a branched linker selected from:

[0210] Trimesic-[Pegio]3;

[0211] TCA-[Peg23]3;

[0212]

[0213] Methane-N-(PEG5-acid)-Tri(MeOPr-amide-PEG4-azide);

[0214]

[0215] Methane-N-(PEGio-acid)-T ri(MeOPr-amide-PEGw-azide); and

[0216] Bis-N-aminopropyl-glycine-(PEG5)2.

[0217] 17. The heterotandem bicyclic peptide complex according to any of aspects 12 to 16, wherein the linker is:

[0218] N-(acid-PEG3)-N-bis(PEG3-azide).

[0219] 18. The heterotandem bicyclic peptide complex according to any of aspects 12 to 17, which is selected from BCY27047:

[0220] or BCY26129:

[0221]

[0222] 19. A pharmaceutical composition which comprises the peptide ligand according to any of aspects 1 to 5, or the bicyclic peptide ligand according to any of aspects 6 to 10, or the multimeric binding complex according to aspect 11 , or the heterotandem bicyclic peptide complex according to any of aspects 12 to 18, in combination with one or more pharmaceutically acceptable excipients.

[0223] 20. The peptide ligand according to any of aspects 1 to 5, or the bicyclic peptide ligand according to any of aspects 6 to 10, or the multimeric binding complex according to aspect 11 , or the heterotandem bicyclic peptide complex according to any of aspects 12 to 18, or the pharmaceutical composition according to aspect 19, for use in preventing, suppressing or treating a disease or disorder mediated by natural killer (NK) cells. 21. The peptide ligand according to any of aspects 1 to 5, or the bicyclic peptide ligand according to any of aspects 6 to 10, or the multimeric binding complex according to aspect 11 , or the heterotandem bicyclic peptide complex according to any of aspects 12 to 18, or the pharmaceutical composition according to aspect 19, for use in preventing, suppressing or treating a disease or disorder selected from inflammatory disorders, autoimmune disease and cancer.

Claims

CLAIMS1. A peptide ligand, comprising a polypeptide having an amino acid sequence which is:[dC]Y[Cba]PDYLCXDEYC (SEQ ID NO: 1 ); wherein X represents dNva or dA, wherein dNva represents D-norvaline, dA represents D-alanine, dC represents D-cysteine, and Cba represents cyclobutylalanine; or a pharmaceutically acceptable salt thereof.

2. The peptide ligand according to claim 1 , wherein X represents dNva and the peptide ligand comprises a polypeptide of sequence:[dC]Y[Cba]PDYLC[dNva]DEYC (SEQ ID NO: 2); wherein dNva represents D-norvaline, dC represents D-cysteine, and Cba represents cyclobutylalanine, or a pharmaceutically acceptable salt thereof.

3. The peptide ligand according to claim 1 , wherein X represents [dA] and the peptide ligand comprises a polypeptide of sequence:[dC]Y[Cba]PDYLC[dA]DEYC (SEQ ID NO: 3); wherein dA represents D-alanine, dC represents D-cysteine, and Cba represents cyclobutylalanine, or a pharmaceutically acceptable salt thereof.

4. The peptide ligand according to any of claims 1 to 3, wherein the polypeptide comprises one or more N- and / or C-terminal additions.

5. The peptide ligand according to claim 4, comprising a polypeptide having an amino acid sequence which is selected from:Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4), andAc-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5), wherein dNva represents D-norvaline, dA represents D-alanine, dC represents D-cysteine, Cba represents cyclobutylalanine, and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

6. The peptide ligand according to any of claims 1 to 3, comprising a polypeptide of sequence which is:Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4),wherein dC represents D-cysteine, Cba represents cyclobutylalanine, dNva represents D- norvaline and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

7. The peptide ligand according to any one of claims 4 to 6, wherein the C-terminus is amidated.

8. A peptide ligand according to any of claims 1 to 7, wherein the polypeptide is attached to a molecular scaffold.

9. A bicyclic peptide ligand which comprises a peptide ligand according to any of claims 1 to 8, wherein the polypeptide is attached to a molecular scaffold, wherein the three cysteine residues of said peptide ligand form covalent bonds with the molecular scaffold to form two loop sequences.

10. The peptide ligand of claim 8 or the bicyclic peptide ligand according to claim 9, wherein the molecular scaffold is a derivative of TATA which has the following structure:wherein * denotes the point of attachment to the polypeptide; optionally the point of attachment of the three cysteine residues of the polypeptide.

11. The bicyclic peptide ligand according to claim 9 or claim 10, comprising a molecular scaffold which is a derivative of TATA which has the following structure:wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises a polypeptide having an amino acid sequence which is selected from:Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (wherein said bicyclic peptide is herein referred to as BCY26631), andAc-([dC]Y[Cba]PDYLC[dA]DEYC)-[K(PYA)] (SEQ ID NO: 5) (wherein said bicyclic peptide is herein referred to as BCY24188), wherein Cba represents cyclobutylalanine, dNva represents D-norvaline, dA represents D- alanine, dC represents D-cysteine, and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

12. The bicyclic peptide ligand according to any one of claims 9 to 11 , wherein the bicyclic peptide comprises a molecular scaffold which is a derivative of TATA which has the following structure:wherein * denotes the point of attachment of the three cysteine residues, and the peptide ligand comprises a polypeptide having an amino acid sequence which is:Ac-([dC]Y[Cba]PDYLC[dNva]DEYC)-[K(PYA)] (SEQ ID NO: 4) (wherein said bicyclic peptide is herein referred to as BCY26631), and wherein Cba represents cyclobutylalanine, dNva represents D-norvaline, dC represents D- cysteine and PYA represents pentynoic acid, or a pharmaceutically acceptable salt thereof.

13. The peptide ligand of any of claims 1 to 8 or 10 or the bicyclic peptide ligand of any of claims 9 to 12, wherein the pharmaceutically acceptable salt is selected from the free acid or the sodium, potassium, calcium or ammonium salt.

14. The peptide ligand of any of claims 1 to 8, 10 or 13 or the bicyclic peptide ligand of any of claims 9 to 13, which is specific for natural killer (NK) cells.

15. A multimeric binding complex comprising at least two bicyclic peptide ligands which may be the same or different, wherein at least one bicyclic peptide ligand is as defined in any one of claims 9 to 14; optionally wherein the multimeric binding complex comprises one or more cytotoxic agents, chelators, chromophores and / or fluorophores.

16. A multimeric binding complex according to claim 15, which comprises at least two bicyclic peptide ligands according to any of claims 9 to 14, wherein said peptide ligands may be the same or different; optionally wherein the multimeric binding complex comprises one or more cytotoxic agents, chelators, chromophores and / or fluorophores.

17. A heterotandem bicyclic peptide complex comprising:(a) a first bicyclic peptide ligand capable of binding to a component present on a cancer cell; attached to(b) one or more second bicyclic peptide ligands according to any of claims 9 to 14, wherein said one or more second bicyclic peptide ligands may be the same or different.

18. A heterotandem bicyclic peptide complex according to claim 17, comprising:(a) a first bicyclic peptide ligand which binds to a component present on a cancer cell; conjugated via a linker to(b) one or more second bicyclic peptide ligands according to any of claims 9 to 14.

19. The heterotandem bicyclic peptide complex according to claim 17 or 18, wherein the first bicyclic peptide ligand binds to EphA2, Nectin-4, PD-L1 , MT1 , or PSMA.

20. The heterotandem bicyclic peptide complex according to any one of claims 17 to 19, wherein the first bicyclic peptide ligand comprises an EphA2 binding bicyclic peptide ligand.21 . The heterotandem bicyclic peptide complex according to claim 20, wherein the EphA2 binding bicyclic peptide ligand comprises a polypeptide having an amino acid sequence which is:C[HyP]LVNPLCLEP[d1 Nal]WTC (SEQ ID NO: 6); wherein HyP represents trans-4-hydroxy-L-proline and d1 Nal represents D-1 -naphthylalanine, or a pharmaceutically acceptable salt thereof.

22. The heterotandem bicyclic peptide complex according to claim 21 , wherein the EphA2 binding bicyclic peptide ligand comprises one or more N-terminal and / or C-terminal modifications.

23. The heterotandem bicyclic peptide complex according to any one of claims 18 to 22, wherein the polypeptide of the first bicyclic peptide ligand is attached to a molecular scaffold.

24. The heterotandem bicyclic peptide complex according to claim 23, wherein the molecular scaffold is a derivative of TATA which has the following structure:wherein * denotes the point of attachment to the polypeptide; optionally the point of attachment of the three cysteine residues of the polypeptide.

25. The heterotandem bicyclic peptide complex according to any one of claims 17 to 24, wherein the first bicyclic peptide ligand comprises an EphA2 binding bicyclic peptide ligand comprising a molecular scaffold which is a derivative of TATA which has the following structure:wherein * denotes the point of attachment of the three cysteine residues, and the EphA2 binding bicyclic peptide ligand optionally comprises N-terminal and / or C-terminal modifications and comprises:A[HArg]DC[HyP]LVNPLCLEP[d1 Nal]WTC (SEQ ID NO: 7) (wherein said bicyclic peptide is herein referred to as BCY13118), wherein HArg represents homoarginine, HyP represents trans-4-hydroxy-L-proline and d1 Nal represents D-1 -naphthylalanine,or a pharmaceutically acceptable salt thereof.

26. The heterotandem bicyclic peptide complex according to any of claims 18 to 25, wherein the linker is a linear linker or a branched linker, optionally wherein said branched linker comprises three or four branches and is capable of binding to three of four bicyclic peptide ligands.

27. The heterotandem bicyclic peptide complex according to any of claims 18 to 26, wherein the linker comprises one or more PEG groups, optionally wherein the linker comprises one or more PEGngroups where each n is independently an integer from about 2 to about 25; optionally wherein the linker comprises one or more azide groups capable of reacting with one or more alkyne groups of the one or more peptide ligands; and / or one or more carboxylic acid groups or activated derivatives thereof capable of reacting with one or more amine groups of one or more peptide ligands.

28. The heterotandem bicyclic peptide complex according to any of claims 18 to 27, wherein the first bicyclic peptide ligand is conjugated to the one or more second bicyclic peptide ligands via a linker selected from(a) a linear linker selected from:azide-PEG24-acid; or(b) a branched linker selected from:Trimesic-[Peg-io]3;TCA-[Peg23]3;Methane-N-(PEG5-acid)-Tri(MeOPr-amide-PEG4-azide);Methane-N-(PEGio-acid)-T ri(MeOPr-amide-PEGw-azide); andBis-N-aminopropyl-glycine-(PEG5)2.

29. The heterotandem bicyclic peptide complex according to any of claims 18 to 28, wherein the linker is:N-(acid-PEG3)-N-bis(PEG3-azide).

30. A heterotandem bicyclic peptide complex, which is selected from BCY27047:or a pharmaceutically acceptable salt thereof; orBCY26129:or a pharmaceutically acceptable salt thereof.31 . A pharmaceutical composition which comprises the peptide ligand according to any of claims 1 to 8, or the bicyclic peptide ligand according to any of claims 9 to 14, or the multimeric binding complex according to claim 15, or the heterotandem bicyclic peptide complex according to any of claims 16 to 30, in combination with one or more pharmaceutically acceptable excipients.

32. The peptide ligand according to any of claims 1 to 8, or the bicyclic peptide ligand according to any of claims 9 to 14, or the multimeric binding complex according to claim 15, or the heterotandem bicyclic peptide complex according to any of claims 16 to 30, or the pharmaceutical composition according to claim 31 , for use in preventing, suppressing or treating a disease or disorder mediated by natural killer (NK) cells.

33. The peptide ligand according to any of claims 1 to 8, or the bicyclic peptide ligand according to any of claims 9 to 14, or the multimeric binding complex according to claim 15, or the heterotandem bicyclic peptide complex according to any of claims 16 to 30, or the pharmaceutical composition according to claim 31 , for use in preventing, suppressing or treating a disease or disorder selected from inflammatory disorders, autoimmune disease and cancer.

Images