Multivalent dendrimer conjugated protacs for cell-targeted targeted protein degradation

Abstract

Conjugates containing hydroxylated polyamidoamines (hydroxyl PAMAMs) or a dendrimer formed of a sugar such as a glucose dendrimer and (i) elements of PROTAC or (ii) PROTACs ,have been developed, which increase the efficacy of the PROTAC technology by increasing selective delivery to, and uptake at, sites of inflammation such as in the brain. The conjugates can be used for targeted intracellular delivery to degrade misfolded proteins and / or disease-associated proteins located in the cytosol, such that the conjugates can take advantage of a cell’s intracellular protein degradation machinery. 

Description

MULTIVALENT DENDRIMER CONJUGATED PROTACS FOR CELL-TARGETED TARGETED PROTEIN DEGRADATION FIELD OF THE INVENTIONThis invention is generally in the field of drug conjugates for targeted delivery, particularly dendrimers designed as PROteolysis TArgeting Chimeras (PROTACs) for intracellular delivery to exploit a cell’s protein degradation machinery.CROSS-REFERENCE TO RELATED APPLICATIONSThis application claims priority to U.S.S.N. 63 / 623,573 filed January 22, 2024, which is incorporated herein in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCHThis invention was made with government support under NS093416 and AG063831 awarded by the National Institutes of Health. The government has certain rights in the invention.BACKGROUND OF THE INVENTIONTargeted protein reduction is typically accomplished at the transcription level using nucleic acid-based techniques, including RNA interference (RNAi) and CRISPR / Cs9 mediated gene knockout technology. However, safer and more efficient intracellular delivery of nucleic acid-based molecules is challenging due to poor metabolic stability, off-target effects, and potential immunogenicity. Also, many disease-causing proteins lack specific targeting surfaces on the protein to inhibit protein functions via conventional small molecule inhibitors or antibodies. PROteolysis TArgeting Chimeras, or PROTACs, were discovered by Crews and coworkers in 2001 are emerging as a promising therapeutic strategy depending on targeted protein degradation (Pettersson et al., Drug Discov Today Technol. 2019 Apr;31:15-27. doi: 10.1016 / j.ddtec.2019.01.002.) PROTACs remove specific disease-associated proteins by exploiting the cells’ own destruction machinery, provided they can be stably brought into cells. PROTACs are hetero-bifunctional molecules containing at least two binding domains covalently connected via a spacer containing 5-15 atoms. PROTACs are designed to simultaneously bind one end, a proximity-induced modulator element, to a biomolecule, such as an E3 ubiquitin (E3) ligase (von Hippel-Lindau or cereblon), while the other end, a protein binding element, binds to the protein of interest (POI). Mechanistically, upon binding to POI, the PROTAC recruits the E3 ligase to the POI and causes proximity-induced ubiquitination of the target followed by its degradation by the ubiquitin-proteosome system (UPS). PROTACs undergoes a catalytic-type mechanism, in which the PROTAC is recycled to target another copy of the POI. Due to their catalytic nature, PROTACs are referred to as “programmable essential activators”. PROTACs can be programmed to target any POI. The presence of PROTAC is essential for ubiquitination transfer. The PROTAC activates the ternary complex formation in a catalytic fashion. Small molecule ligands for E3 ligase such as MDM2, CRBN and VHL are beneficial in expanding potential targets. PROTAC technologies have been widely applied in many different protein targets, including cytoplasmic, membrane bound nuclear and transmembrane proteins. However, only a limited number, about 50, of POI-PROTACs have been reported to date. These are primarily protein kinases such as BCR-ab1, BTK, c-Abl, ALK, CDK4 / CDK6, CDK8, CDK9, PI3K, ABL, FLT-3, AKT1-3, FAK, TBK1, SGK3, IRAK4, EGFR, PTK2, MEK1, MEK2, TrKC, JAK, PLK1, CK2, MCL1, BCL-2 / BCL-XL and Wee1, nuclear receptors such as AR, Era, cellular retinoic acid binding protein (CRABPs), transcriptional regulators such as BRD4, BET, HDAC6, BCL6, Prin, MDM2, STAT3, Smad3, Aiolos (IKZF3), Ikaros (IKZF1), IKZF, PRC2(EED, EZH2) and SUZ12, and regulatory proteins such as RIPK2, Sirtuin 2, PCAF / GCN5, FKBP12, PARP1 and TGF-β. Two compounds are currently in clinical trials for the treatment of prostate and breast cancer. Despite the recent efforts, PROTAC-based drug development is limited due to poor membrane permeability, unfavorable pharmacokinetics, inadequate delivery to the target site and target cells and low in vivo efficacy. Delivering PROTACs successfully into target cells, decreasing off-target side effects, and improving efficient degrader construction and linker design are major obstacles to the translation for PROTAC therapeutic application.In recent years, the field of bifunctional drugs has witnessed significant advancements, encompassing therapeutic modalities such as Proteolysis Targeting Chimeras (PROTACs), Lysosome Targeting Chimeras (LYTACs), molecular glues, and RNA Interference-Targeting Chimeras (RIPTACs), among others. These innovative drug classes leverage the power of bifunctionality to achieve their therapeutic effects, acting as connectors between distinct target molecules to facilitate their degradation, modulation, or relocalization within the cellular context. PROTACs, for instance, function by recruiting an E3 ubiquitin ligase to the target protein, leading to the ubiquitination and subsequent proteasomal degradation of the latter. See FIG. 6. Bifunctionals broadly consist of one “target”-binding molecule linked to one “effector”-binding molecule; in the PROTAC case, that would be an E3 ligase as the effector, and a small molecule binder of the target - such as EGFR - as the target-binder. These bifunctional drugs hold great promise in addressing previously undruggable targets and overcoming resistance mechanisms, thereby paving the way for new therapeutic opportunities.Despite the potential of bifunctional drugs in revolutionizing disease treatment, one of the critical challenges hindering their clinical translation is the efficient and targeted delivery of these large, often hydrophobic, and highly charged molecules into cells. Traditional drug delivery methods, such as oral or intravenous administration, may not be well-suited for these molecules due to their size, susceptibility to enzymatic degradation, and poor membrane permeability. Moreover, nonspecific uptake by healthy cells and rapid clearance from circulation can lead to suboptimal therapeutic concentrations at the target site and increased risk of off-target effects. To overcome these delivery challenges, researchers have explored various strategies, including the use of nanocarriers, cell-penetrating peptides, and bioconjugation approaches, to enhance cellular uptake, prolong circulation time, and minimize off-target effects. However, the development of robust, safe, and efficient delivery systems remains a significant hurdle in the clinical translation of bifunctional drugs, necessitating further research and optimization to unlock their full therapeutic potential. Currently, no nanoparticle-bifunctional drugs or controlled release / drug delivery systems for bifunctionals are in clinical development. The targeted delivery of PROTACs has been investigated using ligands such as antibody-PROTACs, Folate -PROTACs and aptamer-PROTAC conjugates. These modifications have shown improved cellular uptake in vitro as well as increased tumor accumulation and antitumor potency in vivo compared to conventional PROTACs. However, even these modifications do not completely address the low serum stability and precise delivery of PROTACs to specifically target tissues and efficient POI degradation. Improving linker design continues to be a significant challenge in degrader development. Converting a protein-targeting moiety such as a small molecule or antibody and a ubiquitin ligase recruiter into a single, functional degrader construct is challenging. This process requires the efficient formation of a ternary complex while maintaining strong binding affinity to both the protein target and the ubiquitin ligase.Therefore, it is an object of the present invention to provide a delivery platform for targeted delivery of degrader constructs such as PROTACs or combinations of protein binders and ubiquitin ligase recruiters while protecting these payloads from degradation.. SUMMARY OF THE INVENTIONConjugates containing dendrimers and (i) elements of PROTAC and / or (ii) PROTACs have been developed. These conjugates increase the efficacy of the PROTAC technology by increasing selective delivery to, and uptake at, sites of inflammation such as in the brain. The dendrimer can be selected to increase targeted delivery, such as using a sugar based dendrimer or a hydroxylated dendrimer to increase delivery into regions such as the brain. Preferred dendrimers are hydroxylated PAMAMs, such as generation 6 hydroxyl PAMAM and / or a sugar dendrimer, such as generation 2 glucose dendrimer, composed of 24 glucose molecules and containing 96 surface hydroxyl groups. The PROTACs include a proximity-induced modulator element(s) and protein binding element(s). The proximity-induced modulator element binds to an E3 ubiquitin (E3) ligase (von Hippel-Lindau or cereblon), while the protein binding element binds to a protein of interest that is to be degraded.In one embodiment, the conjugates include a dendrimer covalently conjugated to elements of PROTAC through linkers, preferably containing an ester bond, an ether bond, an amide bond, or a combination thereof. In these embodiments, each PROTAC element is independently covalently conjugated to the dendrimer, and the bonds between the dendrimer and the PROTAC elements are non-cleavable. The linkers may be cleavable or non-cleavable. The proximity-induced modulator elements and receptor binding elements are covalently conjugated to each other via a suitable spacer containing 5-15 carbon atoms or other atoms. The PROTACs are conjugated to these dendrimers via the suitable spacer.The conjugates can be used for targeted intracellular delivery to effect the degradation of misfolded proteins and / or disease-associated proteins, preferably proteins located in the cytosol, such that the conjugates can take advantage of a cell’s intracellular protein degradation machinery. The conjugates can be administered intravenously, orally, subcutaneously, intraperitonially, transdermally, intranasally, or a combination thereof, and can be administered once every day, once every other day, once a every week, or once every month, depending on dose and pharmacokinetics.The conjugates can penetrate the central nervous system, including through the blood-brain barrier, and can therefore be used to treat neurodegenerative disorders such as Alzheimer’s, Parkinson’s, Huntington’s disease, and amyotrophic lateral sclerosis (ALS). Further, the conjugates can be delivered to specific cells in the body, such as neurons, reactive immune cells, reactive microglia, macrophages, astrocytes, retinal ganglion cells, and retinal pigmental epithelial (RPE cells).BRIEF DESCRIPTION OF THE DRAWINGSFIGs. 1A–1Care a schematic representations of D-PROTAC mediated protein degradation in cytosol wheremultiple E3 ligase ligand / ligands, von Hippel-Lindau (VHL)-recruiter / Cereblon (CRBN), inhibitor of apoptosis protein (IAP), and mouse double minute 2 (MDM2) and multiple POI binding ligand / ligands were directly conjugated to the hydroxyl PAMAM dendrimer or glucose dendrimer using non cleavable linker chemistry.FIGs. 2A-2D are synthetic construct schemes: Scheme 1 (FIG. 2A); Scheme 2 (FIG. 2B); Scheme 3 (FIG. 2C); and Scheme 4 (FIG. 2D).FIG. 3 is a schematic of D-PROTAC mediated protein degradation, covalently conjugated single / multiple PROTAC units to hydroxyl PAMAM dendrimer / glucose dendrimer using i) non cleavable ii) cleavable linker chemistry.FIGs. 4A-4J: FK-HaloGFP plasmid cultivated bacterial colony after 12 hours incubation (FIG. 4A);Confocal images ofHEK-293 cellstransfected with HaloGFP after 24 h, 5X and 10X magnification (FIG. 4B);Percent GFP positive cells in FK-HaloGFP treated HEK293T cells compared to untreated HEK 293T cells using FACS study (FIG. 4C); Flow cytometry analysis of FK-HaloGFP treated HEK 293T cells compared to untreated HEK 293 T cells (FIG. 4D);Cell viability measured by CCK-8 assay after treatment with dendrimer conjugated PROTAC: D-HaloPROTAC, HaloPROTAC, D-entHaloPROTAC D-POI. Data are presented as mean±s.d. (n=3) (FIG. 4E);Average fluorescence per 1000 nM D-HaloPROTAC treated HaloGFP transfected HEK 293 cells compared to untreated control measured by fluorescence plate reader with time (FIG. 4F);Average fluorescence of different concentrations of D-HaloPROTAC treated HaloGFP transfected HEK 293 cells with the time compared to untreated control measure by fluorescence plate reader (FIG. 4G);confocal microscopy images show loss of fluorescence upon 24 h treatment with D-Haloprotac compared to control group (FIG. 4H); Average fluorescence per 100 nM D-HaloPROTAC treated HaloGFP transfected HEK 293 cells compared to untreated control measured by fluorescence plate reader with time (FIG. 4I);Flow cytometry analysis of HaloGFP expressing HEK 293 cells treated with D-POI, D-HaloPROTAC and HaloPROTAC (FIG. 4J).FIGs.5A and 5B are line graphs showing the free aflibercept vs D-aflibercept dose response curve for pro-inflammatory cytokines hVGFA (FIG. 5A) and hPIGF (FIG. 5B). kD values were calculated using the graph pad / Prism software.FIG. 6 is a schematic of D-aflibercept-PROTAC mediated protein degradation mechanism.FIG. 7 is a scheme for the synthesis of D-IDO1-PROTRAC 1FIGs.8A-8D show the synthesis and characterization of HD-COOH bifunctional dendrimer for PROTRAC conjugation.FIG. 9 are bar graphs showing the percent GFP positive cells in pcDNA3-IDO1-p2A-eGFP treated HEK293T cells compared to untreated HEK 293T cells using confocal and plate reader.Data are presented as mean±s.d. (n=3). FIGs. 10A and 10B are graphs showing IDO1 expression by varying concentrations of IFN-γ LPS and IFN: LPS combination. The concentrations of IFN-γ were quantified using Human IDO1 ELISA using Manufacture’s protocol.FIGs. 11Aand 11B are bar graphs showing degradation of IDO1 in vitro by novel PROTAC designs. The degradation of IDO1 was measured using sandwich ELISA, which detects IDO1 in both cell supernatants and cell lysates. Human microglial (HMC3) cells were stimulated using IFN (50 ng / mL) for 18 hours. After that, IFN γ was removed, the cells replenished with new media, and the cells treated them with D-IDO1-PROTAC (1 and 20 µg PROTAC basis considering 10 % loading of PROTAC to dendrimer) and small molecular PROTAC (20 µg / mL). The treatment was continued for 48 hours, and the IDO1 amounts in each condition were quantified using a Human ELISA kit. FIG. 11A shows quantification of cell supernatant IDO1. FIG. 11B shows quantification of cell lysate IDO1.DETAILED DESCRIPTION OF THE INVENTIONI.DEFINITIONSThe term "cleavable", such as used in the term "cleavable linker" or "cleavable bond" has its regular scientific meaning, and here refers to being subject to cleavage under acidic conditions, reductive conditions, enzymatic conditions or light-induced conditions. A cleavable linker may be subject to cleavage under acidic conditions, for example the cleavable linker is subject to cleavage in vivo under acidic conditions as present in endosomes and / or lysosomes of mammalian cells, preferably human cells, preferably at pH 4.0 - 6.5, and more preferably at pH ≤ 5.5. A cleavable linker may be subject to cleavage by an enzyme, e.g., by cathepsin. An example of a covalent bond cleavable under reductive conditions is a disulfide bond. As such, a “non-cleavable linker” or “non-cleavable bond” refers to bond or linker containing a bond that is not cleaved under these conditions.The term "therapeutic agent" refers to an agent that can be administered to treat one or more symptoms of a disease or disorder. The term “diagnostic agent” generally refers to an agent that can be administered to reveal, pinpoint, and define the localization of a pathological process. The diagnostic agents can label target cells that allow subsequent detection or imaging of these labeled target cells. The term “prophylactic agent” refers to an agent that reduces the likelihood of disease or defect occurring.The term "therapeutically effective amount" refers to an amount of the therapeutic agent that, when incorporated into and / or onto dendrimers, produces some desired effect at a reasonable benefit / risk ratio applicable to any medical treatment. The effective amount may vary depending on such factors as the disease or condition being treated, the particular targeted construct being administered, the size of the subject, or the severity of the disease or condition. One of ordinary skill in the art may empirically determine the effective amount of a particular compound without necessitating undue experimentation. In some embodiments, the term “effective amount” refers to an amount of a therapeutic agent or prophylactic agent to reduce or diminish the symptoms of one or more diseases. The terms “inhibit” or “reduce” in the context of inhibition, mean to reduce, or decrease in activity and quantity. This can be a complete inhibition or reduction in activity or quantity, or a partial inhibition or reduction. Inhibition or reduction can be compared to a control or to a standard level. Inhibition can be 5, 10, 25, 50, 75, 80, 85, 90, 95, 99, or 100%. For example, dendrimer compositions including one or more inhibitors may inhibit or reduce the activity and / or quantity of diseased neurons by about 10%, 20%, 30%, 40%, 50%, 75%, 85%, 90%, 95%, or 99% from the activity and / or quantity of the same cells in equivalent tissues of subjects that did not receive, or were not treated with, the dendrimer compositions. In some embodiments, the inhibition and reduction are compared at the level of mRNAs, proteins, cells, tissues, and / or organs. For example, an inhibition and reduction in the rate of neural loss, in the rate of decrease of brain weight, or in the rate of decrease of hippocampal volume, as compared to an untreated control subject. The term “treating” or “preventing” mean to ameliorate, reduce or otherwise stop a disease, disorder or condition from occurring or progressing in an animal which may be predisposed to the disease, disorder and / or condition but has not yet been diagnosed as having it; inhibiting the disease, disorder or condition, e.g., impeding its progress; and relieving the disease, disorder, or condition, e.g., causing regression of the disease, disorder and / or condition. Treating the disease or condition includes ameliorating at least one symptom of the particular disease or condition, even if the underlying pathophysiology is not affected, such as treating the pain of a subject by administration of an analgesic agent even though such agent does not treat the cause of the pain. Desirable effects of treatment include decreasing the rate of disease progression, ameliorating, or palliating the disease state, and remission or improved prognosis. For example, an individual is successfully “treated” if one or more symptoms associated with cancer are mitigated or eliminated, including, but are not limited to, reducing and / or inhibiting rate of tumor cell proliferation / growth, increasing the quality of life of those suffering from the disease, decreasing the dose of other medications required to treat the disease, delaying the progression of the disease, and / or prolonging survival of individuals.The phrase "pharmaceutically acceptable" or “biocompatible” refers to compositions, excipients, and other materials and / or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other problem or complication, commensurate with a reasonable benefit / risk ratio. The phrase "pharmaceutically acceptable carrier" refers to pharmaceutically acceptable materials, compositions, or vehicles, such as a liquid or solid filler, diluent, solvent, or encapsulating material involved in carrying or transporting any subject composition, from one organ, or portion of the body, to another organ, or portion of the body. Each carrier must be "acceptable" in the sense of being compatible with the other ingredients of a subject composition and not injurious to the patient.The term "dendrimer" includes, but is not limited to, a molecular architecture with an interior core, interior layers, or "generations" of repeating units regularly attached to this initiator core, and an exterior surface of terminal groups attached to the outermost generation.The term “functionalize” means to modify a compound or molecule in a manner that results in the attachment of a functional group or moiety. For example, a molecule may be functionalized by the introduction of a molecule that makes the molecule a strong nucleophile or strong electrophile. The term "targeting moiety" refers to a moiety that localizes to or away from a specific location. The moiety may be, for example, a protein, nucleic acid, nucleic acid analog, carbohydrate, or small molecule. The location may be a tissue, a particular cell type, a subcellular compartment, or a molecule such as a receptor. The term "prolonged residence time" refers to an increase in the time required for an agent to be cleared from a patient's body, or organ or tissue of that patient. In certain embodiments, "prolonged residence time" refers to an agent that is cleared with a half-life that is 10%, 20%, 50% or 75% longer than a standard of comparison such as a comparable agent without conjugation to a delivery vehicle such as a dendrimer. In certain embodiments, "prolonged residence time" refers to an agent that is cleared with a half-life of 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000, or 10000 times longer than a standard of comparison such as a comparable agent without a dendrimer that specifically target specific cell types.The terms "incorporated" and "encapsulated" refer to incorporating, formulating, or otherwise including an agent into and / or onto a composition that allows for release, such as sustained release, of such agent in the desired application. The agent or other material can be incorporated into a dendrimer, by binding to one or more surface functional groups of such dendrimer (by covalent, ionic, or other binding interaction), by physical admixture, by enveloping the agent within the dendritic structure, and / or by encapsulating the agent inside the dendritic structure.The term “central nervous system” (“CNS”) includes the brain and spinal cord. As used herein, peripheral nervous system (“PNS”) refers to the nerves other than in the brain and spinal cord.Dendrimers (e.g., glucose, or polyamidoamine (PAMAM)) are multifunctional nano constructs that can be further conjugated with functional ligands including therapeutic agents, pro-drugs, and imaging agents for many targeted drug delivery applications in the central nervous system (CNS) and retinal disorders. Systemically injected dendrimer delivers therapeutic across the blood-brain barrier (BBB) and preferentially localized in areas of inflammation and within tumor associated macrophages (TAMs) without any directing ligands. Additionally, the dendrimer-N-acetyl-cysteine conjugate has shown improvement in survival in severe COVID-19 patients, in randomized, placebo-controlled, double blinded phase II, stage I clinical trial suggesting the clinical promise and positive human safety of PAMAM hydroxyl dendrimer. Herein, the synthesis and characterization of new PROTAC designs composed of hydroxyl PAMAM dendrimer conjugated PROTACs was demonstrated. II.COMPOSITIONSProvided are dendrimer conjugates containing (i) one or more elements of a PROTAC and / or (ii) one or more PROTACs (referred to herein as “conjugates” or “dendrimer conjugates”). The dendrimer conjugates are suitable for targeted delivery of PROTACs to cells and protecting the PROTAC payload from degradation. For example, the dendrimer conjugates have properties which facilitate their delivery to the intracellular or extracellular space, where they can utilize the cell’s degradation mechanisms.A.Dendrimers 1 The scaffold of the conjugates is a dendrimer. Dendrimers are three-dimensional, hyperbranched, monodispersed, globular and polyvalent macromolecules including surface end groups (Tomalia, D. A., et al., Biochemical Society Transactions, 35, 61 (2007); and Sharma, A., et al., ACS Macro Letters, 3, 1079 (2014)). 2 The term “dendrimer” includes, but is not limited to, a molecular architecture with an interior core (“G0”) and layers (or "generations") of repeating units which are attached to and extend from this interior core, each layer having one or more branching points, and an exterior surface of terminal groups attached to the outermost generation. In some embodiments, dendrimers have regular dendrimeric molecular structures, in other cases they can be hyperbranched structures with irregular branch lengths.3 Generally, the dendrimers have a diameter between about 1 nm and about 60 nm, more preferably between about 1 nm and about 50 nm, between about 1 nm and about 40 nm, between about 1 nm and about 30 nm, between about 1 nm and about 20 nm, between about 1 nm and about 10 nm, or between about 1 nm and about 5 nm. 4 In some embodiments, the dendrimers have a diameter effective to penetrate blood brain barrier (“BBB”) and to be retained close to or internalized into target neural and / or glial cells for delivery of the agents conjugated thereto, such as for example, neurons, oligodendrocytes, astrocytes, microglial, and neuroglial support cells. Optionally, the diameter effective for crossing the BBB is less than 5 nm. 5 In some embodiments, the dendrimers have a diameter effective to penetrate a barrier interface, such as a blood nerve barrier (“BNB”), and to be internalized into neural and glial cells of the peripheral nervous system for delivery of the agents conjugated thereto such as for example, neurons, Schwann cells, satellite cells, and neuroglial support cells. 6 In some forms, the dendrimer has a diameter effective for staying in the peripheral circulation. Preferably, the diameter of the dendrimer for staying in peripheral circulation is more than 5 nm. In some embodiments, the dendrimers have a diameter effective to be retained in the peripheral circulation for delivery of the agents conjugated thereto to target cells of the peripheral nervous system. In some embodiments, the dendrimers have a molecular weight between about 500 Daltons and about 100,000 Daltons inclusive, between about 500 Daltons and about 50,000 Daltons inclusive, or between about 1,000 Daltons and about 20,000 Daltons inclusive. Dendrimer sizes <30,000 Da are preferred for transport across the BBB, and sizes of >50,000 Da are preferred for confinement to the periphery.Suitable dendrimer scaffolds for use in conjugates include a variety of types, such as poly(amidoamine) (PAMAM) or STARBURST™ dendrimers, polypropylamine (POPAM), polyethylenimine, polylysine, polyester, iptycene, aliphatic poly(ether), aromatic polyether dendrimers, and dendrimers derived from sugars like glucose, galactose, mannose, or fructose. Additionally, dendrimers can be copolymers, such as those formed by one or more sugars and an alkylene glycol (e.g., glucose and ethylene glycol building blocks). The dendrimers can have a plurality of surface functional groups, such as carboxylic, amine, hydroxyl, and acetamide groups. In some embodiments, dendrimers feature surface hydroxyl groups, and in preferred embodiments, these groups are modified with sugars (e.g., glucose, galactose, mannose, fructose) and / or polyalkylene glycols like polyethylene glycol, resulting in terminal sugar molecules and / or polyalkylene glycols.Dendrimers can belong to any generation, ranging from generation 1 to generation 10, although 4-6 are preferred. In some embodiments, PAMAM dendrimers are used and can be further modified to include surface hydroxyl groups. A preferred dendrimer is a generation 2, 3, or higher glucose-based dendrimer. In some embodiments, the dendrimers are made entirely of glucose building blocks. In other embodiments, the dendrimers are PAMAM dendrimers modified by sugar moieties or hydroxyl groups. The dendrimers are suitable for the synthesis of dendrimer-PROTAC conjugates or for bonding to elements of a PROTAC, such as proximity-induced modulator elements or receptor-binding elements. In preferred embodiments, the dendrimer used as the scaffold in the dendrimer-PROTAC conjugate is a hydroxyl PAMAM or glucose dendrimer. In some embodiments, the total number of hydroxyl groups available for conjugation to a PROTAC or one or more of its element’s ranges from about 100 to about 300 (e.g., 256 for hydroxyl PAMAM) or between about 50 and about 120 (e.g., 96 for a generation 2 glucose dendrimer).1.Core In some embodiments, dendrimers are prepared using methods in which the dendrimer is assembled from a multifunctional core, which is extended outward by a series of reactions. A multifunctional core moiety allows stepwise addition of branching units (i.e., generations) around the core. Exemplary chemical structures suitable for use as core moieties are shown in Table 1 below. Additional examples of structures suitable for use as core moieties include monosaccharide, disaccharides, trisaccharides, oligosaccharides, or azide-, alkyne-modified moieties thereof. In some embodiments, the core moiety is chitosan. Thus, azide-modified chitosan, or alkyne-modified chitosan are suitable for conjugating to branching units using click chemistry. In some embodiments, the core moiety is ethylenediamine, or tetra(ethylene oxide). In some embodiments, the core moiety is dipentaerythritol. Table 1. Structural representation of various building blocks (cores, branching units, surface functional groups, monomers) for the synthesis of dendrimers.Building blocksStructureDipentaerythritolPentaerythritol2-(aminomethyl)-2-(hydroxymethyl)propane-1,3-diol 2-ethyl-2-(hydroxymethyl)propane-1,3-diol3,3',3'',3'''-silanetetrayltetrakis(propane-1-thiol)3,3-divinylpenta-1,4-diene3,3',3''-nitrilotripropionic acid3,3',3''-nitrilotris(N-(2-aminoethyl)propanamide)3,3',3'',3'''-(ethane-1,2-diylbis(azanetriyl))tetrapropanamide3-(carboxymethyl)-3-hydroxypentanedioic acid2,2'-((2,2-bis((2-hydroxyethoxy)methyl)propane-1,3-diyl)bis(oxy))bis(ethan-1-ol)tetrakis(3-(trichlorosilyl)propyl)silane1-ThioglycerolAll the sugar based scaffoldsincluding mono, di, tri, or oligomers2,2,4,4,6,6-hexachloro-1,3,5,2l5,4l5,6l5-triazatriphosphinine3-(hydroxymethyl)-5,5-dimethylhexane-2,4-diol4,4',4''-(ethane-1,1,1-triyl)triphenol2,4,6-trichloro-1,3,5-triazine5-(hydroxymethyl)benzene-1,2,3-triol5-(hydroxymethyl)benzene-1,3-diol1,3,5-tris(dimethyl(vinyl)silyl)benzeneCarbosiloxane corenitrilotrimethanolethylene diaminepropane-1,3-diaminebutane-1,4-diamine2,2',2''-nitrilotris(ethan-1-ol)   benzene-1,2,3,4,5,6-hexathiolalpha cyclodextrinbeta cyclodextringamma cyclodextrinCucurbituril 2.Branching Units The dendrimers generally have one or more inner repeating branched arms or branching units, formed of amides, hydroxyl, and amine groups known as generations attached radially to the core. The chemical structures listed in Table 1, are also suitable as building blocks to form the branching units of the dendrimer. For example, the branching units of the dendrimers can be formed of dipentaerythritol, monosaccharide, disaccharides, trisaccharides, oligosaccharides, or azide- , alkyne-modified moieties thereof, or a combination thereof. Other examples of chemical structures that are suitable for forming the branching units of the dendrimers disclosed herein include, but are not limited to, sugar moieties, such as glucose, galactose, mannose, and fructose, and alkylene glycol, such as ethylene glycol, and combinations thereof. In some embodiments, the branching unit is chitosan. Thus, azide- modified chitosan, or alkyne-modified chitosan are suitable for conjugating to the core moiety or additional same or different branching units using click chemistry. In some embodiments, the branching unit is methyl acrylate or ethylenediamine, or a combination thereof. In some embodiments, the branching unit is polyethylene glycerol linear or branched. In some embodiments, the branching unit is a copolymer of an alkylene glycol (such as ethylene glycol) and a sugar moiety, such as glucose, galactose, mannose, and / or fructose.In some embodiments, the branching units are hyper-monomers i.e., ABn building blocks. Exemplary hyper-monomers include AB4, AB5, AB6, AB7, AB8 building blocks. Hyper-monomer strategy drastically increases the number of available end groups. 3.Surface Functional Groups The dendrimers typically have a plurality of surface functional groups or molecules. The terms “surface functional groups” and “terminal groups” are used interchangeably herein. Exemplary functional groups include primary amine end groups, hydroxyl end groups, carboxylic acid end groups, acetamide end groups, sugar molecules, oligo- or poly-alkylene glycols, and thiol end groups. In some embodiments, the desired terminal functional groups may be introduced through conjugation methods applied to the core and branching units.The surface functional groups in the dendrimers can include hydroxyl groups, such as those found in PAMAM dendrimers, generation 2 PEG dendrimers (e.g., see Structure I), or terminal glucose units in dendrimers with glucose-based branching units (e.g., see Structures III and IV). These functional groups may also be modified or added through various conjugation techniques. Alternatively, the dendrimers can be formed of glucose and oligoethylene glycol building blocks. Structures III and IV depict exemplary generation 1 and generation 2 glucose dendrimers, respectively. In these forms, the dendrimers can have one or more surface functional groups, e.g., hydroxyl (-OH), amine, acetamide, or carboxyl groups, located on the dendrimer periphery. The surface density of the peripheral functional groups is at least functional group per square nanometer (nm²). For example, the surface density of surface functional groups, e.g. hydroxyl groups, carbohydrate group, etc., may exceed 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 groups per nm². In some embodiments, the surface density of the surface functional groups e.g., hydroxyl groups may be in a range from between about 1 and about 50 or more groups per nm². For example, volumetric density values for surface functional groups, such as hydroxyl groups, can range from about 1 to about 10 groups per nm³, from about 4 to about 50 groups per nm³, from about 5 and about 30 groups per nm³, or from about 10 and about 20 groups per nm³, preferably, from about 5 to about 20 groups per nm², while having a molecular weight of between about 500 Da and about 10 kDa.In some embodiments, the quantity of surface functional groups, such as hydroxyl groups, is at least about 40%, about 50%, or more of the dendrimer. In some embodiments, the surface functional groups can be further modified by conjugating at least 40% of the dendrimer with carbohydrate molecules and / or polyalkylene glycols, such as polyethylene glycols. In these embodiments, the surface density of terminal carbohydrate moieties or polyalkylene glycols can have the same ranges as described above for hydroxyl groups. 7 The dendrimers include an effective number of terminal groups e.g., hydroxyl groups and / or amine groups for targeting specific tissues and / or cell types such as the CNS cells and PNS cells as generally described above. For example, the dendrimer can specifically target a particular tissue region and / or cell type without a targeting moiety and the active agent conjugated thereto bind directly to a receptor on the surface and / or interior of target neural and / or glial cells. For delivery to the brain, hydroxyl PAMAM dendrimers, PAMAM dendrimers with surface modifications incorporating sugar moieties (where over 10% of the surface groups are modified with sugars, preferably glucose), and glucose dendrimers made from glucose building blocks are preferred. Constructs with a total molecular weight of less than 30,000 Da are preferred for brain delivery, whereas constructs exceeding 50,000 Da are preferable for confinement to peripheral circulation.When dendrimers incorporate sugar moieties at their termini, such as glucose, the terminal hydroxyl groups may either be part of the sugar moieties, represent additional hydroxyl groups not included in the sugar moieties, or a combination of both. In some embodiments, all terminal hydroxyl groups are derived from the terminal sugar moieties.a.Hydroxyl-terminated Dendrimers 8 In some embodiments, dendrimers include a plurality of hydroxyl groups. Examples of dendrimers containing high-density hydroxyl groups include commercially available polyester dendritic polymers such as hyperbranched 2,2-Bis(hydroxyl-methyl)propionic acid polyester polymers such as hyperbranched bis-MPA polyester with 64 hydroxyl groups (generation 4) and dendritic polyglycerols.9 In some embodiments, dendrimers with high-density hydroxyl groups contain oligoethylene glycol (OEG). For example, a generation 2 OEG dendrimer (D2-OH-60) can be synthesized using highly efficient and robust chemical reactions like Cu(I)-catalyzed alkyne–azide click chemistry and photo-catalyzed thiol-ene click chemistry. These methods, employing orthogonal hypermonomer and hypercore strategies as described in for example WO 2019 / 094952, facilitate the creation of dense polyol dendrimers at low generation levels with minimal reaction steps. In some embodiments, the dendrimer backbone has non-cleavable polyether bonds, preventing in vivo disintegration and enabling elimination as single, non-biodegradable entities. 10 Structure I. A generation two (G2) oligo ethylene glycol-like dendrimerThe range for the surface density of hydroxyl (-OH) on the periphery of the dendrimer is generally described above. The amount of the surface hydroxyl groups on the periphery of the dendrimer is preferably greater than 35%, at least 40%, at least 50%, more than 40%, more than 50%, or in a range from more than 40% to 100%. In some embodiments, the dendrimers may have a fraction of the hydroxyl groups exposed on the outer surface, with the others in the interior core of the dendrimers. b.Dendrimers Modified with Carbohydrates In some embodiments, the dendrimers contain one or more carbohydrate molecules at the termination. These terminal carbohydrate molecules can be prepared by conjugating one or more surface functional groups of dendrimers, such as amine groups, carboxyl groups, or hydroxyl groups, with one or more carbohydrate molecules. In preferred embodiments, the dendrimers, prior to carbohydrate conjugation, are hydroxyl-terminated dendrimers such as hydroxyl-terminated PAMAM dendrimers and one or more of the hydroxyl groups are conjugated with one or more carbohydrate molecules. In some embodiments, the carbohydrate moieties used to modify one or more surface functional groups of the dendrimers are monosaccharides. Exemplary monosaccharides suitable for modifying the dendrimers include glucose, glucosamine, galactose, mannose, fructose, dehydroascorbic acid, urate, myo-inositol. In some embodiments, the dendrimers are conjugated to glucose and thus contain glucose as terminal moieties / molecules. In some embodiments, hydroxyl-terminated dendrimers are modified with one or more glucose moieties to the dendrimer (“D-Glu”). In some embodiments, the dendrimers are conjugated to one or more monosaccharides other than glucose, such as galactose, mannose, and / or fructose. For example, the carbohydrate moieties are oligosaccharides which terminate in one or more monosaccharides including glucose, glucosamine, mannose, fructose, thus, exposing these sugar moieties on the surface.In some embodiments, the dendrimers are conjugated to glucose and / or glucosamine moieties. For example, the dendrimer can be a glucose dendrimer. Glucose dendrimers or glucose-modified dendrimers are capable of achieving selective uptake by target cells. In some embodiments, the dendrimers are conjugated to one or more carbohydrate moieties that exhibit affinity for and suitability in binding specific transporters. These carbohydrate moieties, or sugar-based components, can facilitate transport via various glucose transporters, such as GLUT1, GLUT2, GLUT3, GLUT4, GLUT5, GLUT6, GLUT7, GLUT8, GLUT9, GLUT10, GLUT11, GLUT12, GLUT13, and GLUT14. Alternatively, the dendrimers are conjugated to one or more oligosaccharides terminating in glucose and / or glucosamine, i.e., glucose and / or glucosamine moieties are exposed on the surface of the dendrimer conjugates suitable for binding to one or more of the GLUTs. The range for the surface density of carbohydrate moieties / molecules such as monosaccharides, e.g., glucose, on the periphery of the dendrimers, is same as generally described above. In preferred embodiments, the surface density of carbohydrate molecules is between about 1 and about 50, between about 5 and about 20, per nm2, with each carbohydrate moiety having a molecular weight of between about 100 Da and about 1000 Da. In these embodiments, i.e., one or more surface functional groups of the dendrimer are modified to introduce one or more sugar moieties / molecules at termination, the terminal hydroxyl groups may be part of the terminal sugar moieties / molecules or extra hydroxyl groups that are not modified with sugar moieties / molecules and thus are not part of the sugar moieties / molecules, or a combination thereof.In some embodiments, carbohydrate molecules such as monosaccharides, e.g., glucose, are present in an amount by weight that is between about 1% and 40% of the total weight of the glycosylated dendrimer, for example, between about 2% and 20%, between about 5% and 15%, or between 9 % and 12 % of the total weight of the glycosylated dendrimer. For example, in some embodiments, the carbohydrate moieties are present in an amount that is about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the total weight of the glycosylated dendrimer following conjugation. In some embodiments, conjugation of carbohydrate molecules through one or more surface functional groups occurs via about 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, or 25% of the total available surface functional groups, preferably hydroxyl groups, of the dendrimers prior to the conjugation. In other embodiments, the conjugation of carbohydrate molecules occurs on less than 5%, less than 10%, less than 15%, less than 20%, less than 25%, less than 30%, less than 35%, less than 40% of total available surface functional groups of the dendrimers prior to the conjugation.c.Dendrimers Modified with Polyalkylene Glycol In some embodiments, the dendrimers contain one or more polyalkylene glycols at the termination. These terminal polyalkylene glycols can be prepared by conjugating one or more of surface functional groups of the dendrimers, such as hydroxyl groups, with a polyalkylene glycol, such as PEG. In some embodiments, the dendrimers, prior to conjugation, are hydroxyl-terminated dendrimers such as hydroxyl-terminated PAMAM dendrimers and at least a portion of the surface hydroxyl groups are conjugated with PEG. The range for the surface density of polyalkylene glycols, such as PEG, on the periphery of the dendrimers, is the same as generally described for surface groups above. In preferred embodiments, the surface density of polyalkylene glycols such as PEG is between about 1 and about 50, between about 5 and about 20, per nm2 (number of surface polyalkylene glycols / surface area in nm2) while having a molecular weight of between about 100 Da and about 10 kDa. In some embodiments, the polyalkylene glycol molecules such as PEG can be present in an amount by weight that is between about 1% and 40% of the total weight of the pegylated dendrimer, for example, between about 2% and 20%, between about 5% and 15%, or between 9 % and 12 % of the total weight of the pegylated dendrimer. For example, in some embodiments, the polyalkylene glycol molecules, such as PEG, are present in an amount that is about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the total weight of the pegylated dendrimer following conjugation. In some embodiments, conjugation of polyalkylene glycol molecules such as PEG through one or more surface functional groups of the dendrimer occurs via about 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, or 25% of the total available surface functional groups, preferably hydroxyl groups, of the dendrimers prior to the conjugation. In other embodiments, the conjugation of polyalkylene glycol molecules such as PEG occurs on less than 5%, less than 10%, less than 15%, less than 20%, less than 25%, less than 30%, less than 35%, less than 40% of total available surface functional groups of the dendrimers prior to the conjugation.4.Exemplary Dendrimers a. Monosaccharide-based DendrimersDendrimer compositions that can selectively accumulate inside neurons, particularly in the nucleus of injured and / or hyperactive neurons, referred to as “glucose dendrimers” have been developed. These dendrimers can also accumulate at a high level inside activated microglia. However, compared to hydroxyl dendrimers which primarily accumulate in microglia, these dendrimers primarily go to neurons. Glucose dendrimers are described in U.S.S.N. 63 / 327,610 “Dendrimer Compositions for Targeted Delivery of Therapeutics to Neurons” by The Johns Hopkins University, inventors Kannan Rangaramanujam, Rishi Sharma, Anjali Sharma, Sujatha Kannan, Nirnath Sah, Mira Sachdeva, and Siva P. Kambhampati filed April 5, 2022.Glucose dendrimers generally contain (a) a central core, (b) one or more branching units, wherein the branching units are monosaccharide glucose-based branching units, optionally with a linker conjugated thereto; and optionally (c) one or more therapeutic, prophylactic and / or diagnostic agents. In some embodiments, the monosaccharide dendrimers have a hypercore (e.g., dipentaerythritol) and one or more monosaccharide branching units. In some embodiments, the hypercore is dipentaerythritol and the monosaccharide branching unit is glucose-based branching unit. In further embodiments, spacer molecules can also be alkyl (CH2)n–hydrocarbon-like units. The monosaccharide branching units may be conjugated to the dendrimer core or to the prior generation of monomers via linkers, such as polyethylene glycol (PEG) chains. For example, glucose-based branching units can be used in some embodiments. In some embodiments, the branching units may include PEG and / or alkyl chain linkers between different dendrimer generations. For example, glucose layers may be connected via PEG linkers and triazole rings. In some embodiments, the branching units are the same for each generation of dendrimers generated from the core. Therefore, for example, the branching units can be glucose-based branching units for generating generation 1 dendrimers and generation 2 dendrimers. In a preferred embodiment, the branching units are β-D-Glucopyranoside tetraethylene glycol azide having the following structure, or peracetylated derivatives thereof.Structure II: β-D-Glucopyranoside tetraethylene glycol azideIn some embodiments, dendrimers are made of glucose and oligoethylene glycol building blocks. Exemplary glucose dendrimers are shown in Structures III and IV. Some exemplary glucose dendrimers include a generation 1 glucose dendrimer having 24 hydroxyl (-OH) end groups, a generation 2 glucose dendrimer having 96 hydroxyl (-OH) end groups, a generation 3 glucose dendrimer having 396 hydroxyl (-OH) end groups, and generation 4 glucose dendrimer having 1584 hydroxyl (-OH) end groups. For example, the glucose dendrimer is a generation 2 glucose-based dendrimer that has 24 glucose molecules at the periphery and 6 embedded glucose molecules in the backbone held together by PEG segments.In some embodiments, the glucose dendrimer is a generation 1, generation 2, generation 3, generation 4, generation 5, or generation 6 dendrimer. In one embodiment, the dendrimer is a generation 1 dendrimer having the following structure: Structure III: a generation 1 glucose dendrimer In a preferred embodiment, the dendrimer is a generation 2 dendrimer having the following structure: Structure IV: a generation 2 glucose dendrimer b.PAMAM DendrimersThe term “PAMAM dendrimer” refers to poly(amidoamine) dendrimer, which may contain different cores, with amidoamine building blocks, and can have carboxylic, amine, acetamide, and / or hydroxyl terminations of any generation including, but not limited to, generation 1 PAMAM dendrimers, generation 2 PAMAM dendrimers, generation 3 PAMAM dendrimers, generation 4 PAMAM dendrimers, generation 5 PAMAM dendrimers, generation 6 PAMAM dendrimers, generation 7 PAMAM dendrimers, generation 8 PAMAM dendrimers, generation 9 PAMAM dendrimers, or generation 10 PAMAM dendrimers. In some embodiment, the dendrimers are generation (“G”) 4, 5 or 6 dendrimers. In some embodiments, the PAMAM dendrimers have hydroxyl terminations.Generally, the complete architecture of dendrimers can be distinguished into the inner core moiety followed by radially attached branching units (i.e., generations) which are further decorated with chemical functional groups carrying desired terminal groups at the exterior surface of the dendrimers. In some embodiments, the dendrimers are in nanoparticle form and are described in detail in U.S. Published Application Nos. US 2011 / 0034422, US 2012 / 0003155, and US 2013 / 0136697. For example, the molecular weight of the dendrimers can be varied to prepare polymeric nanoparticles that form particles having properties, such as drug release rate, optimized for specific applications. In some embodiments, different variations of dendrimers may be used as a delivery vehicle to conjugate and deliver one or more active agents, including, but not limited to, dendrons and tectodendrimers. Dendrons are dendritic wedges that comprise one type of functionality at the core (functional groups, f=1) and another at the periphery (f=8, 16, 32, etc.). Tectodendrimers are generally composed of a central dendrimer with multiple dendrimers attached at its periphery. Preferred dendrimers are hydroxyl PAMAMs, for example, a generation 1-9 hydroxyl PAMAM (such as generation 6 hydroxyl PAMAM) and / or a glucose dendrimer, for example a generation 1-5 glucose dendrimer (such as generation 2 glucose dendrimer (GD2) composed of 24 glucose molecules and containing 96 surface hydroxyl groups).B.PROTACsThe disclosed dendrimer conjugates include a dendrimer conjugated with one or more molecules involved in the degradation of proteins, dysfunctional organelles, bacteria, and / or viruses in vitro and / or in vivo. For example, the disclosed dendrimer conjugates can include a dendrimer conjugated with one or more elements of PROTACs (e.g., ARV-110 for targeting androgen receptors, ACBI1 for targeting Tau protein, DT2216 for targeting BCL-XL proteins involved in apoptosis regulation), lysosome-targeting chimeras (LYTACs, such as cationic amphiphilic drugs for lysosomal degradation e.g., imipramine, amiodarone), RNase-targeting chimeras (RIBOTACs, e.g., ribonuclease inhibitors conjugated to small molecules for RNA cleavage), glycosyltransferase-targeting molecules (e.g., nanobody-OGT targeting O-linked N-acetylglucosamine transferase), autophagosome-targeting chimeras (AUTACs, such as small molecules with guanine derivatives for autophagy activation), phosphatase-targeting chimeras (PhosTACs, e.g., molecules targeting protein tyrosine phosphatases), acetyltransferase-targeting molecules (AceTAGs, such as bromodomain inhibitors conjugated to acetyl-CoA mimics), kinase-targeting molecules (phosphorylation-inducing chimeric small molecules, e.g., molecules targeting cyclin-dependent kinases), and molecular glues (e.g., thalidomide derivatives for E3 ubiquitin ligase modulation), other targeting moieties (such as an antibody, an RNA aptamer, a nanobody, a small molecule), and combinations thereof. PROTACs are bifunctional molecules that contain a protein binding element and a proximity-induced modulator element that binds to a molecule and alters the activity of the protein through proximity mediated effects, such as degradation and post-translational modifications. Typically, one or more molecules are recruited that bind to the protein or chemically modifies the protein, thereby altering the activity of the protein. In some embodiments, the bifunctional molecule contains a protein (e.g., protein receptor) binding element and a ubiquitination recognition element (that mediates its binding to another protein, such as E3 ubiquitin ligase). The protein binding element binds to a protein (e.g., receptor protein) and brings the protein (e.g., receptor protein) into close proximity of an E3 ubiquitin ligase through binding to the ubiquitination recognition element. The close proximity results in the ubiquitination of the protein (e.g., receptor protein) and subsequent degradation of the receptor protein by a proteasome. PROTACs are described in Smith, et al., Bioorg. Med. Chem. Lett. 2008, 18(2): 5904-5908; Buckley, et al., ACS Chem. Biol. 2015, 10(8): 1831-1837; Jarvis, Chemical and Engineering News, February 19, 2018, 96(8); Wang, et al., Acta Pharmaceutica Sinica B 2020, 10(2), 207-238; Takahashi, et al., Molecular Cell 2019, 76(5), 797-810; Banik, et al., ChemRxiv November 11, 2019; Lai and Crews, Nat. Rev. Drug Discov. 2017, 16(2), 101–114; and Ding, et al., Trends in Pharmacological Sciences 2020, 41(7), 464-474; Siriwardena, et al., J. Am. Chem. Soc., 2020, 142 (33), 14052-14057; Costales, et al., Proc. Natl. Acad. Sci. USA, 2020, 117(5), 2406-2411; Yamazoe, et al., J. Med. Chem., 2020, 63, 2807-2813; Petrilli, et al., Cell Chem. Biol., 2020, 27(1), 32-40e; the contents of which are herein incorporated by reference in their entirety.The elements of PROTACs include proximity-induced modulator element(s) and / or protein binding element(s). The proximity-induced modulator element binds to a biomolecule, such as an E3 ubiquitin (E3) ligase (von Hippel-Lindau or cereblon), while the protein binding element binds to a protein of interest. In some embodiments, multiple proximity-induced modulator elements as well as multiple protein binding elementscan be independently conjugated to a dendrimer (e.g., a chemical moiety on the surface of the dendrimer), covalently or non-covalently. The protein binding element can be a recruiting moiety or a targeting moiety. Examples of targeting moieties include antibodies, RNA aptamers, nanobody, small molecule (a non-polymeric molecule having a molecular weight less than 2,500 Da, or between 100 Da and 2,500 Da), etc.C.Linking of Dendrimer to PROTACsPreferably, the conjugation of these elements to a dendrimer (e.g., a chemical moiety on the surface of the dendrimer) occurs covalently. In some embodiments, a dendrimer is conjugated to an element of PROTAC via a suitable linker or directly to the PROTAC element. Preferably, the conjugation is formed via a suitable linker. The conjugation between multiple proximity-induced modulator elements as well as multiple protein binding elements to the surface of the dendrimer can be directly, non-covalently, or involve linkers. Preferably, the conjugation involves a linker, independently containing: an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof. Preferably, the linkers independently contain an ether bond, an amide bond, or a combination thereof. An exemplary linker can contain -C(O)NH(CH2)mC(O)-, -(OCH2CH2)n-, or both, where n is an integer between 1 and 4, inclusive, such as 1, 2, 3, or 4, and n is an integer between 1 and 6, such as 1, 2, 3, 4, 5 or 6. In some embodiments, an exemplary linker contains -C(O)NH(CH2)3C(O)- and -(OCH2CH2)n-, and n is an integer between 1 and 6, such as 1, 2, 3, 4, 5 or 6. In these forms, the linkers between the dendrimer and the proximity-induced modulator elements as well as multiple protein binding elements, are preferably non-cleavable.The conjugation between multiple proximity-induced modulator elements as well as multiple protein binding elements can involve linkers independently containing an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof. Preferably, the linkers independently contain an ester bond, an ether bond, an amide bond, or a combination thereof. An exemplary linker can contain -C(O)NH(CH2)mC(O)-, -(OCH2CH2)n-, or both, where n is an integer between 1 and 4, inclusive, such as 1, 2, 3, or 4, and n is an integer between 1 and 6, such as 1, 2, 3, 4, 5 or 6. In some embodiments, an exemplary linker contains -C(O)NH(CH2)3C(O)- and -(OCH2CH2)n-, and n is an integer between 1 and 6, such as 1, 2, 3, 4, 5 or 6. In these forms where the conjugates contain elements of PROTACs such as proximity-induced modulator element(s) and protein binding element(s) independently conjugated to a dendrimer, the linkers between the dendrimer surface and the proximity-induced modulator elements as well as multiple protein binding elements, are preferably non-cleavable.The PROTAC containing both the proximity-induced modulator element and the receptor binding element is conjugated to the dendrimer surface. The PROTAC is conjugated to a dendrimer (e.g., a chemical moiety on the surface of the dendrimer) via a suitable linker or directly to the dendrimer. Preferably, the conjugation is formed via a suitable linker. In some embodiments, the suitable linker is conjugated to the proximity-induced modulator element within the PROTAC or to the receptor binding element within the PROTAC. In other embodiments, the suitable linker is conjugated to a spacer between the proximity-induced modulator element and the receptor binding element of the PROTAC. The suitable linker bound to the PROTAC is independently conjugated to a dendrimer (e.g., a chemical moiety on the surface of a dendrimer), covalently or non-covalently. Preferably, the conjugation of the linker to the surface of the dendrimer occurs covalently.In some embodiments, the bond and / or suitable linker conjugating the PROTAC to a dendrimer (e.g., a chemical moiety on the surface of the dendrimer) is cleavable and / or contains a cleavable bond. The cleavable functional bond on the linker can independently involve chemically cleavable groups (e.g., solvolysis (such as hydrolysis), reduction, oxidation, etc.), enzymatically cleavable bonds, or a combination thereof. Some combinations can include glutathione / esterases. Leriche, et al., Bioorg. Med. Chem. 2012, 20, 571-582; Li and Chen, Nat. Chem. Bio. 2016, 12, 129-139; Wang, et al., ACS Cent. Sci. 2021, 7, 929-943; Schauenburg and Weil, Adv. Sci. 2023, 2303396 describe cleavable bonds in chemical biology.Non-limiting illustrations of a dendrimer independently functionalized with multiple proximity-induced modulator elements as well as multiple protein binding elementsis shown in FIG. 1A, 1B and 1C. For example, a proximity-induced element such as thalidomide based cereblon ligand and protein binding element such as 1-methyl-D-tryptophan were conjugated to a hydroxyl PAMAM dendrimer initially containing 256 surface hydroxyl groups. The subscripted numbers in the formulas indicate the number of attachments per dendrimer.In other embodiments, the bond and / or suitable linker conjugating the PROTAC to a dendrimer (e.g., a chemical moiety on the surface of the dendrimer) is non-cleavable. Examples of bonds that can be included can be selected from: an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof.PROTACs are hetero-bifunctional molecules containing a proximity-induced modulator element and a protein binding element covalently connected via a spacer (5-15 carbon or other atoms). The spacer may independently contain an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof. In these forms, the spacers between the proximity-induced modulator elements and the protein binding elements are preferably non-cleavable.D. Incorporation of Additional Agents into the PROTAC conjugated to dendrimerDendrimer-PROTAC conjugates can be formed from multiple PROTACs being covalently conjugated or non-covalently conjugated to a dendrimer. In preferred embodiments, the multiple PROTACs are covalently conjugated to the dendrimer. The dendrimer may be conjugated to the PROTAC through the proximity-induced modulator element, the protein binding element, or a spacer connecting the PROTAC elements. Optionally, the PROTAC is conjugated to the dendrimer directly or through a suitable linker. The linker can be either a single chemical entity or two or more chemical entities linked together. The linker can include any small chemical entity (molecule having a molecular weight of 1500 D or less, more preferably 1000 D or less), peptide, or polymer. The conjugation between the PROTAC and a dendrimer can be cleavable or non-cleavable.In some embodiments, one or more additional therapeutic agents, prophylactic agents, and / or diagnostic agents are encapsulated, associated, and / or conjugated in the dendrimer, at a concentration of between about 0.01% to about 30%, preferably about 1% to about 20%, more preferably about 5% to about 20% by weight. In some embodiments, the dendrimer is conjugated to a small molecule, an antibody or antigen-binding fragment thereof, a nucleic acid, or a polypeptide. In some embodiments, the therapeutic agents conjugated to the dendrimer are anti-inflammatory agents, antioxidant agents, or immune-modulating agents. In other embodiments, the dendrimers are conjugated to one or more diagnostic agents such as fluorescent dyes, near infra-red dyes, SPECT imaging agents, PET imaging agents, and radioisotopes.In some embodiments, the dendrimer and the therapeutic, prophylactic, or diagnostic agent(s) are conjugated via one or more linkers or coupling agents such as one or more hydrocarbon or oligoethylene glycol chains. Exemplary linkages are disulfide, ester, ether, thioester, and amide linkages.  E.Pharmaceutical FormulationsIn some forms, pharmaceutical compositions include a suitable diluent or carrier, such as a pharmaceutically or veterinary acceptable excipient or carrier. Compositions according to the present invention may include any excipient or carrier, such as thickeners, diluents, buffers, preservatives, and / or surface active agents.For liquid formulation, saline, sterile water, Ringer's solution, buffered physiological saline, albumin infusion solution, dextrose solution, maltodextrin solution, glycerol, ethanol, and mixtures thereof may be used as a pharmaceutically or veterinary acceptable excipient or carrier. If appropriate, other conventional additives such as thickeners, diluents, buffers, preservatives, surface active agents, antioxidants and bacteriostatic agents may be added. Further, diluents, dispersants, surfactants, binders and lubricants may be additionally added to the composition to prepare injectable formulations such as aqueous solutions, suspensions, and emulsions, oral formulations such as pills, capsules, granules, or tablets, or powdered formulations.Other materials which can offer better control over release and targeting in specific tissues or cells can be useful for oral delivery or controlled-release applications. Encapsulation protects from external conditions like acidity (in the stomach), UV radiation, or proteolytic enzymes. In some forms, the carriers enhances release at specific sites in the body (e.g., in the intestines) or over a prolonged period, improving their efficacy. In some forms, encapsulation methods can be designed for targeting specific tissues or bacterial infections, enhancing the therapeutic effect. III.Methods of Making Dendrimer ConjugatesA.Methods of Making DendrimersMethods of making dendrimers, such as hydroxyl PAMAM dendrimers and glucose dendrimers, are known in the art. Exemplary methods of making dendrimers are described in detail in International Patent Publication Nos. WO2009 / 046446, WO2015168347, WO2016025745, WO2016025741, WO2019094952, and U.S. Patent No. 8,889,101. In some embodiments, the dendrimer used for conjugation can be purchased, for instance, as described in the Examples section below.Described herein are methods of generating multivalent dendrimer conjugated to one or more molecules involved in the degradation of proteins, dysfunctional organelles, bacteria, and / or viruses in vitro and / or in vivo. The non-limiting details below involve elements of PROTAC and PROTACs, and can be extended to the LYTACs, RIBOTACs, nanobody-OGT, AUTACs, PhosTACs, AceTAGs, PHICS, molecular glues, and other targeting moieties such as antibodies, RNA aptamers, nanobodies, and small molecules.B.Conjugating multiple proximity-induced modulator elements and multiple protein binding elements to a dendrimer surface(i) Direct Conjugation to DendrimerIn some embodiments, multiple proximity-induced modulator elements as well as multiple protein binding elementscan be independently conjugated to the surface of the dendrimer, covalently or non-covalently. Preferably, the conjugation of these elements occurs covalently. In a non-limiting example, a dendrimer (such as a hydroxyl PAMAM, for example, a generation 6 hydroxyl PAMAM or a glucose dendrimer, such as generation 2 glucose dendrimer (GD2) composed of 24 glucose molecules (96 surface hydroxyl groups)) can be reacted with a suitable linker. Preferably, the linker is a bifunctional linker optionally having one of its functional groups protected. An exemplary linker can be (4-tert-butoxycarbonylamino)butyric acid (Boc-protected gamma-aminobutyric acid (GABA)). Where a linker containing a protecting group is used, the linker can be deprotected to expose the protected functional group using a suitable solvent system. In the case of Boc-protected GABA dichloromethane (DCM) / trifluoracetic acid(TFA) (4:1) can be used. In some embodiments, the proximity-induced modulator element is conjugate first to the surface of the dendrimer, before the conjugation of the protein binding element. The order of conjugation is not crucial. In other embodiments, the protein binding element is conjugated first to the surface of the dendrimer, before conjugating the proximity-induced binding element. Non-limiting illustrations of a dendrimer independently functionalized with multiple proximity-induced modulator elements as well as multiple protein binding elementsis shown in Figure 1, Scheme 2 and Scheme 4 (FIG. 2A-2D, respectively). For example, proximity-induced elements such as thalidomide based cereblon ligand and protein binding elements such as 1-methyl-D-tryptophan were conjugated to a hydroxyl PAMAM dendrimer initially containing 256 surface hydroxyl groups. The subscripted numbers in the formulas indicate the number of attachments per dendrimer.The conjugation between the multiple proximity-induced modulator elements as well as multiple protein binding elements to the surface of the dendrimer can involve linkers independently containing: an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof. Preferably, the linkers independently contain an ether bond, an amide bond, or a combination thereof. In these forms, the linkers between the dendrimer surface and the proximity-induced modulator elements as well as multiple protein binding elements, are preferably non-cleavable.Additional details are provided in the Examples section.(ii) Conjugating PROTAC to dendrimer surface via a cleavable bond or non-cleavable bondIn some embodiments, the proximity-induced modulator element and the receptor binding element are conjugated to each other, covalently or non-covalently. Preferably, the conjugation between the proximity-induced modulator element and the receptor binding element occurs via covalent bonding, and more preferably via non-cleavable covalent bonding. The PROTAC containing both the proximity-induced modulator element and the receptor binding element then is conjugated to the dendrimer surface. In some embodiments, conjugation of the PROTAC containing both the proximity-induced modulator element and the receptor binding element to the surface of the dendrimer involves a suitable linker.In some embodiments, the suitable linker is conjugated to the proximity-induced modulator element within the PROTAC. In other embodiments, the suitable linker is conjugated to the receptor binding element within the PROTAC. In other embodiments, the suitable linker is conjugated to the covalent or non-covalent bond between the proximity-induced modulator element and the receptor binding element of the PROTAC. The suitable linker bound to the PROTAC is independently conjugated to the surface of a dendrimer, covalently or non-covalently. Preferably, the conjugation of the linker and the surface of the dendrimer occurs covalently.The bond and / or suitable linker conjugating the PROTAC to the surface of a dendrimer is cleavable and / or contains a cleavable bond. The cleavable functional bond on the linker can independently involve chemically cleavable groups (e.g., solvolysis (such as hydrolysis), reduction, oxidation, etc.), enzymatically cleavable bonds, or a combination thereof. Some combinations can include glutathione / esterases. Leriche, et al., Bioorg. Med. Chem. 2012, 20, 571-582; Li and Chen, Nat. Chem. Bio. 2016, 12, 129-139; Wang, et al., ACS Cent. Sci. 2021, 7, 929-943; Schauenburg and Weil, Adv. Sci. 2023, 2303396 describe cleavable bonds in chemical biology, the contents of which are incorporated herein by reference.In other embodiments, the bond and / or suitable linker conjugating the PROTAC to the surface of a dendrimer is non-cleavable. Examples of bonds that can be included are an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof.The dendrimers discussed above can be used in the synthesis of these dendrimer-PROTAC conjugates or dendrimer bound to elements of a PROTAC (such as the proximity-induced modulator element and the receptor binding element). Preferred dendrimers are hydroxyl PAMAM or glucose dendrimers. In some embodiments, the total hydroxyl groups for conjugation to a PROTAC or elements of a PROTAC between 100- 300, such as 256 for hydroxyl PAMAM or between 50 and 120, such as 96 for a generation 2 glucose dendrimer.IV.METHODS OF USEDendrimer-PROTAC conjugates provide efficient targeted delivery, while protecting the PROTAC payload from premature degradation en route to cytosolic targets, for efficient protein degradation.The conjugates can be used to treat one or more diseases or disorders involving misfolded proteins, disease-associated proteins, dysfunctional organelles, bacteria, and / or virus. The proteins can be extracellular or intracellular proteins. In some forms, these proteins are located in an intracellular compartment, such as the cytosol, such that the conjugates can take advantage of a cell’s intracellular protein degradation machinery. The conjugates can be administered intravenously, orally, subcutaneously, intraperitonially, transdermally, intranasally, or a combination thereof. The administration can be once every day, once every other day, once a every week, once every month, depending on disease, dosage, route of administration and pharmacological kinetics. The conjugates penetrate the blood-brain barrier and therefore have applications in neurological systems, ophthalmological systems, and / or central nervous system (such as brain and / or spinal cord) disorders. As such, the conjugates can be used to treat one or more symptoms of the the neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and amyotrophic lateral sclerosis (ALS). In some embodiments, the conjugates are those that contain or are formed from hydroxyl PAMAM dendrimers or glucose dendrimers. The conjugates can be used to deliver PROTACs and / or elements of PROTACs to specific cells in the body including neurons, reactive immune cells, reactive microglia, macrophages, astrocytes, retinal ganglion cells, or retinal pigmental epithelial (RPE cells) since these dendrimers preferentially target these cells. In some embodiments, where the conjugates contain or are formed from hydroxyl PAMAM dendrimers, the conjugates can be used to deliver PROTACs and / or elements of PROTACs to specific cells in the body including reactive immune cells, including reactive microglia, macrophages, astrocytes, or retinal pigmental epithelial (RPE cells). In some embodiments, where the conjugates contain or are formed from glucose dendrimers, the conjugates can be used to deliver PROTACs and / or elements of PROTACs to specific cells in the body including neurons, retinal ganglion cells, and / or reactive immune cells, including reactive microglia, macrophages, astrocytes, photoreceptors, or retinal pigmental epithelial (RPE cells).The compounds, compositions, and methods herein described are further illustrated in the following examples, which are provided by way of illustration and are not intended to be limiting. All parts or amounts, unless otherwise specified, are by weight.ExamplesExample 1:Syntheses and use of multivalent dendrimer-PROTAC compounds demonstrating Gene EditingCentral nervous system (CNS) related diseases are mostly undruggable due to lack of specific targeting surfaces on the disease-causing proteins and secondarily due to poor transport of neuro-pharmaceuticals to CNS. Heterobifunctional molecules termed PROteolysis TArgeting Chimera, or PROTACs can be used for targeted delivery of compounds that affect protein degradation by recruiting E3 ligase to the protein of interest (POI) and causing proximity induced ubiquitination of the target followed by its degradation at the proteasome. Hydroxyl poly(amidoamine) PAMAM dendrimers are versatile drug carriers that show great potential in targeted delivery of drugs to the CNS. Therefore conjugates of the PROTACS were made with the dendrimers.Materials and MethodsBiomolecules, chemicals, and reagentsUnless stated otherwise, reactions were performed in flame dried glassware under a positive pressure of nitrogen using dry solvents. Commercial grade reagents and anhydrous solvents were purchased from chemical suppliers and used without further purification. 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC.HCl), N, N-diisoprpylethylamine (DIPEA), 4-(dimethylamino)pyridine (DMAP) trifluoracetic acid (TFA), γ-(Boc-amino)butyric acid (Boc-GABA-OH), anhydrous dichloromethane (DCM), N,Nʹ-dimethylformamide (DMF) were purchased from Sigma-Aldrich (St. Louis, MO,USA). Cyanine 5 (Cy5)-mono-NHS ester was purchased from Amersham Bioscience-GE Healthcare. Cyanine 3 (Cy3) trans-cyclooctene (TCO) was purchased from AAT bioquest, Inc. Deuterated solvents dimethylsulfoxide (DMSO-d6), water (D2O), and Chloroform (CDCl3) were purchased from Cambridge Isotope Laboratories Inc. (Andover, MA). Ethylenediamine-core polyamidoamine (PAMAM) dendrimer, generation 6.0, hydroxy surface (G6-OH; diagnostic grade; consisting of 256 hydroxyl end-groups), methanol solution (13.75% w / w) was purchased from Dendritech Inc. (Midland, MI, USA). Dialysis membranes were purchased from Spectrum Laboratories Inc. (Rancho Dominguez, CA, USA). Cas9 nuclease 2NLS, S. Pyrogenes, and all primers were purchased from Synthego Corporation (Redwood City, CA).InstrumentationProton nuclear magnetic resonance (1H NMR) spectra were recorded on a Bruker 500 MHz spectrometer at ambient temperatures and analyzed using software. 1H NMR chemical shifts were reported as δ using residual solvent as an internal standard (DMSO-d6, 2.50), and (D2O, 4.79 ppm). Analytical high-performance liquid chromatography (HPLC) was performed using a Shimadzu LC-AD HPLC system equipped with a variable wavelength absorbance detector and a C18 reverse phase column (Waters, BEH300 5 µm, 19×250 mm). The eluents were monitored at 210 nm using a photodiode array (PDA) detector, and fluorescently labeled conjugate was monitored at both 650 and 210 nm using fluorescence and PDI detectors respectively. HPLC elution was carried out with a 40 min linear gradient of 0%-90% HPLC grade acetonitrile (CH3CN) in water (containing 0.1% TFA) maintaining the flow rate at 1.0 mL / min.Synthesis of compoundsSynthesis of D-GABABoc, 3A solution of PAMAM G6-OH 1 (1.00 g, 0.017 mmol) in DMF (12 mL) was treated with Boc-GABA-OH (0.069 g, 0.34 mmol), DMAP (0.0782 g, 0.408 mmol) and stirred at room temperature for 5 min. Then EDC.HCI (0.046 g, 0.374 mmol) was added in portions to the reaction mixture over the period of 5 min. The reaction mixture was stirred at room temperature for 36 h. The crude product was transferred to 3kD MW cut-off cellulose dialysis tubing and dialysed against DMF 12 h followed by water for 24 h. The aqueous layer was frozen and lyophilized to yield desired product 3 as a hygroscopic white solid (0.973 g, 95%). 1H NMR (500 MHz, DMSO-d6) 8.10-7.70 (m, internal amide H), 6.60 (s, GABA amide H, 10H), 4.74 (s, surface OH, 213H), 3.99 (s, ester linked H, 22H) 3.39 (t, J = 5.0 Hz, dendrimer –CH2), 3.40-3.35 (m, dendrimer CH2), 3.11 (m, dendrimer-CH2), 2.89 (m, dendrimer CH2), 2.73-2.65(m, dendrimer CH2), 2.45(m, dendrimer-CH2), 2.21(m, dendrimer CH2), 1.64-1.59 (m, GABA linker-CH2, 25H), 1.36 (s, Boc group, 85H). HPLC C18 retention time 19 min.Synthesis of D-GABA-NH2, 4The Boc-protected GABA linker containing PAMAM G6-OH 3 (250 mg, 0.004 mmol) was treated with TFA / DCM (3:4) solvent mixture. The reaction was stirred at room temperature for 12 h, then diluted with MeOH, and concentrated in vacuo (this step is necessary to remove excess TFA and hydrolytic cleavage of GABA linker). The crude product was used for the next step without any further purification. 1H NMR (500 MHz, DMSO-d6) δ 8.50-7.75 (m, internal amide H), 5.50-4.50 (broad s, surface -OH), 4.00 (s, ester linked H), 3.50-2.25(m, dendrimer-CH2), 1.93-1.59 (m, GABA linker-CH2). Synthesis of D-HaloPROTACThe HaloTag protein is a bacterial dehalogenase protein, non-native to mammalian cells and has a chloroalkane reactive binding pocket. Under physiological conditions, the reaction between the HaloTag and chloroalkane linker is fast and irreversible to form a stable covalent adduct.Scheme 1 shows the synthesis of D-HaloPROTAC 1. The hydroxyl PAMAM dendrimer generation 6 (PAMAM-G6-OH) was treated with 4-tert-butoxycarbonylamino)butyric acid (Boc-protected GABA) linker, 2 and the resulted product, 3 was deprotected using dichloromethane (DCM) / trifluoracetic acid(TFA) (4:1). Product 4 was conjugated with V032 amide-PEG5-acid 5 and the resulted product was conjugated with 6-chlorohexanoic acid to obtain product 8. The subscripted numbers in the formulas indicate the number of attachments per dendrimer.The D-HaloPROTAC conjugate was synthesized using PAMAM-G6-OH (D6-OH) dendrimer composed of ~256 terminal hydroxyl groups (Scheme 1, FIG. 2A). The commercially available D6-OH dendrimer in methanol (13.75% w / w) was dried under reduced pressure, and further dissolution in water and lyophilized to form mono-functional D6-OH. The D6-OH was first functionalized with Boc protected amine by treatment with BOC-GABA-OH under EDC.HCl and 4-DMAP in DMF for 36 h to yield Boc protected bifunctional dendrimer. The Boc groups were de-protected under mild acidic conditions (TFA: DCM 1:4) to obtain bi-functional dendrimer 4 with ~10 amine groups. The bifunctional dendrimer 4 was treated with VO32-PEG5-acid followed by 6-chlorohexonic acid to obtain final product 8 (Scheme 1, FIG. 3).FKHaloGFP plasmid transfectionGreen fluorescent protein (GFP) is a fluorescent protein that has been used in protein behavior in living cells like protein localization, translocation, interactions, and conformational change. The modular protein tagging system used here, HaloTag, a hydrolase, is genetically engineered to have a chloroalkane reactive binding pocket. Under physiological conditions, the reaction between the HaloTag and chloroalkane linker is fast and irreversible and forms a stable covalent adduct which cannot proceed through general regeneration of enzyme. This Halo-GFP25 fluorescent tag was used to capture the protein of interest ligand and then to proceed to targeted protein degradation. Low-passage, 90% viable cells containing HEK293T cells were used for FKHaloGFP plasmid transfection and RNAiMAX transfection reagent was used herein. The GFP fluorescence gain was measured 24 h after transfection via flow cytometry to assay the editing efficiency.The cytotoxicity / cell viability of D-HaloProtac was evaluated using WST-8 assay (Dojindo Molecular technologies) following the manufacture’s protocol.Image analysisLive-cell images were taken with a Zeiss Axiovert 200 phase-contrast microscope (Carl Zeiss) at set time points. The threshold for the images were automated with the built-in Triangle method in ImageJ.Unless otherwise noted all compounds and were tested in triplicate. ResultsHalo-tag / VHL-recruiting proteolysis-targeting chimera (HaloPROTAC) was used to make dendrimers based on a multivalent PROTAC system containing multiple E3 ligase ligand, von Hippel-Lindau (VHL)-recruiter and ligands that can bind to POI. The dendrimer conjugated PROTAC (Scheme 1, FIG. 2A, and FIG. 3) binds to the bacterial dehalogenase (HaloTag protein) fused protein of interest (POI) and induces the degradation of cytosolic Halotag fusion proteins in cell culture. The dendrimer based PROTAC is multivalent, consisting of multiple copies of von Hippel-Lindau (VHL) E3 ligase ligand and POI binding ligands. Dendrimer PROTAC contains chloroalkane warheads which form covalent bond with HaloTag-fused target protein while von Hippel-Lindau (VHL) E3 ligase ligands. FIGs. 4A-4J: FK-HaloGFP plasmid cultivated bacterial colony after 12 hours incubation (FIG. 4A);Confocal images ofHEK-293 cellstransfected with HaloGFP after 24 h, 5X and 10X magnification (FIG. 4B);Percent GFP positive cells in FK-HaloGFP treated HEK293T cells compared to untreated HEK 293T cells using FACS study (FIG. 4C); Flow cytometry analysis of FK-HaloGFP treated HEK 293T cells compared to untreated HEK 293 T cells (FIG. 4D);Cell viability measured by CCK-8 assay after treatment with dendrimer conjugated PROTAC: D-HaloPROTAC, HaloPROTAC, D-entHaloPROTAC D-POI. Data are presented as mean±s.d. (n=3) (FIG. 4E);Average fluorescence per 1000 nM D-HaloPROTAC treated HaloGFP transfected HEK 293 cells compared to untreated control measured by fluorescence plate reader with time (FIG. 4F);Average fluorescence of different concentrations of D-HaloPROTAC treated HaloGFP transfected HEK 293 cells with the time compared to untreated control measure by fluorescence plate reader (FIG. 4G);confocal microscopy images show loss of fluorescence upon 24 h treatment with D-Haloprotac compared to control group (FIG. 4H); Average fluorescence per 100 nM D-HaloPROTAC treated HaloGFP transfected HEK 293 cells compared to untreated control measured by fluorescence plate reader with time (FIG. 4I);Flow cytometry analysis of HaloGFP expressing HEK 293 cells treated with D-POI, D-HaloPROTAC and HaloPROTAC (FIG. 4J).Successful gene editing (FIG. 4A) results in the gain of green fluorescence that can easily be detectable through flow cytometry (FIG. 4B). Compared to the untreated HEK293T cell control, HaloGFP transfected HEK293 cells induced ~47% editing (FIG. 4C-D). D-HaloPROTAC (10-1000 nM) does not cause significant cytotoxicity in HaloGFP expressing HEK293 cells, whereas higher concentrations of HaloPROTAC (1000 nM) shows significantly higher cytotoxicity (~50% cell death) (FIG. 4E). The concentration and time dependent relative fluorescence were measured for D-HaloPROTAC treated HaloGFP transfectd HEK293 cells compared to untreated HEK293T control using fluorescent plate reader (FIG. 4F and FIG. 4G). After 24 h treatment D-HaloPROTAC (1000 nM) induced nearly 60 % degradation of GFPHaloTag (FIG. 4G). 100 nM D-HaloPROTAC produced nearly 75% degradation of GFPHaloTag after 48 h treatment (FIG. 4I and FIG. 4J). The confocal microscopy images show significant reduction of fluorescence upon 24 h treatment with D-HaloPROTAC compared to untreated control (FIG. 4H). This highly versatile multivalent PAMAM dendrimer based PROTAC system enhances the protein degradation via avidity while multivalency improves the simultaneous binding of multiple copies of target proteins and E3 ligases to form multiple ternary complexes while hydroxyl PAMAM dendrimer improves the targeted delivery of PROTAC to CNS. The results establish that the D-HaloPROTAC construct can induce efficient degradation of GFP-HaloTag in cell-based assays.Example 2:Dendrimer-Antibody / fusion protein mediated protein degradationVascular endothelial growth factor (VEGF) is a key target for treatment of cancer and ocular diseases including age related macular degeneration (AMD). A dendrimer based PROTAC technology was designed for targeted degradation of VEGF. The VEGF inhibition through cytokine trap aflibercept (VEGF TRap-eye (VTE), tradename EYLEA) is being investigated as current “standards-of-treatment” for AMD that is driven by excessive levels of cytokine.  Materials and MethodsDesign and Synthesis of dendrimer-PROTACAflibercept fusion protein was used as a POI binding ligand and CRBN E3 ligase, pomalidomide in the dendrimer-PROTAC design. The pomalidomide acid was first conjugated to bifunctional G6 PAMAM dendrimer, 4 using EDC coupling conditions and the aflibercept conjugation was conducted using trans-cyclooctene-tetrazene (TCO-TZ) click chemistry strategy (Scheme 3 FIG. 2C and Scheme 4 FIG. 2D).Scheme 3 FIG. 2C shows the synthesis of functionalized Cy5-D-PEG4-TCO. The hydroxyl PAMAM dendrimer generation 6 (PAMAM-G6-OH) was treated with 4-tert-butoxycarbonylamino)butyric acid (Boc-protected GABA) linker, 2 and the resulted product, 3 was deprotected using dichloromethane (DCM) / trifluoroacetic acid (TFA) (4:1). The product, 4 was labeled with Cy5 fluorophore using Cy5 N-hydroxysuccinimide (NHS) ester and the resulted intermediate was reacted with pomalidomide based Cereblon ligand, 5, to obtain intermediate 6 that was conjugated with trans-cyclooctene (TCO) linker, PEG4-TCO to obtain functionalized Cy5-D-PEG4-TCO 7.The subscripted numbers in the formulas indicate the number of GABA BOC, PEG4-TCO, or flurophore attached per dendrimer.Scheme 4 FIG. 2D shows the synthesis of Cy5-D-aflibercept-PROTAC conjugate. The aflibercept fusion protein was modified for conjugation with dendrimer. Aflibercept was first substituted with PEGylated tetrazine using NHS-PEG2-Tz reagent to form aflibercept-Tz, was reacted with Cy5-D-PEG4-TCO, 7 to obtain the final product Cy5-D-aflibercept-PROTAC.Free aflibercept vs D-aflibercept dose response curves for pro-inflammatory cytokines hVGFA and hPIGF were prepared and kD values were calculated using the graph pad / Prism software.In vitro delivery of D-aflibercept PROTAC into ARPE-19 cellsIn vitro delivery of D-aflibercept PROTAC into ARPE-19 cells (human retinal pigment epithelial cells) was evaluated. The Cy5-D-aflibercept PROTAC cells were incubated for 24 h. After 24 h, the treatment media was completely removed and replenished with regular media. At 24 h D-aflibercept showed significant intracellular accumulation, evidenced from observing confocal microscopy images of the cellular uptake of Cy5-D-aflibercept PROTAC staining the cell nucleus with the color blue, and the dendrimer with the color red, suggesting successful intracellular delivery enabled by the dendrimer. The binding properties of D-aflibercept PROTAC and aflibercept to VEGFA were assessed using ELISA.  ResultsThrough confocal microscopy imaging, it was shown that D- D-aflibercept-PROTAC conjugate successfully delivers PROTAC into cells. The binding properties of D-aflibercept PROTAC and aflibercept to VEGFA were assessed using ELISA. FIGs.5A and 5B are line graphs showing the free aflibercept vs D-aflibercept dose response curve for pro-inflammatory cytokines hVGFA (FIG. 5A) and hPIGF (FIG. 5B). kD values were calculated using the graph pad / Prism software. The D-aflibercept and aflibercept bound human VEGF in dose dependent manner with calculated KD values of 485 pM and 166 pM. The binding properties of human placental growth factor (hPIGF) were also assessed using ELISA and calculated KD values for D-aflibercept PROTAC and aflibercept 21.8 pM and 531.4pM respectively FIG. 5B.After 24 h, the treatment media was completely removed and replenished with regular media. At 24 h D-aflibercept showed significant intracellular accumulation, evidenced from observing confocal microscopy images of the cellular uptake of Cy5-D-aflibercept PROTAC staining the cell nucleus with the color blue, and the dendrimer with the color red, associated with the Cy5-labeling of the conjugate. FIG. 6 is a schematic of D-aflibercept-PROTAC mediated protein degradation mechanism. This shows that the dendrimer is able to deliver the PROTAC construct into the cell. Example 3:Synthesis of Dendrimer-Based Proteasomal Degradation of Indoleamine 2,3-Dioxygenase 1(IDO1)Indoleamine 2,3-dioxygenase 1 (IDO1) is a heme containing immune checkpoint that engages in tryptophan metabolism along the kynurenine pathway and is involved in autoimmune diseases, chronic inflammation, and tumor immunity. IDO1 is also considered as a key immunomodulator in embryonic immune system while IDO1 is overexpressed in variety of cancers and important in cancer immune escape. The overexpressed IDO1, reduces the L-Trp, which in turn controls the proliferation and function of T cells. Therefore, IDO1 is an important target for cancer immunotherapy. Materials and MethodsDesign and Synthesis of Dendrimer-PROTAC based on IDO1 degraderThere are several highly potent and selective small molecule IDO1 inhibitors that have entered clinical trials. 1-methyl-D-tryptophan (1-D-MT), IDO1 inhibitor (IC50 =7 µM) was used as a POI binding ligand in the dendrimer-PROTAC design. 1-D-MT is in clinical trials in patients with relapsed or refractory solid tumors to inhibit IDO1. The CRBN E3 ligase, thalidomide based CRBN ligand is used as a “warhead”. The dendrimer based IDO1 PROTAC degrader was designed and synthesized as shown in Scheme 2 (FIG. 2B).Scheme 2 (FIG. 2B) shows the synthesis of D-PROTAC (IDO1) 8. The hydroxyl PAMAM dendrimer generation 6 (PAMAM-G6-OH), 1 was treated with 4-tert-butoxycarbonylamino)butyric acid (Boc-protected GABA) linker, 2 and the resulted product, 3 was deprotected using dichloromethane (DCM) / trifluoracetic acid(TFA) (4:1). Product 4 was conjugated with thalidomide based cereblon ligand, 5 and the resulted product was conjugated with POI, 1-methyl-D-Tryphtophan, 7 to obtain product 8. The subscripted numbers in the formulas indicate the number of attachments per dendrimer.FIG. 7 is a scheme for the synthesis of D-IDO1-PROTRAC 1FIGs. 8A-8D show the synthesis and characterization of HD-COOH bifunctional dendrimer for PROTRAC conjugation.Example 4: Delivery of pre-constructed PROTACs and efficacy of dendrimer-IDO1-PROTRACTo assess the ability of the dendrimer to delivery premade PROTACs, a IDO1-PROTAC construct was conjugated to a dendrimer (FIG. 7), and the dendrimer-IDO1 protac conjugate was characterized (FIGs. 8A-8D), and its efficacy was tested in cells.Synthesis of D-IDO1-PROTAC 1The hydroxyl PAMAM dendrimer generation 4 (PAMAM-G4-OH)) was functionalized with hexynoic acid and further conjugated with N3-PEG4-COOH groups using Cu(I) catalyzed click (CuAAC) reaction in the presence of catalytic amount of CuSO4.5H2O and sodium ascorbate. The bifunctional dendrimer was further reacted with IDO1-PROTAC using EDC coupling. The subscripted numbers in the formulas indicate the number of attachments per dendrimer.Synthesis and Characterization of the D-IDO1-PROTACThe IDO1-D-PROTAC conjugate was synthesized using PAMAM-G4-OH (D4-OH) dendrimer composed of ~64 terminal hydroxyl groups (FIGs. 8A-8D and FIG. 7). The commercially available D4-OH dendrimerin Methanol (13.75% w / w) was dried under reduced pressure and further dissolved in water and lyophilized. Then, D4-OH was functionalized with hexynoic acid (~6) groups for click reaction with N3-PEG4-COOH using Cu(I) catalyzed click (CuAAC) reaction in the presence of catalytic amount of CuSO4.5H2O and sodium ascorbate to obtain D-COOH conjugate. The bifunctional D-COOH dendrimer was further reacted with a novel IDO1-PROTAC construct using the EDC coupling reaction to produce the final D-IDO1-PROTAC (FIG. 7). The D-IDO1-PROTAC was further characterized by 1H NMR and HPLC.Characterization of Efficacy in HEK293 cellsTo test the D-IDO1-PROTAC compound, two different in vitro IDO1 expression methods were used.Transient Transfection of GFP-IDO1 plasmid in HEK293 cells.HEK293T cells were used for pcDNA3.1-IDO1-p2A-eGFP (IDO1-GFP) plasmid transfection, and RNAiMAX transfection reagent was used. The GFP fluorescence gain was measured 6 h and 24 h after transfection via flow cytometry to assay the editing efficiency. Successful gene editing increased green fluorescence that was easily detectable through flow cytometry (FIG. 8B). Recent evidence suggests that the biology of IDO1 is complex. For example, in human monocyte-derived macrophages and tumor cells, whether in their natural state or stimulated with IFN-γ, most IDO1 protein molecules do not bind heme. As a result, a significant percentage of IDO1 exists in its apo form, whose biology and function is unclear. Additionally, IDO1 is not confined to the cytosol; it can have distinct intra- and extracellular localizations depending on the cell's microenvironment.Measuring IDO1 Expression via Stimulation MethodsAmong various stimulating agents for IDO1 expression, lipopolysaccharide (LPS) and interferons are popular choices. Human microglia cells (HMC3) cells were used for this study. HMC3, a human microglia cell line, was used for this study. Cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM, ATCC, Manassas, VA) supplemented with 10% (v / v) heat-inactivated fetal bovine serum (FBS, Invitrogen Corp., Carlsbad, CA) and 1% penicillin / streptomycin (P / S, Invitrogen Corp., Carlsbad, CA). Cells were maintained at 37°C and 5% CO₂ in a humidified atmosphere.Lipopolysaccharide (LPS, derived from Escherichia coli O127:B8, Lot#125M4091V) (Sigma-Aldrich, St. Louis, MO) and Interferon γ (IF005) (Sigma-Aldrich, St. Louis, MO).were also used in this study. Once confluent, HMC3 cells were stimulated with lipopolysaccharide (500 ng / ml) and INF-γ (100 ng / ml). After 24 hours, the media was changed, and all cells were checked for IDO1 expression.Quantification of IDO1 was done using the ELISA (Human IDO1ELISA kit (Thermofisher, Catalog # EH246RB). The human IDO1 ELISA kit is a solid-phase sandwich enzyme-linked immunosorbent assay designed to detect and quantify human IDO levels in cell culture supernatants. HMC3 cells were seeded in 96-well plates at a density of 10,000 cells per well and cultured under standard conditions (37°C, 5% CO₂). To induce an inflammatory response, the cells were pre-treated with 100 ng / mL IFN-γ) for 18 hours. After IFN-γ, cells were treated with varying concentrations of IDO1-PROTAC and D-IDO1-PROTAC. At each time point, the culture medium was collected and centrifuged at 5,000 rpm for 5 minutes at 4°C, and the supernatant was stored at -80°C until analysis. Absorbance was measured at 450 nm using a microplate reader.The degradation of IDO1 was measured using sandwich ELISA, which detects IDO1 in both cell supernatants and cell lysates. Human microglial (HMC3) cells were stimulated using IFN (50 ng / mL) for 18 hours. After that, IFN γ was removed and the cells replenished with new media, and treated them with D-IDO1-PROTAC (1 and 20 µg PROTAC basis considering 10 % loading of PROTAC to dendrimer) and small molecular PROTAC (20 µg / mL). The treatment was continued for 48 hours, and the IDO1 amounts in each condition were quantified using a Human ELISA kit. ResultsIFN-γ is an effective inducer of IDO1 and can significantly upregulate the expression of cellular IDO1 levels. It was reported that this cellular IDO1 upregulation happened via IFN-γ-STAT1 / 3 pathways. FIG. 9 are bar graphs showing the percent GFP positive cells in pcDNA3-IDO1-p2A-eGFP treated HEK293T cells compared to untreated HEK 293T cells using confocal and plate reader.After treatment with IFN- for 24 h, the IDO1 expression was markedly increased compared to the LPS group. Compared to the untreated HEK293T cell control, IDO1-GFP transfected HEK293 cells induced approximately40% editing at 24 h (FIG. 9). FIGs. 10A and 10B are graphs showing IDO1 expression by varying concentrations of IFN-γ LPS and IFN: LPS combination. The concentrations of IFN-γ were quantified using Human IDO1 ELISA using Manufacture’s protocol.FIGs. 11A and 11B are bar graphs showing degradation of IDO1 in vitro with the PROTAC constructs. FIG. 11A shows quantification of well supernatant IDO1. FIG. 11B shows quantification of cell lysate IDO1.The effects of D-IDO1-PROTAC and the corresponding small PROTAC-treated cells after 48 hours of treatment were assessed. An ELISA assay was run to measure levels of IDO1 in the PROTAC-treated cells. The results demonstrated that stimulation with IFN-γ led to increased levels of IDO1 in the cells. Notably, after 48 hours, a significant dose-dependent decrease was observed in IDO1 levels in the D-IDO1-PROTAC-treated cells, both in the cell supernatant and lysate. The IDO1 PROTAC used in this study was a commercially available IDO1 degrader (HY-131911, MedChemExpress) and the concentration of IDO1 PROTAC used was based on previous ELISA studies.In the supernatant, the PROTAC construct exhibited attenuated IDO1 compared to control (FIG. 11A). However, the dendrimer contract was 5-fold better than free PROTAC at 1 / 20th the dose (100-fold better), attenuating IDO1 by >99% compared to control (FIG. 11A). At an equivalent concentration to free PROTAC, the dendrimer-PROTAC is >20-fold more effective. In the cell lysate the dendrimer conjugate performed better than free PROTAC (FIG. 11B). While the free PROTAC did not attenuate IDO1 expression, the dendrimer conjugate, significantly attenuated IDO1 in the cell lysate. At a 20-fold lower concentration of the free PROTAC dose, the D-PROTAC was >3-fold better than free PROTAC (FIG. 11B). Therefore, the dendrimer conjugate performed better than free PROTAC in both the supernatant and cell lysate IDO1 expression, suggesting that the dendrimer delivered PROTAC constructs into cells. These results indicate that the D-IDO1-PROTAC effectively triggered the destruction of the IDO1 protein. This approach utilized dendrimer chemistry to deliver PROTAC to targeted cells. The dendrimer PROTAC addressed the limitations of existing small-molecule PROTACs by improving efficacy and enhancing control of delivery for a wider range of applications.SummaryThe use of the dendrimer to deliver these otherwise difficult-to-deliver bifunctionals represents a major advance both over the state-of-the-art in bifunctional drug development, but also in small-molecule / nanoparticle inhibitor development. By engineering the ability to deliver these into cells, we now access the ability to catalytically degrade many intracellular targets in all targetable cell types, effectively buying a many-fold improvement over the 1:1 inhibition of conventional small molecules. Additionally, the multivalent nature of the dendrimer lends itself to using LYTACs to simultaneously drag many extracellular target proteins into the lysosome for degradation as opposed to the 1:1 degradation of current LYTACs. Finally, the unique properties of the dendrimer allow it to function as the linker, eliminating much of the need for improvement or alteration of traditional linkers. This simplifies the process of converting any protein-binding molecule into a catalytic degrader. Broadly, the demonstration of dendrimer-bifunctional conjugates represents a significant improvement over the state-of-the-art on all fronts.

Claims

1. A dendrimer conjugate comprising a dendrimer selected from the group consisting of hydroxylated dendrimers, sugar-terminated dendrimers, and a sugar-based dendrimers, conjugated to one or more PROteolysis TArgeting Chimeras (PROTACs) molecules or elements thereof, wherein the PROTAC molecules are involved in the degradation of proteins, dysfunctional organelles, bacteria, and / or viruses in vitro and / or in vivo.

2. The conjugate of claim 1, wherein the dendrimer is covalently conjugated to the PROTAC molecules or elements thereof.

3. The conjugate of claim 1 or 2; comprising a targeting agent.

4. The conjugate of claim 3 wherein the targeting agent is selected from the group consisting of lysosome-targeting chimeras (LYTACs), catalytic lysosome-targeting chimeras (cataLYTACs), RNase targeting chimeras (RIBOTACs), glycosyltransferase targeting molecule (nanobody-OGT), autophagosome-targeting chimeras (AUTACs), phosphatase-targeting chimeras (PhosTACs), acetyltransferase targeting molecules (AceTAGs), kinase-targeting molecules (PHICS), antibodies, RNA aptamers, and nanobodies.

5. The conjugate of any of claims 1-4, wherein the one or more PROTAC molecules or elements thereof are independently conjugated to the dendrimer via cleavable bonds.

6. The conjugate of any of claims 1-4 wherein the one or more PROTAC molecules or elements thereof are conjugated to the dendrimer via non-cleavable bonds.

7. The conjugate of any of claims 1-6 wherein the one or more PROTAC elements are selected from the group consisting of proximity-induced modulator elements and protein binding element, optionally wherein the PROTAC elements comprise a proximity-induced modulator element and protein binding element covalently bonded via a spacer to the dendrimer.

8. The conjugate of any one of claims 1 to 5, wherein conjugation of the PROTAC or one or more elements of PROTACs to the dendrimers independently comprises an ester bond, an ether bond, an amide bond, a triazole, a carbamate, an oxime ether, a hydrazone, a thio-ether, a carbonyl, an imine, a sulfonamide, an azo, a dialkyl dialkoxysilane, a diaryl dialkoxysilane, an orthoester, an acetal, an aconityl, a β-thiopropionate, a phosphoramidate, a trityl, a vinyl ether, a polyketal, or a combination thereof.

9. The conjugate of any one of claims 1 to 8, wherein the dendrimer is a polyamidoamine (PAMAM) dendrimer of generation 1 to generation 9 (such as generation 1, generation 2, generation 3, generation 4, generation 5, generation 6, generation 7, generation 8, or generation 9), preferably with between greater than 40 and 100% of the surface groups being hydroxylated.

10. The conjugate of any one of claims 1 to 9, wherein the dendrimer is a glucose dendrimer or a glucose-based dendrimer.

11. The conjugate of claim 10, wherein the dendrimer is a generation 1 to generation 5 glucose or galactose dendrimer.

12. The conjugate of any one of claims 1 to 11, wherein the protein binding element is a recruiting moiety, a targeting moiety selected from the group consisting of an antibody, an RNA aptamer, a nanobody, a small molecule, and combinations thereof.

13. The conjugate of any of claims 1 to 12, where the conjugate is confined to the peripheral circulation by the use of higher generation dendrimer selected from the group consisting of generation 4, 5, or 6 hydroxyl PAMAM dendrimer, generation 2, 3, or higher glucose dendrimer, or functionalized with PEG.

14. A pharmaceutical composition comprising the conjugate of any one of claims 1 to 13, and a pharmaceutically acceptable carrier or excipient.

15. The pharmaceutical composition of claim 14 for administration intravenously, orally, subcutaneously, intraperitonially, transdermally, intranasally.

16. The pharmaceutical composition of claim 14 for treatment of cells in the neurological system, ophthalmological system, or central nervous system including the brain and spinal cord.

17. The pharmaceutical composition of claim 16, wherein the composition is for treatment of a subject having or displaying signs and / or symptoms of, Alzheimer’s, Parkinson’s, Huntington’s disease, or amyotrophic lateral sclerosis (ALS). 

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