Design of Non-Immunogenic PEG-like Polymers for Applications in Medicine

Abstract

Poly(ethylene glycol) (PEG) has long served as the gold standard for improving the pharmacokinetics and biocompatibility of therapeutic agents. However, its widespread presence in pharmaceuticals and consumer products has led to a rise in anti-PEG antibodies, compromising the safety and efficacy of PEGylated drugs. This dissertation addresses the urgent need for a non-immunogenic, chemically versatile alternative to PEG by developing a modular polymer platform based on poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA).In the first part of this dissertation, I systematically explored how precise control over POEGMA architecture can be leveraged to create materials with finely tuned properties. Utilized the LCST phase behavior of POEGMA, we designed and synthesized polymeric nanoparticles composed entirely of POEGMA. Our design choices were guided by previous findings that POEGMA with three or fewer ethylene glycol (EG) repeats in the side chain retain stealth properties and avoid recognition by anti-PEG antibodies. I designed a library of simple and complex AB-type block copolymers of POEGMA with precisely tuned side-chain lengths and block compositions using reversible addition–fragmentation chain-transfer (RAFT) polymerization. The simple EG3-EG2 diblock POEGMA library revealed that even a single EG unit difference between the two blocks is sufficient to induce amphiphilic self-assembly if at least 25% of the polymer's total length is contributed by each block. Additionally, partial phase diagrams of these simple diblocks show that self-assembling diblocks exhibit a concentration-independent transition temperature (Tt), characteristic of a micelle-to-coacervate transition whereas, non-assembling diblocks displayed a concentration-dependent Tt indicative of a unimer-to-coacervate transition. In the first set of complex diblocks, the amphiphilicity of POEGMA was increased by incorporation of a more hydrophobic monomer, EG1MA, into the core-forming hydrophobic block to enhance thermal stability, yielding nanoparticles that remained stable at room and body temperature. These POEGMA nanoparticles demonstrated high drug-loading efficiency for a variety of hydrophobic small molecules, including doxorubicin. Compared to the free drug, POEGMA-formulated doxorubicin exhibited similar in vitro potency but improved in vivo antitumor efficacy, driven by enhanced circulation half-life. Importantly, the nanoparticles were not recognized by anti-PEG antibodies in an in vitro ELISA, validating POEGMA’s stealth properties. Furthermore, by designing complex diblock copolymers with tailored LCST behavior, I developed injectable, physically crosslinked POEGMA hydrogels that form via reversible micelle-to-coacervate transitions. These materials showed strong potential for sustained and localized drug delivery. In the second part, I extended the POEGMA platform to bioconjugates by site-specifically attaching POEGMA to the immunostimulatory protein Neo2/15 via strain-promoted azide-alkyne cycloaddition. The conjugate retained in vitro bioactivity but showed modest anti-tumor effects in vivo, indicating the need for combination strategies. I also synthesized a heterobifunctional POEGMA bearing orthogonal azide and thiol end-groups for dual conjugation of biologics. While low protein yields limited experimental validation, this approach lays the groundwork for future development of unimolecular dual agonist therapies for metabolic disease. In conclusion, this dissertation establishes POEGMA as a versatile, stealth, and non-immunogenic alternative to PEG for next-generation drug delivery systems. Through systematic control of polymer architecture, POEGMA can form self-assembled nanoparticles, thermoresponsive hydrogels, and site-specific bioconjugates. The findings demonstrate that rational design of POEGMA polymers enables fine-tuning of structure–property relationships and offers a broadly applicable strategy for safer, more effective polymer therapeutics. Building on the complex architecture, I decreased the hydrophilicity of the corona forming block to tune the Tt below body temperature enabling depot formation upon s.c. injection. These complex diblock POEGMAs exist as micelles at room temperature below the polymer Tt and form physically crosslinked micro-network like structures upon heating above the Tt. Importantly, the micelle-to-coacervate transition is reversible and the Tt is tuned to below body temperature suitable for designing injectable hydrogels and sustained drug release applications. In the second part, I explored the utility of POEGMA as a bioconjugation platform. I engineered a long-acting conjugate of Neo2/15—a synthetic IL-2/IL-15 mimetic cytokine—using strain-promoted azide-alkyne click chemistry to couple POEGMA to the protein in a site-specific fashion. The conjugate retained its bioactivity in T-cell proliferation assays but showed limited tumor regression in vivo, suggesting combination regimens may be required for therapeutic efficacy. Finally, I designed a heterobifunctional POEGMA polymer bearing azide and thiol end-groups to enable orthogonal conjugation of two distinct therapeutics. Although low protein yields prevented full evaluation of a dual agonist conjugate, a fusion protein model was used to demonstrate the therapeutic potential of such unimolecular constructs for treating multifaceted metabolic diseases like fatty liver disease. Collectively, this work establishes POEGMA as a robust, non-immunogenic, and modular polymeric platform for next-generation therapeutic delivery. Its tunable phase behavior, stealth properties, and bioconjugation versatility provide a strong foundation for the rational design of safe and effective polymer-based systems in medicine.