Scale-up and Toxicity Studies of POEGMA-Uricase

Project Summary The goal of this Phase II SBIR is to continue development of Gateway Bio’s proprietary alternative for poly(ethylene glycol) (PEG) for use as a conjugate to stabilize and increase the circulation half-life of biological therapeutics. PEG is used in a broad range of products, including biopharmaceuticals and cosmetics, causing increasing numbers of individuals to develop anti-PEG antibodies. Once established in circulation, anti-PEG antibodies can interfere with PEGylated therapeutics or trigger an allergic reaction, both of which result in reduced drug tolerability and efficacy. An urgent unmet need has therefore emerged for PEG-free therapeutics, requiring new moieties capable of producing the same circulation half-life and stability improvements required for many biotherapeutics. In response to this need, Gateway Bio has developed poly(oligoethylene glycol methyl methacrylate) (POEGMA), which has short oligoethylene glycol chains distributed along a polymer backbone. These features eliminate PEG’s immunogenicity, while still providing prolonged circulation half-life and compound stability. During a previous Phase I SBIR grant, Gateway demonstrated reliable synthesis of POEGMA as well as conjugation to an FDA approved enzyme drug, uricase, currently marketed as a PEGylated therapeutic, pegloticase (trade name: Krystexxa™), for the treatment of treatment-refractory chronic gout. Pegloticase has been linked with high titers of anti-PEG antibodies, leading to severe allergic reactions as well as reduced drug efficacy. Dynamic light scattering (DLS) showed that both PEG and POEGMA conjugation increase the hydration radius of uricase with no change in the enzyme’s activity. In vivo pharmacokinetic studies in mice also showed that both modifications result in dramatic improvements in circulating enzyme at 24, 48, and 72 hours over unmodified enzyme, with POEGMAylated enzyme showing increased serum levels over PEGylated enzyme. Serum drawn from animals treated with PEG conjugated enzyme contained relatively high titers of anti-PEG antibodies, including both IgG and IgM species. In contrast, after treatment with POEGMA- conjugated enzyme, anti-POEGMA antibodies were undetectable. These data provide compelling evidence that POEGMA can improve the drug properties of biotherapeutics without the fear of immune responses that reduce efficacy or tolerability of the drug. Here, Gateway Bio proposes a Phase II program to accomplish the following goals: 1) scaling up production of uricase (Gateway Bio) and POEGMA (with contractor CuraPath, Inc.); 2) developing a high-volume conjugation method to generate POEGMA-uricase (Curapath); 3) a comparative study between POEGMA-uricase and pegloticase in a murine model (Duke University subaward); and 4) initial toxicity and biocompatibility studies to support a pre-IND meeting with the FDA to enable future clinical studies (with contractor Charles River Labs). These efforts will support the continued development of POEGMA-uricase, as initial technical and market validation for the company’s novel PEG alternative.