Abstract 3422: Targeted optimized interferon alpha demonstrates improved safety and efficacy in tumors with low PD-L1 expression

Abstract Introduction: Type 1 interferons (IFN), including IFN alpha, have potent antitumor and immune stimulating effects. Though approved for treatment of multiple cancers, clinical use of IFN alpha is hindered by its short serum half-life and poor tolerability due to the broad expression of the Type 1 IFN receptor (IFNAR). A systematic approach was taken to improve the therapeutic window of IFN alpha. First, site specific mutations were designed to attenuate binding to IFNAR resulting in modified interferons with optimized activity. Then, the optimized interferons were fused to tumor antigen targeting antibodies (Abs) to generate immunocytokine molecules called Tumor Activated Interferon (TAI). Behaving as agonists, TAIs exhibit improved on-target activity once bound to antigen-positive cells. Moreover, TAIs also display significantly reduced systemic toxicity due to their attenuated non-targeted IFN activity. These characteristics contribute to the improved therapeutic window of TAIs. REMD-456 is our lead candidate consisting of optimized IFN alpha fused to PD-L1 Ab. Methods: TAIs were screened for their IFN activity by reporter assay using cells with or without PD-L1 expression. Tumor cell growth inhibition activity of TAIs was assessed by MTS and CellTiter-Glo proliferation assays. Equimolar doses of pegylated IFN alpha-2a (PEGASYS) and TAI were evaluated in human tumor xenograft models using cell lines with various levels of PD-L1 expression. A single dose non-GLP tox study was conducted in Syrian golden hamsters with both PEGASYS and TAIs to assess PK and safety. Furthermore, PK, toxicity and biomarkers of TAIs were assessed in cynomolgus monkeys. Results: Various TAIs containing different peptide linkers and optimized IFNs fused to PD-L1 Ab were screened for their PD-L1 targeted and non-targeted IFN activity. Compared to IFN alpha, the TAIs showed up to 9000-fold reduced non-targeted activity and up to 14-fold improved targeted activity. Tumor cell growth inhibition assays showed a similar activity profile. TAIs, at doses as low as 1 ug/kg, demonstrated superior in vivo anti-tumor activity compared to PEGASYS against NCI-N87 (PD-L1 low) and NCI-H820 (PD-L1 high) human tumor xenografts. In Syrian golden hamsters, high dose TAI did not affect body weight while PEGASYS at equimolar dose caused significant body weight loss. In cynomolgus monkeys REMD-456 had an acceptable safety profile at all doses tested. Conclusions: REMD-456 was selected for its efficacy and safety profile in vitro and in vivo and manufacturability. It showed enhanced IFN activity only on PD-L1+ cells, resulting in an improved therapeutic window. In vivo, REMD-456 demonstrated superior anti-tumor efficacy in human tumor xenografts. Moreover, REMD-456 displayed an improved safety profile in hamster and primate single dose toxicity studies. IND enabling studies are in progress with anticipated filing in late 2025. Citation Format: Kristopher Steward, Wuyi Wang, Yanmei Sun, Chengwei Shang, Chun Yang, Tom Boone, Hai Yan. Targeted optimized interferon alpha demonstrates improved safety and efficacy in tumors with low PD-L1 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3422.