Abstract 4068: In vitro masked effect, in vivo anti-tumor activity and toxicology study of KGX101, an interleukin-12 prodrug, in monotherapy or in combination with anti-PD-L1 antibody

Abstract Interleukin-12 (IL-12) has long been limited in its clinical use due to its short half-life (t1/2) and dose-related toxicity, despite its remarkable ability to activate effector functions in T cells and natural killer (NK) cells. To address these challenges, we engineered an IL-12 prodrug called KGX101. In KGX101, the C-terminus of IL-12 is fused with ADCC-impaired IgG1 Fc to extend its half-life. Meanwhile, the N-terminus is concealed with its corresponding receptor soluble domains, IL-12Rβ1 and IL-12Rβ2, using tumor-specific protease cleavable linkers. This innovative design prevents systemic immune system overactivation. Once the linker is cleaved by tumor microenvironment (TME) -specific proteases, KGX101 functions like IL-12, effectively stimulating T cells and NK cells, reshaping the TME, and displaying significant potential in cancer therapy. To confirm KGX101's masking effect, we conducted IFNγ induction efficacy tests using peripheral blood mononuclear cells (PBMCs) from three donors. KGX101 demonstrated a 300 to 2500-fold reduction in activity compared to unmasked IL-12-Fc. Importantly, the masking effect of KGX101 was nearly abolished after protease digestion, affirming its mechanism of action. To further establish KGX101's effectiveness, we conducted in vivo antitumor studies in hPBMC xenograft mouse models using human colorectal cancer HCT116 and PD-L1-overexpressed human malignant melanoma A375. Mice were subcutaneously implanted with a specific mixture of cancer cells and hPBMCs, and then intravenously injected with PBS or KGX101 at various dose levels twice a week for 4-5 cycles. Compared to the PBS control group, KGX101 demonstrated up to a 42% tumor growth inhibition (TGI) in the HCT116 model at 0. 18 mg/kg and a 76% TGI in the hPD-L1-A375 model at 0. 06 mg/kg. Analysis of tumor-infiltrating lymphocytes (TILs) revealed that KGX101 increased the percentage of T cells in the tumor environment in a dose-dependent manner. We also evaluated the combination of KGX101 with an anti-PD-L1 antibody in an HCT116/hPBMC xenograft mouse model, which showed limited response to anti-PD-L1 monotherapy. The TGI% for KGX101 at 0. 06 mg/kg, anti-PD-L1 antibody at 1 mg/kg, and their combination were 36. 56%, 6. 93%, and 66. 22%, respectively, demonstrating a promising antitumor synergy. In terms of pharmacokinetics, a single dose of KGX101 at 0. 06 mg/kg and 0. 18 mg/kg in the HCT116/hPBMC xenograft mouse model resulted in a serum half-life ranging from 52. 75 to 64. 87 hours, while the t1/2 in Cynomolgus monkeys was approximately 3 days. In a 4-week repeat dose toxicity study in Cynomolgus monkeys, the highest non-severely toxic dose (HNSTD) of KGX101 was determined to be 0. 1 mg/kg. The results from nonclinical toxicology studies support the potential of KGX101 as a well-tolerated therapy for the First-in-Human (FIH) clinical trial. Citation Format: Shumin Yang, Nuo Li, Jing Wang, Li Ma, Yi Zhao, Hui Chen, Haixiang Wu, Weidong Jiang. In vitro masked effect, in vivo anti-tumor activity and toxicology study of KGX101, an interleukin-12 prodrug, in monotherapy or in combination with anti-PD-L1 antibody abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4068.