Abstract 6982: First-in-class inhibitors of the proton-sensing receptor GPR68 for oncology

Abstract Background: Aggressive tumors are often characterized by a fibrotic and acidic microenvironment. These features are associated with immune dysfunction, reduced survival, and impaired efficacy of chemo- and immunotherapies. One axis mediating these functions acts via GPR68, a proton-sensing receptor thought to be selectively enriched in cancer associated fibroblasts (CAFs). In mouse models, GPR68 deletion is associated with reduced tumor burden and increased overall survival, potentially by reversing immunosuppressive effects of the tumor environment. To date, a single compound purported to be a GPR68 antagonist (FT011) has entered clinical development for fibrosis. There has been limited evaluation of the efficacy of GPR68 antagonists as anti-tumor agents. Methods: We assessed the efficacy of compounds developed using generative AI on GPR68 signaling pathways, explored GPR68-mediated effects on CAF biology, and evaluated the effects of GPR68 antagonism via CAFs on T-cell mediated cancer cell killing in vitro. We evaluated the in vivo efficacy of GPR68 antagonism on tumor growth in syngeneic models alone and in combination with immune checkpoint inhibitors. Results: Expression of GPR68 in patient CAFs was confirmed by qPCR and signaling assays. In vitro, GPR68 stimulation induced changes in CAF-secreted factors, which were robustly reversed by GPR68 antagonism. GPR68 activating stimuli had no measured effect on a wildtype fibroblast cell line. GPR68 activation in CAFs led to significant changes in collagen production, which were blocked by GPR68 antagonism. Conditioned media from GPR68-activated CAFs impaired T-cell cytokine release and inhibited the ability of activated primary T-cells to kill PC-3 cancer cells. This effect was reversed by GPR68 antagonism. In vivo, GPR68 antagonism significantly reduced tumor growth in multiple aggressive syngeneic models. Tumor material from the 4T1 tumor-bearing animals treated with GPR68 antagonist revealed significantly increased tumor necrosis, suggesting more pronounced effects than those indicated by tumor volume alone. In support of GPR68 antagonism promoting an adaptive anti-tumor immune response, we observed enhanced efficacy when GPR68 antagonism was combined with different immune checkpoint inhibitors in a colon cancer model. Conclusions: GPR68 acts via CAF signaling to suppress the adaptive immune response to cancer cells. GPR68 antagonism in vivo shows anti-tumor activity across multiple syngeneic models suggesting a broad range of potential indications. These effects are improved in combination with immune-checkpoint inhibitors supporting an immune-targeting axis between GPR68, acidic tumors, and the adaptive immune response. We are currently progressing our first-in-class lead molecules through preclinical development and validating potential in vivo biomarkers for future human clinical trials. Citation Format: Reid Hans Johnson Olsen, Michael Prime, Bellamy Duncan, Berizzi E. Alice, Alex Ceroni, Fonfria Elena, Major Gooyit, Mizuho Horioka, Katherine Lansu, Samuel R. Lawrence, Manisha Naik, Kostantinos Papachristos, Maninder Panesar, Martin Redhead, Simon Richards, David A. Smith-Parkin, Piotr Stepien, Jake Swadling, Diogo M. Tomaz, Bojan Vilagos, Walker S. Andrew. First-in-class inhibitors of the proton-sensing receptor GPR68 for oncology [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 6982.