Specific inhibitor to KRASG12C induces tumor-specific immunity and synergizes with oncolytic virus for enhanced cancer immunotherapy

Background Oncolytic virus (OV)-mediated immunotherapy has been shown limited efficacy. Small molecule inhibitors specific to the KRAS G12C driver oncoprotein have recently been developed for cancer treatment. The combination of a potent OV with a KRAS G12C inhibitor could be a potent combination strategy for treating KRAS G12C cancer. Methods We explored combination therapies using KRAS G12C inhibitor and OV in cancer cells in vitro and in two KRAS G12C cancer models. We employed flow cytometry to evaluate the immune cell profiles, including dendritic cells, macrophages, myeloid-derived suppressor cells, natural killer (NK), subsets of CD4 + and CD8 + T cells, and exhaustion markers (CTLA-4, PD-1, TIM-3), activation markers (granzyme B, IFN-γ and 4-1BB) as well as enzyme-linked immunospot assay to identify tumor-antigen specific T cells. The importance of CD4 + , CD8 + T and NK cells in the therapeutic effects was evaluated by antibody-mediated depletion in vivo. Results We confirmed that three inhibitors for KRAS G12C , AMG510 (sotorasib), MRTX849 (adagrasib) and MRTX1257, all displayed potent cytotoxicity to cancer cells harboring KRAS G12C , but not to cancer cells without this specific KRAS mutation in vitro. All three inhibitors exhibited potent antitumor activity in KRAS G12C Lewis lung cancer, but not in MC38 colon cancer with wild-type KRAS. In two KRAS G12C tumor models, either an IL-36γ-armed OV or orally delivered MRTX1257 inhibited tumor growth, but the combination worked much more efficiently, and efficacy was further improved with PD-1 blockade although with no statistical difference in survival, leading to complete tumor remission in a large fraction of the mice. Mechanistic studies revealed that MRTX1257, and other KRAS G12C inhibitors as well, are potent inducers of antitumor immunity by themselves, and that it worked with OV to elicit potent innate and adaptive tumor-specific immunity. The combination therapeutic efficacy depended largely on increased tumor-specific CD8 + cytotoxic T cells, and to a smaller degree, on CD4 + T and NK cells. Conclusions Small molecule inhibitors of KRAS G12C are novel inducers of tumor-specific immunity, and a unique triple combination regimen is highly efficacious through elicited potent antitumor immunity for KRAS G12C cancers.