Specific inhibitor to KRAS 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 driver oncoprotein have recently been developed for cancer treatment. The combination of a potent OV with a KRAS inhibitor could be a potent combination strategy for treating KRAS cancer.

Methods: We explored combination therapies using KRAS inhibitor and OV in cancer cells in vitro and in two KRAS 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, AMG510 (sotorasib), MRTX849 (adagrasib) and MRTX1257, all displayed potent cytotoxicity to cancer cells harboring KRAS, but not to cancer cells without this specific KRAS mutation in vitro. All three inhibitors exhibited potent antitumor activity in KRAS Lewis lung cancer, but not in MC38 colon cancer with wild-type KRAS. In two KRAS 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 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 are novel inducers of tumor-specific immunity, and a unique triple combination regimen is highly efficacious through elicited potent antitumor immunity for KRAS cancers.