RAS(ON) Multiselective Inhibition Drives Antitumor Immunity in Preclinical Models of NRAS-Mutant Melanoma

Targeted therapies for NRAS-mutant melanoma remain an unmet clinical need. In this study, we demonstrate that RMC-7977, a preclinical RAS(ON) multiselective inhibitor representative of the investigational agent daraxonrasib (RMC-6236), was able to elicit potent antitumor immune responses across multiple NRAS-mutant melanoma models. Treatment with RMC-7977 led to rapid tumor regressions driven by inhibition of MAPK signaling, upregulation of MHC and PD-L1 proteins, and enhanced infiltration of CD4+ and CD8+ T cells. Complete responses were dependent on adaptive immunity, as both CD4+ and CD8+ T cells were essential for extended survival. Resistance to treatment was marked by reduced T-cell infiltration, loss of MHC class I expression, and expansion of myeloid-derived suppressor cells. Combining RMC-7977 with anti-PD-1 boosted cytotoxic T-cell infiltration, reprogrammed myeloid cells toward an antigen-presenting phenotype, and improved survival in models resistant to PD-1 blockade. Consistent with these preclinical data, objective clinical responses were observed in two patients with NRAS-mutant melanoma treated with daraxonrasib in an ongoing phase I/Ib clinical trial. Together, these data support the continued clinical evaluation of RAS(ON) multiselective inhibitors for the treatment of NRAS-mutant melanoma.