Melanoma is the most aggressive skin cancer, characterized by remarkable cancer cell plasticity, contributing to intra-tumoral heterogeneity and therapeutic resistance. NRAS-mutant melanoma remains a clinical problem, particularly in patients who do not respond to immunotherapies. As a second-line option, MEK inhibitors as single agents fail to provide a significant overall survival benefit. Therefore, there is an unmet need for new therapeutic strategies to improve the management of NRAS-mutant melanoma. Here we assessed in vitro and in vivo the response of NRAS-mutant melanoma cells to RMC-6236, a novel non-covalent inhibitor of both oncogenic and wild type RAS isoforms currently undergoing clinical investigation in various cancers.

Loss-of-function approaches using RMC-6236, IAG933 (a YAP-TEAD interaction inhibitor), or siRNAs were employed to evaluate the impact of NRAS inhibition on phenotypic adaptation (RNA-seq, RT-qPCR, western blot analyses) as well as cell proliferation and survival (colony formation assay, flow cytometry) in human and murine NRAS-mutant cell line models. A murine and human melanoma models using MaNRAS and C8161 cells grafted into syngeneic C57BL/6 and xenograft NSG mice was used to assess the effect of RMC-6236 or/and IAG933 on tumor growth and mouse survival.

Our transcriptomic and proteomic analyses revealed that the anti-proliferative effect of RMC-6236 on NRAS-mutant melanoma cell lines is characterized by a phenotypic transition towards a less differentiated state, with increased expression of mesenchymal and extracellular matrix remodeling markers, along with the activation of a YAP-driven transcriptional signature and focal adhesion kinase (FAK) signaling. In vivo RMC-6236 slowed tumor growth and improved mouse survival. Melanoma cells treated with RMC-6236 in vivo exhibited reduced pigmentation and expressed mesenchymal and neural crest stem cell markers and YAP-target genes. The combination of RMC-6236 and IAG933 in vitro synergistically reduced proliferation, prevented phenotypic transition, and induced apoptosis in NRAS-mutant cells. In vivo the IAG933 significantly improve the efficacy of RMC-6236 and improved mouse survival. These findings suggest that YAP-TEAD pathway inhibition by IAG933 targets the adaptive response induced by RMC-6236 and enhances treatment efficacy in vitro and in vivo.

NRAS inhibition in melanoma cells induces a mesenchymal phenotypic transition linked to YAP pathway activation. YAP/TEAD inhibition can overcome resistance to NRAS inhibition by preventing adaptive phenotype switching and inducing tumor cell death. This work provides a scientific rationale for treating NRAS-mutant melanomas with a combination of RAS and YAP-TEAD inhibitors.