Mutation-Resolved Drug Sensitivity Atlas Reveals Broad RAS(ON) Inhibitor Vulnerabilities and a STAT3 Co-Dependency in NRAS-Mutant Melanoma
Abstract NRAS mutations drive 20–30% of melanomas and are associated with poor response to immunotherapies. RAS(ON) inhibitors such as daraxonrasib (RMC-6236) have shown promising activity in NRAS-mutant melanoma, yet mutation-specific sensitivity, resistance mechanisms, and rational combination strategies remain largely unresolved. Here, we performed saturation mutagenesis across NRAS mutation hotspots to systematically evaluate mutation-resolved oncogenic fitness and drug responsiveness to six direct RAS inhibitors (sotorasib, adagrasib, ADT-007, BI-2865, RMC-6236, and RMC-7977) using isogenic melanoma spheroids, xenografts, and pooled drug-sensitivity profiling. RMC-6236 and RMC-7977 displayed the broadest activity, sensitizing ∼80% of recurrent NRAS mutations across the P-loop and Switch II regions. Several clinically observed mutations, including Q61P, G13D/V/R, and G60E, showed reduced susceptibility to RAS(ON) inhibition. Structural modelling and thermostability analysis indicated impaired inhibitor engagement or reduced tricomplex stability as potential mechanisms of resistance. RAS(ON) blockade also induced STAT3 activation, particularly in oncogenic Q61 mutants. Co-targeting STAT3 with napabucasin or siRNA enhanced apoptosis, suppressed MYC, and improved tumour control in vitro and in vivo. Together, this study provides the first comprehensive mutation-resolved sensitivity atlas for NRAS-mutant melanoma, highlights structural mechanisms underlying resistance to RAS(ON) inhibitors, and identifies STAT3 inhibition as a rational combination strategy. These findings offer preclinical evidence supporting mutation-guided patient stratification and combination-therapy development for NRAS-mutated melanoma. Statement of Translational Significance NRAS-mutated melanoma lacks effective targeted treatments, and clinical responses to immunotherapy remain suboptimal. This study presents the first comprehensive drug sensitivity map across 95 NRAS mutations in melanoma, identifying the pan-RAS(ON) inhibitors RMC-6236 and RMC-7977 as broadly effective agents. Multiple mutants with reduced susceptibility are identified, providing mutation-specific guidance for patient selection and clinical trial stratification. Mechanistic analyses reveal that STAT3 activation functions as a key survival pathway under RAS(ON) blockade, and its inhibition markedly enhances the efficacy of pan-RAS(ON) inhibitors. These findings support mutation-guided utilization of RAS(ON) inhibition and highlight STAT3 co-targeting as a rational strategy to strengthen and prolong therapeutic responses in NRAS-mutant melanoma. Highlights - Generation of mutation-resolved functional and drug-sensitivity atlas for 95 NRAS missense variants covering >99% of all NRAS recurrent mutation - RMC-6236 and RMC-7977 shows broad and potent activity across major NRAS hotspot mutations - Defines NRAS mutations with reduced susceptibility to provide actionable information for clinical trial stratification - RAS(ON) inhibition and napabucasin shows synergistic anti-tumor activity in NRAS-mutated melanoma
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