Resistance mechanisms to genetic suppression of mutant NRAS in melanoma.

Targeted therapies have revolutionized cancer care, but the development of resistance remains a challenge in the clinic. To identify rational targets for combination strategies, we used an established melanoma mouse model and selected for resistant tumors following genetic suppression of NRAS expression. Complete tumor regression was observed in all mice, but 40% of tumors recurred. Analysis of resistant tumors showed that the most common mechanism of resistance was overexpression and activation of receptor tyrosine kinases (RTKs). Interestingly, the most commonly overexpressed RTK was Met and inhibition of Met overcame NRAS resistance in this context. Analysis of NRAS mutant human melanoma cells showed enhanced efficacy of cytotoxicity with combined RTK and mitogen-activated protein kinase kinase inhibition. In this study, we establish the importance of adaptive RTK signaling in the escape of NRAS mutant melanoma from inhibition of RAS and provide the rationale for combined blockade of RAS and RTK signaling in this context.