Resistance mechanisms to genetic suppression of mutant NRAS in melanoma

Abstract

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 revealed 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 revealed enhanced efficacy of cytotoxicity with combined RTK and MEK 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.

Combining ERBB family and MET inhibitors is an effective therapeutic strategy in cutaneous malignant melanoma independent of BRAF/NRAS mutation status

“…Increased expression levels of MET, EGFR, and ERBB3 have been previously associated with increase in both CMM progression and metastasis 24,25 . To study the effects mediated by drug combination on cell migration, we performed a scratch assay.…”

BRAF inhibition in melanoma is associated with the dysregulation of histone methylation and histone methyltransferases

“…Multiple genetic alterations can be introduced into the same cell, in the context of an unaltered microenvironment. We previously established the validity of the RCAS/TVA system to generate melanoma in vivo by delivering viral BRAF, NRAS, AKT, and MEK mutants in combination with Cre to melanocytes in Cdkn2a lox/lox and Pten lox/lox mice [33] , [39] , [40] . To allow for regulation of activated BRAF expression in vivo using the Tet-regulated system, we utilized the RCAN(A) vector as opposed to RCAS, wherein expression is decoupled from the viral long-terminal repeat (LTR) through the deletion of a key splice acceptor site, and is instead driven from a Tet-responsive element (TRE) [33] .…”

“…3 ). We previously reported c-Met amplification and overexpression can drive the escape of NRAS mutant melanoma from inhibition of RAS [40] . Accordingly, we evaluated tumor samples and controls for overexpression of Met; however, less than 3 of the resistant tumors overexpressed c-Met ( Supplementary Fig.…”

“…This approach is useful as paired pre-biopsied samples of melanomas that are responding to treatment are nearly impossible to obtain. The targeted delivery of BRAF V600E , NRAS Q61R , or MEK mutants in combination with Cre to Cdkn2 lox/lox Pten lox/lox melanocytes led to the development of melanomas that closely mimic the human disease [26] , [39] , [40] . Targeted delivery of Tet-Off, CRE, and TRE-BRAF VE , Dct::TVA; Cdkn2a lox/lox ; Pten lox/lox to melanocytes caused mice to develop melanomas that regressed when they were fed doxycycline-containing food; however, after a long latency, the tumors re-occurred.…”

Pathology and Molecular Biology of Melanoma

“…One of the first tested and effective strategies is combining BRAF inhibitors with MEK inhibitors, leading to improved response rates and delayed resistance compared to BRAF inhibitor monotherapy like in COMBI-d and COMBI-v trials, but resistance to BRAF inhibitors often involves the activation of parallel signaling pathways [73][74][75][76][77].…”