RASA1 and NF1 are preferentially co-mutated and define a distinct genetic subset of smoking-associated non-small cell lung carcinomas sensitive to MEK inhibition.

Abstract

Purpose: Ras-GTPase activating proteins (RasGAPs), notably NF1 and RASA1, mediate negative control of the RAS/MAPK pathway. We evaluated clinical and molecular characteristics of NSCLC with RASA1 mutations in comparison with NF1-mutated cases. Experimental Design: Large genomic datasets of NSCLC [MSK-IMPACT™ dataset at MSKCC (n=2004), TCGA combined lung cancer dataset (n=1144)] were analyzed to define concurrent mutations and clinical features of RASA1-mutated NSCLCs. Functional studies were performed using immortalized human bronchial epithelial cells (HBECs) and NSCLC lines with RasGAP truncating mutations in RASA1, NF1, or both. Results: Overall, approximately 2% of NSCLCs had RASA1 truncating mutations, and this alteration was statistically, but not completely, mutually exclusive with known activating EGFR (p=0.02) and KRAS (p=0.02) mutations. Unexpectedly, RASA1 truncating mutations had a strong tendency to co-occur with NF1 truncating mutations (p<0.001). Furthermore, all patients (16/16) with concurrent RASA1/NF1 truncating mutations lacked other known lung cancer drivers. Knockdown of RASA1 in HBECs activated signaling downstream of RAS and promoted cell growth. Conversely, restoration of RASA1 expression in RASA1-mutated cells reduced MAPK and PI3K signaling. While growth of cell lines with inactivation of only one of these two RasGAPs showed moderate and variable sensitivity to inhibitors of MEK or PI3K, cells with concurrent RASA1/NF1 mutations were profoundly more sensitive (IC50: 0.040μM trametinib). Finally, simultaneous genetic silencing of RASA1 and NF1 sensitized both HBECs and NSCLC cells to MEK inhibition. Conclusions: Cancer genomic and functional data nominate concurrent RASA1/NF1 loss of function mutations as a strong mitogenic driver in NSCLC which may sensitize to trametinib.