Characteristics of lung cancers harboring NRAS mutations

Abstract

Purpose: We sought to determine the frequency and clinical characteristics of patients with lung cancer harboring NRAS mutations. We used preclinical models to identify targeted therapies likely to be of benefit against NRAS-mutant lung cancer cells.

Experimental design: We reviewed clinical data from patients whose lung cancers were identified at six institutions or reported in the Catalogue of Somatic Mutations in Cancer (COSMIC) to harbor NRAS mutations. Six NRAS-mutant cell lines were screened for sensitivity against inhibitors of multiple kinases (i.e., EGFR, ALK, MET, IGF-1R, BRAF, PI3K, and MEK).

Results: Among 4,562 patients with lung cancers tested, NRAS mutations were present in 30 (0.7%; 95% confidence interval, 0.45%-0.94%); 28 of these had no other driver mutations. 83% had adenocarcinoma histology with no significant differences in gender. While 95% of patients were former or current smokers, smoking-related G:C>T:A transversions were significantly less frequent in NRAS-mutated lung tumors than KRAS-mutant non-small cell lung cancer [NSCLC; NRAS: 13% (4/30), KRAS: 66% (1772/2733), P < 0.00000001]. Five of 6 NRAS-mutant cell lines were sensitive to the MEK inhibitors, selumetinib and trametinib, but not to other inhibitors tested.

Conclusion: NRAS mutations define a distinct subset of lung cancers (∼1%) with potential sensitivity to MEK inhibitors. Although NRAS mutations are more common in current/former smokers, the types of mutations are not those classically associated with smoking.

Figure 1. Distribution of the types of mutations in NRAS and KRAS mutated lung cancers

A. Q61 was the most frequently mutated codon in 30 NRAS mutated lung cancers (80%). B. The type of mutations in KRAS (COSMIC). 92% of mutations occurred at codon G12. C. Comparison of the types of mutations in KRAS (COSMIC) and NRAS. G:C >T:A transversions were significantly more common in KRAS (1772/2733, 66%) than NRAS (4/30, 13%) mutated lung cancers (Chi-square test; p<0.00000001).

Figure 2. Sensitivity profiles of 6 NRAS mutant lung cancer cell lines tested against various kinase inhibitors

A. IC50 values derived from growth inhibition assays were plotted for each drug and each cell line. HCC15 cells were resistant to MEK inhibitors but sensitive to the combination of a MEK inhibitor plus linsitinib (see text and Figure S2 for details). B. MEK inhibitors but not erlotinib led to de-phosphorylation of ERK in NRAS mutated cells. Erlotinib inhibited phosphorylation of EGFR, AKT and ERK in PC-9 cells which harbor an EGFR mutation. C. siRNA-mediated knockdown of NRAS inhibits growth of the NRAS mutated HCC1195 and H1299 cells but not of PC-9 cells. Mean +- SD of three independent experiments performed in hextuplicate replicates is shown. *, **, P < 0.01 (Student’s t-test) for the comparison of siRNAs against NRAS versus scrambled controls in HCC1195 and H1299. Lipo – lipofectamine control; scr – scrambled siRNA control.