Abstract 5511: Characterization of molecular and functional consequences of somatic NF1 mutations in non-small cell lung cancers

Abstract

Driver molecular alterations are found in >20% of non-small cell lung cancers (NSCLCs). They specifically target the RAS-MAPK pathway, including the EGFR, KRAS, and BRAF oncogenes. NF1 is a tumor suppressor gene that encodes neurofibromin, an inhibitor of the RAS-MAPK pathway. NF1 mutation detection is challenging owing to its large size, the presence of numerous pseudogenes, and the absence of mutation hotspot. According to The Cancer Genome Atlas data (TCGA), NF1 somatic mutations are found in ~15% of lung cancer. However, NF1 mutations in NSCLCs are not extensively explored in NSCLC to date. We hypothesized that NF1 alterations could define a specific NSCLC population with distinct clinical and molecular profiles. We performed NF1 analysis using next-generation sequencing in NSCLC surgical specimens with known KRAS, EGFR, TP53, BRAF, HER2, and PIK3CA status. We evaluated the specificities of NF1-mutated NSCLCs. Then, we established of NF1-mutated cellular models with different NF1 wild-type (WT) cell lines. We chose two NSCLC cell lines (A549 and NCI H-1703, ATCC), and one nontumorigenic human bronchial epithelial cell line (HBE4-E6/E7-C1, ATCC). Mono- and biallelic NF1 mutations were established using CRISPR-Cas9 and nickase CRISPR-Cas9 technologies. In vitro functional tests and drug screening were performed using these isogenic cell models. In our series of 138 lung adenocarcinoma specimens, 25 tumors showed NF1 mutations (18%) and 11 showed NF1 deletions (8%). NF1 mutations were rarely associated with other mutations. Most of patients with NF1 alterations were males (72%) and smokers (75%). Overall survival and disease-free survival were statistically better in patients with NF1 alteration patients (N=35) than in KRAS mutated patients (N=30) in univariate analysis. There were more NF1 mutations in patients treated by neoadjuvant chemotherapy (p = 0.01). Then, we established cellular models of NF1-mutated NSCLC, using nickase and CRISPR-Cas9 technology. In HBE4-E6/E7-C1 cells, mono- and biallelic NF1 mutations were generated. Loss of NF1 expression was confirmed by Western blot: partial and total loss-of-expression of neurofibromin was found in monoallelic and biallelic NF1 mutated cell lines, respectively. Using Western blot, we showed that pERK/ERK ratio was higher in NF1-mutated cell lines versus WT cell lines, confirming that NF1 loss-of-function triggered RAS-MAPK pathway activation. Transcriptome analysis confirmed this activation. Pharmacologic screen (including MEK inhibitors) in this isogenic NSCLC model will enable us to assess specific vulnerabilities due to NF1 mono- or biallelic mutations. Our results confirm that NF1 is frequently mutated and represents a distinct subtype of NSCLCs. A better comprehension of functional consequences of NF1 mutations, including mono- and biallelic alterations, may open new avenues for NSCLC therapy. Citation Format: Camille Tlemsani, Nicolas Pecuchet, Aurélia Gruber, Audrey Mansuet-Lupo, Diane Damotte, Marco Alifano, Jennifer Varin, Ingrid Laurendeau, Armelle Luscan, Benoit Rousseau, Beatrice Parfait, Ivan Bieche, Audrey Briand, Benoit Terris, Helene Blons, Karen Leroy, Dominique Vidaud, Michel Vidaud, Pierre Laurent-Puig, Eric Pasmant. Characterization of molecular and functional consequences of somatic NF1 mutations in non-small cell lung cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5511.