BRAF Mutations: Classes I, II and III in NSCLC Patients Included in the SLLIP Trial, Targeted Treatment According to Class

Background: BRAF V600 mutations have been found in 2% of non-small cell lung cancer (NSCLC) patients, with FDA approved treatment of dabrafenib plus trametinib and progression free survival (PFS) of 10.9 months. However, 50-80% of BRAF mutations in lung cancer are non-V600, and can be class 2, with intermediate to high kinase activity and RAS independence, or class 3, with impaired kinase activity, upstream signaling dependence and consequently sensitivity to receptor tyrosine kinase (RTK) inhibitors. Non-V600 tumors require combinatory therapy with RAF/MEK inhibitors and blockers of RTK signaling, like SHP2 (PTPN11) inhibitors. Method: Plasma DNA of 185 newly diagnosed advanced lung adenocarcinoma patients was examined for BRAF and other mutations with a clinically validated cell-free DNA (cfDNA) assay (Guardant360, Guardant Health Inc. CA, U.S), and results were correlated with patient outcome. In addition, two NSCLC cell lines and one Triple Negative Breast Cancer (TNBC), H1395 (class 2 BRAF mutation), H1666 (class 3 BRAF mutation) and MDA-MB-231 (class 2 BRAF mutation) were treated with single or combined BRAF, MEK and SHP2 inhibitors and cell viability was assessed. Result: BRAF mutations were found in 17/185 (9%) and BRAF amplification in five patients (3%). Three patients had BRAF V600E mutations (2%) and 14 patients non-V600 BRAF mutations (8%), including four class 2 and four class 3 mutations. Patients were treated with chemotherapy and/or immunotherapy, or targeted therapy for other co-alterations. PFS was 1.8, 6.1, 5.0, 5.3 and 5.3 months for Class 1, 2, 3, other BRAF, and BRAF amplification, respectively. These low survival rates indicate that new treatment options are urgently needed. In vitro results confirm sensitivity of class 3, and resistance of class 2 BRAF mutations to single SHP2 inhibition with RMC-4550 and SHP099, with similar results in TNBC and lung cancer cells. Combined dabrafenib and trametinib treatment indicated antagonistic effects, especially in the class 3 BRAF mutant cell line. Concomitant MEK and SHP2 inhibition was synergistic in both class 2 and 3 BRAF mutations. Conclusion: It is evident that different classes of BRAF mutations require distinct treatments, which could even outweigh tumor type. Therefore, we should examine BRAF class in daily clinical practice. Upfront targeting of the MAPK signaling pathway combined with SHP2 inhibitors reveals synergistic interactions, and additional inquisition may pave the way for new treatment options in the most frequently found mutations in BRAF patients. Keywords: BRAF mutations, NSCLC, SLLIP trial