Clinical and Preclinical Activity of EGFR Tyrosine Kinase Inhibitors in Non-Small-Cell Lung Cancer Harboring <i>BRAF</i> Class 3 Mutations.

Abstract

Patients with tumors harboring <i>BRAF</i> class 3 mutations lack targeted therapies. These mutations are characterized by low/absent BRAF kinase domain activation and are believed to amplify already active RAS signaling, potentially triggered by receptor tyrosine kinases like EGFR. Two patients with <i>BRAF</i> class 3-mutated metastatic non-small-cell lung cancer (NSCLC) were treated with erlotinib at our Institution after failure of standard therapies. Two cell lines were established from patients with <i>BRAF</i> class 3-mutated NSCLC, and their sensitivity to EGFR tyrosine kinase inhibitors (EGFR-TKIs) was assessed using <i>EGFR-</i>mutated, <i>BRAF</i> class 1 and 2-mutated, and <i>KRAS</i>-mutated NSCLC cell lines as controls. Patient 1, a 60-year-old male with BRAF^D594N-mutated NSCLC, achieved complete response to erlotinib after progression on first- and second-line chemotherapy. Patient 2, a 60-year-old female with BRAF^D594G-mutated NSCLC, achieved partial response to erlotinib after progression on first-line chemoimmunotherapy. High baseline phosphorylated EGFR values and reduced EGFR activation following erlotinib were observed in <i>BRAF</i> class 3-mutated and <i>EGFR</i>-mutated cell lines, but not in <i>BRAF</i> class 1-mutated, <i>BRAF</i> class 2-mutated, or <i>KRAS</i>-mutated lines. Erlotinib inhibited 2-dimensional growth in <i>BRAF</i> class 3-mutated cell lines (IC₅₀ 6.33 and 7.11 µM) and in the <i>BRAF</i> class 2-mutated cell line (IC₅₀ 5.51 µM), albeit at higher concentrations than in <i>EGFR</i>-mutated lines, whereas it showed no effect on <i>BRAF</i> class 1-mutated (IC₅₀, >25 µM) or <i>KRAS</i>-mutated (IC₅₀, >25 µM) lines. These findings were corroborated by 3-dimensional and sphere formation assays. In the Cancer Cell Line Encyclopedia, <i>BRAF</i> class 3-mutated NSCLC cell lines showed greater sensitivity to EGFR-TKIs compared with <i>BRAF</i> class 2-mutated and <i>KRAS</i>-mutated lines. <i>BRAF</i> class 3 mutations in NSCLC may identify a novel targetable population sensitive to EGFR-TKIs.