Lung cancer driven by BRAF G469V mutation is targetable by EGFR kinase inhibitors

J Thorac Oncol. 2021 Oct 11;S1556-0864(21)03205-6. doi: 10.1016/j.jtho.2021.09.008. Online ahead of print.

Abstract

Introduction: Mutations in BRAF occur in 2-4% of lung adenocarcinoma (LUAD) patients. Combination dabrafenib/trametinib or single-agent vemurafenib is approved only for patients with cancers driven by the V600E BRAF mutation. Targeted therapy is not currently available for patients harboring non-V600 BRAF mutations.

Methods: An LUAD patient-derived xenograft (PDX) model (PHLC12) with wild-type and non-amplified epidermal growth factor receptor (EGFR) was tested for response to EGFR tyrosine kinase inhibitors (TKI). A cell line derived from this model (X12CL) was also used to evaluate drug sensitivity and to identify potential drivers by siRNA knockdown. Kinase assays were used to test direct targeting of the candidate driver by the EGFR TKIs. Structural modeling including, molecular dynamics (MD) simulations, and binding assays were conducted to explore the mechanism of off-target inhibition by EGFR TKIs on the model 12 driver.

Results: Both PDX PHLC12 and the X12CL cell line were sensitive to multiple EGFR TKIs. The BRAFG469V mutation was found to be the only known oncogenic mutation in this model. siRNA knockdown of BRAF, but not the EGFR, killed X12CL, confirming BRAFG469V as the oncogenic driver. Kinase activity of the BRAF protein isolated from X12CL was inhibited by treatment with the EGFR TKIs gefitinib and osimertinib, and expression of BRAFG469V in non-EGFR-expressing NR6 cells promoted growth in low serum, which was also sensitive to EGFR TKIs. . Structural modeling, MD simulations, and in vitro binding assays support BRAFG469V being a direct target of the TKIs.

Conclusion: Clinically approved EGFR TKIs can be repurposed to treat NSCLC patients harboring the BRAFG469V mutation.

Keywords: NSCLC; drug repurposing; off-target; therapeutics; tyrosine kinase inhibitor.