Abstract A90: Feedback activation of EGFR drives resistance to BRAF(V600E) inhibition in breast cancer.

Abstract

Abstract Purpose: The BRAFV600E mutation has shown significant activity in the several tumor types, including breast, melanoma, and colorectal cancer. The selective inhibitor of BRAFV600, PLX4032 (vemurafenib), has shown clinical response in patients with BRAFV600Emelanoma, especially but not in 20-40% of patients despite the presence of a BRAFV600E. Thus, it is important to understand the molecular mechanisms of resistance to improve outcomes in patient with BRAF mutation. We aimed to investigate the cause of the limited therapeutic effect of PLX4032 in cancers harboring the mutant BRAFV600E gene. Experiment Design: We investigated the correlation between RTK pathway activation and sensitivity to PLX4032 in several types of cancer cell lines harboring the BRAFV600E. Cell lines were exposed to PLX4032 and pharmacologic inhibitors and in combination with each other to inhibit RTK signaling. Cell survival and apoptosis were measured using MTT assay, Annexin V/PI staining, and colony forming assay. Real-time PCR, Western blots were performed to determine possible mechanisms of resistance and predictors of synergy.Results: In a comparison with BRAFV600E cancer cells, we show that PLX4032-resistant MDA-MB breast cancer cells have the enhanced level of p-EGFR in the presence of PLX4032. PLX4032 treatment causes a rapid feedback activation of EGFR and up-regulation of AKT in MDA-MB cells, which supports continued proliferation in the presence of BRAFV600E inhibition. We show that EGFR activation acquired resistance to BRAF inhibition using EGFR inhibitor. Gefitinib, EGFR inhibitor, shows strong synergy with a BRAFV600E inhibitor in short-time and long-time treatment. In addition, we investigated that rapid feedback activation of EGFR regulates the expression of epithelial to mesenchymal transition (EMT) regulators by Real-time PCR, which resulted in high migratory potentials in invasion assay and wound healing assay. These results provide rational therapeutic strategies for clinical studies in this poor prognosis subtype of BRAFV600E inhibitor. Conclusions: Our data suggest that BRAFV600E mutant breast cancers, for which there are currently no targeted treatment options available, might benefit from combination therapy consisting of BRAF and EGFR inhibitors. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A90. Citation Format: Yj Yang, HJ Na, Ws Kim, JP Bong, SJ Beak, Jw Kim, Jk Park, Hj Hong, Dy Shin, Jh Kwon, Ej Lee, Yw Koh, Ec Choi. Feedback activation of EGFR drives resistance to BRAF(V600E) inhibition in breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A90.