Abstract A041: Targeting EGFR reverses paclitaxel resistance associated with ABCB1 overexpression in triple-negative breast cancer

Background: Breast cancer represents a heterogeneous group of tumors that exhibit a wide spectrum of clinical, pathologic, and molecular features. Of these tumors, triple-negative breast cancer (TNBCs), shows one of the most aggressive clinical behaviors with distinctive metastatic patterns and very poor prognosis. TNBC is characterized by the absence of expression of estrogen receptor, progesterone receptor, and low levels of human epidermal growth factor (HER2). Paclitaxel (PTX) is among the most effective anti-cancer agents developed in the past decades, which is widely used in the treatment of patients with locally advanced and metastatic breast cancer. TNBCs are initially highly responsive to PTX however; the majorities of TNBC patients acquire resistance and develop progressive disease. Therefore, acquired resistance to paclitaxel has become one of the major obstacles in the successful treatment of patients with TNBC. Several mechanisms of resistance to paclitaxel has been identified, however there is little data about mechanisms of resistance to chemotherapy in TNBCs. Methods: In order to investigate the molecular mechanisms of acquired resistance to PTX in TNBCs, we developed four resistant TNBC cell lines (BT20, SUM149, MA-MB-231 and MDA-MB-436) by exposure of cells to increasing concentrations of PTX. We used an integrative analysis of array CGH and gene expression data to gain insights into the interplay of functional changes of the genome in TNBC resistant cell lines. Results: We found a novel amplification of the ABCB1 gene in BT20 and SUM149 resistant cell lines only. Gene expression analysis revealed significant up-regulation of expression of ABCB1 and EGFR ligands in SUM149 and BT20 resistant cells compared to parental cell lines. The functional activity of ABC transporters assessed using Rhodamine 123 efflux assay demonstrated a marked increase in the efflux of rhodamine in SUM149-R and BT20-R, which was reversed by verapamil. We treated resistant cells with two anti-EGFR drugs, lapatinib and neratinib, which are also known ABC transporter inhibitors, and found that both drugs inhibited rhodamine 123 efflux and restored sensitivity to PTX in these PTX-resistant TNBC cells. Conclusion: This is the first report of ABCB1 gene amplification in paclitaxel resistant triple negative breast cancer cells. Our results suggest that ABCB1 gene amplification and EGFR ligand over-expression plays a critical role in the development of PTX resistance in TNBC cells, and that this resistance can be targeted by therapy with anti-EGFR agents. Thus, ABCB1 gene amplification and EGFR ligand expression may be novel predictive biomarkers for both chemotherapy and anti-EGFR therapy in TNBCs. Citation Format: Elaheh Ahmadzadeh, Ewa Przybytkowski, Adriana Aguilar-Mahecha, Mark Basik. Targeting EGFR reverses paclitaxel resistance associated with ABCB1 overexpression in triple-negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A041.