P3-16-16: Overcoming EGFR Resistance Using Dasatinib in Combination with Cetuximab and Cisplatin in Triple Negative Breast Cancer Cell Lines.

Abstract Background: Patients presenting with triple negative breast cancers (TNBC's) have a poorer prognosis compared to those with other subtypes of breast cancer, and effective therapeutic targets have yet to be identified. The majority of TNBC's overexpress EGFR, however studies have demonstrated that EGFR inhibition as a monotherapy is ineffective. Interestingly, adding the EGFR inhibitor, cetuximab to cisplatin chemotherapy doubled both the response rate and time to progression compared with patients only on cisplatin. c-Src tyrosine kinase plays a critical role in signal transduction downstream of growth factor receptors, and has been found to contribute to the resistance of TNBC cell lines through the phosphorylation of EGFR. We hypothesize that dasatinib, a c-Src inhibitor, may help overcome EGFR resistance and in combination therapy enhance the cytotoxic activity. Material and Methods: A panel of breast cancer cell lines, including 7 triple negative cell lines, were tested using increasing doses of dasatinib (1 nM to 10 μM), cetuximab (1 μg/ml to 100 μg/ml), and cisplatin (10 nM to 10 μM) alone and in combination. Growth inhibition was determined after 3 days of treatment using the MTT colorimetric assay, and apoptosis was assessed through Caspase-3 activation and TUNEL assays. Results: All cell lines were generally resistant to cetuximab, with 100 μg/ml required to decrease cell viability. Two TNBC lines, SUM149 and SUM229, showed an additional decrease in cell viability with dasatinib added to cetuximab, while SUM102 and BT20 cells showed an additional decrease in viability using the dasatinib and cisplatin combination, compared to single agents. In 4 out of 7 TNBC lines, the combination of dasatinib, cisplatin, and cetuximab showed a significant decrease in cell viability compared to the combination without dasatinib (p-value < 0.02). The decrease in proliferation using the combination of dasatinib, cisplatin, and cetuximab was due to an increase in apoptosis. In contrast, this combination did not increase the loss of cell viability or apoptosis in ER/PR+ and HER2+ breast cancer cell lines. Discussion: Targeting c-Src family kinases with dasatinib may help overcome the resistance to EGFR inhibition in triple-negative breast cancer. This may have significant clinical implications in treating TNBC patients, and hence further investigation into the mechanism of this effect is warranted. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-16.