Epidermal growth factor receptor (EGFR) inhibition in triple-negative breast cancer (BrCa)

Abstract

14071 Background: Triple-negative BrCa lacks expression of hormone receptors and HER-2 but does express EGFR. It is associated with early relapse and poor survival. There is no targeted therapy for triple-negative BrCa. We are studying the potential role of EGFR inhibition. Methods: EGFR expression was examined in triple-negative BrCa cell lines, (BT20, HCC1937, and MDA-MB-231) by western blot. IC50 assays were determined for three EGFR inhibitors, gefitinib (G) and erlotinib (T), which are small-molecule tyrosine kinase inhibitors, and cetuximab (E) which is a monoclonal antibody against EGFR, and chemotherapy (CRx) drugs docetaxel (D) and carboplatin (P)), using the acid phosphatase assay. The controls were HER2+ BrCa cell lines, BT474 and SKBR3 which express low levels of EGFR. Results: The three triple-negative cell lines over-express EGFR. IC50 values for G and T were significantly higher in the triple-negative than in the HER2+ cell lines. E did not cause significant inhibition in any cell line (max inhibition 20% at 100 μg/ml E). IC50 values for G were lower than for T in the triple-negative cell lines (IC50s for HCC1937: G - 8.4 ± 1.5 μM; T - 26.2 ± 9.3 μM). Combined EGFR inhibition with CRx was tested in HCC1937 cells. G combined with P or with D for 5 days showed an additive effect on inhibition of proliferation ( Table 1 ). Alternate scheduling of the drugs did not significantly influence response. Conclusions: Our results suggest that triple-negative BrCa cells over-express EGFR but are not as sensitive to EGFR inhibition as HER2+ BrCa cells. However, EGFR inhibition may enhance response to CRx in triple-negative BrCa. [Table: see text] No significant financial relationships to disclose.