Abstract 3581: Characterization of human breast cancer cells with acquired resistance to the EGFR/ErbB-2 tyrosine kinase inhibitor lapatinib

The epidermal growth factor receptor (EGFR) and the ErbB-2 receptor are co-expressed in a subset of breast carcinomas that show a more aggressive phenotype. The dual EGFR/ErbB-2 tyrosine kinase inhibitor lapatinib has been recently approved for the treatment of metastatic breast cancer patients whose tumors overexpress ErbB-2. We investigated the mechanisms of acquired resistance to lapatinib in breast cancer cells. For this purpose, we used as model the SK-Br-3 human breast carcinoma cell line that express high levels of ErbB-2, and moderate levels of EGFR and ErbB-3. We selected lapatinib-resistant SK-Br-3 cells by stepwise dose escalation of lapatinib. After six months of selection, we isolated SK-Br-3 cells that were able to grow in 1 μM lapatinib. The IC50 of lapatinib for parental SK-Br-3 cells was 140 nM, whereas the IC50 for the lapatinib-resistant SK-Br-3 derived cell line (Lap-R) was > 4 μM. Treatment with lapatinib significantly inhibited the activation of EGFR, ErbB-2 and ErbB-3 in both parental and Lap-R SK-Br-3 cells. However, following treatment with lapatinib, Lap-R cells showed a persistent activation of AKT and MAPK, which in contrast were completely inhibited in parental SK-Br-3 cells, as measured by both western blotting and a Luminex-based phosphoprotein array. In addition, treatment with lapatinib produced a slight activation of c-Src in parental cells, whereas significant levels of c-Src activation were detected in Lap-R cells cultured in presence of lapatinib. Lap-R cells also showed higher levels of expression of the chemokine receptor CXCR-4 than parental cells. In agreement with these findings, Lap-R cells showed a significantly higher ability to invade a matrigel-coated membrane as compared with parental SK-Br-3 cells, as measured with a Boyden-chamber based colorimetric invasion assay. Preliminary findings demonstrate that inhibition of c-Src with the selective src kinase inhibitor saracatinib produces a more significant inhibition of Lap-R cell invasion as compared with parental SK-Br-3 cells. Taken together, these findings suggest that activation of c-Src signalling might play a role in acquired resistance to lapatinib in breast cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3581. doi:10.1158/1538-7445.AM2011-3581