Effects of SRC Inhibition on Survival, Migration and Invasion of Human Breast Cancer Cells Resistant to Lapatinib

ABSTRACT Background HER2, a member of the HER family, is a transmembrane tyrosine kinase receptor overexpressed in almost 30% of breast cancer patients. Lapatinib is a small molecule HER2 inhibitor approved in metastatic breast cancer patients after trastuzumab failure. Unfortunately, the resistance against lapatinib is observed even in responding patients. Src is an intracellular kinase involved in tumor growth, angiogenesis and migration and it is related to trastuzumab resistance in human breast cancer cell lines. Materials and methods We used different HER2 expressing human breast cancer cell lines, such as MDA-MB-361, MDA-MB-231 and BT474 (sensitive to lapatinib) JIMT-1 and KPL-4 (low sensitivity against lapatinib), and MDA-MB-361-LR (acquired resistance to lapatinib). We performed survival, migration and invasion assays and WB analysis in all cell lines treated with lapatinib, saracatinib (a Src inhibitor) or the combination. We also used nude mice xenografted with JIMT-1 cells and in vivo artificial metastatic assay. Results We observed that the combination treatment of lapatinib plus saracatinib is able to inhibit survival, migration and invasion in vitro and to regulate several proteins such as Src, Akt, MAPK, paxillin and FAK in all cancer cell lines tested. In nude mice xenografted with JIMT-1 cells, the combined treatment reduced tumor growth, prolonged survival and strongly decreased the incidence of lung metastases. Interestingly, we observed that Src preferentially binds to HER2 in lapatinib sensitive cells and with EGFR in resistant ones. EGFR inhibition, through the use of cetuximab or siRNA silencing, strongly enhanced the effect of lapatinib on the growth of resistant cancer cells. The combined treatment of lapatinib and cetuximab, moreover, significantly reduced the activation of several intracellular transducers. Conclusions We demonstrated that Src plays an important role in the development of resistance to lapatinib in breast cancer cell lines, in particular affecting invasion and migration, and that EGFR may mediate its activation. These results may suggest the clinical development of lapatinib and cetuximab combination in patients resistant to lapatinib. Disclosure All authors have declared no conflicts of interest.