Downregulation and subcellular distribution of HER2 involved in MDA-MB-453 breast cancer cell apoptosis induced by lapatinib/celastrol combination.

PURPOSE To investigate the effect and related molecular mechanisms of lapatinib/celastrol combination or single-agent treatment in HER2/neu-overexpressing MDA-MB-453 breast cancer cells. METHODS The effects of treatment with lapatinib, celastrol or their combination on cell growth were determined using MTT assay. Drug synergy was determined using the combination index (CI) methods derived from Chou-Talalay equations using CalcuSyn software. Apoptotic morphology was observed by fluorescence microscope with Hoechst 33258 staining. Changes of apoptotic and growth pathways-related proteins were analysed by Western blot. The expression of HER2 of cell surface was performed by flow cytometry. Subcellular distribution of HER2 was observed by immunofluorescence study. RESULTS Combination celastrol and lapatinib produced strong synergy in growth inhibition and apoptosis in comparison to single-agent treatment in HER2/neu-overexpressing MDA-MB-453 cells. Interestingly, compared with celastrol treatment alone, lapatinib/celastrol combination induced more HER2 membrane protein downregulation and ectopic to cytoplasm and nucleus in MDA-MB-453 cells. CONCLUSION The combination of celastrol and lapatinib could be used as a novel combination regimen which provides a strong anticancer synergy in the treatment of HER2/neu-overexpressing cancer cells.