Alterations in tyrosine kinase expression or functionality have been linked to tumor growth, and detailed analysis of tyrosine kinase pathways has led to the development of novel anticancer drugs based on their inhibition. The aim of the present work was to examine the cytotoxicity and cellular alterations correlated with multidrug resistance mechanisms induced by three tyrosine kinase inhibitors, lapatinib, sorafenib and gefitinib. The study was performed on three breast cancer cell lines (BRC-230, MCF-7 and SkBr3). Drug-induced growth inhibition was detected by Sulforhodamine B analysis. Apoptosis, cytosolic calcium alteration, extrusion pump activity and mitochondrial membrane depolarization were assessed by flow cytometry. Drug efflux-related gene expression was analyzed by RT-PCR and drug target protein expression was evaluated by Western Blot. Lapatinib and gefitinib induced a cytotoxic effect and mitochondrial membrane depolarization in BRC-230 and SkBr3 cells, while sorafenib induced apoptosis and a high and rapid dissipation of mitochondrial potential in all cell lines. Moreover, all three drugs produced a rapid cytosolic calcium mobilization from endoplasmic reticulum stores in the investigated cell lines and a strong decrease in multidrug transporter activity in BRC- 230 and MCF-7 cells. Mitochondrial membrane depolarization and inhibition of multidrug transporter activity induced by tyrosine kinase inhibitors were independent of cytosolic calcium mobilization. These data suggest that the investigated drugs possess mechanisms of action that are independent of drug target expression, opening up further possibilities for the development of new therapeutic strategies.
Keywords: Tyrosine kinase inhibitor, breast cancer, in vitro study, calcium, multidrug resistance, mitochondrial depolarization, ABC transporters
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