Simvastatin Enhances the Cytotoxic Effects of Doxorubicin in a Mammary Adenocarcinoma Cell Model by Involving Connexin 43

Gap Junctions channels formed by Connexins (Cx) provide intercellular communication enabling the coordination of cell growth, differentiation, and metabolism, and their reduction has been shown in many tumor types. Expression levels of Cx43, the most extensively studied Gap Junctions forming protein, are reduced or completely absent in breast cancer cells, while their overexpression correlates with increased cellular permeability to anticancer agents and, consequently, reduced resistance to drug treatments. So, drug associations targeting Cx43 are being considered to overcome chemoresistance. Previous studies demonstrated that Simvastatin (Sim) interferes with Cx43 expression and localization, and chemo-sensitizing effects of Sim in several tumor cell lines treated with antineoplastic chemotherapeutics have been shown. This study aimed to evaluate whether Sim cotreatment enhances Doxorubicin-induced cytotoxicity by affecting Cx43 expression and/or phosphorylation, so MCF-7 cells were treated with Sim (10 µM) for 4 h and then coexposed to Sim and Doxorubicin (1 µM) for 20 h. In Sim cotreated cells, increased membrane levels of Cx43 have been shown; moreover, decreased levels of Cx43 phosphorylated on Ser368 and Ser262 residues, involved in channel closure and disruption of cell-cell communication, have been demonstrated in these cells. In Sim cotreated cells increased Doxorubicin uptake and enhanced Doxorubicin-induced cytotoxic effects have been demonstrated together with reduced migratory capacity. Our data support the notion that Sim cotreatment could be a possible strategy to overcome chemoresistance, since the observed increase in Cx43 membrane levels, and the concomitant reduction of Cx43 phosphorylation, could be responsible for increased sensitization of cells to Doxorubicin treatment.