Integration of Ca signaling regulates the breast tumor cell response to simvastatin and doxorubicin.

Recent studies have suggested that the lipid-lowering agent simvastatin holds great promise as a cancer therapeutic; it inhibits the growth of multiple tumors, including triple-negative breast cancer. Doxorubicin- and simvastatin-induced cytotoxicity has been associated with the modulation of Ca signaling, but the underlying mechanisms remain incompletely understood. Here we identify how Ca signaling regulates the breast tumor cell response to doxorubicin and simvastatin. These two drugs inhibit cell survival while increasing apoptosis in two human breast cancer cell lines and five primary breast tumor specimens through the modulation of Ca signaling. Signal transduction and functional studies revealed that both simvastatin and doxorubicin trigger persistent cytosolic Ca release, thereby stimulating the proapoptotic BIM pathway and mitochondrial Ca overload, which are responsible for metabolic dysfunction and apoptosis induction. Simvastatin and doxorubicin suppress the prosurvival ERK1/2 pathway in a Ca-independent and Ca-dependent manner, respectively. In addition, reduction of the Ca signal by chelation or pharmacological inhibition significantly prevents drug-mediated anticancer signaling. Unexpectedly, a scratch-wound assay indicated that these two drugs induce rapid cell migration, while inhibiting cell invasion and colony formation in a Ca-dependent manner. Further, the in vivo data for MDA-MB-231 xenografts demonstrate that upon chelation of Ca, the ability of both drugs to reduce the tumor burden was significantly reduced via caspase-3 deactivation. Our results establish a calcium-based mechanism as crucial for executing the cell death process triggered by simvastatin and doxorubicin, and suggest that combining simvastatin with doxorubicin may be an effective regimen for the treatment of breast cancer.