Curcumin-Induced Apoptosis in PC3 Prostate Carcinoma Cells Is Caspase-Independent and Involves Cellular Ceramide Accumulation and Damage to Mitochondria

Abstract

Curcumin, the principal curcuminoid of tumeric, has potent anticancer activity. To determine the mechanism of curcumin-induced cytotoxicity in prostate cancer cells, we exposed PC3 prostate carcinoma cells to 25 to 100 μ M curcumin for 24 to 72 h. Curcumin treatment of PC3 cells caused time- and dose-dependent induction of apoptosis and depletion of cellular reduced glutathione (GSH). Exogenous GSH and its precursor N-acetyl-cysteine, but not ascorbic acid (AA) or ebselen, decreased curcumin accumulation in PC3 cells and also prevented curcumin-induced DNA fragmentation. The failure of AA and ebselen to protect PC3 cells from curcumin-induced apoptosis argued against the involvement of reactive oxygen species; rather, GSH-mediated inhibition of curcumin-induced cytotoxicity was due to reduced curcumin accumulation in PC3 cells. Curcumin-treated PC3 cells showed apoptosis-inducing cellular ceramide accumulation and activation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase (JNK). Caspase-3, caspase-8, and caspase-9 were activated, and cytochrome c and apoptosis-inducing factor (AIF) were released from mitochondria following curcumin treatment. Interestingly, curcumin-induced apoptosis was not prevented by p38 MAPK, JNK, or caspase inhibition. We conclude that curcumin-induced cytotoxicity was due to cellular ceramide accumulation and damage to mitochondria that resulted in apoptosis mediated by AIF and other caspase-independent processes.

ACKNOWLEDGMENTS

This work was supported by the Natural Sciences and Engineering Research Council (NSERC) and the Department of Surgery, Dalhousie University. A. Hilchie was supported by an NSERC Undergraduate Summer Research Award, a Trainee Award from the Cancer Research Training Program with funding from the Canadian Cancer Society, and an NSERC Postgraduate Studentship. S. Furlong was supported by an NSERC Postgraduate Studentship. A. Richardson was supported by a Trainee Award from the Cancer Research Training Program with funding from the Canadian Cancer Society. K. Sutton was supported by an NSERC Postgraduate Studentship and a Trainee Award from the Cancer Research Training Program with funding from the Canadian Breast Cancer Foundation–Atlantic Region.