Raloxifene, a selective estrogen receptor modulator, induces mitochondria-mediated apoptosis in human endometrial carcinoma cells

Abstract

Raloxifene is a nonsteroidal benzothiophene that has also been classified as a selective estrogen receptor modulator (SERM) on the basis of studies in which it produced both estrogen-agonistic effects on bone and lipid metabolism and estrogen-antagonistic effects on uterine endometrium and breast tissue. We investigated apoptotic cell death and the apoptotic pathway in human endometrial carcinoma cells (Ishikawa cells) expressing estrogen receptor treated with raloxifene. Cell viability was significantly decreased in Ishikawa cells treated with raloxifene at 20 μM and higher levels. Raloxifene at 20 μM induced 54% inhibition of cell viability after 48 h treatment. Apoptotic parameters were analyzed for determination of apoptotic pathway in Ishikawa cells treated with 20 μM or 40 μM raloxifene for 48 h. The numbers of apoptotic cells were significantly increased in cells treated with raloxifene as compared with control cells. Activities of caspase-3,-8, and-9 were significantly elevated in Ishikawa cells treated with raloxifene. A significant decrease in mitochondrial membrane potential was observed in this treatment. In addition, the levels of cytosolic cytochrome c were significantly elevated in raloxifene-treated cells. Expression of Bid was detected in both control and raloxifene-treated cells, but Bid cleavage was not observed. In caspase inhibitor experiments, cell viability was significantly increased by the caspase-9 inhibitor z-LEHD-fmk and by the caspase-3 inhibitor z-DEVD-fmk. However, cell viability was unaffected by addition of the caspase-8 inhibitor z-IETD-fmk. Thus, raloxifene induced mitochondria-mediated apoptosis in endometrial cancer cells but not via the Bid-mitochondria pathway. It is possibly that raloxifene may be useful as an adjuvant to current chemotherapies for endometrial cancer and possibly is useful as a chemopreventive agent.