Mifepristone-induced secretion of transforming growth factor β1-induced apoptosis in prostate cancer cells

Successful therapy should induce apoptosis in prostate cancer cells irrespective of their androgen response. We have investigated the possibility of utilizing Mifepristone and Tamoxifen as treatment options for prostate cancer cells. Because preliminary results demonstrated induction of apoptosis by these drugs, the mechanism of induction of apoptosis was investigated. LNCaP-C4 prostate cancer cells were treated with Mifepristone and/or Tamoxifen. To confirm cytotoxic effects, nude mice with LNCaP-C4 xenografts were treated with Mifepristone and Tamoxifen. Cell viability was assayed using Sulforhodamine B (SRB) assay and DNA fragmentation was measured by ELISA. Culture media from vehicle- and drug-treated cells were collected and secretion of transforming growth factor β1 (TGFβ1) was estimated by ELISA. Role of TGFβ1 was confirmed by inhibiting its function using TGFβ1 antibody or M6P, which blocked activation of TGFβ1. Apoptotic effects were determined by immunoblots of cytochrome c levels in cytosol and by in vitro colorimetric assay of caspase-3 activity. Results showed that although both drugs induced apoptosis in LNCaP-C4 cells, Mifepristone was more effective. The effects of these drugs on xenografts confirmed in vitro results. It was hypothesized that drug-induced secretion of TGFβ1 may be responsible for induction of apoptosis. Neutralization of TGFβ1 with an antibody or blocking the activation of TGFβ1 by M6P abrogated the effects of Mifepristone and Tamoxifen confirming our hypothesis. Furthermore, treatment with Mifepristone and/or Tamoxifen released cytochrome c into the cytoplasm and induced activity of caspase-3, providing evidence that the drug-stimulated secretion of TGFβ1 was responsible for induction of apoptosis in these cells. In conclusion, both Mifepristone and Tamoxifen induced apoptosis mediated through TGFβ1. However, no critical advantage was noted by the addition of Tamoxifen to Mifepristone treatment.