Purpose: To determine the growth inhibitory effects of mifepristone on endometrial cancer cell growth and evaluate its effect on apoptosis using HEC-1-A and Ishikawa human endometrial cancer cell lines.
Methods: The human endometrial cancer cell lines, HEC-1-A and Ishikawa, were cultured in vitro. MTT assays were completed in order to estimate the IC(50) of mifepristone. Both cell lines were then treated with the respective IC(50) values. Immunohistochemistry assays were performed to investigate the expression of estrogen receptors alpha and beta (ERalpha/beta), progesterone receptor alpha and beta (PR alpha/beta), cyclooxygenase-2 (COX-2), bax, p53, and bcl-2. Flow cytometry analysis was performed to study cell cycle arrest and apoptosis.
Results: The estimated IC(50) of mifepristone for HEC-1-A and Ishikawa was found to be 16 and 19 mug/ml respectively. At this concentration, there was no change in either ERalpha/beta or PR alpha/beta in Ishikawa. However, PR beta expression increased with time of treatment in HEC-1-A. Expression of p53 was increased with duration of treatment in both cell lines. Consequently a decrease in bcl-2 and an increase in COX-2 expression were seen in HEC-1-A and Ishikawa cells, respectively. Lastly, flow cytometry analysis confirmed an accumulation of cells in G0 phase after 72 h of treatment in both cell lines.
Conclusions: Mifepristone demonstrates activity in both HEC-1-A and Ishikawa cells at clinically relevant concentrations based on an oral human dose of about 200 mg/day. While its mechanism of action remains unknown, this data supports an increase in apoptosis that may be due to p53 activation rather than hormone receptor mediation. Additional studies are needed to help further identify mifepristone mechanism of action.