Objective: To determine the mechanism by which mifepristone improves breakthrough bleeding, the effects of mifepristone on proliferation and apoptosis of Ishikawa endometrial carcinoma cells were evaluated in the presence and absence of progestin.
Design: Prospective basic research study.
Setting: Research laboratories for reproductive health at a university medical school.
Patient(s): None.
Intervention(s): Ishikawa cells were cultured in vitro. Mifepristone and/or medroxyprogesterone acetate at various concentrations were added to the cells.
Main outcome measure(s): Determination of cell proliferation and apoptosis.
Result(s): Colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and bromodeoxyuridine (BrdU) labeling analysis demonstrated that mifepristone inhibited the growth of Ishikawa cells and percentage of BrdU-labeled cells in a time- and dose-dependent manner. Flow cytometry analysis demonstrated that mifepristone at 100 micromol/L, which completely inhibited cell proliferation, increased the proportion of cells in the S phase and diminished the cells in the G2/M phase. Apoptosis was identified by annexin-V-fluorescein isothiocyanate binding and caspase-3 activation. Immunofluorescent double labeling of Ishikawa cells in the absence or presence of mifepristone revealed that BAX protein expression increased and translocated from cytosol to mitochondria.
Conclusion(s): Mifepristone inhibited cell growth by arresting cell cycle progression at S phase, induced apoptosis through caspase-3 activation, and modulated apoptosis regulatory genes BCL2/BAX and FAS/FASLG in Ishikawa cells. Together, these data imply that the improvement in breakthrough bleeding observed with mifepristone might be due to diminished volume of endometrial tissue similar to that seen with endometrial atrophy.