Effects of antiprogestins RU486 and ZK98299 on the expression of cell cycle proteins of a medroxyprogesterone acetate (MPA)-induced murine mammary tumor.

This study links the tumor inhibitory effect of anti-progestins RU486 and ZK98299 to the expression of cell cycle proteins. Medroxyprogesterone acetate-induced ductal mammary adenocarcinoma-bearing female BALB/c mice were treated daily either with RU486 or ZK98299, observing tumor growth retardation. p21 increased after 24 h treatment, peaked at day 4 and returned to control levels at day 7. Cyclin D1, cyclin E, CDK2 and CDK4, did not change during treatment. These results suggest that p21 might play a role in early inhibitory stages of tumor growth induced by RU486 and ZK98299.