In vivo characterization of progestins with reduced non-genomic activity in vitro.

Postmenopausal women that still have an uterus and suffer from hot flushes are treated with combinations of estrogens and progestins. Whereas estrogens are indispensable for treating postmenopausal symptoms, progestins are added to counteract the proliferative activity of estrogens on uterine epithelial cells. However, in the mammary gland, progestins, given together with estrogens, stimulate the proliferation of mammary epithelial cells. Therefore, progestins with reduced proliferative activity in the mammary gland would be of advantage for hormone therapy of postmenopausal women. In order to identify progestins with better tissue-selectivity, we exploited the activation of different signal transduction pathways by the classical progesterone receptor. We demonstrated that progestins with reduced non-genomic versus genomic activity in vitro show a better dissociation of uterine versus mammary gland effects in vivo than medroxyprogesterone acetate (MPA), a synthetic progestin that is widely used in hormone therapy.