Animal studies on the endocrinological profile of dienogest, a novel synthetic steroid

Dienogest is an orally active synthetic steroid that is used for contraception and is currently being studied for the possible treatment of endometriosis. Earlier we demonstrated that dienogest had therapeutic effects on experimental endometriosis in rats and that its mechanisms of action were different from those of drugs currently on the market for the treatment of endometriosis. We also reported preclinically that dienogest showed a potential anticancer action against hormone-dependent cancers that was different from that of progestins. Accordingly we obtained preclinical background data for the above-described clinical applications and extension of the clinical use of the drug in the near future by investigating the endocrinological profile of dienogest in rabbits and rats. Dienogest was characterized by having a moderate binding affinity for progesterone receptors and by progestational activities: it stimulated endometrial proliferation (≤ 0.01 mg/kg) that was only partially inhibited by RU-486, and induced carbonic anhydrase activity in endometrium (≤ 0.01 mg/kg). Also, it was slightly uterotrophic (≤ 1 mg/kg) with very low binding affinity for oestrogen receptors and slightly antioestrogenic (≤ 1 mg/kg). In addition, dienogest showed slight binding to androgen receptors but without biological androgenic and anabolic activities (100 mg/kg), with neither glucocorticoid activity nor mineralocorticoid activity (100 mg/kg), and with very slight binding affinity for human sex hormone-binding globulin. These findings suggest that dienogest is not a pure progestin and appears to induce fewer side effects than drugs currently on the market for the treatment of endometriosis.