Context: Endometriosis, the growth of endometrial tissue outside the uterus, is principally an estrogen-dependent disease. In contrast, exposure to progesterone during pregnancy or therapeutically has been shown to provide benefit to some women with this disease. However, recent research suggests that the presence of endometriosis impairs the capacity of the eutopic endometrium to respond to endogenous progesterone.

Objective: Reduced progesterone responsiveness results in an elevated endometrial expression of matrix metalloproteinases (MMPs) during the secretory phase of the menstrual cycle in women with endometriosis. Although cyclic MMP expression is critical for endometrial growth and remodeling, the failure of progesterone to down-regulate MMPs may impair nidation and promote the invasive establishment of endometriosis. In the current study we examined the ability of a newly developed progesterone receptor (PR) agonist, tanaproget (TNPR), to down-regulate endometrial MMP expression in vitro and regress experimental endometriosis in vivo.

Setting: This study was performed at a university-based medical center.

Participants: Asymptomatic volunteers and patients with endometriosis were studied.

Main outcome measures: We examined the ability of TNPR to down-regulate endometrial MMP expression in vitro compared with that of natural progesterone and two currently marketed synthetic steroidal progestins. Using a human/mouse model of endometriosis, we also tested the in vivo ability of TNPR to regress ectopic lesions established by tissues with reduced progesterone sensitivity.

Results: TNPR effectively down-regulated MMP expression in vitro and induced significant reduction of lesions in mice with disease established by tissues from endometriosis patients.

Conclusion: Given the positive preclinical pharmacological profile of TNPR that has recently been reported, additional development of this compound for the treatment of endometriosis is warranted.