The company announced in December 2018 that it was halting trials of vilaprisan after long-term toxicology studies in rodents indicated a potential problem. The issue was not reported in any of the human trials, but Bayer stopped patient recruitment to investigate further.
How vilaprisan works
Endometriosis affects up to 10 percent of women of reproductive age worldwide. It is characterized by the abnormal growth elsewhere in the body of tissue resembling that which normally lines the uterus. This growth leads to the formation of endometrial lesions, and the disease is known to cause infertility in about half of all patients. Its symptoms include inflammation and recurring pelvic pain, which can be chronic or occur during menstruation.
Vilaprisan is a highly selective progesterone receptor modulator (SPRM). It is a partial agonist of the progesterone receptor, which means that it activates progesterone receptors to a certain degree upon binding. This triggers a cascade of biochemical reactions that result in the suppression of prostaglandin production, to possibly relieve symptoms such as pain and bleeding. Modulating progesterone by taking vilaprisan might help to treat endometriosis over the long term.
Vilaprisan in clinical trials
The results of a randomized, placebo-controlled Phase 1 study in healthy post-menopausal women showed that vilaprisan to be well-tolerated. A Phase 1 trial (NCT02262663) in healthy young women of reproductive age produced similar results.
The treatment was also investigated in an open-label Phase 1 clinical trial (NCT02975440) of the interaction between vilaprisan and the antibiotic Rifadin (rifampicin). Researchers completed this study on a group of 12 healthy post-menopausal women in June 2017, but no results have been posted.
A Phase 2b randomized, double-blind clinical trial (NCT03573336) called VILLENDO aims to investigate two different doses of vilaprisan compared to placebo in women with endometriosis. The study, which is listed as ongoing, opened with the intent of enrolling 315 patients and finishing in June 2020.
Vilaprisan was studied for safety and efficacy in several trials in women with uterine fibroids. A Phase 2 trial (NCT02465814, called ASTEROID 2) compared the treatment to placebo in 120 women with uterine fibroids. ASTEROID 2 ended in 2016, but no results appear to have been published. A paper was posted detailing the study’s design and rationale.
Two Phase 3 trials, called ASTEROID 6 (NCT03194646) and ASTEROID 7 (NCT03699176), opened in women with uterine fibroids to test vilaprisan against standard care. These studies, both scheduled to end in September 2021, are apparently on hold.
Last updated: July 30, 2019
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