OBE2109 is an antagonist of the gonadotropin-releasing hormone (GnRH). It is being tested by ObsEva in several clinical trials to treat menstrual bleeding and pain associated with endometriosis and uterine fibroids (UF). The oral drug was initially developed by Kissei Pharmaceutical.

During the menstrual cycle, endometrium cells in the walls of the uterus grow to accommodate a baby in case of pregnancy. If a woman does not become pregnant, endometrium cells detach from the walls of the uterus and are discharged during menstruation.

The growth and detachment of the endometrium are regulated by a complex system of hormones. In the case of the menstrual cycle, hormones are produced in two main organs: the brain and the ovaries. The hormones produced in the brain act on the ovaries and stimulate the production of ovarian hormones that in turn activate the growth of endometrium cells in the uterus.

How does OBE2109 work?

At the top of the hormonal regulation of the menstrual cycle is the hormone GnRH. OBE2109 blocks the receptors of GnRH and reduces its effect on the production of the downstream hormones.

Women with endometriosis experience the growth of endometrium cells outside the uterus, which causes pain due to inflammation of the affected areas. OBE2109 stops the abnormal growth of endometrium cells anywhere in the body, which helps decrease inflammation and relieves pain.

Studies with OBE2109

In a Phase 2a clinical trial in Japan, which included patients with endometriosis and uterine fibroids, treatment with OBE2109 led to a decrease in the levels of the menstrual cycle hormones.

The study participants had a reduction of endometriosis-associated pain and bleeding days. The use of OBE2109 also led to a reduction in the use of pain medication to manage endometriosis symptoms.

In uterine fibroid patients, OBE2109 treatment showed a reduction of bleeding days within the first month of treatment and anemia was corrected within three months.

ObsEva is now performing a randomized, double-blind, placebo-controlled Phase 2b dose-ranging study to assess the effectiveness and safety of OBE2109 in subjects with endometriosis-associated pain in the U.S. and Europe (NCT02778399).

Additionally, two Phase 3, randomized, double-blind, placebo-controlled studies investigating the effectiveness and safety of daily oral administration of OBE2109 alone and in combination with add-back therapy for the management of heavy menstrual bleeding associated with uterine fibroids in premenopausal women are also being performed by ObsEva (NCT03070899, NCT03070951).

Other details about OBE2109

Estrogen is one of the hormones produced by the ovaries and, besides stimulating endometrium growth, it is fundamental to the growth of bones. GnRH antagonist drugs usually lead to bone density loss because of the reduction of estrogen levels. However, OBE2109 is believed to provide relief from the pain associated with endometriosis without compromising bone density, since the drug can be tailored to a patient’s optimal dosage to lower estrogen levels without affecting mineral density.

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