Selective progesterone receptor modulator

A selective progesterone receptor modulator (SPRM) is an agent that acts on the progesterone receptor (PR), the biological target of progestogens like progesterone. A characteristic that distinguishes such substances from full receptor agonists (e.g., progesterone, progestins) and full antagonists (e.g., aglepristone) is that their action differs in different tissues, i.e. agonist in some tissues while antagonist in others. This mixed profile of action leads to stimulation or inhibition in tissue-specific manner, which further raises the possibility of dissociating undesirable adverse effects from the development of synthetic PR-modulator drug candidates. Ever since the discovery of the progesterone hormone in the mid-1930s. and especially after the discovery of its receptor in 1970 there has been a significant interest in developing an antagonistic agent for therapeutic use. Various progesterone analogs, known as progestins, were synthesized and in 1981 the first progesterone receptor antagonist was introduced by the name RU 38486 (RU 486, mifepristone). However, the clinical limitation of mifepristone due to its relatively high binding affinity for glucocorticoid receptor compared to the progesterone receptor has sparked the demand for more selective progesterone antagonist to minimize risk of adverse effects. As a contribution, so-called Selective Progesterone Receptor Modulators (SPRMs) have been developed. They have been described as agents with mixed antagonistic and agonistic effects on progesterone receptors in a tissue specific manner, while minimizing interactions with other steroidal receptors. Opposed to progesterone antagonists, the mixed agonist-antagonist SPRM, due to their intrinsic progesterone agonistic activity, have an absent or only a minimal effect on pregnancy termination and are thus ideal for treating gynecological conditions without eliminating the potential of pregnancy. Both steroidal and non steroidal SPRMs have been described and the most notable examples are asoprisnil, which failed phase 3 clinical trial in 2008, and ulipristal acetate, the first SPRM on the market (2009 in Europe).