L-649,923

L-649,923 is a small molecule drug developed as a selective and competitive antagonist of cysteinyl leukotriene receptors (CysLT1), specifically inhibiting the actions of leukotrienes C4, D4, E4, and F4. It was designed to block bronchoconstriction and other inflammatory responses mediated by these leukotrienes. Preclinical studies demonstrated that L-649,923 selectively blocked bronchoconstriction induced by leukotriene C4 and D4 in animal models without affecting responses to histamine or other mediators. In human studies, oral administration antagonized LTD4-induced bronchoconstriction but not histamine-induced effects. The compound was investigated for potential use in respiratory diseases such as asthma and allergic rhinitis but development was discontinued due to adverse gastrointestinal effects[5][7][8][10].