CDRI-85/287: studies on competition to estrogen binding sites in the immature rat uterus

Ability of compound CDRI-85/287, a new nonsteroidal antiestrogen with negligible inherent estrogenicity, to inhibit uptake of 3H-estradiol (3H-E2) by the immature rat uterus in vivo was investigated. Different doses of 85/287 were administered either intraperitoneally 30 min before 3H-E2 or orally 1 and 6 hr before 3H-E2. A dose dependent inhibition in 3H-E2 uptake was observed after administration of the compound by either route and was 69% at 50 micrograms/rat ip dose and 80% at 2.5 mg/kg po dose. In in vitro competitive binding assay, however, the compound showed poor affinity (RBA 0.42% of estradiol-17 beta) for cytosolic estrogen receptors. Considering the potent anti-estrogenic as well as anti-implantation efficacy of the compound, its action in vivo appears to be mediated via its active metabolite(s).