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).

Duration of antiestrogenecity of compound CDRI-85/287: a new orally active nonsteroidal antiimplantation agent.

Duration of antiestrogenic and antiimplantation action of CDRI-85/287, (2-(4-(2-N-piperidino)ethoxy phenyl)-3-phenyl(2H)benzo(2)pyran), was studied in rat. Pretreatment of ovariectomized immature rats with this compound caused translocation of cytoplasmic estrogen receptor (ER) to the nucleus and a marked depletion of cytoplasmic ER pool resulting in a nonresponsive state of the uterus to subsequent estrogen administration until day 4. While in rats pretreated with estradiol, increased cytoplasmic ER level made the uterus responsive to a second injection of estrogen. In the delayed implantation model, 85/287 pretreated rats were given estrone on days 4, 5 or 6 post-antiestrogen treatment. No implantations were observed after estrone administration on day 4, but were present when estrone was given on days 5 or 6. Summation of these results suggests the duration of action of 85/287 to be 3-4 days in rat.