Mixed estrogenic and anti-estrogenic activities of yuehchukene--a bis-indole alkaloid

Anti-estrogenic effects of yuehchukene were observed in rat uterotrophic, mice vaginal smear and MCF-7 cell growth assays. Whereas yuehchukene per se was estrogenic in these bioassay models, the co-administration of yuehchukene and an optimal dose of 3,17 beta-estradiol (estradiol) could attenuate the maximum estrogenic response due to estradiol alone. The anti-estrogenic effect of yuehchukene in rat uterine hypertrophy was corroborated by a parallel attenuation of ornithine decarboxylase activity in these tissues. Yuehchukene binds to rat, mice and MCF-7 cell estrogen receptors with a relative binding affinity of 1/150 to 1/300. This binding affinity was positively related to estrogenicity as determined by uterotrophic assay and MCF-7 cell growth. However, this estrogenic effect did not correlate with the degree of competitive receptor binding by a weaker agonist. Indole-3-carbinol and methylbutadienylindole could induce ethoxyresorufin O-deethylase and estradiol-2-hydroxylase in rat liver and MCF-7 cells. It is postulated that the 'free' indole moiety of yuehchukene could possess similar induction activity. Thus yuehchukene may have a dual pharmacological function. While the intact molecule is a weak estrogen, the 'free' indole moiety in yuehchukene may induce an enhancement of estradiol-2-hydroxylase, thus terminating the biological activity of the endogenous estrogen pool. There is obvious benefit in attenuating the estrogen level in post-menopausal breast cancer patients without going directly to the use of tamoxifen or aromatase inhibitor. Yuehchukene may serve this purpose. In this context, the pharmacological evaluation of a hydroxylated yuehchukene analogue and the anti-estrogenic effect of methylbutadienylindole acid-condensation products are now being studied in earnest.