Effect of molecular manipulation on the estrogenic activity of a brain-targeting estradiol chemical delivery system.

The structural parameters important for biological efficacy of an estradiol chemical delivery system (CDS), a brain-targeting approach based on redox trapping, were examined by molecular manipulation of a prototype derivative, estradiol 17-(1-methyl-1, 4-dihydronicotinate) (E2-CDS). Seven E2-CDS analogs in which the N-methyl substituent was altered were prepared including N-substituted short and medium straight chain alkyl, short branched chain alkyl, and aralkyl derivatives. Chemical and in vitro testing indicated that the most stable derivative was the N-benzyl E2-CDS. The analogs were tested in an intact male rat model to assess various central estrogenic manifestations including the rate of body weight gain, serum E2 and testosterone concentrations, and seminal vesicle, prostate and pituitary weight changes. Results indicated that all prepared CDS derivatives exerted some degree of central estrogenization with the most potent compounds being the parent E2-CDS and its ethyl homologue. Importantly, while the ethyl E2-CDS was equipotent to E2-CDS in various biological assays, it did not significantly elevate serum E2 compared to vehicle control at day 14.