Design, synthesis and evaluation of novel analogues of 2-methoxyestradiol as potential anti-cancer agents.

摘要

2-Methoxyestradiol (2ME2), an endogenous metabolite of estradiol, exhibits potent antiproliferative activity against a wide range of tumor and non-tumor cell types in vitro, and anti-angiogenic and anti-tumor activities in vivo with minimal toxicity at pharmacologically active doses. The anti-cancer activity of 2ME2 is independent of estrogen receptors, and although the mechanistic pathways have not been fully elucidated, the disruption of microtubule polymerization and inhibition of HIF activity appear to be essential to its mode of action. Clinical studies in humans and in vivo studies in mice and rats have demonstrated that metabolism of 2ME2 occurs mainly by processes like those reported for estradiol, producing metabolites with conjugation at the 3- and 17-position, oxidation at the 17-position to form 2-methoxyestrone and demethylation at the 2-position. Like many other steroid hormones, 2ME2 displays low aqueous solubility and low circulating plasma levels. In the described research, we designed and synthesized novel steroid-based analogues of 2ME2 by introducing substituents at positions 2, 3, and 17. Additionally, we generated potential phosphate prodrugs to increase aqueous solubility and improve the pharmacokinetic profile of 2ME2. Screening of these analogues evaluated the inhibition of tubulin polymerization, cytotoxicity and antiproliferative activity in endothelial and various tumor cell types, ensuring that the new compounds retained the activities of 2ME2. The analogues were also examined in a proliferation assay using the MCF7 estrogen-dependent cell line to demonstrate minimal intrinsic or metabolically induced estrogenic activity. Several of the analogues showed similar cytotoxicity, anti-tubulin and antiproliferative activity to 2ME2 and reduced relative estrogenicity. Additionally, certain substitutions conferred specificity toward inhibiting endothelial cell proliferation, indicating the potential for more specific anti-angiogenic compounds to be derived using a synthetic approach. From the analogues that showed minimal activity in the in vitro screens relative to sterically similar derivatives, new relationships between structure and activity were identified, indicating that electronic characteristics of substituents at the A-ring and the D-ring, as well as steric effects, contribute significantly to the overall activity. Subsequent screening in animal models and toxicology studies at EntreMed, Inc. will allow the most promising candidate(s) including the phosphate analogues to potentially progress to the clinic.