SYNTHESIS, ANTITUBULIN AND ANTIMITOTIC ACTIVITY, AND CYTOTOXICITY OF ANALOGS OF 2-METHOXYESTRADIOL, AN ENDOGENOUS MAMMALIAN METABOLITE OF ESTRADIOL THAT INHIBITS TUBULIN POLYMERIZATION BY BINDING TO THE COLCHICINE BINDING-SITE

In order to define the structural parameters associated with the antit ubulin activity and cytotoxicity of 8-methoxyestradiol, a mammalian me tabolite of estradiol, an array of analogs was synthesized and evaluat ed. The potencies of the new congeners as inhibitors of tubulin polyme rization and colchicine binding were determined using tubulin purified from bovine brain, and the cytotoxicities of the new compounds were s tudied in a variety of cancer cell cultures. Maximum antitubulin activ ity was observed in estradiols having unbranched chain substituents at the 2-position with three non-hydrogen atoms. 2-Ethoxyestradiol and 2 -((E)-1-propenyl)-estradiol were substantially more potent than 2-meth oxyestradiol itself. The tubulin polymerization inhibitors in this ser ies displayed significantly higher cytotoxicities in the MDA-MB-435 br east cancer cell line than in the other cell lines studied. The potenc ies of the analogs as cytotoxic and antimitotic agents in cancer cell cultures correlated with their potencies as inhibitors;of tubulin poly merization, supporting the hypothesis that inhibition of tubulin polym erization is the mechanism of the cytotoxic action of 2-methoxyestradi ol and its congeners. Several of the more potent analogs were tested i n an estrogen receptor binding assay, and their affinities relative to estradiol were found to be very low.