DEVELOPMENT OF POTENT NON-ESTROGENIC ESTRONE SULFATASE INHIBITORS

Estrogen levels in breast tumors of post-menopausal women are as much as 10 times higher than estrogen levels in plasma, presumably due to i n situ formation of estrogen. The major source of estrogen in breast c ancer cells may be conversion of estrone sulfate to estrone by the enz yme estrone sulfatase. Thus inhibitors of estrone sulfatase have poten tial for the treatment of estrogen-dependent breast cancers. Several s teroidal agents have been developed that are potent estrone sulfatase inhibitors, most notably estrone-3-O-sulfamate. These compounds may ha ve undesired actions, especially estrogenicity. Recently, non-steroida l estrone sulfatase inhibitors have been designed that avoid the probl ems associated with an active steroid nucleus; however, these have not achieved the potency of estrone-3-O sulfamate. We have designed and s ynthesized a series of compounds, 17 kylcarbamoyl)-estra-1,3,5(10)-tri en-3-O-sulfamates (6a-d) and 17 -(n-alkanoyl)-estra-1,3,5(10)-trien-3- O-sulfamates (11a-d) that combine the structural features of the stero idal estrone sulfatase inhibitors with a membrane insertion region tha t should increase the affinity for the sulfatase enzyme and decrease t he estrogenicity of the steroid. We tested the compounds for estrone s ulfatase inhibition by measuring estrone sulfatase activity in intact cultures of human breast cancer cells (MDA-MB-231). We tested for estr ogenicity by measuring growth of estrogen-dependent MCF-7 human breast cancer cells. All of the test compounds (10 nM) substantially inhibit ed estrone sulfatase activity of intact MDA-MB-231 cells. Dose-respons e analysis indicated an IC50 of approximately 0.5 nM for two of the co mpounds (6a and 11a). In the test for estrogenicity, estrone and estro ne-3-O-sulfamate significantly stimulated MCF-7 cell growth. In contra st, neither the 17 kylcarbamoyl)-estra-1,3,5(10)-trien-3-O-sulfamates nor the 17 (N)-alkanoyl)-estra-1,3,5(10)-trien-3-O-sulfamates stimulat ed growth of MCF-7 cells at a concentration of 1 mu M, indicating that they are not estrogenic at levels 2000 greater than their IC50 for es trone sulfatase. Our data indicate the utility of the new compounds fo r inhibition of breast cancer cell estrone sulfatase activity. Further our data support the concept that estrone sulfatase inhibitors may be useful as therapeutic agents for estrogen-dependent breast cancers. ( C) 1998 by Elsevier Science Inc.