Inhibition of estrone sulfatase and proliferation of human breast cancer cells by nonsteroidal (p-O-sulfamoyl)-N-alkanoyl tyramines.

Estrogen levels in breast tumors of postmenopausal women are as much as 10 times higher than estrogen levels in plasma, presumably due to in situ formation of estrogen. The major source of estrogen in breast cancer cells may be the conversion of estrone sulfate to estrone by the enzyme estrone sulfatase. Thus, inhibitors of estrone sulfatase have potential for the treatment of estrogen-dependent breast cancers. Several steroidal agents have been developed that are potent estrone sulfatase inhibitors, most notably estrone-3-O-sulfamate. However, these compounds may be metabolized to forms that have undesired actions, including estrogenicity. To avoid the problems associated with a potentially active steroid nucleus, we designed and synthesized a series of (p-O-sulfamoyl)-N-alkanoyl tyramines as nonsteroidal estrone sulfatase inhibitors. These nine compounds differ in the length of their alkanoyl chains. We tested the ability of the (p-O-sulfamoyl)-N-alkanoyl tyramines to inhibit: (a) estrone sulfatase activity in intact cultures of human breast cancer cells (MDA-MB-231); and (b) the growth of estrogen-dependent human breast cancer cells (MCF-7). All of the test compounds (1 microM) inhibited the estrone sulfatase activity of intact MDA-MB-231 cells; however, compounds with a longer alkanoyl chain were more effective than those with a shorter chain. Dose-response analysis indicated an IC50 of 350 nM for (p-O-sulfamoyl)-N-tetradecanoyl tyramine for the inhibition of MDA-MB-231 estrone sulfatase activity. The inhibition of MDA-MB-231 cell estrone sulfatase activity by this compound was found to be irreversible. Cell proliferation assays involved the treatment of estrogen-deprived MCF-7 cells with test compounds (10 microM) in the presence of estrone sulfate (1 microM) as the only source of estrogen. All compounds inhibited cell proliferation to some extent, but the longer-chain analogues again were more effective. Dose-response analysis indicated an IC50 of 38 nM for (p-O-sulfamoyl)-N-tetradecanoyl tyramine for the inhibition of MCF-7 cell proliferation. Our data indicate the utility of (p-O-sulfamoyl)-N-alkanoyl tyramines for the inhibition of breast cancer cell estrone sulfatase activity. Furthermore, our data support the concept that nonsteroidal estrone sulfatase inhibitors may be useful as therapeutic agents for estrogen-dependent breast cancers.