Structure-activity relationships of 17 alpha-derivatives of estradiol as inhibitors of steroid sulfatase

The steroid sulfatase or steryl sulfatase is a microsomal enzyme widely dis tributed in human tissues that catalyzes the hydrolysis of sulfated 3-hydro xy steroids to the corresponding free active 3-hydroxy steroids. Since andr ogens and estrogens may be synthesized inside the cancerous cells starting from aehydroepiandrosterone sulfate (DHEAS) and estrone sulfate (E1S) avail able in blood circulation, the use of therapeutic agents that inhibit stero id sulfatase activity may be a rewarding approach to the treatment of andro geno-sensitive and estrogeno-sensitive diseases. In the present study, we r eport the chemical synthesis and biological evaluation of a new family of s teroid sulfatase inhibitors. The inhibitors were designed by adding an alky l, a phenyl, a benzyl, or a benzyl substituted at position 17 alpha of estr adiol (E-2), a C18-steroid, and enzymatic assays were performed using the s teroid sulfatase of homogenized JEG-3 cells or transfected in HEK-293 cells . We observed that a hydrophobic substituent induces powerful inhibition of steroid sulfatase while a hydrophilic one was weak. Although a hydrophobic group at the 17 alpha -position increased the inhibitory activity, the ste ric factors contribute to the opposite effect. As exemplified by 17 alpha - decyl-E-2 and 17 alpha -dodecyl-E-2, a long flexible side chain prevents ad equate fitting into the enzyme catalytic site, thus decreasing capacity to inhibit the steroid sulfatase activity. In the alkyl series, the best compr omise between hydrophobicity and steric hindrance was obtained with the oct yl group (IC50 = 440 nM) but judicious branching of side chain could improv e this further. Benzyl substituted derivatives of estradiol were better inh ibitors than alkyl analogues. Among the series of 17 alpha-(benzyl substitu ted)-E-2 derivatives studied, the 3'-bromobenzyl, 4'-tert-butylbenzyl, 4'-b utylbenzyl, and 4'-benzyloxybenzyl groups provided the most potent inhibiti on of steroid sulfatase transformation of E1S into E-1 (IC50 = 24, 28, 25, and 22 nM, respectively). As an example, the tert-butylbenzyl group increas es the ability of the E-2 nucleus to inhibit the steroid sulfatase by 3000- fold, and it also inhibits similarly the steroid sulfatase transformations of both natural substrates, E1S and DHEAS. Interestingly, the newly reporte d family of steroid sulfatase inhibitors acts by a reversible mechanism of action that is different from the irreversible mechanism of the known inhib itor estrone sulfamate (EMATE).