Potent inhibition of steroid sulfatase activity by 3-O-sulfamate 17 alpha-benzyl(or 4 '-tert-butylbenzyl)estra-1,3,5(10)-trienes: Combination of two substituents at positions C3 and C17 alpha of estradiol

Steroid sulfates are precursors of hormones that stimulate androgen- and es trogen-dependent cancers. Thus, steroid sulfatase, the enzyme that catalyze s conversion of DHEAS and E1S to the corresponding unconjugated steroids DH EA and E-1, appears to be one of the key enzymes regulating the level of ac tive androgenic and estrogenic steroids. Since 17 alpha-substituted benzyle stradiols and 3-O-sulfamate estrone (EMATE) represent two families of stero id sulfatase inhibitors that probably act through different mechanisms, we synthesized compounds 3-O-sulfamate 17 alpha-benzylestradiol (4) and 3-O-su lfamate 17 alpha-(tert-butylbenzyl)estradiol (5) that contain two kinds of substituents on the same molecule. In our enzymatic assay using a homogenat e of human embryonal (293) cells transfected with steroid sulfatase, compou nds 4 and 5 were found to be more potent inhibitors than already known ster oid sulfatase inhibitors that have only a C17 alpha-substituent or only a C 3-sulfamate group (EMATE). The IC50 values of 4 and 5 were, respectively, 0 .39 and 0.15 nM for the transformation of E1S to E-1 and 4.1 and 1.4 nM for the transformation of DHEAS to DHEA. Compound 5 inhibited the steroid sulf atase activity in intact transfected (293) cell culture assays by inactivat ing the enzyme activity. Compound 5 also inactivates the steroid sulfatase activity at lower concentration than EMATE in microsomes of transfected (29 3) cells. In this assay, an excess of natural substrate E1S protects enzyme against inactivation by 5 or EMATE. Furthermore, the unsulfamoylated analo gue of 5, compound 3, did not inactivate the steroid sulfatase.