Synthesis, biological evaluation, and stability studies of raloxifene mono-and bis-sulfamates as dual-targeting agents

All three possible sulfamate derivatives of the selective estrogen receptor modulator Raloxifene (bis-sulfamate 7 and two mono-sulfamates 8-9) were synthesized and evaluated as inhibitors of the clinical drug target steroid sulfatase (STS), both in cell -free and in cell -based assays, and also as estrogen receptor (ER) modulators. Bissulfamate 7 was the most potent STS inhibitor with an IC50 of 12.2 nM in a whole JEG3 cell -based assay, with the two mono-sulfamates significantly weaker. The estrogen receptor -modulating activities of 7-9 showed generally lower affinities compared to Raloxifene HCl, diethylstilbestrol and other known ligands, with monosulfamate 8 being the best ligand (Ki of 1.5 nM) for ER alpha binding, although 7 had a Ki of 13 nM and both showed desirable antagonist activity. The antiproliferative activities of the sulfamate derivatives against the T47D breast cancer cell line showed 7 as most potent (GI50 = 7.12 mu M), comparable to that of Raloxifene. Compound 7 also showed good antiproliferative potency in the NCI -60 cell line panel with a GI50 of 1.34 mu M against MDA-MB-231 breast cancer cells. Stability testing of 7-9 showed that bis-sulfamate 7 hydrolyzed by desulfamoylation at a surprisingly rapid rate, initially leading selectively to 8 and finally to Raloxifene 3 without formation of 9. The mechanisms of these hydrolysis reactions could be extensively rationalized. Conversion of Raloxifene (3) into its bis-sulfamate (7) thus produced a promising drug lead with nanomolar dual activity as an STS inhibitor and ER alpha antagonist, as a potential candidate for treatment of estrogen -dependent breast cancer.