The simultaneous activation of many distinct G proteincoupled receptors (GPCRs) and heterotrimeric G proteins play a major role in various pathological conditions. Pan-inhibition of GPCR signaling by small molecules thus represents a novel strategy to treat various diseases. To better understand such therapeutic approach, we have characterized the biomolecular target of BIM-46187, a small molecule pan-inhibitor of GPCR signaling. Combining bioluminescence and fluorescence resonance energy transfer techniques in living cells as well as in reconstituted receptor-G protein complexes, we observed that, by direct binding to the G␣ subunit, BIM-46187 prevents the conformational changes of the receptor-G protein complex associated with GPCR activation. Such a binding prevents the proper interaction of receptors with the G protein heterotrimer and inhibits the agonist-promoted GDP/GTP exchange. These observations bring further evidence that inhibiting G protein activation through direct binding to the G␣ subunit is feasible and should constitute a new strategy for therapeutic intervention.

Estradiol-3,17-O,O-bis-sulfamates inhibit steroid sulfatase (STS), carbonic anhydrase (CA), and, when substituted at C-2, cancer cell proliferation and angiogenesis. C-2 Substitution and 17-sulfamate replacement of the estradiol-3,17-O,O-bis-sulfamates were explored with efficient and practical syntheses developed. Evaluation against human cancer cell lines revealed the 2-methyl derivative 27 (DU145 GI(50) = 0.38 microM) as the most active novel bis-sulfamate, while 2-ethyl-17-carbamate derivative 52 (GI(50) = 0.22 microM) proved most active of its series (cf. 2-ethylestradiol-3,17-O,O-bis-sulfamate 4 GI(50) = 0.21 microM). Larger C-2 substituents were deleterious to activity. 2-Methoxy-17-carbamate 50 was studied by X-ray crystallography and was surprisingly 13-fold weaker as an STS inhibitor compared to parent bis-sulfamate 3. The potential of 4 as an orally dosed anti-tumor agent is confirmed using breast and prostate cancer xenografts. In the MDA-MB-231 model, dramatic reduction in tumor growth or regression was observed, with effects sustained after cessation of treatment. 3-O-Sulfamoylated 2-alkylestradiol-17-O-carbamates and sulfamates have considerable potential as anticancer agents.