Synthesis and biological activities of flavonoid sulfamates as steroid sulfatase inhibitors

Synthesis of potent flavonoid sulfamate inhibitors of the enzyme steroid sulfatase (STS), a topical target in treating postmenopausal women with hormone-dependent breast cancer, is described in the current article. Novel compounds were examined for estrone sulfatase (E1-STS) inhibition in intact MCF-7 breast cells. The strategies adopted to develop STS inhibitors which, while active in vivo, are devoid of any estrogenicity that would limit their use for breast cancer therapy (e.g. estrone 3-O-sulfamate, EMATE), were broadly successful. Several molecules of flavonoid sulfamates were synthesized that potentially possess both aromatase and steroid sulfatase inhibitory properties. The isoflavane-4',7-O,O-bis-sulfamate (equol bis-sulfamate) and flavone-6,4'-O,O-bis-sulfamate were found to be the most potent inhibitors of all the flavonoid sulfamate analogs in vitro, inhibiting STS by about 99% at 0.1µM in MCF-7 cells. Some of these flavonoid sulfamates were also found to be active against both enzymes’ STS and aromatase (e.g., 5-hydroxy-7-methoxyflavone-4'-O-sulfamate, 5-hydroxy-flavone-4',7-O,O-bis-sulfamate, and 5,7-dihydroxy flavanone-4'-O-sulfamate), thus demonstrating the novel concept of a dual inhibitor. The availability of flavonoid sulfamates as STS inhibitors may enable to use of them as a therapy in the treatment of breast cancer.