Synthetic routes to potent steroidal and nonsteroidal
sulfamate-based active site-directed inhibitors of the
enzyme steroid sulfatase, a topical target in the treatment of postmenopausal women with
hormone-dependent
breast cancer, are described. Novel compounds were examined for
estrone sulfatase (E1-STS) inhibition in intact MCF-7
breast cancer cells and placental microsomes. Reaction of the
sodium salt of
estrone with sulfamoyl
chloride gave
estrone 3-O-sulfamate (EMATE, 2) which inhibits E1-STS activity potently (> 99% at 0.1 microM in intact MCF-7 cells, IC50 = 65 pM) in a time- and concentration-dependent manner, suggesting that EMATE is an active site-directed inhibitor. EMATE is also active in vivo orally. 5,6,7,8-Tetrahydronaphthalene 2-O-sulfamate (7) and its N-methylated derivatives (8 and 9) were synthesized, and 7 inhibits the E1-STS activity in intact MCF-7 cells by 79%
at 10 microM.
4-Methylcoumarin 7-O-sulfamate (
COUMATE) and its derivatives (14, 16, and 18) were prepared to extend this series of nonsteroidal inhibitors, and
COUMATE reduces the E1-STS activity in placental microsomes by > 90%
at 10 microM. Although the orally active
COUMATE is less potent than EMATE as an active site-directed inhibitor, it has the important advantage of being nonestrogenic. Analogues (20, 22, 24, 26, 27, 31, 33, 39, and 44) of
COUMATE were synthesized to study its structure-activity relationships, and sulfamates of
tetralones (46 and 48) and
indanones (49, 51, and 53) were also prepared. While most of these compounds were found to inhibit E1-STS activity less effectively than
COUMATE, one analogue, 3,4-dimethylcoumarin 3-O-sulfamate (24), was found to be some 12-fold more potent than
COUMATE as an E1-STS inhibitor in intact MCF-7 cells (IC50 = 30 nM for 24, cf. 380 nM for
COUMATE). Hence, highly potent
sulfamate-based inhibitors of
steroid sulfatase, such as EMATE,
COUMATE, and 24, possess therapeutic potential and will allow the importance of
estrogen formation in
breast tumors via the E1-STS pathway to be assessed. A pharmacophore for active site-directed
sulfatase inhibition is proposed.