Strong inhibition of estrone-3-sulfatase activity by pregnenolone 16 alpha-carbonitrile but not by several analogs lacking a 16 alpha-nitrile group

In recent years. development of potent inhibitors for estrogen sulfatases h as become an actively pursued strategy for chemoprevention and/or chemother apy of estrogen-dependent human breast cancers. We report here our findings that pregnenolone 16 alpha-carbonitrile (PCN) is a potent inhibitor of est rone-3-sulfatase activity of rats and also humans. PCN inhibited in a conce ntration-dependent manner the desulfation of estrone-3-sulfate catalyzed by liver microsomal and nuclear fractions of female Sprague-Dawley rats. The inhibition of estrone-3-sulfatase activity in these two subcellular fractio ns showed a biphasic pattern, with a highly sensitive phase seen at 78 nM t o 1.25 mu m of PCN followed by a markedly less-sensitive phase at > 2.5 mu m of PCN. Interestingly, several of PCN's structural analogs without a 16 a lpha-nitrile group showed little or no inhibitory effect on rat liver micro somal E-1-3-sulfatase activity. Double-reciprocal analysis showed that the inhibition of rat liver microsomal E-1-3-sulfatase activity by PCN was esse ntially competitive in nature. When microsomes from six human term placenta s were tested for their E-1-3-sulfatase activity, PCN showed a similar biph asic inhibition of placental E-1-3-sulfatase. Likewise, several of its stru ctural analogs showed little or no inhibitory effect on placental E-1-3-sul fatase activity. Computational analysis of the D-ring structure of PCN and other structurally similar analogs used in the study suggests that the pote nt sulfatase-inhibiting activity of PCN may be partly due to its unique ste ric orientation and size of the 16 alpha-nitrile group. This knowledge may be useful for the rational design of more potent steroidal inhibitors of E- 1-3-sulfatase by introducing an additional nitrile group to their C16 alpha -position. (C) 2000 Elsevier Science Inc. All rights reserved.