In vitro and in vivo models for the evaluation of new inhibitors of human steroid sulfatase, devoid of residual estrogenic activity

Abstract

The goal of our research project is to develop a new class of orally active drugs, estrone sulfatase inhibitors, for the treatment of estrogen-dependent (receptor positive) breast cancer. Several compounds were synthesized and their pharmacological potencies explored. Based on encouraging preliminary results, three of them, TX 1299, TX 1492 and TX 1506 were further studied in vitro as well as in vivo. They proved to be strong inhibitors of estrone sulfatase when measured on the whole human JEG-3 choriocarcinoma and MCF-7 breast cancer cells and their IC 50s found to be in the range of known standard inhibitors. Their residual estrogenic activity was checked as negative in the test of induction of alkaline phosphatase (APase) activity in whole human endometrial adenocarcinoma Ishikawa cells. In addition, their effect on aromatase activity in JEG-3 cells was also examined, since the goal of inhibiting both sulfatase and aromatase activities appears very attractive. However, it has been unsuccessful so far. Then, in vivo potencies of TX 1299, the lead compound in our chemical series, were evaluated in comparison with 6,6,7-COUMATE, a non-steroidal standard, in two different rat models and by oral route. First, the absence of any residual estrogenic activity for these compounds was checked in the uterotrophic model in prepubescent female rats. Second, antiuterotrophic activity in adult ovariectomized rat supplemented with estrone sulfate (E 1S), showed that both compounds were potent inhibitors, the power of TX 1299 relative to 6,6,7-COUMATE being around 80%. This assay was combined with uterine sulfatase level determination and confirmed the complete inhibition of this enzyme within the target organ. Preliminary studies indicated that other non-steroid compounds in the Théramex series were potent in vitro and in vivo inhibitors of estrone sulfatase in rats and further studies are in progress.