Steroid sulfatase inhibition success and limitation in breast cancer clinical assays: An underlying mechanism.

Steroid sulfatase is detectable in most hormone-dependent breast cancers. STX64, an STS inhibitor, induced tumor reduction in animal assay. Despite success in phase І clinical trial, the results of phase II trial were not that significant. Breast Cancer epithelial cells (MCF-7 and T47D) were treated with two STS inhibitors (STX64 and EM1913). Cell proliferation, cell cycle, and the concentrations of estradiol and 5α-dihydrotestosterone were measured to determine the endocrinological mechanism of sulfatase inhibition. Comparisons were made with inhibitions of reductive 17ß-hydroxysteroid dehydrogenases (17ß-HSDs). Proliferation studies showed that DNA synthesis in cancer cells was modestly decreased (approximately 20%), accompanied by an up to 6.5% in cells in the G0/G1 phase and cyclin D1 expression reduction. The concentrations of estradiol and 5α-dihydrotestosterone were decreased by 26% and 3% respectively. However, supplementation of 5α-dihydrotestosterone produced a significant increase (approximately 35.6%) in the anti-proliferative effect of sulfatase inhibition. This study has clarified sex-hormone control by sulfatase in BC, suggesting that the different roles of estradiol and 5α-dihydrotestosterone can lead to a reduction in the effect of sulfatase inhibition when compared with 17ß-HSD7 inhibition. This suggests that combined treatment of sulfatase inhibitors with 17ß-HSD inhibitors such as the type7 inhibitor could hold promise for hormone-dependent breast cancer.

Ligand-based pharmacophore modeling and virtual screening for the discovery of novel 17ß-hydroxysteroid dehydrogenase 2 inhibitors.

17ß-Hydroxysteroid dehydrogenase 2 (17ß-HSD2) catalyzes the inactivation of estradiol into estrone. This enzyme is expressed only in a few tissues, and therefore its inhibition is considered as a treatment option for osteoporosis to ameliorate estrogen deficiency. In this study, ligand-based pharmacophore models for 17ß-HSD2 inhibitors were constructed and employed for virtual screening. From the virtual screening hits, 29 substances were evaluated in vitro for 17ß-HSD2 inhibition. Seven compounds inhibited 17ß-HSD2 with low micromolar IC50 values. To investigate structure-activity relationships (SAR), 30 more derivatives of the original hits were tested. The three most potent hits, 12, 22, and 15, had IC50 values of 240 nM, 1 µM, and 1.5 µM, respectively. All but 1 of the 13 identified inhibitors were selective over 17ß-HSD1, the enzyme catalyzing conversion of estrone into estradiol. Three of the new, small, synthetic 17ß-HSD2 inhibitors showed acceptable selectivity over other related HSDs, and six of them did not affect other HSDs.

Chemical synthesis, characterisation and biological evaluation of lactonic-estradiol derivatives as inhibitors of 17ß-hydroxysteroid dehydrogenase type 1.

To control estradiol (E2) formation, we are interested in synthesizing inhibitors of 17ß-hydroxyteroid dehydrogenase type 1 (17ß-HSD1). Since the results of docking experiments have shown that E2-lactone derivatives substituted in position 19 or 20 (E-ring) could generate interactions with the active site of the enzyme, we carried out their chemical synthesis. After having prepared the 16ß,17ß-γ-lactone-E2 in four steps starting from estrone (E1), we introduced the molecular diversity by adding a hydroxymethyl, a methylcarboxylate, a carboxy or an allyl group. The allyl derivative was used as a key intermediate to generate a hydroxyethyl side chain in α or ß position. Two lactols were also obtained from two hydroxyalkyl lactones. Enzymatic assays revealed that lactone and lactol derivatives weakly inhibited 17ß-HSD1 in homogenized HEK-293 cells overexpressing 17ß-HSD1 (34-60% at 1 µM) and in intact T-47D cells expressing 17ß-HSD1 (10-40% at 10 µM). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Synthesis and biological evaluation of phenyl substituted 1H-1,2,4-triazoles as non-steroidal inhibitors of 17ß-hydroxysteroid dehydrogenase type 2.

A series of disubstituted-1H-1,2,4-triazole derivatives was synthesized with the aim of developing new non-steroidal inhibitors of 17ß-hydroxysteroid dehydrogenase type 2 (17ßHSD2) - a novel and attractive target for the treatment of osteoporosis. 17ßHSD2 catalyzes the oxidation of the highly active estrogen 17ß-estradiol (E2) and androgen testosterone (T) into the weak estrone and androstenedione, respectively. Inhibition of this enzyme will locally in the bone lead to an increase in E2 and T levels, two key players in the maintenance of the balance between bone resorption and bone formation. In this study, a new class of 17ßHSD2 inhibitors with a 1H-1,2,4-triazole scaffold was identified; the three best compounds 8b, 8f, and 13a showed moderate 17ßHSD2 inhibitory activity and a good selectivity toward 17ßHSD1. They could be a useful tool to map the unexplored enzyme active site.

Species used for drug testing reveal different inhibition susceptibility for 17beta-hydroxysteroid dehydrogenase type 1.

Steroid-related cancers can be treated by inhibitors of steroid metabolism. In searching for new inhibitors of human 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD 1) for the treatment of breast cancer or endometriosis, novel substances based on 15-substituted estrone were validated. We checked the specificity for different 17beta-HSD types and species. Compounds were tested for specificity in vitro not only towards recombinant human 17beta-HSD types 1, 2, 4, 5 and 7 but also against 17beta-HSD 1 of several other species including marmoset, pig, mouse, and rat. The latter are used in the processes of pharmacophore screening. We present the quantification of inhibitor preferences between human and animal models. Profound differences in the susceptibility to inhibition of steroid conversion among all 17beta-HSDs analyzed were observed. Especially, the rodent 17beta-HSDs 1 were significantly less sensitive to inhibition compared to the human ortholog, while the most similar inhibition pattern to the human 17beta-HSD 1 was obtained with the marmoset enzyme. Molecular docking experiments predicted estrone as the most potent inhibitor. The best performing compound in enzymatic assays was also highly ranked by docking scoring for the human enzyme. However, species-specific prediction of inhibitor performance by molecular docking was not possible. We show that experiments with good candidate compounds would out-select them in the rodent model during preclinical optimization steps. Potentially active human-relevant drugs, therefore, would no longer be further developed. Activity and efficacy screens in heterologous species systems must be evaluated with caution.

Ethanolic extracts of black cohosh (Actaea racemosa) inhibit growth and oestradiol synthesis from oestrone sulphate in breast cancer cells.

Extracts of black cohosh (Actaea racemosa) and soy are used as 'natural' alternatives to conventional hormone replacement therapy (HRT) and there is some evidence that soy may protect against breast cancer by inhibiting the production of active oestrogens. This study compares the action of ethanolic extracts of black cohosh (BCE) and genistein on growth and enzyme activity in MCF-7 and MDA-MB-123 breast cancer cells. BCE inhibited growth at the two highest doses tested, i.e. 50 and 100 microg/ml, whilst genistein stimulated growth in the oestrogen receptor positive (ER(+)) MCF-7 cells, but at high doses it inhibited growth in both cell lines. BCE did not affect the conversion of androstenedione to oestradiol and only the highest doses (50 and 100 microg/ml) significantly inhibited the conversion of oestrone to oestradiol in MDA cells. In contrast, BCE induced a dose-dependent inhibition of the conversion of oestrone sulphate to oestradiol in both cell lines, whilst in human granulosa lutein (GL) cells enzyme activity was only inhibited at the highest dose of BCE. Genistein had no significant effect on enzyme activity in breast cancer cells and like BCE only the highest doses (10 and 50 microM) inhibited enzyme activity in human GL cells. In vivo genistein may have growth stimulatory effects on breast tissue but BCE not only inhibits growth but inhibits the conversion of oestrone sulphate to active oestradiol, considered by some, to be the preferred pathway of oestradiol synthesis in breast tissue.