Alexander Oster

17β-Hydroxysteroid dehydrogenases (17β-HSDs) as therapeutic targets: protein structures, functions, and recent progress in inhibitor development.

17β-Hydroxysteroid dehydrogenases (17β-HSDs) are oxidoreductases, which play a key role in estrogen and androgen steroid metabolism by catalyzing final steps of the steroid biosynthesis. Up to now, 14 different subtypes have been identified in mammals, which catalyze NAD(P)H or NAD(P)(+) dependent reductions/oxidations at the 17-position of the steroid. Depending on their reductive or oxidative activities, they modulate the intracellular concentration of inactive and active steroids. As the genomic mechanism of steroid action involves binding to a steroid nuclear receptor, 17β-HSDs act like pre-receptor molecular switches. 17β-HSDs are thus key enzymes implicated in the different functions of the reproductive tissues in both males and females. The crucial role of estrogens and androgens in the genesis and development of hormone dependent diseases is well recognized. Considering the pivotal role of 17β-HSDs in steroid hormone modulation and their substrate specificity, these proteins are promising therapeutic targets for diseases like breast cancer, endometriosis, osteoporosis, and prostate cancer. The selective inhibition of the concerned enzymes might provide an effective treatment and a good alternative to the existing endocrine therapies. Herein, we give an overview of functional and structural aspects for the different 17β-HSDs. We focus on steroidal and non-steroidal inhibitors recently published for each subtype and report on existing animal models for the different 17β-HSDs and the respective diseases. Article from the Special issue on Targeted Inhibitors.

Design, Synthesis, Biological Evaluation and Pharmacokinetics of Bis(hydroxyphenyl) substituted Azoles, Thiophenes, Benzenes, and Aza-Benzenes as Potent and Selective Nonsteroidal Inhibitors of 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1)

17beta-Estradiol (E2), the most potent female sex hormone, stimulates the growth of mammary tumors and endometriosis via activation of the estrogen receptor alpha (ERalpha). 17beta-Hydroxysteroid dehydrogenase type 1 (17beta-HSD1), which is responsible for the catalytic reduction of the weakly active estrogen estrone (E1) into E2, is therefore discussed as a novel drug target. Recently, we have discovered a 2,5-bis(hydroxyphenyl) oxazole to be a potent inhibitor of 17beta-HSD1. In this paper, further structural optimizations were performed: 39 bis(hydroxyphenyl) azoles, thiophenes, benzenes, and aza-benzenes were synthesized and their biological properties were evaluated. The most promising compounds of this study show enhanced IC 50 values in the low nanomolar range, a high selectivity toward 17beta-HSD2, a low binding affinity to ERalpha, a good metabolic stability in rat liver microsomes, and a reasonable pharmacokinetic profile after peroral application. Calculation of the molecular electrostatic potentials revealed a correlation between 17beta-HSD1 inhibition and the electron density distribution.

New Insights into the SAR and Binding Modes of Bis(hydroxyphenyl)thiophenes and -benzenes: Influence of Additional Substituents on 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1) Inhibitory Activity and Selectivity

17beta-Hydroxysteroid dehydrogenase type 1 (17beta-HSD1) is responsible for the catalytic reduction of weakly active E1 to highly potent E2. E2 stimulates the proliferation of hormone-dependent diseases via activation of the estrogen receptor alpha (ERalpha). Because of the overexpression of 17beta-HSD1 in mammary tumors, this enzyme should be an attractive target for the treatment of estrogen-dependent pathologies. Recently, we have reported on a series of potent 17beta-HSD1 inhibitors: bis(hydroxyphenyl) azoles, thiophenes, and benzenes. In this paper, different substituents are introduced into the core structure and the biological properties of the corresponding inhibitors are evaluated. Computational methods and analysis of different X-rays of 17beta-HSD1 lead to identification of two different binding modes for these inhibitors. The fluorine compound 23 exhibits an IC(50) of 8 nM and is the most potent nonsteroidal inhibitor described so far. It also shows a high selectivity (17beta-HSD2, ERalpha) and excellent pharmacokinetic properties after peroral application to rats.

Design, synthesis and biological evaluation of bis(hydroxyphenyl) azoles as potent and selective non-steroidal inhibitors of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) for the treatment of estrogen-dependent diseases

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) catalyses the reduction of the weakly active estrone (E1) into the most potent estrogen, 17beta-estradiol (E2). E2 stimulates the growth of hormone-dependent diseases via activation of the estrogen receptors (ERs). 17beta-HSD1 is often over-expressed in breast cancer cells. Thus, it is an attractive target for the treatment of mammary tumours. The combination of a ligand- and a structure-based drug design approach led to the identification of bis(hydroxyphenyl) azoles as potential inhibitors of 17beta-HSD1. Different azoles and hydroxy substitution patterns were investigated. The compounds were evaluated for activity and selectivity with regard to 17beta-HSD2, ERalpha and ERbeta. The most potent compound is 3-[5-(4-hydroxyphenyl)-1,3-oxazol-2-yl]phenol (18, IC(50)=0.31 microM), showing very good selectivity, high cell permeability and medium CaCo-2 permeability.

Bicyclic Substituted Hydroxyphenylmethanones as Novel Inhibitors of 17β-Hydroxysteroid Dehydrogenase Type 1 (17β-HSD1) for the Treatment of Estrogen-Dependent Diseases

Estradiol (E2), the most important estrogen in humans, is involved in the initiation and progression of estrogen-dependent diseases such as breast cancer and endometriosis. Its local production in the target cell is regulated by 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), which catalyzes E2-formation by reduction of the weak estrogen estrone (E1). Because the enzyme is expressed in the diseased tissues, inhibition of 17β-HSD1 is considered as a promising therapy for the treatment of estrogen-dependent diseases. For the development of novel inhibitors, a structure- and ligand-based design strategy was applied, resulting in bicyclic substituted hydroxyphenylmethanones. In vitro testing revealed high inhibitory potencies toward human placental 17β-HSD1. Compounds were further evaluated with regard to selectivity (17β-HSD2, estrogen receptors ERα and ERβ), intracellular activity (T47D cells), and metabolic stability. The most promising compounds, 14 and 15, showed IC(50) values in the low nanomolar range in the cell-free and cellular assays (8-27 nM), more than 30-fold selectivity toward 17β-HSD2 and no affinity toward the ERs. The data obtained make these inhibitors interesting candidates for further preclinical evaluation.

Novel estrone mimetics with high 17β-HSD1 inhibitory activity

17Beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) catalyzes the reduction of estrone into estradiol, which is the most potent estrogen in humans. Lowering intracellular estradiol concentration by inhibition of this enzyme is a promising new option for the treatment of estrogen-dependent diseases like breast cancer and endometriosis. Combination of ligand- and structure-based design resulted in heterocyclic substituted biphenylols and their aza-analogs as new 17beta-HSD1 inhibitors. The design was based on mimicking estrone, especially focusing on the imitation of the D-ring keto group with (substituted) heterocycles. Molecular docking provided insights into plausible protein-ligand interactions for this class of compounds. The most promising compound 12 showed an inhibitory activity in the high nanomolar range and very low affinity for the estrogen receptors alpha and beta. Thus, compound 12 is a novel tool for the elucidation of the pharmacological relevance of 17beta-HSD1 and might be a lead for the treatment of estrogen-dependent diseases.

Selective inhibition of 17β-hydroxysteroid dehydrogenase type 1 (17βHSD1) reduces estrogen responsive cell growth of T47-D breast cancer cells

The most potent estrogen estradiol (E2) plays a pivotal role in the initiation and progression of estrogen dependent diseases. 17beta-Hydroxysteroid dehydrogenase type 1 (17betaHSD1) catalyses the NADPH-dependent E2-formation from estrone (E1). It is often overexpressed in breast cancer and endometriosis. For this reason, inhibition of 17betaHSD1 is a promising strategy for the treatment of these diseases. In the present paper, we investigate the estrogen responsive cell growth of T47-D breast cancer cells, the intracellular inhibitory activity of non-steroidal 17betaHSD1-inhibitors and their effects on estrogen dependent cell growth in vitro. At equal concentrations the estrogens E1 and E2 induced the same extent of growth stimulation indicating fast intracellular conversion of E1 into E2. Application of inhibitors selectively prevented stimulation of proliferation evoked by E1-treatment whereas E2-mediated stimulation was not affected. Furthermore, intracellular E2-formation from E1 was significantly inhibited with IC(50)-values in the nanomolar range. In conclusion, our findings strongly support suitability of non-steroidal 17betaHSD1-inhibitors for the treatment of estrogen dependent diseases.

The role of the heterocycle in bis(hydroxyphenyl)triazoles for inhibition of 17β-Hydroxysteroid Dehydrogenase (17β-HSD) type 1 and type 2

17beta-Hydroxysteroid dehydrogenase type 1 (17beta-HSD1) is responsible for the catalytic reduction of the weak estrogen estrone (E1) into the highly potent 17beta-estradiol (E2). As 17beta-HSD1 is often overexpressed in mammary tumors and endometriosis, the selective inhibition of this enzyme is discussed as a promising approach for the treatment of estrogen-dependent diseases. Recently, we reported on bis(hydroxyphenyl)azoles as a new class of potent inhibitors of 17beta-HSD1. In this paper, we focused on bis(hydroxyphenyl)triazoles. The influence of nitrogens on the potency as well as the space available around the heterocycle was investigated. Substituents were introduced on the triazole core in order to establish additional interactions with the enzyme active site. The compounds were evaluated for activity towards 17beta-HSD1 and selectivity with regard to 17beta-HSD2, the enzyme which is responsible for the deactivation of E2 into E1. 3-[4-(4-Hydroxyphenyl)-1H-1,2,3-triazol-1-yl]phenol (3) was the most active compound discovered in this study with an IC(50) value of 840nM and a reasonable selectivity towards 17beta-HSD2.

Bicyclic Substituted Hydroxyphenylmethanone Type Inhibitors of 17 β‐Hydroxysteroid Dehydrogenase Type 1 (17 β‐HSD1): The Role of the Bicyclic Moiety

An attractive target that has still to be explored for the treatment of estrogen‐dependent diseases, such as breast cancer and endometriosis, is the enzyme responsible for the last step in the biosynthesis of estradiol (E2): 17β‐hydroxysteroid dehydrogenase type 1 (17β‐HSD1). It catalyzes the reduction of the weakly active estrone (E1) into E2, which is the most potent estrogen in humans. Inhibition of 17β‐HSD1 lowers intracellular E2 concentrations and thus presents a therapeutic target for estrogen‐dependent pathologies. Recently, we reported a new class of highly active and selective 17β‐HSD1 inhibitors: bicyclic substituted hydroxyphenylmethanones. Here, further structural variations on the bicyclic moiety are described, especially focusing on the exchange of its hydroxy function. Twenty‐nine novel inhibitors were synthesized and evaluated for 17β‐HSD1 inhibition in a cell‐free and cellular assay, for selectivity toward 17βHSD2 and estrogen receptors (ER) alpha and beta, as well as for metabolic stability. The best compound exhibited IC50 values of 12 nM (cell‐free assay) and 78 nM (cellular assay), high selectivity for 17β‐HSD1, and reasonable metabolic stability. A molecular docking study provided insight into the protein–ligand interactions of this compound with 17β‐HSD1.