Substrate inhibition of 17β-HSD1 in living cells and regulation of 17β-HSD7 by 17β-HSD1 knockdown

This study addresses first the role of human 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) in breast cancer (BC) cells. The enzyme has a high estrone-activating activity that is subject to strong substrate inhibition as shown by enzyme kinetics at the molecular level. We used BC cells to verify this phenomenon in living cells: estrone concentration increase did reduce the reaction with 0.025 to 4μM substrate. Moreover, 5α-dihydrotestosterone (DHT) demonstrated some inhibition of estrogen activation at both the molecular and cellular levels. The presence of DHT did not change the tendency toward substrate inhibition for estrone conversion, but shifted the inhibition toward higher substrate concentrations. Moreover, a binding study demonstrated that both DHT and dehydroepiandrosterone (DHEA) can be bound to the enzyme, thereby supporting the multi-specificity of 17β-HSD1. We then followed the concentrations of estradiol and performed q-RT-PCR measurements of reductive 17β-HSDs after 17β-HSD1 inhibition. The estradiol decrease by the 17β-HSD1 inhibition was demonstrated lending support to this observation. Knockdown and inhibition of 17β-HSD1 produced reduction in estradiol levels and the down-regulation of another reductive enzyme 17β-HSD7, thus "amplifying" the reduction of estradiol by the 17β-HSD1 modulation itself. The critical positioning of 17β-HSD7 in sex-hormone-regulation as well as the mutual regulation of steroid enzymes via estradiol in BC, are clearly demonstrated. Our study demonstrates that fundamental enzymological mechanisms are relevant in living cells. Moreover, further enzyme study in cells is merited to advance biological and medical research. We also demonstrated the central role of 17β-HSD7 in sex-hormone conversion and regulation, supporting it as a novel target for estrogen-dependent (ER+) BC.

Current knowledge of the multifunctional 17β-hydroxysteroid dehydrogenase type 1 (HSD17B1)

At the late 1940s, 17β-HSD1 was discovered as the first member of the 17β-HSD family with its gene cloned. The three-dimensional structure of human 17β-HSD1 is the first example of any human steroid converting enzyme. The human enzyme's structure and biological function have thus been studied extensively in the last two decades. In humans, the enzyme is expressed in placenta, ovary, endometrium and breast. The high activity of estrogen activation provides the basis of 17β-HSD1's implication in estrogen-dependent diseases, such as breast cancer, endometriosis and non-small cell lung carcinomas. Its dual function in estrogen activation and androgen inactivation has been revealed in molecular and breast cancer cell levels, significantly stimulating the proliferation of such cells. The enzyme's overexpression in breast cancer was demonstrated by clinical samples. Inhibition of human 17β-HSD1 led to xenograft tumor shrinkage. Unfortunately, through decades of studies, there is still no drug using the enzyme's inhibitors available. This is due to the difficulty to get rid of the estrogenic activity of its inhibitors, which are mostly estrogen analogues. New non-steroid inhibitors for the enzyme provide new hope for non-estrogenic inhibitors of the enzyme.

Contribution to the development of inhibitors of 17β-hydroxysteroid dehydrogenase types 1 and 7: key tools for studying and treating estrogen-dependent diseases

17β-Hydroxysteroid dehydrogenases (17β-HSDs) belong to a group of key enzymes involved in the biosynthesis of steroidal hormones by catalyzing the reduction of 17-ketosteroids or the oxidation of 17β-hydroxysteroids. From three members known in the early nineties, the 17β-HSD functional family has grown to 15 members over the last 20 years. This growing number of 17β-HSD isoforms questioned the importance of each member, especially in their implication in estrogen- and androgen-dependent diseases, such as breast and prostate cancers. One of the strategies used to address the physiological importance of 17β-HSDs is to use potent and selective inhibitors. Furthermore, enzyme inhibitors could also be of therapeutic interest by reducing the level of estradiol (E2). Focusing on estrogens, we targeted 17β-HSD types 1 and 7, two enzymes able to transform the weak estrogen estrone (E1) into the potent estrogen E2. The present review article gives a description of different classes of inhibitors of 17β-HSD1 (C6-derivatives of E2, C16-derivatives of E2 as alkylating and dual action compounds, E2-adenosine hybrids, E2-simplified adenosine hybrids, and C16-derivatives of E1 or E2) and of inhibitors of 17β-HSD7, all these inhibitors developed in our laboratory. The chemical structures and inhibitory activity of these steroidal inhibitors, their potential as therapeutic agents, and their use as tools to elucidate the role of these enzymes in particular biological systems will be discussed. Article from the Special issue on Targeted Inhibitors.

Preparation of 6beta-estradiol derivative libraries as bisubstrate inhibitors of 7beta-hydroxysteroid dehydrogenase type using the multidetachable sulfamate linker

Combinatorial chemistry is a powerful tool used to rapidly generate a large number of potentially biologically active compounds. In our goal to develop bisubstrate inhibitors of 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) that interact with both the substrate (estrone or estradiol) and the cofactor (NAD(P)H) binding sites, we used parallel solid-phase synthesis to prepare three libraries of 16beta-estradiol derivatives with two or three levels of molecular diversity. From estrone, we first synthesized a sulfamate precursor that we loaded on trityl chloride resin using the efficient multidetachable sulfamate linker strategy recently developed in our laboratory. We then introduced molecular diversity [one or two amino acid(s) followed by a carboxylic acid] on steroid nucleus by Fmoc peptide chemistry. Finally, after a nucleophilic cleavage, libraries of 30, 63 and 25 estradiol derivatives were provided. A library of 30 sulfamoylated estradiol derivatives was also generated by acidic cleavage and its members were screened for inhibition of steroid sulfatase. Biological evaluation on homogenated HEK-293 cells overexpressing 17beta-HSD1 of the estradiol derivatives carrying different oligoamide-type chains at C-16 first revealed that three levels of molecular diversity (a spacer of two amino acids) were necessary to interact with the adenosine part of the cofactor binding site. Second, the best inhibition was obtained when hydrophobic residues (phenylalanine) were used as building blocks.

Design, chemical synthesis, and in vitro biological evaluation of simplified estradiol–adenosine hybrids as inhibitors of 17β-hydroxysteroid dehydrogenase type 1

A series of estradiol (E2) derivatives were designed to interact with both the substrate- and the cofactor-binding sites of 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1). These analogues of potent E2–adenosine hybrid inhibitor EM-1745, where the adenosine moiety was replaced by a more stable benzene derivative, were synthesized from estrone using alkene cross-metathesis and Sonogashira coupling reactions as key steps. In vitro biological evaluation of these steroid derivatives revealed that a spacer of 13 methylenes, between the 16β-position of E2 and the adenosine mimic bearing a carboxylic acid group, gave the best inhibition of 17β-HSD1.

A 3D QSAR model of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core applying molecular dynamics simulations and ligand-protein docking

The 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) enzyme plays a crucial role in female hormonal regulation by catalysing the NADPH-dependent reduction of the less potent estrone E1 into the biologically active estradiol E2. Because 17beta-HSD1 is a key enzyme in E2 biosynthesis, it has emerged as an attractive drug target for inhibitor development. Herein we report the plausible binding modes and a 3D QSAR model of 17beta-HSD1 inhibitors based on a (di)cycloalkenothieno[2,3-d]pyrimidin-4(3H)-one core. Two generated enzyme complexes with potent inhibitors were subjected to molecular dynamics simulation to mimic the dynamic process of inhibitor binding. A set of 17beta-HSD1 inhibitors based on the thieno[2,3-d]pyrimidin-4(3H)-one core were docked into the resulting active site, and a CoMFA model employing the most extensive training set to date was generated. The model was validated with an external test set. Active site residues involved in inhibitor binding and CoMFA fields for steric and electrostatic interactions were identified. The model will be used to guide structural modifications of 17beta-HSD1 inhibitors based on a thieno[2,3-d]pyrimidin-4(3H)-one core in order to improve the biological activity as well as in the design of novel 17beta-HSD1 inhibitors.

Novel inhibitors of 17beta-hydroxysteroid dehydrogenase type 1: templates for design

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the interconversion between the oxidized and reduced forms of androgens and estrogens at the 17 position. The 17beta-HSD type 1 enzyme (17beta-HSD1) catalyzes the reduction of estrone (E1) to estradiol and is expressed in malignant breast cells. Inhibitors of this enzyme thus have potential as treatments for hormone dependent breast cancer. Syntheses and biological evaluation of novel non-steroidal inhibitors designed to mimic the E1 template are reported using information from potent steroidal inhibitors. Of the templates investigated biphenyl ethanone was promising and led to inhibitors with IC(50) values in the low micromolar range.

Design and synthesis of bisubstrate inhibitors of type 1 17beta-hydroxysteroid dehydrogenase: overview and perspectives

Type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD1) is a key steroidogenic enzyme that catalyses the reduction of steroid estrone into the most potent endogenous estrogen estradiol using the cofactor NAD(P)H. Bisubstrate inhibition is a good way to enhance the potency of inhibitors of cofactor-assisted enzymes. The design of a bisubstrate inhibitor of 17beta-HSD1, the estradiol/adenosine hybrid EM-1745, is reviewed and strategies for future designs of inhibitors are proposed.

Focused Libraries of 16-Substituted Estrone Derivatives and Modified E-Ring Steroids: Inhibitors of 17ß-Hydroxysteroid Dehydrogenase Type 1

17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), an oxidoreductase which has a preferential reductive activity using NADPH as cofactor, converts estrone to estradiol and is expressed in many steroidogenic tissues including breast and in malignant breast cells. As estradiol stimulates the growth and development of hormone-dependent breast cancer, inhibition of the final step of its synthesis is an attractive target for the treatment of this disease. The parallel synthesis of novel focused libraries of 16-substituted estrone derivatives and modified E-ring pyrazole steroids as new potent 17beta-HSD1 inhibitors is described. Substituted 3-O-sulfamoylated estrone derivatives were used as templates and were immobilised on 2-chlorotrityl chloride resin to give resin-bound scaffolds with a multi-detachable linker. Novel focused libraries of 16-substituted estrone derivatives and new modified E-ring steroids were assembled from these immobilised templates using solid-phase organic synthesis and solution-phase methodologies. Among the derivatives synthesised, the most potent 17beta-HSD1 inhibitors were 25 and 26 with IC50 values in T-47D human breast cancer cells of 27 and 165 nm, respectively. Parallel synthesis resulting in a library of C5'-linked amides from the pyrazole E-ring led to the identification of 62 with an IC50 value of 700 nM. These potent inhibitors of 17beta-HSD1 have a 2-ethyl substituent which will decrease their estrogenic potential. Several novel 17beta-HSD1 inhibitors emerged from these libraries and these provide direction for further template exploration in this area. A new efficient diastereoselective synthesis of 25 has also been developed to facilitate supply for in vivo evaluation, and an X-ray crystal structure of this inhibitor is presented.

Modification of estrone at the 6, 16, and 17 positions: novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase type 1

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the interconversion between the oxidized and reduced forms of androgens and estrogens at the 17 position. The 17beta-HSD type 1 enzyme (17beta-HSD1) catalyzes the reduction of estrone to estradiol and is expressed in malignant breast cells. Inhibitors of this enzyme thus have potential as treatments for hormone dependent breast cancer. Here we report the syntheses and biological evaluation of novel inhibitors based on the estrone or estradiol template. These have been investigated by modification at the 6, 16 or 17 positions or combinations of these in order to gain information about structure-activity relationships by probing different areas in the enzyme active site. Activity data have been incorporated into a QSAR with predictive power, and the X-ray crystal structures of compounds 15 and 16c have been determined. Compound 15 has an IC50 of 320 nM for 17beta-HSD1 and is selective for 17beta-HSD1 over 17beta-HSD2. Three libraries of amides are also reported that led to the identification of inhibitors 19e and 20a, which have IC50 values of 510 and 380 nM respectively, and 20 h which, having an IC50 value of 37 nM, is the most potent inhibitor of 17beta-HSD1 reported to date. These amides are also selective for 17beta-HSD1 over 17beta-HSD2.

Estradiol−Adenosine Hybrid Compounds Designed to Inhibit Type 1 17β-Hydroxysteroid Dehydrogenase

The steroidogenic enzyme type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the synthesis of estradiol (E(2)), a hormone well-known to stimulate the growth of estrogen-sensitive tumors. To obtain compounds able to control E(2) formation, two moieties were linked with a methylene side chain: an adenosine moiety for interacting with the cofactor-binding site and an E(2) moiety for interacting with the substrate-binding site. When tested as inhibitors of type 1 17beta-HSD, the hybrid compounds inhibited the reductive activity (E(1) into E(2)) with IC(50) values ranging from 52 to 1,000 nM. The optimal side-chain length was determined to be eight methylene groups for a 16 beta-orientation. The presence of two components (E(2) and adenosine) is essential for good inhibition, since 16 beta-nonyl-E(2) and 5-nonanoyl-O-adenosine, two compounds having only one of the components, did not inhibit the enzyme. Moreover, the 3D-structure analysis of EM-1,745 complexed with type 1 17beta-HSD showed key interactions with both substrate- and cofactor-binding sites.

Novel and potent 17beta-hydroxysteroid dehydrogenase type 1 inhibitors

Structure-based drug design using the crystal structure of human 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) led to the discovery of novel, selective, and the most potent inhibitors of 17beta-HSD1 reported to date. Compounds 1 and 2 contain a side chain with an m-pyridylmethyl-amide functionality extended from the 16beta position of a steroid scaffold. A mode of binding is proposed for these inhibitors, and 2 is a steroid-based 17beta-HSD1 inhibitor with the potential for further development.

Steroids: reactions and partial synthesis

This article reviews the progress in the chemistry of the steroids that was published between January and December 2003. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 152 references.

Synthesis of Simplified Hybrid Inhibitors of Type 1 17β-Hydroxysteroid Dehydrogenase via Cross-Metathesis and Sonogashira Coupling Reactions

[structure: see text] The inhibitor of type 1 17beta-hydroxysteroid dehydrogenase EM-1745 (1) exhibits affinity for both the substrate (estrone or estradiol) and the cofactor (NAD(P)H) binding domains. However, to increase its bioavailability, this compound needs to be simplified. The efficient and convergent synthesis of simplified substrate/cofactor hybrid inhibitors (compounds 2) involving a cross-metathesis and a Sonogashira coupling reaction as key steps is described. Compounds 2a-c were also tested as enzyme inhibitors and compared to EM-1745.