Potent Dual Inhibitors of Steroid Sulfatase and 17ß-Hydroxysteroid Dehydrogenase Type 1 with a Suitable Pharmacokinetic Profile for In Vivo Proof-of-Principle Studies in an Endometriosis Mouse Model.

Treating estrogen-dependent diseases like endometriosis with drugs suppressing local estrogen activation may be superior to existing endocrine therapies. Steroid sulfatase (STS) and 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) are key enzymes of local estrogen activation. We describe the rational design, synthesis, and biological profilation of furan-based compounds as a novel class of dual STS/17ß-HSD1 inhibitors (DSHIs). In T47D cells, compound 5 showed irreversible inhibition of STS and potent, reversible inhibition of 17ß-HSD1. It was selective over 17ß-HSD2 and displayed high metabolic stabilities in human and mouse liver S9 fractions. No effect on cell viability was detected up to 31 µM (HEK293) and 23 µM (HepG2), respectively, and there was no activation of the aryl hydrocarbon receptor (AhR) up to 3.16 µM. Single daily application to mice revealed steady-state plasma levels high enough to make this compound eligible for an in vivo proof-of-principle study in a mouse endometriosis model.

Dual Targeting of Steroid Sulfatase and 17ß-Hydroxysteroid Dehydrogenase Type 1 by a Novel Drug-Prodrug Approach: A Potential Therapeutic Option for the Treatment of Endometriosis.

A novel approach for the dual inhibition of steroid sulfatase (STS) and 17ß-hydroxysteroid dehydrogenase type 1(17ß HSD1) by a single drug was explored, starting from in-house 17ß HSD1 inhibitors via masking their phenolic OH group with a sulfamate ester. The sulfamates were intentionally designed as drugs for the inhibition of STS and, at the same time, prodrugs for 17ß-HSD1 inhibition ("drug-prodrug approach"). The most promising sulfamates 13, 16, 18-20, 22-24, 36, and 37 showed nanomolar IC50 values for STS inhibition in a cellular assay and their corresponding phenols displayed potent 17ß-HSD1 inhibition in cell-free and cellular assays, high selectivity over 17ß-HSD2, reasonable metabolic stability, and low estrogen receptor α affinity. A close relationship was found between the liberation of the phenolic compound by sulfamate hydrolysis and 17ß-HSD1 inactivation. These results showed that the envisaged drug-prodrug concept was successfully implemented. The novel compounds constitute a promising class of therapeutics for the treatment of endometriosis and other estrogen-dependent diseases.

17ß-Hydroxysteroid Dehydrogenase Type 1 Inhibition: A Potential Treatment Option for Non-Small Cell Lung Cancer.

In the face of the clinical challenge posed by non-small cell lung cancer (NSCLC), the present need for new therapeutic approaches is genuine. Up to now, no proof existed that 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) is a viable target for treating this disease. Synthesis of a rationally designed library of 2,5-disubstituted furan derivatives followed by biological screening led to the discovery of 17ß-HSD1 inhibitor 1, capable of fully inhibiting human NSCLC Calu-1 cell proliferation. Its pharmacological profile renders it eligible for further in vivo studies. The very high selectivity of 1 over 17ß-HSD2 was investigated, revealing a rational approach for the design of selective inhibitors. 17ß-HSD1 and 1 hold promise in fighting NSCLC.

A Hybrid In Silico/In Vitro Target Fishing Study to Mine Novel Targets of Urolithin A and B: A Step Towards a Better Comprehension of Their Estrogenicity.

SCOPE: Urolithin A and B are gut metabolites of ellagic acid and ellagitannins associated with many beneficial effects. Evidence in vitro pointed to their potential as estrogenic modulators. However, both molecular mechanisms and biological targets involved in such activity are still poorly characterized, preventing a comprehensive understanding of their bioactivity in living organisms. This study aimed at rationally identifying novel biological targets underlying the estrogenic-modulatory activity of urolithins. METHODS AND RESULTS: The work relies on an in silico/in vitro target fishing study coupling molecular modeling with biochemical and cell-based assays. Estrogen sulfotransferase and 17ß-hydroxysteroid dehydrogenase are identified as potentially subject to inhibition by the investigated urolithins. The inhibition of the latter undergoes experimental confirmation either in a cell-free or cell-based assay, validating computational outcomes. CONCLUSIONS: The work describes target fishing as an effective tool to identify unexpected targets of food bioactives detailing the interaction at a molecular level. Specifically, it described, for the first time, 17ß-hydroxysteroid dehydrogenase as a target of urolithins and highlighted the need of further investigations to widen the understanding of urolithins as estrogen modulators in living organisms.

Design, Synthesis, and Biological Characterization of Orally Active 17ß-Hydroxysteroid Dehydrogenase Type 2 Inhibitors Targeting the Prevention of Osteoporosis.

Osteoporosis is predominantly treated with drugs that inhibit further bone resorption due to estrogen deficiency. Yet, osteoporosis drugs that not only inhibit bone resorption but also stimulate bone formation, such as potentially inhibitors of 17ß-hydroxysteroid dehydrogenase type 2 (17ß-HSD2), may be more efficacious in the treatment of osteoporosis. Blockade of 17ß-HSD2 is thought to increase intracellular estradiol and testosterone in bone, thereby inhibiting bone resorption by osteoclasts and stimulating bone formation by osteoblasts, respectively. We here describe the design, synthesis, and biological characterization of a novel bicyclic-substituted hydroxyphenylmethanone 17ß-HSD2 inhibitor (compound 24). Compound 24 is a nanomolar potent inhibitor of human 17ß-HSD2 (IC50 of 6.1 nM) and rodent 17ß-HSD2 with low in vitro cellular toxicity, devoid of detectable estrogen receptor α affinity, displays high aqueous solubility and in vitro metabolic stability, and has an excellent oral pharmacokinetic profile for testing in a rat osteoporosis model. Administration of 24 in a rat osteoporosis model demonstrates its bone-sparing efficacy.

Development of potential preclinical candidates with promising in vitro ADME profile for the inhibition of type 1 and type 2 17ß-Hydroxysteroid dehydrogenases: Design, synthesis, and biological evaluation.

Estrogens are the major female sex steroid hormones, estradiol (E2) being the most potent form in humans. Disturbing the balance between E2 and its weakly active oxidized form estrone (E1) leads to diverse types of estrogen-dependent diseases such as endometriosis or osteoporosis. 17ß-Hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyzes the biosynthesis of E2 by reduction of E1 while the type 2 enzyme catalyzes the reverse reaction. Thus, 17ß-HSD1 and 17ß-HSD2 are attractive targets for treatment of estrogen-dependent diseases. Recently, we reported the first proof-of-principle study of a 17ß-HSD2 inhibitor in a bone fracture mouse model, using subcutaneous administration. In the present study, our aim was to improve the in vitro ADME profile of the most potent 17ß-HSD1 and 17ß-HSD2 inhibitors described so far. The optimized compounds show strong and selective inhibition of both the human enzymes and their murine orthologs. In addition, they display good metabolic stability in human liver microsomes (S9 fraction), low in vitro cytotoxicity as well as better aqueous solubility and physicochemical properties compared to the lead compounds. These achievements make the compounds eligible for testing in preclinical in vivo animal model studies on the effects of inhibition of 17ß-HSD1 and 17ß-HSD2.

Targeted Endocrine Therapy: Design, Synthesis, and Proof-of-Principle of 17ß-Hydroxysteroid Dehydrogenase Type 2 Inhibitors in Bone Fracture Healing.

Current therapies of steroid hormone-dependent diseases predominantly alter steroid hormone concentrations (or their actions) in plasma, in target and nontarget tissues alike, rather than in target organs only. Targeted therapy through the inhibition of steroidogenic enzymes may pose an attractive alternative with much less side effects. Here, we describe the design of a nanomolar potent 17ß-hydroxysteroid dehydrogenase type 2 (17ß-HSD2) inhibitor (compound 15) and successful targeted intracrine therapy in a mouse bone fracture model. Blockade of 17ß-HSD2 in bone is thought to increase intracellular estradiol (E2) and testosterone (T), which thereby inhibits bone resorption by osteoclasts and stimulates bone formation by osteoblasts, respectively. Administration of compound 15 in the mouse fracture model strongly increases the mechanical stability of the healing fractured bone because of a larger periosteal callus with newly formed bone without changing the plasma E2 and T concentrations. Steroidogenic 17ß-HSD2 inhibition thus enables targeted intracrine therapy.

Inhibitors of 17ß-hydroxysteroid dehydrogenase type 1, 2 and 14: Structures, biological activities and future challenges.

During the past 25 years, the modulation of estrogen action by inhibition of 17ß-hydroxysteroid dehydrogenase types 1 and 2 (17ß-HSD1 and 17ß-HSD2), respectively, has been pursued intensively. In the search for novel treatment options for estrogen-dependent diseases (EDD) and in order to explore estrogenic signaling pathways, a large number of steroidal and nonsteroidal inhibitors of these enzymes has been described in the literature. The present review gives a survey on the development of inhibitor classes as well as the structural formulas and biological properties of their most interesting representatives. In addition, rationally designed dual inhibitors of both 17ß-HSD1 and steroid sulfatase (STS) as well as the first inhibitors of 17ß-HSD14 are covered.

Highly Potent 17ß-HSD2 Inhibitors with a Promising Pharmacokinetic Profile for Targeted Osteoporosis Therapy.

Intracellular elevation of E2 levels in bone by inhibition of 17ß hydroxysteroid dehydrogenase type 2 (17ß-HSD2) without affecting systemic E2 levels is an attractive approach for a targeted therapy against osteoporosis, a disease which is characterized by loss of bone mineral density. Previously identified inhibitor A shows high potency on human and mouse 17ß-HSD2, but poor pharmacokinetic properties when applied perorally in mice. A combinatorial chemistry approach was utilized to synthesize truncated derivatives of A, leading to highly potent compounds with activities in the low nanomolar to picomolar range. Compound 33, comparable to A in terms of inhibitor potency against both human and mouse enzymes, displays high in vitro metabolic stability in human and mouse liver S9 fraction as well as low toxicity and moderate hepatic CYP inhibition. Thus, compound 33 showed a highly improved peroral pharmacokinetic profile in comparison to A, making 33 a promising candidate for further development.

Structure-based design and profiling of novel 17ß-HSD14 inhibitors.

The human enzyme 17ß-hydroxysteroid dehydrogenase 14 (17ß-HSD14) oxidizes the hydroxyl group at position 17 of estradiol and 5-androstenediol using NAD+ as cofactor. However, the physiological role of the enzyme remains unclear. We recently described the first class of nonsteroidal inhibitors for this enzyme with compound 1 showing a high 17ß-HSD14 inhibitory activity. Its crystal structure was used as starting point for a structure-based optimization in this study. The goal was to develop a promising chemical probe to further investigate the enzyme. The newly designed compounds revealed mostly very high inhibition of the enzyme and for seven of them the crystal structures of the corresponding inhibitor-enzyme complexes were resolved. The crystal structures disclosed that a small change in the substitution pattern of the compounds resulted in an alternative binding mode for one inhibitor. The profiling of a set of the most potent inhibitors identified 13 (Ki = 9 nM) with a good selectivity profile toward three 17ß-HSDs and the estrogen receptor alpha. This inhibitor displayed no cytotoxicity, good solubility, and auspicious predicted bioavailability. Overall, 13 is a highly interesting 17ß-HSD14 inhibitor, which might be used as chemical probe for further investigation of the target enzyme.

First Dual Inhibitors of Steroid Sulfatase (STS) and 17ß-Hydroxysteroid Dehydrogenase Type 1 (17ß-HSD1): Designed Multiple Ligands as Novel Potential Therapeutics for Estrogen-Dependent Diseases.

STS and 17ß-HSD1 are attractive targets for the treatment of estrogen-dependent diseases like endometriosis and breast cancer. The simultaneous inhibition of both enzymes appears more promising than blockage of either protein alone. We describe a designed multiple ligand approach resulting in highly potent dual inhibitors. The most interesting compound 9 showed nanomolar IC50 values for both proteins, membrane permeability, and no interference with estrogen receptors. It efficiently reversed E1S- and E1-induced T47D cell proliferation.

Treatment of estrogen-dependent diseases: Design, synthesis and profiling of a selective 17ß-HSD1 inhibitor with sub-nanomolar IC50 for a proof-of-principle study.

Current endocrine therapeutics for the estrogen-dependent disease endometriosis often lead to considerable side-effects as they act by reducing estrogen action systemically. A more recent approach takes advantage of the fact that the weak estrogen estrone (E1) which is abundant in the plasma, is activated in the target cell to the highly estrogenic estradiol (E2) by 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1). 17ß-HSD1 is overexpressed in endometriosis and thus a promising target for the treatment of this disease, with the prospect of less target-associated side-effects. Potent inhibitors from the class of bicyclic substituted hydroxyphenylmethanones with sulfonamide moiety recently described by us suffered from high molecular weight and low selectivity over 17ßHSD2, the physiological adversary of 17ß-HSD1. We describe the structural optimizations leading to the discovery of (5-(3,5-dichloro-4-methoxyphenyl)thiophen-2-yl)(2,6-difluoro-3-hydroxyphenyl)methanone 20, which displayed a sub-nanomolar IC50 towards 17ß-HSD1 as well as high selectivity over the type 2 enzyme, the estrogen receptors α and ß and a range of hepatic CYP enzymes. The compound did neither show cellular toxicity, nor PXR activation nor mutagenicity in the AMES II assay. Additional favourable pharmacokinetic properties (rat) make 20 a suitable candidate for proof-of-principle studies using xenotransplanted immunodeficient rats.

Towards the evaluation in an animal disease model: Fluorinated 17ß-HSD1 inhibitors showing strong activity towards both the human and the rat enzyme.

17ß-Estradiol (E2), the most potent human estrogen, is known to be involved in the etiology of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17ß-Hydroxysteroid dehydrogenase type 1 (17ß-HSD1) catalyses the last step of E2 biosynthesis and is thus a promising target for the treatment of EDD. The previously described bicyclic substituted hydroxyphenylmethanones (BSHs) display high inhibitory potency towards human 17ß-HSD1, but marginal activity towards rodent 17ß-HSD1, precluding a proof of principle study in an animal endometriosis model. The aim of this work was to perform structural optimizations in the BSHs class to enhance inhibitory activity against rodent (mouse and rat) 17ß-HSD1 while maintaining activity against the human enzyme. The introduction of fluorine atoms on the benzoyl moiety resulted in compounds with the desired properties. Molecular docking and homology modeling were applied to elucidate the binding mode and interspecies differences in activity. Compound 33 is the most potent inhibitor of both human and rat 17ß-HSD1 up to date (IC50 = 2 nM and 97 nM, respectively).

17ß-Hydroxysteroid Dehydrogenase Type 2 Inhibition: Discovery of Selective and Metabolically Stable Compounds Inhibiting Both the Human Enzyme and Its Murine Ortholog.

Design and synthesis of a new class of inhibitors for the treatment of osteoporosis and its comparative h17ß-HSD2 and m17ß-HSD2 SAR study are described. 17a is the first compound to show strong inhibition of both h17ß-HSD2 and m17ß-HSD2, intracellular activity, metabolic stability, selectivity toward h17ß-HSD1, m17ß-HSD1 and estrogen receptors α and ß as well as appropriate physicochemical properties for oral bioavailability. These properties make it eligible for pre-clinical animal studies, prior to human studies.

6-Hydroxybenzothiophene ketones: potent inhibitors of 17ß-hydroxysteroid dehydrogenase type†1 (17ß-HSD1) owing to favorable molecule geometry and conformational preorganization.

The inhibition of 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1), which catalyzes the conversion of estrone into the potent estrogen receptor agonist estradiol (E2), is discussed as a novel therapeutic approach for the treatment of estrogen-dependent diseases. Because the reduction of E2 would be basically limited to the target tissues, this approach is expected to cause fewer side effects than the currently employed antihormonal therapies. Recently, we reported on 6-hydroxybenzothiazole ketones as a new class of 17ß-HSD1 inhibitors with a notable activity/selectivity profile. In an attempt to further optimize these parameters, we modified the benzothiazole core by a systematic bioisosteric replacement. Thus, we were able to identify a new 6-hydroxybenzothiophene derivative that displayed stronger inhibition of 17ß-HSD1 (IC50 =13 nM) and that was also more selective than a benzothiazole analog. Using ab initio calculations, we found that the higher potency of the 6-hydroxybenzothiophene derivative was probably due to more favorable conformational preorganization of the scaffold for binding to the enzyme.

Inhibition of 17ß-HSD1: SAR of bicyclic substituted hydroxyphenylmethanones and discovery of new potent inhibitors with thioether linker.

Estradiol is the most potent estrogen in humans. It is known to be involved in the development and proliferation of estrogen dependent diseases such as breast cancer and endometriosis. The last step of its biosynthesis is catalyzed by 17ß-hydroxysteroid dehydrogenase type 1 (17ß- HSD1) which consequently is a promising target for the treatment of these diseases. Recently, we reported on bicyclic substituted hydroxyphenylmethanones as potent inhibitors of 17ß-HSD1. The present study focuses on rational structural modifications in this compound class with the aim of gaining more insight into its structure-activity relationship (SAR). (4-Hydroxyphenyl)-(5-(3-hydroxyphenylsulfanyl)-thiophen-2-yl)methanone (25) was discovered as a member of a novel potent class of human 17ß-HSD1 inhibitors. Computational methods were used to elucidate its interactions with the target protein. The compound showed activity also towards the murine 17ß-HSD1 enzyme and thus is a starting point for the design of compounds suitable for evaluation in an animal disease model.

Direct antiproliferative effect of nonsteroidal 17ß-hydroxysteroid dehydrogenase type 1 inhibitors in vitro.

Inhibition of the local formation of estrogens seems to be an attractive strategy for pharmacological intervention in hormone-dependent disorders. The direct antiproliferative properties of ten nonsteroidal 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1) inhibitors were investigated on human cancer cell lines of gynecological origin. The mechanism of the antiproliferative action was approximated by cell cycle analysis, fluorescent microscopy, BrdU assay, determination of caspase-3 activity and quantification of the expression of cell cycle regulators at mRNA level. Treatment of HeLa cells with some of the compounds resulted in a concentration-dependent inhibition of the G1-S transition and an increase in the apoptotic population. The most effective agents increased the expression of tumor suppressors p21 and p53, while CDK2 and Rb were down-regulated. The reported anticancer actions of the tested compounds are independent of the 17ß-HSD1-inhibiting capacity. These results indicate that it is possible to combine direct antiproliferative activity and 17ß-HSD1 inhibition resulting in novel agents with dual mode of action.

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.

Lead optimization of 17ß-HSD1 inhibitors of the (hydroxyphenyl)naphthol sulfonamide type for the treatment of endometriosis.

The reduction of estrone to estradiol, the most potent estrogen in human, is catalyzed by 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1). A promising approach for the treatment of estrogen-dependent diseases is the reduction of intracellular estradiol formation by inhibition of 17ß-HSD1. For the species-specific optimization of the (hydroxyphenyl)naphthols, a combinatorial approach was applied and enhanced by a focused synthesis that resulted in the aromatic-substituted (hydroxyphenyl)naphthol sulfonamides. Rigidification of 12 led to the 4-indolylsulfonamide 30, which is a highly active and selective human 17ß-HSD1 inhibitor, as well as a highly potent and selective inhibitor of 17ß-HSD1 from Callithrix jacchus. It shows no affinity to the estrogen receptors α and ß and good intracellular activity (T47D). Thus, compound 30 shows good properties for further ADMET studies and might be a candidate for the in vivo proof of concept in C. jacchus.

Hydroxybenzothiazoles as new nonsteroidal inhibitors of 17ß-hydroxysteroid dehydrogenase type 1 (17ß-HSD1).

17ß-estradiol (E2), the most potent estrogen in humans, known to be involved in the development and progession of estrogen-dependent diseases (EDD) like breast cancer and endometriosis. 17ß-HSD1, which catalyses the reduction of the weak estrogen estrone (E1) to E2, is often overexpressed in breast cancer and endometriotic tissues. An inhibition of 17ß-HSD1 could selectively reduce the local E2-level thus allowing for a novel, targeted approach in the treatment of EDD. Continuing our search for new nonsteroidal 17ß-HSD1 inhibitors, a novel pharmacophore model was derived from crystallographic data and used for the virtual screening of a small library of compounds. Subsequent experimental verification of the virtual hits led to the identification of the moderately active compound 5. Rigidification and further structure modifications resulted in the discovery of a novel class of 17ß-HSD1 inhibitors bearing a benzothiazole-scaffold linked to a phenyl ring via keto- or amide-bridge. Their putative binding modes were investigated by correlating their biological data with features of the pharmacophore model. The most active keto-derivative 6 shows IC50-values in the nanomolar range for the transformation of E1 to E2 by 17ß-HSD1, reasonable selectivity against 17ß-HSD2 but pronounced affinity to the estrogen receptors (ERs). On the other hand, the best amide-derivative 21 shows only medium 17ß-HSD1 inhibitory activity at the target enzyme as well as fair selectivity against 17ß-HSD2 and ERs. The compounds 6 and 21 can be regarded as first benzothiazole-type 17ß-HSD1 inhibitors for the development of potential therapeutics.