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

Recent advances in the development of 17beta-hydroxysteroid dehydrogenase inhibitors

The family of 17β-hydroxysteroid dehydrogenases (17β-HSDs) occupies a prominent place due to its number of isoforms, which carry out a bidirectional transformation (reduction of a steroid carbonyl to alcohol and oxidation of a steroid alcohol to ketone) depending on the nature of the cofactor present. Involved in the activation or inactivation of key estrogens and androgens, 17β-HSDs are therefore therapeutic targets whose selective inhibition would make it possible to be considered for the treatment of several diseases, such as breast cancer, prostate cancer, endometriosis, Alzheimer's disease and osteoporosis. This review article is a continuation of those having reported the great diversity of inhibitors developed over the last years but focusses on inhibitors recently developed. Work to obtain more effective inhibitors that target the first known isoforms (types 1, 2, 3, 5 and 7) has continued, among others, but new inhibitors that target the isoforms more recently reported in the literature (types 10, 12, 13 and 14) are now being reported. Dual inhibitors of two enzymes (17β-HSD1 and steroid sulfatase) were also reported. These inhibitors were grouped according to the 17β-HSD type inhibited and their backbone (steroidal or non-steroidal) when necessary. They were also reported in chronological order and according to the research group.

Dual Targeting of Steroid Sulfatase and 17β-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 17β-hydroxysteroid dehydrogenase type 1(17β HSD1) by a single drug was explored, starting from in-house 17β 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 17β-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 17β-HSD1 inhibition in cell-free and cellular assays, high selectivity over 17β-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 17β-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.

N-Phenyl-1,2,3,4-tetrahydroisoquinoline: An Alternative Scaffold for the Design of 17β-Hydroxysteroid Dehydrogenase 1 Inhibitors

17β-Hydroxysteroid dehydrogenases catalyse interconversion at the C17 position between oxidized and reduced forms of steroidal nuclear receptor ligands. The type 1 enzyme, expressed in malignant cells, catalyses reduction of the less-active estrone to estradiol, and inhibitors have therapeutic potential in estrogen-dependent diseases such as breast and ovarian cancers and in endometriosis. Synthetic decoration of the nonsteroidal N-phenyl-1,2,3,4-tetrahydroisoquinoline (THIQ) template was pursued by using Pomeranz-Fritsch-Bobbitt, Pictet-Spengler and Bischler-Napieralski approaches to explore the viability of this scaffold as a steroid mimic. Derivatives were evaluated biologically in vitro as type 1 enzyme inhibitors in a bacterial cell homogenate as source of recombinant protein. Structure-activity relationships are discussed. THIQs possessing a 6-hydroxy group, lipophilic substitutions at the 1- or 4-positions in combination with N-4'-chlorophenyl substitution were most favourable for activity. Of these, one compound had an IC₅₀ of ca. 350 nM as a racemate, testifying to the applicability of this novel approach.

Development of potential preclinical candidates with promising in vitro ADME profile for the inhibition of type 1 and type 2 17β-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. 17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) catalyzes the biosynthesis of E2 by reduction of E1 while the type 2 enzyme catalyzes the reverse reaction. Thus, 17β-HSD1 and 17β-HSD2 are attractive targets for treatment of estrogen-dependent diseases. Recently, we reported the first proof-of-principle study of a 17β-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 17β-HSD1 and 17β-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 17β-HSD1 and 17β-HSD2.

Inhibitors of 17β-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 17β-hydroxysteroid dehydrogenase types 1 and 2 (17β-HSD1 and 17β-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 17β-HSD1 and steroid sulfatase (STS) as well as the first inhibitors of 17β-HSD14 are covered.

Targeted Endocrine Therapy: Design, Synthesis, and Proof-of-Principle of 17β-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 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2) inhibitor (compound 15) and successful targeted intracrine therapy in a mouse bone fracture model. Blockade of 17β-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 17β-HSD2 inhibition thus enables targeted intracrine therapy.

Discovery of (E)-1-amino-4-phenylbut-3-en-2-ol derivatives as novel neuraminidase inhibitors

Neuraminidase has been considered as an important target for designing agents against influenza viruses. In a discovery of anti-influenza agents with epigoitrin as the initial lead compound, a series of 1-amino-2-alkanols were synthesized and biologically evaluated. The in vitro evaluation indicated that (E)-1-amino-4-phenylbut-3-en-2-ol (C1) had better inhibitory activities than 2-amino-1-arylethan-1-ol derivatives. To our surprise, sulfonation of C1 with 4-methoxybenzenesulfonyl chloride afforded more active inhibitor II with up to 6.4 μM IC₅₀ value against neuraminidase. Furthermore, docking of inhibitor II into the active site of NA found that the H atoms in both NH₂ and OH groups of inhibitor II were the key factors for potency. Molecular docking research did not explained very well the observed structure-activity relationship (SAR) from amino acid residue level, but also aided the discovery of (E)-1-amino-4-phenylbut-3-en-2-ol derivatives as novel and potent NA inhibitors.

Virtual screening applications in short-chain dehydrogenase/reductase research

Several members of the short-chain dehydrogenase/reductase (SDR) enzyme family play fundamental roles in adrenal and gonadal steroidogenesis as well as in the metabolism of steroids, oxysterols, bile acids, and retinoids in peripheral tissues, thereby controlling the local activation of their cognate receptors. Some of these SDRs are considered as promising therapeutic targets, for example to treat estrogen-/androgen-dependent and corticosteroid-related diseases, whereas others are considered as anti-targets as their inhibition may lead to disturbances of endocrine functions, thereby contributing to the development and progression of diseases. Nevertheless, the physiological functions of about half of all SDR members are still unknown. In this respect, in silico tools are highly valuable in drug discovery for lead molecule identification, in toxicology screenings to facilitate the identification of hazardous chemicals, and in fundamental research for substrate identification and enzyme characterization. Regarding SDRs, computational methods have been employed for a variety of applications including drug discovery, enzyme characterization and substrate identification, as well as identification of potential endocrine disrupting chemicals (EDC). This review provides an overview of the efforts undertaken in the field of virtual screening supported identification of bioactive molecules in SDR research. In addition, it presents an outlook and addresses the opportunities and limitations of computational modeling and in vitro validation methods.