17β-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 17β-hydroxysteroid dehydrogenase type 1 (17β-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 17β-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 17β-HSD2 was investigated, revealing a rational approach for the design of selective inhibitors. 17β-HSD1 and 1 hold promise in fighting NSCLC.

Homology modeling meets site-directed mutagenesis: An ideal combination to elucidate the topology of 17β-HSD2

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the conversion of highly active estrogens and androgens into their less active forms using NAD⁺ as cofactor. Substrate and cofactor specificities of 17β-HSD2 have been reported and potent 17β-HSD2 inhibitors have been discovered in a ligand-based approach. However, the molecular basis and the amino acids involved in the enzymatic functionality are poorly understood, as no crystal structure of the membrane-associated 17β-HSD2 exists. The functional properties of only few amino acids are known. The lack of topological information impedes structure-based drug design studies and limits the design of biochemical experiments. The aim of this work was the determination of the 17β-HSD2 topology. For this, the first homology model of 17β-HSD2 in complex with NAD⁺ and 17β-estradiol was built, using a multi-fragment "patchwork" approach. To confirm the quality of the model, fifteen selected amino acids were exchanged one by one using site directed mutagenesis. The mutants' functional behavior demonstrated that the generated model was of very good quality and allowed the identification of several key amino acids involved in either ligand or internal structure stabilization. The final model is an optimal basis for further experiments like, for example, lead optimization.

Effects of 17β-HSD2 inhibition in bones on osteoporosis based on an animal rat model

Hormone replacement therapy is a viable option to protect bone from postmenopausal osteoporosis. Systemically elevated estrogen levels, however, are disadvantageous because of the risk of harmful side effects in other organs. The rationale of the study presented here is to target a key enzyme in estradiol (E2) and testosterone (T) metabolism to increase E2 levels in an organ-specific manner, thereby avoiding the disadvantages of systemically increased E2 levels. The 17ß-hydroxysteroid dehydrogenase (17β-HSD2), which is e.g. expressed in bone, catalyzes the oxidation of E2 and T into estrone (E1) and androstenedione. We postulate that inhibiting 17β-HSD2 should lead to elevated E2 and T levels in organs expressing the enzyme. Therefore, we can use the benefits of E2 directly, or those of T following aromatization into E2, in the bone without affecting systemic levels. We tested for the first time, the novel and potent 17β-HSD2 inhibitor, compound 24 (C24), to explore the therapeutic potential of a 17β-HSD2 inhibition in an ovariectomy (ovx)-induced rat model of bone loss. We tested the inhibitor alone and, together with low dose estrogen supplementation to model estrogen levels in the postmenopausal situation. Female mature Wistar-Hannover rats were treated for 8 weeks with doses of 2, 10, 50 mg C24 per kg body weight per day alone or in the presence of estradiol benzoate (E2B) supplementation to alleviate ovx-induced bone loss. Ovx placebo and sham operated animals served as negative and positive controls. The experiment was evaluated regarding aspects of efficacy and safety: Bone was analyzed to evaluate bone protective effects, and uterus for potential, unwanted E2-mediated side effects. We observed a good bioavailability of C24 as very high plasma concentrations were measured, up to a group mean of 15,412 nM for the ovx C24-high group. Histomorphometrical analyses and in vivo &ex vivo μCT revealed significant bone protective effects for the lowest inhibitor concentration used. Irrespective of the plasma concentration, no proliferative effects in the uterus could be observed. These results support our approach of intracellular targeting key enzymes of E2 and T metabolism to increase E2 and T levels in an organ specific manner.

Design, Synthesis, and Biological Characterization of Orally Active 17β-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 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2), may be more efficacious in the treatment of osteoporosis. Blockade of 17β-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 17β-HSD2 inhibitor (compound 24). Compound 24 is a nanomolar potent inhibitor of human 17β-HSD2 (IC₅₀ of 6.1 nM) and rodent 17β-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.

Mutational and structural studies uncover crucial amino acids determining activity and stability of 17β-HSD14

17β-Hydroxysteroid dehydrogenase type 14 (17β-HSD14) catalyzes the conversion of highly active estrogens and androgens into their less active oxidized forms in presence of NAD⁺ as cofactor. The crystal structure of 17β-HSD14 has been determined, however, the role of individual amino acids likely involved in the enzymatic function remains poorly understood. Objective of this study was to further characterize the enzyme by site-directed mutagenesis considering five amino acids next to the catalytic center. The tools used for the characterization of the enzyme variants are X-ray crystallography and enzyme kinetics. Lys158 was confirmed to belong to the catalytic triad. Tyr253', located on the C-terminal loop of the adjacent monomer, enters into the active site of the neighboring monomer and interacts with the catalytic Tyr154. Therefore, Tyr253' helps to tie the two monomers together. Cys255, located at the interface between both monomers, can form a disulfide bridge with the Cys255' from the adjacent monomer. In contrast to the contact provided by Tyr253, the latter interaction is not crucial for dimer formation. His93 and Gln148 are located at the rim of the substrate binding pocket. His93 does not interact directly with the ligand in the active site. However, it influences the turnover of the enzyme. The Gln148 restricts in size the access tunnel of the substrate to the binding pocket.

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.

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

Intracellular elevation of E2 levels in bone by inhibition of 17β hydroxysteroid dehydrogenase type 2 (17β-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 17β-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.

17β-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 h17β-HSD2 and m17β-HSD2 SAR study are described. 17a is the first compound to show strong inhibition of both h17β-HSD2 and m17β-HSD2, intracellular activity, metabolic stability, selectivity toward h17β-HSD1, m17β-HSD1 and estrogen receptors α and β as well as appropriate physicochemical properties for oral bioavailability. These properties make it eligible for pre-clinical animal studies, prior to human studies.

Structural requirements of steroidal agonists of transient receptor potential melastatin 3 (TRPM3) cation channels

Background and Purpose

Transient receptor potential melastatin 3 (TRPM3) proteins form non-selective but calcium-permeable membrane channels, rapidly activated by extracellular application of the steroid pregnenolone sulphate and the dihydropyridine nifedipine. Our aim was to characterize the steroid binding site by analysing the structural chemical requirements for TRPM3 activation.

Experimental Approach

Whole-cell patch-clamp recordings and measurements of intracellular calcium concentrations were performed on HEK293 cells transfected with TRPM3 (or untransfected controls) during superfusion with pharmacological substances.

Key Results

Pregnenolone sulphate and nifedipine activated TRPM3 channels supra-additively over a wide concentration range. Other dihydropyridines inhibited TRPM3 channels. The natural enantiomer of pregnenolone sulphate was more efficient in activating TRPM3 channels than its synthetic mirror image. However, both enantiomers exerted very similar inhibitory effects on proton-activated outwardly rectifying anion channels. Epiallopregnanolone sulphate activated TRPM3 almost equally as well as pregnenolone sulphate. Exchanging the sulphate for other chemical moieties showed that a negative charge at this position is required for activating TRPM3 channels.

Conclusions and Implications

Our data demonstrate that nifedipine and pregnenolone sulphate act at different binding sites when activating TRPM3. The latter activates TRPM3 by binding to a chiral and thus proteinaceous binding site, as inferred from the differential effects of the enantiomers. The double bond between position C5 and C6 of pregnenolone sulphate is not strictly necessary for the activation of TRPM3 channels, but a negative charge at position C3 of the steroid is highly important. These results provide a solid basis for understanding mechanistically the rapid chemical activation of TRPM3 channels.

Synthesis and biological evaluation of thieno[3,2-d]- pyrimidinones, thieno[3,2-d]pyrimidines and quinazolinones: conformationally restricted 17b-hydroxysteroid dehydrogenase type 2 (17b-HSD2) inhibitors

In this study, a series of conformationally restricted thieno[3,2-d]pyrimidinones, thieno[3,2-d]pyrimidines and quinazolinones was designed and synthesized with the goal of improving the biological activity as 17b-hydroxysteroid dehydrogenase type 2 inhibitors of the corresponding amidothiophene derivatives. Two moderately active compounds were discovered and this allowed the identification of the biologically active open conformer as well as the extension of the enzyme binding site characterisation.

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

17β-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. 17β-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 17β-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 17β-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 17β-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 17β-HSD1, reasonable selectivity against 17β-HSD2 but pronounced affinity to the estrogen receptors (ERs). On the other hand, the best amide-derivative 21 shows only medium 17β-HSD1 inhibitory activity at the target enzyme as well as fair selectivity against 17β-HSD2 and ERs. The compounds 6 and 21 can be regarded as first benzothiazole-type 17β-HSD1 inhibitors for the development of potential therapeutics.

Triazole ring-opening leads to the discovery of potent nonsteroidal 17β-hydroxysteroid dehydrogenase type 2 inhibitors

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the oxidation of the highly potent steroids: the estrogen estradiol (E2) and the androgen testosterone (T) to the less active estrone and androstenedione, respectively. Inhibition of this enzyme may help maintain the local E2 level in bone tissue when the circulating E2 level drops and is therefore a novel and promising approach for the treatment of osteoporosis. In this work, a series of new nonsteroidal and achiral 17β-HSD2 inhibitors, namely N-benzyl-diphenyl-3(or 4)-carboxamide and N-benzyl-5-phenyl-thiophene-2-carboxamide was designed and the compounds were synthesized in a two to three steps reaction. A small library was built applying parallel synthesis. Highly potent 17β-HSD2 inhibitors could be identified in the thiophene-2-carboxamide class with IC(50) in the low nanomolar range. These compounds also showed a good selectivity profile toward 17β-HSD1 and toward the estrogen receptors α and β. The most interesting 17β-HSD2 inhibitor identified in this study is the 5-(2-fluoro-3-methoxyphenyl)-N-(3-hydroxybenzyl)-N-methylthiophene-2-carboxamide 6w displaying an IC(50) of 61 nM and a selectivity factor of 73 toward 17β-HSD1.

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.

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.

Selective inhibition of 17beta-hydroxysteroid dehydrogenase type 1 (17betaHSD1) 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 17beta-Hydroxysteroid Dehydrogenase (17beta-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.

Structure-activity study in the class of 6-(3'-hydroxyphenyl)naphthalenes leading to an optimization of a pharmacophore model for 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) inhibitors

17beta-Hydroxysteroid dehydrogenase type 1 (17beta-HSD1) catalyzes the transformation of estrone (E1) into the most potent estrogen, estradiol (E2), which stimulates cell proliferation and decreases apoptosis. 17beta-HSD1 is often strongly overexpressed in estrogen-dependent diseases (like breast cancer and endometriosis). Thus, this over expressed enzyme is a promising novel target for the development of selective inhibitors, which could be used as drugs for the treatment of these diseases. Using a structure- and ligand-based approach, a pharmacophore model was proposed and a new class of non-steroidal inhibitors of 17beta-HSD1 was designed. Enzyme inhibition was evaluated in vitro using the human enzyme. After identification of the 6-(3'-hydroxyphenyl)-2-naphthol scaffold 1, the potency of this class of inhibitors was further improved by substitution of the 1-position of the naphthalene ring by a phenyl group (compound 18, IC(50)=20nM). Compound 18 also showed a good selectivity toward 17beta-HSD2 and the estrogen receptors alpha and beta.

Development of a biological screening system for the evaluation of highly active and selective 17beta-HSD1-inhibitors as potential therapeutic agents

17beta-Hydroxysteroid dehydrogenase type 1 (17beta-HSD1) catalyses the intracellular conversion of oestrone (E1) to oestradiol (E2). E2 is known to be involved in the development and progression of breast cancer and endometriosis. Since 17beta-HSD1 is overexpressed in these oestrogen-dependent diseases, inhibition of this enzyme may be a more target-directed therapeutical approach compared to established medical treatments. For the identification of highly active and selective 17beta-HSD1-inhibitors that are suitable for application as potential therapeutics, there is a need for an appropriate, efficient and reliable screening system. Here, we report the development and application of our screening system using our in house library of potential 17beta-HSD1-inhibitors. Four potent and selective compounds with a good first pharmacokinetic profile were identified.

Design, synthesis, biological evaluation and pharmacokinetics of bis(hydroxyphenyl) substituted azoles, thiophenes, benzenes, and aza-benzenes as potent and selective nonsteroidal inhibitors of 17beta-hydroxysteroid dehydrogenase type 1 (17beta-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.

Synthesis and evaluation of heteroaryl-substituted dihydronaphthalenes and indenes: potent and selective inhibitors of aldosterone synthase (CYP11B2) for the treatment of congestive heart failure and myocardial fibrosis

In this study, the synthesis and biological evaluation of heteroaryl-substituted dihydronaphthalenes and indenes (1-16) is described. The compounds were tested for activity by use of human CYP11B2 expressed in fission yeast and V79 MZh cells and for selectivity by use of human CYP11B1, CYP17, and CYP19. The most active inhibitor was the 6-methoxydihydronaphthalene 4 (IC(50) = 2 nM), showing a K(i) value of 1.3 nM and a competitive type of inhibition. The 5-methoxyindene 3 was found to be the most selective CYP11B2 inhibitor (IC(50) = 4 nM; CYP11B1 IC(50) = 5684 nM), which also showed only marginal inhibition of human CYP3A4 and CYP2D6. Docking and molecular dynamics studies using our homology-modeled CYP11B2 structure were performed to understand some structure-activity relationships. Caco-2 cell experiments revealed highly cell-permeable compounds, and metabolic studies with 4 using rat liver microsomes showed sufficient stability.

Heteroaryl-Substituted Naphthalenes and Structurally Modified Derivatives: Selective Inhibitors of CYP11B2 for the Treatment of Congestive Heart Failure and Myocardial Fibrosis

Recently we proposed inhibition of aldosterone synthase (CYP11B2) as a novel strategy for the treatment of congestive heart failure and myocardial fibrosis. In this study the synthesis and biological evaluation of heteroaryl-substituted naphthalenes and quinolines (1-31) is described. Key step for the preparation of the compounds was a Suzuki cross-coupling. Activity of the compounds was determined in vitro using human CYP11B2 and selectivity was evaluated toward the human steroidogenic enzymes CYP11B1, CYP19, and CYP17. A large number of highly active and selective inhibitors of CYP11B2 was identified. The most active inhibitor was the 6-cyano compound 8 (IC50 = 3 nM) showing a competitive type of inhibition (K(i) value = 1.9 nM). The 6-ethoxy derivative 5 was found to be the most selective CYP11B2 inhibitor (IC50 = 12 nM; K(i) value = 8 nM; CYP11B1 IC50 = 5419 nM; selectivity factor = 451), showing no inhibition of human CYP3A4 (50 nM) and CYP2D6 (20 nM). Docking and molecular dynamics studies using our homology modeled CYP11B2 structure with selected compounds were performed. Caco-2 cell experiments revealed a large number of medium and highly permeable compounds and metabolic studies with 2 using rat liver microsomes showed sufficient stability.

Two C-Methyl Derivatives of [11C]WAY-100635 – Effects of an Amido α-Methyl Group on Metabolism and Brain 5-HT1A Receptor Radioligand Behavior in Monkey*

PURPOSE

[carbonyl-11C]N-(2-(1-(4-(2-methoxyphenyl)-piperazinyl)ethyl)-N-pyridinyl)cyclohexanecarboxamide ([carbonyl-11C]WAY-100635) is an effective radioligand for imaging brain 5-HT1A receptors with positron emission tomography (PET). However, this radioligand has some drawbacks for deriving relative regional receptor densities, including rapid metabolism, which acts against accurate definition of an arterial input function for compartmental modeling, and very low nonspecific binding in brain, which detracts from the accuracy of modeling by a simplified reference tissue (cerebellum) approach. Here, in a search for a radioligand that overcomes these limitations, we investigated the effects of introducing a single methyl group at either of the carbon atoms alpha to the amide bond in [11C]WAY-100635.

PROCEDURES

Ligands with a methyl group on the alpha carbon of the cyclohexyl group (SWAY) or the alpha carbon of the C2H4 linker ((R,S)-JWAY) were synthesized and tested for binding affinity and intrinsic activity at 5-HT1A receptors. SWAY was labeled with carbon-11 (t1/2 = 20.4 minutes; beta+ = 99.8%) in its O-methyl group and (R,S)-JWAY in its carbonyl group. Each radioligand was evaluated by PET experiments in cynomolgus monkey.

RESULTS

SWAY and (R,S)-JWAY were found to be high-affinity antagonists at 5-HT1A receptors. After injection of [11C]SWAY into monkey, radioactivity uptake in brain reached a maximum of 3% at 4.5 minutes and decreased to 0.7% at 72 minutes. However, over the time span of the experiment, radioactivity concentrations in 5-HT1A receptor-rich brain regions were only fractionally higher than in cerebellum. Radioactivity represented by parent radioligand in plasma was 39% at 45 minutes. After injection of [11C](R,S)-JWAY alone, radioactivity uptake in brain reached a maximum of 4.8% at 2.5 minutes and decreased to 1.2% at 90 minutes. At this time, radioactivity concentration in 5-HT1A receptor-rich brain regions was markedly greater than in cerebellum. In another PET experiment, the monkey was predosed with WAY-100635 before [11C](R,S)-JWAY injection. At 90 minutes after injection, the ratio of radioactivity in 5-HT1A receptor-rich regions to that in cerebellum was reduced to near unity. Radioactivity represented by parent radioligand in plasma was 12% at 45 minutes.

CONCLUSIONS

[11C](R,S)-JWAY, but not [11C]SWAY, gives a sizeable 5-HT1A receptor-selective PET signal in monkey. The presence of a C-methyl group adjacent to the amide bond in SWAY or (R,S)-JWAY fails to counter metabolism.

N-Oxide analogs of WAY-100635: new high affinity 5-HT1A receptor antagonists

WAY-100635 [N-(2-(1-(4-(2-methoxyphenyl)piperazinyl)ethyl))-N-(2-pyridinyl)cyclohexanecarboxamide] 1 and its O-desmethyl derivative DWAY 2 are well-known high affinity 5-HT(1A) receptor antagonists, which when labeled with carbon-11 (beta+; t(1/2) = 20.4 min) in the carbonyl group are effective radioligands for imaging brain 5-HT(1A) receptors with positron emission tomography (PET). In a search for new 5-HT(1A) antagonists with different pharmacokinetic and metabolic properties, the pyridinyl N-oxide moiety was incorporated into analogs of 1 and 2. NOWAY 3, in which the pyridinyl ring of 1 was oxidized to the pyridinyl N-oxide, was prepared via nucleophilic substitution of 2-[4-(2-methoxyphenyl)piperazin-1-yl]ethylamine on 2-chloropyridine-N-oxide followed by acylation with cyclohexanecarbonyl chloride. 6Cl-NOWAY 4, a more lipophilic (pyridinyl-6)-chloro derivative of 3, was prepared by treating 1-(2-methoxyphenyl)-4-(2-(2-(6-bromo)aminopyridinyl-N-oxide)ethyl)piperazine with cyclohexanecarbonyl chloride for acylation and concomitant chloro for bromo substitution. NEWWAY 5, in which the 2-hydroxy-phenyl group of 2 is replaced with a 2-pyridinyl N-oxide group with the intention of mimicking the topology of 2, was prepared in five steps from 2-(chloroacetylamino)pyridine. N-Oxides 3-5 were found to be high affinity antagonists at 5-HT(1A) receptors, with 3 having the highest affinity and a Ki value (0.22 nM) comparable to that of 1 (0.17 nM). By calculation the lipophilicity of 3 (LogP = 1.87) is lower than that of 1 by 1.25 LogP units while TLC and reverse phase HPLC indicate that 3 has slightly lower lipophilicity than 1. On the basis of these encouraging findings, the N-oxide 3 was selected for labeling with carbon-11 in its carbonyl group and for evaluation as a radioligand with PET. After intravenous injection of [carbonyl-11C]3 into cynomolgus monkey there was very low uptake of radioactivity into brain and no PET image of brain 5-HT(1A) receptors was obtained. Either 3 inadequately penetrates the blood-brain barrier or it is excluded from brain by an active efflux mechanism. Rapid deacylation of 3 was not apparent in vivo; in cynomolgus monkey plasma radioactive metabolites of [carbonyl-11C]3 appeared less rapidly than from the radioligands [carbonyl-11C]1 and [carbonyl-11C]2, which are known to be primarily metabolized by deacylation. Ligand 3 may have value as a new pharmacological tool, but not as a radioligand for brain imaging.

Synthesis of Amidinohydrazones and Evaluation of Their Inhibitory Effect towards Aldosterone Synthase (CYP11B2) and the Formation of Selected Steroids

The synthesis and biological evaluation of a series of amidinohydrazones (3a-h, 6a-c, 8 and 9) as potential nonsteroidal inhibitors of aldosterone synthase (CYP11B2) are described. The compounds were tested in vitro using CYP11B2-expressing fission yeast; they showed only marginal inhibitory effect. Compound 6c was evaluated for its effect on the formation of aldosterone, cortisol, androstenedione, and DHEA in the adrenocortical tumor cell line NCI-H295R. It exhibited no significant effect on the production of these products.

The Pyridinyl-6 Position of WAY-100635 as a site for radiofluorination—effect on 5-HT1A receptor radioligand behavior in vivo

PURPOSE

We aimed to evaluate radiofluorination at the pyridinyl-6 position of the selective 5-HT(1A) receptor antagonist, WAY-100635 [N-(2-(1-(4-(2-methoxyphenyl)piperazinyl)ethyl))-N-(2-pyridinyl)cyclohexanecarboxamide)], on 5-HT(1A) receptor radioligand behavior in vivo.

PROCEDURES

The pyridinyl-6 [(18)F]fluoro derivative of WAY-100635 ([(18)F]6FPWAY) was obtained by direct nucleophilic substitution with [(18)F]fluoride ion in a bromo precursor. After intravenous injection of [(18)F]6FPWAY into Cynomolgus monkey, the uptake of radioactivity into brain regions was assessed with positron emission tomography (PET) and blood samples analyzed by high performance liquid chromatography (HPLC) for parent radioligand and radioactive metabolites. The experiment was repeated after pretreatment of the monkey with a dose of WAY-100635 that blocks brain 5-HT(1A) receptors.

RESULTS

After intravenous injection of [(18)F]6FPWAY into Cynomolgus monkey, the uptake of radioactivity into whole brain reached 4.33% of injected dose at 7.5 min. Uptake was highest in 5-HT(1A) receptor-rich regions. Pretreatment with WAY-100635 reduced uptake in these regions to near the levels in receptor-devoid cerebellum. [(18)F]6FPWAY was rapidly metabolized in vivo, as evidenced by the rapid appearance of radioactive metabolites in plasma.

CONCLUSION

[(18)F]6FPWAY is selective and moderately useful for imaging brain 5-HT(1A) receptors in vivo. The pyridinyl-6 position is resistant to defluorination and may be an attractive site for the (18)F-labeling of 6FPWAY analogs that resist hydrolysis.