Novel imidazolyl and triazolyl substituted biphenyl compounds: synthesis and evaluation as nonsteroidal inhibitors of human 17alpha-hydroxylase-C17, 20-lyase (P450 17)

Non-steroidal CYP17A1 Inhibitors: Discovery and Assessment

CYP17A1 is an enzyme that plays a major role in steroidogenesis and is critically involved in the biosynthesis of steroid hormones. Therefore, it remains an attractive target in several serious hormone-dependent cancer diseases, such as prostate cancer and breast cancer. The medicinal chemistry community has been committed to the discovery and development of CYP17A1 inhibitors for many years, particularly for the treatment of castration-resistant prostate cancer. The current Perspective reflects upon the discovery and evaluation of non-steroidal CYP17A1 inhibitors from a medicinal chemistry angle. Emphasis is placed on the structural aspects of the target, key learnings from the presented chemotypes, and design guidelines for future inhibitors.

Nickel-Catalyzed Suzuki Coupling of Phenols Enabled by SuFEx of Tosyl Fluoride

A practical and efficient Suzuki coupling of phenols has been developed by using trans-NiCl(o-Tol)(PCy₃)₂/2PCy₃ as a catalyst in the presence of tosyl fluoride as an activator. The key for the direct use of phenols lies in the compatibility of the nickel catalyst with tosyl fluoride (TsF) and its sulfur(VI) fluoride exchange (SuFEx) with C_Ar-OH. Water has been found to improve the one-pot process remarkably. The steric and electronic effects and the functional group compatibility of the one-pot Suzuki coupling of phenols appear to be comparable to the conventional one of pre-prepared aryl tosylates. A series of electronically and sterically various biaryls could be obtained in good to excellent yields by using 3-10 mol% loading of the nickel catalyst. The applications of this one-pot procedure in chemoselective derivatization of complex molecules have been demonstrated in 3-phenylation of estradiol and estrone.

Prospective computational design and in vitro bio-analytical tests of new chemical entities as potential selective CYP17A1 lyase inhibitors

The development and advancement of prostate cancer (PCa) into stage 4, where it metastasize, is a major problem mostly in elder males. The growth of PCa cells is stirred up by androgens and androgen receptor (AR). Therefore, therapeutic strategies such as blocking androgens synthesis and inhibiting AR binding have been explored in recent years. However, recently approved drugs (or in clinical phase) failed in improving the expected survival rates for this metastatic-castration resistant prostate cancer (mCRPC) patients. The selective CYP17A1 inhibition of 17,20-lyase route has emerged as a novel strategy. Such inhibition blocks the production of androgens everywhere they are found in the body. In this work, a three dimensional-quantitative structure activity relationship (3D-QSAR) pharmacophore model is developed on a diverse set of non-steroidal inhibitors of CYP17A1 enzyme. Highly active compounds are selected to define a six-point pharmacophore hypothesis with a unique geometrical arrangement fitting the following description: two hydrogen bond acceptors (A), two hydrogen bond donors (D) and two aromatic rings (R). The QSAR model showed adequate predictive statistics. The 3D-QSAR model is further used for database virtual screening of potential inhibitory hit structures. Density functional theory (DFT) optimization provides the electronic properties explaining the reactivity of the hits. Docking simulations discovers hydrogen bonding and hydrophobic interactions as responsible for the binding affinities of hits to the CYP17A1 Protein Data Bank structure. 13 hits from the database search (including five derivatives) are then synthesized in the laboratory as different scaffolds. Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in vitro experiments reveals three new chemical entities (NCEs) with half maximal inhibitory concentration (IC₅₀) values against the lyase route at mid-micromolar range with favorable selectivity to the lyase over the hydroxylase route (one of them with null hydroxylase inhibition). Thus, prospective computational design has enabled the design of potential lead lyase-selective inhibitors for further studies.

Discovery of orteronel (TAK-700), a naphthylmethylimidazole derivative, as a highly selective 17,20-lyase inhibitor with potential utility in the treatment of prostate cancer

A novel naphthylmethylimidazole derivative 1 and its related compounds were identified as 17,20-lyase inhibitors. Based on the structure-activity relationship around the naphthalene scaffold and the results of a docking study of 1a in the homology model of 17,20-lyase, the 6,7-dihydro-5H-pyrrolo[1,2-c]imidazole derivative (+)-3c was synthesized and identified as a potent and highly selective 17,20-lyase inhibitor. Biological evaluation of (+)-3c at a dose of 1mg/kg in a male monkey model revealed marked reductions in both serum testosterone and dehydroepiandrosterone concentrations. Therefore, (+)-3c (termed orteronel [TAK-700]) was selected as a candidate for clinical evaluation and is currently in phase III clinical trials for the treatment of castration-resistant prostate cancer.

Optimization of the First Selective Steroid-11β-hydroxylase (CYP11B1) Inhibitors for the Treatment of Cortisol Dependent Diseases

CYP11B1 is the key enzyme in cortisol biosynthesis, and its inhibition with selective compounds is a promising strategy for the treatment of diseases associated with elevated cortisol levels, such as Cushing's syndrome or metabolic disease. Expanding on a previous study from our group resulting in the first potent and rather selective inhibitor described so far (1, IC50 = 152 nM), we herein describe further optimizations of the imidazolylmethyl pyridine core. Five compounds among the 42 substances synthesized showed IC50 values below 50 nM. Most interesting was the naphth-1-yl compound 23 (IC50 = 42 nM), showing a 49-fold selectivity toward the highly homologous CYP11B2 (1: 18-fold) as well as selectivity toward the androgen and estrogen forming enzymes CYP17 and CYP19, respectively.

Design, synthesis, and biological evaluation of imidazolyl derivatives of 4,7-disubstituted coumarins as aromatase inhibitors selective over 17-α-hydroxylase/C17-20 lyase

The design, synthesis, and biological evaluation of a series of new aromatase (AR, CYP19) inhibitors bearing an imidazole ring linked to a 7-substituted coumarin scaffold at position 4 (or 3) are reported. Many compounds exhibited an aromatase inhibitory potency in the nanomolar range along with a high selectivity over 17-α-hydroxylase/C17-20 lyase (CYP17). The most potent AR inhibitor was the 7-(3,4-difluorophenoxy)-4-imidazolylmethyl coumarin 24 endowed with an IC(50) = 47 nM. Docking simulations on a selected number of coumarin derivatives allowed the identification of the most important interactions driving the binding and clearly indicated the allowed and disallowed regions for appropriate structural modifications of coumarins and closely related heterocyclic molecular scaffolds.

First Selective CYP11B1 Inhibitors for the Treatment of Cortisol-Dependent Diseases

Outgoing from an etomidate-based design concept, we succeeded in the development of a series of highly active and selective inhibitors of CYP11B1, the key enzyme of cortisol biosynthesis, as potential drugs for the treatment of Cushing's syndrome and related diseases. Thus, compound 33 (IC50 = 152 nM) is the first CYP11B1 inhibitor showing a rather good selectivity toward the most important steroidogenic CYP enzymes aldosterone synthase (CYP11B2), the androgen-forming CYP17, and aromatase (estrogen synthase, CYP19).

Molecular modeling on inhibitor complexes and active-site dynamics of cytochrome P450 C17, a target for prostate cancer therapy

A molecular model for the P450 enzyme cytochrome P450 C17 (CYP17) is presented based on sequence alignments of multiple template structures and homology modeling. This enzyme plays a central role in the biosynthesis of testosterone and is emerging as a major target in prostate cancer, with the recently developed inhibitor abiraterone currently in advanced clinical trials. The model is described in detail, together with its validation, by providing structural explanations to available site-directed mutagenesis data. The CYP17 molecule in this model is in the form of a triangular prism, with an edge of approximately 55 A and a thickness of approximately 37 A. It is predominantly helical, comprising 13 alpha helices interspersed by six 3(10) helices and 11 beta-sheets. Multinanosecond molecular dynamics simulations in explicit solvent have been carried out, and principal components analysis has been used to reveal the details of dynamics around the active site. Coarse-grained methods have also been used to verify low-frequency motions, which have been correlated with active-site gating. The work also describes the results of docking synthetic inhibitors, including the drug abiraterone and the natural substrate pregnenolone, in the CYP17 active site together with molecular dynamics simulations on the complexes.

CYP17 inhibitors. Annulations of additional rings in methylene imidazole substituted biphenyls: synthesis, biological evaluation and molecular modelling

Twenty-one novel compounds originating from two classes of annulated biphenyls were synthesized as mimetics of the steroidal A- and C-rings and examined for their potency as inhibitors of human CYP17. Selected compounds were tested for inhibition of the hepatic CYP enzyme 3A4. Potent CYP17 inhibitors were found for each class, compound 9 (17 and 71% at 0.2 and 2 microM, respectively) and 21 (591 nM). Compound 21 showed only weak inhibition of CYP3A4 (32 and 64% at 2 and 10 microM, respectively). Both compounds, however, exhibited moderate to strong inhibition of the glucocorticoid-forming enzyme CYP11B1. The most interesting compounds were docked into our protein model. They bound into one of the modes which we have previously published. New interaction regions were identified.

CYP17 inhibition as a hormonal strategy for prostate cancer

Androgen receptor (AR) signaling has a key role in the pathogenesis of prostate cancer. AR gene amplification, AR overexpression, and activating mutations in the AR occur more frequently as castration-resistant prostate cancer (CRPC) evolves, with intratumoral androgen levels remaining sufficient for AR activation despite castration. The source of these androgens might be either adrenal or intratumoral. AR signaling, therefore, remains a valid treatment target for patients with CRPC. CYP17 is a key enzyme for androgen biosynthesis. The imidazole antifungal agent ketoconazole weakly and nonspecifically inhibits CYP17, but remains unlicensed for this indication. Chemists at the Cancer Research UK Centre for Cancer Therapeutics have designed a novel, selective, irreversible inhibitor of CYP17 called abiraterone, which is more than 20 times more potent than ketoconazole. Abiraterone acetate, a prodrug, has undergone phase I assessment, and is rapidly progressing from phase II to phase III trials, in view of its high level of antitumor activity. This agent is safe and well tolerated, and activity profiles suggest that approximately 50% of CRPC remains AR-ligand driven. Other CYP17 inhibitors with alternative mechanisms of action, for example VN/124-1, are in preclinical development. The rationale for and implications of CYP17 inhibition and the CYP17-targeting agents in development are discussed in this Review.

A fission yeast-based test system for the determination of IC50values of anti-prostate tumor drugs acting on CYP21

Human steroid 21-hydroxylase (CYP21) and steroid 17alpha-hydroxylase/17,20-lyase (CYP17) are two closely related cytochrome P450 enzymes involved in the steroidogenesis of glucocorticoids, mineralocorticoids, and sex hormones, respectively. Compounds that inhibit CYP17 activity are of pharmacological interest as they could be used for the treatment of prostate cancer. However, in many cases little is known about a possible co-inhibition of CYP21 activity by CYP17 inhibitors, which would greatly reduce their pharmacological value. We have previously shown that fission yeast strains expressing mammalian cytochrome P450 steroid hydroxylases are suitable systems for whole-cell conversion of steroids and may be used for biotechnological applications or for screening of inhibitors. In this study, we developed a very simple and fast method for the determination of enzyme inhibition using Schizosaccharomyces pombe strains that functionally express either human CYP17 or CYP21. Using this system we tested several compounds of different structural classes with known CYP17 inhibitory potency (i.e. Sa 40, YZ5ay, BW33, and ketoconazole) and determined IC50 values that were about one order of magnitude higher in comparison to data previously reported using human testes microsomes. One compound, YZ5ay, was found to be a moderate CYP21 inhibitor with an IC50 value of 15 microM, which is about eight-fold higher than the value determined for CYP17 inhibition (1.8 microM) in fission yeast. We conclude that, in principle, co-inhibition of CYP21 by CYP17 inhibitors cannot be ruled out.

Synthesis of Hydroxy Derivatives of Highly Potent Non-steroidal CYP 17 Inhibitors as Potential Metabolites and Evaluation of their Activity by a Non Cellular Assay using Recombinant Human Enzyme

Inhibition of CYP 17 is a promising strategy for the treatment of prostate cancer. Recently two non-steroidal compounds with high in vitro activity were synthesized in our group (BW19 and BW95). However, after a few hours they showed in vivo a strong decrease in their activity. This might be due to a fast biodegradation. Potential hydroxy and epoxy metabolites were synthesized and their inhibitory activities were tested by a new non-cellular assay using recombinant enzyme. As source, membrane fractions of E. coli pJL17/OR coexpressing human CYP 17 and rat NADPH-P450-reductase were, used. Showing a high and constant CYP 17 activity and a fast and easy isolation procedure the new method was advantageous compared with the microsomal assay. Interestingly, all the new synthesized hydroxy and epoxy compounds except one showed a lower inhibition of CYP 17 than the parent compounds. Thus, the loss of in vivo activity may be partly explained.

Synthesis, biological evaluation, and molecular modeling of abiraterone analogues: novel CYP17 inhibitors for the treatment of prostate cancer

Abiraterone, a steroidal cytochrome P450 17alpha-hydroxylase-17,20-lyase inhibitor (CYP17), is currently undergoing phase II clinical trials as a potential drug for the treatment of androgen-dependent prostate cancer. Since steroidal compounds often show side effects attributable to their structure, we have tried to replace the sterane scaffold by nonsteroidal core structures. The design and synthesis of 20 new abiraterone mimetics are described. Their activities have been tested with recombinant human CYP17 expressed in E. coli. Promising compounds were further evaluated for selectivity against CYP11B1, CYP11B2, and the hepatic CYP3A4. Compounds 19 and 20 showed comparable activity to abiraterone (IC50 values of 144 and 64 nM vs 72 nM) and similar or even better selectivity against the other CYP enzymes. Selected compounds were also docked into our homology model, and the same binding modes as for abiraterone were found.

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.

CYP17- and CYP11B-dependent steroid hydroxylases as drug development targets

Steroid hormone biosynthesis is catalyzed by the action of a series of cytochrome P450 enzymes as well as reductases. Defects in steroid hydroxylating P450s are the cause of several severe defects such as the adrenogenital syndrome (AGS), corticosterone methyl oxidase (CMO) I or II deficiencies, or pseudohermaphroditism. In contrast, overproduction of steroid hormones can be involved in breast or prostate cancer, in hypertension, and heart fibrosis. Besides inhibiting the action of the steroid hormones on the level of steroid hormone receptors by using antihormones, which often is connected with severe side effects, more recently the steroid hydroxylases themselves turned out to be promising new targets for drug development. Since the 3-dimensional structures of steroid hydroxylases are not yet available, computer models of the corresponding CYPs may help to develop new inhibitors of these enzymes. During the past years, the necessary test systems have been developed and new compounds have been synthesized, which displayed selective and specific inhibition of CYP17, CYP11B2, and CYP11B1. With some of these potential new drugs, clinical trials are under way. It can be expected that in the near future some of these compounds will contribute to our arsenal of new and selective drugs.

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.

C(17,20)-lyase inhibitors. Part 2: design, synthesis and structure-activity relationships of (2-naphthylmethyl)-1H-imidazoles as novel C(17,20)-lyase inhibitors

A series of 1- and 4-(2-naphthylmethyl)-1H-imidazoles (3 and 4) has been synthesized and evaluated as C(17,20)-lyase inhibitors. Several 6-methoxynaphthyl derivatives showed potent C(17,20)-lyase inhibition, suppression of testosterone biosynthesis in rats and reduction in the weight of prostate and seminal vesicles in rats, whereas most of these compounds increased the liver weight after consecutive administrations. The effect on the liver weight was removed by incorporation of a hydroxy group and an isopropyl group at the methylene bridge, as seen in (S)-28d and (S)-42. Selectivity for C(17,20)-lyase over 11beta-hydroxylase is also discussed, and (S)-42 was found to be a more than 260-fold selective inhibitor. Furthermore, (S)-42 showed a potent suppression of testosterone biosynthesis after a single oral administration in monkeys. These data suggest that (S)-42 may be a promising agent for the treatment of androgen-dependent prostate cancer.

C17,20-lyase inhibitors I. Structure-based de novo design and SAR study of C17,20-lyase inhibitors

Novel nonsteroidal C(17,20)-lyase inhibitors were synthesized using de novo design based on its substrate, 17 alpha-hydroxypregnenolone, and several compounds exhibited potent C(17,20)-lyase inhibition. However, in vivo activities were found to be short-lasting, and in order to improve the duration of action, a series of benzothiophene derivatives were evaluated. As a result, compounds 9h, (S)-9i, and 9k with nanomolar enzyme inhibition (IC(50)=4-9 nM) and 9e (IC(50)=27 nM) were identified to have powerful in vivo efficacy with extended duration of action. The key structural determinants for the in vivo efficacy were demonstrated to be the 5-fluoro group on the benzothiophene ring and the 4-imidazolyl moiety. Superimposition of 9k and 17 alpha-hydroxypregnenolone demonstrated their structural similarity and enabled rationalization of the pharmacological results. In addition, selected compounds were also identified to be potent inhibitors of human enzyme with IC(50) values of 20-30 nM.

Effects of novel 17alpha-hydroxylase/C17, 20-lyase (P450 17, CYP 17) inhibitors on androgen biosynthesis in vitro and in vivo

Aiming at the development of new drugs for the treatment of prostate cancer, the effects of steroidal compounds and one non-steroidal substance on androgen biosynthesis were evaluated in vitro and in vivo. Sa 40 [17-(5-pyrimidyl)androsta-5,16-diene-3beta-ol], its 3-acetyl derivate Sa 41 and BW 19 [3,4-dihydro-2-(4-imidazolylmethyl)-6-methoxy-1-methyl-naphthalene] are compounds from our group, which have been developed as inhibitors of CYP 17 (17alpha-hydroxylase-C17, 20-lyase, the key enzyme in androgen biosynthesis). They have been compared with CB 7598 [abiraterone: 17-(3-pyridyl)androsta-5,16-diene-3beta-ol], its 3-acetyl compound CB 7630 and ketoconazole, compounds which already have been used clinically. The most potent compound toward human CYP 17 (testicular microsomes) was Sa 40 (IC(50) value of 24 nM), followed by Sa 41, CB 7598, BW 19, CB 7630 and ketoconazole. Sa 40 shows a type II difference spectrum and a non-competitive type of inhibition (K(i) value of 16 nM). No recovery of enzyme activity was observed after preincubation of CYP 17 with Sa 40 and subsequent charcoal treatment. In Escherichia coli cells coexpressing human CYP 17 and NADPH-P450 reductase, Sa 40 was more active than CB 7598 and BW 19, whereas the acetyl compounds were not active. The latter three compounds were equally active towards rat CYP 17. Male Sprague-Dawley (SD) rats were administered daily for 14 days BW 19 and the acetyl derivatives Sa 41 and CB 7630 as prodrugs (0.1 mmol/kg intraperitoneally). The test compounds strongly reduced plasma testosterone concentration, as well as prostate and seminal vesicles weights. They showed moderate inhibitory effects on the weights of levator ani, bulbocavernosus and testes, whereas they led to an increase in adrenal and pituitary weights. The only exception was BW 19 which did not change pituitary weights. Based on its superiority on the human enzyme, it was concluded that Sa 40 in its 3beta-acetate form (Sa 41) could be a promising candidate for clinical evaluation.

Development of a test system for inhibitors of human aldosterone synthase (CYP11B2): screening in fission yeast and evaluation of selectivity in V79 cells

Aldosterone synthase (CYP11B2) is a mitochondrial cytochrome P450 enzyme catalyzing the last steps of aldosterone production in the adrenal cortex. A new pharmacological approach for the treatment of the aldosterone induced effects in congestive heart failure and all forms of hyperaldosteronism could be the use of CYP11B2 inhibitors. In search for such compounds, it was our goal to develop a cellular enzyme assay suitable for screening high numbers of compounds. An assay procedure for the evaluation of inhibitors using the human CYP11B2 expressed in fission yeast Schizosaccharomyces pombe was established and a series of 10 compounds was tested in this whole cellular system. Human 11beta-hydroxylase (CYP11B1), which catalyzes the production of glucocorticoids, shows more than 90% homology compared to human CYP11B2. As this enzyme should not be affected, strong inhibitors of CYP11B2 have to be tested for selectivity. For that purpose, an assay procedure with V79MZ cells that express human CYP11B1 and CYP11B2, respectively, was integrated into the evaluation process. Using these screening procedures a potent and rather selective non-steroidal inhibitor of human CYP11B2 was detected with an IC(50) value of 59nM. We also identified a very potent inhibitor of both enzymes showing a stronger inhibitory activity against the cortisol producing CYP11B1.

Inhibition of CYP 17, a new strategy for the treatment of prostate cancer

Androgens are growth factors for approximately 80 percent of all prostate cancers. Suppressing androgen biosynthesis is therefore an important therapeutic strategy in order to inhibit tumor growth. Unfortunately, the drugs currently applied to lower androgen levels only affect testicular androgen production. Since androgens are also synthesized in the adrenal glands, tumor stimulation cannot be blocked completely. A new therapeutic target, CYP 17 (P450 17, 17alpha-hydroxylase-C17, C20 lyase), is likely to improve this situation. CYP 17 is a P450 enzyme and catalyzes the last step of androgen biosynthesis in both testes and adrenals. Inhibition of this enzyme will therefore result in a complete block of androgen production. This paper gives an overview of the current situation in this novel field of drug research and focuses on the development of steroidal and non-steroidal inhibitors of CYP 17.

5-Phenyl substituted 1-methyl-2-pyridones and 4'-substituted biphenyl-4-carboxylic acids. synthesis and evaluation as inhibitors of steroid-5alpha-reductase type 1 and 2

The synthesis of a series of 5-phenyl substituted 1-methyl-2-pyridones (I) and 4'-substituted biphenyl-4-carboxylic acids (II) as novel A-C ring steroidomimetic inhibitors of 5alpha-reductase (5alphaR) is described. Compounds 1-4 (I) were synthesized by palladium catalyzed cross coupling (Ishikura) reaction between diethyl(3-pyridyl)borane and aryl halides (1b-4b) followed by alpha-oxidation with sodium ferrocyanate of the 1-methyl-pyridinium salt. Inhibitors II (5-18) were obtained either by two successive Friedel-Crafts acylations from biphenyl (5a-10a) followed by saponification to yield the corresponding carboxylic acids (5-10) or by Suzuki cross coupling reaction to give the 4'-substituted biphenyl-4-carbaldehydes 11a-18a. The latter compounds were subjected to a Lindgren oxidation to yield compounds 11-18. The compounds were tested for inhibitory activity toward human and rat 5alphaR1 and 2. The test compounds inhibited 5alphaR, showing a broad range of inhibitory potencies. The best compound in series I was the N-(dicyclohexyl)-4-(1,2-dihydro-1-methyl-2-oxopyrid-5-yl)benzamide 4 exhibiting an IC(50) value for the human type 2 enzyme of 10 microM. In series II, the most active compound toward human type 2 isozyme was the 4'-(dicyclohexyl)acetyl-4-biphenyl carboxylic acid (10; IC(50)=220nM). Both series showed only marginal activity toward the human type 1 isozyme. In conclusion, the biphenyl carboxylic acids (II) are more appropriate for 5alphaR inhibition than the 5-phenyl-1-methyl-2-pyridones (I). Especially the 4'-carbonyl compounds 5-10 represent new lead structures for the development of novel human type 2 inhibitors.

Synthesis and evaluation of steroidal hydroxamic acids as inhibitors of P450 17 (17 alpha-hydroxylase/C17-20-lyase)

With the aim of developing new inhibitors of 17 alpha-hydroxylase/C17,20-lyase (P450 17, CYP 17), two steroidal hydroxamic acids (compounds 2 and 3) were synthesized and evaluated as inhibitors of CYP 17. The synthesis was performed using carboxylic acids as starting material to give acid chlorides which were reacted with N,N,O-tris(trimethylsilyl) hydroxylamine. Using microsomal fractions of human and rat testes and progesterone as a substrate, both compounds moderately inhibited the human and rat enzyme.

Development of a simple and rapid assay for the evaluation of inhibitors of human 17alpha-hydroxylase-C(17,20)-lyase (P450cl7) by coexpression of P450cl7 with NADPH-cytochrome-P450-reductase in Escherichia coli

P450c17 is a microsomal enzyme catalyzing the last step in androgen biosynthesis. As inhibitors of P450c17 are promising drug candidates for the treatment of prostate cancer, it was our goal to develop a new cellular assay for the in vitro evaluation of potential inhibitors. Human P450c17 was expressed in E. coli and hydroxylase activity was determined using 1,2[3H]-progesterone. As the activity was low (1.7 pmol/min/mg protein), due to a lack of the requisite electron transfer partner NADPH-cytochrome-P450-reductase (NADPH-P450-reductase), coexpression of both the enzymes had to be performed. For that purpose, a plasmid was constructed which encoded human P450c17 and rat NADPH-P450-reductase in a transcriptional unit. This strategy led to a 100-fold increase in P450cl7 activity (175 pmol/min/mg protein). Time, pH and temperature dependence of progesterone conversion of this new monooxygenase system was determined. The K(M) of progesterone was 2.75 microM. An assay procedure for the evaluation of inhibitors was established and modified for high throughput screening using 96-well plates. Selected compounds were tested for their inhibitory activity using this whole cell assay. The data was compared to the results obtained in microsomal testicular preparations.

Synthesis and evaluation of 17-aliphatic heterocycle-substituted steroidal inhibitors of 17alpha-hydroxylase/C17-20-lyase (P450 17)

In the search for potent inhibitors of P450 17, the key enzyme in androgen biosynthesis, a series of steroidal inhibitors were synthesized and tested toward rat and human P450 17. Small aliphatic heterocycles (aziridine, oxirane, thiirane, diaziridine, diazirine, azetidine) were introduced into the 17beta-position of anstrost-5-en-3beta-ol. After identifying that aziridine is the most suitable functional group to coordinate with the heme iron, modifications of the steroidal skeleton were performed for further optimization. A wide range of inhibitory potencies toward P450 17 were found for the 21 test compounds. The most potent inhibitors toward the human and rat enzyme were aziridine compounds 3 (IC(50) rat: 0.21 microM, K(i) = 3 nM; IC(50) human: 0.54 microM, K(i) = 8 nM), 5 (IC(50) rat: 0.43 microM, K(i) = 7 nM; IC(50) human: 0.29 microM, K(i) = 4 nM), and 8 (21R:21S = 1:1; IC(50) rat: 0.53 microM, K(i) = 9 nM; IC(50) human: 0.40 microM, K(i) = 6 nM) which were more potent than the reference ketoconazole (IC(50) rat: 67 microM; IC(50) human: 0.74 microM). The inhibitory potency depends markedly on the stereochemistry at C20 of the inhibitors. This effect is more pronounced for the rat enzyme. Tested for selectivity, the highly potent inhibitors show poor inhibitory activity toward P450 arom, P450 scc, P450 TxA(2), and 5alpha-reductase. Tested for in vivo activity, 3 and 8 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats by 81% and 84% after 2 h.

Synthesis and evaluation of novel steroidal oxime inhibitors of P450 17 (17 alpha-hydroxylase/C17-20-lyase) and 5 alpha-reductase types 1 and 2

17 alpha-Hydroxylase/C17-20-lyase (P450 17, CYP 17) and 5 alpha-reductase are the key enzymes in androgen biosynthesis and targets for the treatment of prostate cancer and benign prostatic hyperplasia. In the search of inhibitors for both enzymes, 23 pregnenolone- or progesterone-based steroids were synthesized bearing an oxime group connected directly or via a spacer to the steroidal D-ring. Tested for inhibition of human and rat P450 17, some pregnenolone (9, 11, 14) and a series of progesterone compounds (17-20) turned out to be highly active inhibitors of the human enzyme. The most active compound was Z-21-hydroxyiminopregna-5, 17(20)-dien-3 beta-ol (9) showing K(i) values of 44 and 3.4 nM for the human and rat enzymes, respectively, and a type II UV-difference spectrum indicating a coordinate bond between the oxime group and the heme iron. In contrast to the pregnenolones which showed no inhibition of 5 alpha-reductase isozymes 1 and 2, the progesterones 16, 17, 20, 21, and 23 showed marked inhibition, especially toward the type 2 enzyme. Compounds 17 and 20 were identified as potent dual inhibitors of both P450 17 and 5 alpha-reductase. Tested for selectivity, the most potent P450 17 inhibitors 9, 10, and 14 showed no or only marginal inhibition of P450 arom, P450 scc, and P450 TxA(2). Selected compounds were tested for inhibition of the target enzymes using whole-cell assays. Compounds 9-11 strongly inhibited P450 17 being coexpressed with NADPH-P450 reductase in E. coli cells, and 16, 20, and 23 markedly inhibited 5 alpha-reductase expressed in HEK 293 cells. Tested for in vivo activity, 9 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats after 2 and 6 h by 57% and 44%.