Imidazole substituted biphenyls: a new class of highly potent and in vivo active inhibitors of P450 17 as potential therapeutics for treatment of prostate cancer

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.

Antitumor Effect of Zwitterions of Imidazolium Derived from L-methionine in BALB/c Mice with Lymphoma L5178Y

BACKGROUND

In the therapy of cancer, several treatments have been designed using nanomaterials, among which gold nanoparticles (AuNPs) have been featured as a promising antitumoral agent. Our research group has developed the synthesis of gold nanoparticles L-AuNPs and D-AuNPs stabilized with zwitterions of imidazolium (L-1 and D-1) derived from L-methionine and D-methionine. Because the stabilizer agent is chiral, we observed through circular dichroism that AuNPs also present chirality; such chirality as well as the fact that the stabilizing agent contains fragments of methionine and imidazolium that are commonly involved in biological processes, opens up the possibility that this system may have biological compatibility. Additionally, the presence of methionine in the stabilizing agent opens the application of this system as a possible antitumor agent because methionine is involved in methylation processes of molecules such as DNA.

OBJECTIVE

The aim of this research is the evaluation of the antitumor activity of gold nanoparticles stabilized with zwitterions of imidazolium (L-AuNPs) derived from L-methionine in the model of BALB/c mice with lymphoma L5178Y.

METHODS

Taking as a parameter cell density, the evaluation of the inhibitory effect of L-AuNPs was carried out with a series of in vivo tests in BALB/c type mice; three groups of five mice each were formed (Groups 1, 2 and 3); all mice were i.p. inoculated with the lymphoblast murine L5178Y. Group 1 consisted of mice without treatment. In the Groups 2 and 3 the mice were treated with L-AuNPs at 0.3 mg/Kg on days 1, 7 and 14 by orally and intraperitonally respectively.

RESULTS

These results show low antitumor activity of these gold nanoparticles (L-NPsAu) but interestingly, the imidazolium stabilizing agent of gold nanoparticle (L-1) displayed promising antitumor activity. On the other hand, the enantiomer of L-1, (D-1) as well as asymmetric imidazole derivate from L-methionine (L-2), do not exhibit the same activity as L-1.

CONCLUSION

The imidazolium stabilizing agent (L-1) displayed promising antitumor activity. Modifications in the structure of L-1 showed that, the stereochemistry (like D-1) and the presence of methionine fragments (like L-2) are determinants in the antitumor activity of this compound.

Construction of heterocyclic structures by trivalent cerium salts promoted bond forming reactions

Cerium(III) salts have recently gained increasing attention in the synthetic community, owing to the powerful features that are reviewed in detail in this tutorial. This review reports significant examples of cerium(III) promoted synthesis of heterocyclic structures, initially dealing with the synthesis of five- and six-membered ring nitrogen containing heterocycles, then describing the preparation of their oxygenated analogues and finally discussing the achievement of seven-membered rings and mixed heterocyclic motifs.

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.

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.

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.

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.

Heme oxygenase inhibition by 2-oxy-substituted 1-(1H-imidazol-1-yl)-4-phenylbutanes: effect of halogen substitution in the phenyl ring

A series of 2-oxy-substituted 1-(1H-imidazol-1-yl)-4-phenylbutanes comprising imidazole-ketones, imidazole-dioxolanes, and imidazole-alcohols substituted with halogens in the phenyl ring were synthesized and evaluated as novel inhibitors of heme oxygenase which are structurally distinct from metalloporphyrins. The entire library of compounds was found to be highly active, with the bromine- and iodine-substituted derivatives being the most potent. The imidazole-dioxolanes were all selective for the HO-1 isozyme (inducible) and exhibited substantially lower activity toward the HO-2 isozyme (constitutive). The corresponding imidazole-ketones and imidazole-alcohols showed selectivity toward HO-1 to a lesser degree than the similarly substituted imidazole-dioxolanes.

Synthesis, biochemical evaluation and rationalisation of the inhibitory activity of a range of 4-substituted phenyl alkyl imidazole-based inhibitors of the enzyme complex 17α-hydroxylase/17,20-lyase (P45017α)

We report the preliminary results of the synthesis, biochemical evaluation and rationalisation of the inhibitory activity of a number of phenyl alkyl imidazole-based compounds as inhibitors of the two components of 17alpha-hydroxylase/17,20-lyase (P450(17alpha)), that is, 17alpha-hydroxylase (17alpha-OHase) and 17,20-lyase (lyase). The results show that N-3-(4-bromophenyl) propyl imidazole (12) (IC50 = 2.95 microM against 17alpha-OHase and IC50 = 0.33 microM against lyase) is the most potent compound within the current study, in comparison to ketoconazole (KTZ) (IC50 = 3.76 microM against 17alpha-OHase and IC50 = 1.66 microM against lyase). Modelling of these compounds suggests that the length of the alkyl chain enhances the interaction between the inhibitor and the area of the active site corresponding to the C3 area of the steroid backbone, thereby increasing potency.

Pharmacophore Modeling and in Silico Screening for New P450 19 (Aromatase) Inhibitors

Cytochrome P450 19 (P450 19, aromatase) constitutes a successful target for the treatment of breast cancer. This study analyzes chemical features common to P450 19 inhibitors to develop ligand-based, selective pharmacophore models for this enzyme. The HipHop and HypoRefine algorithms implemented in the Catalyst software package were employed to create both common feature and quantitative models. The common feature model for P450 19 includes two ring aromatic features in its core and two hydrogen bond acceptors at the ends. The models were used as database search queries to identify active compounds from the NCI database.

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.

CYP 17 and CYP 19 inhibitors. Evaluation of fluorine effects on the inhibiting activity of regioselectively fluorinated 1-(Naphthalen-2-ylmethyl)imidazoles

Regioselectively fluorinated 1-(naphth-2-ylmethyl)imidazoles 1a-h have been synthesized starting from the corresponding (naphth-2-yl)methanols (2). 2a-d have been obtained by LiAlH4-promoted reduction of fluorinated 1-methyl-2-naphthaldehydes. The latter were easily prepared in fairly good overall yields by ceric ammonium nitrate (CAN)-promoted oxidative addition of the suitable 3-(fluoroaryl)-1-trimethylsilyloxy-1-butenes to ethyl vinyl ether in methanol followed by cyclization of the resulting acetals in strongly acidic medium in the presence of DDQ. 2e-h were prepared by LiAlH4-promoted reduction of the corresponding fluorinated methyl 2-naphthoates. The latter were more profitably obtained by reacting the suitable benzyl bromide with the sodium salt of dimethyl 2-(2,2-dimethoxyethyl)malonate in DMF followed by demethoxycarbonylation and acid catalysed cyclization of the resulting acetals. Compared with the nonfluorinated parent compounds 1i-1, fluorinated 1-(naphth-2-yl)methylimidazoles 1a-h turned out to be potent inhibitors of CYP17 and CYP19 enzymes. The most active inhibitor of CYP17 is 1c, whereas CYP19 is strongly inhibited by 1b, 1e, and 1g. Interestingly, 1g is a potent dual inhibitor also being very active towards CYP19.

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.

Design, synthesis, and 3D QSAR of novel potent and selective aromatase inhibitors

The design, synthesis, and biological evaluation of a series of new aromatase inhibitors bearing an imidazole or triazole ring linked to a fluorene (A), indenodiazine (B), or coumarin scaffold (C) are reported. Properly substituted coumarin derivatives displayed the highest aromatase inhibitory potency and selectivity over 17-alpha-hydroxylase/17-20 lyase. The modeling of the aromatase inhibition data by Comparative Molecular Field Analysis (CoMFA/GOLPE 3D QSAR approach) led to the development of a PLS model with good fitting and predictive powers (n = 22, ONC = 3, r(2) = 0.949, s = 0.216, and q(2) = 0.715). The relationship between aromatase inhibition and the steric and electrostatic fields generated by the examined azole inhibitors enables a clear understanding of the nature and spatial location of the main interactions modulating the aromatase inhibitory potency.

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.

Discovery of Inhibitors of MCF-7 Tumor Cell Adhesion to Endothelial Cells and Investigation on their Mode of Action

Metastasis, the main reason for high mortality of cancer, is a multistep process. One important step in this process is the adhesion of tumor cells to vascular endothelium at sites distant from primary tumors during hematogenous dissemination. In order to investigate and quantify the adhesion of tumor cells to endothelial cells we developed an in vitro model using MCF-7 breast cancer cells and monolayers of human umbilical vein endothelial cells (HUVEC). The tumor cells were specifically labeled with a fluorescent dye for quantification; for increasing the amount of adherent cells, HUVEC monolayers were stimulated with phorbol ester before the addition of the tumor cells. Due to previous reports that products of several P450 enzymes contribute to the progression of certain kinds of cancer, inhibitors of CYP5 (thromboxane A(2) synthase), CYP17 (17alpha-hydroxylase-C17, 20-lyase), and CYP19 (aromatase) were tested in this in vitro model for their potency to reduce cancer cell adhesion. Within each series of P450 inhibitors, compounds with high inhibitory activity on tumor cell adhesion were identified. At an initial concentration of 100 microM, BW26, a potent inhibitor of CYP5, reduced tumor cell adhesion of MCF-7 to HUVECs to 15%, BW40 (CYP17) to 29%, and SU5a (CYP19) to 11% of the corresponding controls (no inhibitor). Reduction of tumor cell adhesion was shown to occur in a concentration-dependent manner. In addition to these inhibitors of CYP5, CYP17, and CYP19, liarozole, known to be a potent inhibitor of CYP26 (retinoic acid-4-hydroxylase) and ATRA (all-trans-retinoic acid) metabolism, was able to reduce tumor cell adhesion to 51% of the initial rate. Experiments elucidating the mode of action of these compounds revealed that inhibition of the mentioned CYP enzymes is not responsible for their ability to reduce tumor cell adhesion.

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.

Discovery of selective CYP11B2 (aldosterone synthase) inhibitors for the therapy of congestive heart failure and myocardial fibrosis

An increased aldosterone concentration due to congestive heart failure leads to a further progression of the disease as well as to myocardial fibrosis. To interfere with these fatal processes selective inhibition of aldosterone synthase (CYP11B2) is required. CYP11B1, a key enzyme in glucocorticoid biosynthesis showing a high homology to the target enzyme (>93%), must not be inhibited. Screening of our P450 inhibitor library for inhibition of bovine aldosterone synthase resulted in a high number of compounds showing reasonable inhibition. In the next step substances were tested for oral absorption using two artificial membrane assays. The inhibition of human CYP11B2 was evaluated using assays in fission yeast and V79MZ cells stably expressing the active human target enzyme. For selectivity, inhibition of CYP11B1, CYP11A1, CYP17, CYP19 and CYP5 was determined. Rather potent and selective compounds obtained in this way were structurally further optimised, finally leading to inhibitors showing IC(50) values within the low nanomolar range.

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.

A new class of nonsteroidal aromatase inhibitors: design and synthesis of chromone and xanthone derivatives and inhibition of the P450 enzymes aromatase and 17 alpha-hydroxylase/C17,20-lyase

Aromatase (P450arom) is a target of pharmacological interest for the treatment of breast cancer. In this paper, we report the design, synthesis, and in vitro biological evaluation of a series of new (di)benzopyranone-based inhibitors of this enzyme. The design of the new compounds was guided by a CoMFA model previously developed for a series of nonsteroidal aromatase inhibitors. Both the chromone and the xanthone nuclei were taken as molecular skeletons, and the functions supposed to be critical for binding to the aromatase active site - a heterocyclic ring (imidazole or 1,3,4-triazole) linked to the aromatic moiety by a methylene unit and an H-bond accepting function (CN, NO(2), Br) located on the aromatic ring at a suitable distance from the heterocyclic nitrogen carrying the lone pair--were attached to them. The chromone, xanthone, and flavone derivatives were prepared by conventional synthetic methods from the appropriate methyl analogues. Aromatase inhibitory activities were determined by the method of Thompson and Siiteri, using human placental microsomes and [1 beta,2 beta-(3)H]testosterone as the labeled substrate. All the compounds were also tested on 17 alpha-hydroxylase/C17,20-lyase (P450 17), an enzyme of therapeutic interest for the treatment of prostatic diseases. The goal to find new potent inhibitors of aromatase was reached with the xanthone derivatives 22d,e (IC(50) values 43 and 40 nM, respectively), which exceeded the potency of the known reference drug fadrozole and also showed high selectivity with respect to P450 17. Moreover, compounds 22g-i based on the same xanthonic nucleus showed fairly high potency as P450 17 inhibitors (IC(50) values 220, 130, and 42 nM, respectively). Thus, they might be new leads for the development of drug candidates for androgen-dependent diseases.

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%.

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

The synthesis of a new series of P450 17 inhibitors is described. The imidazol-1-yl compounds 5 showed strong inhibition of P450 17 rat and especially human enzyme, the most active compounds being 5ax, 5ay and 5bx with IC50 values of 0.17, 0.24 and 0.25 microM, respectively (ketoconazole: 0.74 microM). The 1,2,4-triazol-1-yl compounds 6 were less active, while the 1,2,4-triazol-4-yl compounds 7 were inactive. The title compounds showed little inhibition of P450 arom. The most active P450 17 inhibitors 5ax and 5ay markedly decreased the testosterone plasma concentration of SD rats 2 h after application of 0.019 mmol/kg. After 6 h, 5ay still exhibited a strong effect.