Testicular microsomal cytochrome P-450 for C21 steroid side chain cleavage. Spectral and binding studies

Single-cell and spatiotemporal profile of ovulation in the mouse ovary

Ovulation is a spatiotemporally coordinated process that involves several tightly controlled events, including oocyte meiotic maturation, cumulus expansion, follicle wall rupture and repair, and ovarian stroma remodeling. To date, no studies have detailed the precise window of ovulation at single-cell resolution. Here, we performed parallel single-cell RNA-seq and spatial transcriptomics on paired mouse ovaries across an ovulation time course to map the spatiotemporal profile of ovarian cell types. We show that major ovarian cell types exhibit time-dependent transcriptional states enriched for distinct functions and have specific localization profiles within the ovary. We also identified gene markers for ovulation-dependent cell states and validated these using orthogonal methods. Finally, we performed cell-cell interaction analyses to identify ligand-receptor pairs that may drive ovulation, revealing previously unappreciated interactions. Taken together, our data provides a rich and comprehensive resource of murine ovulation that can be mined for discovery by the scientific community.

New insights into the all-testis differentiation in zebrafish with compromised endogenous androgen and estrogen synthesis

The regulatory mechanism of gonadal sex differentiation, which is complex and regulated by multiple factors, remains poorly understood in teleosts. Recently, we have shown that compromised androgen and estrogen synthesis with increased progestin leads to all-male differentiation with proper testis development and spermatogenesis in cytochrome P450 17a1 (cyp17a1)-/- zebrafish. In the present study, the phenotypes of female-biased sex ratio were positively correlated with higher Fanconi anemia complementation group L (fancl) expression in the gonads of doublesex and mab-3 related transcription factor 1 (dmrt1)-/- and cyp17a1-/-;dmrt1-/- fish. The additional depletion of fancl in cyp17a1-/-;dmrt1-/- zebrafish reversed the gonadal sex differentiation from all-ovary to all-testis (in cyp17a1-/-;dmrt1-/-;fancl-/- fish). Luciferase assay revealed a synergistic inhibitory effect of Dmrt1 and androgen signaling on fancl transcription. Furthermore, an interaction between Fancl and the apoptotic factor Tumour protein p53 (Tp53) was found in vitro. The interaction between Fancl and Tp53 was observed via the WD repeat domain (WDR) and C-terminal domain (CTD) of Fancl and the DNA binding domain (DBD) of Tp53, leading to the K48-linked polyubiquitination degradation of Tp53 activated by the ubiquitin ligase, Fancl. Our results show that testis fate in cyp17a1-/- fish is determined by Dmrt1, which is thought to stabilize Tp53 by inhibiting fancl transcription during the critical stage of sexual fate determination in zebrafish.

Estrogen Signaling Inhibits the Expression of anti-Müllerian hormone (amh) and gonadal-soma-derived factor (gsdf) during the Critical Time of Sexual Fate Determination in Zebrafish

The mechanism of fish gonadal sex differentiation is complex and regulated by multiple factors. It has been widely known that proper steroidogenesis in Leydig cells and sex-related genes in Sertoli cells play important roles in gonadal sex differentiation. In teleosts, the precise interaction of these signals during the sexual fate determination remains elusive, especially their effect on the bi-potential gonad during the critical stage of sexual fate determination. Recently, all-testis phenotypes have been observed in the cyp17a1-deficient zebrafish and common carp, as well as in cyp19a1a-deficient zebrafish. By mating cyp17a1-deficient fish with transgenic zebrafish Tg(piwil1:EGFP-nanos3UTR), germ cells in the gonads were labelled with enhanced green fluorescent protein (EGFP). We classified the cyp17a1-deficient zebrafish and their control siblings into primordial germ cell (PGC)-rich and -less groups according to the fluorescence area of the EGFP labelling. Intriguingly, the EGFP-labelled bi-potential gonads in cyp17a1+/+ fish from the PGC-rich group were significantly larger than those of the cyp17a1-/- fish at 23 days post-fertilization (dpf). Based on the transcriptome analysis, we observed that the cyp17a1-deficient fish of the PGC-rich group displayed a significantly upregulated expression of amh and gsdf compared to that of control fish. Likewise, the upregulated expressions of amh and gsdf were observed in cyp19a1a-deficient fish as examined at 23 dpf. This upregulation of amh and gsdf could be repressed by treatment with an exogenous supplement of estradiol. Moreover, tamoxifen, an effective antagonist of both estrogen receptor α and β (ERα and Erβ), upregulates the expression of amh and gsdf in wild-type (WT) fish. Using the cyp17a1- and cyp19a1a-deficient zebrafish, we provide evidence to show that the upregulated expression of amh and gsdf due to the compromised estrogen signaling probably determines their sexual fate towards testis differentiation. Collectively, our data suggest that estrogen signaling inhibits the expression of amh and gsdf during the critical time of sexual fate determination, which may broaden the scope of sex steroid hormones in regulating gonadal sex differentiation in fish.

Dissecting the fate of Foxl2-expressing cells in fetal ovary using lineage tracing and single-cell transcriptomics

Gonad somatic cells acquire sex-specific fates during sex determination. In XX gonad, a subset of somatic cells expresses Foxl2 after sex determination which is considered the progenitor of granulosa cells. However, whether these cells also contribute to other cell types at later developmental stages is unknown. In the present study, the cell fate of Foxl2-expressing cells in fetal ovaries was analyzed by lineage tracing and single-cell transcriptomics. We found that Foxl2-expressing cells gave rise to three cell types at later developmental stages, including granulosa cells, theca-interstitial cells, and stromal cells. Series single-cell RNA sequencing revealed FOXL2-positive cells were divided into two clusters at P0. One group further differentiated into granulosa cells and Theca-G (Theca-interstitial cells derived from granulosa) at P14. Another group was classified as stromal cell lineage, then a small portion of them further differentiated into 3β-HSD-positive Theca-S (Theca-interstitial cells derived from stroma). Cyp17a1 was expressed in Theca-S, but not in Theca-G. This study demonstrated that Folx2-expressing cells in XX gonad after sex determination are multipotent and theca-interstitial cells are derived from different progenitors. Our data provided an important resource, at single-cell resolution, for a better understanding of somatic cell differentiation in ovary development.

Synthesis and Structure–Activity Relationships of Novel Non-Steroidal CYP17A1 Inhibitors as Potential Prostate Cancer Agents

Twenty new compounds, targeting CYP17A1, were synthesized, based on our previous work on a benzimidazole scaffold, and their biological activity evaluated. Inhibition of CYP17A1 is an important modality in the treatment of prostate cancer, which remains the most abundant cancer type in men. The biological assessment included CYP17A1 hydroxylase and lyase inhibition, CYP3A4 and P450 oxidoreductase (POR) inhibition, as well as antiproliferative activity in PC3 prostate cancer cells. The most potent compounds were selected for further analyses including in silico modeling. This combined effort resulted in a compound (comp 2, IC₅₀ 1.2 µM, in CYP17A1) with a potency comparable to abiraterone and selectivity towards the other targets tested. In addition, the data provided an understanding of the structure–activity relationship of this novel non-steroidal compound class.

CYP17A1 deficient XY mice display susceptibility to atherosclerosis, altered lipidomic profile and atypical sex development

CYP17A1 is a cytochrome P450 enzyme with 17-alpha-hydroxylase and C17,20-lyase activities. CYP17A1 genetic variants are associated with coronary artery disease, myocardial infarction and visceral and subcutaneous fat distribution; however, the underlying pathological mechanisms remain unknown. We aimed to investigate the function of CYP17A1 and its impact on atherosclerosis in mice. At 4–6 months, CYP17A1-deficient mice were viable, with a KO:Het:WT ratio approximating the expected Mendelian ratio of 1:2:1. All Cyp17a1 knockout (KO) mice were phenotypically female; however, 58% were Y chromosome-positive, resembling the phenotype of human CYP17A1 deficiency, leading to 46,XY differences/disorders of sex development (DSD). Both male and female homozygous KO mice were infertile, due to abnormal genital organs. Plasma steroid analyses revealed a complete lack of testosterone in XY-KO mice and marked accumulation of progesterone in XX-KO mice. Elevated corticosterone levels were observed in both XY and XX KO mice. In addition, Cyp17a1 heterozygous mice were also backcrossed onto an Apoe KO atherogenic background and fed a western-type diet (WTD) to study the effects of CYP17A1 on atherosclerosis. Cyp17a1 x Apoe double KO XY mice developed more atherosclerotic lesions than Apoe KO male controls, regardless of diet (standard or WTD). Increased atherosclerosis in CYP17A1 XY KO mice lacking testosterone was associated with altered lipid profiles. In mice, CYP17A1 deficiency interferes with sex differentiation. Our data also demonstrate its key role in lipidomic profile, and as a risk factor in the pathogenesis of atherosclerosis.

Effect of Hyperin and Icariin on steroid hormone secretion in rat ovarian granulosa cells

AIM OF THE STUDY

This study was designed to investigate the effect of different concentrations of Hyperin and Icariin (ICA)on proliferation and the secretion of estrogen (E2), and progesterone (P) in granulosa cells, and to explore the effect of Hyperin and Icariin on the expression of CYP17 and CYP19.

MATERIALS AND METHODS

Rat ovary granulosa cells were cultured in vitro and treated with different concentrations of Hyperin and Icariin. The proliferation of ovarian granulosa cells was measured with the MTT assay. The concentration of estradiol was measured with a magnetic particle-based enzyme-linked immunosorbent assay (ELISA) kit. The CYP17 and CYP19 mRNA expression was detected by quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR). The CYP17 and CYP19 protein expression was determined with Western blotting.

RESULTS

Hyperin (50 μg/l) and Icariin (10 μg/l) significantly increased proliferation of ovarian granulosa cells and secretion of estrogen and progesterone. Hyperin and Icariin stimulated the mRNA and protein expression of CYP17 and CYP19.

CONCLUSIONS

These results showed that Hyperin and Icariin can promote the secretion of E2 and P through up-regulation of CYP17 and CYP19. Frequently used Chinese herbs like Cuscuta Chinensis Lam and Epimedium Brevicornu maxim, which contain Hyperin and Icariin, could improve the ovarian endocrine function through these effects.

Role of cytochrome b5 in the modulation of the enzymatic activities of cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1)

Cytochrome b5 (cyt b5) is a small hemoprotein that plays a significant role in the modulation of activities of an important steroidogenic enzyme, cytochrome P450 17α-hydroxylase/17,20-lyase (P450 17A1, CYP17A1). Located in the zona fasciculata and zona reticularis of the adrenal cortex and in the gonads, P450 17A1 catalyzes two different reactions in the steroidogenic pathway; the 17α-hydroxylation and 17,20-lyase, in the endoplasmic reticulum of these respective tissues. The activities of P450 17A1 are regulated by cyt b5 that enhances the 17,20-lyase reaction by promoting the coupling of P450 17A1 and cytochrome P450 reductase (CPR), allosterically. Cyt b5 can also act as an electron donor to enhance the 16-ene-synthase activity of human P450 17A1. In this review, we discuss the many roles of cyt b5 and focus on the modulation of CYP17A1 activities by cyt b5 and the mechanisms involved.

Steroidal 5α-reductase and 17α-hydroxylase/17,20-lyase (CYP17) inhibitors useful in the treatment of prostatic diseases

The role of steroidal inhibitors of androgen biosynthesis as potential weapons in the treatment of prostatic diseases, such as benign prostatic hyperplasia and prostatic cancer will be reviewed. Two enzymes have been targeted in the development of inhibitors that potentially could be useful in the management of such conditions. 5α-Reductase is primarily of interest in benign prostatic disease, though some role in the chemoprevention of prostatic carcinoma have been considered, whereas the 17α-hydroxylase/17,20-lyase (CYP17) enzyme is of interest in the treatment of malignant disease. An overview of the main achievements obtained during the past years will be presented, however special focus will be made on steroidal molecules that reached clinical trials or have been commercially launched. Relevant examples of such drugs are finasteride, dutasteride, abiraterone acetate and galeterone (TOK-001, formerly known as VN/124-1). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Effect of a novel 17,20-lyase inhibitor, orteronel (TAK-700), on androgen synthesis in male rats

Endogenous androgens play a role in the development and progression of prostate cancer (PC), thus androgen suppression may offer an effective therapeutic strategy for this disease. Orteronel (TAK-700), 6-[(7S)-7-hydroxy-6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-7-yl]-N-methyl-2-naphthamide, is a novel, non-steroidal, selective inhibitor of the 17,20-lyase activity of CYP17A--a key enzyme in the production of steroidal hormones--and is being developed as a therapy for PC. The purpose of this study was to elucidate the inhibitory activity of orteronel, in particular its specificity for androgen synthesis enzymes, in male rats--an androgen-synthesis model that largely reflects this pathway in humans. Orteronel inhibited 17,20-lyase activity in rats with an IC(50) of 1200 nM but did not inhibit 17α-hydroxylase or 11β-hydroxylase (CYP11B1) activity in rats at concentrations up to 10 μM. In cellular steroidogenesis assays using rat testicular cells, orteronel suppressed testosterone and androstenedione production with an IC(50) of 640 nM and 210 nM, respectively, but did not suppress either corticosterone or aldosterone production in rat adrenal cells at concentrations up to 30 μM. In addition, serum testosterone and androstenedione levels in human chorionic gonadotropin-injected hypophysectomized rats were significantly reduced by single oral administration of orteronel at a dose of 30 mg/kg (both p ≤ 0.01); serum corticosterone and aldosterone levels in ACTH-injected hypophysectomized rats did not result in significant differences compared with controls, following orteronel administration at doses up to 300 mg/kg. Serum testosterone levels in intact male rats were significantly reduced by orteronel 4h after dosing at 100mg/kg (p ≤ 0.01); testosterone levels showed a tendency to recover afterward. In intact male rats, the weight of the prostate glands and seminal vesicles was decreased in a dose-dependent manner following multiple doses of orteronel at 37.5, 150, and 600 mg/kg, TID for 4 days. The reversibility of orteronel was further confirmed using a human adrenocortical tumor cell line. In summary, orteronel is a selective and reversible 17,20-lyase inhibitor, and decreases the weight of androgen-dependent organs in male rats. Our data suggests that orteronel would therefore be effective for androgen-dependent disorders such as PC.

A review of mechanistic studies on aromatase (CYP19) and 17α-hydroxylase-17,20-lyase (CYP17)

In the conventional P-450 dependent hydroxylation reaction, the Fe(III) resting state of the enzyme, by a single electron transfer, is reduced to Fe(II), which reacts with O(2) to produce a Fe(III)-O-O intermediate. The latter following the transfer of another electron furnishes a ferric-peroxyanion, Fe(III)-O-O(-), which after protonation leads to the fission of the O-O bond resulting in the formation of Fe(V)O, the key player in the hydroxylation process. Certain members of the P-450 family, including CYP17 and CYP19, catalyze, at the same active site, not only the hydroxylation process but also an acyl-carbon bond cleavage reaction which has been interpreted to involve the nucleophilic attack of the ferric-peroxyanion, Fe(III)-O-O(-), on the acyl carbon to furnish a tetrahedral intermediate which fragments, leading to acyl-carbon cleavage. Evidence is presented to show that in the case of CYP17 the attack of Fe(III)-O-O(-) on the target carbon is promoted by cytochrome b(5), which acts as a conformational regulator of CYP17. It is this regulation of CYP17 that provides a safety mechanism which ensures that during corticoid biosynthesis, which involves 17α-hydroxylation by CYP17, androgen formation is avoided. Finally, a brief account is presented of the inhibitors, of the two enzymes, which have been designed on the basis of their mechanism of action. Article from the Special issue on 'Targeted Inhibitors'.

Synthesis of novel C17 steroidal carbamates. Studies on CYP17 action, androgen receptor binding and function, and prostate cancer cell growth

We have exploited the reaction of 1,1'-carbonylbis(2-methylimidazole) (CBMI) with several 17beta-hydroxy androstanes to synthesize a series of novel C17 steroidal carbamates. Structural elucidation features have been provided for the final compounds based on 1D and 2D NMR techniques, IR spectroscopy, and related literature. The new compounds were tested for inhibition of human cytochrome 17alpha-hydroxylase-C17,20-lyase (CYP17) and androgen receptor (AR) binding and function effects. Their inhibitory potential against PC-3 cell proliferation was also evaluated. Compounds 11 and 23 were found to inhibit CYP17 with IC50 values of 17.1 and 11.5 microM, respectively. The carbamate moiety at C17 allowed tight binding of the synthesized compounds to both wild-type (wt-) and mutated AR. When bound to the mutated AR, the compounds were found to have a dual effect, stimulating transcription at low concentrations while almost fully blocking it at the higher concentrations tested, in the presence of the natural androgen dihydrotestosterone (DHT). Compounds 8 and 12 were the most active against PC-3 cell proliferation with EC50 values of 2.2 and 0.2 microM, respectively.

Synthesis and evaluation of novel 17-indazole androstene derivatives designed as CYP17 inhibitors

A series of novel 1H- and 2H-indazole derivatives of the commercially available dehydroepiandrosterone acetate have been synthesized and tested for inhibition of human cytochrome 17alpha-hydroxylase-C(17,20)-lyase (CYP17), androgen receptor (AR) binding affinity, and cytotoxic potential against three prostate cancer (PC) cell lines.

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.

A case of ganglioneuroma in which131I-6ß-iodomethyl-19-norcholest-5(10)-en-3ß-ol scintigraphy showed high uptake in the adrenal gland leading to a misdiagnosis

We experienced a case in which 131I-6beta-iodomethyl-19-norcholest-5(10)-en-3beta-ol (131I-adosterol) scintigraphy showed high uptake in the right adrenal gland. We diagnosed functional cortical adenoma because of the finding of 131I-adosterol scintigraphy. However, no positive findings for the existence of cortical adenoma were obtained in other examinations and we performed right adrenalectomy. Unexpectedly, pathological finding showed the right adrenal gland was occupied with a large ganglioneuroma. This is an instructive case in which 131I-adosterol scintigraphy showed abnormal high uptake in the adrenal gland, in spite of the fact that the adrenal gland was occupied by a tumor derived from adrenal medulla.

Regulation of cytochrome P450 by posttranslational modification

Cytochrome P450s are a family of enzymes represented in all kingdoms with expression in many species. Over 3,000 enzymes have been identified in nature. Humans express 57 putatively functional enzymes with a variety of critical physiological roles. They are involved in the metabolic oxidation, peroxidation, and reduction of many endogenous and exogenous compounds including xenobiotics, steroids, bile acids, fatty acids, eicosanoids, environmental pollutants, and carcinogens [Nelson, D. R., Kamataki, T., Waxman, D. J., Guengerich, F. P., Estabrook, R. W., Feyereisen, R., Gonzalez, F. J., Coon, M. J., Gunsalus, I. C., Gotoh, O. (1993) The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature. DNA Cell Biol. 12(1):1-51.] The development of numerous diseases and disorders including cancer and cardiovascular and endocrine dysfunction has been linked to P450s. Several levels of regulation, including transcription, translation, and posttranslational modification, participate in maintaining the proper function of P450s. Modifications including phosphorylation, glycosylation, nitration, and ubiquitination have been described for P450s. Their physiological significance includes modulation of enzyme activity, targeting to specific cellular compartments, and tagging for proteasomal degradation. Knowledge of P450 posttranslational regulation is derived from studies with relatively few enzymes. In many cases, there is only enough evidence to suggest the occurrence and a possible role for the modification. Thus, many P450 enzymes have not been fully characterized. With the introduction of current proteomics tools, we are primed to answer many important questions regarding regulation of P450 in response to a posttranslational modification. This review considers regulation of P450 in a context that describes the potential role and physiological significance of each modification.

Minireview: regulation of steroidogenesis by electron transfer

Cytochrome P450 enzymes catalyze the degradation of drugs and xenobiotics, but also catalyze a wide variety of biosynthetic processes, including most steps in steroidogenesis. The catalytic rate of a P450 enzyme is determined in large part by the rate of electron transfer from its redox partners. Type I P450 enzymes, found in mitochondria, receive electrons from reduced nicotinamide adenine dinucleotide (NADPH) via the intermediacy of two proteins-ferredoxin reductase (a flavoprotein) and ferredoxin (an iron/sulfur protein). Type I P450 enzymes include the cholesterol side-chain cleavage enzyme (P450scc), the two isozymes of 11-hydroxylase (P450c11beta and P450c11AS), and several vitamin D-metabolizing enzymes. Disorders of these enzymes, but not of the two redox partners, have been described. Type II P450 enzymes, found in the endoplasmic reticulum, receive electrons from NADPH via P450 oxidoreductase (POR), which contains two flavin moieties. Steroidogenic Type II P450 enzymes include 17alpha-hydroxylase/17,20 lyase (P450c17), 21-hydroxylase (P450c21), and aromatase (P450aro). All P450 enzymes catalyze multiple reactions, but P450c17 appears to be unique in that the ratio of its activities is regulated at a posttranslational level. Three factors can increase the degree of 17,20 lyase activity relative to the 17alpha-hydroxylase activity by increasing electron flow from POR: a high molar ratio of POR to P450c17, serine phosphorylation of P450c17, and the presence of cytochrome b(5), acting as an allosteric factor to promote the interaction of POR with P450c17. POR is required for the activity of all 50 human Type II P450 enzymes, and ablation of the Por gene in mice causes embryonic lethality. Nevertheless, mutation of the human POR gene is compatible with life, causing multiple steroidogenic defects and a skeletal dysplasia called Antley-Bixler syndrome.

Regulation of 17,20 lyase activity by cytochrome b5 and by serine phosphorylation of P450c17

Cytochrome P450c17 catalyzes the 17alpha-hydroxylase activity required for glucocorticoid synthesis and the 17,20 lyase activity required for sex steroid synthesis. Most P450 enzymes have fixed ratios of their various activities, but the ratio of these two activities of P450c17 is regulated post-translationally. We have shown that serine phosphorylation of P450c17 and the allosteric action of cytochrome b5 increase 17,20 lyase activity, but it has not been apparent whether these two post-translational mechanisms interact. Using purified enzyme systems, we now show that the actions of cytochrome b5 are independent of the state of P450c17 phosphorylation. Suppressing cytochrome b5 expression in human adrenal NCI-H295A cells by >85% with RNA interference had no effect on 17alpha-hydroxylase activity but reduced 17,20 lyase activity by 30%. Increasing P450c17 phosphorylation could compensate for this reduced activity. When expressed in bacteria, human P450c17 required either cytochrome b5 or phosphorylation for 17,20 lyase activity. The combination of cytochrome b5 and phosphorylation was not additive. Cytochrome b5 and phosphorylation enhance 17,20 lyase activity independently of each other, probably by increasing the interaction between P450c17 and NADPH-cytochrome P450 oxidoreductase.

Disorders of androgen synthesis--from cholesterol to dehydroepiandrosterone

Androgens and estrogens are primarily made from dehydroepiandrosterone (DHEA), which is made from cholesterol via four steps. First, cholesterol enters the mitochondria with the assistance of the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia (lipoid CAH), a potentially lethal disease in which virtually no steroids are made. Lipoid CAH is common among Palestinian Arabs and people from eastern Arabia, and among Korean and Japanese people. Second, within the mitochondria, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc; disorder of this enzyme is very rare, probably due to embryonic lethality. Third, pregnenolone undergoes 17alpha-hydroxylation by microsomal P450c17. 17alpha-Hydroxylase deficiency, manifesting as female sexual infantilism and hypertension, is rare except in Brazil. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. The ratio of the 17,20 lyase to 17alpha-hydroxylase activity of P450c17 determines the ratio of C21 to C19 steroids produced. This ratio is regulated posttranslationally by at least three factors: the abundance of the electron-donating protein P450 oxidoreductase (POR), the presence of cytochrome b5 and the serine phosphorylation of P450c17. Mutations of POR are a new, recently described disorder manifesting as the Antley-Bixler skeletal dysplasia syndrome, and a form of polycystic ovary syndrome.

Deletion of the mouse P450c17 gene causes early embryonic lethality

Dehydroepiandrosterone (DHEA), a 19-carbon precursor of sex steroids, is abundantly produced in the human but not the mouse adrenal. However, mice produce DHEA and DHEA-sulfate (DHEAS) in the fetal brain. DHEA stimulates axonal growth from specific populations of mouse neocortical neurons in vitro, while DHEAS stimulates dendritic growth from those cells. The synthesis of DHEA and sex steroids, but not mouse glucocorticoids and mineralocorticoids, requires P450c17, which catalyzes both 17 alpha-hydroxylase and 17,20-lyase activities. We hypothesized that P450c17-knockout mice would have disordered sex steroid synthesis and disordered brain DHEA production and thus provide phenotypic clues about the functions of DHEA in mouse brain development. We deleted the mouse P450c17 gene in 127/SvJ mice and obtained several lines of mice from two lines of targeted embryonic stem cells. Heterozygotes were phenotypically and reproductively normal, but in all mouse lines, P450c17(-/-) zygotes died by embryonic day 7, prior to gastrulation. The cause of this early lethality is unknown, as there is no known function of fetal steroids at embryonic day 7. Immunocytochemistry identified P450c17 in embryonic endoderm in E7 wild-type and heterozygous embryos, but its function in these cells is unknown. Enzyme assays of wild-type embryos showed a rapid rise in 17-hydroxylase activity between E6 and E7 and the presence of C(17,20)-lyase activity at E7. Treatment of pregnant females with subcutaneous pellets releasing DHEA or 17-OH pregnenolone at a constant rate failed to rescue P450c17(-/-) fetuses. Treatment of normal pregnant females with pellets releasing pregnenolone or progesterone did not cause fetal demise. These data suggest that steroid products of P450c17 have heretofore-unknown essential functions in early embryonic mouse development.

CYP17 mutation E305G causes isolated 17,20-lyase deficiency by selectively altering substrate binding

Cytochrome p450c17 (CYP17) converts the C21 steroids pregnenolone and progesterone to the C19 androgen precursors dehydroepiandrosterone (DHEA) and androstenedione, respectively, via sequential 17alpha-hydroxylase and 17,20-lyase reactions. Disabling mutations in CYP17 cause combined 17alpha-hydroxylase/17,20-lyase deficiency, but rare missense mutations cause isolated loss of 17,20-lyase activity by disrupting interactions of redox partner proteins with CYP17. We studied an adolescent male with clinical and biochemical features of isolated 17,20-lyase deficiency, including micropenis, hypospadias, and gynecomastia, who is homozygous for CYP17 mutation E305G, which lies in the active site. When expressed in HEK-293 cells or Saccharomyces cerevisiae, mutation E305G retains 17alpha-hydroxylase activities, converting pregnenolone and progesterone to 17alpha-hydroxysteroids. However, mutation E305G lacks 17,20-lyase activity for the conversion of 17alpha-hydroxypregnenolone to DHEA, which is the dominant pathway to C19 steroids catalyzed by human CYP17 (the delta5-steroid pathway). In contrast, mutation E305G exhibits 11-fold greater catalytic efficiency (kcat/Km) for the cleavage of 17alpha-hydroxyprogesterone to androstenedione compared with wild-type CYP17. We conclude that mutation E305G selectively impairs 17,20-lyase activity for DHEA synthesis despite an increased capacity to form androstenedione. Mutation E305G provides genetic evidence that androstenedione formation from 17alpha-hydroxyprogesterone via the minor delta4-steroid pathway alone is not sufficient for complete formation of the male phenotype in humans.

Pharmacokinetics of novel inhibitors of androgen synthesis after intravenous administration in mice

PURPOSE

The pharmacokinetics of several new androgen synthesis inhibitors were investigated after intravenous administration in mice. The inhibitors were: 3beta-hydroxy-17-(1 H-imidazol-1-yl)androsta-5,16-diene (VN/85-1), 3beta-hydroxy-17-(1 H-1,2,3-triazol-1-yl)androsta-5,16-diene (VN/87-1), 17-(1 H-imidazol-1-yl)androsta-4,16-diene-3-one (VN/108-1) and 17-(5'-isoxazolyl)androsta-4,16-dien-3-one (L-39).

METHODS

Male Balb/c mice were injected with VN/85-1, VN/87-1, VN/108-1 or L-39 at 10, 25 and 50 mg/kg doses. Blood was collected at various times after drug administration via the eye orbit. The concentrations of VN/85-1, VN/87-1, VN/108-1 or L-39 in plasma were analyzed by a reversed-phase HPLC method with UV detection.

RESULTS

The plasma levels of VN/85-1, VN/87-1, VN/108-1 and L-39 declined biexponentially with terminal elimination half-lives ranging from 0.88 to 1.77 h. The terminal half-lives for VN/87-1, VN/85-1 and VN/108-1 were similar. However, the terminal half-life for L-39 was significantly longer than those for VN/87-1, VN/85-1 and VN/108-1. The systemic clearance values for the steroids ranged from 0.85 to 10.91 l/h per kg with a rank order of their clearance of L-39>VN/87-1>VN/108-1>VN/85-1. The apparent volumes of distribution at steady state for the steroids ranged from 0.58 to 18.85 l/kg with a rank order of their apparent V(ss) of L-39>VN/87-1>VN/85-1>VN/108-1. The clearance and apparent V(ss) for all four compounds were dose-independent following intravenous administration of doses up to 50 mg/kg.

CONCLUSIONS

VN/85-1, VN/87-1, VN/108-1 and L-39 are rapidly cleared from the systemic circulation and display linear pharmacokinetics in mice. The information presented may be used to improve the disposition profiles and activities of the steroidal inhibitors of androgen synthesis in animal models of prostate cancer.

Novel steroidal vinyl fluorides as inhibitors of steroid C17(20) lyase

20-fluoro-17(20)-pregnenolone derivatives were designed as enol mimics of pregnenolone. All of the targeted, novel fluoroolefins were potent inhibitors of C17(20) lyase.

Purification of cytochromes P-450(scc) and P-450(17 alpha) by steroid-binding affinity column chromatography

The preparation, testing and use of a variety of cholesterol-, deoxycorticosterone (DOC)- and pregnenolone-binding 1,6-diaminohexyl (EAH)-Sepharose 4B supports for affinity column chromatography of cytochromes P-450(scc) and P-450(17 alpha) from bovine adrenal and pig testis are described. EAH-Sepharose 4B has free amino groups at the end of a 10-atom spacer arm. Hydroxyl groups of cholesterol (3 beta), deoxycorticosterone (21 beta) and pregnenolone (3 beta) are linked to succinic anhydride in pyridine through an ester linkage. These coupling ligands of hemisuccinate were synthesized by a general procedure. Free amino groups of EAH-Sepharose 4B were used to couple ligands, containing carboxyl groups, by the carbodiimide coupling method. Both the purified cytochromes P-450(scc) and P-450(17 alpha) were found to be homogeneous and estimated to have a molecular weight of 52,000 on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The carbon monoxide difference spectra with peaks at 450 and 448 nm exhibit the absorption spectra of typical cytochromes P-450(scc) and P-450(17 alpha), respectively. Cytochromes P-450(scc) and P-450(17 alpha) were determined to have isoelectric points of 8.0 and 6.5 in isoelectric focusing on a pH gradient gel. Cytochrome P-450s can be purified between 425- and 1000-fold from the crude extracts.

Pharmacokinetic profile of 3beta-hydroxy-17-(1H-1,2,3-triazol-1-yl)androsta-5,16-diene (VN/87-1), a potent androgen synthesis inhibitor, in mice

The objective of this study was to assess the pharmacokinetics and bioavailability of 3beta-hydroxy-17-(1H-1,2,3-triazol-1-yl)androsta-5,16-diene (VN/87-1) in normal male mice and in SCID mice bearing human LNCaP tumor xenografts. VN/87-1 is a novel potent steroidal inhibitor of human testicular 17-alpha-hydroxylase/C(17,20)-lyase. The steroid also shows anti-androgenic activity and inhibits the growth of human prostate cancer cell lines (LNCaP) in vitro and in vivo. Male Balb/c mice were given a single oral, subcutaneous (s.c.) or intravenous (i.v.) bolus dose of VN/87-1 (25, 50 or 100 mg/kg). Male SCID mice bearing LNCaP tumor xenografts were injected with a single s.c. dose of VN/87-1 (50 mg/kg). The animals were sacrificed at various times up to 24 h after drug administration and blood was collected. The plasma samples were prepared and analyzed by a reversed phase HPLC system equipped with a diode array detector. A non-compartmental pharmacokinetic approach was used to evaluate the plasma level versus time data. Following i.v. administration of VN/87-1, the plasma levels declined exponentially with an elimination half-life of 1.2+/-0.03 h. The absolute bioavailability of the 50 mg/kg dose after oral or s.c. administration was 12.08+/-2 or 57.2+/-4.5%, respectively. VN/87-1 is a high clearance (5.0+/-1.3 l/h per kg) compound in mice and its volume of distribution was relatively large (6.5+/-1.2 l/kg). The pharmacokinetic parameters of VN/87-1 were not significantly altered in SCID mice bearing human LNCaP tumor xenografts. VN/87-1 is well absorbed from the subcutaneous site compared with absorption from the gastrointestinal tract and shows linear kinetics at doses up to 100 mg/kg.

A simplified procedure for purification of cytochrome P-450 by preparative ampholine gel for isoelectric focusing

The purification process for cytochrome P450 is very complicated, involving five or more column chromatography steps for the final preparation. This paper describes a reduction in the number of the steps; it can be easily purified from pig testis microsomes with improved the yield. As the first step, DEAE-Toyopearl column chromatography is performed only once and then, as the second step, the partially purified cytochrome P450 is completely purified by a preparative Ampholine PAG-plate Gel for Isoelectric Focusing. The combination reduced the purification to a two-step procedure.

Effects of novel 17-azolyl compounds on androgen synthesis in vitro and in vivo

17-Azolyl steroids were synthesized and evaluated as inhibitors of androgen synthesis in vitro and in vivo. Several of the novel compounds exhibit potent noncompetitive inhibition of human 17alpha-hydroxylase/C17,20-lyase with IC50 values ranging from 7 to 90 nM, and Ki values from 1.2 to 41 nM. VN/85-1 and VN/108-1 were the most potent inhibitors against this enzyme with IC50 value of 8 nM (Ki of 1.2 nM) and 7 nM (Ki of 1.9 nM), respectively. VN/107-1, VN/108-1 and VN/109-1 also showed moderate inhibition of 5alpha-reductase in human prostatic microsomes. Normal adult male rats were treated with these novel 17-azolyl steroidal compounds at a dose level of 50 mg/kg, s.c., for 14 consecutive days, sacrificed 1-2 h after the last administered dose and blood, prostate and other tissues were collected. The organs were weighed and tissue concentrations of testosterone (T) and dihydrotestosterone (DHT) were measured. Tissue T levels were significantly (p<0.05) lower in rats treated with the novel 17-azolyl steroids by more than 50% compared to the control group. Similarly, the concentration of DHT in the serum and prostates was significantly (p<0.05) diminished in rats treated with the 17-azolyl steroids by 39-80% compared to the control group. Furthermore, the wet weights of the prostates and seminal vesicles were significantly (p<0.05) reduced by several of the novel steroids. Although only one dose was evaluated in these studies, VN/85-1 was the most effective compound and reduced prostatic androgen levels by more than 80% and the wet weights of the prostate and seminal vesicles in rats by about 50%. These findings suggest that these novel compounds may provide useful leads for the research and development of suitable agents for the treatment of androgen dependent prostate cancer.

Effects of new 17alpha-hydroxylase/C(17,20)-lyase inhibitors on LNCaP prostate cancer cell growth in vitro and in vivo

Our laboratory has been developing new inhibitors of a key regulatory enzyme of testicular and adrenal androgen synthesis 17alpha-hydroxylase/C(17,20)-lyase (P450c17), with the aim of improving prostate cancer treatment. We designed and evaluated two groups of azolyl steroids: delta5-non-competitive inhibitors (delta5NCIs), VN/63-1, VN/85-1, VN/87-1 and their corresponding delta4 derivatives (delta4NCIs), VN/107-1, VN/108-1 and VN/109-1. The human P450c17 gene was transfected into LNCaP human prostate cancer cells, and the resultant LNCaP-CYP17 cells were utilized to evaluate the inhibitory potency of the new azolyl steroids. VN/85-1 and VN/108-1 had the lowest IC50 values of 1.25 +/- 0.44 nM and 2.96 +/- 0.78 nM respectively, which are much lower than that of the known P450 inhibitor ketoconazole (80.7 +/- 1.8 nM). To determine whether the compounds had direct actions on proliferation of wild-type LNCaP cells, cell growth studies were performed. All of the delta5NCIs and VN/108-1 blocked the growth-stimulating effects of androgens. In steroid-free media, the delta5NCIs decreased the proliferation of LNCaP cells by 35-40%, while all of the delta4NCIs stimulated LNCaP cells growth 1.5- to 2-fold. In androgen receptor (AR) binding studies, carried out to determine the mechanism of this effect, all of the delta4NCIs (5 microM) displaced 77-82% of synthetic androgen R1881 (5 nM) from the LNCaP AR. The anti-androgen flutamide and the delta5NCIs displaced 53% and 32-51% of R1881 bound to AR respectively. These results suggested that the delta5NCIs may also be acting as anti-androgens. We further evaluated our inhibitors in male severe combined immunodeficient mice bearing LNCaP tumour xenografts. In this model VN/85-1 was as effective as finasteride at inhibiting tumor growth (26% and 28% inhibition, respectively) and the inhibitory effect of VN/87-1 was similar to that of castration (33% and 36% inhibition respectively). These results suggest that VN/85-1 and VN/87-1 may be potential candidates for treatment of prostate cancer.

Purification of cytochrome P-450 from adult pig testis by hydroxylapatite and deoxycorticosterone affinity column chromatography

Adult testicular cytochrome P-450 was purified by a two-step procedure utilizing hydroxylapatite and deoxycorticosterone affinity column chromatography. Cytochrome P-450 was determined to have an isoelectric point of 6.5 on analytical isoelectric focusing. The purified cytochrome P-450 was found to be homogeneous and its molecular mass was estimated to be 52000 on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The carbon monoxide difference spectrum with a peak at 448 nm exhibited the absorption spectrum of a typical cytochrome P-450. A 1000-fold purification was achieved with a yield of 5%.

Cytochrome P450c17-expressing Escherichia coli as a first-step screening system for 17alpha-hydroxylase-C17,20-lyase inhibitors

We have designed and synthesized a number of cytochrome P450 17alpha-hydroxylase-C17,20-lyase (P450c17) inhibitors with the aim of inhibiting androgen synthesis. To select the most potent inhibitors, we initially used human testicular microsomes, which have a high level of expression of this enzyme. However, due to lack of availability of human tissue and variability among the samples, we utilized recombinant human enzyme expressed in Escherichia coli. We designed a simple and economical protocol based on the report that recombinant bovine P450c17 can be functionally active in live bacteria. In the assay we report here, we substituted high-performance liquid chromatography product isolation with a rapid biochemical acetic acid releasing assay and utilized intact P450c17-expressing E. coli for the source of the enzyme. Enzymatic parameters of the bacterial system (Km = 5.1 x 10(-7) M, Vmax = 15.0 pmol/min/mg) were similar to those of human testicular microsomes (Km = 4.8 x 10(-7) M, Vmax = 40.0 pmol/min/mg), and our compounds displayed a similar pattern of inhibition in both systems. This new system is a fast, reliable, and reproducible method for screening P450c17 inhibitors. Furthermore, it eliminates our dependence on human tissue and potential data fluctuations caused by variations in enzymatic activity between donors.

Early steps in androgen biosynthesis: from cholesterol to DHEA

Sex steroids, both androgens and oestrogens, are made from dehydroepiandrosterone (DHEA). The biosynthesis of DHEA from cholesterol entails four steps. First, cholesterol enters the mitochondria with the assistance of a recently described factor called the steroidogenic acute regulatory protein (StAR). Mutations in the StAR gene cause congenital lipoid adrenal hyperplasia. Next, cholesterol is converted to pregnenolone by the cholesterol side chain cleavage enzyme, P450scc. Mutations in the gene for P450scc and for its electron transfer partners, ferredoxin reductase and ferredoxin, have not been described and are probably incompatible with term gestation. Third, pregnenolone undergoes 17 alpha-hydroxylation by microsomal P450c17. Finally, 17-OH pregnenolone is converted to DHEA by the 17,20 lyase activity of P450c17. Isolated 17,20 lyase deficiency is rare, but the identification of its genetic basis and the study of P450c17 enzymology have recently clarified the mechanisms by which DHEA synthesis may be regulated in adrenarche, and have suggested that the lesion underlying polycystic ovary syndrome might involve a serine kinase.

20beta-hydroxy-C21-steroid 20beta-oxidase activity of cytochrome P450c21 purified from bovine adrenocortical microsomes

We showed previously that cytochrome P450c21 (CYP21A1) from bovine adrenocortical microsomes has a putative 20beta-oxidase activity for 20beta-hydroxyprogesterone leading to a conversion to progesterone [M. Tsubaki, K. Morimoto, S. Tomita, S. Miura, Y. Ichikawa, A. Miyatake, F. Masuya, H. Hori, Biochim. Biophys. Acta 1259 (1995) 89-98]. We have extended the investigation on the 20beta-oxidase activity of cytochrome P450c21. Combination of 17alpha, 20beta-dihydroxyprogesterone with purified cytochrome P450c21 in oxidized form caused an induction of a typical type I difference spectrum (a peak at 390 nm and a trough at 420 nm) with a spectral dissociation constant of 2.3 microM. EPR spectrum at low temperature (15 K) exhibited an appearance of a new low-spin signal at gz=2.42, gy=2.21, and gx=1.966 and an increase in intensity of the high-spin signal (g=8.06, 3.54) upon formation of the enzyme-steroid complex, as previously found for 17alpha-hydroxyprogesterone and 20beta-hydroxyprogesterone. The enzymatic activity for 17alpha, 20beta-dihydroxyprogesterone was confirmed in a reconstituted system consisting of cytochrome P450c21 and NADPH-cytochrome P450 reductase. 17alpha,20beta-Dihydroxyprogesterone was converted to 17alpha-hydroxyprogesterone via the 20beta-oxidase reaction. The high turnover numbers of the 20beta-oxidase activity for 20beta-hydroxy-c21-steroids suggests that this activity is likely to have some physiological roles. Cytochrome P450c21 and 20beta-hydroxysteroid dehydrogenase may regulate the androgen biosynthesis catalyzed by cytochrome P450c17alpha with controlling the concentration of 20beta-hydroxy-C21-steroids.

Synthesis of novel 21-trifluoropregnane steroids: inhibitors of 17 alpha-hydroxylase/17,20-lyase (17 alpha-lyase)

Novel 21-trifluoropregnenolone (6), 21-trifluoroprogesterone (7) and related compounds 4a and 8 have been synthesized in high yields from 3 beta-acetoxyandrost-5-ene-17 beta-carbaldehyde (3). The key reaction was the conversion of 3 into the 21-trifluoromethyl-20-alcohol as a diastereomeric mixture (4) by trifluoromethyltrimethylsilane (TMS-CF3) in the presence of tetrabutylammonium fluoride (TBAF). All compounds, including 6 and 7, were unambiguously characterized by IR, 1H and 19F NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. On this basis, we concluded that the only report of an earlier synthesis of 6 and 7 is erroneous. Enzyme inhibition studies showed that 20 xi-hydroxy-21-trifluoropregn-4-en-3-one (8) is a potent inhibitor (IC50 value = 0.6 microM) of rat 17 alpha-hydroxylase/17,20-lyase.

Protein phosphorylation changes ligand-binding efficiency of cytochrome P450c17 (CYP17) and accelerates its proteolytic degradation: putative relevance for hormonal regulation of CYP17 activity

Two novel mechanisms of protein kinase function in the complex gonadotropic regulation of the bifunctional cytochrome P450c17 (CYP17), the rate-limiting enzyme of androgen synthesis within the smooth endoplasmic reticulum of gonadal endocrine cells, are reported. In microsomal membranes from rat testes, the maximal type I optical difference spectrum induced by the physiological CYP17 substrate, progesterone, as a measure of spin state transition due to hydrophobic ligand-protein interaction is enhanced by 24% within 15 minutes in the presence of MgATP; the dissociation constant decreases from 71 to 43 nM. Testicular cytosol does not modify this effect which is completely abolished by the protein kinase inhibitor, bisindolylmaleimide, and which does not occur with ketoconazole as ligand. Furthermore, CYP17 degradation by cytosolic protease(s) is 2.5-fold accelerated by ATP; this action is completely reversed by the protein kinase inhibitors bisindolylmaleimide (half-maximal protective concentration 2.04 microM) and KT5720 (99 nM). The former compound also prevents human choriogonadotropin-induced testicular CYP17 inactivation in situ. It is concluded that protein kinase A-catalyzed target phosphorylation integrates the known biphasic steroidogenic response upon hormonal stimulation by initial improvement of substrate accommodation followed by counter-regulatory promotion of CYP17 proteolysis.

Regulation of androgen synthesis: the late steroidogenic pathway

Studies of the regulation of androgen synthesis in steroidogenic cells have focused on both transcriptional and post-translational regulation of the proteins that catalyze these reactions: the P450c17 that catalyzes the production of DHEA or androstenedione in consecutive hydroxylase and lyase activities, and the 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) that catalyzes the conversion of androstenedione to testosterone. Our studies of the regulation of the CYP17 lyase activity at the molecular level have utilized species- and tissue-specific differences to identify target regulatory sequences. Adenovirus infection of rat CYP17 promoter/luciferase reporter gene constructs in primary cultures of rat adrenal and rat Leydig cells revealed a rat-specific domain between-1 and -108 bp that cause inhibition of both basal and cAMP-induced CYP17 transcription in the adrenal, but not the Leydig cell. In contrast, similar promoter constructs from other species exhibited substantial cAMP-induced transcriptional activity in the rat adrenal. Mutagenesis of the conserved region of the rat and human proteins reveals significant differences in the amino acid domains required for hydroxylase and lyase activities within and between the two species, consistent with their differential regulation of lyase activity. The 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) reaction requires a viable glucose transporter system for optimal activity, and a high-energy phosphate was discovered to be the requisite product of glucose metabolism in 17 beta-HSD activation. These studies have provided insight into potential mechanisms of control of androgen synthesis in the late steroidogenic pathway, at the transcriptional and post-translational levels.

Inhibition of bovine cytochrome P-450(11 beta) by 18-unsaturated progesterone derivatives

The last step of aldosterone biosynthesis, an 11 beta-hydroxylation followed by two 18-hydroxylations, are catalyzed, in the bovine system, by the same enzyme, the cytochrome P-450(11 beta) (deoxycorticosterone (DOC)-->corticosterone-->18-hydroxycorticosterone-->aldosterone). The 11 beta- and 18-hydroxylase activities were studied separately with a reconstituted enzymic system, using 11-deoxy[14C]corticosterone and [3H]corticosterone, respectively, as substrates. The inhibition of 11 beta-hydroxylase activity by corticosterone was competitive (Ki = 60 microM) showing that transformation of both substrates occurs at the same site. Double-label/double-substrate experiments, using an equimolar mixture of 11-deoxy[14C]corticosterone and [3H]corticosterone, suggested that 18-hydroxycorticosterone is directly formed from 11-deoxycorticosterone without the intermediate corticosterone leaving the enzyme. Inhibitions by 18-vinylprogesterone and 18-ethynylprogesterone, potent inhibitors of aldosterone biosynthesis [Viger, A., Coustal, S., Pérard, S., Piffeteau, A. & Marquet, A. (1989) J. Steroid Biochem. 33, 119-124], were characterized for both activities (11 beta- and 18-hydroxylase). The value of reversible Ki for the 18-hydroxylation (Ki = 5 microM for 18-vinylprogesterone and 30 microM for 18-ethynylprogesterone) is lower than that for the 11 beta-hydroxylation (30 microM and 100-150 microM, respectively); the former inhibitor is stronger than the latter for both steps. The binding of substrates and inhibitors to the active site was also examined by difference absorption spectroscopy. 18-Vinylprogesterone gave rise to a type I spectrum with a Ks value of 35 microM close to that of progesterone, while 18-ethynylprogesterone showed a reverse type I spectrum with a much higher Ks value (140 microM). Based on these results, a hypothetical model, involving a conformational change of the enzyme for the second step, is proposed.

Inhibition of androgen synthesis by 22-hydroximino-23,24-bisnor-4-cholen-3-one

The 22-hydroximino-23,24-bisnor-4-cholen-3-one (22-oxime) was synthesized and evaluated as an inhibitor of 17 alpha-hydroxylase/C17,20-lyase in rat testicular microsomes and the 5 alpha-reducatase of human prostatic microsomes from patients with benign prostatic hypertrophy. The 22-oxime demonstrated moderate inhibition for the 17 alpha-hydroxylase (Ki 74 nM vs. Km 29 nM) with progesterone as substrate and potent inhibition (Ki 18 nM vs. Km 76 nM) for the C17,20-lyase activity with 17 alpha-hydroxyprogesterone as substrate. Further investigation of this enzyme with progesterone as substrate demonstrated the inhibition occurred mainly at the 17 alpha-hydroxylation step of the progesterone substrate. The 22-oxime also demonstrated potent and competitive inhibition of 5 alpha-reductase in human prostatic microsomes (Ki 1.4 nM vs. Km 14 nM). When adult male rats were injected subcutaneously (sc) daily with 22-oxime (50 mg/kg/day) for 21 days, the concentrations of serum and testicular testosterone were significantly reduced by 65% and 59%, respectively, in comparison to vehicle-treated controls. Furthermore, both testosterone and DHT concentrations in rat prostatic tissue were significantly decreased by 60% and 44% compared to control tissue. Serum LH concentrations were unchanged in the 22-oxime-treated group compared to the control group. This indicates that the reduction in androgen concentrations in animals treated with this compound is not due to its influence on pituitary feedback mechanisms which result in reduced LH secretion. These results suggest that 22-oxime is effective in reducing androgen synthesis through the inhibition of 17 alpha-hydroxylase, C17,20-lyase, and 5 alpha-reductase both in vitro and in vivo.

The rat 17 alpha-hydroxylase-17,20-desmolase (CYP17) active site: computerized homology modeling and site directed mutagenesis

A homology model of the rat 17 alpha-hydroxylase-17,20 desmolase (CYP17) steroid binding domain was derived from the alpha/beta F supersecondary structural element of the 3 alpha/20 beta hydroxysteroid dehydrogenase (HSD) of Streptomyces hydrogenans that constitutes a major segment of the C19 steroid binding cavity. A CYP17 arginine-rich domain, including Arg346, Arg361 and Arg363, that has previously been shown to be important to CYP17 catalytic activity, is conserved in this HSD structural element between two HSD domains known to be important to C19 steroid binding. These two HSD motifs, in addition to a C-terminal domain at the apex of the steroid binding cavity, are also present in similar though not identical forms in the rat CYP17 sequence. The model was evaluated in terms of both hydroxylase/lyase activity and stability of CYP17 mutant proteins (Tyr334Phe, Phe343Ile, Arg357Ala, Arg361Ala, Asp345Ala), and further tested with mutagenesis of Glu353, Glu358, and Tyr431. Those amino acids located at folding junctions in the model steroid binding domain (Glu358, Arg361, and Tyr431) are each individually required to prevent degradation of the nascent protein, as well as for basic hydroxylase/lyase activity. Genomic analysis of the rat CYP17 gene reveals that this domain is contained in exon 6, and a correlation exists between the length of exon 6 and the boundaries of the HSD supersecondary element. These studies demonstrate that exon 6 of the rat CYP17 is essential for CYP17 activity, and may be structurally related to the NAD-linked prokaryote alpha/beta F supersecondary element.

Transcriptional regulation of rat cytochrome P450c17 expression in mouse Leydig MA-10 and adrenal Y-1 cells: identification of a single protein that mediates both basal and cAMP-induced activities

Cytochrome P450c17, 17 alpha-hydroxylase/17,20 lyase, is a key enzyme in the steroidogenic pathway leading to the production of corticosteroids and androgens from the adrenal gland and sex steroids from the gonads. Both enzymatic activities of the protein are encoded by a single gene, CYP17, which is expressed in both the human adrenal and gonad but not in the placenta, and in the rodent gonad and placenta but not the rodent adrenal. We isolated and sequenced a full-length rat genomic clone (7,553 bases) containing the entire coding region of the rat P450c17 gene, and all intronic sequences and 1,560 bp of 5'-flanking DNA (EMBL Acc#X69816). To determine which sequences in the rat P450c17 promoter may be responsible for basal and cAMP-stimulated gene transcription, deletion constructs containing between -1,560 and -53 base pairs of 5'-flanking DNA from the rat P450c17 gene were ligated to plasmids expressing the reporter gene luciferase and transfected into two mouse cell lines, adrenal Y-1 cells, and testicular Leydig MA-10 cells. Highest basal and cAMP-stimulated luciferase activity were found in constructions containing 156 bp of 5'-flanking DNA. This construction contains a sequence very similar to the consensus cis element reported to be responsible for cAMP enhancement of the rat somatostatin gene and also overlaps a sequence similar to the consensus element for the orphan steroid receptor SF-1. Gel mobility-shift analysis, using a 30-bp oligonucleotide containing this region incubated with cellular extracts from cultured mouse adrenal Y-1 and mouse Leydig MA-10 cells, revealed all the extracts to contain two proteins that bind to this sequence. Neither DNA-protein complex was further retarded by co-incubation with an anti-CREB antibody, suggesting that cAMP regulation of this gene occurs via a non-CREB protein. Mutation of this oligonucleotide resulted in loss of binding of only one of these proteins, but resulted in loss of both basal and cAMP stimulation of rat P450c17 promoter-regulated gene transcription. Southwestern analysis suggests that one of these proteins is larger than SF-1. This study suggests that a protein that binds to an SF-1 like sequence regulates both basal and cAMP-stimulated rat P450c17 gene expression in rodent cells.

Effect of FK506 on rat Leydig cell function--in vivo and in vitro study

FK506, a macrolide antibiotic, is a potent immunosuppressant and has a biological effect similar to that of cyclosporin A (CsA). In this study, the in vivo and in vitro effects of FK506 on rat Leydig cell function were investigated. In vivo, basal testosterone levels and secretion in response to human chorionic gonadotropin (hCG) stimulation in ACl rats treated with intramuscular (IM) injections of FK506 at a dosage of 1 or 2 mg/kg/d for 14 days were not different from those of age-matched normal controls. Testicular weights (g) from rats treated with 14 injections of 1 mg/kg/d FK506 (1.08 +/- 0.08, n = 14) were similar to weights from age-matched controls (1.04 +/- 0.08, n = 14). Similarly, Wistar (Wi) rats treated with FK506 at a dosage of 1 mg/kg/d for 2 weeks showed basal testosterone and luteinizing hormone (LH) levels and secretion in response to hCG stimulation similar to those of normal controls. Histologically, the Leydig cells and germ cells in FK506-treated animals appeared normal. In vitro, basal testosterone production and response to hCG stimulation by both ACI and Wi rat Leydig cells exposed to overnight treatment of FK506 (10 to 1,000 ng/mL) were not significantly different from those of control Leydig cells. Furthermore, the viability of the Leydig cells cultured for 3 days in FK506 was not significantly different from that of controls, and they continued to secrete testosterone at a rate similar to that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of the acyl-carbon cleavage and related reactions catalyzed by multifunctional P-450s: studies on cytochrome P-450(17)alpha

It is now well-known that conventional cytochrome P-450s catalyze hydroxylation reactions using an iron mono-oxygen species, the structure of which, as inferred from chemical model studies, may be drrepresented by the following canonical forms: FeV==O<-->(.+)FeIV==O<-->FeIV--O(.). Certain multifunctional P-450s, notably those involved in steroid biosynthesis, catalyze, in addition to hydroxylation reactions, an acyl-carbon cleavage process in which the participation of an iron peroxide intermediate, FeIII--OOH, has been suggested. However the possibility still exists that the C--C bond cleavage may also occur using the FeV==O species. We have scrutinized the chemical consequences of involving either an FeV==O or an FeIII--OOH species for five different C--C bond cleavage reactions. With respect to the status as well as the origin of hydrogen and oxygen atoms, in four of the examples the mechanism involving the FeV==O species makes the same prediction as that using the iron peroxide intermediate, that is, the incorporation of an atom of oxygen from O2 into acyl part of the cleaved fragment. The fifth example, however, involving the formation, with pig testes microsomes, of 17 alpha-hydroxyandrogen (androst-5-ene-3 beta,17 alpha-diol) from pregnenolone, presents an interesting contrast--in this case different outcomes are predicted by the two mechanisms. These possibilities have been experimentally evaluated using substrates stereo- and regiospecifically labeled with heavy isotopes and incubated with pig testes microsomes under either 16O2 or 18O2.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid monooxygenation by P450BM-3: product identification and proposed mechanisms for the sequential hydroxylation reactions

The soluble P450 isolated from Bacillus megaterium (the product of the CYP 102 gene) (P450BM-3) is a catalytically self-sufficient fatty acid hydroxylase which converts lauric, myristic, and palmitic acids to omega-1, omega-2, and omega-3 hydroxy analogs. The percentage distribution of the regioisomers depends on the substrate chain length. Lauric and myristic acids were preferentially metabolized to their omega-1 hydroxy counterparts while no hydroxylation occurred when capric acid was used as the substrate. Palmitic acid, when present at concentrations greater than the concentration of oxygen in the reaction medium (greater than 250 microM), was hydroxylated to its omega-1, omega-2, and omega-3 hydroxy analogs, with the percentage distribution of the regioisomers being 21:44:35, respectively. No omega hydroxylation of any of the fatty acids was detected. When the concentration of palmitic acid was less than the concentration of oxygen in the reaction mixture, it was noted that a number of additional products were formed. Under these conditions, unlike lauric and myristic acids, it was observed that palmitic acid was first converted to its monohydroxy isomers which were subsequently metabolized to a mixture of 14-ketohexadecanoic, 15-ketohexadecanoic, 13-hydroxy-14-ketohexadecanoic, 14-hydroxy-15-ketohexadecanoic, and 13,14-dihydroxyhexadecanoic acids with a relative distribution of 8:2:40:30:20, respectively. Thus, P450BM-3 is able not only to monohydroxylate a variety of fatty acids but also to further metabolize some of these primary metabolites to secondary and tertiary products. The present paper characterizes the products formed during the sequential hydroxylation of palmitic acid and proposes reaction pathways to explain these results.

Thermodynamics and modulation of progesterone microcompartmentation and hydrophobic interaction with cytochrome P450XVII based on quantification of local ligand concentrations in a complex multi-component system

An approach towards the determination of hydrophobic ligand distribution in endoplasmic reticulum membrane suspensions, and of hydrophobic ligand interaction with membrane-anchored proteins, based on calculations of local ligand pools, is presented. Rat testicular microsomes containing cytochrome P450XVII (P450XVII) were used as the model system and considered as consisting of three compartments, i.e. membrane lipid phase, aqueous phase and the ligand-binding protein, P450XVII. Combinations of spectrophotometry, ultracentrifugation and equilibrium dialysis were used to quantify progesterone concentrations in each of the three compartments, as well as partition coefficients, Kp. Since the substrate-access channel of P450XVII is likely to face the membrane-lipid phase, corrected spectral dissociation constants, Ks(corr), were calculated on the basis of free, i.e. not enzyme-bound, progesterone concentrations in the membrane compartment. Modulation of individual components and construction of more complex systems demonstrated the validity of this concept for analysis of multicompartment systems. Although ligand distribution was considerably affected by both ligand and membrane concentrations, Kp and Ks(corr) values were found to be independent of both parameters; Kp values amounted to 1920 and 3120, and Ks(corr) values amounted to 260 microM and 96 microM at 4 degrees C and 25 degrees C, respectively. Thermodynamic parameters delta H, delta S and delta G were calculated from Van't Hoff plots for progesterone partition into the membrane compartment, and for progesterone binding to P450XVII. Both of these processes were entropy dominated, and free energy changes amounted to about -18 kJ/mol for Kp and -20 kJ/mol for Ks(corr). Modification of P450XVII by gonadotropin-induced down-regulation, and by addition of a competitive inhibitor (estradiol) had no effect on progesterone partition. Consideration of Kp = 310 for estradiol allowed the determination of a corrected K1 = 3.09 mM. Modification of the membrane-lipid phase by detergents affected progesterone-P450XVII interaction solely by modulation of Kp; modification of the aqueous phase by addition of bovine serum albumin as a fourth compartment acted solely via additional steroid attraction. This model system therefore stresses the relevance of the local environment of membrane-bound enzymes or receptors for quantification of their interaction with substrates or ligands.

Purification and properties of steroid 17 alpha-hydroxylase from calf testis

Steroid 17 alpha-hydroxylase has emerged as a key enzyme in steroidogenic cells: (i) it represents the branch point between the 17-deoxy (mineralo) and the 17-hydroxy (gluco) corticosteroid pathways in the adrenal cortex; (ii) the corresponding specific cytochrome (P-450(17 alpha] is highly dependent upon hormonal regulation; and (iii) the enzyme also catalyzes the steroid 17-20 lyase reaction, leading to the major androgens in the testis. As a prerequisite to the study of its regulation in intact cell, 17 alpha-hydroxylase was purified from calf testis microsomal preparations. Following five chromatographic steps, the enzyme was obtained as an apparently homogeneous protein of Mr = 57 kDa upon gel electrophoresis. The procedure yielded a recovery of about 10% as judged by cytochrome P-450 assay. Whereas 17 alpha-hydroxylase specific activity was about 30-fold enriched during the purification, that of the C17-20 lyase was increased by about 6-fold, strongly suggesting that its organelle environment may modulate the enzymatic activity. The purified enzyme yielded a 20 N-terminal amino-acid sequence showing a complete homology with that of its adrenal counterpart and a polyclonal antibody raised against our preparation revealed a 57 kDa protein band in bovine adrenocortical microsomal extracts, upon immunoblotting experiments. It was thus concluded that bovine 17 alpha-hydroxylase activity is supported by highly similar if not identical enzymatic proteins in both testis and adrenal cortex tissues. The purified P-450(17 alpha) preparation is now being used in reconstitution experiments which suggest that microsomal components may contribute to a different expression of the enzyme specificity in its native testis or adrenocortical intracellular environment, respectively.