Structure/function of the inhibition of human 3beta-hydroxysteroid dehydrogenase type 1 and type 2 by trilostane

Chalcone derivatives from licorice inhibit human and rat gonadal 3β-hydroxysteroid dehydrogenases as therapeutic uses

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, licorice (the roots of Glycyrrhiza glabra and G. inflata) has been used to treat inflammation and sexual debility for over 1000 years. Pharmacological studies have identified many biologically active chalcone derivatives from licorice.

AIM OF THE STUDY

Human 3β-Hydroxysteroid dehydrogenase 2 (h3β-HSD2) catalyzes the formation of precursors for sex hormones and corticosteroids, which play critical roles in reproduction and metabolism. We explored inhibition and mode action of chalcones of inhibiting h3β-HSD2 and compared it with rat 3β-HSD1.

MATERIALS AND METHODS

We investigated the inhibition of 5 chalcones on h3β-HSD2 and compared species-dependent difference with 3β-HSD1.

RESULTS

The inhibitory strength on h3β-HSD2 was isoliquiritigenin (IC50, 0.391 μM) > licochalcone A (0.494 μM) > licochalcone B (1.485 μM) > echinatin (1.746 μM) >chalcone (100.3 μM). The inhibitory strength on r3β-HSD1 was isoliquiritigenin (IC50, 0.829 μM) > licochalcone A (1.165 μM) > licochalcone B (1.866 μM) > echinatin (2.593 μM) > chalcone (101.2 μM). Docking showed that all chemicals bind steroid and/or NAD+-binding site with the mixed mode. Structure-activity relationship analysis showed that strength was correlated with chemical's hydrogen bond acceptor.

CONCLUSION

Some chalcones are potent h3β-HSD2 and r3β-HSD1 inhibitors, possibly being potential drugs to treat Cushing's syndrome or polycystic ovarian syndrome.

Carbon chain length of perfluoroalkylated carboxylic acids determines inhibitory strength on gonadal 3β-hydroxysteroid dehydrogenases in humans, rats, and mice

Perfluoroalkylated carboxylic acids (PFCAs) are a subclass of man-made chemicals that have been widely used in industrial production and consumer products. As a result, PFCAs have been found to accumulate in the environment and bioaccumulate in organisms, leading to potential health and environmental impacts. This study investigated the inhibition of 11 PFCAs on gonadal 3β-hydroxysteroid dehydrogenases in humans, rats, and mice. We observed a V-shaped inhibition pattern against human granulosa (KGN) cell 3β-HSD2 starting from C9 (half-maximal inhibitory concentration, IC50, 100.8 μM) to C11 (8.92 μM), with a V-shaped turn. The same V-shaped inhibition pattern was also observed for PFCAs against rat testicular 3β-HSD1 from C9 (IC50, 50.43 μM) to C11 (6.60 μM). Mouse gonadal 3β-HSD6 was insensitive to the inhibition of PFCAs, with an IC50 of 50.43 μM for C11. All of these PFCAs were mixed inhibitors of gonadal 3β-HSDs. Docking analysis showed that PFCAs bind to the nicotinamide adenine dinucleotide (NAD+)/steroid binding sites of these enzymes and bivariate correlation analysis showed that molecular length determines the inhibitory pattern of PFCAs on these enzymes. In conclusion, the carbon chain length determines the inhibitory strength of PFCAs on human, rat, and mouse gonadal 3β-HSDs, and the inhibitory strength of PFCAs against human and rat 3β-HSD enzymes shows V-shaped turn.

Benzophenone-type ultraviolet filters inhibit human and rat placental 3β-hydroxysteroid dehydrogenases: structure-activity relationship and in silico docking analysis

Benzophenones (BPs) are a class of chemicals found in various personal care and cosmetic products, such as sunscreens and lotions. Their usage is known to cause reproductive and hormonal health risks, but the exact mechanism of action remains unknown. In this study, we investigated the effect of BPs on human and rat placental 3β-hydroxysteroid dehydrogenases (3β-HSDs), which play a crucial role in the biosynthesis of steroid hormones, particularly progesterone. We tested inhibitory effects of 12 BPs, and performed structure-activity relationship (SAR) and in silico docking analysis. The potency of BPs to inhibit human 3β-HSD1 (h3β-HSD1) is BP-1 (IC₅₀, 8.37 μM)>BP-2 (9.06 μM)>BP-12 (94.24 μM)>BP-7 (1160 μM) >BP-6 (1257 μM) >BP-6 (1410 μM) > other BPs (ineffective at 100 μM). The potency of BPs on rat r3β-HSD4 is BP-1 (IC₅₀, 4.31 μM)>BP-2 (117.3 μM)>BP-6 (669 μM) >BP-3 (820 μM)>other BPs (ineffective at 100 μM). BP-1, BP-2, and BP-12 are mixed h3β-HSD1 inhibitors and BP-1 is a mixed r3β-HSD4 inhibitor. LogP, lowest binding energy, and molecular weight were positively associated with IC₅₀ for h3β-HSD1, while LogS was negatively associated with IC₅₀. The 4-OH substitution in the benzene ring play a key role in enhancing the effectiveness of inhibiting h3β-HSD1 and r3β-HSD4, possibly through increasing water solubility and decreasing lipophilicity by forming hydrogen bonds. BP-1 and BP-2 inhibited progesterone production in human JAr cells. Docking analysis shows that 2-OH of BP-1 forms hydrogen bond with catalytic residue Ser125 of h3β-HSD1 and Thr125 of r3β-HSD4. In conclusion, this study demonstrates that BP-1 and BP-2 are moderate inhibitors of h3β-HSD1 and BP-1 is moderate inhibitor of r3β-HSD4. There is a significant SAR difference for 3β-HSD homologues between BPs and distinct species-dependent inhibition of placental 3β-HSDs.

Inhibition of Resveratrol Analogs on Human and Rat 3β-Hydroxysteroid Dehydrogenases: Structure-Activity Relationship and Docking Analysis

Resveratrol and its analogs are phytochemicals. Human 3β-hydroxysteroid dehydrogenase 1 (3β-HSD1) synthesizes steroid hormones for normal pregnancy or promoting cancer metastasis. Whether they inhibit 3β-HSD1 remains unclear. In this study, the inhibitory potency, mode of action, structure-activity relationship, and docking parameters of resveratrol and its analogs on 3β-HSD1 and rat homolog 3β-HSD4 were analyzed. The inhibitory potency of these chemicals on human 3β-HSD1 was 4,4'-dihydroxystilbene (IC₅₀, 3.68 μM) > pinostilbene (8.07 μM) > pinosylvin (10.60 μM) > lunularin (26.84 μM) > resveratrol (30.20 μM) > dihydroresveratrol (>100 μM) = oxyresveratrol (>100 μM) > dihydropinosylvin (ineffective at 100 μM). Resveratrol analogs and metabolites are mixed or competitive inhibitors of human 3β-HSD1. Resveratrol and 4,4'-dihydroxystilbene inhibited progesterone secretion by human JAr cells at ≥1 μM. Resveratrol (IC₅₀, 32.09 μM) and pinosylvin (34.71 μM) significantly inhibited rat placental 3β-HSD4 activity. Docking analysis shows that resveratrol analogs and metabolites bind the steroid-binding sites of human 3β-HSD1 and rat 3β-HSD4 and interact with the catalytic residues Ser125/Thr125 and Tyr155. The negative correlation of LogP and IC₅₀ values for human 3β-HSD1 indicates that lipophilicity of chemicals plays a critical role in the inhibitory effect of chemicals. In conclusion, 4,4'-dihydroxystilbene, pinostilbene, and pinosylvin effectively inhibit human 3β-HSD1 depending on their lipophilicity, thereby acting as potential therapeutic agents.

Curcuminoids inhibit human and rat placental 3β-hydroxysteroid dehydrogenases: Structure-activity relationship and in silico docking analysis

ETHNOPHARMACOLOGICAL RELEVANCE

In traditional Chinese medicine, curcuma longa L has been applied to treat pain and tumour-related symptoms for over thousands of years. Curcuminoids, polyphenolic compounds, are the main pharmacological component from the rhizome of Curcuma longa L. Pharmacological investigations have found that curcuminoids have many pharmacological activities of anti-inflammatory, anti-tumour, and anti-metastasis.

AIM OF THE STUDY

3β-Hydroxysteroid dehydrogenase (3β-HSD1) catalyses the production of steroid precursors for androgens and estrogens, which play an essential role in cancer metastasis. We explored the potency and mode of action of curcuminoids and their metabolites of inhibiting 3β-HSD1 activity and compared the species difference between human and rat.

MATERIALS AND METHODS

In this study, we investigated the direct inhibition of 6 curcuminoids on human placental 3β-HSD1 activity and compared the species-dependent difference in human 3β-HSD1 and rat placental homolog 3β-HSD4.

RESULTS

The inhibitory potency of curcuminoids on human 3β-HSD1 was demethoxycurcumin (IC₅₀, 0.18 μM) > bisdemethoxycurcumin (0.21 μM)>curcumin (2.41 μM)> dihydrocurcumin (4.13 μM)>tetrahydrocurcumin (15.78 μM)>octahydrocurcumin (ineffective at 100 μM). The inhibitory potency of curcuminoids on rat 3β-HSD4 was bisdemethoxycurcumin (3.34 μM)>dihydrocurcumin (5.12 μM)>tetrahydrocurcumin (41.82 μM)>demethoxycurcumin (88.10 μM)>curcumin (137.06 μM)> octahydrocurcumin (ineffective at 100 μM). Human choriocarcinoma JAr cells with curcuminoid treatment showed that these chemicals had similar potency to inhibit progesterone secretion under basal and 8bromo-cAMP stimulated conditions. Docking analysis showed that all chemicals bind pregnenolone-binding site with mixed/competitive mode for 3β-HSD.

CONCLUSION

Some curcuminoids are potent human placental 3β-HSD1 inhibitors, possibly being potential drugs to treat prostate cancer and breast cancer.

The analysis of pesticides and fungicides in the inhibition of human and rat placental 3β-hydroxysteroid dehydrogenase activity: mode of inhibition and mechanism

3β-Hydroxysteroid dehydrogenase/steroid Δ^5,4-isomerase 1 (3β-HSD1) plays a critical role in the biosynthesis of progesterone from pregnenolone in the human placenta to maintain normal pregnancy. Whether they inhibit placental 3β-HSD1 and mode of inhibition remains unclear. In this study, we screened 21 pesticides and fungicides in five classes to inhibit human 3β-HSD1 and compared them to rat homolog 3β-HSD4. 3β-HSD activity was measured by catalyzing pregnenolone to progesterone in the presence of NAD⁺. Of the 21 chemicals, azoles (difenoconazole), thiocarbamates (thiram and ferbam) and organochlorine (hexachlorophene) significantly inhibited human 3β-HSD1 with half maximal inhibitory concentration (IC₅₀) values of 2.77, 0.24, 0.68, and 17.96 μM, respectively. We also found that difenoconazole, ferbam and hexachlorophene are mixed/competitive inhibitors of 3β-HSD1 while thiram is a mixed/noncompetitive inhibitor. Docking analysis showed that difenoconazole and hexachlorophene bound steroid-binding site. Difenoconazole and hexachlorophene except thiram and ferbam also significantly inhibited rat 3β-HSD4 activity with IC₅₀ of 1.12 and 2.28µM, respectively. Thiram and ferbam significantly inhibited human 3β-HSD1 possibly by interfering with cysteine residues, while they had no effects on rat 3β-HSD4. In conclusion, some pesticides potently inhibit placental 3β-HSD, leading to the reduction of progesterone formation.

Effects of phenolic compounds on 3β-hydroxysteroid dehydrogenase activity in human and rat placenta: Screening, mode of action, and docking analysis

Human 3β-hydroxysteroid dehydrogenase type I (HSD3B1) and rat type IV (HSD3B4) in placentas catalyze the conversion of pregnenolone to progesterone, which plays a key role in maintaining pregnancy. Many phenolic compounds potentially inhibit HSD3B in placentas as endocrine disruptors. In this study, the effects of 16 phenolic compounds on the activity of human HSD3B1 and rat HSD3B4 were determined and the structure-activity relationship was compared. HSD3B1 in human placental microsomes and HSD3B4 in rat placental microsomes were used to measure their activities and pregnenolone and NAD⁺ were used as substrates. Of the 16 phenolic compounds, 4-nonylphenol, pentabromophenol, and 2-bromophenol resulted in residual human HSD3B1 activity lower than 50 % and 4-nonylphenol and pentabromophenol resulted in residual rat HSD3B4 activity lower than 50 %. 4-Nonylphenol, pentabromophenol, and 2-bromophenol were mixed inhibitors of human HSD3B1, with Ki values of 2.31, 3.58 and 4.86 µM, respectively, while 4-nonylphenol and pentabromophenol were noncompetitive inhibitors of rat HSD3B4 with Ki values of 20.86 and 141.8 µM. Molecular docking showed that 4-nonylphenol, pentabromophenol, and 2-bromophenol docked to the active sites of human HSD3B1 and rat HSD3B4, and the shift of residue S125 in human HSD3B1 to T125 in rat HSD3B4 could explain the species-dependent difference in their inhibitory potency and mode of action. This study demonstrates that 4-nonylphenol, pentabromophenol, and 2-bromophenol are mixed inhibitors of human placental HSD3B1, while 4-nonylphenol and pentabromophenol are noncompetitive inhibitors of rat HSD3B4, possibly blocking the placental steroidogenesis.

The Efficacy of a 3β-Hydroxysteroid Dehydrogenase Inhibitor for the Termination of Mid-Term Pregnancies in Dogs

Simple Summary

The medical termination of unwanted pregnancies in dogs is practiced throughout the world for many reasons, including at the request of animal owners. For these procedures, it is advised to use rapidly effective drugs with minimal side effects. In this study, we investigated trilostane, which decreases progesterone levels, for its efficacy in terminating mid-term pregnancies in dogs, as well as potential side effects. Although trilostane is not a standalone alternative for the termination of pregnancy in dogs, it has been determined that its combined use with another medical agent of known efficacy reduces both the abortion time and potential side effects. Further studies investigating an increased frequency of administration rather than the administration dose could contribute to determining the efficacy of trilostane in dogs.

Abstract

Progesterone (P4) is the only hormone needed to maintain pregnancy in dogs. Therefore, a competitive inhibitor of 3β-hydroxysteroid dehydrogenase (3β-HSD) could be a safe and effective option to terminate pregnancy by inhibiting P4 synthesis. To address this hypothesis, we investigated the efficacy of trilostane (TRL), a competitive inhibitor of 3β-HSD, in terminating pregnancy in dogs. Twenty-one dogs between days 30 and 38 of pregnancy were randomly assigned to one of two treatment groups (trilostane (TRL) and aglepristone (AGL)) and an untreated control (CON) group (n = 7 dogs each). Fetal heart rates (FHRs) (measured at 12 h intervals) and serum P4 concentrations (measured at 6 h intervals) were evaluated. The pregnancy termination rates were 0% and 100% in the TRL and AGL groups, respectively. The decrease in the FHR in the TRL and AGL groups was significantly lower than that observed in the CON group. There was a marked decrease in P4 concentrations in the TRL group 6, 54, and 102 h after the initiation of treatment. The luteal expression of StAR appeared to be weaker in the AGL group than the CON group. In conclusion, although a treatment-induced decrease was observed in plasma P4 concentrations, a seven-day TRL treatment alone was not effective in terminating pregnancies. Further studies are needed on the effects of the prolonged administration of TRL with varying doses and frequencies for the termination of mid-term pregnancy in dogs.

Structure-activity relationship analysis of perfluoroalkyl carbonic acids on human and rat placental 3β-hydroxysteroid dehydrogenase activity

Placenta contains 3β-hydroxysteroid dehydrogenase/steroid Δ^5,4-isomerase (HSD3B), which catalyzes pregnenolone to progesterone for maintaining pregnancy. Perfluoroalkyl carbonic acids (PFC) are subclass of perfluoroalkyl substances containing 4-14 carbons (C4-C14) in the carbon backbone and are potential endocrine disruptors. Whether PFC inhibit HSD3B and structure-activity relationship (SAR) remains unclear. Herein, we screened 11 PFC for inhibiting human type I HSD3B (HSD3B1) and rat type IV HSD3B (HSD3B4) activities and determined SAR and mode of inhibition. HSD3B was measured by converting pregnenolone to progesterone assisted by NAD⁺ in placental microsomes. Of the 11 PFC, C9-C14 significantly inhibited human HSD3B1 activity at 100 μM. Half-maximal inhibitory concentration (IC₅₀) values of C9-C14 compounds were 363.56 ± 12.14, 12.78 ± 0.69, 6.54 ± 0.65, 20.88 ± 0.41, 118.35 ± 0.16, and 149.26 ± 21.67 μM, respectively. We determined Ki values and mode of inhibition of three most potent PFC (C10-C12), and found that they were mixed inhibitors against pregnenolone, with Ki values of 5.57 ± 4.37, 2.04 ± 2.26, and 9.93 ± 7.71, respectively. Docking analysis showed that they bound steroid-binding site. Effects of PFC on rat placental HSD3B4 were performed. Of the 11 PFC, C10-C12 significantly inhibited rat HSD3B4 activity at 100 μM. IC₅₀ values of C10-C12 compounds were 45.85 ± 1.49, 36.08 ± 1.50, and 88.74 ± 1.99 µM, respectively. Ki values and inhibition modes of the three most potent PFC (C10-C12) were studied. It was found that they were mixed inhibitors against pregnenolone, with Ki values of 48.16 ± 20.44, 36.28 ± 53.07, and 91.79 ± 21.75 μM, respectively. Docking analysis showed that they bound steroid-binding site of rat HSD3B4. In conclusion, PFC showed significant SAR differences. The potency of inhibiting HSD3B activity increased from C9 to C11, and then declined. Human HSD3B1 was more sensitive to the inhibition of rat HSD3B4.

Origin of circulating 18-oxocortisol in the normal human adrenal

18-Oxocortisol is the product of the metabolism of 11-deoxycortisol by the mitochondrial enzyme aldosterone synthase (CYP11B2). The traditional concept is that the CYP11B2 is exclusively expressed in zona glomerulosa cells and the 17α-hydroxylase (CYP17A1) enzyme, required to synthesize 11-deoxycortisol, is in the zona fasciculata of the human adrenal. It has been postulated that the substrate for 18-oxocortisol is either cortisol from the circulation or from zona fasciculata cells adjacent to the zona glomerulosa. P-glycoprotein, which is highly expressed in steroidogenic cells of the adrenal gland, efficiently expels cortisol from the cell. Double immunofluorescence staining for the CYP11B2 and CYP17A1 enzymes in 7 human adrenals demonstrated that a highly variable number of cells in different areas of the zona glomerulosa co-expressed both enzymes. In addition, there were a variable number of cells that exclusively expressed the CYP17A1 embedded within the zona glomerulosa surrounded by CYP11B2-expressing cells. 18-Oxocortisol in the media of human adrenocortical HAC15 cells was measured by ELISA after incubation with and without 10 nM of angiotensin II to stimulate CYP11B2 activity, with and without the 3β-hydroxysteroid dehydrogenase (HSD3B) inhibitor trilostane, and with variable amounts of cortisol or 11-deoxycortisol. Cortisol was a poor substrate, while 11-deoxycortisol was a significant substrate for the synthesis of 18-oxocortisol. These data suggest that the biosynthesis of 18-oxocortisol in the human adrenal is likely catalyzed by co-expression of the two crucial enzymes CYP17A1 and CYP11B2 in a small proportion of cells within the zona glomerulosa. It is also possible that 11-deoxycortisol diffusing from cells expressing only CYP17A1 interspersed with cells expressing the CYP11B2 enzyme may be a paracrine substrate in the synthesis of 18-oxocortisol.

Structure-based rational design of hydroxysteroid dehydrogenases for improving and diversifying steroid synthesis

A group of steroidogenic enzymes, hydroxysteroid dehydrogenases are involved in steroid metabolism which is very important in the cell: signaling, growth, reproduction, and energy homeostasis. The enzymes show an inherent function in the interconversion of ketosteroids and hydroxysteroids in a position- and stereospecific manner on the steroid nucleus and side-chains. However, the biocatalysis of steroids reaction is a vital and demanding, yet challenging, task to produce the desired enantiopure products with non-natural substrates or non-natural cofactors, and/or in non-physiological conditions. This has driven the use of protein design strategies to improve their inherent biosynthetic efficiency or activate their silent catalytic ability. In this review, the innate features and catalytic characteristics of enzymes based on sequence-structure-function relationships of steroidogenic enzymes are reviewed. Combining structure information and catalytic mechanisms, progress in protein redesign to stimulate potential function, for example, substrate specificity, cofactor dependence, and catalytic stability are discussed.

Trilostane, a 3β-hydroxysteroid dehydrogenase inhibitor, suppresses growth of hepatocellular carcinoma and enhances anti-cancer effects of sorafenib

Background Human 3β-hydroxysteroid dehydrogenase type 1 (HSD3B1) is an enzyme associated with steroidogenesis, however its' role in hepatocellular carcinoma (HCC) biology is unknown. Trilostane is an inhibitor of HSD3B1 and has been tested as a treatment for patients with breast cancer but has not been studied in patients with HCC. Methods and Results The expression of HSD3B1 in HCC tumors in 57 patients were examined. A total of 44 out of 57 tumors (77.2%) showed increased HSD3B1 expression. The increased HSD3B1 in tumors was significantly associated with advanced HCC. In vitro, the knockdown of HSD3B1 expression in Mahlavu HCC cells by a short hairpin RNA (shRNA) led to significant decreases in colony formation and cell migration. The suppression of clonogenicity in the HSD3B1-knockdown HCC cells was reversed by testosterone and 17β-estradiol. Trilostane-mediated inhibition of HSD3B1 in different HCC cells also caused significant inhibition of clonogenicity and cell migration. In subcutaneous HCC Mahlavu xenografts, trilostane (30 or 60 mg/kg, intraperitoneal injection) significantly inhibited tumor growth in a dose-dependent manner. Furthermore, the combination of trilostane and sorafenib significantly enhanced the inhibition of clonogenicity and xenograft growth, surpassing the effects of each drug used alone, with no documented additional toxicity to animals. HSD3B1 blockade was found to suppress the phosphorylation of extracellular signal-regulated kinase (ERK). The decreased ERK phosphorylation was reversed by testosterone or 17b-estradiol. Conclusions Trilostane significantly inhibited the growth of HCC by inhibiting HSD3B1 function and augmenting the efficacy of sorafenib.

Hormonal Therapy for Prostate Cancer

Huggins and Hodges demonstrated the therapeutic effect of gonadal testosterone deprivation in the 1940s and therefore firmly established the concept that prostate cancer is a highly androgen-dependent disease. Since that time, hormonal therapy has undergone iterative advancement, from the types of gonadal testosterone deprivation to modalities that block the generation of adrenal and other extragonadal androgens, to those that directly bind and inhibit the androgen receptor (AR). The clinical states of prostate cancer are the product of a superimposition of these therapies with nonmetastatic advanced prostate cancer, as well as frankly metastatic disease. Today's standard of care for advanced prostate cancer includes gonadotropin-releasing hormone agonists (e.g., leuprolide), second-generation nonsteroidal AR antagonists (enzalutamide, apalutamide, and darolutamide) and the androgen biosynthesis inhibitor abiraterone. The purpose of this review is to provide an assessment of hormonal therapies for the various clinical states of prostate cancer. The advancement of today's standard of care will require an accounting of an individual's androgen physiology that also has recently recognized germline determinants of peripheral androgen metabolism, which include HSD3B1 inheritance.

Intracrinology-revisited and prostate cancer

The formation of steroid hormones in peripheral target tissues is referred to as their intracrine formation. This process occurs in hormone dependent malignancies such as prostate and breast cancer in which the disease can be either castrate resistant or occur post-menopausally, respectively. In these instances, the major precursor steroid of androgens and estrogens is dehydroepiandrosterone (DHEA) and DHEA-SO4. This article reviews the major pathways by which adrenal steroids are converted to the potent male sex hormones, testosterone (T) and 5α-dihydrotestosterone (5α-DHT) and the discrete enzyme isoforms involved in castration resistant prostate cancer. Previous studies have mainly utilized radiotracers to investigate these pathways but have not used prevailing concentrations of precursors found in castrate male human serum. In addition, the full power of stable-isotope dilution liquid chromatography tandem mass spectrometry has not been applied routinely. Furthermore, it is clear that adaptive responses occur in the transporters and enzyme isoforms involved in response to androgen deprivation therapy that need to be considered.

Structure-function relationships for the selective inhibition of human 3β-hydroxysteroid dehydrogenase type 1 by a novel androgen analog

3β-Hydroxysteroid dehydrogenase type 1 (3β-HSD1) is selectively expressed in human placenta, mammary glands and breast tumors in women. Human 3β-HSD2 is selectively expressed in adrenal glands and ovaries. Based on AutoDock 3 and 4 results, we have exploited key differences in the amino acid sequences of 3β-HSD1 (Ser194, Arg195) and 3β-HSD2 (Gly194, Pro195) by designing a selective inhibitor of 3β-HSD1. 2,16-Dicyano-4,5-epoxy-androstane-3,17-dione (16-cyano-17-keto-trilostane or DiCN-AND) was synthesized in a 4-step procedure from androstenedione. In purified 3β-HSD inhibition studies, DiCN-AND competitively inhibited 3β- HSD1 with K_i=4.7μM and noncompetitively inhibited 3β-HSD2 with a 6.5-fold higher K_i=30.7μM. We previously reported similar isoenzyme-specific inhibition profiles for trilostane. Based on our docking results, we created, expressed and purified the chimeric S194G-1 mutant of 3β-HSD1. Trilostane inhibited S194G-1 (K_i=0.67μM) with a noncompetitive mode compared to its 6.7-fold higher affinity, competitive inhibition of 3β-HSD1 (K_i=0.10μM). DiCN-AND inhibited S194G-1 with a 6.3-fold higher K_i (29.5μM) than measured for 3β-HSD1 (K_i=4.7μM) but with the same competitive mode for both enzyme species. Since DiCN-AND noncompetitively inhibits 3β-HSD2, which has the Gly194 and Pro195 of 3β-HSD2 in place of the Ser194 and Arg195 in 3β-HSD1, this suggests that Arg195 alone in 3β-HSD1 or S194G-1 is required to bind DiCN-AND in the substrate binding site (competitive inhibition). However, both Ser194 and Arg195 are required to bind trilostane in the 3β-HSD1 substrate site based on its noncompetitive inhibition of S194G-1 and 3β-HSD2. In support of this hypothesis, DiCN-AND inhibited our chimeric R195P-1 mutant noncompetitively with a K_i=41.3μM (similar to the 3β-HSD2 inhibition profile). Since DiCN-AND competitively inhibited S194G-1 that still contains R195 but noncompetitively inhibited R195P-1 that still contains S194, our data provides strong evidence that the Arg195 being mutated to Pro195 (as present in 3β-HSD2) shifts the inhibition mode from competitive to noncompetitive in 3β-HSD1. This supports the key role of Arg195 in 3β-HSD1 for the high affinity, competitive binding of the trilostane analogs. Our new structure/function information for the design of targeted 3β-HSD1 inhibitors may lead to important new treatments for the prevention of spontaneous premature birth.

Regulation of human 3-beta-hydroxysteroid dehydrogenase type-2 (3βHSD2) by molecular chaperones and the mitochondrial environment affects steroidogenesis

Human 3-β-hydroxysteroid dehydrogenase/isomerase types 1 and 2 (3βHSD1 and 3βHSD2, respectively) are expressed in a tissue-specific pattern by different genes. Site-directed mutagenesis studies have confirmed the function of the catalytic amino acids (Tyr154, Lys 158, Ser124 in both isoenzymes), substrate/inhibitor isoform-specific residues (His156 and Arg195 in 3βHSD1) and cofactor binding residues (Asp36 provides NAD(+) specificity in both isoenzymes). However, detailed analysis of isoform-specific organelle localization and characterization is difficult due to the 93% amino acid identity between the two isoforms. With recent advances in the knowledge of mitochondrial architecture and localization of the various translocases, our laboratory has studied the mechanisms regulating mitochondrial 3βHSD2 localization. The mitochondrial N-terminal leader sequence of 3βHSD2 directs its entry into the mitochondria where it is localized to the intermembrane space (IMS). Unlike other mitochondrial proteins, the N-terminal signal sequence of 3βHSD2 is not cleaved upon mitochondrial import. 3βHSD2 interacts with the mitochondrial translocase, Tim50, to regulate progesterone and androstenedione formation. Our studies suggest that its activity at the IMS is facilitated in a partially unfolded "molten globule" conformation by the proton pump between the matrix and IMS. The unfolded protein is refolded by the mitochondrial chaperones. The protons at the IMS are absorbed by the lipid vesicles, to maintain the proton pump and recycle 3βHSD2. As a result, one molecule of 3βHSD2 may participate in multiple catalytic reactions. In summary, the steroidogenic cell recycles 3βHSD2 to catalyze the reactions needed to produce androstenedione, progesterone and 17α-hydroxyprogesterone on demand in coordination with the mitochondrial translocase, Tim50. This article is part of a Special Issue entitled 'Steroid/Sterol signaling'.

Synthesis of methoxycarbonylpyrazolylandrostene derivatives, and their potential inhibitory effect on androgen biosynthesis and cell proliferation

The Claisen condensations of 3β-acetoxypregn-5-en-20-one (1) and 3β-acetoxypregna-5,16-diene (7) with dimethyl oxalate are known to lead to 3β-hydroxy-21-methoxalylpregn-5-en-20-one (2) and 3β-hydroxy-21-methoxalylpregna-5,16-dien-20-one (8), respectively. The reactions of 2 with p-substituted phenylhydrazines afford pyrazol-5-yl derivatives (5) as main, and 3-yl regioisomers (4) as minor products. The corresponding reactions of 16-ene analogue 8 afford only pyrazol-5-yl regioisomer 9. Oppenauer oxidation of the pyrazolyl compounds yields the corresponding Δ(4)-3-ketosteroids. We investigated the antiandrogenic effects of new methoxycarbonylpyrazolyl compounds through determination of their in vitro inhibition of the activities of rat testicular C17,20-lyase, Δ(5)-3β-hydroxysteroid dehydrogenase (Δ(5)-3β-HSD) and 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3). A Δ(5)-3β-hydroxy compound in the D-ring-saturated androst-5-ene series bearing an unsubstituted phenyl group on the pyrazolyl heterocycle (5a) proved to be a potent inhibitor of Δ(5)-3β-HSD. The 4-methoxyphenyl derivative (5e) and the 3-oxo counterpart (6a) of 5a also displayed substantial inhibition. The other tested compounds exerted only weak inhibitory action against the enzymes investigated. The newly synthetized compounds were evaluated in vitro by means of MTT assays for antiproliferative activity against Hela (cervical carcinoma), A431 (skin epidermoid carcinoma) and MCF7 (breast adenocarcinoma) cells. In all four groups (3β-hydroxy- and 3-ketosteroids with saturated or unsaturated ring D), the most potent analogs contain a 4-tolyl or 4-methoxyphenyl group. Compound 5d exhibited substantial antiproliferative action against the three cell lines investigated, whereas 9d inhibited the growth of Hela cells markedly. The most noteworthy inhibition was exerted by 6a against A431 cells.

Disturbances in production of progesterone and their implications in plant studies

Progesterone is a mammalian hormone that has also been discovered in plants but its physiological function in plants is not explained. Experiments using inhibitors of progesterone synthesis and binding would be useful in studies on the significance of this compound in plants. Until now, trilostane and mifepristone have been used in medical sciences as progesterone biosynthesis and binding inhibitors, respectively. We tested these synthetic steroids for the first time in plants and found that they reduced the content of progesterone in wheat. The aim of further experiments was to answer whether the potential disturbances in the production/binding of progesterone, influence resistance to environmental stress (drought) and the development of wheat. Inhibitors and progesterone were applied to plants via roots in a concentration of 0.25-0.5mg/l water. Both inhibitors lowered the activity of CO2 binding enzyme (Rubisco) in wheat exposed to drought stress and trilostane additionally lowered the chlorophyll content. However, trilostane-treated plants were rescued by treatment with exogenous progesterone. The inhibitors also modulated the development of winter wheat, which indicated the significance of steroid regulators and their receptors in this process. In this study, in addition to progesterone and its inhibitors, brassinosteroid (24-epibrassinolide) and an inhibitor of biosynthesis of brassinosteroids were also applied. Mifepristone inhibited the generative development of wheat (like 24-epibrassinolide), while trilostane (like progesterone and an inhibitor of biosynthesis of brassinosteroids) stimulated the development. We propose a model of steroid-induced regulation of the development of winter wheat, where brassinosteroids act as inhibitors of generative development, while progesterone or other pregnane derivatives act as stimulators.

Androgen biosynthesis in castration-resistant prostate cancer

Prostate cancer is the second leading cause of death in adult males in the USA. Recent advances have revealed that the fatal form of this cancer, known as castration-resistant prostate cancer (CRPC), remains hormonally driven despite castrate levels of circulating androgens. CRPC arises as the tumor undergoes adaptation to low levels of androgens by either synthesizing its own androgens (intratumoral androgens) or altering the androgen receptor (AR). This article reviews the major routes to testosterone and dihydrotestosterone synthesis in CRPC cells and examines the enzyme targets and progress in the development of isoform-specific inhibitors that could block intratumoral androgen biosynthesis. Because redundancy exists in these pathways, it is likely that inhibition of a single pathway will lead to upregulation of another so that drug resistance would be anticipated. Drugs that target multiple pathways or bifunctional agents that block intratumoral androgen biosynthesis and antagonize the AR offer the most promise. Optimal use of enzyme inhibitors or AR antagonists to ensure maximal benefits to CRPC patients will also require application of precision molecular medicine to determine whether a tumor in a particular patient will be responsive to these treatments either alone or in combination.

Selective inhibition of human 3β-hydroxysteroid dehydrogenase type 1 as a potential treatment for breast cancer

Human 3β-hydroxysteroid dehydrogenase/isomerase type 1 (3β-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3β-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3β-HSD1 or 3β-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3β-HSD1 cells with 12-16-fold lower IC(50) values compared to the MCF-7 3β-HSD2 cells. Trilostane and epostane also competitively inhibit purified human 3β-HSD1 with 12-16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3β-HSD2. Using our structural model of 3β-HSD1, trilostane was docked in the active site of 3β-HSD1, and Arg195 in 3β-HSD1 or Pro195 in 3β-HSD2 was identified as a potentially critical residue. The R195P-1 mutant of 3β-HSD1 and the P195R-2 mutant of 3β-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high-affinity, competitive inhibition of 3β-HSD1 by trilostane may be related to the presence of Arg195 in 3β-HSD1 versus Pro195 in 3β-HSD2. In addition, His156 in 3β-HSD1 may play a role in the higher affinity of 3β-HSD1 for substrates and inhibitors compared to 3β-HSD2 containing Try156. Structural modeling of the 3β-HSD1 dimer identified a possible interaction between His156 on one subunit and Gln105 on the other. Kinetic analyses of the H156Y-1, Q105M-1 and Q105M-2 support subunit interactions that contribute to the higher affinity of 3β-HSD1 for the inhibitor, epostane, compared to 3β-HSD2. Article from the Special issue on Targeted Inhibitors.

Porcine glutathione transferase Alpha 2-2 is a human GST A3-3 analogue that catalyses steroid double-bond isomerization

A primary role of GSTs (glutathione transferases) is detoxication of electrophilic compounds. In addition to this protective function, hGST (human GST) A3-3, a member of the Alpha class of soluble GSTs, has prominent steroid double-bond isomerase activity. The isomerase reaction is an obligatory step in the biosynthesis of steroid hormones, indicating a special role of hGST A3-3 in steroidogenic tissues. An analogous GST with high steroid isomerase activity has so far not been found in any other biological species. In the present study, we characterized a Sus scrofa (pig) enzyme, pGST A2-2, displaying high steroid isomerase activity. High levels of pGST A2-2 expression were found in ovary, testis and liver. In its functional properties, other than steroid isomerization, pGST A2-2 was most similar to hGST A3-3. The properties of the novel porcine enzyme lend support to the notion that particular GSTs play an important role in steroidogenesis.

The functions of key residues in the inhibitor, substrate and cofactor sites of human 3beta-hydroxysteroid dehydrogenase type 1 are validated by mutagenesis

In postmenopausal women, human 3beta-hydroxysteroid dehydrogenase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors, while 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland. The goals of this project are to determine if Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2 in the substrate/inhibitor binding site is a critical structural difference responsible for the higher affinity of 3beta-HSD1 for inhibitor and substrate steroids compared to 3beta-HSD2 and whether Asp61, Glu192 and Thr8 are fingerprint residues for cofactor and substrate binding using site-directed mutagenesis. The R195P-1 mutant of 3beta-HSD1 and the P195R-2 mutant of 3beta-HSD2 have been created, expressed, purified and characterized kinetically. Dixon analyses of the inhibition of the R195P-1 mutant, P195R-2 mutant, wild-type 3beta-HSD1 and wild-type 3beta-HSD2 by trilostane has produced kinetic profiles that show inhibition of 3beta-HSD1 by trilostane (K(i)=0.10microM, competitive) with a 16-fold lower K(i) and different mode than measured for 3beta-HSD2 (K(i)=1.60microM, noncompetitive). The R195P-1 mutation shifts the high-affinity, competitive inhibition profile of 3beta-HSD1 to a low-affinity (trilostane K(i)=2.56microM), noncompetitive inhibition profile similar to that of 3beta-HSD2 containing Pro195. The P195R-2 mutation shifts the low-affinity, noncompetitive inhibition profile of 3beta-HSD2 to a high-affinity (trilostane K(i)=0.19microM), competitive inhibition profile similar to that of 3beta-HSD1 containing Arg195. Michaelis-Menten kinetics for DHEA, 16beta-hydroxy-DHEA and 16alpha-hydroxy-DHEA substrate utilization by the R195P-1 and P195R-2 enzymes provide further validation for higher affinity binding due to Arg195 in 3beta-HSD1. Comparisons of the Michaelis-Menten values of cofactor and substrate for the targeted mutants of 3beta-HSD1 (D61N, D61V, E192A, T8A) clarify the functions of these residues as well.

Structural basis for the selective inhibition of human 3beta-hydroxysteroid dehydrogenase 1 in human breast tumor MCF-7 cells

Human 3beta-hydroxysteroid dehydrogenase/isomerase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3beta-HSD1 or 3beta-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3beta-HSD1 cells with 12- to 16-fold lower IC(50) values compared to the MCF-7 3beta-HSD2 cells. The compounds also competitively inhibit purified human 3beta-HSD1 with 12- to 16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3beta-HSD2. Using our structural model of 3beta-HSD1, trilostane or 17beta-acetoxy-trilostane was docked in the active site of 3beta-HSD1, and Arg195 in 3beta-HSD1 or Pro195 in 3beta-HSD2 was identified as a potentially critical residue (one of 23 non-identical residues in the two isoenzymes). The P195R mutant of 3beta-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high affinity, competitive inhibition of 3beta-HSD1 by trilostane and epostane may be related to the presence of Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2.