Human 17beta-hydroxysteroid dehydrogenase type 5 is inhibited by dietary flavonoids

AKR1C3 as a target in castrate resistant prostate cancer

Aberrant androgen receptor (AR) activation is the major driver of castrate resistant prostate cancer (CRPC). CRPC is ultimately fatal and more therapeutic agents are needed to treat this disease. Compounds that target the androgen axis by inhibiting androgen biosynthesis and or AR signaling are potential candidates for use in CRPC treatment and are currently being pursued aggressively. Aldo-keto reductase 1C3 (AKR1C3) plays a pivotal role in androgen biosynthesis within the prostate. It catalyzes the 17-ketoreduction of weak androgen precursors to give testosterone and 5α-dihydrotestosterone. AKR1C3 expression and activity has been implicated in the development of CRPC, making it a rational target. Selective inhibition of AKR1C3 will be important, however, due to the presence of closely related isoforms, AKR1C1 and AKR1C2 that are also involved in androgen inactivation. We examine the evidence that supports the vital role of AKR1C3 in CRPC and recent developments in the discovery of potent and selective AKR1C3 inhibitors. This article is part of a Special Issue entitled 'CSR 2013'.

Inhibitors of type 5 17β-hydroxysteroid dehydrogenase (AKR1C3): overview and structural insights

There is considerable interest in the development of an inhibitor of aldo-keto reductase (AKR) 1C3 (type 5 17β-hydroxysteroid dehydrogenase and prostaglandin F synthase) as a potential therapeutic for both hormone-dependent and hormone-independent cancers. AKR1C3 catalyzes the reduction of 4-androstene-3,17-dione to testosterone and estrone to 17β-estradiol in target tissues, which will promote the proliferation of hormone dependent prostate and breast cancers, respectively. AKR1C3 also catalyzes the reduction of prostaglandin (PG) H(2) to PGF(2α) and PGD(2) to 9α,11β-PGF(2), which will limit the formation of anti-proliferative prostaglandins, including 15-deoxy-Δ(12,14)-PGJ(2), and contribute to proliferative signaling. AKR1C3 is overexpressed in a wide variety of cancers, including breast and prostate cancer. An inhibitor of AKR1C3 should not inhibit the closely related isoforms AKR1C1 and AKR1C2, as they are involved in other key steroid hormone biotransformations in target tissues. Several structural leads have been explored as inhibitors of AKR1C3, including non-steroidal anti-inflammatory drugs, steroid hormone analogues, flavonoids, cyclopentanes, and benzodiazepines. Inspection of the available crystal structures of AKR1C3 with multiple ligands bound, along with the crystal structures of the other AKR1C isoforms, provides a structural basis for the rational design of isoform specific inhibitors of AKR1C3. We find that there are subpockets involved in ligand binding that are considerably different in AKR1C3 relative to the closely related AKR1C1 or AKR1C2 isoforms. These pockets can be used to further improve the binding affinity and selectivity of the currently available AKR1C3 inhibitors. Article from the special issue on Targeted Inhibitors.

Flavonoids and cinnamic acid derivatives as inhibitors of 17beta-hydroxysteroid dehydrogenase type 1

17beta-Hydroxysteroid dehydrogenase (17beta-HSD) type 1 converts estrone to estradiol, a potent ligand for estrogen receptors. It represents an important target for the development of drugs for treatment of estrogen-dependent diseases. In the present study, we have examined the inhibitory activities of some flavonoids, their biosynthetic precursors (cinnamic acids and coumaric acid), and their derivatives. The proliferative activity of flavonoids on the T-47D estrogen-receptor-positive breast cancer cell line was also evaluated. Among 10 flavonoids, 7,4'-dihydroxyflavone, diosmetin, chrysoeriol, scutellarein, genkwanin and fisetin showed more than 70% inhibition of 17beta-HSD type 1 at 6microM. In a series of 18 derivatives of cinnamic acid, the best inhibitor was 4'-cyanophenyl 3,4-methylenedioxycinnamate, with more than 70% inhibition of 17beta-HSD type 1. None of flavonoids affected the proliferation of T-47D breast cancer cells.

Effects of dietary soy isoflavones on health, steroidogenesis, and thyroid gland function in dogs

OBJECTIVE

To evaluate the effect of a soy-based diet on general health and adrenocortical and thyroid gland function in dogs. Animals-20 healthy privately owned adult dogs.

PROCEDURES

In a randomized controlled clinical trial, dogs were fed a soy-based diet with high (HID; n = 10) or low (LID; 10) isoflavones content. General health of dogs, clinicopathologic variables, and serum concentrations of adrenal gland and thyroid gland hormones were assessed before treatment was initiated and up to 1 year later. Differences between groups with respect to changes in the values of variables after treatment were assessed by means of a Student t test (2 time points) and repeated-measures ANOVA (3 time points).

RESULTS

No differences were detected between the 2 groups with respect to body condition and results of hematologic, serum biochemical, and urine analyses. Most serum concentrations of hormones did not change significantly after treatment, nor were they affected by diet. However, the mean change in serum concentration of total thyroxine was higher in the HID group (15.7 pmol/L) than that in the LID group (-1.9 pmol/L). The mean change in estradiol concentration after ACTH stimulation at 1 year after diets began was also higher in the HID group (19.0 pg/mL) than that in the LID group (-5.6 pg/mL).

CONCLUSIONS AND CLINICAL RELEVANCE

Phytoestrogens may influence endocrine function in dogs. Feeding soy to dogs on a long-term basis may influence results of studies in which endocrine function is evaluated, although larger studies are needed to confirm this supposition.

Regulation of cellular signals from nutritional molecules: a specific role for phytochemicals, beyond antioxidant activity

Phytochemicals (PhC) are a ubiquitous class of plant secondary metabolites. A "recommended" human diet should warrant a high proportion of energy from fruits and vegetables, therefore providing, among other factors, a huge intake of PhC, in general considered "health promoting" by virtue of their antioxidant activity and positive modulation, either directly or indirectly, of the cellular and tissue redox balance. Diet acts through multiple pathways and the association between the consumption of specific food items and the risk of degenerative diseases is extremely complex. Recent literature suggests that molecules having a chemical structure compatible with a putative antioxidant capacity can actually "perform" activities and roles independent of such capacity, interacting with cellular functions at different levels, such as affecting enzyme activities, binding to membrane or nuclear receptors as either an elective ligand or a ligand mimic. Inductive or signaling effects may occur at concentrations much lower than that required for effective antioxidant activity. Therefore, the "antioxidant hypothesis" is to be considered in some cases an intellectual "shortcut" possibly biasing the real understanding of the molecular mechanisms underlying the beneficial effects of various classes of food items. In the past few years, many exciting new indications elucidating the mechanisms of polyphenols have been published. Here, we summarize the current knowledge of the mechanisms by which specific molecules of nutritional interest, and in particular polyphenols, play a role in cellular response and in preventing pathologies. In particular, their direct interaction with nuclear receptors and their ability to modulate the activity of key enzymes involved in cell signaling and antioxidant responses are presented and discussed.

New inhibitors of fungal 17β-hydroxysteroid dehydrogenase based on the [1,5]-benzodiazepine scaffold

The synthesis and activity of a new series of non-steroidal inhibitors of 17beta-hydroxysteroid dehydrogenase that are based on a 1,5-benzodiazepine scaffold are presented. Their inhibitory potential was screened against 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17beta-HSDcl), a model enzyme of the short-chain dehydrogenase/reductase superfamily. Some of these compounds are potent inhibitors of 17beta-HSDcl activity, with IC50 values in the low micromolar range and represent promising lead compounds that should be further developed and investigated as inhibitors of human 17beta-HSD isoforms, which are the enzymes associated with the development of many hormone-dependent and neuronal diseases.

Structure-based inhibitor design for an enzyme that binds different steroids: a potent inhibitor for human type 5 17beta-hydroxysteroid dehydrogenase

Human type 5 17beta-hydroxysteroid dehydrogenase plays a crucial role in local androgen formation in prostate tissue. Several chemicals were synthesized and tested for their ability to inhibit this enzyme, and a series of estradiol derivatives bearing a lactone on the D-ring were found to inhibit its activity efficiently. The crystal structure of the type 5 enzyme in complex with NADP and such a novel inhibitor, EM1404, was determined to a resolution of 1.30 A. Significantly more hydrogen bonding and hydrophobic interactions were defined between EM1404 and the enzyme than in the substrate ternary complex. The lactone ring of EM1404 accounts for important interactions with the enzyme, whereas the amide group at the opposite end of the inhibitor contributes to the stability of three protein loops involved in the construction of the substrate binding site. EM1404 has a strong competitive inhibition, with a Ki of 6.9+/-1.4 nM, demonstrating 40 times higher affinity than that of the best inhibitor previously reported. This is observed despite the fact that the inhibitor occupies only part of the binding cavity. Attempts to soak the inhibitor into crystals of the binary complex with NADP were unsuccessful, yielding a structure with a polyethylene glycol fragment occupying the substrate binding site. The relative crystal packing is discussed. Combined studies of small molecule inhibitor synthesis, x-ray crystallography, enzyme inhibition, and molecular modeling make it possible to analyze the plasticity of the substrate binding site of the enzyme, which is essential for developing more potent and specific inhibitors for hormone-dependent cancer therapy.

Flavonoids and cinnamic acid esters as inhibitors of fungal 17β-hydroxysteroid dehydrogenase: A synthesis, QSAR and modelling study

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) modulate the biological potency of estrogens and androgens by interconversion of inactive 17-keto-steroids and their active 17beta-hydroxy- counterparts. We have shown previously that flavonoids are potentially useful lead compounds for developing inhibitors of 17beta-HSDs. In this paper, we describe the synthesis and biochemical evaluation of structurally analogous inhibitors, the trans-cinnamic acid esters and related compounds. Additionally, quantitative structure-activity relationship (QSAR) and modelling studies were performed to rationalize the results and to suggest further optimization. The results stress the importance of a hydrogen bond with Asn154 and hydrophobic interactions with the aromatic side chain of Tyr212 for optimal molecular recognition.

Phytoestrogens as inhibitors of the human progesterone metabolizing enzyme AKR1C1

Phytoestrogens are plant-derived, non-steroidal constituents of our diets. They can act as agonists or antagonists of estrogen receptors, and they can modulate the activities of the key enzymes in estrogen biosynthesis. Much less is known about their actions on the androgen and progesterone metabolizing enzymes. We have examined the inhibitory action of phytoestrogens on the key human progesterone-metabolizing enzyme, 20alpha-hydroxysteroid dehydrogenase (AKR1C1). This enzyme inactivates progesterone and the neuroactive 3alpha,5alpha-tetrahydroprogesterone, to form their less active counterparts, 20alpha-hydroxyprogesterone and 5alpha-pregnane-3alpha,20alpha-diol, respectively. We overexpressed recombinant human AKR1C1 in Escherichia coli, purified it to homogeneity, and examined the selected phytoestrogens as inhibitors of NADPH-dependent reduction of a common AKR substrate, 9,10-phenantrenequinone, and progesterone. The most potent inhibitors were 7-hydroxyflavone, 3,7-dihydroxyflavone and flavanone naringenin with IC(50) values in the low microM range. Docking of the flavones in the active site of AKR1C1 revealed their possible binding modes, in which they are sandwiched between the Leu308 and Trp227 of AKR1C1.

Cinnamates and cinnamamides inhibit fungal 17beta-hydroxysteroid dehydrogenase

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) have important roles in the regulation of steroid hormone actions through their catalysis of the oxidation or reduction of estrogens and androgens at position 17. Dysfunctions of the human 17beta-HSDs have been associated with reproduction disorders, neuronal diseases and the development of hormone-dependent forms of cancers. Therefore, these enzymes represent interesting targets for the development of new drugs. Here we present a series of new cinnamic acid esters and amides that inhibit the oxidative and reductive reaction catalyzed by 17beta-HSD from the fungus Cochliobolus lunatus, a model enzyme of the short-chain dehydrogenase/reductase superfamily. We found that esters of unsubstituted cinnamic acid were better inhibitors than esters of 3,4,5-trimethoxycinnamic acid. Cinnamates were also more potent inhibitors than structurally related cinnamamides. The compounds presented in this paper are potential leads for the development of inhibitors of human 17beta-HSD isoforms, which may prove to have different therapeutic applications.

Cinnamic acids as new inhibitors of 17beta-hydroxysteroid dehydrogenase type 5 (AKR1C3)

17Beta-hydroxysteroid dehydrogenase type 5 (AKR1C3) that is involved in the pre-receptor regulation of androgen and estrogen action in the human is an emerging therapeutic target in the treatment of hormone-dependent forms of cancer, such as prostate cancer, breast cancer and endometrial cancer. To discover novel inhibitors, we tested the effect of a series of cinnamic acids on the reductive activity of the human recombinant AKR1C3. The compounds were evaluated in a spectrophotometric assay using 9,10-phenanthrenequinone as a substrate. The best inhibitor in the series was alpha-methylcinnamic acid (IC50=6.4 microM). Also, unsubstituted cinnamic acid was a good inhibitor of AKR1C3 (IC50=50 microM). Small hydrophobic substituents of the phenyl ring did not alter the activity; however, substitution with polar groups decreased the potency of inhibition. The most active compounds in this series represent promising starting points for further structural modifications in the search for more potent inhibitors of AKR1C3.

Phytoestrogens as inhibitors of fungal 17beta-hydroxysteroid dehydrogenase

Different phytoestrogens were tested as inhibitors of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17beta-HSDcl), a member of the short-chain dehydrogenase/reductase superfamily. Phytoestrogens inhibited the oxidation of 100 microM 17beta-hydroxyestra-4-en-3-one and the reduction of 100 microM estra-4-en-3,17-dione, the best substrate pair known. The best inhibitors of oxidation, with IC(50) below 1 microM, were flavones hydroxylated at positions 3, 5 and 7: 3-hydroxyflavone, 3,7-dihydroxyflavone, 5,7-dihydroxyflavone (chrysin) and 5-hydroxyflavone, together with 5-methoxyflavone. The best inhibitors of reduction were less potent; 3-hydroxyflavone, 5-methoxyflavone, coumestrol, 3,5,7,4'-tetrahydroxyflavone (kaempferol) and 5-hydroxyflavone all had IC(50) values between 1 and 5 microM. Docking the representative inhibitors chrysin and kaempferol into the active site of 17beta-HSDcl revealed the possible binding mode, in which they are sandwiched between the nicotinamide moiety and Tyr212. The structural features of phytoestrogens, inhibitors of both oxidation and reduction catalyzed by the fungal 17beta-HSD, are similar to the reported structural features of phytoestrogen inhibitors of human 17beta-HSD types 1 and 2.

Phytoestrogens as inhibitors of fungal 17beta-hydroxysteroid dehydrogenase

Different phytoestrogens were tested as inhibitors of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17beta-HSDcl), a member of the short-chain dehydrogenase/reductase superfamily. Phytoestrogens inhibited the oxidation of 100microM 17beta-hydroxyestra-4-en-3-one and the reduction of 100microM estra-4-en-3,17-dione, the best substrate pair known. The best inhibitors of oxidation, with IC(50) below 1microM, were flavones hydroxylated at positions 3, 5 and 7: 3-hydroxyflavone, 3,7-dihydroxyflavone, 5,7-dihydroxyflavone (chrysin) and 5-hydroxyflavone, together with 5-methoxyflavone. The best inhibitors of reduction were less potent; 3-hydroxyflavone, 5-methoxyflavone, coumestrol, 3,5,7,4'-tetrahydroxyflavone (kaempferol) and 5-hydroxyflavone, all had IC(50) values between 1 and 5microM. Docking the representative inhibitors chrysin and kaempferol into the active site of 17beta-HSDcl revealed the possible binding mode, in which they are sandwiched between the nicotinamide moiety and Tyr212. The structural features of phytoestrogens, inhibitors of both oxidation and reduction catalyzed by the fungal 17beta-HSD, are similar to the reported structural features of phytoestrogen inhibitors of human 17beta-HSD types 1 and 2.

The role of nutrition in preventing prostate cancer: a review of the proposed mechanism of action of various dietary substances

BACKGROUND

Dietary modifications to prevent prostate cancer (PCa) continue to gain attention as research demonstrates that various dietary nutrients/supplements are related to decreased risk of developing prostate cancer (PCa). Several studies have focused on the antioxidant and nonantioxidant effects of various dietary substances in the prevention of PCa. Research into the mechanisms by which PCa is prevented, or its disease severity is reduced by dietary micronutrients and vitamins continues to enrich our understanding of the mechanisms by which PCa is initiated and progresses.

METHODS

We reviewed the literature on dietary nutrients with antioxidant properties that have been shown to have a positive effect in reducing the incidence or preventing the occurrence of PCa including carotenoids (e.g., lycopene), retinoids (e.g., vitamin A), vitamin E, vitamin C, selenium, and polyphenols. Other nutrients examined included vitamin D and calcium.

RESULTS

Many dietary micronutrients have demonstrated significant and complex effects on PCa cell proliferation, differentiation, and signaling related to the initiation, progression, and regression of PCa.

CONCLUSION

Understanding the mechanisms by which various dietary nutrients exert their effects on PCa may make it possible to design effective drugs for treating PCa and to promote better nutrition and lifestyle changes in those at risk for PCa.