Structure of AKR1C3 with 3-phenoxybenzoic acid bound

AKR1C3 regulated by NRF2/MAFG complex promotes proliferation via stabilizing PARP1 in hepatocellular carcinoma

Aldo-keto reductase family 1 member C3 (AKR1C3) serves as a contributor to numerous kinds of tumors, and its expression is elevated in patients with hepatocellular carcinoma (HCC). However, the biological function of AKR1C3 in HCC remains unclear. Here we investigated the role of AKR1C3 in liver carcinogenesis using in vitro and in vivo models. We determined that AKR1C3 is frequently increased in HCC tissues with poor prognosis. Genetically manipulated cells with AKR1C3 construction were examined to highlight the pro-tumoral growth of both wild-type AKR1C3 and mutant in vitro and in vivo. We observed promising treatment effects of AKR1C3 shRNA by intratumoral injection in mice. Mechanically, we demonstrated that the transcription factor heterodimer NRF2/MAFG was able to bind directly to AKR1C3 promoter to activate its transcription. Further, AKR1C3 stabilized PARP1 by decreasing its ubiquitination, which resulted in HCC cell proliferation and low sensitivity of Cisplatin. Moreover, we discovered that the tumorigenic role of AKR1C3 was non-catalytic dependent and the NRF2/MAFG-AKR1C3-PARP1 axis might be one of the important proliferation pathways in HCC. In conclusion, blockage of AKR1C3 expression provides potential therapeutic benefits against HCC.

Analogues of Natural Chalcones as Efficient Inhibitors of AKR1C3

Naturally occurring substances are valuable resources for drug development. In this respect, chalcones are known to be antiproliferative agents against prostate cancer cell lines through various mechanisms or targets. Based on the literature and preliminary results, we aimed to study and optimise the efficiency of a series of chalcones to inhibit androgen-converting AKR1C3, known to promote prostate cancer. A total of 12 chalcones with different substitution patterns were synthesised. Structure-activity relationships associated with these modifications on AKR1C3 inhibition were analysed by performing enzymatic assays and docking simulations. In addition, the selectivity and cytotoxicity of the compounds were assessed. In enzymatic assays, C-6' hydroxylated derivatives were more active than C-6' methoxylated derivatives. In contrast, C-4 methylation increased activity over C-4 hydroxylation. Docking results supported these findings with the most active compounds fitting nicely in the binding site and exhibiting strong interactions with key amino acid residues. The most effective inhibitors were not cytotoxic for HEK293T cells and selective for 17β-hydroxysteroid dehydrogenases not primarily involved in steroid hormone metabolism. Nevertheless, they inhibited several enzymes of the steroid metabolism pathways. Favourable substitutions that enhanced AKR1C3 inhibition of chalcones were identified. This study paves the way to further develop compounds from this series or related flavonoids with improved inhibitory activity against AKR1C3.

Interleukin 17A deficiency alleviates fluoride-induced testicular injury by inhibiting the immune response and apoptosis

The reproductive toxicity of fluoride (F) has been verified by various epidemiological and experimental studies. Our previous work suggested that the interleukin 17A (IL-17A) is involved in the testicular damage induced by excessive F exposure. In this study, we further investigated the role of IL-17A in F-induced testicular injury. Wild type (WT) and IL-17A knockout (IL-17A^-/-) mice were exposed to 0, 25, 50, or 100 mg/L sodium fluoride (NaF) for 90 days. We found that exposure to excessive F levels caused testicular damage, decreased semen quality, negatively affected testicular morphology, and increased the inflammatory response. Specifically, excessive F intake increased the expression levels of IL-17A in the testis and increased the protein levels of Act1, NF-κB, IL-17R, C/EBP-α, and TRAF6 in the IL-17A signaling pathway. The increase in IL-17A expression corresponded to increases expression of IL-17R, IL-6, IL-23, IL-1β, TGF-β and TNF-α as assessed by RT-PCR and ELISA assays. Remarkably, IL-17A knockout in mice ameliorated the effects of F on testicular damage, semen quality, testicular morphology, and the immune response. Additionally, we found the in vitro exposure of Leydig cells to NaF and recombinant IL-17A led to abnormal apoptosis and a decrease in testosterone secretion. Our findings prove that IL-17A plays a key role in the exacerbation of testicular injuries in F-exposed mice, and that IL-17A deficiency can alleviate F-induced injury by inhibiting the immune response and apoptosis in the testis. These data suggest that targeting IL-17A may be a useful therapeutic strategy for treating F-mediated toxicity in the testis.

In situ proteolysis of an N-terminal His tag with thrombin improves the diffraction quality of human aldo-keto reductase 1C3 crystals

Human aldo-keto reductase 1C3 (AKR1C3) stereospecifically reduces steroids and prostaglandins and is involved in the biotransformation of xenobiotics. Its role in various cancers makes it a potential therapeutic target for the development of inhibitors. Recombinant AKR1C3 with a thrombin-cleavable N-terminal His6 tag was expressed from a pET-28(+) vector for structural studies of enzyme-inhibitor complexes. A modified in situ proteolysis approach was applied to specifically remove the His tag by thrombin cleavage during crystallization screening trials. This improved the morphology and diffraction quality of the crystals and allowed the acquisition of high-resolution diffraction data and structure solution. This approach may be generally applicable to other proteins expressed using the pET-28(+) vector.

3D-QSAR studies of 3-(3,4-dihydroisoquinolin-2(1H)-ylsulfonyl)benzoic acids as AKR1C3 inhibitors: Highlight the importance of molecular docking in conformation generation

AKR1C3 is a promising drug target for castration-resistant prostate cancer (CRPC). Here, 3D-QSAR analysis were performed on 3-(3,4-dihydroisoquinolin-2(1H)-ylsulfonyl)benzoic acids to correlate their chemical structures with their observed AKR1C3 inhibitory activity. Three structural alignment methods employing various conformers were used to scrutinize the effect of conformation selection on the predictive accuracy of QSAR models. Using docked conformation, the best CoMFA and CoMSIA models were developed and validated with a training set of 61 molecules and a test set of 7 molecules. Detailed analysis of contour maps provided helpful structural insights to rational design of AKR1C3 inhibitors with enhanced potency.

Discovery of (R)-2-(6-Methoxynaphthalen-2-yl)butanoic Acid as a Potent and Selective Aldo-keto Reductase 1C3 Inhibitor

Type 5 17β-hydroxysteroid dehydrogenase, aldo-keto reductase 1C3 (AKR1C3) converts Δ(4)-androstene-3,17-dione and 5α-androstane-3,17-dione to testosterone (T) and 5α-dihydrotestosterone, respectively, in castration resistant prostate cancer (CRPC). In CRPC, AKR1C3 is implicated in drug resistance, and enzalutamide drug resistance can be surmounted by indomethacin a potent inhibitor of AKR1C3. We examined a series of naproxen analogues and find that (R)-2-(6-methoxynaphthalen-2-yl)butanoic acid (in which the methyl group of R-naproxen was replaced by an ethyl group) acts as a potent AKR1C3 inhibitor that displays selectivity for AKR1C3 over other AKR1C enzymes. This compound was devoid of inhibitory activity on COX isozymes and blocked AKR1C3 mediated production of T and induction of PSA in LNCaP-AKR1C3 cells as a model of a CRPC cell line. R-Profens are substrate selective COX-2 inhibitors and block the oxygenation of endocannabinoids and in the context of advanced prostate cancer R-profens could inhibit intratumoral androgen synthesis and act as analgesics for metastatic disease.

Androgen-metabolizing enzymes: A structural perspective

Androgen-metabolizing enzymes convert cholesterol, a relatively inert molecule, into some of the most potent chemical messengers in vertebrates. This conversion involves thermodynamically challenging reactions catalyzed by P450 enzymes and redox reactions catalyzed by Aldo-Keto Reductases (AKRs). This review covers the structures of these enzymes with a focus on active site interactions and proposed mechanisms. Due to their role in a number of diseases, particularly in cancer, androgen-metabolizing enzymes have been targets of drug design. Hence we will also highlight how existing knowledge of structure is being used to this end.

Structures of complexes of type 5 17β-hydroxysteroid dehydrogenase with structurally diverse inhibitors: insights into the conformational changes upon inhibitor binding

Type 5 17β-hydroxysteroid dehydrogenase (17β-HSD5) is an aldo-keto reductase expressed in the human prostate which catalyzes the conversion of androstenedione to testosterone. Testosterone is converted to 5α-dihydrotestosterone, which is present at high concentrations in patients with castration-resistant prostate cancer (CRPC). Inhibition of 17β-HSD5 is therefore considered to be a promising therapy for treating CRPC. In the present study, crystal structures of complexes of 17β-HSD5 with structurally diverse inhibitors derived from high-throughput screening were determined. In the structures of the complexes, various functional groups, including amide, nitro, pyrazole and hydroxyl groups, form hydrogen bonds to the catalytic residues His117 and Tyr55. In addition, major conformational changes of 17β-HSD5 were observed following the binding of the structurally diverse inhibitors. These results demonstrate interactions between 17β-HSD5 and inhibitors at the atomic level and enable structure-based drug design for anti-CRPC therapy.

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'.

Crystal structures of three classes of non-steroidal anti-inflammatory drugs in complex with aldo-keto reductase 1C3

Aldo-keto reductase 1C3 (AKR1C3) catalyses the NADPH dependent reduction of carbonyl groups in a number of important steroid and prostanoid molecules. The enzyme is also over-expressed in prostate and breast cancer and its expression is correlated with the aggressiveness of the disease. The steroid products of AKR1C3 catalysis are important in proliferative signalling of hormone-responsive cells, while the prostanoid products promote prostaglandin-dependent proliferative pathways. In these ways, AKR1C3 contributes to tumour development and maintenance, and suggest that inhibition of AKR1C3 activity is an attractive target for the development of new anti-cancer therapies. Non-steroidal anti-inflammatory drugs (NSAIDs) are one well-known class of compounds that inhibits AKR1C3, yet crystal structures have only been determined for this enzyme with flufenamic acid, indomethacin, and closely related analogues bound. While the flufenamic acid and indomethacin structures have been used to design novel inhibitors, they provide only limited coverage of the NSAIDs that inhibit AKR1C3 and that may be used for the development of new AKR1C3 targeted drugs. To understand how other NSAIDs bind to AKR1C3, we have determined ten crystal structures of AKR1C3 complexes that cover three different classes of NSAID, N-phenylanthranilic acids (meclofenamic acid, mefenamic acid), arylpropionic acids (flurbiprofen, ibuprofen, naproxen), and indomethacin analogues (indomethacin, sulindac, zomepirac). The N-phenylanthranilic and arylpropionic acids bind to common sites including the enzyme catalytic centre and a constitutive active site pocket, with the arylpropionic acids probing the constitutive pocket more effectively. By contrast, indomethacin and the indomethacin analogues sulindac and zomepirac, display three distinctly different binding modes that explain their relative inhibition of the AKR1C family members. This new data from ten crystal structures greatly broadens the base of structures available for future structure-guided drug discovery efforts.