Inhibiting wild-type and C299S mutant AKR1B10; a homologue of aldose reductase upregulated in cancers

Molecular dynamics of fibric acids

¹H- and ¹³C-NMR chemical shifts were measured for four fibric acids (bezafibrate, clofibric acid, fenofibric acid, and gemfibrozil), which are lipid-lowering drugs. Correlation is found with DFT-computed chemical shifts from the conformational analysis. Equilibrium populations of optimized conformers at 298 K are very different when based on computed Gibbs energies rather than on potential energies. This is due to the significant entropic advantages of extended rather than bent conformational shapes. Abundant conformers with intramolecular hydrogen bonding via five-member rings are computed for three fibric acids, but not gemfibrozil, which lacks suitable connectivity of carboxyl and phenoxy groups. Trends in computed atom-positional deviations, molecular volumes, surface areas, and dipole moments among the fibric acids and their constituent conformations indicate that bezafibrate has the greatest hydrophilicity and fenofibric acid has the greatest flexibility. Theoretical and experimental comparison of chemical shifts of standards with sufficient overlap of fragments containing common atoms, groups, and connectivity may provide a reliable minimal set to benchmark and generate leads.

AKR1B10, One of the Triggers of Cytokine Storm in SARS-CoV2 Severe Acute Respiratory Syndrome

Preventing the cytokine storm observed in COVID-19 is a crucial goal for reducing the occurrence of severe acute respiratory failure and improving outcomes. Here, we identify Aldo-Keto Reductase 1B10 (AKR1B10) as a key enzyme involved in the expression of pro-inflammatory cytokines. The analysis of transcriptomic data from lung samples of patients who died from COVID-19 demonstrates an increased expression of the gene encoding AKR1B10. Measurements of the AKR1B10 protein in sera from hospitalised COVID-19 patients suggests a significant link between AKR1B10 levels and the severity of the disease. In macrophages and lung cells, the over-expression of AKR1B10 induces the expression of the pro-inflammatory cytokines Interleukin-6 (IL-6), Interleukin-1β (IL-1β) and Tumor Necrosis Factor a (TNFα), supporting the biological plausibility of an AKR1B10 involvement in the COVID-19-related cytokine storm. When macrophages were stressed by lipopolysaccharides (LPS) exposure and treated by Zopolrestat, an AKR1B10 inhibitor, the LPS-induced production of IL-6, IL-1β, and TNFα is significantly reduced, reinforcing the hypothesis that the pro-inflammatory expression of cytokines is AKR1B10-dependant. Finally, we also show that AKR1B10 can be secreted and transferred via extracellular vesicles between different cell types, suggesting that this protein may also contribute to the multi-organ systemic impact of COVID-19. These experiments highlight a relationship between AKR1B10 production and severe forms of COVID-19. Our data indicate that AKR1B10 participates in the activation of cytokines production and suggest that modulation of AKR1B10 activity might be an actionable pharmacological target in COVID-19 management.

A facile and chemoselectivity in synthesis of 4-chloro-N-(4-((1-hydroxy-2-methylpropan-2-yl)oxy)phenethyl)benzamide, the alcohol derivative of Bezafibrate

A facile method for the reduction of carboxylic acid group of Bezafibrate, an approved drug, is described. The selective reduction of carboxylic acid group to corresponding alcohol was carried out by activation of the carboxylic acid moiety via mixed anhydride followed by the addition of stoichiometric amount of NaBH₄ and methanol to obtain the first alcohol variant of Bezafibrate. The reaction was completed in 5–10 min in excellent yield and purity. The new alcohol derivative was characterized by spectroscopic methods. This is the first report on this new molecule.

Perspective on the Structural Basis for Human Aldo-Keto Reductase 1B10 Inhibition

Human aldo-keto reductase 1B10 (AKR1B10) is overexpressed in many cancer types and is involved in chemoresistance. This makes AKR1B10 to be an interesting drug target and thus many enzyme inhibitors have been investigated. High-resolution crystallographic structures of AKR1B10 with various reversible inhibitors were deeply analyzed and compared to those of analogous complexes with aldose reductase (AR). In both enzymes, the active site included an anion-binding pocket and, in some cases, inhibitor binding caused the opening of a transient specificity pocket. Different structural conformers were revealed upon inhibitor binding, emphasizing the importance of the highly variable loops, which participate in the transient opening of additional binding subpockets. Two key differences between AKR1B10 and AR were observed regarding the role of external loops in inhibitor binding. The first corresponded to the alternative conformation of Trp112 (Trp111 in AR). The second difference dealt with loop A mobility, which defined a larger and more loosely packed subpocket in AKR1B10. From this analysis, the general features that a selective AKR1B10 inhibitor should comply with are the following: an anchoring moiety to the anion-binding pocket, keeping Trp112 in its native conformation (AKR1B10-like), and not opening the specificity pocket in AR.

Synthesis and Chiral Separation of Fibratol, Isopropyl 2-(4-((4-chlorophenyl)(hydroxyl) methyl)-phenoxy)-2-methylpropanoate

Practical synthetic route for the formation of enantiomeric mixture of Isopropyl 2-(4-((4-chlorophenyl)(hydroxyl)methyl)phenoxy)-2-methylpropanoate (Fibratol 2a/b) from isopropyl 2-(4-(4-chlorobenzoyl)phenoxy)-2-methylpropanoate (Fenofibrate 1) has been developed. Method has also been established for the chiral separation of enantiomers of Fibratol 2a/b that is synthesized using the route mentioned above. The optical activity determined for enantiomerically separated Fibratol (2a) and Fibratol (2b) are −5.2° and 8.0° which reflect their ability to rotate plane polarized light counterclockwise (levo) and clockwise (dextro), respectively.

Aldo-Keto Reductase Family 1 Member B10 Inhibitors: Potential Drugs for Cancer Treatment

Cytosolic NADPH-dependent reductase AKR1B10 is a member of the aldo-keto reductase (AKR) superfamily. This enzyme is normally expressed in the gastrointestinal tract. However, it is overexpressed in many solid tumors, such as hepatocarcinoma, lung cancer and breast cancer. AKR1B10 may play a role in the formation and development of carcinomas through multiple mechanisms including detoxification of cytotoxic carbonyls, modulation of retinoic acid level, and regulation of cellular fatty acid synthesis and lipid metabolism. Studies have suggested that AKR1B10 may be a useful biomarker for cancer diagnosis and a potential target for cancer treatment. Over the last decade, a number of AKR1B10 inhibitors including aldose reductase inhibitors (ARIs), endogenous substances, natural-based derivatives and synthetic compounds have been developed, which could be novel anticancer drugs. This review provides an overview on related articles and patents about AKR1B10 inhibitors, with a focus on their inhibition selectivity and mechanism of function.

Characterization of WY 14,643 and its Complex with Aldose Reductase

The peroxisome proliferator, WY 14,643 exhibits a pure non-competitive inhibition pattern in the aldehyde reduction and in alcohol oxidation activities of human Aldose reductase (hAR). Fluorescence emission measurements of the equilibrium dissociation constants, Kd, of oxidized (hAR•NADP+) and reduced (hAR•NADPH) holoenzyme complexes display a 2-fold difference between them. Kd values for the dissociation of WY 14,643 from the oxidized (hAR•NADP+•WY 14,643) and reduced (hAR•NADPH•WY 14,643) ternary complexes are comparable to each other. The ternary complex structure of hAR•NADP+•WY 14,643 reveals the first structural evidence of a fibrate class drug binding to hAR. These observations demonstrate how fibrate molecules such as WY 14,643, besides being valued as agonists for PPAR, also inhibit hAR.

Substrate Specificity, Inhibitor Selectivity and Structure-Function Relationships of Aldo-Keto Reductase 1B15: A Novel Human Retinaldehyde Reductase

Human aldo-keto reductase 1B15 (AKR1B15) is a newly discovered enzyme which shares 92% amino acid sequence identity with AKR1B10. While AKR1B10 is a well characterized enzyme with high retinaldehyde reductase activity, involved in the development of several cancer types, the enzymatic activity and physiological role of AKR1B15 are still poorly known. Here, the purified recombinant enzyme has been subjected to substrate specificity characterization, kinetic analysis and inhibitor screening, combined with structural modeling. AKR1B15 is active towards a variety of carbonyl substrates, including retinoids, with lower kcat and Km values than AKR1B10. In contrast to AKR1B10, which strongly prefers all-trans-retinaldehyde, AKR1B15 exhibits superior catalytic efficiency with 9-cis-retinaldehyde, the best substrate found for this enzyme. With ketone and dicarbonyl substrates, AKR1B15 also shows higher catalytic activity than AKR1B10. Several typical AKR inhibitors do not significantly affect AKR1B15 activity. Amino acid substitutions clustered in loops A and C result in a smaller, more hydrophobic and more rigid active site in AKR1B15 compared with the AKR1B10 pocket, consistent with distinct substrate specificity and narrower inhibitor selectivity for AKR1B15.

Identification of a novel polyfluorinated compound as a lead to inhibit the human enzymes aldose reductase and AKR1B10: structure determination of both ternary complexes and implications for drug design

Aldo-keto reductases (AKRs) are mostly monomeric enzymes which fold into a highly conserved (α/β)8 barrel, while their substrate specificity and inhibitor selectivity are determined by interaction with residues located in three highly variable external loops. The closely related human enzymes aldose reductase (AR or AKR1B1) and AKR1B10 are of biomedical interest because of their involvement in secondary diabetic complications (AR) and in cancer, e.g. hepatocellular carcinoma and smoking-related lung cancer (AKR1B10). After characterization of the IC50 values of both AKRs with a series of polyhalogenated compounds, 2,2',3,3',5,5',6,6'-octafluoro-4,4'-biphenyldiol (JF0064) was identified as a lead inhibitor of both enzymes with a new scaffold (a 1,1'-biphenyl-4,4'-diol). An ultrahigh-resolution X-ray structure of the AR-NADP(+)-JF0064 complex has been determined at 0.85 Å resolution, allowing it to be observed that JF0064 interacts with the catalytic residue Tyr48 through a negatively charged hydroxyl group (i.e. the acidic phenol). The non-competitive inhibition pattern observed for JF0064 with both enzymes suggests that this acidic hydroxyl group is also present in the case of AKR1B10. Moreover, the combination of surface lysine methylation and the introduction of K125R and V301L mutations enabled the determination of the X-ray crystallographic structure of the corresponding AKR1B10-NADP(+)-JF0064 complex. Comparison of the two structures has unveiled some important hints for subsequent structure-based drug-design efforts.

X-ray structure of the V301L aldo-keto reductase 1B10 complexed with NADP(+) and the potent aldose reductase inhibitor fidarestat: implications for inhibitor binding and selectivity

Only one crystal structure is currently available for tumor marker AKR1B10, complexed with NADP(+) and tolrestat, which is an aldose reductase inhibitor (ARI) of the carboxylic acid type. Here, the X-ray structure of the complex of the V301L substituted AKR1B10 holoenzyme with fidarestat, an ARI of the cyclic imide type, was obtained at 1.60Å resolution by replacement soaking of crystals containing tolrestat. Previously, fidarestat was found to be safe in phase III trials for diabetic neuropathy and, consistent with its low in vivo side effects, was highly selective for aldose reductase (AR or AKR1B1) versus aldehyde reductase (AKR1A1). Now, inhibition studies showed that fidarestat was indeed 1300-fold more selective for AR as compared to AKR1B10, while the change of Val to Leu (found in AR) caused a 20-fold decrease in the IC50 value with fidarestat. Structural analysis of the V301L AKR1B10-fidarestat complex displayed enzyme-inhibitor interactions similar to those of the AR-fidarestat complex. However, a close inspection of both the new crystal structure and a computer model of the wild-type AKR1B10 complex with fidarestat revealed subtle changes that could affect fidarestat binding. In the crystal structure, a significant motion of loop A was observed between AR and V301L AKR1B10, linked to a Phe-122/Phe-123 side chain displacement. This was due to the presence of the more voluminous Gln-303 side chain (Ser-302 in AR) and of a water molecule buried in a subpocket located at the base of flexible loop A. In the wild-type AKR1B10 model, a short contact was predicted between the Val-301 side chain and fidarestat, but would not be present in AR or in V301L AKR1B10. Overall, these changes could contribute to the difference in inhibitory potency of fidarestat between AR and AKR1B10.

Biological role of aldo-keto reductases in retinoic Acid biosynthesis and signaling

Several aldo-keto reductase (AKR) enzymes from subfamilies 1B and 1C show retinaldehyde reductase activity, having low K(m) and k(cat) values. Only AKR1B10 and 1B12, with all-trans-retinaldehyde, and AKR1C3, with 9-cis-retinaldehyde, display high catalytic efficiency. Major structural determinants for retinaldehyde isomer specificity are located in the external loops (A and C for AKR1B10, and B for AKR1C3), as assessed by site-directed mutagenesis and molecular dynamics. Cellular models have shown that AKR1B and 1C enzymes are well suited to work in vivo as retinaldehyde reductases and to regulate retinoic acid (RA) biosynthesis at hormone pre-receptor level. An additional physiological role for the retinaldehyde reductase activity of these enzymes, consistent with their tissue localization, is their participation in β-carotene absorption. Retinaldehyde metabolism may be subjected to subcellular compartmentalization, based on enzyme localization. While retinaldehyde oxidation to RA takes place in the cytosol, reduction to retinol could take place in the cytosol by AKRs or in the membranes of endoplasmic reticulum by microsomal retinaldehyde reductases. Upregulation of some AKR1 enzymes in different cancer types may be linked to their induction by oxidative stress and to their participation in different signaling pathways related to cell proliferation. AKR1B10 and AKR1C3, through their retinaldehyde reductase activity, trigger a decrease in the RA biosynthesis flow, resulting in RA deprivation and consequently lower differentiation, with an increased cancer risk in target tissues. Rational design of selective AKR inhibitors could lead to development of novel drugs for cancer treatment as well as reduction of chemotherapeutic drug resistance.

Biomolecular chemistry of isopropyl fibrates

Isopropyl 2-[4-(4-chlorobenzoyl)-phenoxy]-2-methylpropanoic acid and isopropyl 2-(4-chlorophenoxy)-2-methylpropanoate, also known as fenofibrate and isopropyl (iPr) clofibrate, are hypolipidemic agents of the fibrate family. In a previously reported triclinic structure of fenofibrate (polymorph I), the methyl groups of the iPr moiety are located symmetrically about the carboxylate group. We report a new monoclinic form (polymorph II) of fenofibrate and a first structural description of iPr clofibrate, and in these the methyl groups are placed asymmetrically about the carboxylate group. In particular, the dihedral (torsion) angle between the hydrogen atom on the secondary C and the C atom of the carboxyl group makes a 2.74° angle about the ester O···C bond in the symmetric fenofibrate structure of polymorph I, whereas the same dihedral angle is 45.94° in polymorph II and -30.9° in the crystal structure of iPr clofibrate. Gas-phase density functional theory (DFT) geometry minimizations of fenofibrate and iPr clofibrate result in lowest energy conformations for both molecules with a value of about ±30° for this same angle between the OC-O-C plane and the C-H bond of the iPr group. A survey of crystal structures containing an iPr ester group reveals that the asymmetric conformation is predominant. Although the hydrogen atom on the secondary C atom of the iPr group is located at a comparable distance from the carbonyl oxygen in the symmetric and asymmetric fenofibrate (2.52 and 2.28 Å) and the iPr clofibrate (2.36 Å) structures, this hydrogen atom participates in a puckered five-membered ring arrangement in the latter two that is unlike the planar arrangement found in symmetric fenofibrate (polymorph I). Polar molecular surface area values indicate fenofibrate and iPr clofibrate are less able to act as acceptors of hydrogen bonds than their corresponding acid derivatives. Surface area calculations show that dynamic polar molecular surface area values of the iPr esters of the fibrates are lower than those of their acids, implying that the fibrates have better membrane permeability and a higher absorbability and hence are better prodrugs when these agents need to be orally administered.

AKR1B10 induces cell resistance to daunorubicin and idarubicin by reducing C13 ketonic group

Daunorubicin, idarubicin, doxorubicin and epirubicin are anthracyclines widely used for the treatment of lymphoma, leukemia, and breast, lung, and liver cancers, but tumor resistance limits their clinical success. Aldo-keto reductase family 1 B10 (AKR1B10) is an NADPH-dependent enzyme overexpressed in liver and lung carcinomas. This study was aimed to determine the role of AKR1B10 in tumor resistance to anthracyclines. AKR1B10 activity toward anthracyclines was measured using recombinant protein. Cell resistance to anthracycline was determined by ectopic expression of AKR1B10 or inhibition by epalrestat. Results showed that AKR1B10 reduces C13-ketonic group on side chain of daunorubicin and idarubicin to hydroxyl forms. In vitro, AKR1B10 converted daunorubicin to daunorubicinol at V(max) of 837.42±81.39nmol/mg/min, K(m) of 9.317±2.25mM and k(cat)/K(m) of 3.24. AKR1B10 showed better catalytic efficiency toward idarubicin with V(max) at 460.23±28.12nmol/mg/min, K(m) at 0.461±0.09mM and k(cat)/K(m) at 35.94. AKR1B10 was less active toward doxorubicin and epirubicin with a C14-hydroxyl group. In living cells, AKR1B10 efficiently catalyzed reduction of daunorubicin (50nM) and idarubicin (30nM) to corresponding alcohols. Within 24h, approximately 20±2.7% of daunorubicin (1μM) or 23±2.3% of idarubicin (1μM) was converted to daunorubicinol or idarubicinol in AKR1B10 expression cells compared to 7±0.9% and 5±1.5% in vector control. AKR1B10 expression led to cell resistance to daunorubicin and idarubicin, but inhibitor epalrestat showed a synergistic role with these agents. Together our data suggest that AKR1B10 participates in cellular metabolism of daunorubicin and idarubicin, resulting in drug resistance. These data are informative for the clinical use of idarubicin and daunorubicin.

Identification of aldo-keto reductase AKR1B10 as a selective target for modification and inhibition by prostaglandin A(1): implications for antitumoral activity

Cyclopentenone prostaglandins (cyPG) are reactive eicosanoids that may display anti-inflammatory and antiproliferative actions, possibly offering therapeutic potential. Here we report the identification of members of the aldo-keto reductase (AKR) family as selective targets of the cyPG prostaglandin A(1) (PGA(1)). AKR enzymes metabolize aldehydes and drugs containing carbonyl groups and are involved in inflammation and tumorigenesis. Thus, these enzymes represent a class of targets to develop small molecule inhibitors with therapeutic activity. Molecular modeling studies pointed to the covalent binding of PGA(1) to Cys299, close to the active site of AKR, with His111 and Tyr49, which are highly conserved in the AKR family, playing a role in PGA(1) orientation. Among AKR enzymes, AKR1B10 is considered as a tumor marker and contributes to tumor development and chemoresistance. We validated the direct modification of AKR1B10 by biotinylated PGA(1) (PGA(1)-B) in cells, and confirmed that mutation of Cys299 abolishes PGA(1)-B incorporation, whereas substitution of His111 or Tyr49 reduced the interaction. Modification of AKR1B10 by PGA(1) correlated with loss of enzymatic activity and both effects were increased by depletion of cellular glutathione. Moreover, in lung cancer cells PGA(1) reduced tumorigenic potential and increased accumulation of the AKR substrate doxorubicin, potentiating cell-cycle arrest induced by this chemotherapeutic agent. Our findings define PGA(1) as a new AKR inhibitor and they offer a framework to develop compounds that could counteract cancer chemoresistance.

Human and rodent aldo-keto reductases from the AKR1B subfamily and their specificity with retinaldehyde

NADP(H)-dependent cytosolic aldo-keto reductases (AKR) are mostly monomeric enzymes which fold into a typical (α/β)(8)-barrel structure. Substrate specificity and inhibitor selectivity are determined by interaction with residues located in three highly variable loops (A, B, and C). Based on sequence identity, AKR have been grouped into families, namely AKR1-AKR15, containing multiple subfamilies. Two human enzymes from the AKR1B subfamily (AKR1B1 and AKR1B10) are of special interest. AKR1B1 (aldose reductase) is related to secondary diabetic complications, while AKR1B10 is induced in cancer cells and is highly active with all-trans-retinaldehyde. Residues interacting with all-trans-retinaldehyde and differing between AKR1B1 and AKR1B10 are Leu125Lys and Val131Ala (loop A), Leu301Val, Ser303Gln, and Cys304Ser (loop C). Recently, we demonstrated the importance of Lys125 as a determinant of AKR1B10 specificity for retinoids. Residues 301 and 304 are also involved in interactions with substrates or inhibitors, and thus we checked their contribution to retinoid specificity. We also extended our study with retinoids to rodent members of the AKR1B subfamily: AKR1B3 (aldose reductase), AKR1B7 (mouse vas deferens protein), AKR1B8 (fibroblast-growth factor 1-regulated protein), and AKR1B9 (Chinese hamster ovary reductase), which were tested against all-trans isomers of retinaldehyde and retinol. All enzymes were active with retinaldehyde, but with k(cat) values (0.02-0.52 min(-1)) much lower than that of AKR1B10 (27 min(-1)). None of the enzymes showed oxidizing activity with retinol. Since these enzymes (except AKR1B3) have Lys125, other residues should account for retinaldehyde specificity. Here, by using site-directed mutagenesis and molecular modeling, we further delineate the contribution of residues 301 and 304. We demonstrate that besides Lys125, Ser304 is a major structural determinant for all-trans-retinaldehyde specificity of AKR1B10.

Selective inhibition of the tumor marker AKR1B10 by antiinflammatory N-phenylanthranilic acids and glycyrrhetic acid

A human aldose reductase-like protein, AKR1B10 in the aldo-keto reductase (AKR) superfamily, was recently identified as a tumor marker of several types of cancer. Tolrestat, an aldose reductase inhibitor (ARI), is known to be the most potent inhibitor of the enzyme. In this study, we compared the inhibitory effects of other ARIs including flavonoids on AKR1B10 and aldose reductase to evaluate their specificity. However, ARIs showed lower inhibitory potency for AKR1B10 than for aldose reductase. In the search for potent and selective inhibitors of AKR1B10 from other drugs used clinically, we found that non-steroidal antiinflammatory N-phenylanthranilic acids, diclofenac and glycyrrhetic acid competitively inhibited AKR1B10, showing K(i) values of 0.35-2.9 microM and high selectivity to this enzyme (43-57 fold versus aldose reductase). Molecular docking studies of mefenamic acid and glycyrrhetic acid in the AKR1B10-nicotinamide adenine dinucleotide phosphate (NADP(+)) complex and site-directed mutagenesis of the putative binding residues suggest that the side chain of Val301 and a hydrogen-bonding network among residues Val301, Gln114 and Ser304 are important for determining the inhibitory potency and selectivity of the non-steroidal antiinflammatory drugs. Thus, the potent and selective inhibition may be related to the cancer chemopreventive roles of the drugs, and their structural features may facilitate the design of new anti-cancer agents targeting AKR1B10.

Smoking-induced upregulation of AKR1B10 expression in the airway epithelium of healthy individuals

BACKGROUND

The aldo-keto reductase (AKR) gene superfamily codes for monomeric, soluble reduced nicotinamide adenine dinucleotide phosphate-dependent oxidoreductases that mediate elimination reactions. AKR1B10, an AKR that eliminates retinals, has been observed as upregulated in squamous metaplasia and non-small cell lung cancer and has been suggested as a diagnostic marker specific to tobacco-related carcinogenesis. We hypothesized that upregulation of AKR1B10 expression may be initiated in healthy smokers prior to the development of evidence of lung cancer.

METHODS

Expression of AKR1B10 was assessed at the mRNA level using microarrays with TaqMan confirmation in the large airway epithelium (21 healthy nonsmokers, 31 healthy smokers) and small airway epithelium (51 healthy nonsmokers, 58 healthy smokers) obtained by fiberoptic bronchoscopy and brushing.

RESULTS

Compared with healthy nonsmokers, AKR1B10 mRNA levels were significantly upregulated in both large and small airway epithelia of healthy smokers. Consistent with the mRNA data, AKR1B10 protein was significantly upregulated in the airway epithelium of healthy smokers as assessed by Western blot analysis and immunohistochemistry, with AKR1B10 expressed in both differentiated and basal cells. Finally, cigarette smoke extract mediated upregulation of AKR1B10 in airway epithelial cells in vitro, and transfection of AKR1B10 into airway epithelial cells enhanced the conversion of retinal to retinol.

CONCLUSIONS

Smoking per se mediates upregulation of AKR1B10 expression in the airway epithelia of healthy smokers with no evidence of lung cancer. In the context of these observations and the link of AKR1B10 to the metabolism of retinals and to lung cancer, the smoking-induced upregulation of AKR1B10 may be an early process in the multiple events leading to lung cancer.

Potent and selective inhibition of the tumor marker AKR1B10 by bisdemethoxycurcumin: probing the active site of the enzyme with molecular modeling and site-directed mutagenesis

A human member of the aldo-keto reductase (AKR) superfamily, AKR1B10, shares high sequence identity with aldose reductase (AR), and was recently identified as a therapeutic target in the treatment of several types of cancer. We have compared the inhibitory effects of plant components on recombinant AKR1B10 and AR. AKR1B10 was inhibited by curcuminoids, magnolol, honokiol and resveratrol, with IC(50) values of 0.06-5 microM, which were lower than their values for AR. Among them, bisdemethoxycurcumin was the most potent competitive inhibitor (K(i)=22 nM) with the highest selectivity (85-fold versus AR), and acted as an effective inhibitor in cellular level. In contrast, demethoxycurcumin and curcumin showed >3-fold less potency and selectivity. Molecular docking studies of the curcuminoids in the AKR1B10-NADP(+) complex and site-directed mutagenesis of the putative binding residues suggest that Gln114, Val301 and Gln303 are important for determining the inhibitory potency and selectivity of the curcuminoids.

Aldo-keto reductase family 1 member B10 promotes cell survival by regulating lipid synthesis and eliminating carbonyls

Aldo-keto reductase family 1 member B10 (AKR1B10) is primarily expressed in the normal human colon and small intestine but overexpressed in liver and lung cancer. Our previous studies have shown that AKR1B10 mediates the ubiquitin-dependent degradation of acetyl-CoA carboxylase-alpha. In this study, we demonstrate that AKR1B10 is critical to cell survival. In human colon carcinoma cells (HCT-8) and lung carcinoma cells (NCI-H460), small-interfering RNA-induced AKR1B10 silencing resulted in caspase-3-mediated apoptosis. In these cells, the total and subspecies of cellular lipids, particularly of phospholipids, were decreased by more than 50%, concomitant with 2-3-fold increase in reactive oxygen species, mitochondrial cytochrome c efflux, and caspase-3 cleavage. AKR1B10 silencing also increased the levels of alpha,beta-unsaturated carbonyls, leading to the 2-3-fold increase of cellular lipid peroxides. Supplementing the HCT-8 cells with palmitic acid (80 mum), the end product of fatty acid synthesis, partially rescued the apoptosis induced by AKR1B10 silencing, whereas exposing the HCT-8 cells to epalrestat, an AKR1B10 inhibitor, led to more than 2-fold elevation of the intracellular lipid peroxides, resulting in apoptosis. These data suggest that AKR1B10 affects cell survival through modulating lipid synthesis, mitochondrial function, and oxidative status, as well as carbonyl levels, being an important cell survival protein.

Kinetic studies of AKR1B10, human aldose reductase-like protein: endogenous substrates and inhibition by steroids

A human member of the aldo-keto reductase (AKR) superfamily, AKR1B10, was identified as a biomarker of lung cancer, exhibiting high sequence identity with human aldose reductase (AKR1B1). Using recombinant AKR1B10 and AKR1B1, we compared their substrate specificity for biogenic compounds and inhibition by endogenous compounds and found the following unique features of AKR1B10. AKR1B10 efficiently reduced long-chain aliphatic aldehydes including farnesal and geranylgeranial, which are generated from degradation of prenylated proteins and metabolism of farnesol and geranylgeraniol derived from the mevalonate pathway. The enzyme oxidized aliphatic and aromatic alcohols including 20alpha-hydroxysteroids. In addition, AKR1B10 was inhibited by steroid hormones, bile acids and their metabolites, showing IC(50) values of 0.03-25 microM. Kinetic analyses of the alcohol oxidation and inhibition by the steroids and tolrestat, together with the docked model of AKR1B10-inhibitor complex, suggest that the inhibitory steroids and tolrestat bind to overlapping sites within the active site of the enzyme-coenzyme complex. Thus, we propose a novel role of AKR1B10 in controlling isoprenoid homeostasis that is important in cholesterol synthesis and cell proliferation through salvaging isoprenoid alcohols, as well as its metabolic regulation by endogenous steroids.

Fibrates in the chemical action of daunorubicin

Anthracyclines are an important reagent in many chemotherapy regimes for treating a wide range of tumors. One of the primary mechanisms of anthracycline action involves DNA damage caused by inhibition of topoisomerase II. Enzymatic detoxification of anthracycline is a major critical factor that determines anthracycline resistance. Natural product, daunorubicin a toxic analogue of anthracycline is reduced to less toxic daunorubicinol by the AKR1B10, enzyme, which is overexpressed in most cases of smoking associate squamous cell carcinoma (SCC) and adenocarcinoma. In addition, AKR1B10 was discovered as an enzyme overexpressed in human liver, cervical and endometrial cancer cases in samples from uterine cancer patients. Also, the expression of AKR1B10 was associated with tumor recurrence after surgery and keratinization of squamous cell carcinoma in cervical cancer and estimated to have the potential as a tumor intervention target colorectal cancer cells (HCT-8) and diagnostic marker for non-small-cell lung cancer. This article presents the mechanism of daunorubicin action and a method to improve the effectiveness of daunorubicin by modulating the activity of AKR1B10.

Cancer biomarker AKR1B10 and carbonyl metabolism

A member of the aldo-keto reductase (AKR) protein superfamily, AKR1B10, is overexpressed in human liver cancers as well as in many adenocarcinoma cases due to smoking. AKR1B10 is also detected in instances of cervical and endometrial cancer in uterine cancer patients. In addition, AKR1B10 has been identified as a biomarker for non-small-cell lung cancer by a combined bioinformatics and clinical analysis. Furthermore, in breast cancer cells, fatty acid biosynthesis is regulated by AKR1B10. AKR1B10 contains 316 residues, shares 70% sequence identity with aldose reductase (AKR1B1) and has the conserved Cys residue at position 299. Carbonyl groups in some anticancer drugs and dl-glyceraldehyde are converted by AKR1B10 to their corresponding alcohols. The anticancer drug daunorubicin, which is currently used in the clinical treatment of various forms of cancer, is converted by AKR1B10 to daunorubicinol with a K(m) and k(cat) of 1.1+/-0.18 mM and 1.4+/-0.16 min(-1), respectively. This carbonyl reducing activity of AKR1B10 decreases the anticancer effectiveness of daunorubicin. Similarly, kinetic parameters K(m) and k(cat) (NADPH, DL-glyceraldehyde) for the reduction of dl-glyceraldehyde by wild-type AKR1B10 are 2.2+/-0.2 mM and 0.71+/-0.05 sec(-1), respectively. Mutation of residue 299 from Cys to Ser in AKR1B10 reduces the protein affinity for dl-glyceraldehyde and enhances AKR1B10's catalytic activity but overall catalytic efficiency is reduced. For dl-glyceraldehyde reduction that is catalyzed by the Cys299Ser mutant AKR1B10, K(m) is 15.8+/-1.0mM and k(cat) (NADPH, DL-glyceraldehyde) is 2.8+/-0.2 sec(-1). This implies that the substrate specificity of AKR1B10 is drastically affected by mutation of residue 299 from Cys to Ser. In the present paper, we use this mutation in AKR1B10 to characterize a library of compounds regarding their different inhibitory potency on the carbonyl reducing activity of wild-type and the Cys299Ser mutant AKR1B10.

Characterization of a rat NADPH-dependent aldo-keto reductase (AKR1B13) induced by oxidative stress

A rat aldo-keto reductase (AKR1B13) was identified as a hepatoma-derived protein, exhibiting high sequence identity with mouse fibroblast growth factor (FGF)-induced reductase, AKR1B8. In this study, AKR1B13 was characterized in terms of its enzymatic properties, tissue distribution and regulation. Recombinant AKR1B13 exhibited NADPH-linked reductase activity towards various aldehydes and alpha-dicarbonyl compounds, which include reactive compounds such as methylglyoxal, glyoxal, acrolein, 4-hydroxynonenal and 3-deoxyglucosone. The enzyme exhibited low NADP(+)-linked dehydrogenase activity towards aliphatic and aromatic alcohols, and was inhibited by aldose reductase inhibitors, flavonoids, benzbromarone and hexestrol. Immunochemical and reverse transcription-PCR analyses revealed that the enzyme is expressed in many rat tissues, endothelial cells and fibroblasts. Gene expression in YPEN-1 and NRK cells was up-regulated by treatments with submicromolar concentrations of hydrogen peroxide and 1,4-naphthoquinone, but not with FGF-1, FGF-2, 5alpha-dihydrotestosterone and 17beta-estradiol. These results indicate that AKR1B13 differs from AKR1B8 in tissue distribution and gene regulation, and suggest that it functions as a defense system against oxidative stress in rat tissues.

The aldo-keto reductase superfamily and its role in drug metabolism and detoxification

The aldo-keto reductase (AKR) superfamily comprises enzymes that catalyze redox transformations involved in biosynthesis, intermediary metabolism, and detoxification. Substrates of AKRs include glucose, steroids, glycosylation end-products, lipid peroxidation products, and environmental pollutants. These proteins adopt a (beta/alpha)(8) barrel structural motif interrupted by a number of extraneous loops and helixes that vary between proteins and bring structural identity to individual families. The human AKR family differs from the rodent families. Due to their broad substrate specificity, AKRs play an important role in the phase II detoxification of a large number of pharmaceuticals, drugs, and xenobiotics.