A High-Throughput Dose-Response Cellular Thermal Shift Assay for Rapid Screening of Drug Target Engagement in Living Cells, Exemplified Using SMYD3 and IDO1.

A persistent problem in early small-molecule drug discovery is the frequent lack of rank-order correlation between biochemical potencies derived from initial screens using purified proteins and the diminished potency and efficacy observed in subsequent disease-relevant cellular phenotypic assays. The introduction of the cellular thermal shift assay (CETSA) has bridged this gap by enabling assessment of drug target engagement directly in live cells based on ligand-induced changes in protein thermal stability. Initial success in applying CETSA across multiple drug target classes motivated our investigation into replacing the low-throughput, manually intensive Western blot readout with a quantitative, automated higher-throughput assay that would provide sufficient capacity to use CETSA as a primary hit qualification strategy. We introduce a high-throughput dose-response cellular thermal shift assay (HTDR-CETSA), a single-pot homogenous assay adapted for high-density microtiter plate format. The assay features titratable BacMam expression of full-length target proteins fused to the DiscoverX 42 amino acid ePL tag in HeLa suspension cells, facilitating enzyme fragment complementation-based chemiluminescent quantification of ligand-stabilized soluble protein. This simplified format can accommodate determination of full-dose CETSA curves for hundreds of individual compounds/analyst/day in replicates. HTDR-CETSA data generated for substrate site and alternate binding mode inhibitors of the histone-lysine N-methyltransferase SMYD3 in HeLa suspension cells demonstrate excellent correlation with rank-order potencies observed in cellular mechanistic assays and direct translation to target engagement of endogenous Smyd3 in cancer-relevant cell lines. We envision this workflow to be generically applicable to HTDR-CETSA screening spanning a wide variety of soluble intracellular protein target classes.

Favorable Outcomes of Preterm Infants With Parenteral Nutrition-associated Liver Disease Treated With Intravenous Fish Oil-based Lipid Emulsion.

OBJECTIVES: The aim of the study was to determine the acute and long-term outcomes of preterm infants treated with an intravenous fish oil-based lipid emulsion (FishLE) for parenteral nutrition-associated liver disease (PNALD). METHODS: Preterm infants 14 days to 24 months of age with anatomic short gut or severe intestinal dysmotility, serum direct bilirubin ≥4 mg/dL, and requiring >60% calories from parenteral nutrition were eligible. Enrolled infants received 1 g ·â€Škg ·â€Šday of FishLE until resolution of direct hyperbilirubinemia or return of enteral nutrition. Acute clinical effects and biochemical markers of liver function were monitored. Growth and developmental scores at 6 and 12 months postmenstrual age (PMA) were assessed and compared with controls matched by gestational age (GA). RESULTS: Thirteen patients with mean GA of 28 ±â€Š4 weeks were treated and compared with 119 GA-matched controls. Their mean direct bilirubin was 9.8 ±â€Š6.4 mg/dL at enrollment. All infants had resolution of cholestasis after study completion. There were no acute adverse events, deaths, or liver/intestinal transplants. Weight and head circumference were similar between FishLE-treated patients and controls at 6- and 12-month PMA. Cognitive and motor scores were decreased at 6 and 12 months PMA in FishLE-treated infants. Logistic regression analysis showed that prolonged hospitalization was detrimental to cognitive and motor development, whereas treatment was not. CONCLUSIONS: The use of intravenous FishLEs in premature infants appears to be safe and reverses PNALD despite significant liver disease and intestinal failure. This therapy should be used in preterm infants with PNALD and followed long term to evaluate development.

Multicenter study of pectus excavatum, final report: complications, static/exercise pulmonary function, and anatomic outcomes.

BACKGROUND: A multicenter study of pectus excavatum was described previously. This report presents our final results. STUDY DESIGN: Patients treated surgically at 11 centers were followed prospectively. Each underwent a preoperative evaluation with CT scan, pulmonary function tests, and body image survey. Data were collected about associated conditions, complications, and perioperative pain. One year after treatment, patients underwent repeat chest CT scan, pulmonary function tests, and body image survey. A subset of 50 underwent exercise pulmonary function testing. RESULTS: Of 327 patients, 284 underwent Nuss procedure and 43 underwent open procedure without mortality. Of 182 patients with complete follow-up (56%), 18% had late complications, similarly distributed, including substernal bar displacement in 7% and wound infection in 2%. Mean initial CT scan index of 4.4 improved to 3.0 post operation (severe >3.2, normal = 2.5). Computed tomography index improved at the deepest point (xiphoid) and also upper and middle sternum. Pulmonary function tests improved (forced vital capacity from 88% to 93%, forced expiratory volume in 1 second from 87% to 90%, and total lung capacity from 94% to 100% of predicted (p < 0.001 for each). VO2 max during peak exercise increased by 10.1% (p = 0.015) and O2 pulse by 19% (p = 0.007) in 20 subjects who completed both pre- and postoperative exercise tests. CONCLUSIONS: There is significant improvement in lung function at rest and in VO2 max and O2 pulse after surgical correction of pectus excavatum, with CT index >3.2. Operative correction significantly reduces CT index and markedly improves the shape of the entire chest, and can be performed safely in a variety of centers.

A small molecule modulates Jumonji histone demethylase activity and selectively inhibits cancer growth.

The pharmacological inhibition of general transcriptional regulators has the potential to block growth through targeting multiple tumorigenic signalling pathways simultaneously. Here, using an innovative cell-based screen, we identify a structurally unique small molecule (named JIB-04) that specifically inhibits the activity of the Jumonji family of histone demethylases in vitro, in cancer cells, and in tumours in vivo. Unlike known inhibitors, JIB-04 is not a competitive inhibitor of α-ketoglutarate. In cancer, but not in patient-matched normal cells, JIB-04 alters a subset of transcriptional pathways and blocks viability. In mice, JIB-04 reduces tumour burden and prolongs survival. Importantly, we find that patients with breast tumours that overexpress Jumonji demethylases have significantly lower survival. Thus, JIB-04, a novel inhibitor of Jumonji demethylases in vitro and in vivo, constitutes a unique potential therapeutic and research tool against cancer, and validates the use of unbiased cellular screens to discover chemical modulators with disease relevance.

Dysmorphology of chest wall deformities: frequency distribution of subtypes of typical pectus excavatum and rare subtypes.

BACKGROUND/PURPOSE: More than forty percent of patients with pectus excavatum have a family history of chest deformity. However, no studies of the frequency of the different phenotypes of pectus excavatum have been published. METHODS: A random sample of 300 non-syndromic pectus excavatum patients, from the chest wall deformities clinic at Children's Hospital of The King's Daughters in Norfolk, Va., was studied and classified according to a previously described classification system. Photographs and computed tomography (CT) scans were utilized. RESULTS: Typical pectus excavatum. Photo data: localized deep depression (cup-shaped) deformity occurred in 67%; diffuse (saucer-shaped) 21%, trench-like (furrow-shaped) 10%, and Currarino-Silverman (mixed pectus excavatum/chondromanubrial carinatum) 1%. The deepest point was to the right of midline in 80%, left in 10% and central in 10%. By photo, the deepest point was in the lower sternum in 75%. When asymmetric, the deepest point of the deformity was to the right of midline in 90%. CT data: the average Haller index was 4.9. Severe sternal torsion (>30 degrees) was associated with greater Haller index (6.3) than mild torsion (4.5). The deepest point of the depression was at the mid- or lower sternum in more than 99%. It proved impossible to estimate width or length of the depression because of poorly defined borders. CONCLUSIONS: Typical PE is cup-shaped in 67% of cases, to the right of the midline in 80%, and involving the mid-to-lower sternum in 99%. However, other phenotypes, like the saucer and long trench, comprised one-third. Definition of the deformity is more reliable by CT scan.

Methods for Activity Analysis of the Proteins that Regulate Histone Methylation.

The enzymes that regulate histone methylation states and the protein domains that recognize methylated histone residues have been implicated in a number of human diseases, including cancer, as a result of their ability to affect transcriptional changes by altering chromatin structure. These proteins are recognized as potential therapeutic targets for the treatment of diseases associated with epigenetic disruption; however, few inhibitors of their activity have been identified. The majority of histone demethylase and methyltransferase enzyme inhibitors have been discovered on the basis of their structural similarity to substrates or known inhibitors of enzymes with analogous mechanisms. The general lack of potency and specificity of these compounds indicates that novel chemotypes are needed to address the large number of recently discovered histone-modifying enzymes. High-throughput screening (HTS) allows rapid testing of chemically diverse small molecule libraries, provided assays amenable to HTS exist. Here we review the biochemical and cellular assays available for testing the proteins and enzymes that regulate histone methylation. Progress in the development of high-throughput, sensitive, and robust assays will enable discovery of small molecules for epigenetic therapy.

Specificity of human aldo-keto reductases, NAD(P)H:quinone oxidoreductase, and carbonyl reductases to redox-cycle polycyclic aromatic hydrocarbon diones and 4-hydroxyequilenin-o-quinone.

Polycyclic aromatic hydrocarbons (PAHs) are suspect human lung carcinogens and can be metabolically activated to remote quinones, for example, benzo[a]pyrene-1,6-dione (B[a]P-1,6-dione) and B[a]P-3,6-dione by the action of either P450 monooxygenase or peroxidases, and to non-K region o-quinones, for example B[a]P-7,8-dione, by the action of aldo keto reductases (AKRs). B[a]P-7,8-dione also structurally resembles 4-hydroxyequilenin o-quinone. These three classes of quinones can redox cycle, generate reactive oxygen species (ROS), and produce the mutagenic lesion 8-oxo-dGuo and may contribute to PAH- and estrogen-induced carcinogenesis. We compared the ability of a complete panel of human recombinant AKRs to catalyze the reduction of PAH o-quinones in the phenanthrene, chrysene, pyrene, and anthracene series. The specific activities for NADPH-dependent quinone reduction were often 100-1000 times greater than the ability of the same AKR isoform to oxidize the cognate PAH-trans-dihydrodiol. However, the AKR with the highest quinone reductase activity for a particular PAH o-quinone was not always identical to the AKR isoform with the highest dihydrodiol dehydrogenase activity for the respective PAH-trans-dihydrodiol. Discrete AKRs also catalyzed the reduction of B[a]P-1,6-dione, B[a]P-3,6-dione, and 4-hydroxyequilenin o-quinone. Concurrent measurements of oxygen consumption, superoxide anion, and hydrogen peroxide formation established that ROS were produced as a result of the redox cycling. When compared with human recombinant NAD(P)H:quinone oxidoreductase (NQO1) and carbonyl reductases (CBR1 and CBR3), NQO1 was a superior catalyst of these reactions followed by AKRs and last CBR1 and CBR3. In A549 cells, two-electron reduction of PAH o-quinones causes intracellular ROS formation. ROS formation was unaffected by the addition of dicumarol, suggesting that NQO1 is not responsible for the two-electron reduction observed and does not offer protection against ROS formation from PAH o-quinones.

Quantitative high-throughput screening identifies 8-hydroxyquinolines as cell-active histone demethylase inhibitors.

BACKGROUND: Small molecule modulators of epigenetic processes are currently sought as basic probes for biochemical mechanisms, and as starting points for development of therapeutic agents. N(ε)-Methylation of lysine residues on histone tails is one of a number of post-translational modifications that together enable transcriptional regulation. Histone lysine demethylases antagonize the action of histone methyltransferases in a site- and methylation state-specific manner. N(ε)-Methyllysine demethylases that use 2-oxoglutarate as co-factor are associated with diverse human diseases, including cancer, inflammation and X-linked mental retardation; they are proposed as targets for the therapeutic modulation of transcription. There are few reports on the identification of templates that are amenable to development as potent inhibitors in vivo and large diverse collections have yet to be exploited for the discovery of demethylase inhibitors. PRINCIPAL FINDINGS: High-throughput screening of a ∼236,000-member collection of diverse molecules arrayed as dilution series was used to identify inhibitors of the JMJD2 (KDM4) family of 2-oxoglutarate-dependent histone demethylases. Initial screening hits were prioritized by a combination of cheminformatics, counterscreening using a coupled assay enzyme, and orthogonal confirmatory detection of inhibition by mass spectrometric assays. Follow-up studies were carried out on one of the series identified, 8-hydroxyquinolines, which were shown by crystallographic analyses to inhibit by binding to the active site Fe(II) and to modulate demethylation at the H3K9 locus in a cell-based assay. CONCLUSIONS: These studies demonstrate that diverse compound screening can yield novel inhibitors of 2OG dependent histone demethylases and provide starting points for the development of potent and selective agents to interrogate epigenetic regulation.

Protein lysine methyltransferase G9a inhibitors: design, synthesis, and structure activity relationships of 2,4-diamino-7-aminoalkoxy-quinazolines.

Protein lysine methyltransferase G9a, which catalyzes methylation of lysine 9 of histone H3 (H3K9) and lysine 373 (K373) of p53, is overexpressed in human cancers. Genetic knockdown of G9a inhibits cancer cell growth, and the dimethylation of p53 K373 results in the inactivation of p53. Initial SAR exploration of the 2,4-diamino-6,7-dimethoxyquinazoline template represented by 3a (BIX01294), a selective small molecule inhibitor of G9a and GLP, led to the discovery of 10 (UNC0224) as a potent G9a inhibitor with excellent selectivity. A high resolution X-ray crystal structure of the G9a-10 complex, the first cocrystal structure of G9a with a small molecule inhibitor, was obtained. On the basis of the structural insights revealed by this cocrystal structure, optimization of the 7-dimethylaminopropoxy side chain of 10 resulted in the discovery of 29 (UNC0321) (Morrison K(i) = 63 pM), which is the first G9a inhibitor with picomolar potency and the most potent G9a inhibitor to date.

A chemiluminescence-based method for identification of histone lysine methyltransferase inhibitors.

Methylation of lysine residues, catalyzed by histone methyltransferase (HMT) enzymes, is one of many modifications of core histone proteins that regulate transcription and chromatin structure. G9a is the predominant HMT in mammalian euchromatin and recent data suggest that it is required to perpetuate a malignant phenotype in cancer cells and is implicated in metastasis, supporting this HMT as a therapeutic target for cancer and other diseases associated with epigenetic regulation. Of the methods currently used to measure methyltransferase activity, many involve a separation step or utilize coupling enzymes complicating implementation and data interpretation. Here we describe a homogeneous assay to measure G9a HMT activity using the chemiluminescence-based AlphaScreen immunoassay technology. Methylation of biotinylated-histone peptide is measured through specific antibody-based detection, in conjunction with streptavidin-coated donor and secondary antibody-coated acceptor beads. The method is particularly well suited for detection of inhibitors acting by the desired histone peptide competitive mechanism and is applicable to testing other HMTs, demonstrated here with the G9a homolog EHMT1, also known as GLP.

A highly potent and selective caspase 1 inhibitor that utilizes a key 3-cyanopropanoic acid moiety.

Herein, we examine the potential of a nitrile-containing propionic acid moiety as an electrophile for covalent attack by the active-site cysteine residue of caspase 1. The syntheses of several cyanopropanate-containing small molecules based on the optimized peptidic scaffold of prodrug VX-765 were accomplished. These compounds were found to be potent inhibitors of caspase 1 (IC(50) values < or =1 nM). Examination of these novel small molecules against a caspase panel demonstrated an impressive degree of selectivity for caspase 1 inhibition over other caspase isozymes. Assessment of hydrolytic stability and selected ADME properties highlighted these agents as potentially useful tools for studying caspase 1 down-regulation in various settings, including in vivo analyses.

A homogeneous method for investigation of methylation-dependent protein-protein interactions in epigenetics.

Methylation of lysine residues on the tails of histone proteins is a major determinant of the transcription state of associated DNA coding regions. The interplay among methylation states and other histone modifications to direct transcriptional outcome is referred to as the histone code. In addition to histone methyltransferases and demethylases which function to modify the methylation state of lysine sidechains, other proteins recognize specific histone methylation marks essentially serving as code readers. While these interactions are highly specific with respect to site and methylation state of particular lysine residues, they are generally weak and therefore difficult to monitor by traditional assay techniques. Herein, we present the design and implementation of a homogeneous, miniaturizable, and sensitive assay for histone methylation-dependent interactions. We use AlphaScreen, a chemiluminescence-based technique, to monitor the interactions of chromodomains (MPP8, HP1beta and CHD1), tudor domains (JMJD2A) and plant homeodomains (RAG2) with their cognate trimethyllysine histone partners. The utility of the method was demonstrated by profiling the binding specificities of chromo- and tudor domains toward several histone marks. The simplicity of design and the sensitive and robust nature of this assay should make it applicable to a range of epigenetic studies, including the search for novel inhibitors of methylation-dependent interactions.

A monoclonal antibody for detection of folylpolyglutamate synthetase in paraffin embedded tissues.

Folate biochemical pathway enzymes such as folylpolyglutamate synthetase (FPGS) are key elements in the folate pathway. The role of FPGS is to add glutamate residues to folates and antifolates, trapping them in the cell and increasing their affinity for subsequent enzymatic reactions. FPGS may also be an indicator of response to both clinically established and novel antifolate drugs such as pemetrexed; knowledge of their level of expression in tumors may enable their optimal use by identifying potentially responsive subgroups of patients. In spite of its key role in both nucleotide biosynthesis and possible role as a determinant of response in chemotherapy, monoclonal antibodies to FPGS suitable for immunohistochemical analysis of formalin fixed and paraffin embedded biopsy samples, or that can be used for Western blot analysis, are not commercially available. The aim of this study was to generate a monoclonal antibody that could be used to detect specific expression of FPGS in paraffin embedded tissues. A 228 amino acid region of the FPGS sequence was expressed as a recombinant fusion protein and used as an antigen to generate monoclonal antibodies. ELISA and Western blot studies identified specific reactivity of the NN3.2 antibody to the recombinant protein and a single 60 kDa protein in whole cell lysates from cell lines known to express FPGS. Immunohistochemical analysis of FPGS using hybridoma clone NN3.2 in a panel of normal tissues demonstrated wide expression including strong immunoreactivity in the brush border and crypts of colon, liver hepatocytes, and lymphoid cells. Analysis of a panel of malignant and benign tissues demonstrated wide expression with variable intensities of staining and patterns of cytoplasmic reactivity. Stronger staining was observed in malignant tissue compared with that of normal adjacent tissue, particularly in ovarian and colon adenocarcinoma cases. Our results show that clone NN3.2 is a sensitive tool for detection of FPGS in paraffin-embedded tissues.

Phospho-STAT5 and phospho-Akt expression in chronic myeloproliferative neoplasms.

The majority of Myeloproliferative Neoplasms (MPNs) are characterised by mutations in genes encoding molecules or receptors involved in cell signalling, the most common being the JAK2 V617F mutation. This mutation leads to ligand-independent activation of downstream signalling pathways by constitutive phosphorylation. The signalling pathways affected include the Janus kinase-signal transducers and activators of transcription (JAK-STAT) and phosphotidylinositide-3 kinase (PI3K) pathways, which regulate cell survival and apoptosis respectively. Monoclonal antibodies to phospho-STAT5 and phospho-Akt were generated and assessed by immunocytochemistry on bone marrow biopsies of MPN patients with JAK2 V617F, JAK2 exon 12, MPL exon 10 and KIT D816V mutations. JAK2 V617F mutation was associated with significantly increased levels of phosphorylated STAT5 and Akt in haemopoietic cells, most marked in megakaryocytes. In contrast, JAK2 exon 12 and MPL exon 10 mutations did not affect the level of phosphorylation. In systemic mastocytosis with KIT D618V mutation there was significantly increased expression of phosphorylated STAT5 and Akt in neoplastic mast cells although there was no change in the expression in other haemopoietic cells. JAK2 V617F is associated with upregulated phosphorylation of STAT5 and Akt in megakaryocytes, and to a lesser extent in other haemopoietic cells. Immunocytochemistry of bone marrow trephines for these phospho-proteins can be used as a supplementary diagnostic test with a high negative predictive value.

Surgical repair of pectus excavatum markedly improves body image and perceived ability for physical activity: multicenter study.

OBJECTIVE: This study evaluated changes in both physical and psychosocial quality of life reported by the parent and child after surgical repair of pectus excavatum. METHODS: As part of a multicenter study of pectus excavatum, a previously validated tool called the Pectus Excavatum Evaluation Questionnaire was administered by the research coordinator, via telephone, to parents and patients (8-21 years of age) before and 1 year after surgery. Eleven North American children's hospitals participated. From 2001 to 2006, 264 patients and 291 parents completed the initial questionnaire, and 247 patients and 274 parents completed the postoperative questionnaire. Responses used a Likert-type scale of 1 to 4, reflecting the extent or frequency of a particular experience, with higher values conveying less-desirable experience. RESULTS: Preoperative psychosocial functioning was unrelated to objective pectus excavatum severity (computed tomographic index). Patients and their parents reported significant positive postoperative changes. Improvements occurred in both physical and psychosocial functioning, including less social self-consciousness and a more-favorable body image. For children, the body image component improved from 2.30+/-0.62 (mean+/-SD) to 1.40+/-0.42 after surgery and the physical difficulties component improved from 2.11+/-0.82 to 1.37+/-0.44. For the parent questionnaire, the child's emotional difficulties improved from 1.81+/-0.70 to 1.24+/-0.36, social self-consciousness improved from 2.86+/-1.03 to 1.33+/-0.68, and physical difficulties improved from 2.14+/-0.75 to 1.32+/-0.39. Ninety-seven percent of patients thought that surgery improved how their chest looked. CONCLUSIONS: Surgical repair of pectus excavatum can significantly improve the body image difficulties and limitations on physical activity experienced by patients. These results should prompt physicians to consider the physiologic and psychological implications of pectus excavatum just as they would any other physical deformity known to have such consequences.

Oxidation of PAH trans-dihydrodiols by human aldo-keto reductase AKR1B10.

AKR1B10 has been identified as a potential biomarker for human nonsmall cell lung carcinoma and as a tobacco exposure and response gene. AKR1B10 functions as an efficient retinal reductase in vitro and may regulate retinoic acid homeostasis. However, the possibility that this enzyme is able to activate polycyclic aromatic hydrocarbon (PAH) trans-dihydrodiols to form reactive and redox-active o-quinones has not been investigated to date. AKR1B10 was found to oxidize a wide range of PAH trans-dihydrodiol substrates in vitro to yield PAH o-quinones. Reactions of AKR1B10 proceeded with improper stereochemistry, since it was specific for the minor (+)-benzo[a]pyrene-7S,8S-dihydrodiol diastereomer formed in vivo. However, AKR1B10 displayed reasonable activity in the oxidation of both the (-)-R,R and (+)-S,S stereoisomers of benzo[g]chrysene-11,12-dihydrodiol and oxidized the potentially relevant, albeit minor, (+)-benz[a]anthracene-3S,4S-dihydrodiol metabolite. We find that AKR1B10 is therefore likely to play a contributing role in the activation of PAH trans-dihydrodiols in human lung. AKR1B10 retinal reductase activity was confirmed in vitro and found to be 5- to 150-fold greater than the oxidation of PAH trans-dihydrodiols examined. AKR1B10 was highly expressed at the mRNA and protein levels in human lung adenocarcinoma A549 cells, and robust retinal reductase activity was measured in lysates of these cells. The much greater catalytic efficiency of retinal reduction compared to PAH trans-dihydrodiol metabolism suggests AKR1B10 may play a greater role in lung carcinogenesis through dysregulation of retinoic acid homeostasis than through oxidation of PAH trans-dihydrodiols.

Evidence for the aldo-keto reductase pathway of polycyclic aromatic trans-dihydrodiol activation in human lung A549 cells.

Polycyclic aromatic hydrocarbons (PAHs) are tobacco carcinogens implicated in the causation of human lung cancer. Metabolic activation is a key prerequisite for PAHs to cause their deleterious effects. Using human lung adenocarcinoma (A549) cells, we provide evidence for the metabolic activation of (+/-)-trans-7,8dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-trans-dihydrodiol) by aldo-keto reductases (AKRs) to yield benzo[a]pyrene-7,8-dione (B[a]P-7,8-dione), a redox-active o-quinone. We show that B[a]P-7,8-trans-dihydrodiol (AKR substrate) and B[a]P-7,8-dione (AKR product) lead to the production of intracellular reactive oxygen species (ROS) (measured as an increase in dichlorofluorescin diacetate fluores-cence) and that similar changes were not observed with the regioisomer (+/-)-trans-4,5-dihydroxy-4,5-dihydrobenzo[a]pyrene or the diol-epoxide, (+/-)-anti-7,8-dihydroxy-9alpha,10beta-epoxy-7,8,9,10-tetrahydro-B[a]P. B[a]P-7,8-trans-dihydrodiol and B[a]P-7,8-dione also caused a decrease in glutathione levels and an increase in NADP(+)/NADPH ratios, with a concomitant increase in single-strand breaks (as measured by the comet assay) and 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dGuo). The specificity of the comet assay was validated by coupling it to human 8-oxo-guanine glycosylase (hOGG1), which excises 8-oxo-Gua to yield single-strand breaks. The levels of 8-oxo-dGuo observed were confirmed by an immunoaffinity purification stable isotope dilution ([(15)N(5)]-8-oxo-dGuo) liquid chromatography-electrospray ionization/multiple reaction monitoring/mass spectrometry (LC-ESI/MRM/MS) assay. B[a]P-7,8-trans-dihydrodiol produced DNA strand breaks in the hOGG1-coupled comet assay as well as 8-oxo-dGuo (as measured by LC-ESI/MRM/MS) and was enhanced by a catechol O-methyl transferase (COMT) inhibitor, suggesting that COMT protects against o-quinone-mediated redox cycling. We conclude that activation of PAH-trans-dihydrodiols by AKRs in lung cells leads to ROS-mediated genotoxicity and contributes to lung carcinogenesis.

Comparisons of (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol activation by human cytochrome P450 and aldo-keto reductase enzymes: effect of redox state and expression levels.

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants that are metabolically activated to proximate carcinogenic trans-dihydrodiols. PAH trans-dihydrodiols are further activated in humans by cytochrome P450 (P450) 1A1 and 1B1 to yield diol-epoxides or by aldo-keto reductases (AKR) 1A1 and 1C1-1C4 to yield reactive and redox-active o-quinones. Reconstituted in vitro systems were used to compare the steady-state kinetic constants for human P450 (P450 1A1 and 1B1) and AKR (AKR1A1, AKR1C1-1C4) mediated metabolism of (+/-)- trans-7,8-dihydroxy-7,8-dihydrobenzo[ a]pyrene ((+/-)-B[ a]P-7,8-diol) at physiological pH. It was found that P450 isoforms yielded much greater k cat/ K m values than AKR enzymes. Initial rates of (+/-)-B[ a]P-7,8-diol oxidation were measured for AKR1A1, AKR1C2, P450 1A1, and P450 1B1 as the ratio of NADPH/NAD (+) cofactors was varied to determine the redox state necessary for AKRs to successfully compete for trans-dihydrodiols. P450 and AKR enzymes equally competed for (+/-)-B[ a]P-7,8-diol substrate at an NADPH/NAD (+) ratio equal to 0.001. The resting NADPH/NAD (+) ratio was determined in A549 human lung adenocarcinoma cells to be 0.28. These data suggest that the P450 pathway would be favored over the AKR pathway if the enzymes were equally expressed. Basal mRNA transcript levels of AKR1C1-1C3 exceed those of both basal and 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD)-induced P450 1A1 and 1B1 by up to 90-fold in A549 cells as measured by real-time reverse transcriptase polymerase chain reaction (RT-PCR) methods. AKR expression levels were comparable to TCDD-induced P450 1A1 and 1B1 in HBEC-KT immortalized normal human bronchial epithelial cells. Functional assays of both A549 and HBEC-KT cell lysates demonstrated a lack of TCDD-inducible P450 1A1/1B1 activity but robust basal expression of AKR1A1 and AKR1C activities, where the functional assay for P450 detection is 300-fold more sensitive than the functional assay for AKR isoforms. These data suggest that AKR enzymes may effectively compete with P450 1A1/1B1 for PAH trans-dihydrodiol activation in human lung cells.

Competing roles of cytochrome P450 1A1/1B1 and aldo-keto reductase 1A1 in the metabolic activation of (+/-)-7,8-dihydroxy-7,8-dihydro-benzo[a]pyrene in human bronchoalveolar cell extracts.

(+/-)-7,8-Dihydroxy-7,8-dihydrobenzo[a]pyrene (BP-7,8-diol), a proximate carcinogen derived from benzo[a]pyrene (BP) requires further metabolic activation to exert its carcinogenic effects. Two principal pathways have been implicated, and these involve either the formation of (+/-)-trans-7,8-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE) catalyzed by P450 1A1/P450 1B1 (NADPH-dependent monoxygenases) or the formation of benzo[a]pyrene-7,8-dione (BP-7,8-dione) catalyzed by human aldo-keto reductases AKR1A1 and AKR1C1-AKR1C4 [NAD(P)(H)-dependent oxidoreductases]. The relative contributions of the two pathways to PAH activation are unknown. In this study, BP-7,8-diol metabolism was studied in human bronchoalveolar H358 cell extracts. Parental H358 cells do not constitutively express P450 1A1/P450 1B1 or AKRs but were manipulated by induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to express P450 1A1/P450 1B1 or by stable transfection to express AKR1A1 (aldehyde reductase). TCDD induction of AKR1A1 transfectants provided a cell line that expressed both pathways. Extracts derived from parental H358 cells plus TCDD (P450 induction) produced electrophilic anti-BPDE, which hydrolyzed to benzo[a]pyrene tetrahydrotetrols (BP-tetrols), extracts derived from AKR1A1-transfected cells (AKR1A1 expression) produced reactive and redox-active BP-7,8-dione, which was trapped in situ as its mono(thioether) conjugate, and extracts derived from AKR1A1 transfectants plus TCDD (coexpression of P450 1A1/P450 1B1 and AKR1A1) produced both anti-BPDE and BP-7,8-dione. The competing activation of BP-7,8-diol by P450 1A1/P450 1B1 and AKR1A1 was studied with varied NADPH:NAD+ ratios. The system with a relatively higher concentration of NADPH favored formation of anti-BPDE via P450 1A1/P450 1B1, while the system with the higher concentration of NAD+ favored formation of BP-7,8-dione via AKR1A1. Under conditions that mimic the cellular redox state, 10 microM NADPH and 1 mM NAD+, equal amounts of BP-tetrols and BP-7,8-dione were formed. This suggests that P450 1A1/P450 1B1 and AKR1A1 play competing roles in the metabolic activation of BP-7,8-diol and that the dominant pathway of BP-7,8-diol activation depends on the redox state of the cells. These model systems provide a cellular context in which the dominant DNA adducts/lesions formed by either pathway may be compared.