Human carbonyl reductase 1 (hCBR1) is an NADPH-dependent short chain dehydrogenase/reductase with broad substrate specificity and is thought to be responsible for the in vivo reduction of quinones, prostaglandins, and other carbonyl-containing compounds including xenobiotics. In addition, hCBR1 possesses a glutathione binding site that allows for increased affinity toward GSH-conjugated molecules. It has been suggested that the GSH-binding site is near the active site; however, no structures with GSH or GSH conjugates have been reported. We have solved the x-ray crystal structures of hCBR1 and a substrate mimic in complex with GSH and the catalytically inert GSH conjugate hydroxymethylglutathione (HMGSH). The structures reveal the GSH-binding site and provide insight into the affinity determinants for GSH-conjugated substrates. We further demonstrate that the structural isostere of HMGSH, S-nitrosoglutathione, is an ideal hCBR1 substrate (Km = 30 μm, kcat = 450 min-1) with kinetic constants comparable with the best known hCBR1 substrates. Furthermore, we demonstrate that hCBR1 dependent GSNO reduction occurs in A549 lung adenocarcinoma cell lysates and suggest that hCBR1 may be involved in regulation of tissue levels of GSNO.

Current approaches to inhibit nuclear receptor (NR) activity target the hormone binding pocket but face limitations. We have proposed that inhibitors, which bind to nuclear receptor surfaces that mediate assembly of the receptor's binding partners, might overcome some of these limitations. The androgen receptor (AR) plays a central role in prostate cancer, but conventional inhibitors lose effectiveness as cancer treatments because anti-androgen resistance usually develops. We conducted functional and x-ray screens to identify compounds that bind the AR surface and block binding of coactivators for AR activation function 2 (AF-2). Four compounds that block coactivator binding in solution with IC 50 ≈ 50 μM and inhibit AF-2 activity in cells were detected: three nonsteroidal antiinflammatory drugs and the thyroid hormone 3,3′,5-triiodothyroacetic acid. Although visualization of compounds at the AR surface reveals weak binding at AF-2, the most potent inhibitors bind preferentially to a previously unknown regulatory surface cleft termed binding function (BF)-3, which is a known target for mutations in prostate cancer and androgen insensitivity syndrome. X-ray structural analysis reveals that 3,3′,5-triiodothyroacetic acid binding to BF-3 remodels the adjacent interaction site AF-2 to weaken coactivator binding. Mutation of residues that form BF-3 inhibits AR function and AR AF-2 activity. We propose that BF-3 is a previously unrecognized allosteric regulatory site needed for AR activity in vivo and a possible pharmaceutical target.

Glutathione forms complex reaction products with formaldehyde, which can be further modified through enzymatic modification. We studied the non-enzymatic reaction between glutathione and formaldehyde and identified a bicyclic complex containing two equivalents of formaldehyde and one glutathione molecule by protein X-ray crystallography (PDB accession number 2PFG). We have also used (1)H, (13)C and 2D NMR spectroscopy to confirm the structure of this unusual adduct. The key feature of this adduct is the involvement of the gamma-glutamyl alpha-amine and the Cys thiol in the formation of the bicyclic ring structure. These findings suggest that the structure of GSH allows for bi-dentate masking of the reactivity of formaldehyde. As this species predominates at near physiological pH values, we suggest this adduct may have biological significance.

FAH (fumarylacetoacetate hydrolase) catalyses the final step of tyrosine catabolism to produce fumarate and acetoacetate. HT1 (hereditary tyrosinaemia type 1) results from deficiency of this enzyme. Previously, we prepared a partial mimic of the putative tetrahedral intermediate in the reaction catalysed by FAH co-crystallized with the enzyme to reveal details of the mechanism [Bateman, Bhanumoorthy, Witte, McClard, Grompe and Timm (2001) J. Biol. Chem. 276, 15284-15291]. We have now successfully synthesized complete mimics CEHPOBA {4-[(2-carboxyethyl)-hydroxyphosphinyl]-3-oxobutyrate} and COPHPAA {3-[(3-carboxy-2-oxopropyl)hydroxyphosphinyl]acrylate}, which inhibit FAH in slow-onset tight-binding mode with K(i) values of 41 and 12 nM respectively. A high-resolution (1.35 A; 1 A=0.1 nm) crystal structure of the FAH.CEHPOBA complex was solved to reveal the affinity determinants for these compounds and to provide further insight into the mechanism of FAH catalysis. These compounds are active in vivo, and CEHPOBA demonstrated a notable dose-dependent increase in SA (succinylacetone; a metabolite seen in patients with HT1) in mouse serum after repeated injections, and, following a single injection (1 mumol/g; intraperitoneal), only a modest regain of FAH enzyme activity was detected in liver protein isolates after 24 h. These potent inhibitors provide a means to chemically phenocopy the metabolic defects of either HT1 or FAH knockout mice and promise future pharmacological utility for hepatocyte transplantation.

RATIONALE: In lung tissue, the anti-inflammatory steroid cortisol is converted to inactive cortisone by 11beta-Hydroxysteroid dehydrogenase 2 (11beta-HSD2). Therefore, inhibition of 11beta-HSD2 activity in lung tissue may suppress the inflammatory response in asthma. METHODS: We have developed a novel inhibitor of a structurally related enzyme, Carbonyl reductase 1 (CBR1) and have elucidated the mechanism of inhibition both kinetically and crystallographically [Tanaka, et al (2005) PloS Biol. 3, 764-776]. The affinity of this compound for CBR1 is mediated through hydrogen-bond interactions with catalytic residues conserved in 11beta-HSD2. Using the structure as a model, we have applied our knowledge of the binding mode to inform the development of a library of compounds to target the homologous but not yet structurally described 11beta-HSD2. RESULTS: We have developed an efficient synthetic route to produce numerous compounds well suited to inhibit 11beta-HSD2. These compounds retain the putative pharmacophore necessary for interaction with conserved catalytic amino acid residues and possess additional substituents that should provide 11beta-HSD2 specificity. We are in the process of implementing an in vitro activity assay to screen for inhibitors of this enzyme. CONCLUSIONS: Using techniques of structure based drug design we have developed and synthesized a library of compounds likely to include potent 11beta-HSD2 inhibitors. Structure activity relationships identified from the in vitro assay should allow further optimization of potency and specificity.

Rapid, quantitative methods for characterizing the biological activities of kinase inhibitors in complex human cell systems could allow the biological consequences of differential target selectivity to be monitored early in development, improving the selection of drug candidates. We have previously shown that Biologically Multiplexed Activity Profiling (BioMAP) permits rapid characterization of drug function based on statistical analysis of protein expression data sets from complex primary human cellbased models of disease biology. Here, using four such model systems containing primary human endothelial cells and peripheral blood mononuclear cells in which multiple signaling pathways relevant to inflammation and immune responses are simultaneously activated, we demonstrate that BioMAP analysis can detect and distinguish a wide range of inhibitors directed against different kinase targets. Using a panel of p38 mitogen-activated protein kinase antagonists as a test set, we show further that related compounds can be distinguished by unique features of the biological responses they induce in complex systems, and can be classified according to their induction of shared (on-target) and secondary activities. Statistical comparisons of quantitative BioMAP profiles and analysis of profile features allow correlation of induced biological effects with chemical structure and mapping of biological responses to chemical series or substituents on a common scaffold. Integration of automated BioMAP analysis for prioritization of hits and for structure-activity relationship studies may improve and accelerate the design and selection of optimal therapeutic candidates.

Objective. Fanconi anemia (FA) is a genetically heterogeneous disorder associated with defects in at least eight genes. The biochemical function(s) of the FA proteins are unknown, but together they define the FA pathway, which is involved in cellular responses to DNA damage and in other cellular processes. It is currently unknown whether all FA proteins are involved in controlling a single function or whether some of the FA proteins have additional roles. The aim of this study was 1) to determine whether the FA group A and group C genes have identical or partially distinct functions, and 2) to have a better model for human FA.Materials and Methods. We generated mice with a targeted mutation in fanca and crossed them with fancc disrupted animals. Several phenotypes including sensitivity to DNA cross linkers and ionizing radiation, hematopoietic colony growth, and germ cell loss were analyzed infanca-/-,fancc-/-,fanca/fancc double -/-, and controls.Results. Fibroblast cells and hematopoietic precursors from fanca/fancc double-mutant mice were not more sensitive to MMC than those of either single mutant. fanca/fancc double mutants had no evidence for an additive phenotype at the cellular or organismal level.Conclusions. These results support a model where both FANCA and FANCC are part of a multi-protein nuclear FA complex with identical function in cellular responses to DNA damage and germ cell survival. (C) 2002 International Society for Experimental Hematology. Published by Elsevier Science Inc.