FK 506 prevents islet xenograft rejection: a study in the pig-to-rat model.
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Animals↗
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Potent immunosuppressive effects by a newly synthesized compound KF20444.
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Animals↗
Letter: Effect of broxyquinoline and broxaldine in leprosy.
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Amebiasis↗
Flow cytometric analysis of the molecular mechanisms of immunosuppressive action of the active metabolite of leflunomide and its malononitrilamide analogues in a novel whole blood assay.
Malononitrilamides (MNAs) are a new class of immunomodulatory drug highly effective in in vivo models of allo- and xenotransplantation. Knowledge of their effects on immune cells, however, is limited and has been derived solely from investigations using isolated mononuclear cells. This use of purified cells to investigate drug activity is not ideal, so we have combined the analytical power of flow cytometry with our mitogen-driven, whole blood lymphocyte activation and proliferation assays to investigate the in vitro mechanism of action of MNAs. We first show that MNAs (A77 1726, HMR1279, and HMR1715), as well as brequinar (BQR) and cyclosporine (CsA), effectively inhibit cell activation antigen expression and lymphocyte proliferation. We next show that the inhibitory effects of MNAs and BQR, but not CsA, are reversed by the addition of uridine to the culture. These results suggest that inhibition of pyrimidine biosynthesis may be a mechanism by which MNAs suppress both lymphocyte activation and proliferation since these effects were reversed when uridine nucleotide pools were replenished. This novel finding of suppression of activation antigen expression by MNAs in whole blood expands our understanding of the effects of this new class of drug.
Acrylamides↗
Preclinical phase II studies in human tumor lines: a European multicenter study.
In an attempt to increase the predictability and to extend the differential capacity of the anticancer drug development program the American National Cancer Institute has recently proposed the introduction of a screening system consisting of human tumor cell lines to select drugs in a disease-oriented fashion rather than by the previously applied drug-oriented strategy. Although this new approach offers great advantages, assay limitations can be identified in testing unknown compounds for antitumor activity in vitro. Human tumor xenografts grown in nude mice may play an additional role in the prediction of clinical activity and the assessment of the spectrum of activity of potential anticancer drugs, because they have a better relationship with the clinical situation of cancer treatment. In a European multicenter collaboration it has been proposed to use panels of human tumor lines from solid tumor types to study: the antitumor activity of three different drugs per tumor type; the reliability of 'preclinical' phase II studies by comparison of the obtained data with results of phase II clinical trials; the feasibility of this joint project, such as the methodology, the reproducibility of experimental data and the introduction of uniform activity criteria. If preclinical phase II studies in human tumor lines generate reliable results, this in vivo screening system will create a unique possibility to better identify promising clinical candidate compounds or analogs of conventional cytostatic agents as well as those tumor types likely to respond to the selected investigational drugs.
Amsacrine↗
Side effects of brequinar and brequinar analogues, in combination with cyclosporine, in the rat.
Brequinar is an immunosuppressant with the potential to be combined with cyclosporine in synergistic combination therapy. The drug tends to accumulate when given daily per os, and pharmacokinetic interaction with cyclosporine appears to enhance toxicity. Analogues with similar immunosuppressive activity have been identified at Du Pont Merck Pharmaceutical Co., that do not accumulate upon daily oral dosing in rats, and hence could have an improved potential in combination treatment with cyclosporine. We performed a toxicity study with brequinar and two brequinar analogues, administered orally once daily for 4 weeks, either alone or in combination with cyclosporine (Neoral, Novartis Pharma AG). In a first study relatively high doses were evaluated with cyclosporine at non-toxic doses of 5 and 10 mg/kg/d. The maximum tolerated dose of brequinar alone was estimated between 5 and 10 mg/kg/d; that of the analogues was estimated between 10 and 20 mg/kg/d, and above 20 mg/kg/d, respectively. In combination with cyclosporine at 5 and 10 mg/kg/d, approximately a 2-fold reduction in the maximum tolerated dose was observed. In a second study lower doses were evaluated in combination with cyclosporine at 2.5 and 5 mg/kg/d. Also this study revealed increased toxicity of brequinar (analogues) when given in combination with cyclosporine. The side effects observed were typical for drugs in the brequinar class and included leukocytopenia and thrombocytopenia, reduced body weight gain or body weight loss, thymic atrophy, cellular depletion of bone marrow and splenic white pulp, and villous atrophy in jejunum. Concentrations of brequinar (analogues) were determined in blood sampled 4 h after administration at day 1, 14 and 21-28 of the experiment. There was a tendency for drug accumulation in some groups treated with brequinar and cyclosporine. For one of the analogues at a low dose, higher concentrations were measured in groups treated with combinations of this compound and cyclosporine. We conclude that a potential synergism in immunosuppression using combinations of brequinar (analogues) and cyclosporine can be complicated by enhanced toxicity of the compounds. This indicates the need for a careful evaluation of the therapeutic window in a combined treatment together with detailed pharmacokinetics.
Administration, Oral↗
Simultaneous separation by high-performance liquid chromatography of carbamoyl aspartate, carbamoyl phosphate and dihydroorotic acid.
Leflunomide is an immunomodulatory drug which acts by inhibiting dihydroorotic acid dehydrogenase, the fourth enzyme of pyrimidine biosynthesis. We modified our high-performance liquid chromatography method to demonstrate that the principal metabolite in mitogen-stimulated human T-lymphocytes incubated with leflunomide was not dihydroorotic acid, but carbamoyl aspartate. Identification involved preparation of [14C]carbamoyl aspartate from [14C]aspartic acid and mammalian aspartate transcarbamoylase. Accumulation of carbamoyl aspartate indicates that under these conditions the equilibrium constant for dihydroorotase favours the reverse reaction. This HPLC method, enabling simultaneous separation of the first four intermediates in the de novo pyrimidine pathway may be of use in a variety of experimental situations.
Anti-Inflammatory Agents, Non-Steroidal↗
Phase I and pharmacokinetic study of brequinar (DUP 785; NSC 368390) in cancer patients.
Brequinar (DUP 785, NSC 368390) is a 4-quinoline carboxylic acid derivative with broad spectrum antitumour activity in experimental models that acts as an antimetabolite by specific inhibition of de novo pyrimidine synthesis. We performed a phase I study of brequinar administered as a 10 min intravenous (i.v.) infusion for 5 consecutive days, every 4 weeks. 67 evaluable patients were entered in this study and a total of 130 courses were administered at doses ranging from 2 to 350 mg/m2. The dose-limiting toxicity was myelosuppression with predominant thrombocytopenia. Myelosuppression was dose-related and non-cumulative, with considerable interpatient variability depending on haematological risk factors. The maximum tolerated dose of brequinar was 210 mg/m2/day in poor risk patients whereas patients with good risk haematological profile tolerated higher doses (up to 350 mg/m2/day). Other non-limiting toxicities included nausea and vomiting, mucositis and skin reactions. Brequinar plasma pharmacokinetic profiles were biphasic with alpha half-life ranging from 0.1 to 0.7 h, and beta half-life ranging from 1.5 to 8.2 h. Increase in brequinar area under the plasma concentration versus time curves (AUC) was nonlinear. Day 5 brequinar pharmacokinetics obtained in 21 patients indicated a significant increase in AUC (47%) and half-life beta (133%) compared to day 1 pharmacokinetics in the same patient. Brequinar plasma AUC and the per cent change in platelet count at nadir were correlated (P < 0.001). Although no objective response was observed in this study, one minor response was noted in cervical lymph nodes of a Hodgkin's disease patient.
Adult↗
Structure-activity relationships (SAR) of some tetracyclic heterocycles related to the immunosuppressive agent Brequinar Sodium.
The structure-activity relationships of some tetracyclic heterocycles related to Brequinar were explored. Activities as inhibitors of dihydroorotate dehydrogenase and the mixed lymphocyte reaction are related to ring system, heteroatom placement, and pendant ring substitution.
Biphenyl Compounds↗
Cytokine mRNA expression in tolerant heart allografts after immunosuppression with cyclosporine, sirolimus or brequinar.
We sought to examine the impact of the preferential activation of Th2 cells on the induction and maintenance of a tolerant state in heart allograft rat recipients treated with a short course of cyclosporine (CsA), sirolimus (SRL) or brequinar (BQR). A quantitative polymerase chain reaction (PCR) method was used to measure the levels of cytokine mRNAs, namely interferon (IFN)-gamma and interleukin (IL)-2 in T helper 1 (Th1) cells and IL-4, IL-5 and IL-10 in Th2 cells. Our main findings were that on day 5 postgrafting allografts from untreated recipients had increased levels of IFN-gamma (216 +/- 119 fg), IL-2 (449 +/- 75 fg), IL-4 (6.2 +/- 1.3 fg), IL-5 (34.8 +/- 9.3 fg) and IL-10 (1554 +/- 184 fg) mRNAs compared with normal hearts. CsA reduced the levels of IFN-gamma, IL-2, IL-5 and IL-10, but not IL-4, mRNAs. SRL did not affect the expression of cytokine mRNAs. BQR decreased the levels of IFN-gamma, IL-2 and IL-10, but not IL-5 or IL-4 mRNAs. Compared with grafts from untreated recipients, those from CsA- or BQR-treated tolerant hosts (day 100) displayed undetectable IL-2 mRNA levels, and reduced levels of IFN-gamma, IL-4 and IL-10 mRNAs. In fact, the patterns of cytokine mRNA expression in grafts from CsA- and BQR-treated tolerant hosts were similar to those of normal hearts. Grafts from SRL-treated tolerant hosts merely showed slightly increased Th2 cell activity. In conclusion the selective activation of Th2 cells is not absolutely required for induction or maintenance of tolerance.
Animals↗
Structures of human dihydroorotate dehydrogenase in complex with antiproliferative agents.
BACKGROUND: Dihydroorotate dehydrogenase (DHODH) catalyzes the fourth committed step in the de novo biosynthesis of pyrimidines. As rapidly proliferating human T cells have an exceptional requirement for de novo pyrimidine biosynthesis, small molecule DHODH inhibitors constitute an attractive therapeutic approach to autoimmune diseases, immunosuppression, and cancer. Neither the structure of human DHODH nor any member of its family was known. RESULTS: The high-resolution crystal structures of human DHODH in complex with two different inhibitors have been solved. The initial set of phases was obtained using multiwavelength anomalous diffraction phasing with selenomethionine-containing DHODH. The structures have been refined to crystallographic R factors of 16.8% and 16.2% at resolutions of 1. 6 A and 1.8 A for inhibitors related to brequinar and leflunomide, respectively. CONCLUSIONS: Human DHODH has two domains: an alpha/beta-barrel domain containing the active site and an alpha-helical domain that forms the opening of a tunnel leading to the active site. Both inhibitors share a common binding site in this tunnel, and differences in the binding region govern drug sensitivity or resistance. The active site of human DHODH is generally similar to that of the previously reported bacterial active site. The greatest differences are that the catalytic base removing the proton from dihydroorotate is a serine rather than a cysteine, and that packing of the flavin mononucleotide in its binding site is tighter.
Amino Acid Sequence↗
Multiple inhibitor analysis of the brequinar and leflunomide binding sites on human dihydroorotate dehydrogenase.
Brequinar and the active metabolite of leflunomide, A77 1726, have been clearly shown to inhibit human dihydroorotate dehydrogenase (DHODH), but conflicting mechanisms for their inhibition have been reported. DHODH catalyses the conversion of dihydroorotate (DHO) to orotate concurrent with the reduction of ubiquinone. This study presents data that indicates brequinar is a competitive inhibitor versus ubiquinone; A77 1726 is noncompetitive versus ubiquinone and both are uncompetitive versus DHO. 2-Phenyl 5-quinolinecarboxylic acid (PQC), the core moiety of brequinar also shows competitive inhibition versus ubiquinone. Multiple inhibition experiments indicate that PQC (and thus brequinar) and A77 1726 have overlapping binding sites. Both PQC and A77 1726 are also mutually exclusive with barbituric acid (a competitive inhibitor versus DHO). In addition, we failed to observe brequinar binding to E.orotate by isothermal titration calorimetry (ITC). These results indicate that the E.DHO.inhibitor and E.orotate.inhibitor ternary complexes do not form. The absence of these complexes is consistent with the two-site ping-pong mechanism reported for DHODH. This kinetic data suggests that recent crystal structures of human DHODH complexed with orotate and A77 1726 or brequinar may not represent the relevant physiological binding sites for these inhibitors [Liu, S., Neidhardt, E. A., Grossman, T. H., Ocain, T., and Clardy J. (2000) Structure 8, 25-33].
Aniline Compounds↗
Dioxygenases without requirement for cofactors and their chemical model reaction: compulsory order ternary complex mechanism of 1H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase involving general base catalysis by histidine 251 and single-electron oxidation of the substrate dianion.
1H-3-Hydroxy-4-oxoquinaldine 2,4-dioxygenase (Hod) is a cofactor-less dioxygenase belonging to the alpha/beta hydrolase fold family, catalyzing the cleavage of 1H-3-hydroxy-4-oxoquinaldine (I) and 1H-3-hydroxy-4-oxoquinoline (II) to N-acetyl- and N-formylanthranilate, respectively, and carbon monoxide. Bisubstrate steady-state kinetics and product inhibition patterns of HodC, the C69A protein variant of Hod, suggested a compulsory-order ternary-complex mechanism, in which binding of the organic substrate precedes dioxygen binding, and carbon monoxide is released first. The specificity constants, k(cat)/K(m,A) and k(cat)/K(m,O)()2, were 1.4 x 10(8) and 3.0 x 10(5) M(-1) s(-1) with I and 1.2 x 10(5) and 0.41 x 10(5) M(-1) s(-1) with II, respectively. Whereas HodC catalyzes formation of the dianion of its organic substrate prior to dioxygen binding, HodC-H251A does not, suggesting that H251, which aligns with the histidine of the catalytic triad of the alpha/beta hydrolases, acts as general base in catalysis. Investigation of base-catalyzed dioxygenolysis of I by electron paramagnetic resonance (EPR) spectroscopy revealed formation of a resonance-stabilized radical upon exposure to dioxygen. Since in D(2)O spectral properties are not affected, exchangeable protons are not involved, confirming that the dianion is the reactive intermediate that undergoes single-electron oxidation. We suggest that in the ternary complex of the enzyme, direct single-electron transfer from the substrate dianion to dioxygen may occur, resulting in a radical pair. Based on the estimated spin distribution within the radical anion (observed in the model reaction of I), radical recombination may produce a C4- or C2-hydroperoxy(di)anion. Subsequent intramolecular attack would result in the 2,4-endoperoxy (di)anion that may collapse to the reaction products.
Alanine↗
Modified electrodes with synthetic biocatalytic membranes.
A biocatalytic membrane based on an immobilized enzyme molecule has been prepared. Oxidative electropolymerization of 8-hydroxyquinaldine (8-OHQ) monomers in 0.2 M, pH 7 phosphate buffer containing glucose oxidase (GOx) has been carried out to modify the surfaces of GC, Au, and Pt rotating disk electrodes. The biocatalytic properties of the synthesized membrane were characterized by studying the catalytic activities of the immobilized GOx. Signals obtained from modified GC electrodes with this biomembrane were mainly attributed to the immobilized GOx. Signals obtained from modified Pt or Au electrodes were due to the combined contribution of the enzyme and the native electrode's material. The potential analytical applications of these modified electrodes as bioelectrochemical sensors were also investigated.
Biotechnology↗
An in situ attenuated total reflection infrared study of a chiral catalytic solid-liquid interface: cinchonidine adsorption on pt.
An in situ attenuated total reflection study of the chiral solid-liquid interface created by cinchonidine adsorption on a Pt/Al(2)O(3) model catalyst is presented. Experiments were performed in the presence of dissolved hydrogen, that is under conditions used for the heterogeneous enantioselective hydrogenation of alpha-functionalized ketones. Cinchonidine adsorbs via the quinoline moiety. The adsorption mode is coverage dependent and several species coexist on the surface. At low concentration (10(-6)M) a predominantly flat adsorption mode prevails. At increasing coverage two different tilted species, alpha-H abstracted and N lone pair bonded cinchonidine, are observed. The latter is only weakly bound and in a fast dynamic equilibrium with dissolved cinchonidine. At high concentration (10(-4)-10(-3) M) all three species coexist on the Pt surface. A slow transition from an adsorbate layer with a high fraction of alpha-H abstracted cinchonidine to one with a high fraction of N lone pair bonded cinchonidine is observed with the cinchonidine concentration being the driving force for the process. The reverse transition in the absence of dissolved cinchonidine is fast. Cinchonidine competes with solvent decomposition products for adsorption sites on the Pt, which may contribute to the observed solvent dependence of the heterogeneous enantioselective hydrogenation of ketones by cinchonidine-modified Pt.
Adsorption↗
A sensitive probe for the detection of Zn(II) by time-resolved fluorescence.
A new, highly sensitive fluorescent sensor for Zn(II) ion (a tris(2-pyridylmethyl)amine derivative) shows very strong binding and Zn(II) concentration-dependent biexponential time-resolved fluorescence (TRF) decay profiles that can be used for ratiometric estimates of Zn(II) concentrations. The ligand-metal complexes were characterized in solution by spectroscopic techniques and in the solid state by X-ray crystallography. The TRF studies revealed that the sensor aggregates in the absence of Zn(II) in a ligand concentration-dependent manner, a complication that is discerned by TRF but not by steady-state fluorescence ratiometric sensing techniques. It is shown that the same TRF methods are highly useful for monitoring Zn(II) concentrations in A549 epithelial lung cells in vitro and that the results were consistent with those in solution.
Cations, Divalent↗
Quinoline derivatives as antiallergy agents. 2. Fused-ring quinaldic acids.
A series of compounds containing two or more 4-oxo-1,4-dihydropyridine-2-carboxylic acid units fused to a central aromatic nucleus was synthesized and tested in the rat passive cutaneous anaphylaxis (PCA) assay for potential antiallergy activity. Most of the compounds of this series showed significant activity in the PCA assay. Three of these compounds. 11d, 13f, and 21, were more than 250 times as active as the standard drug, cromolyn sodium. The synthesis and biological activity are discussed.
Animals↗
Dual binding mode of a novel series of DHODH inhibitors.
Human dihydroorotate dehydrogenase (DHODH) represents an important target for the treatment of hyperproliferative and inflammatory diseases. In the cell DHODH catalyzes the rate-limiting step of the de novo pyrimidine biosynthesis. DHODH inhibition results in beneficial immunosuppressant and antiproliferative effects in diseases such as rheumatoid arthritis. Here, we present high-resolution X-ray structures of human DHODH in complex with a novel class of low molecular weight compounds that inhibit the enzyme in the nanomolar range. Some compounds showed an interesting dual binding mode within the same cocrystal strongly depending on the nature of chemical substitution. Measured in vitro activity data correlated with the prevailing mode of binding and explained the observed structure-activity relationship. Additionally, the X-ray data confirmed the competitive nature of the inhibitors toward the putative ubiquinone binding site and will guide structure-based design and synthesis of molecules with higher activity.
Amides↗