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This phase I, pilot clinical study was designed to evaluate the safety and the pharmacokinetic (PK) profiles of the CIME (Metabolic Identity Card) combination of ten drugs, with a view to its use as a phenotyping cocktail. Ten healthy Caucasian subjects were orally dosed with the CIME combination (caffeine–CYP1A2, repaglinide–CYP2C8, tolbutamide–CYP2C9, omeprazole–CYP2C19, dextromethorphan–CYP2D6, midazolam–CYP3A, acetaminophen–UGT1A1, 6&9 and 2B15, digoxin–P-gp, rosuvastatin–OATP1B1&3 and memantine–active renal transport). Blood was collected over 3 days and on day 7. CIME probes and relevant metabolites were assayed by LC–MS/MS and PK parameters were calculated. Main results were: (1) good safety with reversible mild or moderate adverse effects, (2) an analytical method able to quantify simultaneously the 10 probes and the major metabolites, (3) calculation of PK parameters for all probes in general agreed with published values, and (4) identification of the low CYP2D6 metabolizer. This pilot study showed that the CIME combination was well tolerated and that its pharmacokinetics could be accurately measured in healthy volunteers. This combination can now confidently be checked for sensitivity and specificity and for lack of interaction to be validated as a phenotyping cocktail.

Phenylahistin is a fungal diketopiperazine derived from isoprenylated (Phe-ΔHis) cyclodipeptide. The (-)-enantiomer is a cell cycle inhibitor, which can be potentially used as an antitumor agent. By contrast, the (+)-enantiomer exhibits no antimicrotubule activity. To better understand the differences that could arise from a difference of bioavailability, we investigated the interaction and metabolism of both enantiomers with mammalian cytochromes P450 (P450s). We found that both enantiomers were metabolized by various isoforms of mammal P450 with a noticeable activity for the (+)-enantiomer. P450 3A isoforms were mainly responsible for this metabolism, the bioactive (-)-enantiomer being 1.5 to 8 times less metabolized than the (+)-enantiomer. Spectral analysis of the interaction with P450s revealed that (-)-phenylahistin led to a hydrophobic type I signature, whereas the (+)-isomer yielded a Fe-N type II one. Structural analysis of metabolites by liquid chromatography-tandem mass spectrometry allowed us to characterize two major metabolites (P1 and P3) for both enantiomers. In human liver microsomal preparations, P1 was predominant in the (-)-phenylahistin metabolic profile. In contrast, (+)-phenylahistin mainly produced P3 in human microsomes and CYP3A human expressed P450s. (-)-Phenylahistin proved to be less toxic on P450-rich hepatocytes than on P450-deprived KB lines. The slower metabolism of this enantiomer could account for its higher toxicity. This is strengthened by the fact that isolated metabolites of (-)-phenylahistin showed no toxic effects toward KB lines. Finally, differences of metabolism and interaction mode between both phenylahistin enantiomers and CYP3A4 were supported by in silico molecular docking calculations.

Cyclophosphamide (CPA) is a chemotherapeutic agent that is primarily activated in the liver by cytochrome P4502B6 (CYP2B6) and then transported to the tumor via blood flow. To prevent deleterious secondary effects, P450-based gene-directed enzyme prodrug therapy (GDEPT) consists of expressing CYP2B6 in tumor cells before CPA treatment. Given the relatively low affinity of CYP2B6 for CPA, the aim of our work was to modify CYP2B6 to increase its catalytic efficiency (Vmax/Km) to metabolize CPA into 4'-OH CPA. A molecular model of CYP2B6 was built, and four residues in close contact with the substrate were subjected to mutagenesis. Canine CYP2B11 exhibiting a particularly low Kmto CPA, the amino acids exclusively present in the CYP2B11 substrate recognition sequences were substituted in human CYP2B6. All mutants (n = 26) were expressed in Saccharomyces cerevisiae and their enzymatic constants (Km, Vmax) evaluated using CPA as substrate. Five mutants exhibited a 2- to 3-fold higher catalytic efficiency than wild-type CYP2B6. A double mutant, comprising the two most effective mutations, showed a 4-fold increase in Km/Vmax. Molecular dynamic simulations of several mutants were found to be consistent with the observed modifications in catalytic efficiency. Finally, expression of the CYP2B6 114V/477W double mutant, contrary to wt CYP2B6, allowed switching of a resistant human head and neck cancer cell line (A-253) into a sensitive cell line toward CPA. Thus, we were able to obtain a new efficient CYP2B6 mutant able to metabolize CPA, an important step in the GDEPT strategy for human cancer treatment.

Interaction of rat and human cystathionine-β-synthase (CBS) with various potential ligands has been studied by visible and EPR spectroscopy in order to explore the coordination chemistry of this atypical hemeprotein. Ferric CBS did not react with any classical hemeprotein ligands, such as various imidazole and pyridine derivatives, N−3 and isonitriles RNC. Ferrous CBS also failed to bind these nitrogenous ligands or nitrosoalkanes. However, it reacts with various isonitriles RNC, leading to complexes characterized by a Soret peak at 433 ± 2 nm. Binding of isonitriles to ferrous CBS is a relatively slow process; its rate markedly depends on the nature of R. It thus seems that the only exogenous ligands able to bind CBS iron are carbon-centered, very strong heme–Fe(II) ligands such as CNR, CO, and CN−, presumably after dissociation of the CBS–iron(II)–cysteinate bond. Isonitriles appear as interesting tools for further studies on the topology of CBS active site.

The potent 14-membered macrolide antibiotics displayed a strong NMR response in the TRNOESY experiments whereas their metabolites which do not retain antimicrobial activity gave essentially blank TRNOESY spectra. These TRNOESY experiments are here extended to a macrolide ( josamycin) belonging to the 16-atom macrolide class in order to compare responses according to the macrocycle size. Analysis of transferred nuclear Overhauser effect (TRNOE) experiments resulted in a set of constraints for all proton pairs. These constraints were used in structure determination procedures based on molecular modelling to obtain a bound structure compatible with the experimental NMR data. This study allowed us to identify the binding structure at the ribosome for the active 16-membered macrolide. The different conformations existing in solution for this antibiotic in the free state will be compared and correlated with the binding conformation at the ribosome obtained with TRNOE experiments so as to establish a structure–activity relationship. The comparative results indicate that one conformation (called S3) pre-existing in the conformational equilibrium of macrocycle in solution and close to the major one S5, is preferred in the bound state.

Arachidonic acid (0.01–1μM) induced relaxation of precontracted rings of rabbit saphenous vein, which was counteracted by contraction at concentrations higher than 1μM. Concentrations higher than 1μMwere required to induce dose‐dependent contraction of vena cava and thoracic aorta from the same animals.Pretreatment with a TP receptor antagonist (GR32191B or SQ29548, 3μM) potentiated the relaxant effect in the saphenous vein, revealed a vasorelaxant component in the vena cava response and did not affect the response of the aorta.Removal of the endothelium from the venous rings, caused a 10 fold rightward shift in the concentration‐relaxation curves to arachidonic acid. Whether or not the endothelium was present, the arachidonic acid‐induced relaxations were prevented by indomethacin (10μM) pretreatment.In the saphenous vein, PGE2was respectively a 50 and 100 fold more potent relaxant prostaglandin than PGI2and PGD2. Pretreatment with the EP4receptor antagonist, AH23848B, shifted the concentration‐relaxation curves of this tissue to arachidonic acid in a dose‐dependent manner.In the presence of 1μMarachidonic acid, venous rings produced 8–10 fold more PGE2than did aorta whereas 6keto‐PGF1αand TXB2productions remained comparable.Intact rings of saphenous vein relaxed in response to A23187. Pretreatment with L‐NAME (100μM) or indomethacin (10μM) reduced this response by 50% whereas concomitant pretreatment totally suppressed it. After endothelium removal, the remaining relaxing response to A23187 was prevented by indomethacin but not affected by L‐NAME.We conclude that stimulation of the cyclo‐oxygenase pathway by arachidonic acid induced endothelium‐dependent, PGE2/EP4mediated relaxation of the rabbit saphenous vein. This process might participate in the A23187‐induced relaxation of the saphenous vein and account for a relaxing component in the response of the vena cava to arachidonic acid. It was not observed in thoracic aorta because of the lack of a vasodilatory receptor and/or the poorer ability of this tissue than veins to produce PGE2.

NO generation in the course of two acute, non immune, inflammatory reactions (pleurisy induced by rat isologous serum and carrageenan) was assessed by means of nitrite measurement in pleural exudate from 0.5 to 24 h. NO release varied time-dependently, similarly for the two inflammatory reactions. A first, but transient, peak was reached in 30 min while a second peak, more sustained, began at the fourth hour and was maximum at the tenth. Kinetic evolution of NO release was consistent with activation, in a first step, of a constitutive NO synthase probably from endothelial origin (inhibited by 2-Methyl-2-Thiopseudourea sulfate but not by dexamethasone) and with activation, in a second wave, of inducible NOS from endothelial and exudative cells. NO release was potentiated by administration per os of L-Arginine and seems to be involved in the evolution of acute inflammatory reactions and oxygen metabolite production.

Abstract:  The effects of various compounds bearing an N-OH group such as N-hydroxy-guanidines, amidoximes, and hydroxylamines, on bovine and rat liver arginases was studied. Some of these compounds with an l-α-amino acid function at an appropriate distance from the N-OH group acted as strong competitive liver arginase inhibitors, displaying Ki values between 4 and 150 μM. Two compounds, N ε-hydroxy-l-lysine and N ω-hydroxy-d,l-indospicine, which exhibited Ki values of 4 and 20 μM (at pH 7.4), were the most potent inhibitors of arginase described to date. The distance between the α-amino acid and N-OH functions appeared to be crucial for potent inhibition of arginase, as N δ-hydroxy-l-ornithine, which has one -CH2 group less than N ε-hydroxy-l-lysine, exhibited a 37-fold higher Ki value than N ε-hydroxy-l-lysine. Based on these results, a model for the interaction of N ω-hydroxyamino-l-α-amino acids with the arginase active site is proposed. This model involves the binding of the N-OH group of the inhibitors to the arginase Mn(II) center and suggests that N ε-hydroxy-l-lysine is a good transition state analog of arginase.

We have developed two bromocriptine enzyme immunoassays with different specificities for applications in human and animal pharmacokinetic studies. The first assay uses antibodies directed against the cyclopeptide stucture of bromocriptine, and is specific for untransformed bromocriptine. The second assay uses antibodies directed against the bromolysergic part of the molecule and allows the measurement of both bromocriptine and its metabolites. Enzymatic tracers were obtained by covalent coupling of bromocriptine analogs to acetylcholinesterase from the electric eel Electrophorus electricus. Both assays have a limit of detection of 10 pg/ml and a limit of quantification of 50 pg/ml. The specificity of the assays was determined following fractionation by high-performance liquid chromatography of rat samples obtained after administration of bromocriptine.

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The precise location of a substrate in cytochrome P450 (CYP) governs the orientation of the oxidation position. Such information is generally obtained from biochemical data, but modeling approaches have also been used to explain these locations. We used X-ray data and modeling techniques to distinguish between the series of putative linear or curved channels which lead the substrate from the outer side of the protein to the inner, and then into the heme pocket; these techniques were also used to identify the largest such channels. Two new methods for precisely determining the 3-D structure of proteins using X-ray crystallography were proposed in order to identify these channels: first, the use of both straight and curved channels, and second, the sphere method. These data are compared with Poulos channels, and with Caver (or Mol on line) modeling methodologies. Our methods were developed from studies of the interaction between cytochrome P450CAM (CYP101) from Pseudomonas putida (as expressed in Escherichia coli) and the indolic base ß-carboline. Apart from the identification of potential access channels leading to the heme-containing active site, a new explanation was advanced for the substrate's hydroxylation position. The sphere method seems to have potential to become a general and direct method for prediction of substrate access channels from reduced- or low-resolution crystallographic data.

The analogue of isoprene, 2-methyl-2-vinyloxirane, a versatile isoprene auxiliary, was reacted with some indolic and imidazolic bases, to add one or more isoprene unit(s), to these compounds. This prenylation was realised by using thermal and microwave assisted pathways, via the nucleophilic opening of the epoxide ring. The biological importance of the prenylated derivatives resides in their potential application as drugs. The aminoacids and small protein biomarkers are obtained from simple epoxide opening reactions. All new compounds were characterised by high resolution NMR, mass spectroscopy, GC-MS and LC-MS as well.