Structural characterization of novel adenine dinucleotide phosphate conjugates of imatinib in incubations with rat and human liver microsomes

A Method to Monitor the NAD+ Metabolome-From Mechanistic to Clinical Applications

Nicotinamide adenine dinucleotide (NAD+) and its reduced form (NADH) are coenzymes employed in hundreds of metabolic reactions. NAD+ also serves as a substrate for enzymes such as sirtuins, poly(ADP-ribose) polymerases (PARPs) and ADP-ribosyl cyclases. Given the pivotal role of NAD(H) in health and disease, studying NAD+ metabolism has become essential to monitor genetic- and/or drug-induced perturbations related to metabolic status and diseases (such as ageing, cancer or obesity), and its possible therapies. Here, we present a strategy based on liquid chromatography-tandem mass spectrometry (LC-MS/MS), for the analysis of the NAD+ metabolome in biological samples. In this method, hydrophilic interaction chromatography (HILIC) was used to separate a total of 18 metabolites belonging to pathways leading to NAD+ biosynthesis, including precursors, intermediates and catabolites. As redox cofactors are known for their instability, a sample preparation procedure was developed to handle a variety of biological matrices: cell models, rodent tissues and biofluids, as well as human biofluids (urine, plasma, serum, whole blood). For clinical applications, quantitative LC-MS/MS for a subset of metabolites was demonstrated for the analysis of the human whole blood of nine volunteers. Using this developed workflow, our methodology allows studying NAD+ biology from mechanistic to clinical applications.

Factors Influencing the Steady-State Plasma Concentration of Imatinib Mesylate in Patients With Gastrointestinal Stromal Tumors and Chronic Myeloid Leukemia

Imatinib mesylate (IM) is the standard treatment for advanced, metastatic gastrointestinal stromal tumors (GISTs) and chronic myeloid leukemia (CML) with a fixed daily standard dosage via the oral route. Interindividual and intraindividual variability in plasma concentrations have been closely linked to the efficacy of IM therapy. Therefore, this review identifies and describes the key factors influencing the plasma concentration of IM in patients with GISTs and CML. We used the following keywords to search the PubMed, EMBASE, Ovid, Wangfang, and CNKI databases to identify published reports: IM, plasma concentration, GISTs, CML, drug combination/interaction, pathology, and genotype/genetic polymorphism, either alone or in combination. This literature review revealed that only 10 countries have reported the mean concentrations of IM in GISTs or CML patients and the clinical outcomes in different ethnic groups and populations. There were totally 24 different gene polymorphisms, which were examined for any potential influence on the steady-state plasma concentration of IM. As a result, some genotype locus made discrepant conclusion. Herein, the more sample capacity, multicenter, long-term study was worthy to carry out. Eleven reports were enumerated on clinical drug interactions with IM, while there is not sufficient information on the pharmacokinetic parameters altered by drug combinations with IM that could help in investigating the actual drug interactions. The drug interaction with IM should be paid more attention in the future research.

Discovery and structure activity relationships of 7-benzyl triazolopyridines as stable, selective, and reversible inhibitors of myeloperoxidase

Myeloperoxidase (MPO) is a heme peroxidase found in neutrophils, monocytes and macrophages that efficiently catalyzes the oxidation of endogenous chloride into hypochlorous acid for antimicrobial activity. Chronic MPO activation can lead to indiscriminate protein modification causing tissue damage, and has been associated with chronic inflammatory diseases, atherosclerosis, and acute cardiovascular events. Triazolopyrimidine 5 is a reversible MPO inhibitor; however it suffers from poor stability in acid, and is an irreversible inhibitor of the DNA repair protein methyl guanine methyl transferase (MGMT). Structure-based drug design was employed to discover benzyl triazolopyridines with improved MPO potency, as well as acid stability, no reactivity with MGMT, and selectivity against thyroid peroxidase (TPO). Structure-activity relationships, a crystal structure of the MPO-inhibitor complex, and acute in vivo pharmacodynamic data are described herein.

Pharmacokinetics interaction between imatinib and genistein in rats

The objective of this work was to investigate the effect of orally administered genistein on the pharmacokinetics of imatinib and N-desmethyl imatinib in rats. Twenty-five healthy male SD (Sprague-Dawley) rats were randomly divided into five groups: A group (control group), B group (multiple dose of 100 mg/kg genistein for consecutive 15 days), C group (multiple dose of 50 mg/kg genistein for consecutive 15 days), D group (a single dose of 100 mg/kg genistein), and E group (a single dose of 50 mg/kg genistein). A single dose of imatinib is administered orally 30 min after administration of genistein (100 mg/kg or 50 mg/kg). The pharmacokinetic parameters of imatinib and N-desmethyl imatinib were calculated by DAS 3.0 software. The multiple dose of 100 mg/kg or 50 mg/kg genistein significantly (P < 0.05) decreased the AUC0-t and C max of imatinib. AUC0-t and the C max of N-desmethyl imatinib were also increased, but without any significant difference. However, the single dose of 100 mg/kg or 50 mg/kg genistein has no effect on the pharmacokinetics of imatinib and N-desmethyl imatinib. Those results indicated that multiple dose of genistein (100 mg/kg or 50 mg/kg) induces the metabolism of imatinib, while single dose of genistein has no effect.

Elucidation of the mechanism of ribose conjugation in a pyrazole-containing compound in rodent liver

1. Here we report on the mechanism of ribose conjugation, through NADH as a cofactor, of a pyrazole-containing compound (PT). Incubation of PT in rat liver microsomes supplemented with NADP⁺/H, NAD⁺/H, and β-nicotinamide mononucleotide (NMN) resulted in complete conjugation to the adenine dinucleotide phosphate conjugate (ADP-C), adenine dinucleotide conjugate (AD-C), and 5-phosphoribose conjugate (Rib-C1), respectively. In hepatocytes, PT predominantly formed three ribose conjugates: Rib-C1, the ribose conjugate (Rib-C2), and the carboxylic acid of Rib-C2 (Rib-C3). 2. Phosphatase inhibitors were added to hepatocyte incubations. AD-C was detected in this reaction, which suggests that one of the major pathways for the formation of the ribose conjugates is through NAD⁺/H. When AD-C was incubated with phosphatase, Rib-C1 and Rib-C2 formed. 3. To understand the in vivo relevance of this metabolic pathway, rats were dosed with PT and Rib-C2 was found in the urine. 4. Structure-activity relationship shows that replacement of the distal thiazole group in the PT to a phenyl group abolishes this conjugation. Three amino acid residues in the active site preferentially interact with the sulfur atom in the thiazole of PT. 5. In summary, PT forms direct AD-C in hepatocytes, which is further hydrolyzed by phosphatase to give ribose conjugates.

Characterization of imatinib metabolites in rat and human liver microsomes: differentiation of hydroxylation from N-oxidation by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

In vitro metabolism of imatinib was investigated in rat and human liver microsomes. Atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) was applied in differentiating hydroxyl metabolites from N-oxides of imatinib because N-oxides are known to undergo deoxygenation during APCI. In addition, the major oxidative metabolite (M9, N-oxidation on the piperazine ring) was observed to undergo in-source fragmentation by elimination of formaldehyde. This fragment ion resulted from Meisenheimer rearrangement with migration of the N-methyl group to the corresponding N-methoxyl piperazine, followed by elimination of formaldehyde due to thermal energy activation at the vaporizer of APCI source. The presence of this fragment ion distinguished not only N-oxide from isomeric hydroxylated metabolite, but also unambiguously indicated that oxidation occurred on the N-4 of the piperazine ring where the methyl group was attached.