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Abstract: Drug metabolism can result in the production of highly reactive metabolites that may form adducts with cellular macromolecules, and thus initiate adverse drug reactions, cause toxicity, and even require the withdrawal of drug from the market. In this study, a 2′-deoxyguanosine (dG)-based chemical trapping test system was developed for use as a fast screening tool for DNA adducting metabolites of new drug candidates. Reactive metabolites were generated from parent compounds in in vitro incubations with phenobarbital-induced mouse liver microsomes, human liver microsomes and different recombinant human CYP enzymes in the presence of dG. The formed dG-adducts were separated, characterized and their stability was studied by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The method was evaluated with six test compounds, aflatoxin B1, estrone, clozapine, tolcapone, ticlopidine and imipramine. Estrone and aflatoxin B1 formed dG adducts with phenobarbital-induced mouse liver microsomes, human liver microsomes and human recombinant CYP enzymes. Adduct formation was also observed with tolcapone when phenobarbital-induced mouse liver microsomes were used as the enzyme source. The stability of each formed adduct was independent of the different enzyme sources. No dG-adducts were identified with ticlopidine, clozapine and imipramine. Compared to other classical DNA reactivity tests, e.g. Ames test, the present surrogate endpoint, the dG adduct, is faster, enables the characterization of the formed compounds, and also permits the investigation of more unstable adducts. [Copyright &y& Elsevier]

The serotonin receptor 5-HT ligand 4-[F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-2-pyridinyl-benzamide ( p-[F]MPPF) was produced by a simplified method of Le Bars et al. Traditional oil bath heating was compared to microwave heating. Various radioanalytical methods, radio-Thin Layer Chromatography (TLC), High Pressure Liquid Chromatography (HPLC) and Mass Spectrometry (MS), were compared in the evaluation of the labelled product(s). The crude reaction mixture consisted of p-[F]MPPF and 2-4 radioactive by-products eluting after the product fraction, and the reverse-phase HPLC method failed occasionally to separate p-[F]MPPF from the radioactive by-product with close retention time. The heating method had no significant effect on the composition of labelled by-products. In LC-(ESI)-MS analysis of p-[F]MPPF the labelled product was identified with m/ z ratio of 435 ([M + H]). The other HPLC fractions were measured to have following m/ z ratios: (1) 327; 349; (675) (2) 402; 407/408; (791) and (3) 436, suggesting different kind of decomposition of the labelled product and/or the inactive precursor. The ion trap mass spectrometer was sufficient for the qualitative analysis of p-[F]MPPF. However, differentiation of by-products arising from the decomposition of p-[F]MPPF or from its precursor p-MPPNO proved to be challenging. [ABSTRACT FROM AUTHOR]