Comparative Studies on the Cytochrome P450-Associated Metabolism and Interaction Potential of Selegiline Between Human Liver-Derived in Vitro Systems

Abstract

This article is available online at http://dmd.aspetjournals.org ABSTRACT:Selegiline was used as a model compound in a project aimed at comparing, evaluating, and integrating different in vitro approaches for the prediction of cytochrome P450 (P450)-catalyzed hepatic drug metabolism in humans (EUROCYP). Metabolic predictions were generated using homology modeling, cDNA-expressed P450 enzymes, human liver microsomes, primary cultured human hepatocytes, and precision-cut human liver slices. All of the in vitro systems correctly indicated the formation of two dealkylated metabolites, desmethylselegiline and methamphetamine. The metabolic instability of selegiline was demonstrated by all of the in vitro systems studied. Estimates of clearance varied from 16 l/h to 223 l/h. With the exception of one approach, all systems underpredicted the in vivo clearance in humans (236 l/h). Despite this, all approaches successfully classified selegiline as a high clearance compound. Homology modeling suggested the participation of CYP2B6 in the demethylation of selegiline and of CYP2D6 in the depropargylation of the drug. Studies with recombinant expressed enzymes and with human hepatic microsomal fraction supported the involvement of CYP2B6 but not of CYP2D6. These techniques also suggested the involvement of CYP1A2, CYP2C8, and CYP2C19 in the biotransformation of selegiline. In vitro, CYP2B6 was the most active form of P450 involved in selegiline metabolism. Metabolism by several enzymes operating in parallel implies a low interaction potential for the drug. None of the techniques alone was able to predict all aspects of the metabolic and kinetic behavior of selegiline in vivo. However, when used as an integrated package, all significant characteristics were predictable.For more than a decade, in vitro techniques have had a well established role in the early phases of drug development in predicting the pharmacokinetic and metabolic behavior of new chemical entities. When properly used, predictions based on results from in vitro studies will save both development costs and time. In addition, they greatly reduce the number of experimental animals used by the industry in absorption, distribution, metabolism, and excretion studies. Support for the increased utilization of in vitro techniques in drug metabolism studies has come from regulatory authorities (CDER/FDA, 1997). Most of these techniques are easily applicable to high throughput screening, which has further promoted their use recently (Rodrigues, 1997).Several in vitro methods for metabolic predictions are in common use, and even commercially available, but little attention has been paid to the validation of the systems in terms of quality of the predictions obtained and their usefulness in the process of drug development. In particular, comparisons of the data produced by different systems have been scarce. The present study was part of the EUROCYP project within the Biomed2 (Framework IV) program of the European Union. The goals of the project were to evaluate, compare, a...

CYP-Dependent Metabolism of PF9601N, A New Monoamine Oxidase-B Inhibitor, by C57BL / 6 Mouse and Human Liver Microsomes

“…Moreover, similarly to what has been observed in mouse, CYPdependent metabolism of PF9601N by human liver microsomes gave rise to a linear EadieHofstee plot suggesting the involvement of only one isozyme, with Km and Vmax values very close to the values observed in the mouse (Table 2). In contrast, the apparent Km values detected with l-deprenyl in mouse were quite different from the values given by human liver microsomes (35)(36). This suggests that the use of mouse liver microsomes to predict l-deprenyl metabolism in humans is inconsistent.…”

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“…See also articles of Andersson et al (2001); Pelkonen et al (2001) and Salonen et al (2003). the entity.…”

Functional Characterization of CYP2B6 Allelic Variants in Demethylation of Antimalarial Artemether

“…In contrast, it has been reported that CYP2D6 and CYP2C19 make no major contribution to this reaction (van Agtmael et al, 1998), and the role of other P450s remains unclear. CYP2B6 plays a major role in the biotransformation of several therapeutically important drugs, including cyclophosph-amide, bupropion, selegiline, efavirenz, nevirapine, and methadone (Roy et al, 1999;Hesse et al, 2000;Hidestrand et al, 2001;Salonen et al, 2003). Many genetic polymorphisms in the CYP2B6 gene have been reported, and these are thought to be responsible for interindividual and interethnic differences in responses to CYP2B6 substrate drugs [Zanger et al, 2007; Human Cytochrome P450 (CYP) Allele Nomenclature Committee, 2008;Mo et al, 2009].…”