Functional Characterization of CYP2B6 Allelic Variants in Demethylation of Antimalarial Artemether

Abstract

ABSTRACT:Artemether (AM) is one of the most effective antimalarial drugs. The elimination half-life of AM is very short, and it shows large interindividual variability in pharmacokinetic parameters. The aim of this study was to identify cytochrome P450 (P450) isozymes responsible for the demethylation of AM and to evaluate functional differences between 26 CYP2B6 allelic variants in vitro. Of 14 recombinant P450s examined in this study, CYP2B6 and CYP3A4 were primarily responsible for production of the desmethyl metabolite dihydroartemisinin. The intrinsic clearance (V max /K m ) of CYP2B6 was 6-fold higher than that of CYP3A4. AM demethylation activity was correlated with CYP2B6 protein levels (P ‫؍‬ 0.004); however, it was not correlated with CYP3A4 protein levels (P ‫؍‬

Differences in Methadone Metabolism by CYP2B6 Variants

“…In a COS-1 system, the activities of CYP2B6.6 and CYP2B6.9, in which 516G.T is the common polymorphism, were both extremely low, but this was attributed to minimal expression (Hofmann et al, 2008). CYP2B6.9 activity toward artemether was somewhat lower than CYP2B6.1 in COS-7 cells (Honda et al, 2011), and toward 7-ethoxy-4-trifluoromethylcoumarin, bupropion, and efavirenz in a reconstituted bacterial expression system (Zhang et al, 2011). The present results suggest that methadone is also one of the more catalytically diminished substrates with CYP2B6.9.…”

“…In an insect cell system with coexpressed P450 reductase and b 5 , CYP2B6.6 Cl int for bupropion 4-hydroxylation was lower, whereas efavirenz 8-hydroxylation was less but not significantly different from CYP2B6.1 (Xu et al, 2012). CYP2B6.6 activity in other systems (E. coli, Cos-1, Cos-7) was lower toward bupropion and efavirenz (Zhang et al, 2011), and ketamine (Li et al, 2013), but greater for cyclophosphamide (Xie et al, 2003;Ariyoshi et al, 2011;Raccor et al, 2012) and artemether (Honda et al, 2011), and unchanged for selegiline (Watanabe et al, 2010). The present and previous (Gadel et al, 2013) experiments show that methadone is one of the most catalytically diminished substrates for CYP2B6.6.…”

“…CYP2B6.4 results are even more substrate-dependent. In E. coli, Cos-1, and Cos-7 systems, CYP2B6.4 cyclophosphamide 4-hydroxylation was 25% lower than CYP2B6.1 (Ariyoshi et al, 2011;Raccor et al, 2012), the catalytic efficiency for 7-ethoxy-4-trifluoromethylcoumarin, bupropion, and efavirenz was decreased to half, one-third, and unchanged, respectively (Zhang et al, 2011), and artemether and selegiline metabolism was almost doubled (Watanabe et al, 2010;Honda et al, 2011). Methadone metabolism by CYP2B6.4 in the present investigation was greater than by CYP2B6.1.…”

“…CYP2B6.5 activities are variable with other substrates. CYP2B6.5 cyclophosphamide 4-hydroxylation in E. coli, Cos-1, and Cos-7 systems was half that of CYP2B6.1 (Raccor et al, dmd.aspetjournals.org 2012), and artemether and selegiline metabolism was diminished (Watanabe et al, 2010;Honda et al, 2011), whereas 7-ethoxy-4-trifluoromethylcoumarin, bupropion, and efavirenz metabolism was decreased by one-third, half, and increased, respectively, compared with CYP2B6.1 (Zhang et al, 2011;Radloff et al, 2013). CYP2B6.4 results are even more substrate-dependent.…”

Which CYP2B6 Variants Have Functional Consequences for Cyclophosphamide Bioactivation?: TABLE 1

“…The R487C amino acid change associated with this SNP (C1459T) results in an approximately 50% decrease in the intrinsic clearance of cyclophosphamide (Raccor et al, 2011) (Table 1). CYP2B6.5 variant protein also has decreased artemether and bupropion intrinsic clearance (Honda et al, 2011;Zhang et al, 2011). However, in marked contrast, there is an increase in the biotransformation of efavirenz (Zhang et al, 2011) with this variant (Table 1).…”