ABSTRACT:Genetic variants of three human organic cation transporter genes (hOCTs) were extensively explored in a Korean population. The functional changes of hOCT2 variants were evaluated in vitro, and those genetic polymorphisms of hOCTs were compared among different ethnic populations. From direct DNA sequencing, 7 of 13 coding variants were nonsynonymous single-nucleotide polymorphisms (SNPs), including four variants from hOCT1 (F160L, P283L, P341L, and M408V) and three from hOCT2 (T199I, T201M, and A270S), whereas 6 were synonymous SNPs. The linkage disequilibrium analysis presented for three independent LD blocks for each hOCT gene showed no significant linkage among all three hOCT genes. The transporter activities of MDCK cells that overexpress the hOCT2-T199I, -T201M, and -A270S variants showed significantly decreased uptake of showed a 2-to 5-fold increase in K m values and a 10-to 20-fold decrease in V max values. The allele frequencies of the five functional variants hOCT1-P283L, -P341L, and hOCT2-T199I, -T201M, and -A270S were 1.3, 17, 0.7, 0.7, and 11%, respectively, in a Korean population; the frequency distributions of these variants were not significantly different from those of Chinese and Vietnamese populations. These findings suggest that genetic variants of hOCTs are not linked among three genes in a Korean population, and several of the hOCT genetic variants cause decreased transport activity in vitro compared with the wild type, although the clinical relevance of these variants remains to be evaluated.The human organic cation transporters hOCT1, hOCT2, and hOCT3 mediate electrogenic transport of small organic cations with different molecular structures, independent of sodium gradient (Koepsell, 1999). These organic cation substrates include clinically important therapeutics (e.g., metformin, procainamide, and cimetidine), endogenous compounds (e.g., dopamine and norepinephrine), as well as toxic substances [e.g., tetraethylammonium bromide (TEA), HPP ϩ , and methyl-4-phenylpyridinium acetate (MPP ϩ )] (Gorboulev et al., 1997;Zhang et al., 1997;Kang et al., 2006). Although these transporters show extensive overlaps in their substrate specificities, they exhibit distinct differences in tissue distribution; hOCT1 is primarily found in the sinusoidal membrane of hepatocytes and, to a lesser extent, in intestinal epithelial cells, whereas hOCT2 is mainly expressed in the basolateral membrane of kidney proximal tubules, and hOCT3 shows a widespread tissue distribution that includes the brain, heart, and liver. Based on their properties and tissue distributions, hOCT1, hOCT2, and hOCT3 are thought to play important roles in the excretion and distribution of organic cations in the liver, kidney, and brain (Jonker and Schinkel, 2004).Knockout mouse models have been generated for the Oct1, Oct2, and Oct3 genes to elucidate the in vivo function of the OCT transporters. Oct1-, Oct2-, and Oct3-deficient mice are viable and display no obvious phenotypic abnormalities (Jonker et al., 2001Zwart et al., 2001...

Phenotypic differences in drug responses have been associated with known pharmacogenomic loci, but many remain to be characterized. Therefore, we developed next-generation sequencing (NGS) panels to enable broad and unbiased inspection of genes that are involved in pharmacokinetics (PKs) and pharmacodynamics (PDs). These panels feature repetitively optimized probes to capture up to 114 PK/PD-related genes with high coverage (99.6%) and accuracy (99.9%). Sequencing of a Korean cohort (n = 376) with the panels enabled profiling of actionable variants as well as rare variants of unknown functional consequences. Notably, variants that occurred at low frequency were enriched with likely protein-damaging variants and previously unreported variants. Furthermore, in vitro evaluation of four pharmacogenes, including cytochrome P450 2C19 (CYP2C19), confirmed that many of these rare variants have considerable functional impact. The present study suggests that targeted NGS panels are readily applicable platforms to facilitate comprehensive profiling of pharmacogenes, including common but also rare variants that warrant screening for personalized medicine.

ABSTRACT:Our objectives were to identify CYP2D6 genetic polymorphisms in a Korean population, to compare the allele frequencies with those of other ethnic groups, and to evaluate variant-induced functional variations in dextromethorphan (DM) metabolism in vitro and in vivo. Thirty-eight single nucleotide polymorphisms of CYP2D6 were identified by direct DNA sequencing in 51 Koreans. An extended set of 707 subjects were screened for the identified variants. A group of 202 healthy subjects was subjected to phenotypic analysis on DM metabolism. CYP2D6*10 was found to be the most frequent allele (45.6%), followed by CYP2D6*1 (32.3%), *2 (9.9%), *5 (5.6%), *41 (2.2%), *49 (1.4%), and some other rare alleles (<1%). The newly identified E418K and S183Stop were assigned as CYP2D6*52 and CYP2D6*60, respectively, by the Human P450 (CYP) Allele Nomenclature Committee. Individuals having the CYP2D6*10/*49 genotype (n ‫؍‬ 5) exhibited a significant decrease in CYP2D6 metabolic activity compared with those with the CYP2D6*1/*1 genotype (n ‫؍‬ 31) (P < 0.019). Variations in CYP2D6 protein levels in liver tissues (n ‫؍‬ 49) were observed with CYP2D6 genotypes, and correlation between the CYP2D6 protein content and the activity was significant (r 2 ‫؍‬ 0.7). Given the importance of CYP2D6 in drug metabolism, subjects with the CYP2D6*10/*49 genotype may benefit from genotype analysis to achieve optimal drug therapy.Polymorphisms of the gene for cytochrome P450 2D6 (CYP2D6) influence the rate of elimination of CYP2D6 substrates, which represent approximately 20% of commonly prescribed therapeutic drugs. CYP2D6 substrates include antipsychotic drugs (haloperidol and risperidone), antiarrhythmic agents (flecainide and perphenazine), tricyclic antidepressants (imipramine and amitriptyline), ␤-blockers (metoprolol and carvedilol), and opioids (codeine and tramadol) (Zanger et al., 2004;Ingelman-Sundberg, 2005). The CYP2D6 gene locus is highly polymorphic, and various point mutations, nucleotide deletions or insertions, gene rearrangements, and multiplication/deletion of the entire CYP2D6 gene, resulting in more than 106 different alleles

This article is available online at http://dmd.aspetjournals.org ABSTRACT:The stereoselective metabolism of lansoprazole enantiomers was evaluated by incubation of human liver microsomes and cDNAexpressed cytochrome P450 (P450) enzymes to understand and predict their stereoselective disposition in humans in vivo. The intrinsic clearances (Cl int ) of the formation of both hydroxy and sulfone metabolites from S-lansoprazole were 4.9-and 2.4-fold higher than those from the R-form, respectively. The sums of formation Cl int of both metabolites were 13.5 and 57.3 l/min/mg protein for R-and S-lansoprazole, respectively, suggesting that S-lansoprazole would be cleared more rapidly than the R-form. The P450 isoform selective inhibition study in liver microsomes, and the incubation study of cDNA-expressed enzymes, demonstrated that the stereoselective sulfoxidation is mediated by CYP3A4 and that the hydroxylation is mediated by CYP2C9 and CYP3A4 as well as by CYP2C19. Total Cl int values of hydroxy and sulfone metabolite formation catalyzed by all these P450 enzymes were consistently higher for S-lansoprazole than for the R-form. The CYP3A4 produced the greatest difference of Cl int between Sand R-enantiomers, mainly due to a difference of sulfoxidation metabolism (Cl int 76.5 versus 10.8 l/min/nmol of P450, respectively), whereas CYP2C19-catalyzed hydroxylation resulted in a minor difference of Cl int between S-and R-enantiomers (179.6 versus 143.3 l/min/nmol of P450, respectively). However, the affinity of CYP2C19 on hydroxylation was 5.7-fold higher for S-enantiomer than for the R-form (K m 2.3 versus 13.1 M), suggesting that the role of CYP2C19 on stereoselective hydroxylation would be more prominent at concentrations around the usual therapeutic level. These findings suggest that both CYP2C19 and CYP3A4 are major enzymes contributing to the stereoselective disposition of lansoprazole, but stereoselective hydroxylation of lansoprazole enantiomers is mainly influenced by CYP2C19, especially at the usual therapeutic doses.

ABSTRACT:The breast cancer resistance protein (BCRP) is a member of the ATP-binding cassette transporters. The aim of the present study was to identify genetic variants of BCRP in Koreans and to assess the functional consequences of BCRP polymorphisms. Twenty single nucleotide polymorphisms (SNP), including four nonsynonymous SNP, were identified by DNA sequencing of the BCRP gene in 92 Korean subjects. BCRP V12M, Q141K, P269S, and Q126Stop were detected at frequencies of 23, 28, 0.2, and 1.9%, respectively. These four coding variants were also screened in Chinese and Vietnamese subjects; the allelic frequencies among the three populations were compared; and predictions were made as to the potential frequency of each variant.