Jae-Gook Shin

Interferon regulatory factor-1 is prerequisite to the constitutive expression and IFN-γ-induced upregulation of B7-H1 (CD274)

Majority of cancer cells upregulate co‐inhibitory molecule B7‐H1 which confers resistance to anti‐tumor immunity, allowing cancers to escape from host immune surveillance. We addressed the molecular mechanism underlying the regulation of cancer‐associated B7‐H1 expression in response to interferon‐γ (IFN‐γ). Using promoter constructs in luciferase assay, the region between 202 and 320 bp from the translational start site is responsible for B7‐H1 expression. Electrophoretic mobility shift assay, site‐directed mutagenesis and knockdown experiment using siRNA revealed that interferon regulatory factor‐1 (IRF‐1) is primarily responsible for the constitutive B7‐H1 expression as well as for the IFN‐γ‐mediated B7‐H1 upregulation in a human lung cancer cell line A549. Additionally, AG490, a Janus activated kinase/signal transducer and activator of transcription inhibitor, greatly abolished the responsiveness of A549 cells to IFN‐γ by reducing the IRF‐1 transcription. Our findings support a critical role of IRF‐1 in the regulation of constitutive and IFN‐γ‐induced expression of B7‐H1 in cancer cells.

Incidence of S‐mephenytoin hydroxylation deficiency in a Korean population and the interphenotypic differences in diazepam pharmacokinetics

We studied the genetically determined hydroxylation polymorphism of S‐mephenytoin in a Korean population (N = 206) and the pharmacokinetics of diazepam and demethyldiazepam after an oral 8 mg dose of diazepam administered to the nine extensive metabolizers and eight poor metabolizers recruited from the population. The log10 percentage of 4‐hydroxymephenytoin excreted in the urine 8 hours after administration showed a bimodal distribution with an antimode of 0.3. The frequency of occurrence of the poor metabolizers was 12.6% in the population. In the panel study of diazepam in relation to the mephenytoin phenotype, there was a significant correlation between the oral clearance of diazepam and log10 urinary excretion of 4‐hydroxymephenytoin (rs = 0.777, p < 0.01). The plasma half‐life of diazepam in the poor metabolizers was longer than that in the extensive metabolizers (mean ± SEM, 91.0 ± 5.6 and 59.7 ± 5.4 hours, p < 0.005), and the poor metabolizers had the lower clearance of diazepam than the extensive metabolizers (9.4 ± 0.5 and 17.0 ± 1.4 ml/min, p < 0.001). In addition, the plasma half‐life of demethyldiazepam showed a statistically significant (p < 0.001) difference between the extensive metabolizers (95.9 ± 11.3 hours) and poor metabolizers (213.1 ± 10.7 hours), and correlated with the log10 urinary excretion of 4‐hydroxymephenytoin (rs = −0.615, p < 0.01). The findings indicate that the Korean subjects have a greater incidence of poor metabolizer phenotype of mephenytoin hydroxylation compared with that reported from white subjects and that the metabolism of diazepam and demethyldiazepam is related to the genetically determined mephenytoin hydroxylation polymorphism in Korean subjects.

The effect of SLCO1B1*15 on the disposition of pravastatin and pitavastatin is substrate dependent: the contribution of transporting activity changes by SLCO1B1*15.

Objective This study was addressed to understand the underlying mechanism of the substrate-dependent effect of genetic variation in SLCO1B1, which encodes OATP1B1 (organic anion transporting polypeptide) transporter, on the disposition of two OATP1B1 substrates, pravastatin and pitavastatin, in relation to their transport activities. Methods The uptake of pravastatin, pitavastatin, and fluvastatin was measured in oocytes overexpressing SLCO1B1*1a and SLCO1B1*15 to compare the alterations of in-vitro transporting activity. After 40-mg pravastatin or 4-mg pitavastatin was administered to 11 healthy volunteers with homozygous genotypes of SLCO1B1*1a/*1a and SLCO1B1*15/*15, the pharmacokinetic parameters of pravastatin and pitavastatin were compared among participants with SLCO1B1*1a/*1a and SLCO1B1*15/*15 genotypes. Results The uptake of pravastatin and pitavastatin in SLCO1B1*15 overexpressing oocytes was decreased compared with that in SLCO1B1*15, but no change occurred with fluvastatin. The fold change of in-vitro intrinsic clearance (Clint) for pitavastatin in SLCO1B1*15 compared with SLCO1B1*1a was larger than that of pravastatin (P<0.0001). The clearance (Cl/F) of pitavastatin was decreased to a greater degree in participant with SLCO1B1*15/*15 compared with that of pravastatin in vivo (P<0.01), consistent with in-vitro study. As a result, Cmax and area under the plasma concentration–time curve of these nonmetabolized substrates were increased by SLCO1B1*15 variant. The greater decrease in the transport activity for pitavastatin in SLCO1B1*15 variant compared with SLCO1B1*1a was, however, associated with the greater effect on the pharmacokinetics of pitavastatin compared with pravastatin in relation to the SLCO1B1 genetic polymorphism. Conclusion This study suggests that substrate dependency in the consequences of the SLCO1B1*15 variant could modulate the effect of SLCO1B1 polymorphism on the disposition of pitavastatin and pravastatin.

Effect of the CYP3A5 genotype on the pharmacokinetics of intravenous midazolam during inhibited and induced metabolic states

Our objective was to investigate the effect of the CYP3A5 genotype on the systemic clearance of midazolam in constitutive, inhibited, and induced metabolic conditions.

Hexachlorophene inhibits Wnt/beta-catenin pathway by promoting Siah-mediated beta-catenin degradation.

Aberrant activation of Wnt/β-catenin signaling and subsequent up-regulation of β-catenin response transcription (CRT) is a critical event in the development of human colon cancer. Thus, Wnt/β-catenin signaling is an attractive target for the development of anticancer therapeutics. In this study, we identified hexachlorophene as an inhibitor of Wnt/β-catenin signaling from cell-based small-molecule screening. Hexachlorophene antagonized CRT that was stimulated by Wnt3a-conditioned medium by promoting the degradation of β-catenin. This degradation pathway is Siah-1 and adenomatous polyposis colidependent, but glycogen synthase kinase-3β and F-box β-transducin repeat-containing protein-independent. In addition, hexachlorophene represses the expression of cyclin D1, which is a known β-catenin target gene, and inhibits the growth of colon cancer cells. Our findings suggest that hexachlorophene attenuates Wnt/β-catenin signaling through the Siah-1-mediated β-catenin degradation.

Effects of Cyp2c19 and Cyp2c9 genetic polymorphisms on the disposition of and blood glucose lowering response to tolbutamide in humans

Several recent in-vitro data have revealed that CYP2C19, in addition to CYP2C9, is also involved in the 4-methylhydroxylation of tolbutamide. We evaluated the relative contribution of CYP2C9 and CYP2C19 genetic polymorphisms on the disposition of blood glucose lowering response to tolbutamide in normal healthy Korean subjects in order to reappraise tolbutamide as a selective in-vivo probe substrate of CYP2C9 activity. A single oral dose of tolbutamide (500 mg) or placebo was administered to 18 subjects in a single-blind, randomized, crossover study with a 2-week washout period. Twelve subjects (of whom six were CYP2C19 extensive metabolizer (EM) and six were CYP2C19 poor metabolizer (PM) genotype) were of the homozygous wild-type CYP2C9*1 genotype; the other six subjects were of the CYP2C9*1/*3 and CYP2C19 EM genotype. Pharmacokinetic parameters were estimated from plasma and urine concentrations of tolbutamide and 4-hydroxytolbutamide. Serum glucose concentrations were measured before and after oral intake of 100 g dextrose. In subjects heterozygous for the CYP2C9*3 allele, C(max) and AUC of tolbutamide were significantly greater and the plasma half-life significantly longer than those in homozygous CYP2C9*1 subjects. No pharmacokinetic differences were found between CYP2C19 EM and PM genotype subjects. The estimated AUC of the increase in serum glucose after oral intake of 100 g dextrose was 2.7-fold higher in subjects with the wild-type CYP2C9 genotype than in those with CYP2C9*1/*3, but CYP2C19 genetic polymorphism did not alter the blood glucose lowering effect of tolbutamide. The plasma AUC of 4-hydroxytolbutamide and the ratio of 4-hydroxytolbutamide/tolbutamide did not differ significantly between CYP2C19 PM and EM genotype subjects, while these parameters were about twice as high in subjects with the wild-type CYP2C9 genotype than in heterozygous CYP2C9*3 subjects (P < 0.05). Our results strongly suggest that the disposition and hypoglycemic effect of tolbutamide are affected mainly by CYP2C9 genetic polymorphism, but not by CYP2C19 polymorphism. The in-vivo contribution of CYP2C19 to tolbutamide 4-methylhydroxylation appears to be minor in humans. This suggests that, at least in vivo, tolbutamide remains a selective probe for measuring CYP2C9 activity in humans.

Identification and Functional Characterization of Genetic Variants of Human Organic Cation Transporters in a Korean Population

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 [3H]methyl-4-phenylpyridinium acetate (MPP+) or [14C]tetraethylammonium compared with those cells that overexpress wild-type hOCT2, and the estimated kinetic parameters of these variants for [3H]MPP+ uptake in oocytes showed a 2- to 5-fold increase in Km values and a 10- to 20-fold decrease in Vmax 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.

Inhibitory effects of fruit juices on CYP3A activity

There have been very limited reports on the effects of commercial fruit juices on human CYP3A activity. Therefore, the inhibitory effects of readily available commercial fruit juices on midazolam 1′-hydroxylase activity, a marker of CYP3A, were evaluated in pooled human liver microsomes. The fruit juices investigated were black raspberry, black mulberry, plum, and wild grape. White grapefruit, pomegranate, and orange juice were used as positive and negative controls. The black mulberry juice showed the most potent inhibition of CYP3A except for grapefruit juice. The inhibition depended on the amount of a fruit juice added to the incubation mixture. The inhibitory potential of human CYP3A was in the order: grapefruit > black mulberry > wild grape > pomegranate > black raspberry. The IC50 values of all fruit juices tested were reduced after preincubation with microsomes in the presence of the NADPH-generating system, suggesting that a mechanism-based inhibitory component was present in these fruit juices, as in the case of grapefruit. The results suggest that, like grapefruit juice, commercial fruit juices also have the potential to inhibit CYP3A-catalzyed midazolam 1′-hydroxylation. Therefore, in vivo studies investigating the interactions between fruit juices such as black mulberry and wild grape and CYP3A substrates are necessary to determine whether inhibition of CYP3A activity by fruit juices is clinically relevant.

Protein-kinase-C-mediated β-catenin phosphorylation negatively regulates the Wnt/β-catenin pathway

Normally, the Wnt/β-catenin pathway controls developmental processes and homeostasis, but abnormal activation of this pathway is a frequent event during the development of cancer. The key mechanism in regulation of the Wnt/β-catenin pathway is the amino-terminal phosphorylation of β-catenin, marking it for proteasomal degradation. Here we present small-molecule-based identification of protein kinase C (PKC)-mediated β-catenin phosphorylation as a novel mechanism regulating the Wnt/β-catenin pathway. We used a cell-based chemical screen to identify A23187, which inhibits the Wnt/β-catenin pathway. PKC was activated by A23187 treatment and subsequently phosphorylated N-terminal serine (Ser) residues of β-catenin, which promoted β-catenin degradation. Moreover, the depletion of PKCα inhibited the phosphorylation and degradation of β-catenin. Therefore, our findings suggest that the PKC pathway negatively regulates the β-catenin level outside of the Wnt/β-catenin pathway.

Effect of itraconazole on the pharmacokinetics and pharmacodynamics of fexofenadine in relation to the MDR1 genetic polymorphism

Our objective was to evaluate the effect of itraconazole, a P‐glycoprotein inhibitor, on the pharmacokinetics and pharmacodynamics of fexofenadine, a P‐glycoprotein substrate, in relation to the multidrug resistance 1 gene (MDR1) G2677T/C3435T haplotype.