Severe adverse drug reactions (ADRs) are a major issue for drug therapy because they can cause serious disorders and be life-threatening. Many severe ADRs appear to be idiosyncratic and unpredictable. Genetic factors may underlie susceptibility to severe ADRs, and identification of predisposing genotypes may improve drug therapy by facilitating prescreening of carriers for specific genetic biomarkers. In this review, we clarify the current status of ADRs in Japan from open ADR data sources. Then, we introduce recent progress in the field of pharmacogenetic biomarkers for severe cutaneous ADRs, liver injury, and statin-induced myopathy. Key challenges for discovery of predictable risk alleles for these severe ADRs are also discussed.

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  Glucuronidation is one of the major pathways of metabolism of endo- and xenobiotics. UDP-Glucuronosyltransferase (UGT)-catalyzed glucuronidation accounts for up to 35% of phase II reactions. The expression and function of UGT is modulated by gene regulation, post-translational modifications and protein-protein association. Many studies have focused on drug-drug interactions involving UGT, and there are a number of reports describing the inhibition of UGT by xenobiotics. However, studies about the role of endogenous compounds as an inhibitor or activator of UGT are limited, and it is important to understand any change in the function and regulation of UGT by endogenous compounds. Recent studies in our laboratory have shown that fatty acyl-CoAs are endogenous activators of UGT, although fatty acyl-CoAs had been considered as inhibitors of UGT. Further, we have also suggested that adenine and related compounds are endogenous allosteric inhibitors of UGT. In this review, we summarize the endogenous modulators of UGT and discuss their relevance to UGT function.

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  Specific antibody production is an important issue in crossover pharmacokinetic (PK) studies of protein-based formulations. We recently reported that intravenous co-administration of tacrolimus with multiple human interferon-alpha (h-IFN) administrations successfully suppressed the production of anti-h-IFN antibodies in rats. Since crossover PK studies are preferentially carried out using larger animals such as dogs or monkeys that are capable of accepting the same dosage formulations as those for clinical use, we extended our study of co-administration of tacrolimus with multiple h-IFN administrations to beagle dogs in the present study. Beagle dogs were subcutaneously administered 0.5 million IU/kg of h-IFN once a week for 4 weeks. In some experiments, tacrolimus at 0.01 or 0.1 mg/kg was intravenously co-administered at the same time as the h-IFN administration. Co-administration of the lower dose of tacrolimus (0.01 mg/kg) failed to suppress the anti-h-IFN IgG responses, while co-administration of the higher dose (0.1 mg/kg) successfully suppressed these responses. Moreover, co-administration of tacrolimus had little effect on the serum creatinine concentrations, suggesting that multiple administrations of tacrolimus at the concentrations examined did not cause severe renal disorders. Taken together, the present data confirm that co-administration of tacrolimus is a promising way to assess crossover PK studies of human or humanized proteinic formulations in beagle dogs.

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  The effects of ethanol extracts from Thai plants on P-glycoprotein (P-gp) function and cell viability were examined using paclitaxel-resistant HepG2 (PR-HepG2) cells. KP018 from Ellipeiopsis cherrevensis and AT80 from Ancistrocladus tectorius increased both rhodamine 123, a typical P-gp substrate, and [³H]paclitaxel uptake in PR-HepG2 cells. However, some extracts such as MT80 from Microcos tomentosa increased rhodamine 123, but not [³H]paclitaxel, uptake, while MM80 from Micromelum minutum increased only [³H]paclitaxel uptake. Thus, the effects of extracts of Thai plants on rhodamine 123 uptake were not necessarily the same as those on [³H]paclitaxel uptake. Purified compounds such as bergapten did not affect the uptake of either substrate. KP018, AT80, and MM80 increased [³H]paclitaxel uptake and decreased the cell viability in a concentration-dependent manner. Among these extracts, KP018 showed the most potent cytotoxicity. The cytotoxic potency of KP018 on PR-HepG2 cells was similar to that on wild-type HepG2 cells, and was not potentiated by verapamil. At concentrations resulting in no cytotoxicity, AT80 and MM80 potentiated paclitaxel-induced cytotoxicity in PR-HepG2 cells. These results indicate that K018 may be a useful source to search for a new anticancer drug, while AT80 and MM80 may be useful as modulators of P-gp-mediated multidrug resistance in cancer cells.

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  The transport of antifolate aminopterin by human organic anion transporters hOAT1 (SLC22A6) and hOAT3 (SLC22A8) was characterized using Xenopus laevis oocytes and was compared with that of methotrexate. Although hOAT1 and hOAT3 transported both aminopterin and methotrexate, uptake of methotrexate was greater in hOAT3-expressing oocytes than in hOAT1-expressing oocytes, and aminopterin was transported by hOAT1 more efficiently. The apparent 50% inhibitory concentration (IC₅₀) of aminopterin for p-aminohippurate uptake by hOAT1 was lower than that of methotrexate (methotrexate: 998 μM, aminopterin: 160 μM). On the other hand, IC₅₀ values of these antifolates for estrone sulfate transport by hOAT3 were comparable (methotrexate: 61.5 μM, aminopterin: 59.2 μM). The Michaelis-Menten constant and maximum velocity of aminopterin transport by hOAT1 were calculated to be 226 μM and 72.5 pmol/ oocyte/2 hr, respectively. Probenecid and non-steroidal anti-inflammatory drugs strongly inhibited the transport. These findings show that both aminopterin and methotrexate are substrates of hOAT1 and hOAT3, and that there are differences between the antifolates in terms of their transport characteristics.

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  The inhibition of intestinal breast cancer resistance protein (BCRP), which restricts the absorption of xenobiotics, may increase the systemic availability of its substrates. The aim of this study was to evaluate the inhibitory effects of herbal extracts and their constituents on BCRP-mediated transport. The inhibitory effects of 9 herbal extracts and 23 isoflavonoids, including soybean-derived isoflavones, on BCRP-mediated methotrexate (MTX) transport were evaluated using BCRP-expressing membrane vesicles. The structure-inhibitory potency relationship was investigated by multiple factor analysis. Extracts of soybean, Gymnema sylvestre, black cohosh and passion flower and rutin strongly inhibited BCRP-mediated transport of MTX at 1 mg/ml, while inhibition by chlorella, milk thistle and Siberian ginseng extracts was weak. Among the 23 isoflavonoids examined, all of which inhibited BCRP-mediated transport, coumestrol showed the most potent inhibition (IC₅₀=63 nM). The inhibitory potencies of 6 isoflavonoid glucosides were 10- to 100-fold lower than those of the corresponding aglycones. The addition of a 5-hydroxyl or 6-methoxyl moiety tended to potentiate the inhibition. The inhibitory potency of daidzein was decreased 100-fold by 7-glucuronidation, but was virtually unaffected by 4′-sulfation. Thus, some herbal and dietary supplements and isoflavonoids may increase the systemic availability of BCRP substrates when concomitantly given orally.

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  Human CYP1A1 and CYP1A2 genes are in a head-to-head orientation on chromosome 15 and are separated by a 23-kb intergenic space. To our knowledge, this is the first report on a stable cell line that contains the 23-kb full-length regulatory region and is able to simultaneously assess the transcriptional activation of CYP1A1 and CYP1A2 genes. The stable cell line that constitutively expresses the reporter activities was constructed by inserting the dual reporter plasmid containing the 23-kb region between the CYP1A1 and CYP1A2 genes into the chromosome. Transcriptional activation of the CYP1A1 and CYP1A2 genes was measured simultaneously using luciferase (Luc) and secreted alkaline phosphatase (SEAP) activities, respectively. To demonstrate the utility of the stable cell line, CYP1A1/1A2 induction by the majority of compounds previously identified as CYP1A1/1A2 inducers was measured. The results clearly show that all compounds caused induction of reporter activities. In addition to assessing transcriptional activation of the CYP1A1 and CYP1A2 genes by measuring reporter activities, we determined the intrinsic CYP1A1 and CYP1A2 mRNA levels by treating them with the same compounds. The results suggest that this stable cell line may be used to rapidly and accurately predict CYP1A1/1A2 induction.

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  Hepatic drug transporters are responsible for both hepatic uptake and the biliary excretion of drugs. Expression changes in hepatic drug transporter genes have been observed in various pathophysiological conditions. However, it has not been comprehensively investigated what factors substantially influence the mRNA levels of hepatic drug transporters. In this study, we quantified the mRNA expression of 17 drug transporters using noncancerous liver tissue samples and carried out stepwise multiple regression analysis to identify the factors affecting their expression from 18 clinical variables. For 17 drug transporters, the mRNA level of organic anion transporting polypeptide (OATP) 2B1 was highest, followed by that of organic cation transporter 1, organic anion transporter 2, OATP1B1, OATP1B3, multidrug resistance-associated protein (MRP) 6, and MRP3. Stepwise multiple regression analysis demonstrated MRP4 mRNA level to be predicted with the greatest accuracy among 17 drug transporters. Of clinical variables entered into the prediction model for MRP4, hepatitis C virus (HCV) infection and liver cirrhosis were crucial factors affecting MRP4 mRNA and protein levels. Furthermore, HCV-related cirrhosis influenced the mRNA levels of 8 drug transporters besides MRP4. These findings indicate that HCV-related cirrhosis is a crucial factor affecting the expression of hepatic drug transporters, especially MRP4.

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  Unglycosylated recombinant human α₁-acid glycoprotein (hAGP) variants (rF1^*S and rA) were prepared in an E. coli expression system using the Origami B strain and pET-3c vector. Thioredoxin was co-expressed to promote the appropriate folding of hAGP. SDS-PAGE under reducing conditions showed that rF1^*S and rA migrate as single bands after purification. However, several bands derived from rA were observed under non-reducing conditions because of the high reactivity of a free cystein residue (C149). We therefore prepared a mutant of A variant (C149R-A), and confirmed that this mutant maintained homogeneity. Circular dichroism and intrinsic tryptophan fluorescence spectroscopic analyses indicated that rF1^*S and C149R-A have almost the same conformational structures as F1^*S and A purified from serum. Ligand binding experiments using propranolol as a F1^*S ligand and disopyramide as an A specific ligand indicated that the capacity of rF1^*S and C149R-A is equivalent to those ligands as well as F1^*S and A from serum. These results suggest that the oligosaccharide moieties of hAGP have negligible effects on the structural and ligand binding properties of hAGP. Thus, rF1^*S and C149R-A promise to be useful in studies on the drug binding sites of hAGP.

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  Finasteride, a steroid 5α-reductase (5αR) inhibitor, is used to treat benign prostatic hyperplasia and androgenetic alopecia. We aimed to develop a pharmacokinetic/pharmacodynamic model to explain its nonlinear pharmacokinetics and describe the serum concentration profile of dihydrotestosterone (DHT) after finasteride administration. We developed a pharmacokinetic model incorporating a compartment that represents the binding of finasteride to 5αR. We fitted this model to the time-concentration profiles of finasteride after repeated administration of finasteride 0.2 and 1 mg/day. We constructed a pharmacodynamic model considering the inhibition of 5αR type I and type II (5αR1 and 5αR2). This model was fitted to the time profiles of serum DHT. The developed pharmacokinetic model well described nonlinear increase in AUC after repeated administration of finasteride. The association and dissociation rate constants were estimated to be 0.0293/nmol/hr and 0.0185/hr, respectively. Pharmacodynamic model analysis suggested that the 5αR1 inhibition is dose-dependent in the dose range from 0.2 to 100 mg, while the 5αR2 inhibition is almost saturated in the same dose range. Finasteride's saturable binding to 5αR2 is the likely cause of its nonlinear pharmacokinetics. The developed pharmacokinetic/pharmacodynamic model should allow prediction of plasma concentration profiles of finasteride and DHT.

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  A novel fluorescent bile acid derivative, 4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole- conjugated bile acid was synthesized as a probe to develop a rapid screening method for function analysis of bile salt export pump (BSEP, ABCB 11). The transport properties of the synthetic fluorescent bile acid derivative in membrane vesicles obtained from hBSEP-expressing Sf9 cells were examined using the liquid chromatography-electrospray ionization-mass spectrometry method. The Michaelis-Menten constant and maximum uptake rate for the synthetic fluorescent bile acid derivative by hBSEP were 23.1±1.6 μM and 623.2±22.4 pmol/min/mg protein, respectively. These kinetic parameters of the synthetic fluorescent bile acid derivative were comparable with those of an unlabeled bile acid, taurocholic acid. Moreover, we examined inhibitory effects of various drugs on hBSEP-mediated uptake of the fluorescent bile acid derivative using a fluorescence detection method. The relative uptake activities (percent of control) for the fluorescent bile acid derivative in the presence of an inhibitor were in accordance with previous findings using ³H-labeled taurocholic acid. Our results suggest that the synthetic fluorescent bile acid derivative may be useful for evaluation of the inhibitory effects of various drugs on hBSEP-mediated uptake.

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