Ute Hofmann

Role of Genetic and Nongenetic Factors for Fluorouracil Treatment-Related Severe Toxicity: A Prospective Clinical Trial by the German 5-FU Toxicity Study Group

PURPOSE To assess the predictive value of polymorphisms in dihydropyrimidine dehydrogenase (DPYD ), thymidylate synthase (TYMS ), and methylene tetrahydrofolate reductase (MTHFR ) and of nongenetic factors for severe leukopenia, diarrhea, and mucositis related to fluorouracil (FU) treatment. PATIENTS AND METHODS A multicenter prospective clinical trial included 683 patients with cancer treated with FU monotherapy. Toxicity was documented according to World Health Organization grades. DPYD, TYMS, and MTHFR genotypes were determined, and DPYD was resequenced in patients with severe toxicity. RESULTS Grade 3 to 4 toxicity occurred in 16.1% of patients. The sensitivity of DPYD*2A genotyping for overall toxicity was 5.5% (95%CI, 0.02 to 0.11), with a positive predictive value of 0.46 (95% CI, 0.19 to 0.75; P = .01). Inclusion of additional DPYD variants improved prediction only marginally. Analysis according to toxicity type revealed significant association of DPYD with mucositis and leukopenia, whereas TYMS was associated with diarrhea. Genotype, female sex, mode of FU administration, and modulation by folinic acid were identified as independent risk factors by multivariable analysis. A previously unrecognized significant interaction was found between sex and DPYD, which resulted in an odds ratio for toxicity of 41.8 for male patients (95% CI, 9.2 to 190; P < .0001) but only 1.33 (95% CI, 0.34 to 5.2) in female patients. Homozygosity for the TYMS enhancer region double repeat allele increased risk for toxicity 1.6-fold (95% CI, 1.08 to 2.22; P = .02). CONCLUSION DPYD, TYMS, and MTHFR play a limited role for FU related toxicity but a pronounced DPYD gene/sex-interaction increases prediction rate for male patients. Toxicity risk assessment should include sex, mode of administration, and folinic acid as additional predictive factors.

Gabapentin enhances the analgesic effect of morphine in healthy volunteers.

The most effective group of drugs for the treatment of severe pain is opioid analgesics. Their use, however, is limited by decreased effects in neuropathic and chronic pain as a result of increased pain and development of tolerance. Gabapentin (GBP) is effective in both experimental models of chroni

Antipyrine as a probe for human oxidative drug metabolism: Identification of the cytochrome P450 enzymes catalyzing 4‐hydroxyantipyrine, 3‐hydroxymethylantipyrine, and norantipyrine formation

Antipyrine has been widely used as a probe drug for human oxidative drug metabolism. To evaluate the role of antipyrine as a model drug, we have identified the cytochrome P450 enzymes involved in 4‐hydroxyantipyrine, 3‐hydroxymethylantipyrine, and norantipyrine formation.

Acute effects of pravastatin on cholesterol synthesis are associated with slco1b1 (encoding Oatp1b1) haplotype *17

Objective The aim was to investigate whether polymorphisms in the SLCO1B1 gene, encoding the hepatic uptake transporter OATP1B1, influence the short-term effects of pravastatin on cholesterol synthesis. Methods We determined plasma concentrations of lathosterol and cholesterol up to 12 h after intake of a single dose of 40 mg pravastatin in 41 healthy Caucasian subjects, in whom SLCO1B1 single nucleotide polymorphisms (SNP; 521T>C and −11187G>A) and haplotypes (*15B and *17) had been previously shown to be associated with considerably elevated plasma pravastatin levels. Results The effects of pravastatin on plasma lathosterol concentration and lathosterol to cholesterol concentration ratio, which are established markers of the rate of cholesterol synthesis in vivo, were significantly smaller among the three heterozygous carriers of the SLCO1B1 *17 haplotype (containing the −11187G>A, 388A>G and 521T>C SNPs) as compared with non-carriers. Significant inverse relationships were found between pravastatin area under the concentration–time curve (AUC) values and effects of pravastatin on lathosterol and lathosterol to cholesterol ratio among the whole study population. Conclusion These results suggest that uptake of pravastatin into hepatocytes is impaired in carriers of the SLCO1B1 haplotype *17, resulting in higher plasma pravastatin concentrations but lower concentrations of pravastatin in hepatocytes and thereby in a smaller inhibitory effect on cholesterol synthesis. The cholesterol-lowering response to pravastatin may be impaired in carriers of the *17 haplotype.

Impact of the SLCO1B1 polymorphism on the pharmacokinetics and lipid-lowering efficacy of multiple-dose pravastatin

The polymorphism of SLCO1B1 (solute carrier organic anion transporter family, member 1B1), encoding the hepatic uptake transporter organic anion transporting polypeptide 1B1, has been associated with increased pravastatin concentrations in single‐dose studies. We have investigated whether this polymorphism influences the pharmacokinetics and lipid‐lowering efficacy of multiple‐dose pravastatin.

NUDT15 polymorphisms alter thiopurine metabolism and hematopoietic toxicity

Widely used as anticancer and immunosuppressive agents, thiopurines have narrow therapeutic indices owing to frequent toxicities, partly explained by TPMT genetic polymorphisms. Recent studies identified germline NUDT15 variation as another critical determinant of thiopurine intolerance, but the underlying molecular mechanisms and the clinical implications of this pharmacogenetic association remain unknown. In 270 children enrolled in clinical trials for acute lymphoblastic leukemia in Guatemala, Singapore and Japan, we identified four NUDT15 coding variants (p.Arg139Cys, p.Arg139His, p.Val18Ile and p.Val18_Val19insGlyVal) that resulted in 74.4–100% loss of nucleotide diphosphatase activity. Loss-of-function NUDT15 diplotypes were consistently associated with thiopurine intolerance across the three cohorts (P = 0.021, 2.1 × 10−5 and 0.0054, respectively; meta-analysis P = 4.45 × 10−8, allelic effect size = −11.5). Mechanistically, NUDT15 inactivated thiopurine metabolites and decreased thiopurine cytotoxicity in vitro, and patients with defective NUDT15 alleles showed excessive levels of thiopurine active metabolites and toxicity. Taken together, these results indicate that a comprehensive pharmacogenetic model integrating NUDT15 variants may inform personalized thiopurine therapy.

Proton pump inhibitors inhibit metformin uptake by organic cation transporters (OCTs).

Metformin, an oral insulin-sensitizing drug, is actively transported into cells by organic cation transporters (OCT) 1, 2, and 3 (encoded by SLC22A1, SLC22A2, or SLC22A3), which are tissue specifically expressed at significant levels in various organs such as liver, muscle, and kidney. Because metformin does not undergo hepatic metabolism, drug-drug interaction by inhibition of OCT transporters may be important. So far, comprehensive data on the interaction of proton pump inhibitors (PPIs) with OCTs are missing although PPIs are frequently used in metformin-treated patients. Using in silico modeling and computational analyses, we derived pharmacophore models indicating that PPIs (i.e. omeprazole, pantoprazole, lansoprazole, rabeprazole, and tenatoprazole) are potent OCT inhibitors. We then established stably transfected cell lines expressing the human uptake transporters OCT1, OCT2, or OCT3 and tested whether these PPIs inhibit OCT-mediated metformin uptake in vitro. All tested PPIs significantly inhibited metformin uptake by OCT1, OCT2, and OCT3 in a concentration-dependent manner. Half-maximal inhibitory concentration values (IC50) were in the low micromolar range (3–36 µM) and thereby in the range of IC50 values of other potent OCT drug inhibitors. Finally, we tested whether the PPIs are also transported by OCTs, but did not identify PPIs as OCT substrates. In conclusion, PPIs are potent inhibitors of the OCT-mediated metformin transport in vitro. Further studies are needed to elucidate the clinical relevance of this drug-drug interaction with potential consequences on metformin disposition and/or efficacy.

Influence of age and cytochrome P450 2C9 genotype on the steady-state disposition of diclofenac and celecoxib

ObjectiveTo analyse the influence of age and cytochrome P450 (CYP) 2C9 genotype on the steady-state disposition of the standard NSAID diclofenac and the new COX-2 selective inhibitor celecoxib, both of which are metabolised by the polymorphically expressed CYP2C9.DesignDouble-blind randomised crossover study under steady-state conditions.Subjects12 young (age 32 ± 5 years, bodyweight 71 ± 12kg; mean ± SD) and 12 elderly (68 ± 2 years, 82 ± 15kg) healthy, drug-free, nonsmoking Caucasians of both sexes.MethodsAll subjects received oral celecoxib (200mg twice daily) and diclofenac (75mg twice daily) for 15 days separated by a drug-free interval of at least 3 weeks. Following the last morning dose, multiple blood samples were taken for 25 hours. Concentrations of celecoxib and diclofenac were measured by specific and sensitive high performance liquid chromatography. Identification of CYP2C9 genotype was performed by genomic DNA sequencing. Pharmacokinetic parameters for total and unbound drugs were individually analysed by noncompartmental techniques.ResultsFor diclofenac, area under the concentration-time curve over the dosage interval (AUC τ) was larger in young subjects (3.2 ± 1.0 mg · h/L) than in older individuals (2.4 ± 0.4 mg · h/L; p < 0.05). As the terminal half-life (t½z) was very similar in both groups (3.9 ± 4.4 vs 3.5 ± 3.3 hours), either less complete absorption in the elderly or their higher bodyweight could account for the difference. For celecoxib, AUCτ (5.8 ± 1.7 vs 5.6 ± 2.3 mg · h/L) and t½z (11.8 ± 8.7 vs 11.2 ± 2.9 hours) were almost identical in young and older subjects. Plasma protein binding of both NSAIDs was unaffected by age, and apparent oral clearances for unbound drugs were not different between the two groups of healthy subjects. When considering the genotype of all individuals (CYP2C9*1/*1, n = 10; CYP2C9*1/*2, n = 6; CYP2C9*2/*2, n = 2; CYP2C9*1/*3, n = 4; CYP2C9*3/*3, n = 1), no association with any pharmacokinetic parameter of either drug was apparent. Moreover, there was no significant correlation between the AUC values of celecoxib and diclofenac.ConclusionsAge and CYP2C9 genotype do not significantly affect the steady-state disposition of celecoxib and diclofenac. This would indicate that both drugs need no dosage reduction in the elderly (at least up to 75 years) and that, besides CYP2C9, additional CYP species contribute to the elimination of both agents.

Loss of analgesic effect of morphine due to coadministration of rifampin

Abstract Methadone withdrawal symptoms have been reported in drug addicts treated with the tuberculostatic rifampin. Whereas this interaction can be explained by induction of phase I drug metabolism (CYP3A4), knowledge about induction of phase II metabolism (e.g., UDP‐glucuronosyltransferases=UGTs) and its influence on drug effects in man, however, is very limited. The potent analgesic morphine is metabolized by more than one UGT to the active metabolite morphine‐6‐glucuronide and to morphine‐3‐glucuronide, which is devoid of analgesic activity. Thus, differential induction of UGTs involved in metabolism of morphine might lead to decreased or increased analgesic effects, depending on which UGT is preferentially induced. We therefore investigated the influence of the potent enzyme inducer rifampin on analgesic effects and pharmacokinetics of morphine, which is primarily eliminated by phase II metabolism. Ten healthy male volunteers participated in this double‐blind, placebo‐controlled study with double crossover design. Morphine (10 mg p.o.) and placebo were administered on two separate occasions before and near the end of 13 days of treatment with rifampin (600 mg/day). Blood samples were collected for 31 h. Morphine effects on pain sensation were determined using the cold pressor test. When morphine was given alone, the opioid elicted a significant increase in pain threshold and pain tolerance in comparison to placebo (P≤0.05). However, following administration of rifampin no analgesic effect of morphine was observed. In agreement, the area under the serum concentration‐time curve (AUC) of morphine and the maximum serum concentration of morphine were considerably reduced during coadministration of rifampin (−27.7±19.3% and −40.7±27.1%; P≤0.01). Moreover, during treatment with rifampin a proportional reduction of AUCs of morphine‐3‐glucuronide (P≤0.01), morphine‐6‐glucuronide (P≤0.05) and morphine was observed. Since urinary recoveries of both morphine‐3‐glucuronide and morphine‐6‐glucuronide were also reduced during administration of rifampin, there is no evidence for a contribution of UGT induction to the observed interaction. In summary, a major drug interaction was observed between morphine and rifampin, which could not be attributed to induction of UGTs, but resulted in a complete loss of analgesic effects of the opioid.

UDP‐Glucuronosyltransferase (UGT) Polymorphisms Affect Atorvastatin Lactonization In Vitro and In Vivo

The response to statins shows large interpatient variability. Atorvastatin δ‐lactone is pharmacologically inactive but has been associated with toxicity. We investigated the role of UDP‐glucuronosyltransferases (UGTs) in atorvastatin lactonization. In human liver microsomes, lactonization was correlated with UGT1A3 (rs = 0.61, P < 0.0001) but not with UGT1A1. Surprisingly, lactone formation was significantly higher in carriers of UGT1A1*28, an allele that is associated with lower UGT1A1 expression. We show that this inverse correlation is due to extensive linkage disequilibrium in the UGT1A locus and that several UGT1A3 haplotypes are associated with strong increases in UGT1A3 expression in vitro. Analyses of the pharmacokinetic parameters of atorvastatin and metabolites in genotyped volunteers confirmed that there is an increase in atorvastatin lactonization in carriers of UGT1A3*2 in vivo. The potential of UGT genotyping to identify patients who are at increased risk for failure of therapy and/or adverse effects of statins warrants further investigation.