Pharmacogenetics deals with inherited differences in the response to drugs. The best-recognized examples are genetic polymorphisms of drug-metabolizing enzymes, which affect about 30% of all drugs. ...Loss of function of thiopurine S-methyltransferase (TPMT) results in severe and life-threatening hematopoietic toxicity if patients receive standard doses of mercaptopurine and azathioprine. Gene duplication of cytochrome P4502D6 (CYP2D6), which metabolizes many antidepressants, has been identified as a mechanism of poor response in the treatment of depression. There is also a growing list of genetic polymorphisms in drug targets that have been shown to influence drug response. A major limitation that has heretofore moderated the use of pharmacogenetic testing in the clinical setting is the lack of prospective clinical trials demonstrating that such testing can improve the benefit/risk ratio of drug therapy.
The therapeutic effect of tamoxifen depends on active metabolites, e.g., cytochrome P450 2D6 (CYP2D6) mediated formation of endoxifen. To test for additional relationships, 236 breast cancer patients ...were genotyped for CYP2D6, CYP2C9, CYP2B6, CYP2C19, CYP3A5, UGT1A4, UGT2B7, and UGT2B15; also, plasma concentrations of tamoxifen and 22 of its metabolites, including the (E)‐, (Z)‐, 3‐, and 4′‐hydroxymetabolites as well as their glucuronides, were quantified using liquid chromatography–tandem mass spectrometry (MS). The activity levels of the metabolites were measured using an estrogen response element reporter assay; the strongest estrogen receptor inhibition was found for (Z)‐endoxifen and (Z)‐4‐hydroxytamoxifen (inhibitory concentration 50 (IC50) 3 and 7 nmol/l, respectively). CYP2D6 genotypes explained 39 and 9% of the variability of steady‐state concentrations of (Z)‐endoxifen and (Z)‐4‐hydroxytamoxifen, respectively. Among the poor metabolizers, 93% had (Z)‐endoxifen levels below IC90 values, underscoring the role of CYP2D6 deficiency in compromised tamoxifen bioactivation. For other enzymes tested, carriers of reduced‐function CYP2C9 (*2, *3) alleles had lower plasma concentrations of active metabolites (P < 0.004), pointing to the role of additional pathways.
Clinical Pharmacology & Therapeutics (2011) 89 5, 708–717. doi:10.1038/clpt.2011.27
To assess the association of CYP2B6 allelic diversity with efavirenz (EFV) pharmacokinetics, we performed extensive genotyping of 15 relevant single nucleotide polymorphism in 169 study participants, ...and full resequencing of CYP2B6 in individuals with abnormal EFV plasma levels. Seventy‐seven (45.5%) individuals carried a known (CYP2B6★6,★11,★15, or ★18) or new loss/diminished‐function alleles. Resequencing defined two new loss‐of‐function alleles: allele ★27 (marked by 593T>C M198T), that results in 85% decrease in enzyme activity and allele ★28 (marked by 1132C>T), that results in protein truncation at arginine 378. Median AUC levels were 188.5 μg h/ml for individuals homozygous for a loss/diminished‐function allele, 58.6 μg h/ml for carriers, and 43.7 μg h/ml for noncarriers (P<0.0001). Individuals with a poor metabolizer genotype had a likelihood ratio of 35 (95% CI, 11–110) of presenting very high EFV plasma levels. CYP2B6 poor metabolizer genotypes explain to a large extent EFV pharmacokinetics and identify individuals at risk of extremely elevated EFV plasma levels.
Clinical Pharmacology & Therapeutics (2007) 81, 557–566. doi:10.1038/sj.clpt.6100072; published online 18 January 2007
Tamoxifen is the standard-of-care treatment for estrogen receptor-positive premenopausal breast cancer. We examined tamoxifen metabolism via blood metabolite concentrations and germline variations of ...CYP3A5, CYP2C9, CYP2C19 and CYP2D6 in 587 premenopausal patients (Asians, Middle Eastern Arabs, Caucasian-UK; median age 39 years) and clinical outcome in 306 patients. N-desmethyltamoxifen (DM-Tam)/(Z)-endoxifen and CYP2D6 phenotype significantly correlated across ethnicities (R(2): 53%, P<10(-77)). CYP2C19 and CYP2C9 correlated with norendoxifen and (Z)-4-hydroxytamoxifen concentrations, respectively (P<0.001). DM-Tam was influenced by body mass index (P<0.001). Improved distant relapse-free survival (DRFS) was associated with decreasing DM-Tam/(Z)-endoxifen (P=0.036) and increasing CYP2D6 activity score (hazard ratio (HR)=0.62; 95% confidence interval (CI), 0.43-0.91; P=0.013). Low (<14 nM) compared with high (>35 nM) endoxifen concentrations were associated with shorter DRFS (univariate P=0.03; multivariate HR=1.94; 95% CI, 1.04-4.14; P=0.064). Our data indicate that endoxifen formation in premenopausal women depends on CYP2D6 irrespective of ethnicity. Low endoxifen concentration/formation and decreased CYP2D6 activity predict shorter DRFS.
To evaluate whether alterations in the multidrug-resistance (MDR)-1 gene correlate with intestinal MDR-1 expression and uptake of orally administered P-glycoprotein (PGP) substrates, we analyzed the ...MDR-1 sequence in 21 volunteers whose PGP expression and function in the duodenum had been determined by Western blots and quantitative immunohistology (n = 21) or by plasma concentrations after orally administered digoxin (n = 8 + 14). We observed a significant correlation of a polymorphism in exon 26 (C3435T) of MDR-1 with expression levels and function of MDR-1. Individuals homozygous for this polymorphism had significantly lower duodenal MDR-1 expression and the highest digoxin plasma levels. Homozygosity for this variant was observed in 24% of our sample population (n = 188). This polymorphism is expected to affect the absorption and tissue concentrations of numerous other substrates of MDR-1.
Background and Objective
A large interindividual variability exists in the plasma concentrations of repaglinide. Our aim was to investigate possible associations between the pharmacokinetics of ...repaglinide and single nucleotide polymorphisms (SNPs) in the genes encoding for the drug transporters organic anion transporting polypeptide 1B1 (OATP1B1) (SLCO1B1) and P‐glycoprotein (MDR1, ABCB1) and the drug‐metabolizing enzymes cytochrome P450 (CYP) 2C8 and CYP3A5.
Methods
A total of 56 healthy volunteers ingested a single 0.25‐mg dose of repaglinide. Plasma repaglinide and blood glucose concentrations were measured for up to 7 hours. All subjects were genotyped for the −11187G>A and 521T>C SNPs in SLCO1B1 and the 3435C>T and 2677G>T/A SNPs in ABCB1, as well as for the CYP2C8*3 (416G>A, 1196A>G), CYP2C8*4 (792C>G), and CYP3A5*3 (6986A>G) alleles.
Results
The area under the plasma concentration‐time curve from time 0 to infinity AUC(0‐∞) and peak concentration in plasma (Cmax) of repaglinide varied 16.9‐fold and 10.7‐fold, respectively, between individual subjects. Multiple regression analyses indicated that the SLCO1B1 521T>C SNP and the CYP2C8*3 allele were independent predictors of the AUC(0‐∞) and Cmax of repaglinide (adjusted multiple R2 = 45% and 36%, respectively). In subjects with the SLCO1B1 521CC genotype, the AUC(0‐∞) of repaglinide was 107% and 188% higher, respectively, than in subjects with the SLCO1B1 521TC or 521TT (reference) genotype (P < .0001). In subjects with the CYP2C8*1/*3 genotype, the AUC(0‐∞) and Cmax of repaglinide were 48% and 44% lower, respectively, than in those with the CYP2C8*1/*1 genotype (P < .05). The pharmacokinetics of repaglinide was not associated with the studied ABCB1 SNPs or the CYP3A5*3 allele. The elimination half‐life of repaglinide was not associated with any SNP. Only the SLCO1B1 −11187GA genotype was significantly associated with an enhanced effect of repaglinide on blood glucose.
Conclusions
Genetic polymorphism in SLCO1B1 is a major determinant of interindividual variability in the pharmacokinetics of repaglinide. The effect of SLCO1B1 polymorphism on the pharmacokinetics of repaglinide may be clinically important.
Clinical Pharmacology & Therapeutics (2005) 77, 468–478; doi: 10.1016/j.clpt.2005.01.018
The in situ formation of gold nanoparticles in soda lime silicate glass under constant x-ray irradiation is compared with the ex situ formation in preirradiated glasses. The ASAXS measurements ...confirm that pure Au particles are formed. The comparison shows that the number of particles nucleated under irradiation is about an order of magnitude higher than of those nucleated with preirradiation. The radius, R, remains slightly below 1 nm under in situ conditions and the Ostwald ripening stage is slowed down. Under ex situ conditions Ostwald ripening is clearly observed and R grows up to 3 nm.
The effective spin of paramagnetic centers generated during the reaction of a mixture of CH4 and O2 on activated MgO was determined with transient nutation EPR (TN-EPR). For the first time it could ...be shown that apart from the generation of surface-trapped superoxide radicals O2 –, a significant number of paramagnetic centers are formed with an effective spin larger than 1/2. Results from HYSCORE and other pulsed EPR experiments further give evidence that these centers are localized at the surface of the MgO catalyst. These centers are proposed to be exchange coupled clusters of holes and electrons, respectively, some of them formed at specific exposed sites of the highly structured MgO surface. Judging from the relative high concentration of the centers ascribed to hole clusters, it is tempting to assume that they are involved in the catalytic reaction network of the oxidative coupling of methane.
Cyclosporine (CsA) nephrotoxicity is a severe complication in organ transplantation because it leads to impaired renal function and chronic allograft nephropathy, which is a major predictor of graft ...loss. Animal models and in vivo studies indicate that the transmembrane efflux pump P-glycoprotein contributes substantially to CsA nephrotoxicity. It was hypothesized that the TT genotype at the ABCB1 3435C-->T polymorphism, which is associated with decreased expression of P-glycoprotein in renal tissue, is a risk factor for developing CsA nephrotoxicity. In a case-control study, 18 of 97 patients developed CsA nephrotoxicity and showed complete recovery of renal function in all cases when switched to a calcineurin inhibitor-free regimen. Both recipients and donors were genotyped for ABCB1 polymorphisms at the positions 3435C-->T and 2677G-->T/A. For controlling for population stratification, two additional polymorphisms, CYP2D6*4 and CYP3A5*3, with intermediate allelic frequencies were studied. The P-glycoprotein low expressor genotype 3435TT only of renal organ donors but not of the recipients was overrepresented in patients with CsA nephrotoxicity as compared with patients without toxicity (chi2 = 10.5; P = 0.005). CsA dosage, trough levels, and the concentration per dose ratio were not different between the patient groups. In a multivariate model that included several other nongenetic covariates, only the donor's ABCB1 3435TT genotype was strongly associated with CsA nephrotoxicity (odds ratio, 13.4; 95% confidence interval, 1.2 to 148; P = 0.034). A dominant role of the donor's ABCB1 genotype was identified for development of CsA nephrotoxicity. This suggests that P-glycoprotein is an important factor in CsA nephrotoxicity.
Individuals with the cytochrome P450 (CYP) 2D6 intermediate metabolizer (IM) phenotype have low residual enzyme activity and compose about 10% to 15% of white populations. Their identification is ...clinically relevant but remains unsatisfactory because of incomplete characterization of the major allele involved, termed CYP2D6*41 (-1584C, R296C, S486T).
To search for novel mutations, resequencing of the entire CYP2D6 gene was performed in selected individuals. Genotype-phenotype correlation analysis was done in a population sample of 308 white subjects phenotyped with sparteine and previously genotyped for all major alleles.
A total of 16 novel polymorphic positions were identified, of which 7 were located within 2.4 kilobases of previously uncharacterized 2D7-2D6 intergenic sequence and 9 were located within intronic regions. The novel mutation 2988G>A in intron 6 appeared to be specifically associated with the IM phenotype. Further analysis in the population sample demonstrated that 2988G>A was strongly linked to allele *41 but not to any other alleles including *1, *2, *2xN, *4, *6, *7, *8, *9, *10, and *35. The overall frequency of the novel polymorphism was 8.4% in the normal white population. Compared with conventionally determined *41, 2988G>A was shown to have improved predictivity for the IM phenotype. With 2988G>A being taken into account, alleles *1, *2, and *35 (-1584G, V11M, R296C, S486T) were found to be phenotypically equivalent.
CYP2D6 genotyping can be considerably simplified by using 2988G>A as a marker for *41 and by omitting genotyping for the functionally equivalent alleles *2 and *35.
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