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Richard M Weinshilboum

Publications and source records attributed to Richard M Weinshilboum.

At least 19 recordsLinked to original sources
PubMed2026

Novel association of NAV3 with dilated cardiomyopathy and its role in cardiac fibrosis.

A genome-wide association study (GWAS) identified neuron navigator 3 (NAV3) as a potential genetic determinant of myocardial recovery in dilated cardiomyopathy (DCM). This study aimed to understand its functional role in cardiac pathophysiology by leveraging omics approaches. Single-cell RNA-seq transcriptomic data from previously published adult human hearts indicate that NAV3 expression is highest in cardiac fibroblasts, suggesting its functional role in these cells. In vitro, stimulation of primary human ventricular cardiac fibroblasts with transforming growth factor β1 (TGF-β1) induced NAV3 expression in a dose and time-dependent manner. Small-interfering-RNA-mediated knockdown of NAV3 significantly attenuated TGF-β1-induced fibroblast activation, reducing the expression of α-smooth muscle actin (α-SMA), collagens, and fibronectin. RNA sequencing of NAV3-silenced fibroblasts, confirmed by Western blot, revealed upregulation of cell cycle regulators and downregulation of profibrotic markers, suggesting that NAV3 facilitates TGF-β1-induced cell cycle arrest and fibroblast-to-myofibroblast transition. Notably, NAV3 silencing did not alter canonical SMAD2/3 phosphorylation, implying a role for NAV3 in modulating fibrotic signaling through other pathways. Our findings provide functional and mechanistic insights into NAV3's novel role in cardiac fibrosis, showing that reduced NAV3 expression attenuates TGF-β1-mediated fibroblast activation by regulating cell cycle signaling. These results support further investigation of NAV3 as a potential modulator of cardiac fibrosis and myocardial recovery in DCM.NEW & NOTEWORTHY This study uncovers a previously unrecognized role for NAV3 in TGF-β1-driven cardiac fibroblast activation. We show that NAV3 facilitates profibrotic remodeling through noncanonical signaling and cell cycle arrest, independently of SMAD2/3. These findings position NAV3 as a novel regulator of fibroblast phenotype and a potential modulator of cardiac fibrosis.

Humans↗
PubMed2006

Human SULT1A1 gene: copy number differences and functional implications.

SULT1A1, which catalyzes the sulfate conjugation of a wide variety of natural and synthetic compounds, is genetically polymorphic. Biochemical and pharmacogenetic studies have demonstrated that individual variation in the level of enzyme activity is inherited. Common single-nucleotide polymorphisms (SNPs) located in the open reading frame and in the 5'-flanking region (5'-FR) may account for a portion of this individual variation. In this study, we demonstrate the presence of SULT1A1 gene deletions and duplications, representing an additional source of variability in the metabolic activity of this enzyme. A quantitative multiplex PCR assay was used to measure the extent of copy number differences and the frequency of these events in different populations. An analysis of DNA from 362 Caucasian-American and 99 African-American showed the presence of 1 to approximately 5 copies of SULT1A1 in individual samples: 5% of Caucasian subjects contained a single copy of the gene and 26% had three or more copies, while 63% of African-American subjects had three or more copies. Analysis of the genomic region surrounding the SULT1A1 gene in three separate cases with a deletion demonstrated that the entire SULT1A1 gene was affected. Reporter assays, constructed for each of the various 5'-FR SNP haplotypes, suggest that these may also play a role in SULT1A1 activity. However, the variability in the level of enzyme activity among 23 human platelet and 267 human liver samples was best explained by gene copy number differences when all sources of genetic variability were considered (P < 0.0001). Overall, these observations have obvious implications for the effectiveness of SULT1A1 as a drug and hormone metabolizing enzyme and its potential role as a risk factor for disease.

Adult↗
PubMed2006

Pharmacogenomics: challenges and opportunities.

The outcome of drug therapy is often unpredictable, ranging from beneficial effects to lack of efficacy to serious adverse effects. Variations in single genes are 1 well-recognized cause of such unpredictability, defining the field of pharmacogenetics (see Glossary). Such variations may involve genes controlling drug metabolism, drug transport, disease susceptibility, or drug targets. The sequencing of the human genome and the cataloguing of variants across human genomes are the enabling resources for the nascent field of pharmacogenomics (see Glossary), which tests the idea that genomic variability underlies variability in drug responses. However, there are many challenges that must be overcome to apply rapidly accumulating genomic information to understand variable drug responses, including defining candidate genes and pathways; relating disease genes to drug response genes; precisely defining drug response phenotypes; and addressing analytic, ethical, and technological issues involved in generation and management of large drug response data sets. Overcoming these challenges holds the promise of improving new drug development and ultimately individualizing the selection of appropriate drugs and dosages for individual patients.

Clinical Medicine↗
PubMed2006

The impact of cytochrome P450 2D6 metabolism in women receiving adjuvant tamoxifen.

BACKGROUND: Tamoxifen is biotransformed to the potent anti-estrogen, endoxifen, by the cytochrome P450 (CYP) 2D6 enzyme. CYP2D6 genetic variation and inhibitors of the enzyme markedly reduce endoxifen plasma concentrations in tamoxifen-treated patients. Using a North Central Cancer Treatment Group adjuvant tamoxifen trial, we performed a comprehensive evaluation of CYP2D6 metabolism by assessing the combined effect of genetic variation and inhibition of the enzyme system on breast cancer recurrence and death. METHODS: Medical records were reviewed at each randomizing site to determine whether CYP2D6 inhibitors were co-prescribed with tamoxifen. Extensive metabolizers were defined as patients without a *4 allele (i.e., wt/wt) who were not co-prescribed a CYP2D6 inhibitor. Patients with decreased CYP2D6 metabolism were classified as intermediate or poor metabolizers (PM) based on the presence of one or two CYP2D6*4 alleles or the co-administration of a moderate or potent CYP2D6 inhibitor. The association between CYP2D6 metabolism and clinical outcome was assessed using Cox modeling. RESULTS: Medication history was available in 225/256 eligible patients and CYP2D6*4 genotype in 190 patients. Thirteen patients (6%) were co-prescribed a CYP2D6 inhibitor [potent (n = 3), moderate (n = 10)], resulting in the following CYP2D6 metabolism: extensive (n = 115) and decreased (n = 65). In the multivariate analysis, patients with decreased metabolism had significantly shorter time to recurrence (p = 0.034; adj HR = 1.91; 95% CI 1.05-3.45) and worse relapse-free survival (RFS) (p = 0.017; adj HR = 1.74; 1.10-2.74); relative to patients with extensive metabolism. Cox' modeling demonstrated that compared to extensive metabolizers, PM had the most significant risk of breast cancer relapse (HR 3.12, p = 0.007). CONCLUSION: CYP2D6 metabolism, as measured by genetic variation and enzyme inhibition, is an independent predictor of breast cancer outcome in post-menopausal women receiving tamoxifen for early breast cancer. Determination of CYP2D6 genotype may be of value in selecting adjuvant hormonal therapy and it appears CYP2D6 inhibitors should be avoided in tamoxifen-treated women.

Adult↗
PubMed2006

A comprehensive examination of CYP19 variation and risk of breast cancer using two haplotype-tagging approaches.

BACKGROUND: Numerous studies point to a positive relationship between elevated levels of estrogens and increased risk of breast. Androgens are converted to estrogens by the aromatase enzyme, which is encoded by the CYP19 gene. We recently published resequencing data on 88 polymorphisms identified in that gene. The hypothesis tested in this study was that polymorphisms, or haplotypes, in CYP19 are related to risk of breast cancer. METHODS: Incident cases of breast cancer were identified through the Division of Medical Oncology at the Mayo Clinic in Rochester, MN. Controls were patients visiting Mayo for an annual medical examination. Controls were frequency matched to cases based on age and region of residence. Tag-polymorphisms were selected using 2 methods: (1) 12 variants using the tag-selection method of Carlson et al. (Am J Hum Genet 74:106-120, 2004); and (2) 12 variants using the haplotype method of Stram (Genet Epidemiol 27:365-374, 2004). Six SNPs were selected by both methods. Genotyping was conducted using SNPStream, TaqMan and RFLP analyses. Logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI). Analyses were conducted among all cases and controls, or stratified by estrogen receptor alpha (ER) status and/or menopausal status. RESULTS: A total of 750 cases (60% postmenopausal) and 732 controls (75% postmenopausal) were included. No association with breast cancer risk was detected for individual variants, selected tagSNPs or hap-tag SNPs despite 80% power to detect OR as low as 1.49 for minor allele frequency (MAF) of 0.10. Similarly, stratified analyses based on ER status or menopausal status failed to detect any association with breast cancer risk. CONCLUSION: These analyses suggest that variants of CYP19 are not associated with risk of breast cancer.

Alleles↗
PubMed2006

Pharmacogenomics: catechol O-methyltransferase to thiopurine S-methyltransferase.

1. Pharmacogenomics is the study of the role of inheritance in variation in the drug response phenotype-a phenotype that can vary from adverse drug reactions at one end of the spectrum to lack of therapeutic efficacy at the other. 2. The thiopurine S-methyltransferase (TPMT) genetic polymorphism represents one of the best characterized and most clinically relevant examples of pharmacogenomics. This polymorphism has also served as a valuable "model system" for studies of the ways in which variation in DNA sequence might influence function. 3. The discovery and characterization of the TPMT polymorphism grew directly out of pharmacogenomic studies of catechol O-methyltransferase (COMT), an enzyme discovered by Julius (Julie) Axelrod and his coworkers. 4. This review will outline the process by which common, functionally significant genetic polymorphisms for both COMT and TPMT were discovered and will use these two methyltransferase enzymes to illustrate general principles of pharmacogenomic research-both basic mechanistic and clinical translational research-principles that have been applied to a series of genes encoding methyltransferase enzymes.

Animals↗
PubMed2006

Glutathione S-transferase omega 1 and omega 2 pharmacogenomics.

Glutathione S-transferase omega 1 and omega 2 (GSTO1 and GSTO2) catalyze monomethyl arsenate reduction, the rate-limiting reaction in arsenic biotransformation. As a step toward pharmacogenomic studies of these phase II enzymes, we resequenced human GSTO1 and GSTO2 using DNA samples from four ethnic groups. We identified 31 and 66 polymorphisms in GSTO1 and GSTO2, respectively, with four nonsynonymous-coding single nucleotide polymorphisms (cSNPs) in each gene. There were striking variations among ethnic groups in polymorphism frequencies and types. Expression constructs were created for all eight nonsynonymous cSNPs, as well as a deletion of codon 155 in GSTO1, and those constructs were used to transfect COS-1 cells. Quantitative Western blot analysis, after correction for transfection efficiency, showed a reduction in protein level of greater than 50% for the GSTO1 Tyr32 variant allozyme compared with wild type (WT), whereas levels for the Asp140, Lys208, Val236, and codon 155 deletion variant constructs were similar to that of the WT. For GSTO2, the Tyr130 and Ile158 variant allozymes showed 50 and 84% reductions in levels of expression, respectively, compared with WT, whereas the Ile41 and Asp142 allozymes displayed levels similar to that of WT GSTO2. Rabbit reticulocyte lysate degradation studies showed that the GSTO1 Tyr32 and the GSTO2 Tyr130, Ile158, and Asp142/Ile158 variant allozymes were degraded more rapidly than were their respective WT allozymes. These observations raise the possibility of functionally significant pharmacogenomic variation in the expression and function of GSTO1 and GSTO2.

Black or African American↗
PubMed2006

Role of the glutathione metabolic pathway in lung cancer treatment and prognosis: a review.

Inherent and acquired drug resistance is a cause of chemotherapy failure, and pharmacogenomic studies have begun to define gene variations responsible for varied drug metabolism, which influences drug efficacy. Platinum-based compounds are the most commonly used chemotherapeutic agents in the treatment of advanced stage lung cancer patients, and the glutathione metabolic pathway is directly involved in the detoxification or inactivation of platinum drugs. Consequently, genotypes corresponding to higher drug inactivation enzyme activity may predict poor treatment outcome. Available evidence is consistent with this hypothesis, although a definitive role for glutathione system genes in lung cancer prognosis needs to be elucidated. We present evidence supporting a role of the glutathione system in acquired and inherited drug resistance and/or adverse effects through the impact of either drug detoxification or drug inactivation, thus adversely effecting lung cancer treatment outcome. The potential application of glutathione system polymorphic genetic markers in identifying patients who may respond favorably, selecting effective antitumor drugs, and balancing drug efficacy and toxicity are discussed.

Antineoplastic Agents↗
PubMed2006

Gemcitabine pharmacogenomics: cytidine deaminase and deoxycytidylate deaminase gene resequencing and functional genomics.

PURPOSE: Gemcitabine is a nucleoside analogue with activity against solid tumors. Gemcitabine metabolic inactivation is catalyzed by cytidine deaminase (CDA) or, after phosphorylation, by deoxycytidylate deaminase (DCTD). We set out to study the pharmacogenomics of CDA and DCTD. EXPERIMENTAL DESIGN: The genes encoding CDA and DCTD were resequenced using DNA from 60 African American and 60 Caucasian American subjects. Expression constructs were created for nonsynonymous coding single nucleotide polymorphisms (cSNP) and reporter gene constructs were created for 5'-flanking region polymorphisms. Functional genomic studies were then conducted after the transfection of mammalian cells. RESULTS: CDA resequencing revealed 17 polymorphisms, including one common nonsynonymous cSNP, 79 A>C (Lys27Gln). Recombinant Gln27 CDA had 66 +/- 5.1% (mean +/- SE) of the wild-type (WT) activity for gemcitabine but without a significant decrease in level of immunoreactive protein. The apparent Km (397 +/- 40 micromol/L) for the Gln27 allozyme was significantly higher than that for the WT (289 +/- 20 micromol/L; P < 0.025). CDA 5'-flanking region reporter gene studies showed significant differences among 5'-flanking region haplotypes in their ability to drive transcription. There were 29 SNPs in DCTD, including one nonsynonymous cSNP, 172 A>G (Asn58Asp), in Caucasian American DNA. Recombinant Asp58 DCTD had 11 +/- 1.4% of WT activity for gemcitabine monophosphate with a significantly elevated level of immunoreactive protein. No DCTD polymorphisms were observed in the initial 500 bp of the 5'-flanking region. CONCLUSIONS: These results suggest that pharmacogenomic variation in the deamination of gemcitabine and its monophosphate might contribute to variation in therapeutic response to this antineoplastic agent.

Black or African American↗
PubMed2006

Human arsenic methyltransferase (AS3MT) pharmacogenetics: gene resequencing and functional genomics studies.

Arsenic contaminates ground water worldwide. Methylation is an important reaction in the biotransformation of arsenic. We set out to study the pharmacogenetics of human arsenic methyltransferase (AS3MT, previously CYT19). After cloning the human AS3MT cDNA, we annotated the human gene and resequenced its 5'-flanking region, exons, and splice junctions using 60 DNA samples from African-American (AA) and 60 samples from Caucasian-American (CA) subjects. We observed 26 single nucleotide polymorphisms (SNPs), including 3 non-synonymous cSNPs, as well as a variable number of tandem repeats in exon 1 within an area encoding the cDNA 5'-untranslated region. The nonsynonymous cSNPs included T860C (M287T) with frequencies of 10.8 and 10% in AA and CA subjects, respectively, as well as C517T (A173W) in one AA and C917T (T306I) in one CA sample. Haplotype analysis showed that Ile(306) was linked to Thr(287), so this double variant allozyme was also studied functionally. After expression in COS-1 cells and correction for transfection efficiency, the Trp(173) allozyme displayed 31%, Thr(287) 350%, Ile(306) 4.8%, and Thr(287)/Ile(306) 6.2% of the activity of the wild type (WT) allozyme, with 20, 190, 4.4, and 7.9% of the level of WT immunoreactive protein, respectively. Apparent K(m) values for S-adenosyl-l-methionine were 4.6, 3.1, and 11 mum for WT, Trp(173), and Thr(287) allozymes, with K(m) values for sodium arsenite with the same allozymes of 11.8, 8.9, and 4.5mum. The Ile(306) and Thr(287)/Ile(306) allozymes expressed too little activity for inclusion in the substrate kinetic studies. Expression of reporter gene constructs for the 5'-flanking region and the variable number of tandem repeats in the 5'-untranslated region demonstrated cell line-dependent variation in reporter gene expression, with shorter repeats associated with increased transcription in HepG2 cells. These results raise the possibility that inherited variation in AS3MT may contribute to variation in arsenic metabolism and, perhaps, arsenic-dependent carcinogenesis in humans.

5' Untranslated Regions↗
PubMed2006

Human methylenetetrahydrofolate reductase pharmacogenomics: gene resequencing and functional genomics.

5,10-Methylenetetrahydrofolate reductase (MTHFR) is an important enzyme in the folate metabolic pathway. Common genetic polymorphisms in the human MTHFR gene are associated with individual variation in the efficacy and toxicity of chemotherapeutic agents, such as methotrexate and 5-fluorouracil. However, the full range of polymorphisms and intragene haplotypes in the human MTHFR gene remains unclear. Furthermore, cellular mechanisms by which common, naturally occurring nonsynonymous coding single nucleotide polymorphisms (cSNPs) might alter the function of this enzyme have not been defined. The present study focused on the systematic identification and investigation of common polymorphisms and haplotypes in the MTHFR gene using a genotype-to-phenotype strategy, followed by functional genomic studies. Specifically, we resequenced exons, splice junctions and portions of the 5'-flanking region (5'-FR) of the human MTHFR gene using 240 DNA samples from four ethnic groups. A total of 65 polymorphisms were observed, 11 of which were nonsynonymous cSNPs. We then performed functional genomic studies with constructs for wild-type and 15 variant allozymes (some with multiple alterations in amino acid sequence) using a mammalian expression system. Activity for the variant allozymes ranged from 13% to 149% of wild-type activity. Levels of immunoreactive protein for the allozymes ranged from 31% to 120% of wild-type and were significantly correlated with enzyme activity (Rp=0.85, P<0.0001), suggesting that a major mechanism by which nonsynonymous cSNPs influence the function of this gene is by alteration in the quantity of protein. These observations represent steps towards an understanding of molecular genetic mechanisms responsible for variation in MTHFR function that may contribute to individual differences in drug efficacy and toxicity, as well as disease risk.

5' Flanking Region↗
PubMed2006

Pharmacogenetics and pharmacogenomics: development, science, and translation.

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. This discipline evolved from the convergence of rapid advances in molecular pharmacology and genomics. Originally, pharmacogenetic studies focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire "pathways" encoding proteins that influence both pharmacokinetics--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics, the drug target itself, as well as genome-wide approaches. Pharmacogenomics is also increasingly moving across the "translational interface" into the clinic and is being incorporated into the drug development process and the governmental regulation of that process. However, significant challenges remain to be overcome if pharmacogenetics-pharmacogenomics is to achieve its full potential as a major medical application of genomic science.

Drug Design↗
PubMed2005

Human aromatase: gene resequencing and functional genomics.

Aromatase [cytochrome P450 19 (CYP19)] is a critical enzyme for estrogen biosynthesis, and aromatase inhibitors are of increasing importance in the treatment of breast cancer. We set out to identify and characterize genetic polymorphisms in the aromatase gene, CYP19, as a step toward pharmacogenomic studies of aromatase inhibitors. Specifically, we "resequenced" all coding exons, all upstream untranslated exons plus their presumed core promoter regions, all exon-intron splice junctions, and a portion of the 3'-untranslated region of CYP19 using 240 DNA samples from four ethnic groups. Eighty-eight polymorphisms were identified, resulting in 44 haplotypes. Functional genomic studies were done with the four nonsynonymous coding single nucleotide polymorphisms (cSNP) that we observed, two of which were novel. Those cSNPs altered the following amino acids: Trp39Arg, Thr201Met, Arg264Cys, and Met364Thr. The Cys264, Thr364, and double variant Arg39Cys264 allozymes showed significant decreases in levels of activity and immunoreactive protein when compared with the wild-type (WT) enzyme after transient expression in COS-1 cells. A slight decrease in protein level was also observed for the Arg39 allozyme, whereas Met201 displayed no significant changes in either activity or protein level when compared with the WT enzyme. There was also a 4-fold increase in apparent K(m) value for Thr364 with androstenedione as substrate. Of the recombinant allozymes, only the double mutant (Arg39Cys264) displayed a significant change from the WT enzyme in inhibitor constant for the aromatase inhibitors exemestane and letrozole. These observations indicate that genetic variation in CYP19 might contribute to variation in the pathophysiology of estrogen-dependent disease.

Alleles↗
PubMed2005

Human phenylethanolamine N-methyltransferase pharmacogenomics: gene re-sequencing and functional genomics.

Phenylethanolamine N-methyltransferase (PNMT, EC2.1.1.28) catalyzes the N-methylation of norepinephrine to form epinephrine. As a step toward understanding the possible contribution of inheritance to individual variation in PNMT-catalyzed epinephrine formation, we 're-sequenced' the entire human PNMT gene, including the three exons, the introns and approximately 1 kb of the 5'-flanking region (5'-FR), using DNA samples from 60 African-American (AA) and 60 Caucasian-American (CA) subjects. Within the 3.5 kb re-sequenced, 18 single nucleotide polymorphisms (SNPs) were observed, including four non-synonymous coding SNPs (cSNPs) that resulted in the following alterations in encoded amino acid sequence: Asn9Ser, Thr98Ala, Arg112Cys and Ala175Thr. When constructs for the non-synonymous cSNPs were transiently expressed in COS-1 cells, the Ala98 allozyme displayed significantly lower levels of both activity and immunoreactive protein (p < 0.002) than did the wild-type (WT) enzyme due, at least in part, to accelerated protein degradation by a proteasome-mediated process. Luciferase reporter gene constructs were also created for the six common PNMT 5'-FR haplotypes observed. Significant differences were observed among haplotypes in their ability to drive transcription. These observations raise the possibility of inherited variation in the ability to form epinephrine from norepinephrine as a result of variant PNMT polymorphisms and haplotypes.

Animals↗
PubMed2005

Human thiopurine S-methyltransferase pharmacogenetics: variant allozyme misfolding and aggresome formation.

Thiopurine S-methyltransferase (TPMT) catalyzes the S-methylation of thiopurine drugs. TPMT genetic polymorphisms represent a striking example of the potential clinical value of pharmacogenetics. Subjects homozygous for TPMT*3A, the most common variant allele for low activity, an allele that encodes a protein with two changes in amino acid sequence, are at greatly increased risk for life-threatening toxicity when treated with standard doses of thiopurines. These subjects have virtually undetectable levels of TPMT protein. In this study, we tested the hypothesis that TPMT*3A might result in protein misfolding and aggregation. We observed that TPMT*3A forms aggresomes in cultured cells and that it aggregates in vitro, functional mechanisms not previously described in pharmacogenetics. Furthermore, there was a correlation among TPMT half-life values in rabbit reticulocyte lysate, aggresome formation in COS-1 cells, and protein aggregation in vitro for the three variant allozymes encoded by alleles that include the two TPMT*3A single-nucleotide polymorphisms. These observations were compatible with a common structural explanation for all of these effects, a conclusion supported by size-exclusion chromatography and CD spectroscopy. The results of these experiments provide insight into a unique pharmacogenetic mechanism by which common polymorphisms affect TPMT protein function and, as a result, therapeutic response to thiopurine drugs.

Alleles↗
PubMed2005

CYP2D6 genotype, antidepressant use, and tamoxifen metabolism during adjuvant breast cancer treatment.

BACKGROUND: The efficacy of tamoxifen therapy for the treatment of breast cancer varies widely among individuals. Plasma concentrations of the active tamoxifen metabolite endoxifen are associated with the cytochrome P450 (CYP) 2D6 genotype. We examined the effects of concomitant use of selective serotonin reuptake inhibitor antidepressants, which are CYP2D6 enzyme inhibitors commonly prescribed to treat hot flashes in women who take tamoxifen, and genotypes for genes that encode tamoxifen-metabolizing enzymes on plasma concentrations of tamoxifen and its metabolites. METHODS: Eighty patients with newly diagnosed with breast cancer who were beginning tamoxifen therapy (20 mg/day orally), 24 of whom were taking CYP2D6 inhibitors, were genotyped for common alleles of the CYP2D6, CYP2C9, CYP3A5, and sulfotransferase (SULT) 1A1 genes. Plasma concentrations of tamoxifen and its metabolites were measured after 1 and 4 months of tamoxifen therapy. Differences in plasma concentrations of tamoxifen and its metabolites between genotype groups were analyzed by the Wilcoxon rank sum test. All statistical tests were two-sided. RESULTS: Among all women, plasma endoxifen concentrations after 4 months of tamoxifen therapy were statistically significantly lower in subjects with a CYP2D6 homozygous variant genotype (20.0 nM, 95% confidence interval [CI] = 11.1 to 28.9 nM) or a heterozygous genotype (43.1 nM, 95% CI = 33.3 to 52.9 nM) than in those with a homozygous wild-type genotype (78.0 nM, 95%CI = 65.9 to 90.1 nM) (both P = .003). Among subjects who carried a homozygous wild-type genotype, the mean plasma endoxifen concentration for those who were using CYP2D6 inhibitors was 58% lower than that for those who were not (38.6 nM versus 91.4 nM, difference = -52.8 nM, 95% CI = -86.1 to -19.5 nM, P = .0025). The plasma endoxifen concentration was slightly reduced in women taking venlafaxine, a weak inhibitor of CYP2D6, whereas the plasma endoxifen concentration was reduced substantially in subjects who took paroxetine (a potent inhibitor of CYP2D6). Genetic variations of CYP2C9, CYP3A5, or SULT1A1 had no statistically significant associations with plasma concentrations of tamoxifen or its metabolites. CONCLUSION: Interactions between CYP2D6 polymorphisms and coadministered antidepressants and other drugs that are CYP2D6 inhibitors may be associated with altered tamoxifen activity.

Adult↗
PubMed2005

Thiopurine S-methyltransferase pharmacogenetics: variant allele functional and comparative genomics.

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. Genetic polymorphisms for TPMT are a major factor responsible for large individual variations in thiopurine toxicity and therapeutic effect. The present study investigated the functional effects of human TPMT variant alleles that alter the encoded amino acid sequence of the enzyme, TPMT*2, *3A, *3B, *3C and *5 to *13. After expression in COS-1 cells and correction for transfection efficiency, allozymes encoded by these alleles displayed levels of activity that varied from virtually undetectable (*3A,*3B and *5) to 98% (*7) of that observed for the wild-type allele. Although some allozymes had significant elevations in apparent Km values for 6-mercaptopurine and S-adenosyl-L-methionine (i.e. the two cosubstrates for the reaction), the level of enzyme protein was the major factor responsible for variation in activity. Quantitative Western blot analysis demonstrated that the level of enzyme protein correlated closely with level of activity for all allozymes except TPMT*5. Furthermore, protein levels correlated with rates of TPMT degradation. TPMT amino acid sequences were then determined for 16 non-human mammalian species and those sequences (plus seven reported previously, including two nonmammalian vertebrate species) were used to determine amino acid sequence conservation. Most human TPMT variant allozymes had alterations of residues that were highly conserved during vertebrate evolution. Finally, a human TPMT homology structural model was created on the basis of a Pseudomonas structure (the only TPMT structure solved to this time), and the model was used to infer the functional consequences of variant allozyme amino acid sequence alterations. These studies indicate that a common mechanism responsible for alterations in the activity of variant TPMT allozymes involves alteration in the level of enzyme protein due, at least in part, to accelerated degradation.

Alleles↗