Peixian Chen

University of Chicago, Chicago, IL, United States

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Publications (17)107.36 Total impact

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    ABSTRACT: The aim of this study was to discover cis- and trans-acting factors significantly affecting mRNA expression and catalytic activity of human hepatic UDP-glucuronosyltransferases (UGTs). Transcription levels of 5 major hepatic UGT1A (UGT1A1, UGT1A3, UGT1A4, UGT1A6 and UGT1A9) and 5 UGT2B (UGT2B4, UGT2B7, UGT2B10, UGT2B15 and UGT2B17) genes were quantified in human liver tissue samples (n=125) using real-time PCR. Glucuronidation activities of 14 substrates were measured in 47 livers. We genotyped 167 tagSNPs (single nucleotide polymorphisms) in UGT1A (n=43) and UGT2B (n=124), as well as the known functional UGT1A1*28 and UGT2B17 CNV (copy number variation) polymorphisms. Transcription levels of 15 transcription factors (TFs) known to regulate these UGTs were quantified. We found that UGT expression and activity were highly variable among the livers (median and range of coefficient of variations: 135%, 74%-217% and 52%, 39%-105%, respectively). CAR, PXR and ESR1 were found to be the most important trans-regulators of UGT transcription (median and range of correlation coefficients: 46%, 6%-58%; 47%, 9%-58%; and 52%, 24%-75%, respectively). Hepatic UGT activities were mainly determined by UGT gene transcription levels. Twenty one polymorphisms were significantly (FDR adjusted P<0.05) associated with mRNA expression and/or activities of UGT1A1, UGT1A3 and UGT2B17. We found novel SNPs in the UGT2B17 CNV region accounting for variability in UGT2B17 gene transcription and testosterone glucuronidation rate, in addition to that attributable to the UGT2B17 CNV. Our study discovered novel pharmacogenetic markers and provided detailed insight into the genetic network regulating hepatic UGTs.
    Human Molecular Genetics 05/2014; · 7.69 Impact Factor
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    ABSTRACT: There is currently extensive discussion and debate in the literature on how, when, and to whom genetic research results should be returned (see Genetics in Medicine, April 2012 issue). Here, we describe our experience in disclosing genetic information on Mendelian disorders discovered during the course of our research in the Hutterites. We first assessed attitudes toward the disclosure of carrier results, which revealed that many individuals wanted carrier information and that many intended to use the information in family planning. Based on this information, we developed a pilot study to test and disclose cystic fibrosis (CF) carrier status. Next, a larger scale project was developed in order to disclose genetic research results for 14 diseases to those interested in receiving the information. We developed brochures, offered a live interactive educational program, conducted a consent process, and disclosed results in letters mailed to the consented individuals. Overall, ~80 % of individuals who participated in the educational program signed consent forms for the release of their results for 14 diseases. We describe our experience with returning individual genetic research results to participants in a population-based research study.
    Journal of Genetic Counseling 04/2014; · 1.45 Impact Factor
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    ABSTRACT: VEGF receptor 2 (VEGFR-2) plays a crucial role in mediating angiogenic endothelial cell responses via the VEGF pathway, and angiogenesis inhibitors targeting VEGFR-2 are in clinical use. As angiogenesis is a host-driven process, functional heritable variation in KDR, the gene encoding VEGFR-2, may affect VEGFR-2 function and, ultimately, the extent of tumor angiogenesis. We resequenced KDR using 24 DNAs each from healthy Caucasian, African American, and Asian groups. Nonsynonymous genetic variants were assessed for function by phosphorylation assays. Luciferase reporter gene assays were used to examine effects of variants on gene expression. KDR mRNA and protein expression and microvessel density (MVD) were measured in non-small cell lung cancer (NSCLC) tumor samples, and matching patient DNA samples were genotyped to test for associations with variants of interest. KDR resequencing led to the discovery of 120 genetic variants, of which 25 had not been previously reported. Q472H had increased VEGFR-2 protein phosphorylation and associated with increased MVD in NSCLC tumor samples. -2854C and -2455A increased luciferase expression and associated with higher KDR mRNA levels in NSCLC samples. -271A reduced luciferase expression and associated with lower VEGFR-2 levels in NSCLC samples. -906C and 23408G associated with higher KDR mRNA levels in NSCLC samples. This study has defined KDR genetic variation in 3 populations and identified common variants that impact on tumoral KDR expression and vascularization. These findings may have important implications for understanding the molecular basis of genetic associations between KDR variation and clinical phenotypes related to VEGFR-2 function.
    Clinical Cancer Research 06/2011; 17(16):5257-67. · 7.84 Impact Factor
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    ABSTRACT: Cell-based approaches were used to identify genetic markers predictive of patients' risk for poor response prior to chemotherapy. We conducted genome-wide association studies (GWAS) to identify single-nucleotide polymorphisms (SNP) associated with cellular sensitivity to carboplatin through their effects on mRNA expression using International HapMap lymphoblastoid cell lines (LCL) and replicated them in additional LCLs. SNPs passing both stages of the cell-based study were tested for association with progression-free survival (PFS) in patients. Phase 1 validation was based on 377 ovarian cancer patients receiving at least four cycles of carboplatin and paclitaxel from the Australian Ovarian Cancer Study (AOCS). Positive associations were then assessed in phase 2 validation analysis of 1,326 patients from the Ovarian Cancer Association Consortium and The Cancer Genome Atlas. In the initial GWAS, 342 SNPs were associated with carboplatin-induced cytotoxicity, of which 18 unique SNPs were retained after assessing their association with gene expression. One SNP (rs1649942) was replicated in an independent LCL set (Bonferroni adjusted P < 0.05). It was found to be significantly associated with decreased PFS in phase 1 AOCS patients (P(per-allele) = 2 × 10(-2)), with a stronger effect in the subset of women with optimally debulked tumors (P(per-allele) = 4 × 10(-3)). rs1649942 was also associated with poorer overall survival in women with optimally debulked tumors (P(per-allele) = 9 × 10(-3)). However, this SNP was not significant in phase 2 validation analysis with patients from numerous cohorts. This study shows the potential of cell-based, genome-wide approaches to identify germline predictors of treatment outcome and highlights the need for extensive validation in patients to assess their clinical effect.
    Clinical Cancer Research 06/2011; 17(16):5490-500. · 7.84 Impact Factor
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    ABSTRACT: Identifying patients prior to treatment who are more likely to benefit from chemotherapeutic agents or more likely to experience adverse events is an aim of personalized medicine. Pharmacogenomics offers a potential means of achieving this goal through the discovery of predictive germline genetic biomarkers. When applied particularly to the treatment of head and neck cancers, such information could offer significant benefit to patients as a means of potentially reducing morbidity associated with platinum-based chemotherapy. We developed a genome-wide, cell-based approach to identify single nucleotide polymorphisms (SNPs) associated with platinum susceptibility and then evaluated these SNPs as predictors for response and toxicity in head and neck cancer patients treated with platinum-based therapy as part of a phase II clinical trial. Sixty head and neck cancer patients were evaluated. Of 45 genome-wide SNPs examined, we found that 2 SNPs, rs6870861 (P=0.004; false discovery rate [FDR] <0.05) and rs2551038 (P=0.005; FDR <0.05), were associated significantly with overall response to carboplatin-based induction chemotherapy when incorporated into a model along with total carboplatin exposure. Interestingly, these 2 SNPs are associated strongly with the baseline expression of >20 genes (all P ≤10(-4)), and that 2 genes (SLC22A5 and SLCO4C1) are important organic cation/anion transporters known to affect platinum uptake and clearance. Several other SNPs were associated nominally with carboplatin-related hematologic toxicities. These findings demonstrate importantly that a genome-wide, cell-based model can identify novel germline genetic biomarkers of platinum susceptibility, which are replicable in a clinical setting with treated cancer patients and seem clinically meaningful for potentially enabling future personalization of care in such patients.
    Translational research : the journal of laboratory and clinical medicine. 05/2011; 157(5):265-72.
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    ABSTRACT: Exome sequencing is a powerful tool for discovery of the Mendelian disease genes. Previously, we reported a novel locus for autosomal recessive non-syndromic mental retardation (NSMR) in a consanguineous family [Nolan, D.K., Chen, P., Das, S., Ober, C. and Waggoner, D. (2008) Fine mapping of a locus for nonsyndromic mental retardation on chromosome 19p13. Am. J. Med. Genet. A, 146A, 1414-1422]. Using linkage and homozygosity mapping, we previously localized the gene to chromosome 19p13. The parents of this sibship were recently included in an exome sequencing project. Using a series of filters, we narrowed the putative causal mutation to a single variant site that segregated with NSMR: the mutation was homozygous in five affected siblings but in none of eight unaffected siblings. This mutation causes a substitution of a leucine for a highly conserved proline at amino acid 182 in TECR (trans-2,3-enoyl-CoA reductase), a synaptic glycoprotein. Our results reveal the value of massively parallel sequencing for identification of novel disease genes that could not be found using traditional approaches and identifies only the seventh causal mutation for autosomal recessive NSMR.
    Human Molecular Genetics 01/2011; 20(7):1285-9. · 7.69 Impact Factor
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    ABSTRACT: We aim to identify genetic variation, in addition to the UGT1A1*28 polymorphism, that can explain the variability in irinotecan (CPT-11) pharmacokinetics and neutropenia in cancer patients. Pharmacokinetic, genetic, and clinical data were obtained from 85 advanced cancer patients treated with single-agent CPT-11 every 3 weeks at doses of 300 mg/m(2) (n = 20) and 350 mg/m(2) (n = 65). Forty-two common variants were genotyped in 12 candidate genes of the CPT-11 pathway using several methodologies. Univariate and multivariate models of absolute neutrophil count (ANC) nadir and pharmacokinetic parameters were evaluated. Almost 50% of the variation in ANC nadir is explained by UGT1A1*93, ABCC1 IVS11 -48C>T, SLCO1B1*1b, ANC baseline levels, sex, and race (P < .0001). More than 40% of the variation in CPT-11 area under the curve (AUC) is explained by ABCC2 -24C>T, SLCO1B1*5, HNF1A 79A>C, age, and CPT-11 dose (P < .0001). Almost 30% of the variability in SN-38 (the active metabolite of CPT-11) AUC is explained by ABCC1 1684T>C, ABCB1 IVS9 -44A>G, and UGT1A1*93 (P = .004). Other models explained 17%, 23%, and 27% of the variation in APC (a metabolite of CPT-11), SN-38 glucuronide (SN-38G), and SN-38G/SN-38 AUCs, respectively. When tested in univariate models, pretreatment total bilirubin was able to modify the existing associations between genotypes and phenotypes. On the basis of this exploratory analysis, common polymorphisms in genes encoding for ABC and SLC transporters may have a significant impact on the pharmacokinetics and pharmacodynamics of CPT-11. Confirmatory studies are required.
    Journal of Clinical Oncology 04/2009; 27(16):2604-14. · 18.04 Impact Factor
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    ABSTRACT: As one of the major glutathione conjugation enzymes, GSTM1 detoxifies a number of drugs and xenobiotics. Its expression and activity have been shown to correlate both with cancer risks and drug resistance. Through a genome-wide association study, we identified a significant association between HapMap SNP rs366631 and GSTM1 expression. In this study, utilizing lymphoblastoid cell lines derived from International HapMap Consortium CEU and YRI populations, we designed and performed site-specific genotyping assays for both rs366631 and a highly homologous GSTM1 upstream site. Copy number variation (CNV) assays were performed for three different regions of the GSTM1 gene. We demonstrated that HapMap SNP rs366631 is a non-polymorphic site. The false genotyping call arises from sequence homology, a common GSTM1 region deletion and a non-specific genotyping platform used to identify the SNP. However, the HapMap call for rs366631 genotype is an indicator of GSTM1 upstream region deletion. Furthermore, this upstream deletion can be used as a marker of GSTM1 gene deletion. Using a novel GSTM1 CNV assay, we showed a population-specific CNV in this region upstream of the gene. More than 75% of the Caucasian (CEU) samples exhibit GSTM1 deletion and none contain two copies of GSTM1. In contrast, up to 25% of African (YRI) samples were found to have two copies of GSTM1. In conclusion, HapMap rs366631 is a pseudo-SNP that can be used as a GSTM1 deletion marker. Both the pseudo-SNP allele frequency and GSTM1 upstream region CNV show population-specific patterns between CEU and YRI samples.
    Human Molecular Genetics 11/2008; 18(2):366-72. · 7.69 Impact Factor
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    ABSTRACT: UDP-glucuronosyltransferase 2B7 (UGT2B7) plays a central role in the liver-mediated biotransformation of endogenous and exogenous compounds. The genetic basis of interindividual variability in UGT2B7 function is unknown. This study aimed to discover novel gene variants of functional significance. Caucasian human livers (n=54) were used. UGT2B7 was resequenced in 12 samples [(six highest and six lowest for the formation of morphine-3-glucuronide (M3G)]. Haplotype-tagging single nucleotide polymorphisms were genotyped in the entire sample set. Samples were phenotyped for mRNA expression. 10 haplotype-tagging single nucleotide polymorphisms were identified and their haplotypes were inferred. Haplotype 4 (-45597G; -6682_-6683A; 372A; IVS1+9_IVS1+10A; IVS1+829T; IVS1+985G; IVS1+999C; IVS1+1250G; 801T; IVS4+185C) (frequency of 0.12) was associated with an increase in enzyme activity and gene expression. The 1/4 and 4/6 diplotypes had higher M3G formation compared with 1/1 (P<0.05) and 2/3 (P<0.01) diplotypes. Diplotypes containing haplotype 4 resulted in a significant 45% average increase in the formation of M3G compared with diplotypes without haplotype 4 (P=0.002). There was also an association between haplotype 4 and increased mRNA expression. IVS1+985A>G, 735A>G, and 1062C>T are the putative functional variants of haplotype 4. We also identified two mRNA splicing variants (UGT2B7_v2 and UGT2B7_v3) splicing out exon 1, 4, 5, and 6 but sharing exons 2 and 3 with the involvement of additional 5' exons. UGT2B7_v2 was detected in all livers tested, but UGT2B7_v3 was present at much lower levels compared with UGT2B7_v2. The UGT2B7 reference sequence mRNA is now named UGT2B7_v1. UGT2B7 haplotype 4 is functional and its effects on the biotransformation of UGT2B7 substrates should be tested in controlled clinical trials. Biochemical studies should investigate the functional role of the newly discovered mRNA splicing variants.
    Pharmacogenetics and Genomics 08/2008; 18(8):683-97. · 3.61 Impact Factor
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    ABSTRACT: To assess the pharmacogenomic and pharmacokinetic determinants of skin rash and diarrhea, the two primary dose-limiting toxicities of the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor erlotinib. A prospective clinical study of 80 patients with non-small-cell lung cancer, head and neck cancer, and ovarian cancer was performed. Detailed pharmacokinetics and toxicity of erlotinib were assessed. Polymorphic loci in EGFR, ABCG2, CYP3A4, and CYP3A5 were genotyped, and their effects on pharmacokinetics and toxicities were evaluated. A novel diplotype of two polymorphic loci in the ABCG2 promoter involving -15622C/T and 1143C/T was identified, with alleles conferring lower ABCG2 levels associated with higher erlotinib pharmacokinetic parameters, including area under the curve (P = .019) and maximum concentration (P = .006). Variability in skin rash was best explained by a multivariate logistic regression model incorporating the trough erlotinib plasma concentration (P = .034) and the EGFR intron 1 polymorphism (P = .044). Variability in diarrhea was associated with the two linked polymorphisms in the EGFR promoter (P < .01), but not with erlotinib concentration. Although exploratory in nature, this combined pharmacogenomic and pharmacokinetic model helps to define and differentiate the primary determinants of skin and gastrointestinal toxicity of erlotinib. The findings may be of use both in designing trials targeting a particular severity of rash and in considering dose and schedule modifications in patients experiencing dose-limiting toxicities of erlotinib or similarly targeted agents. Further studies of the relationship between germline polymorphisms in EGFR and the toxicity and efficacy of EGFR inhibitors are warranted.
    Journal of Clinical Oncology 03/2008; 26(7):1119-27. · 18.04 Impact Factor
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    ABSTRACT: Interindividual variability in the glucuronidation of xenobiotics metabolized by UDP-glucuronosyltransferase 1A9 (UGT1A9) suggests the presence of functional UGT1A9 variants. The aim of this study was to evaluate whether the putative functionality of the UGT1A9 variants-118T(9>10) (rs3832043), I399C>T (rs2741049), -275T>A (rs6714486), and-2152C>T (rs17868320) could be confirmed in an independent study. UGT1A9 genotypes and UGT1A9 activity (i.e., flavopiridol and mycophenolic acid glucuronidation) were determined in 46 Caucasian human livers. mRNA levels were quantitated by real-time polymerase chain reaction in 35 of these livers. In addition, samples from 60 unrelated Caucasians belonging to the HapMap Project were also genotyped to confirm the allele frequencies and linkage disequilibrium (LD) pattern observed in our Caucasian livers. The allele frequencies of the-118T(9>10), I399C>T, -275T>A, and-2152C>T variants were 0.39, 0.39, 0.02, and 0.02 in the livers, respectively. The I399C>T variant was in complete LD (r(2) = 1) with-118T(9>10) (linked alleles: C and T(9), respectively). Complete LD between these two variants was also found in the HapMap samples (frequencies of-118T(9>10) and I399C>T = 0.38). I399C>T and-118T(9>10) correlated with neither UGT1A9 activities nor mRNA levels. Because of the low frequencies of the-275T>A and-2152C>T variants, an effect on phenotype could not be evaluated. Our data demonstrate that the common I399C>T and-118T(9>10) polymorphisms do not explain interindividual variation in hepatic UGT1A9 activity and mRNA expression and are in complete LD in the donor liver samples we studied.
    Drug Metabolism and Disposition 01/2008; 35(12):2149-53. · 3.36 Impact Factor
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    ABSTRACT: Nine different functional UGT1A enzymes are generated from a single UGT1A gene by alternative splicing, with each enzyme having a unique exon 1. SN-38, the active metabolite of the anticancer agent irinotecan, is metabolized by both UGT1A1 and UGT1A9. We aim to characterize the UGT1A9-UGT1A1 haplotypes in Asians and Caucasians and gain insights on their functional consequences. Asian and Caucasian individuals were genotyped for UGT1A1 and UGT1A9 variants. A higher frequency of the UGT1A9 -118T10 allele was observed in Asians compared to Caucasians, while the -275T>A and -2152C>T variants were relatively uncommon in Caucasians and not found in Asians. The strongest linkage disequilibrium (LD) was observed between the UGT1A1 -53 and -3156 and between the UGT1A9 -275 and -2152 loci. Lower LD was observed between the -118 UGT1A9 variant and the UGT1A1 variants. Fourteen UGT1A9-UGT1A1 haplotypes were found in Asians, seven of them found to be shared by both populations. Common UGT1A9-UGT1A1 diplotypes were defined, and a difference was observed across the SN-38 glucuronidation rates in Caucasian livers stratified by diplotypes. This study for the first time described common UGT1A9-UGT1A1 haplotypes, highlighting important ethnic differences between Asians and Caucasians. If the functional effect of these haplotypes can be confirmed, this haplotypic information would be applicable to the correct design of prospective clinical studies of irinotecan, as well as of other drugs primarily metabolized by both UGT1A1 and UGT1A9.
    Pharmacogenetics and Genomics 05/2005; 15(5):295-301. · 3.61 Impact Factor
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    ABSTRACT: Carboxylesterases are members of the serine esterase super family important in the metabolism of a wide variety of substrates, including xenobiotics and prodrugs. There are two known carboxylesterases expressed in human liver, small intestine and other tissues, carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2). The aim of this study was to identify polymorphisms in the CES2 gene and determine whether these polymorphisms affect expression levels of CES2 or rate of metabolism of irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxy-camptothecin). Microsome samples prepared from liver tissues of 78 normal individuals were used to determine the rate of hydrolysis of irinotecan and procaine (an anaesthetic hydrolysed by CES2 but not CES1). The rate of hydrolysis of irinotecan is highly variable among individuals, ranging from 2.7-138 pmol/mg protein/h (mean +/- SD 26.0 +/- 22.9). Fifteen single nucleotide polymorphisms (SNPs) were identified, one is in an exon, 9 are in introns, three are in the 3'-untranslated region (UTR), and two are in the 5'-flanking region. Eight of the 15 SNP loci have rare allele frequencies greater than 5%, of which three were greater than 20%. Genotyping of samples from the SNP Consortium demonstrated different distributions among African-Americans, Asian-Americans and European-Americans. We also analysed the haplotype structure and estimated linkage disequilibrium (LD). A SNP located in the 5'-UTR (5'-UTR-363) was found in LD with loci in intron 1 (Intron1 + 947, Intron1 + 1361, Intron1 + 1643). Haplotypes with homozygous rare alleles on these loci exhibit lower mRNA levels as determined by real time polymerase chain reaction (P < 0.01) and the incorporation of rare alleles in haplotypes correlate with reduced mRNA (P = 0.03). The 5'-UTR-363 SNP is located in one of the three promoters of CES2. However, we did not observe significant differences in CES2 activities (irinotecan and procaine hydrolysis) among individuals with different haplotypes.
    Pharmacogenetics 10/2004; 14(9):595-605.
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    ABSTRACT: Carboxylesterases are members of the serine esterase super family important in the metabolism of a wide variety of substrates, including xenobiotics and prodrugs. There are two known carboxylesterases expressed in human liver, small intestine and other tissues, carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2). The aim of this study was to identify polymorphisms in the CES2 gene and determine whether these polymorphisms affect expression levels of CES2 or rate of metabolism of irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxy-camptothecin). Microsome samples prepared from liver tissues of 78 normal individuals were used to determine the rate of hydrolysis of irinotecan and procaine (an anaesthetic hydrolysed by CES2 but not CES1). The rate of hydrolysis of irinotecan is highly variable among individuals, ranging from 2.7-138 pmol/mg protein/h (mean ± SD 26.0 ± 22.9). Fifteen single nucleotide polymorphisms (SNPs) were identified, one is in an exon, 9 are in introns, three are in the 3′-untranslated region (UTR), and two are in the 5′-flanking region. Eight of the 15 SNP loci have rare allele frequencies greater than 5%, of which three were greater than 20%. Genotyping of samples from the SNP Consortium demonstrated different distributions among African-Americans, Asian-Americans and European-Americans. We also analysed the haplotype structure and estimated linkage disequilibrium (LD). A SNP located in the 5′-UTR (5′-UTR-363) was found in LD with loci in intron 1 (Intron1 + 947, Intron1 + 1361, Intron1 + 1643). Haplotypes with homozygous rare alleles on these loci exhibit lower mRNA levels as determined by real time polymerase chain reaction (P < 0.01) and the incorporation of rare alleles in haplotypes correlate with reduced mRNA (P = 0.03). The 5′-UTR-363 SNP is located in one of the three promoters of CES2. However, we did not observe significant differences in CES2 activities (irinotecan and procaine hydrolysis) among individuals with different haplotypes.
    Pharmacogenetics and Genomics 08/2004; 14(9):595-605. · 3.61 Impact Factor
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    ABSTRACT: Etoposide is a substrate for P-glycoprotein, CYP3A4, CYP3A5, and UGT1A1. Glucocorticoids modulate CYP3A and P-glycoprotein in preclinical models, but their effect on clinical etoposide disposition is unknown. We studied the pharmacokinetics of etoposide and its catechol metabolite in children with acute lymphoblastic leukemia, along with polymorphisms in CYP3A4, CYP3A5, MDR1, GSTP1, UGT1A1, and VDR. Plasma pharmacokinetics were assessed at day 29, after 1 month of prednisone (n = 102), and at week 54, without prednisone (n = 44). On day 29, etoposide clearance was higher (47.4 versus 29.2 mL/min/m2, P <.0001) than at week 54. The day 29 etoposide or catechol area under the curve (AUC) was correlated with neutropenia (P =.027 and P =.0008, respectively). The relationship between genotype and etoposide disposition differed by race and by prednisone use. The MDR1 exon 26 CC genotype predicted higher day 29 etoposide clearance (P =.002) for all patients, and the CYP3A5 AA and GSTP1 AA genotypes predicted lower clearance in blacks (P =.02 and.03, respectively). The UGT1A1 6/6, VDR intron 8 GG, and VDR Fok 1 CC genotypes predicted higher week 54 clearance in blacks (P =.039,.036, and.052, respectively). The UGT1A1 6/6 genotype predicted lower catechol AUC. Prednisone strongly induces etoposide clearance, genetic polymorphisms may predict the constitutive and induced clearance of etoposide, and the relationship between genotype and phenotype differs by race.
    Blood 01/2004; 103(1):67-72. · 9.06 Impact Factor
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    ABSTRACT: Carboxylesterases are a broad class of enzymes important in the detoxification of many ester- or amide-bond containing xenobiotics. They also activate analgesics, anticancer prodrugs, and other biologically active compounds, such as cocaine and heroin. The objective of this work was to identify the CES2 gene structure, complex 5' untranslated regions and three potential promoters for the initiation of transcription in different human tissues. Using bioinformatics and progressive reverse transcriptase-polymerase chain reaction, we found that the 5' untranslated region is more than 1100 bases longer than previously reported. Rapid amplification of cDNA ends showed three distinctive transcription start sites at -74, -629 and -1187. DNA fragments upstream of each of the three transcription start sites were found to be transcriptionally active in HepG2 cells. The distal promoter is active in both orientations, suggesting its potential role in the transcription of another gene, CGI-128, located immediately upstream to the distal promoter in the opposite direction with respect to CES2. Hybridization analyses showed that CES2 is highly expressed in the heart, skeletal muscle, colon, spleen, kidney and liver, but considerably less expressed in fetal tissues (e.g. fetal heart, kidney, spleen, and liver) and cancer cells. It is also evident that the distal promoter is responsible for low level expression of the gene in many tissues, whereas the other two promoters are tissue specific. These findings shed some light on CES2 gene regulation, a gene important in the metabolism of many drugs.
    Pharmacogenetics 08/2003; 13(7):425-35.
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    ABSTRACT: Epidermal growth factor receptor (EGFR) plays a critical role in signal transduction and is a target for a novel class of anticancer agents that aim to inhibit EGFR-mediated cancer cell growth. Previous studies have demonstrated a dinucleotide (CA)(n) repeat polymorphism in intron 1 of EGFR, ranging from 14 to 21 repeats, that has been suggested to regulate EGFR expression. The longer allele with 21 repeats showed an 80% reduction of gene expression compared with the shorter allele with 16 repeats. Therefore, the evaluation of the allelic distribution of this polymorphism in populations of various ethnic origins will be crucial to understand the interindividual variability in EGFR expression. We evaluated the influence of ethnicity on this polymorphism by genotyping individuals of Caucasian (n = 183), African-American (n = 84), and Asian (n = 66) background. The frequency of one of the longer alleles, allele 20 is significantly higher in Asian individuals (63% compared with 21% in Caucasians, P = 2 x 10(-18)). In confirmation of prior studies, the shorter allele 16 was the most common allele in Caucasians (43%) and African-Americans (42%), but its frequency was significantly lower in Asians (average 17%, P = 10(-7) compared with Caucasians). Major interethnic differences in the allelic frequencies of the EGFR intron 1 polymorphism exist. Our results may contribute to a better understanding of the molecular basis underlying ethnic differences in drug response and may be helpful for future strategies of individualized therapy with EGFR inhibitors.
    Clinical Cancer Research 04/2003; 9(3):1009-12. · 7.84 Impact Factor