Germline TYMS genotype is highly predictive in patients with metastatic gastrointestinal malignancies receiving capecitabine-based chemotherapy.

PURPOSE: This work was initiated to extend data on the effect of pharmacogenetics and chemotherapy pharmacokinetics (PK) on clinical outcome in patients with gastrointestinal malignancies. METHODS: We assessed 44 gene polymorphisms in 16 genes (TYMS, MTHFR, GSTP1, GSTM1, GSTT1, DPYD, XRCC1, XRCC3, XPD, ERCC1, RECQ1, RAD54L, ABCB1, ABCC2, ABCG2 and UGT2B7) in 64 patients with metastatic colorectal cancer (CRC) receiving capecitabine/oxaliplatin and 76 patients with advanced gastroesophageal cancer (GEC) receiving epirubicin/cisplatin/capecitabine, respectively. Plasma concentrations of anticancer drugs were measured for up to 24 h, and results were submitted to population PK analysis. We calculated the association between gene polymorphisms, chemotherapy exposure, tumor response, progression-free survival (PFS), overall survival (OS) and chemotherapy-related toxicity using appropriate statistical tests. RESULTS: Patients with a low clearance of 5FU were at increased risk of neutropenia (P < 0.05) and hand-foot syndrome (P = 0.002). DPYD T85C, T1896C and A2846T mutant variants were associated with diarrhea (P < 0.05) and HFS (P < 0.02), and IVS14+1G>A additionally with diarrhea (P < 0.001). The TYMS 2R/3G, 3C/3G or 3G/3G promoter variants were associated with worse PFS in the CRC (HR = 2.0, P < 0.01) and GEC group (HR = 5.4, P < 0.001) and worse OS in the GEC group (HR = 4.7, P < 0.001). The GSTP1 A313G mutant variant was associated with a higher PFS (HR = 0.55, P = 0.001) and OS (HR = 0.60, P = 0.002) in the CRC group. CONCLUSIONS: Germline polymorphisms of DPYD, TYMS and GSTP1 have a significant effect on toxicity and clinical outcome in patients receiving capecitabine-based chemotherapy for advanced colorectal or gastroesophageal cancer. These data should further be validated in prospective clinical studies.

Gene polymorphisms, pharmacokinetics, and hematological toxicity in advanced non-small-cell lung cancer patients receiving cisplatin/gemcitabine.

BACKGROUND: This study quantified the impact of drug pathway-associated genetic variants on the pharmacokinetics (PK) of gemcitabine and cisplatin in patients with advanced non-small-cell lung cancer (NSCLC). METHODS: Thirty-seven patients with advanced NSCLC were sampled for plasma concentrations of gemcitabine, difluoro-deoxy uridine (dFdU), intracellular gemcitabine triphosphates (dFdCTP), and unbound platinum concentrations after gemcitabine 1,250 mg/m(2) i.v. followed by cisplatin 75 mg/m(2). We analyzed 13 germline single nucleotide polymorphisms and one deletion-glutathione S-transferase (GST) M1-within six drug pathway-associated genes (GSTM1, GSTP1, cytidine deaminase (CDA), solute carrier (SLC) 28A1, SLC28A2, and deoxycytidine kinase). PK models were fitted to the data using nonlinear mixed-effects modeling, and genetic data were tested on drug PK and hematological toxicity. RESULTS: Patients carrying the nonsynonymous CDA SNP 79A >C (CDA*2) had a 21% lower gemcitabine clearance as compared to wild-type patients (outcomes and complications.0.0009), but the risk for chemotherapy-associated neutropenia (61% vs. 32%, P = 0.07) and severe neutropenia (17% vs. 5%, P = 0.26) was not significantly higher. Other gene polymorphisms were not associated with drug PK parameters or hematological toxicity. The known functional mutant variant CDA*3 was not found in any of the patients. CONCLUSIONS: Although the mutant CDA*2 allele results in an increased exposure to gemcitabine in Caucasian patients, this study gives no definite conclusion on the clinical relevance of this finding. Further studies should look into the relationship between CDA genotypes, plasmatic CDA activity, and clinical outcome in patients receiving gemcitabine-based chemotherapy.

Pharmacogenetic screening for polymorphisms in drug-metabolizing enzymes and drug transporters in a Dutch population.

BACKGROUND: A possible explanation for the wide interindividual variability in toxicity and efficacy of drug therapy is variation in genes encoding drug-metabolizing enzymes and drug transporters. The allelic frequency of these genetic variants, linkage disequilibrium (LD), and haplotype of these polymorphisms are important parameters in determining the genetic differences between patients. The aim of this study was to explore the frequencies of polymorphisms in drug-metabolizing enzymes (CYP1A1, CYP2C9, CYP2C19, CYP3A4, CYP2D6, CYP3A5, DPYD, UGT1A1, GSTM1, GSTP1, GSTT1) and drug transporters (ABCB1[MDR1] and ABCC2[MRP2]), and to investigate the LD and perform haplotype analysis of these polymorphisms in a Dutch population. METHODS: Blood samples were obtained from 100 healthy volunteers and genomic DNA was isolated and amplified by PCR. The amplification products were sequenced and analyzed for the presence of polymorphisms by sequence alignment. RESULTS: In the study population, we identified 13 new single nucleotide polymorphisms (SNPs) in Caucasians and three new SNPs in non-Caucasians, in addition to previously recognized SNPs. Three of the new SNPs were found within exons, of which two resulted in amino acid changes (A428T in CYP2C9 resulting in the amino acid substitution D143V; and C4461T in ABCC2 in a non-Caucasian producing the amino acid change T1476M). Several LDs and haplotypes were found in the Caucasian individuals. CONCLUSION: In this Dutch population, the frequencies of 16 new SNPs and those of previously recognized SNPs were determined in genes coding for drug-metabolizing enzymes and drug transporters. Several LDs and haplotypes were also inferred. These data are important for further research to help explain the interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

Novel deoxycytidine kinase gene polymorphisms: a population screening study in Caucasian healthy volunteers.

INTRODUCTION: Deoxycytidine kinase (DCK) is the rate-limiting enzyme of the intracellular phosphorylation of nucleoside anticancer drugs, including gemcitabine and beta-arabinofuranosylcytosine, to their active triphosphates. This study was performed to assess the occurrence and frequency of DCK polymorphisms in a predominantly Caucasian population and to choose candidate polymorphisms for subsequent functionality studies. METHODS AND MATERIALS: All seven DCK exons and the promoter region were sequenced from 100 healthy volunteers (79 females and 21 males). With respect to ethnicity, the study cohort comprised 93 Caucasian, one Asian, one African, and five mixed-race individuals. RESULTS: Six novel single nucleotide polymorphisms (SNPs) were found (-243G>T, -135G>C, 261G>A, 364C>T, 727A>C, IVS6+41T>A). Two SNPs are nonsynonymous and lead to changes in the amino acid sequence [C364T in exon 3 (P121S) and A727C in exon 6 (K242Q)]. The presence of the linked promoter polymorphism -360C>G/-201C>T was confirmed in Caucasians, but was less frequent than what has been reported from Asians (allele frequencies 2 versus 15.6%). The most prevalent haplotype was the wild-type plus IVS6+41TT (85.8%). This study found novel DCK polymorphisms, including nonsynonymous SNPs, in exons 3 and 6. A comparison of the data obtained in this study with those reported in a previous study on Asians [Shi et al. (2004) Pharmacogenetics 14:759-768] illustrates marked inter-ethnic differences in the occurrence and frequency of DCK polymorphisms. CONCLUSION: The higher allelic frequency of the promoter polymorphism -C360G/-C201T in Asians than in Caucasians might predispose Asians to nucleoside drug-associated toxicity. These data will be used to assess the effect of DCK candidate SNPs (promoter, exons 3 and 6) in patients receiving gemcitabine anticancer treatment.