Uridine 5'-diphospho-glucuronosyltransferase genetic polymorphisms and response to cancer chemotherapy

Pharmacogenetics aims to elucidate how genetic variation affects the efficacy and side effects of drugs, with the ultimate goal of personalizing medicine. Clinical studies of the genetic variation in the uridine 5'-diphosphoglucuronosyltransferase gene have demonstrated how reduced-function allele variants can predict the risk of severe toxicity and help identify cancer patients who could benefit from reduced-dose schedules or alternative chemotherapy. Candidate polymorphisms have also been identified in vitro, although the functional consequences of these variants still need to be tested in the clinical setting. Future approaches in uridine 5'-diphosphoglucuronosyltransferase pharmacogenetics include genetic testing prior to drug treatment, genotype-directed dose-escalation studies, study of genetic variation at the haplotype level and genome-wide studies.

Phase I study of irinotecan and doxifluridine for metastatic colorectal cancer focusing on the UGT1A1*28 polymorphism

Although individuals carrying the UGT1A1 allele *28 have an increased risk of severe toxicities associated with irinotecan, no phase I study has been conducted based on the polymorphism. This report presents the recommended doses of irinotecan for patients with the respective genotypes. Twenty-seven patients with advanced colorectal cancer were enrolled in this study, and the UGT1A1*28 polymorphism was genotyped before chemotherapy. One course of chemotherapy consisted of irinotecan infused once every 2 weeks at 70, 100, 120, and 150 mg/m(2) at dose levels 1, 2, 3, and 4, respectively, and doxifluridine was administered orally. This treatment continued for at least 12 weeks. The dose-limiting toxicity was determined as grade 3 hematological and non-hematological toxicities for the TA(6)/TA(6) (6/6) and TA(6)/TA(7) (6/7) genotypes. The pharmacokinetics of irinotecan, SN-38, and SN-38 glucuronide, was assessed at dose level 2. Eighteen and nine patients had the 6/6 and 6/7 genotypes, respectively. The maximum tolerated dose (MTD) was not observed up to dose level 4 in patients with the 6/6 genotype. In contrast, MTD was observed at dose level 2 (100 mg/m(2)) in patients with the 6/7 genotype. Patients with the 6/7 genotype had a significantly higher area under the plasma time-concentration curve (0-infinity) SN-38 (P = 0.022) and biliary index (P = 0.030) than those with 6/6. The recommended starting doses of biweekly irinotecan for phase II/III were 150 mg/m(2) for patients with the UGT1A1 6/6 genotype and 70 mg/m(2) for those with the 6/7 genotype, respectively. The gene polymorphism should be considered when determining the precise recommended doses to be administered in phase I studies.