Chemotherapy-induced unconjugated hyperbilirubinemia caused by a mutation of the bilirubin uridine-5'-diphosphate-glucuronosyltransferase gene

Contribution of UGT1A1 variations to chemotherapy-induced unconjugated hyperbilirubinemia in pediatric leukemia patients

BACKGROUND

Chemotherapy for malignant neoplasms sometimes induces unconjugated hyperbilirubinemia, resulting in the early cessation of treatment. We evaluated the role of variations in the bilirubin uridine-5-diphosphate (UDP)-glucuronosyltransferase gene (UGT1A1) in unconjugated hyperbilirubinemia development during chemotherapy in pediatric patients with leukemia.

METHODS

UGT1A1 allelic variations were evaluated in 25 Japanese pediatric leukemia patients with hyperbilirubinemia (peak serum bilirubin concentration 3.57 ± 1.02 mg/dl) and 25 control patients without hyperbilirubinemia (0.92 ± 0.32 mg/dl) by PCR-direct sequencing.

RESULTS

In the hyperbilirubinemic group, 22 of 25 patients showed biallelic variations of UGT1A1. Nine (36%) patients were homozygous for UGT1A1*6 and eight (32%) were compound heterozygous for UGT1A1*6 and UGT1A1*28. Three (12%) patients were homozygous for UGT1A1*28. There were no biallelic variations in UGT1A1 in the non-hyperbilirubinemic group. The allelic frequencies of UGT1A1*6 in the hyperbilirubinemic group (0.58) was significantly higher than those of the non-hyperbilirubinemic group (0.1) (χ(2) = 25.7, P < 0.05).

CONCLUSION

The high frequency of biallelic variations of UGT1A1 in the hyperbilirubinemic group suggests an association with Gilbert syndrome. Therefore, it is not necessary to cease chemotherapy in patients with these mutations who develop unconjugated hyperbilirubinemia without associated liver dysfunction.

Outcome and toxicities associated to chemotherapy in children with acute lymphoblastic leukemia and Gilbert syndrome. Usefulness of UGT1A1 mutational screening

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most frequent cancer in childhood. Although intensive chemotherapy has improved survival in those patients, important side effects, including hyperbilirubinemia, are frequent. Gilbert syndrome (GS) is a frequent condition that causes a reduction in glucuronidation and intermittent hyperbilirubinemia episodes. This could provoke a greater exposure to some cytotoxic agents used in ALL, increasing the risk of toxicity. On the other hand, unexplained hyperbilirubinemia could lead to unnecessary modifications or even treatment withdrawals, which could increase the risk of relapse, but data regarding this in ALL pediatric population are scarce.

METHODS

Retrospective study to analyze toxicity, outcome and treatment modifications related to GS in children diagnosed with ALL.

RESULTS

A total of 23 of 159 patients were diagnosed with GS. They had statistically higher hyperbilirubinemias during all treatment phases (P < 0.0001) and a slower methotrexate clearance when it was administered during a 24-hr infusion at high doses (patients with GS: 74 hr ± 19 vs. patients without GS: 64 hr ± 8; P <  .002). However, no relevant toxicity or delays in treatment were found in them. Finally, changes in treatment due to hyperbilirubinemia were only done in 5 patients with GS.

CONCLUSIONS

Differences in outcome were not found in patients with GS. Universal screening for GS appears to be not necessary in pediatric patients with ALL. However, when hyperbilirubinemia is observed, it must be rule out in order to avoid unnecessary changes in treatment.

Comparison of three methods for genotyping the UGT1A1 (TA)n repeat polymorphism

OBJECTIVES

The UGT1A1 promoter contains a (TA)n repeat polymorphism. The 7 repeat allele is associated with decreased enzyme activity and patients homozygous for this allele treated with irinotecan may experience life-threatening toxicity. Here, we have compared three methods [DNA sequencing, fragment analysis, and the Invader assay (Third Wave Technologies)] for genotyping this polymorphism.

RESULTS

All of the DNA samples (n=119) had concordant genotype calls between the sequencing and size-based methods. The Invader method was also concordant if the genotypes were 6/6, 6/7, or 7/7. Both the size-based method and the Invader method had straightforward data analysis, while interpretation of the sequencing results was occasionally more challenging. The Invader method required more concentrated DNA for analysis, was more expensive, and had a limited genotyping spectrum.

CONCLUSION

All three methods were valuable for genotyping the UGT1A1 (TA)n repeat, with the sequencing and size-based assays having the fewest drawbacks.

Pharmacogenetic determinants of outcome in acute lymphoblastic leukaemia

Present day paediatric co-operative group acute lymphoblastic leukaemia (ALL) protocols cure approximately 80% of patients, a result achieved largely through the use of risk-stratified therapies that employ multiple chemotherapy agents. These risk-based therapies utilize host and leukaemia traits to select the most appropriate therapy. However, these risk-stratified approaches predict therapy response imperfectly and an important fraction of patients experience relapse or therapy-related toxicity. Pharmacogenetics, the study of genetic variations in drug-processing genes and individual responses to drugs, may enable the improved identification of patients at higher risk for either disease relapse or chemotherapy-associated side effects. While the impact of genetic variation in the thiopurine-S-methyltransferase gene on ALL treatment outcome and toxicity has been extensively studied, the role of other polymorphisms remains less well known. This review summarizes current research on the impact of genetic variation in drug-processing genes in paediatric ALL and reviews important methodological and statistical issues presently challenging the field of pharmacogenetics.

Genetic variation of human UDP-glucuronosyltransferase: implications in disease and drug glucuronidation

The uridine diphosphate (UDP)-glucuronosyltransferases (UGTs) are key enzymes in human detoxication of xeno- and endobiotics. Potentially toxic endogenous compounds such as bilirubin, or exogenous compounds such as drugs, pesticides, and carcinogens, are generally transformed into water-soluble glucuronides for excretion in bile and urine. The UGTs are encoded by a multigene family in humans. A relatively small number of human enzymes catalyze the glucuronidation of thousands of compounds. Genetic variations and single nucleotide polymorphisms (SNPs) within the UGT genes are remarkably common, and lead to genetic polymorphisms. The multiplicity of transferases, some exhibiting overlapping substrate specificity, may provide functional compensation for genetic deficit in some cases. Genetic variation may cause different phenotypes by affecting expression levels or activities of individual UGTs. This inter-individual variation in UGTs has resulted in functional deficit affecting endogenous metabolism and leading to jaundice and other diseases. Disruption of the normal metabolic physiology, by the reduction of bile acid excretion or steroid glucuronidation, may lead to cholestasis and organ dysfunction. Deficient glucuronidation of drugs and xenobiotics have an important pharmacological impact, which may lead to drug-induced adverse reactions, and even cancer. Additional novel polymorphisms in this gene family are yet to be revealed and studied, but will have a profound effect on the development of new drugs and therapies.

Role of pharmacogenomics and pharmacodynamics in the treatment of acute lymphoblastic leukaemia

Pharmacodynamic studies have been used to establish the relationships between the administered dosage and the concentration of drugs and metabolites in the blood or tissues and that between these concentrations and pharmacological effects. Polymorphisms in the genes that encode drug-metabolizing enzymes, drug transporters and drug targets can affect a person's response to therapy and may affect the development of de novo or therapy-related leukaemias. The burgeoning field of pharmacogenomics elucidates inherited differences in drug metabolism and treatment response. Increasingly, pharmacodynamic and pharmacogenomic studies are being used to individualize therapy to enhance efficacy and reduce toxicity.