Thiopurine S-methyltransferase Genetic Polymorphism And Its Effect On Mercaptopurine Tolerance In Adult Acute Lymphoblastic Leukemia

Objective To determine the incidence of the thiopurine S-methyltransferase(TPMT) genetic polymorphism in adult acute lymphoblastic leukemia(ALL), and develop a simple non-radioactive assay to measure TPMT activity. The assay was used to study the distribution of TPMT activity in a adult ALL population. Then to assess TPMT phenotype and genotype in 20 adult ALL who were given maintenance treatment with mercaptopurine(6-MP) and evaluate their clinical management for individualizing 6-MP chemotherapy.Methods Part 1: Genomic DNA was extracted from peripheral blood leukocytes of 78 adult ALL patients and 154 healthy Han Chinese. The frequencies of four allelic variants of the TPMT gene, TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C were determined using allele specific polymerase chain reaction(ASPCR) or PCR-Restriction fragment length polymorphism technique. Part 2: The assay is based on the conversion of 6-mercatopurine(6-MP) to 6-methylmercatopurine (methyl-MP) using non-radiolabelled S-adenosyl-L-methionine(SAM) as the methyl donor. At the end of the incubation period methyl-MP was extracted into toluene as a phenyl-mercury adduct and back-extracted into 0.1 mmol·L^-1 HCl. Methyl-MP was quantitated by reversed-phase high-performance liquid chromatography (HPLC).One unit of enzyme activity represented the formation of 1 nmol of methyl-MP per hour of incubation, per milliliter of packed red cells at 37℃. Part 3: TPMT activities and genotypes have been determined in 20 adult ALL with 6-mercatopurine maintenance therapy based on the...