Anti-TPMT monoclonal antibody, clone FQS21931(C)

Introduction: Acute Lymphoblastic Leukaemia (ALL) treatment protocols widely used thiopurine drugs as an anti-cancer agent, which over the course of time results in drug toxicity. Thiopurine S-Methyltransferase Enzyme (TPMT) is responsible for the activation of 6-Mercaptopurine (6-MP) to Thioguanine Nucleotides (TGNs) that are incorporated into DNA and trigger cell death. Low TPMT activity is strongly correlated to TPMT genetic polymorphism. Aim: To identify the level of TPMT activity and the most common TPMT polymorphism (TPMT*3A, TPMT*3B and TPMT*3C) and its frequencies in a sample of Iraqi ALL paediatric patients. Materials and Methods: Eighty-one Iraqi ALL paediatric patients receiving 6-MP in the maintenance phase of treatment were enrolled in the study. TPMT activity in the serum was measured by using Enzyme-Linked Immunosorbent Assay Technique (ELISA) in the serum and TPMT genetic polymorphism (TPMT*3A, TPMT*3B and TPMT*3C) was detected by allele-specific multiplex-PCR analysis. Statistical analysis was performed by using a two-sample t-test to evaluate the difference in allele frequencies proportion in TPMT polymorphism. Pearson's correlation analysis was done to determine the correlation between TPMT enzyme genotype and phenotype. Results: There were 51 paediatric ALL patients carrying the wildtype allele with allele frequencies of (62.96%), 30 paediatric ALL patients carrying the mutant alleles either TPMT*3A or TPMT*3C with allele frequencies of 29.62% and 7.4% respectively. The mutant allele TPMT*3B was not detected in the patients under study. The difference in mean of the TPMT enzyme activity between the ALL patients carrying the wild-type allele and the mutant allele was highly significant with p-value <= 0.001. A highly significant positive co-relation (r=0.939) was found between TPMT low activity and presence of genetic mutation across the TPMT gene (p-value <= 0.001). Conclusion: TMPT genotyping and phenotyping is an essential tool to reduce the cytotoxic effects of the anti-cancer drug 6-MP in Iraqi paediatric patients with ALL for a successful recovery.

To explore the levels of thioguanine incorporated into DNA (DNA-TG), and erythrocyte levels of 6-thioguanine nucleotides (Ery-TGN) and methylated metabolites (Ery-MeMP) during 6-mercaptopurine (6MP)/Methotrexate (MTX) therapy of childhood acute lymphoblastic leukemia (ALL) and the relation to inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT) gene variants. Blood samples were drawn during 6MP/MTX maintenance therapy from 132 children treated for ALL at Rigshospitalet, Copenhagen. The samples were analysed for thiopurine metabolites and compared to TPMT (rs1800460 and rs1142345) and ITPA (rs1127354) genotypes. Median DNA-TG (mDNA-TG) levels were higher in TPMT and ITPA low-activity patients as compared to wildtype patients (TPMT (LA) 549 vs. 364 fmol/A mu g DNA, p = 0.007, ITPA (LA) 465 vs. 387 fmol/A mu g DNA, p = 0.04). mDNA-TG levels were positively correlated to median Ery-TGN (mEry-TGN)(r (s) = 0.37, p = 0.001), but plateaued at higher mEry-TGN levels. DNA-TG indices (mDNA-TG/mEry-TGN) were 42% higher in TPMT (WT) patients as compared to TPMT (LA) patients but no difference in DNA-TG indices was observed between ITPA (WT) and ITPA (LA) patients (median 1.7 vs. 1.6 fmol/A mu g DNA/ nmol/mmol Hb, p = 0.81). DNA-TG indices increased with median Ery-MeMP (mEry-MeMP) levels (r (s) = 0.25, p = 0.001). TPMT and ITPA genotypes significantly influence the metabolism of 6MP. DNA-TG may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than cytosolic metabolites. Prospective trials are needed to evaluate the usefulness of DNA-TGN for individual dose adjustments in childhood ALL maintenance therapy.