Effect of genetic alterations of cytarabine-metabolizing enzymes in childhood acute lymphoblastic leukemia

Single nucleotide polymorphisms [SNPs] of deoxyctidine kinase [dCK] and cytidine deaminase [CDA] are known to alter their enzymatic activities, which affect the metabolism of cytarabine. Currently, treatment of childhood acute lymphoblastic leukemia [ALL] includes cytarabine, especially in high-risk patients. Therefore we hypothesized that a genetic variation of dCK and CDA genes may influence the risk of cytarabine-related toxicities and early response to treatment. We included children diagnosed with ALL and lymphoblastic lymphoma [LL] stage III and IV. The patients received a modified ST Jude Total Therapy Study XV protocol. Cytarabine was used during induction remission [low-dose cytarabine] and reinduction II [high-dose cytarabine] phases. Genotyping of dCK -360 > G and -201 > T and CDA 79A > C and 208G > A was performed. Minimal residual disease [MRD] at the end of the induction phase was measured using flow cytomery. Ninety-four children with ALL [n=90] and LL [n=4] were analyzed. The median age at diagnosis was 5.8 years [range, 0.4-15 years]. All four SNPs showed predominant wild type alleles. There was no CDA-208A allele in our population. Children with dCK-360G allele were at risk of mycositis after receiving low-dose cytarabine [OR=3.7; 95% CI, 1.2-11.3]. Neither dCK nor CDA polymorphisms affected the MRD status at the end of induction phase. The dCK-360G allele was found to found to increase the risk of mucositis after expose to low-dose cytarabine in childhood ALL therapy

Cytosine arabinoside-metabolizing enzyme genes are underexpressed in children with MLL gene-rearranged acute lymphoblastic leukemia

Infant acute lymphoblastic leukemia (IALL) is characterized by mixed lineage leukemia (MLL) gene rearrangements, unique gene expression profiles, poor prognosis, and drug resistance. One exception is cytosine arabinoside (Ara-C) to which IALL cells seem to be more sensitive. We quantified mRNA expression of Ara-C key enzymes in leukemic lymphoblasts from 64 Brazilian ALL children, 15 of them presenting MLL gene rearrangement, and correlated it with clinical and biological features. The diagnosis was based on morphological criteria and immunophenotyping using monoclonal antibodies. MLL gene rearrangements were detected by conventional cytogenetic analysis, RT-PCR and/or fluorescence in situ hybridization. The DCK and HENT1 expression levels were determined by real-time quantitative PCR using SYBR Green I. Relative quantification was made by the standard curve method. The results were analyzed by Mann-Whitney and Fisher exact tests. A P value of ú0.05 was considered to be statistically significant. DCK and HENT1 expression levels were significantly lower in children with MLL gene-rearranged ALL compared to children with MLL germ line ALL (P = 0.0003 and 0.03, respectively). Our results differ from previous ones concerning HENT1 mRNA expression that observed a higher expression level in MLL gene-rearranged leukemias. In conclusion, the expression of the genes related to Ara-C metabolism was lower in MLL-positive children in the sample studied, suggesting the presence of population differences in the expression profile of these genes especially for HENT1.