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

Abstract

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 ≤0.05 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.

Expression Levels of Human Equilibrative Nucleoside Transporter 1 and Deoxycytidine Kinase Enzyme as Prognostic Factors in Patients with Acute Myeloid Leukemia Treated with Cytarabine

“…Thereafter, the dCK enzyme produces a monophosphorylated product (dCMP), which is bi- and triphosphorylated to act as an antimetabolite. Resistance to Ara-C has been documented in AML cells with defective dCK or hENT1 expression [12,15,16]. Our results clearly show that recently diagnosed, untreated AML patients with higher hENT1 and dCK expression levels have a higher response rate and a better OS.…”

“…The health economic impact of induction chemotherapy using high-dose Ara-C compared to the standard dose was proposed by Fedele et al [11]. High-dose Ara-C has a higher toxicity rate and higher costs for patients who require complete hospitalization until neutrophil recovery, and this schema is only adopted for young and fit patients [12]. Along the same lines, allotransplantation has been proposed for normal-karyotype AML patients who achieve a median survival of almost 18 months [13].…”

Caracterização de subpopulações de Leucemia Mielóide Aguda portadora do rearranjo MLL quanto à resposta diferencial ao tratamento em longo prazo com Citarabina

“…Os primeiros estudos que objetivaram relacionar a alta taxa de recaída dos pacientes com LMA-MLL à resposta diferencial ao Ara-C, verificaram que a sensibilidade a esta droga não está relacionada ao metabolismo da droga (Mata et al, 2006;Stam et al, 2006;Jo et al, 2009): tanto a expressão quanto a atividade de suas enzimas metabolizadoras, especialmente hENT, cDK e PH-I, não foi correlacionada à taxa de recaída à LMA-MLL ou sensibilidade à droga. Como hipótese alternativa para justificar a alta taxa de recidiva e a sensibilidade diferencial às drogas, acredita-se que outros mecanismos que acelerem a proliferação celular ou mesmo dificultem a morte celular estejam desregulados (Balgobind et al, 2009;Krauter et al, 2009).…”

“…Contudo, a expressão de PN-I não afetou a sensibilidade ao Ara-C, visto que, as amostras de LLA não apresentaram diferenças na citotoxidade in vitro, quando comparadas às amostras MLL - (Stam et al, 2006). Ainda em LLA, Mata et al (2006) demonstraram a redução da expressão dos genes dCK, a quinase responsável por fosforilar Ara-C a Ara-CMP, e hENT1, o transportador de Ara-C do meio extra para o intracelular.…”

“…Ambos os genes subexpressos são indícios de que a sensibilidade à droga seria atribuída à desregulação de enzimas metabolizadoras. Entretanto, os pesquisadores não realizaram ensaios de citotoxidade in vitro, ou a medida do acúmulo de Ara-CTP, que evidenciariam a sensibilidade ao Ara-C (Mata et al, 2006).…”