Chromosomal translocations are characteristic of hematopoietic neoplasias and can lead to unregulated oncogene expression or the fusion of genes to yield novel functions. In recent years, different lymphoma/leukemia-associated rearrangements have been detected in healthy individuals. In this study, we used inverse PCR to screen peripheral lymphocytes from 100 healthy individuals for the presence of MLL (Mixed Lineage Leukemia) translocations. Forty-nine percent of the probands showed MLL rearrangements. Sequence analysis showed that these rearrangements were specific for MLL translocations that corresponded to t(4;11)(q21;q23) (66%) and t(9;11) (20%). However, RT-PCR failed to detect any expression of t(4;11)(q21;q23) in our population. We suggest that 11q23 rearrangements in peripheral lymphocytes from normal individuals may result from exposure to endogenous or exogenous DNA-damaging agents. In practical terms, the high susceptibility of the MLL gene to chemically-induced damage suggests that monitoring the aberrations associated with this gene in peripheral lymphocytes may be a sensitive assay for assessing genomic instability in individuals exposed to genotoxic stress.

CONTEXTO: Apesar dos avanços nos índices de cura da leucemia linfoblástica aguda (LLA) aproximadamente 25% das crianças sofrem recaídas da doença. A expressão dos genes de resistência múltipla a drogas (MDR-1), genes relacionados à proteína de resistência múltipla a drogas (MRP) e genes da proteína de resistência pulmonar (LRP) podem conferir o fenótipo de resistência ao tratamento das neoplasias. OBJETIVO: Analisar a expressão dos genes de resistência MDR-1, MRP e LRP em crianças diagnosticadas com LLA por meio da técnica da reação em cadeia da polimerase da transcriptase reversa (RT-PCR) semiquantitativa, associando estas expressões à sobrevida livre de eventos (SLE) e a variáveis clínico-laboratoriais. TIPO DE ESTUDO: Estudo clínico retrospectivo. LOCAL: Laboratório de Oncologia Pediátrica do Departamento de Puericultura e Pediatria da Faculdade de Medicina de Ribeirão Preto - Universidade de São Paulo, Brasil. MÉTODOS: Amostras de medula óssea de 30 crianças com o diagnóstico de leucemia linfoblástica aguda foram avaliadas quanto à expressão do RNA-mensageiro para os genes MDR-1, MRP e LRP, pela reação em cadeia da RT-PCR semiquantitativa. RESULTADOS: Dos três genes estudados, somente a expressão aumentada de LRP esteve relacionada a uma pior SLE (p = 0.005). A presença do antígeno para leucemia linfoblástica aguda comum (CALLA) se correlacionou à expressão aumentada de LRP (p = 0.009) e a risco aumentado de ocorrência de recaída ou óbito (p = 0.05). O risco relativo de ocorrência de recaída ou óbito é seis vezes maior em crianças com alta expressão de LRP ao diagnóstico (p = 0.05), o que se confirma na análise multivariada dos três genes estudados (p = 0.035). DISCUSSÃO: A resistência celular a drogas é um determinante de resposta ao tratamento oncológico e sua avaliação por RT-PCR pode ser de importância. CONCLUSÕES: A avaliação da expressão dos genes de resistência a drogas antineoplásicas na leucemia linfoblástica aguda da criança ao diagnóstico, particularmente do gene LRP, pode ser de relevância clínica e deve ser objeto de estudos prospectivos.

CONTEXT: Despite the advances in the cure rate for acute lymphoblastic leukemia, approximately 25% of affected children suffer relapses. Expression of genes for the multiple drug resistance protein (MDR-1), multidrug resistance-related protein (MRP), and lung resistance protein (LRP) may confer the phenotype of resistance to the treatment of neoplasias. OBJECTIVE: To analyze the expression of the MDR-1, MRP and LRP genes in children with a diagnosis of acute lymphoblastic leukemia via the semiquantitative reverse transcription polymerase chain reaction (RT-PCR), and to determine the correlation between expression and event-free survival and clinical and laboratory variables. DESIGN: A retrospective clinical study. SETTING: Laboratory of Pediatric Oncology, Department of Pediatrics, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brazil. METHODS: Bone marrow aspirates from 30 children with a diagnosis of acute lymphoblastic leukemia were assessed for the expression of messenger RNA for the MDR-1, MRP and LRP genes by semi-quantitative RT-PCR. RESULTS: In the three groups studied, only the increased expression of LRP was related to worsened event-free survival (p = 0.005). The presence of the common acute lymphoblastic leukemia antigen (CALLA) was correlated with increased LRP expression (p = 0.009) and increased risk of relapse or death (p = 0.05). The relative risk of relapse or death was six times higher among children with high LRP expression upon diagnosis (p = 0.05), as confirmed by multivariate analysis of the three genes studied (p = 0.035). DISCUSSION: Cell resistance to drugs is a determinant of the response to chemotherapy and its detection via RT-PCR may be of clinical importance. CONCLUSIONS: Evaluation of the expression of genes for resistance to antineoplastic drugs in childhood acute lymphoblastic leukemia upon diagnosis, and particularly the expression of the LRP gene, may be of clinical relevance, and should be the object of prospective studies.