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Epigenetic down-regulation of BIM expression is associated with reduced optimal responses to imatinib treatment in chronic myeloid leukaemia

2009; Elsevier BV; Volume: 45; Issue: 10 Linguagem: Inglês

10.1016/j.ejca.2009.04.005

1879-0852

Edurne San José‐Eneriz, Xabier Agirre, Antonio Jiménez‐Velasco, Lucía Cordeu, Vanesa Martı́n, Víctor Arqueros, Leire Gárate, Vicente Fresquet, Francisco Cervantes, José A. Martínez-Climent, Anabel Heiniger, António Torres, Felipe Prósper, José Román‐Gómez,

Myeloproliferative Neoplasms: Diagnosis and Treatment

Background Expression of the pro-apoptotic BCL-2-interacting mediator (BIM) has recently been implicated in imatinib-induced apoptosis of BCR-ABL1+ cells. However, the mechanisms involved in the regulation of BIM in CML and its role in the clinical setting have not been established. Design and methods We analysed the mRNA expression of BIM in 100 newly diagnosed patients with CML in chronic phase by Q-RT-PCR and the protein levels by Western blot analysis. Methylation status was analysed by bisulphite genomic sequencing and MSP. CML cell lines were treated with imatinib and 5-aza-2’-deoxycytidine, and were transfected with two different siRNAs against BIM and cell proliferation and apoptosis were analysed. Results We demonstrated that down-regulation of BIM expression was present in 36% of the patients and was significantly associated with a lack of optimal response to imatinib as indicated by the decrease in cytogenetic and molecular responses at 6, 12 and 18 months in comparison with patients with normal BIM expression (p < 0.05). Expression of BIM was mediated by promoter hypermethylation as demonstrated by restoration of BIM expression after treatment of CML cells with 5-aza-2′-deoxycytidine. Using CML cell lines with low and normal expression of BIM we further demonstrated that the expression of BIM is required for imatinib-induced CML apoptosis. Conclusion Our data indicate that down-regulation of BIM is epigenetically controlled by methylation in a percentage of CML patients and has an unfavourable prognostic impact, and that the combination of imatinib with a de-methylating agent may result in improved responses in patients with decreased expression of BIM.