• Edurne San José-Eneriz, Xabier Agirre, Antonio Jiménez-Velasco, Lucia Cordeu, Vanesa Martín, Victor Arqueros, Leire Gárate, Vicente Fresquet, Francisco Cervantes, José A Martínez-Climent, Anabel Heiniger, Antonio Torres, Felipe Prósper, and Jose Roman-Gomez.
• Hematology Department and Area of Cell Therapy, Clinica Universitaria, Foundation for Applied Medical Research, University of Navarra, Pamplona, Spain.
• Eur. J. Cancer. 2009 Jul 1; 45 (10): 1877-89.

BackgroundExpression 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 MethodsWe 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.ResultsWe 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.ConclusionOur 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.

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