Since these miRNAs regulate expression of BCL2 and other apoptosis regulators, the data demonstrate the crucial balance between proliferative signals and apoptosis in BCR-ABL-positive ALL. pharmacological BCL2 inhibition than unfavorable ones. Finally, in a xenograft model using patient-derived leukaemic blasts, real-time,in vivoimaging confirmed pharmacological inhibition of BCL2 as a new therapeutic strategy in BCR-ABL-positive ALL. These data demonstrate the role of miR-1792 in regulation of apoptosis, and identify BCL2 as a therapeutic target of particular relevance in BCR-ABL-positive ALL. Keywords:BCR-ABL, BCL2, acute lymphoblastic leukaemia, miRNA-1792 == Introduction == Acute lymphoblastic leukaemia (ALL) is usually a heterogeneous disease with multiple, prognostically relevant genetic aberrations. In adults, 3040% of patients with precursor-B ALL express the BCR-ABL oncogene as the result of the Philadelphia-translocationt(9;22)(q34;q11) defining a very high-risk profile.1,2The BCR-ABL oncoprotein is a constitutively active tyrosine kinase involved in hematopoietic cell transformation. Inhibition of its enzymatic activity by specific tyrosine kinase inhibitors has substantially improved and fundamentally changed the treatment of chronic myeloid leukaemia and enhanced cure rates in BCR-ABL-positive childhood ALL.3,4However, treatment of adult BCR-ABL-positive ALL remains challenging. The historically poor outcome of Ph+ ALL patients has been substantially improved by combining tyrosine kinase inhibitors with induction and post-remission chemotherapy, resulting in higher Alagebrium Chloride remission rates and therefore a greater proportion of patients undergoing allogeneic hematopoietic stem cell transplantation (SCT).5,6,7At present, myeloablative conditioning followed by allogeneic SCT remains the only established curative therapy, with several prospective trials showing an overall survival of 3065%.8,9,10Despite these advances, high transplant-associated mortality and relapse remain considerable obstacles, and the majority of elderly patients are not considered suitable candidates for allogeneic SCT, resulting in a still dismal long-term outcome.6This has not been altered dramatically by the recent availability of more potent second generation tyrosine kinase inhibitors,11and most likely involves mechanisms of resistance distinct from BCR-ABL tyrosine kinase domain mutations.12Therefore, it is important to develop new targeted agents alongside tyrosine kinase inhibitors to improve survival and reduce morbidity in those patients currently able to undergo allogeneic SCT as well as to offer improved pharmacotherapy for patients not suitable for SCT. miRNAs are a class of small non-coding RNAs involved in posttranscriptional control of gene expression. Upon processing, miRNAs are incorporated in an effector complex RNA induced silencing complex Alagebrium Chloride (RISC) which is usually recruited to at least partially complementary sites in target-gene mRNAs. Individual miRNAs can bind to multiple mRNAs with differential effects on gene expression of multiple targets. We hypothesised that miRNAs may be used to identify potential leukaemia-relevant therapeutic targets if they are differentially expressed in tumour cells and if they are linked to disease-relevant phenotypes. The polycistronic microRNA cluster miR-1792 encodes miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1 and miR-92-1.13Notably, miR-1792-deficient mice suffer significant developmental cardiac defects and lung hypoplasia though interrogation of haematopoiesis identified isolated defects in B-lineage development.14Moreover, we observed a high expression of miR-1792 in adult heart Rabbit Polyclonal to DP-1 and in postnatal cardiomyocytes. miR-1792 has also been Alagebrium Chloride strongly implicated in both solid and haematopoietic malignancies.15,16Of these, the first and now best-studied group is the mature B-lymphoid malignancies.17 Conditional knockout of the cluster-revealed modulation of apoptosis as the predominant mechanism of action of miR-1792.18In normal lymphopoiesis, loss of miR-1792 results in upregulation of Bim (Bcl2l11) and increased apoptosis, inhibiting the pro-B to pre-B transition.14Conversely, moderate overexpression of miR-1792 causes a reduction in Bim and Pten expression, resulting in lymphoproliferation and autoimmune disease.19Dissection of the miR-1792 cluster has demonstrated that miR-19 is both necessary and sufficient to abrogate apoptosis, at least in Myc-mediated lymphomagenesis most likely by repression of PTEN and BIM.18,20 Based on our previous work in chronic myeloid leukaemia,21we first analysed miR-1792 expression in ALL and observed a.