Abstract Acute myeloid leukemia (AML) is a heterogeneous neoplasm characterized by the accumulation of poorly differentiated myeloid cells in the bone marrow and blood of patients. Differentiation therapy is an attractive therapeutic approach for treating patients with AML. All-Trans Retionic Acid, induces differentiation of patients with the PML/RARa oncogene, but is ineffective in treating other more frequent types of AML. Here we describe the use of microRNAs to target the oncogene formed as a result of the (8;21) translocation, The goals was to identify miRNAs that could target the breakpoint region of the fusion protein, and determine if this would reduce expression of AML1-ETO and promote differentiation and/or apoptosis. Bioinformatics analysis was used to identify 28 different miRNAs that could potentially target AML1-ETO transcripts. Among those, miRNA-520 and -373 showed the highest degree of complimentary to AML1-ETO transcripts at the braikpoint. To look for miR-520 and -373 efficacy, we transfected two AML cell lines, Kasumi 1 and SKNO1, which have AML1-ETO translocation, with pre-miR-520 and -373 LNA probes, as well as HL60 cells which lack AML1-ETO. Expression of the LNA pre-miR-520/373 in Kasumi-1 and SKNO-1 cell lines decreased AML1-ETO transcripts and led to a significant reduction of AML1-ETO protein levels. The inhibition of AML1-ETO fusion protein also induced apoptosis of leukemic cells in vitro, but had no effect on HL60 cells. Moreover, the administration of LNA pre-miR-520 in an AML xenografts murine model increased apoptosis of leukemic cells and reduced tumor burden without obvious toxicity. We are currently testing the effects of miR-520 and -373 on differentiation and proliferation of primary blasts from patients with the AML1-ETO translocation. Our results suggest that small molecules such as miRNAs can be identified that directly target a frequent AML oncogene. miRNAs are naturally accruing molecules and have the potential advantage of producing modest side effects, with highly significant specificity. The approaches we developed in this study can be used to evaluate and optimize other pre-miRs and anti-miRs as therapeutic agents to target other types oncogenes not currently amenable to small molecule drugs. Citation Format: Patricia A. Toniolo, Patrick M. Pilarski, Christian Bach, James D. Griffin, Sophia Adamia. MicroRNAs as potential therapeutic agents for AML: Targeting the AML1-ETO Oncogene by pre-miR-520 and -373. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3972. doi:10.1158/1538-7445.AM2015-3972