Abstract 1013: Enriched miR-126 bioactivity marks the primitive compartment in human AML and regulates leukemia stem cell numbers
Authors: Lechman Eric R. , Gentner Bernhard , van Galen Peter , Eppert Kolja , Takenaka Katsuto , Minden Mark , Naldini Luigi , Dick John E. 
Published: August 2012

Abstract
Previous work has shown miRNAs are dysregulated in acute myeloid leukemia (AML), however, there is little known regarding miRNA expression and function in human leukemia stem cells (LSC). In order to elucidate the role of miRNA in LSC, we performed miRNA profiling on fractionated subpopulations of primary AML patient samples. Supervised analysis guided by the in vivo SCID leukemia initiating cell (SL-IC) capacity of each sub-population generated a unique miRNA signature associated with LSC enriched fractions. The biological activity of our top candidate, miR-126, was confirmed at single cell resolution by using a novel bidirectional lentivirus miRNA reporter system in vitro and within primary AML patient samples xenografted into immune-deficient NSG mice. These data suggest that primitive AML cells may express high levels of bioactive miR-126 relative to more “differentiated” blast populations. To test this hypothesis, we FACS sorted miR-126 genetic reporter vector transduced primary AML patient samples and transplanted these populations into immune-compromised secondary mouse recipients. The results of these proof-of-concept experiments demonstrates our ability to prospectively isolate LSC enriched fractions in all 4 AML patient samples tested using only a single biomarker, miR-126. Finally, to understand the functional relevance of miR-126 expression within primitive human AML cells, stable enforced expression and knockdown of miR-126 was achieved using lentiviral vectors. Enforced expression in four primary AML xenografts resulted in a several fold increase of CD34+CD117+ lentivirus marked leukemia cells after 12 weeks. In addition, the miR-126/OE cells showed reduced differentiation marker expression (CD14, CD15) with no significant differences in AML graft size. To determine if the expanded population had SL-IC activity or was a downstream leukemic progenitor, limiting dilution assays were performed by transplantation of FACS sorted lentivirus marked cells into secondary recipient mice for 12 weeks. A 3-20 fold increase in LSC activity was observed with miR-126 forced expression compared to control cells. These data suggest that high levels of miR-126 bioactivity support self-renewal/maintenance of primitive AML cells at the cost of aberrant differentiation. We performed microarray analysis of a primitive human AML cells after miR-126/OE and miR-126/KD. The principal signalling pathway(s) under direct control of miR-126 in primitive AML cells were revealed by subjecting our array data to Gene Set Enrichment Analysis (GSEA) in combination with several published miRNA target prediction algorithms. In summary, this work demonstrates that miR-126 is more abundant and biologically active within the leukemia stem/progenitor cell compartment of the AML functional hierarchy and serves to regulate AML stem cell numbers.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1013. doi:1538-7445.AM2012-1013