MicroRNA (miR) expression signatures in molecular subsets of cytogenetically normal (CN) acute myeloid leukemia (AML): A Cancer and Leukemia Group B (CALGB) study

Abstract

7010 Background: Aberrantly expressed miRs contribute to malignant transformation by hybridizing to specific mRNA targets and suppressing their translation into proteins. In CN AML, the largest cytogenetic AML subset, several molecular markers are associated with favorable [e.g., NPM1 mutation (mutNPM1)] or unfavorable [e.g., FLT3 internal tandem duplication (ITD) or high ERG expression (↑ERG)] outcome. We explored if differentially expressed miRs are associated with the aforementioned markers. If so, this might indicate a role for miRs in leukemogenesis and prognosis in CN AML. Methods: Diagnostic samples from 100 adults <60 years, treated on CALGB 19808 (Blood 2005; 106:122a), were analyzed on miR microarrays. Among 305 miR probes, we identified differentially expressed miRs (P<0.005) when comparing patients (pts) with or without mutNPM1, FLT3 ITD or ↑ERG. Results: Nine miRs were differentially expressed in FLT3 ITD compared with FLT3 wild-type pts. miR 155, previously reported in aggressive cancers, was upregulated in FLT3 ITD pts. Strong signatures were associated with mutNPM1 (42 miR probes) and ↑ERG groups (54 miR probes). Consistent with their better prognosis, pts with mutNPM1 had upregulated miRs 10 and 196 targeting HOX genes, miRs 15 and 16 targeting BCL2 and let-7 targeting RAS. Consistent with a more aggressive phenotype, ↑ERG pts had downregulation of let-7 and miR 15 and 16 but also miRs 30, 103, and 24 which target, respectively, CDK6, FBXW11 and MAPK14, all involved in cell cycle regulation and proliferation. Four miRs were associated with event free survival (EFS); all were also associated with ↑ERG. High expression of miRs 124, 129, and 194 was significantly associated with worse EFS and ↑ERG. Low expression of miR 181 was associated with worse EFS and ↑ERG. Notably, downregulation of mir 181 has also been reported in pts with aggressive B-cell chronic lymphocytic leukemia. Conclusions: We report the first miR expression signatures within molecular subsets of CN AML. Further study is warranted to elucidate mechanisms by which miRs contribute to leukemogenesis and impact prognosis, and to determine whether miRs can be therapeutically targeted. No significant financial relationships to disclose.