MicroRNA Expression Profiles in Chronic Myelomonocytic Leukemia

Chronic myelomonocytic leukemia (CMML) is a hematopoietic malignancy with hybrid myeloproliferative and myelodysplastic features. The diagnostic criteria for CMML are evolving with the progress of our knowledge on various genetic lesions involved in the pathogenesis of myeloid neoplasms. This shift, including molecular genetic lesions in the diagnosis process, is highlighted in updated 2008 WHO classification system, which excludes myeloproliferative neoplasms with PDGFRB rearrangement, monocytosis and eosinophilia from CMML category. Despite these recent advancements, CMML remains a heterogeneous group of diseases with variable patient outcomes and no well-defined targeted therapy. To further investigate the biological diversity of this disorder, we studied microRNA (miRNA) expression profiles, their relation to the diagnostic and clinical parameters in CMML, and compared these profiles to global miRNA expression in normal reference bone marrow samples. MicroRNAs are a class of non-coding RNA molecules that alter gene expression by targeting and blocking mRNA. The role of miRNAs in carcinogenesis is related to their targeting of messenger RNAs encoding for oncogenes and tumor suppressor genes. Bone marrow samples from 22 patients with CMML were included in the study. Median age of the patients was 71 years with a range from 39 to 92 years. There were 15 males and 7 females. Seventeen patients presented with CMML-1 (blasts less than 5% in peripheral blood and less than 10% of bone marrow differential count). The remaining patients showed CMML-2. Nine patients had WBC below 13×10⁹/L defining a myelodysplastic type of CMML. Cytogenetic results were available in 20 patients. Fourteen patients demonstrated a normal karyotype. Normal pooled bone marrow samples were used as a reference. The total RNA was isolated using RecoverAll RNA extraction kit. Micoroarray studies were performed using Agilent human miRNA microarrays (version 1.0) containing probes for 470 human and 64 human viral miRNAs cataloged in the Sanger database v9.1. The results were analyzed using BRB array tool and Genesis software. Unsupervised hierarchical clustering discovered two different groups of CMML samples with patterns of miRNA expression distinct from normal bone marrows (oneway ANOVA). Twenty seven miRNAs were differentially expressed in normal bone marrow reference samples vs. CMML-1 and -2. There was an overlap in miRNA profiles between groups of CMML based on blast percentage (CMML-1 vs. CMML-2), WBC count (<13×10⁹/L vs. ≥13×10⁹/L) and presence or absence of cytogenetic abnormalities. However, using PAM algorithm the following miRNAs showed predictive power: hsa-miR-519b (in CMML-1 vs. 2); hsa-miR-15b and hsa-miR-432* (in groups of samples separated by a cut-off WBC of 13×10⁹/L) and hsa-miR-223 (comparing CMML with and without cytogenetic abnormalities). In summary, significantly different miRNA profiles were seen in CMML as compared to normal reference bone marrow. Two distinct subgroups of CMML were defined by the miRNA expression profiles. Select miRNAs were differentially expressed in known biological and clinical subgroups of CMML. Further correlation of clinical and outcome data with subgroups of CMML defined by miRNA expression profiles will be presented.