Increases In Mirna-145 and Mirna-146a Expression In Patients with IPSS Lower-Risk Myelodysplastic Syndromes and Del(5q) Treated with Lenalidomide.

The erythroid differentiation defect observed in 5q– syndrome has been attributed to the RPS14 gene located within the CDR of the long arm of chromosome 5. We have recently demonstrated that RPS14 expression increases during lenalidomide treatment. However, haploinsufficiency of RPS14, which encodes ribosomal protein S14, does not explain clonal dominance. The expression of miRNAs, miR-145 (5q33.1) and miR-146a (5q33.3), in CD34+ bone marrow (BM) cells of individuals with MDS with deletion of the long arm of chromosome 5 (del(5q)) is lower compared to normal controls (Starczynowski et al, Nature Medicine, 2010). miRNAs are small noncoding RNAs that post-transcriptionally repress specific messenger RNA targets through interaction with the 3′ untranslated region (UTR). Loss of noncoding transcripts encoding miRNAs within the CDR may result in haploinsufficiency by loss of inhibition of their targets. Concurrent loss of both miR-145 and miR-146a resulted in activation of innate immune signalling through elevated expression of their respective targets, TIRAP and TRAF6. Furthermore, knockdown of miR-145 and miR-146a or overexpression of TRAF6 in mouse HSPC (Hematopoietic stem and progenitor cells) recapitulated features of 5q– syndrome, such as bone marrow dysplasia, anemia and thrombocytosis. We present preliminary results of changes in miRNA expression in IPSS lower-risk MDS with del(5q) during treatment with lenalidomide.

A prospective single-arm trial investigating the efficacy and safety of lenalidomide in 46 patients with MDS with del(5q) with/without additional cytogenetic abnormalities and Hb < 10 g/dL. Lenalidomide was administered orally at a starting dose of 10 mg/day for a maximum of 12 months. When necessary, dosing was reduced to 5 mg/day or 5 mg on alternate days. Bone marrow assessments were performed at baseline and every 3 months, thereafter. For the evaluation of miRNA-145 and miRNA-146a in patient samples, 300 ng/μl of miRNAs were isolated in each purified BM sample by using mirVana™ miRNA Isolation Kit-Ambion and TaqMan miRNA Array Analysis was performed to determine the expression of miRNAs (7900HT Sequence Detection System Applied Biosystems). Patient BM-miRNAs were calibrated with miRNAs from BM of healthy volunteer donors. It was assumed that BM expression value of each calibrator miRNA was 1 unit. RPS14 gene assays were performed using TaqMan® Low Density Array Fluidic card (TaqMan® Human Array, Applied Biosystems, Foster City, CA, USA) based on Applied Biosystems PRISM® 7900HT comparative ddCT method, according to the manufacturer's instructions. Target gene expression levels were measured in triplicate and normalized against the expression of the 18S housekeeping gene from a BM pool of normal, healthy subjects at all timepoints. Median relative gene expression values in MDS patients were compared to healthy subjects, set as a value of 1.

Four patients have been evaluated (1 M, 3 F; ages 65, 66, 73 and 76 years, respectively) at baseline and after 12 weeks. At baseline, 2 patients were RBC-transfusion dependent. One patient had one additional cytogenetic abnormality (+8 in 15% metaphases). All patients obtained an erythroid response by week 12: mean Hb values significantly increased from 8.4 ± 0.9 at baseline to 11.6 ± 0.9 g/dL (p=0.01). All patients obtained a cytogenetic response, 2 of which were complete. miRNA-145 and miRNA-146a expression were both low at baseline and significantly increased by week 12 (Table).

Preliminary results confirm that, in IPSS lower-risk MDS with del(5q), miRNA-145 and miRNA-146a expression is low. Lenalidomide treatment is associated with erythroid responses and cytogenetic remissions concurrent with significant increases in miRNA-145 and miRNA-146a expression.

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