Molecular Characterization By miRNA Expression Profiling in Acute Promyelocytic Leukemia (APL): deregulation Of Mirnas May Identify Patients At Risk Of Early Death

APL is a highly curable malignancy with large co-operative group trials showing mortality under 10%. Despite aggressive care 30% of patients die early at presentation or shortly after initiation of treatment. Understanding the biology of the disease may help us identify the causes for these poor outcomes and allow for even better outcomes. Recently, a class of noncoding RNAs called miRNAs has emerged as critical gene regulators in cell growth, disease, and development. miRNAs are 18–24 nucleotide long noncoding RNAs, which regulate gene expression by pairing with 3’ untranslated region (UTR) of target mRNA and inhibiting protein translation and/or inducing mRNA degradation. miRNAs modulate critical cell processes including cell growth, development, and differentiation. Our study investigates the differences in expression of miRs in APL patients with early mortality versus surviving patients.

The miRNA expression profile of APL survived (n=7), vs APL died (n=6) were evaluated using the Affymetrix miRNA microarray platform on GeneChip miRNA 3.0 array in paraffin-embedded samples. Following hybridization and data acquisition, we used Partek Genomics Suite ® software for RMA normalization and to determine statistically significant differences in miRNA expression between experimental groups by ANOVA and pairwise comparisons (two-sided α=0.05).

The miRNA expression profiles of dead versus alive patients shows statistically significant (1.5 to 14X, p<0.05) downregulation of a set of 30 miRNAs, and upregulation of 6 miRNAs (p<0.05). Although the role of these miRNAs has not been studied in APL, they have been described in other tumors, having a role in tumor suppression, differentiation, cell proliferation, chemoresistance and inflammation. The miRNA (mir-100), which plays a key role in the myeloid differentiation, was amongst the highest miRNAs that were downregulated in our dead patients (14X).

To the best of our knowledge, the current study represents the first global miRNA profiling exploration in understanding the early death in APL patients. Previous studies have demonstrated that miR-100 regulates G1/S transition and S-phase entry and blocks the terminal differentiation by targeting RBSP3 (a phosphatase-like tumor suppressor). Although it is overexpressed in APL patients compared to normal cells, in patients who died it shows a significant down regulation (14X). Other tumor cell lines have shown that a down regulation in miR-100 imparts chemotherapy resistance. Combined with down regulation in miR-27a (3.5 X), which has been shown to impart chemoresistance in APL cell lines, and dysregulation of miR 30c (down 5 fold) and miR-663 (up 2.3 fold), we predict that these patients may be less sensitive to treatment. Reduction in tumor suppressor function is another way that tumors can be more aggressive. Multiple miRNAs that have been implicated as tumor suppressive were down regulated in dead patients. miRs-100, -125b, -150 (down 14X, 10X and 9X respectively) have been shown to have tumor suppressive function in non-APL studies. This finding in combination with other downregulated miRNAs (a set of 15 miRs that have confirmed tumor suppressive roles), and two upregulated miRs may lead to a collective decrease in tumor suppression leading to more aggressive disease and poor outcome. miR-125b and 27a have been implicated in pro-inflammatory pathways and their dysregulation may lead to a sustained pro-inflammatory state that is peculiar to this disease and may contribute to the early morbidity and mortality observed in this group.

We hypothesize that dysregulation of microRNAs leads to a sustained pro-inflammatory state and might impart decreased sensitivity to treatment, and that eventually may lead to the poor outcomes observed. Further studies are needed to validate these results in a larger patient population. If confirmed, our findings can lead to targeted approaches to improve APL outcomes.

No relevant conflicts of interest to declare.