miR-324-3p and miR-508-5p expression levels could serve as potential diagnostic and multidrug-resistant biomarkers in childhood acute lymphoblastic leukemia

Highlights

• miR-324-3p and miR-508-5p were significantly downregulated in the pediatric ALL patients as well as drug-resistant ones.

• The expression level of miR-508-5p was lower in ALL relapsed patients.

• A clear inverse correlation was detected for miR-324-3p-ABCA3 and miR-508-5p-ABCA3 pairs.

Abstract

Acute lymphoblastic leukemia (ALL) is one of the most frequent hematological malignancies in children, representing approximately 25 % of all pediatric cancers. Despite striking advances in ALL treatments, a small population of patients does not still respond to chemotherapy, raising the number of deaths in children. ABC transporters are one of the major causes of multidrug resistance (MDR) in cancers and overexpression of ABCA3 is directly associated with increased chemo-resistance in pediatric ALL. Here, we aimed to identify the microRNAs (miRNAs) which may regulate the expression of ABCA3 in childhood ALL. Bone marrow samples from a total of 50 ALLs and 59 controls were collected and after in silico and literature search, miR-324-3p and miR-508-5p were nominated from a list of putative miRNAs targeting ABCA3. Our qPCR analysis showed a low expression profile of selected miRNAs in pediatric ALL patients compared with non-cancer controls. Furthermore, we found that both miR-324-3p and miR-508-5p were significantly differentially expressed between patients with positive and negative minimal residual disease (MRD + vs MRD-) after one year of chemotherapy while only miR-508-5p was underexpressed in relapsed ALL patients. Additionally, a negative correlation was identified between the expression of these two miRNAs and ABCA3, supporting the regulatory effect of them on drug resistance through interacting with ABCA3. Overall, we suggested miR-324-3p and miR-508-5p as potential diagnostic and drug-resistant biomarkers in pediatric ALL. Moreover, our findings presented miR-508-5p to behave as a promising relapsed indicator in childhood ALL which can be applied in the development of novel therapeutic strategies.

Introduction

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy accounting for nearly a quarter of all cancers diagnosed in children (<15 years) and comprises 72–78 % of childhood leukemia cases [1,2]. ALL is a heterozygous disease in which various predisposing factors and molecular defects result in abnormal proliferation and transformation of lymphoid progenitor cells [3,4] and are associated with distinctive clinical outcomes. Although contemporary antileukemic drugs have improved the overall survival rates in childhood ALL to more than 90 % [5,6], relapsed ALL is still the dominant cause of pediatric cancer death [4,7]. Generally, multidrug resistance (MDR) leads to survival of cancer cells against various anti-cancer drugs [8] and is the key characteristic of relapsed ALL patients [9,10]. One of the most significant causes of MDR is increased multidrug efflux transporters such as ATP-binding cassette transporters (ABC transporters) [11,12]. Investigation into the underlying regulatory mechanisms on ABC transporters expression can improve our understanding of relapse and MDR pathophysiology and provide new insights into ALL therapeutic design.

MicroRNAs (miRNAs), small endogenous non-coding RNAs, can be involved in a variety of biological processes through regulation of their targeted genes [13]. Recently, a number of studies have shown the importance of miRNAs on the aberrant expression of genes relevant to drug resistance [[14], [15], [16], [17]]. Therefore, targeting those miRNAs can be used as a therapeutic procedure to overcome drug resistance and consequently improve responsiveness to anti-cancer agents.

Aberuyi et al. previously reported ABCA3, a member of ABC transporter family, as a robust biomarker for MDR in childhood ALL to be significantly upregulated [18]. Here we searched for the list of potential ABCA3 regulatory miRNAs using in silico analysis and among them, two candidates (miR-324-3p and miR-508-5p) were selected. miR-508-5p is a tumor suppressor miRNA associated with various types of cancers, including, glioma [19], hepatocellular carcinoma [20] and gastric cancer [21]. Furthermore, it can mediate MDR in gastric cancer by targeting ABCB1 and ZNRD1 [22]. MiR-324-3p was also reported as a prognostic biomarker for hepatocellular carcinoma [23] and a tumor suppressor in nasopharyngeal carcinoma [24]. Moreover, a recent study displayed a significant role for SLC25A21-AS1/miR-324-3p/IL-6 axis in MDR in nasopharyngeal carcinoma [25].

Owing to the significant effect of miR-324-3p and miR-508-5p in cancers and MDR and their predicted interaction with ABCA3, the present study aims to evaluate the transcript levels of these two miRNAs in childhood ALL patients and consequently, investigate their correlation with ABCA3 transporter.