MicroRNA-212/ABCG2-axis contributes to development of imatinib-resistance in leukemic cells

// Meike Kaehler 1 , Johanna Ruemenapp 1 , Daniel Gonnermann 2 , Inga Nagel 1 , Oliver Bruhn 1 , Sierk Haenisch 1 , Ole Ammerpohl 3 , Daniela Wesch 2 , Ingolf Cascorbi 1 and Henrike Bruckmueller 1 1 Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany 2 Institute of Immunology, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany 3 Institute of Human Genetics, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany Correspondence to: Ingolf Cascorbi, email: cascorbi@pharmakologie.uni-kiel.de Keywords: drug resistance, drug transporters, ABCG2, miR-212, methylation Received: June 03, 2017      Accepted: September 08, 2017      Published: September 26, 2017 ABSTRACT BCR-ABL-independent resistance against tyrosine kinase inhibitor is an emerging problem in therapy of chronic myeloid leukemia. Such drug resistance can be linked to dysregulation of ATP-binding cassette (ABC)-transporters leading to increased tyrosine kinase inhibitor efflux, potentially caused by changes in microRNA expression or DNA-methylation. In an in vitro -imatinib-resistance model using K-562 cells, microRNA-212 was found to be dysregulated and inversely correlated to ABC-transporter ABCG2 expression, targeting its 3’-UTR. However, the functional impact on drug sensitivity remained unknown. Therefore, we performed transfection experiments using microRNA-mimics and –inhibitors and investigated their effect on imatinib-susceptibility in sensitive and resistant leukemic cell lines. Under imatinib-treatment, miR-212 inhibition led to enhanced cell viability ( p = 0.01), reduced apoptosis ( p = 0.01) and cytotoxicity ( p = 0.03). These effects were limited to treatment-naive cells and were not observed in cells, which were resistant to various imatinib-concentrations (0.1 μM to 2 μM). Further analysis in treatment-naive cells revealed that miR-212 inhibition resulted in ABCG2 upregulation and increased ABCG2-dependent efflux. Furthermore, we observed miR-212 promoter hypermethylation in 0.5 and 2 μM IM-resistant sublines, whereas ABCG2 methylation status was not altered. Taken together, the miR-212/ABCG2-axis influences imatinib-susceptibility contributing to development of imatinib-resistance. Our data reveal new insights into mechanisms initiating imatinib-resistance in leukemic cells.