Abstract 2073: Changes in microRNA expression in response to short-term chemotherapeutic exposure is associated with transient anticancer drug resistance

MicroRNAs (miRNAs) are small, noncoding RNAs that act as posttranscriptional repressors of gene expression by binding the 3’ untranslated region of target genes. There is emerging evidence showing that miRNAs regulate diverse biologic processes including multidrug resistance (MDR). Our previous profiling study revealed that certain miRNAs are differentially expressed in multidrug resistant human T-cell leukemia cell line CEM/VM-1-5 compared to drug-sensitive parental cell line CCRF-CEM. To investigate whether these expression-altered miRNAs have a role in MDR, we ectopically expressed three miRNAs that are highly upregulated in CEM/VM-1-5 cells (hsa-miR-135b, −146b, and −196b) in CCRF-CEM cells with the use of lentiviral vectors. We found that overexpression of these miRNAs, individually or in combination, resulted in only slight increases in resistance of CCRF-CEM cells to teniposide, the agent used to select CEM/VM-1-5 cells. Moreover, we were unable to sensitize CEM/VM-1-5 cells to etoposide by suppression of hsa-miR-135b expression using LNA antisense oligonucleotide. Our data implied that these miRNAs do not confer drug resistance directly. However, it is still not clear whether these miRNAs play any role in the development of MDR. Therefore, we asked whether the expression of these miRNAs changed in CCRF-CEM cells after short exposure (3 to 48 hours) to various chemotherapeutic drugs at concentrations below their IC50-values. We observed substantial increases in hsa-miR-135b and −196b expression in cells treated with etoposide, doxorubicin and topotecan, but not in cells treated with vinblastine. These results suggested that the upregulation of these two miRNAs might be the consequence of DNA damage. Time-course and dose-response studies showed that the elevation of hsa-miR-135b and −196b correlated positively with the drug exposure time and drug concentration. Furthermore, the levels of miRNAs gradually decreased after the withdrawal of etoposide from the media following 48 h exposure to etoposide. Strikingly, the elevated expression of the miRNAs accompanied increased drug resistance. CCRF-CEM cells exposed to etoposide for 48 h were over 50-fold more resistant than control cells. The acquired drug resistance, like elevated expression of miRNAs, did not appear to be stable and became attenuated with increasing duration of the drug-free incubation. Together, our results suggest that miRNAs might play a significant role in cellular response to genotoxic agents and could be involved in the development of cancer drug resistance, but their roles in conferring resistance remain to be determined. That said, targeting miRNA expression could be a potential approach to prevent multidrug resistance. (Supported in part by 5RO1CA040570 from NCI to WTB, and in part by UIC) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2073.