Abstract
Introduction: In recent years, an emerging role for microRNAs (miRNAs) in human cancer has been proposed. Our group has previously identified miR-451 as a potential tumor suppressor microRNA involved in cell cycle progression and radiation response. We hypothesized whether miRNAs may be involved in drug resistance mechanisms among cytotoxic agents commonly used in metastatic colorectal cancer (mCRC).
Experimental Design: miR-451 was overexpressed by ectopically synthetic pre-miR-451 transient transfection and by generating stable-miR-451 overexpressed cells through retroviral vectors. The role of miR-451 on chemosensitivity to 5-fluorouracil (5FU), oxaliplatin (LOHP) and SN38, an active metabolite of irinotecan, was characterized by MTS. We sought to determine links between miR-451 and cancer stem cells (CSCs) by colonspheres generation, soft-agar cell invasion and xenograft in vivo experiments. Down-stream targets involved in drug-resistance mechanisms were also identified.
Results: Overexpression of miR-451 significantly increased the sensitivity of CRC cell lines to SN38. The IC50 values were significantly lower in pre-miR-451-transfected cells, including DLD1, LoVo and RKO than in controls (950 nM versus 460 nM for DLD1; 10 nM versus 1.4 nM for LoVo and 20 nM versus 5.9 nM for RKO). No changes were detected for 5-FU and LOHP response. ATP-binding cassette transporter protein 1 (ABCB1) proved to be miR-451-target directly associated with SN38 sensitivity. Moreover, restoring miR-451 levels translated into a reduced tumorigenicity in a xenograft model and a decreased ability of CRC cells to growth under anchorage-independent conditions in soft agar.
These results suggest that miR-451 down-regulation in CRC cells may be involved in CSCs generation. Indeed, overexpression of miR-451 was able to reduce the number and size of CRC cells-derived colonspheres. The phenotype of formed colonspheres was confirmed evaluating overexpression of several putative CSCs markers (CD133, CD44, EpCam and CD166). We also found colonspheres to be more resistant to SN38 treatment and to express higher levels of ABCB1 than parental cells. Finally, miR-451 restoration levels reverted CSCs resistance to SN38 through ABCB1 down-regulation.
Conclusions: Our findings suggest that miR-451 is involved in SN38 resistance through suppression of ABCB1 and regulation of CRC stem-like cell phenotype. Therefore, miR-451 may represent a novel potential candidate target to circumvent drug resistance in CRC.
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 3549.
- ©2010 American Association for Cancer Research
Volume 70, Issue 8 Supplement
