RADIOSENSITIZING EFFECTS OF ECTOPIC MIR-101 ON NON-SMALL-CELL LUNG CANCER CELLS DEPEND ON THE ENDOGENOUS MIR-101 LEVEL

Purpose: Previously, we showed that ectopic miR-101 could sensitize human tumor cells to radiation by targeting ATM and DNA-PK catalytic subunit (DNA-PKcs) to inhibit DNA repair, as the endogenous miR-101 levels are low in tumors in general. However, the heterogeneity of human cancers may result in an exception. The purpose of this study was to test the hypothesis that a few tumor cell lines with a high level of endogenous miR-101 would prove less response to ectopic miR-101. Methods and Materials: Fourteeen non-small-cell lung cancer (NSCLC) cell lines and one immortalized nonmalignant lung epithelial cell line (NL20) were used for comparing endogenous miR-101 levels by real-time reverse transcription-polymerase chain reaction. Based on the different miR-101 levels, four cell lines with different miR-101 levels were chosen for transfection with a green fluorescent protein-lentiviral plasmid encoding miR-101. The target protein levels were measured by using Western blotting. The radiosensitizing effects of ectopic miR-101 on these NSCLC cell lines were determined by a clonogenic assay and xenograft mouse model. Results: The endogenous miR-101 level was similar or lower in 13 NSCLC cell lines but was 11-fold higher in one cell line (H157) than in NL20 cells. Although ectopic miR-101 efficiently decreased the ATM and DNA-PKcs levels and increased the radiosensitization level in H1299, 111975, and A549 cells, it did not change the levels of the miR-101 targets or radiosensitivity in H157 cells. Similar results were observed in xenograft mice. Conclusions: A small number of NSCLC cell lines could have a high level of endogenous miR-101. The ectopic miR-101 was able to radiosensitize most NSCLC cells, except for the NSCLC cell lines that had a much higher endogenous miR-101 level. These results suggest that when we choose one miRNA as a therapeutic tool, the endogenous level of the miRNA in each tumor should be considered. (C) 2011 Elsevier Inc.