Sensitization of human cancer cells to ionizing radiation through microRNAs targeting genes of DNA-double strand break repair

Therapeutic resistance to ionizing radiation (IR) is the primary factor that limits the effectiveness of radiotherapy. IR kills tumor cells mainly by inducing DNA double-strand breaks (DSBs) causing reproductive cell death; however, the efficient repair of DSBs in tumor cells frequently prevents successful treatment. The possibility to affect DNA DSB repair may represent an efficient way to sensitize human cells to IR induced killing. To this purpose, microRNAs (miRNAs) could have an important role in tumor radio-sensitivity. MiRNAs are endogenous non-coding RNA molecules that suppress gene expression by binding to the complementary sequence in the 3’-untranslated region (UTR) of target transcripts. Therefore, the delivery into cells of synthetic miRNAs that mimic miRNAs targeting genes of DNA DSB repair can perturb the process making the cells more sensitive to IR1. We constructed luciferase vectors containing the 3’UTR of RAD51, DNA-PKcs and LIG1 genes, involved respectively in homologous recombination (HR), in classical non-homologous end joining (c-NHEJ) and in alternative non-homologous end joining (a-NHEJ) and by luciferase assays2 we validated miRNAs targeting such genes. MiRNA-mRNA interactions were validated through western blotting and site directed mutagenesis. Our results clearly show that over-expression of miRNAs sensitized radio-resistant human lung cancer cells to y-irradiation.