PO-114 Overexpression of miR-205–3 p increases sensitivity to low-dose ionising radiation in DLD-1 cells

Introduction Enhanced radiosensitivity at low doses of ionising radiation (IR) (0.2 to 0.6 Gy) has been reported in several cell lines. This phenomenon, known as low doses hyper–radiosensitivity (LDHRS), appears as an opportunity to decrease toxicity of radiotherapy. However, this effect is subtle and the mechanism underlying LDHRS has not been clearly explained, limiting the benefit of LDHRS in clinical practice. Material and methods To determinate LDHRS in DLD–1 human colorectal cancer cells, viability, DNA damage, cell death and apoptosis were evaluated by: MTS, γ–H2AX immunofluorescence, trypan blue dye assays, Caspase 3/7 activity and hypoploidy determination; in cells exposed to low (0.6 Gy) and high (12 Gy) doses IR. LDHRS in DLD.-1 cells was confirmed by clonogenic assays and mathematical modelling. Then, to understand the mechanisms responsible for cell death induced by low-dose IR, we evaluated a panel of 86 miRNAs in array-PCR format. Validation of targets was made by qRT-PCR and functional assays were achieved by transient overexpression. Results and discussions Our results show that DLD–1 cells display LDHRS. Also, doses of 0.6 Gy induced an early but transient DNA damage response. miRNA expression assays revealed an overexpression of 3 microRNAs (miR-205–3 p, miR–1 and miR–133b) and down regulation of 2 miRNAs (miR–122–5 p, and miR–134–5 p). This miRNA profile differed from the one in cells exposed to high-dose IR (12 Gy). Transfection with mimetic of miR-205–3 p, the most overexpressed miRNA in cells exposed to 0.6 Gy, induced cell death at lower dose, increasing LDHRS response. Interestingly, at higher doses (12 Gy), miR–205–3 p induced formation of multi- and micronuclei, features associated with mitotic catastrophe. Thus, IR evoked differents miRNAs profiles, in agreement with a distinct low dose radiation-induced cell death mechanism. Moreover, MiR–205–3 p increased radiosentitivity by two-ways: at low doses, by apoptosis induction, and higher doses by mitotic catastrophe. This effect could be used to boost the outcome of IR, while decreasing therapeutic doses. Conclusion We propose miR-205–3 p as a potential radiosensitizer to low-dose IR. Acknowledgments This work was supported by grant Anillo ACT115, PIA Program, CONICYT, FONDECYT 1151435, 1160889 and the national doctoral fellowship 21130246 CONICYT