en Radiation Biology Radiation Biology مطالعه موردي Case Report Background: The expression alterations of specific miRNAs were analysed in response to gamma-irradiation in two breast cancer cell lines MCF-7 and MDA-MB-231 with low and high BCSCs content to design probable strategies for sensitizing breast cancer stem-like cells MDA-MB-231 to radiation. Materials and Methods: The expression levels of hsa-miR-34a, hsa-let-7i and hsa-miR-21 were assessed by QRT-PCR in MCF-7 and MDA-MB-231 breast cancer cells at three time points after gamma irradiation using three different doses. Results: The results showed that the over-expression of hsa-miR-34a in MCF-7 cells was much more significant than MDA-MB-231 cells. Furthermore, there was a considerable over-expression of hsa-miR-21 in MDA-MB-231 cells following exposure to ionizing radiation (IR). The hsa-let-7i expression changes were different, depending on radiation dose, time post irradiation and cell type. Conclusion: According to the results, we may be able to sensitize stem-like MDA-MB-231 breast cancer cells to radiation by increasing miR-34a and decreasing miR-21 expression levels simultaneously. miR-34a, miR-21, let-7i, ionizing radiation, breast cancer. 383 388 http://ijrr.com/browse.php?a_code=A-10-1-737&slc_lang=en&sid=1 S. Dehghan Kouhestani 7900319475328460012383 7900319475328460012383 Yes Department of Medical Biotechnology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran M. Forouzandeh foroz@modares.ac.ir 7900319475328460012384 7900319475328460012384 No Department of Medical Biotechnology, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran M. Aghili 7900319475328460012385 7900319475328460012385 No Department of Radiation Oncology, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran