PO-115 Radiation resistance mechanisms of breast cancer cells

Introduction Despite the high efficacy of Radiation therapy (RT) to treat breast carcinoma (BC), the problem of radioresistance and tumour recurrence is still not solved. It is believed that radioresistance can be associated with the presence of a subpopulation of cells, called ‘cancer stem cells’ (CSCs). However, it is still unclear which molecular profiling of BC cells should be used as a predictor of poor clinical outcome after RT. Therefore, the main aim of this study was to determine the molecular phenotype of BC cells with acquired radiation resistance and stemness properties. Material and methods Two carcinoma cell lines, MDA-MB-231 and T47D, representing the most common molecular subtypes of breast cancer (triple negative and luminal A) were repetitively irradiated at a total dose of 100 Gy, and finally, radioresistant (RR) BC cell lines were obtained. To confirm the radioresistant phenotype of the newly received RR cells, their radiation sensitivities were compared with those in their parental counterparts using a clonogenic survival assay. FACS analysis was performed to detect the content of BC stem cell markers CD44 + /CD24 - . Additionally, a sphere forming assay was performed to detect the stemness abilities of the investigated breast carcinoma cells. Parental and RR cells were examined for their protein patterns using nano-LC mass spectrometry followed by PathwayStudio-based computational analysis. Western Blot, FACS, and metabolic patterns of parental and RR cells were performed to prove the proteomic results. Results and discussions Newly obtained RR breast carcinoma cell lines possess a prominent radiation resistance accompanied by enhanced sphere forming abilities and increased number of CD44 + /CD24 - cells in comparison with parental cells. Proteome analysis has shown an up-regulation of proteins involved in different molecular pathways protecting carcinoma cells from ionising radiation. Molecular pathways regulating DNA repair processes, cell cycle distribution and cell death development, metabolic activities, cell differentiation/dedifferentiation, have demonstrated the most pronounced connectivities with radiation resistance. Conclusion Radioresistant BC cells demonstrate their aggressive behaviour through changed metabolic properties and activation of pro-survival mechanisms associated with affected therapy response.