Effect of extracellular vesicles on the acquisition of radiotherapy resistance in triple-negative human breast cancer and canine mammary carcinoma | The effect of extracellular vesicles on the acquisition of radiotherapy resistance in triple-negative human breast cancer and canine mammary carcinoma

Radiotherapy resistance is a significant challenge in the treatment of recurrent, advanced, and metastatic breast cancer in both humans and canines. Tumours are composed of a mixture of cell populations and can potentiate their own survival by fostering a highly dynamic microenvironment, of which extracellular vesicles (EVs) are emerging as important mediators of cellular communication. EVs are double membrane nanovesicles (30-150 nm) and their content reflects the cell of origin. EVs have active protein, nucleic acid and lipid content that can influence recipient cells proteome, and phenotype. The hypothesis of this project is that EVs derived from radioresistant cancer cells can confer resistance to recipient cells and profiling EV protein content will reveal how they influence oncogenic development, which may lead to the identification of novel targets for anti-cancer intervention. In this project, a panel of radioresistant cell lines derived from human and canine breast cancer cells were characterised, EVs were isolated from these cells and effects of these EVs on recipient cells were analysed. The data showed that EVs derived from radioresistant cells are more readily taken up, and can increase cell viability, colony forming ability, chemoresistance and radioresistance of recipient cells. EVs derived from radioresistant cancer cells could also increase the growth and proliferation of cancer stem cells and further enhance their chemotherapy and radioresistance in both human and canine cancer stem cell populations. To identify potential therapeutic targets or biomarkers of radioresistance, mass spectrometry analyses of protein content from EVs isolated from radioresistant and non-radioresistant breast cancer cells were analysed by bioinformatics. Results showed that overall, the protein content in EVs from radioresistant cells had higher expression of proteins associated with cell growth, proliferation and survival when compared to EVs derived from non-radioresistant cancer cells. Network analyses indicated AKT and CCND1 are potential drivers of radioresistance in both human and canine breast cancer, and theoretical downregulation of these molecules could inhibit the radioresistant phenotype. Biomarker analyses also predicted AKT and cell cycle regulator CCNH as potential biomarkers of radioresistance. These findings could be used as building blocks for the advancement and/or personalisation of cancer treatment plans in human and veterinary medicine. In principle, dual AKT and CCND1 inhibitors could attenuate therapy resistance in radioresistant cells and cancer stem cells. This could mean that the effectiveness chemotherapy and radiotherapy may be increased; therefore, increasing overall survival and lifespan in human and veterinary patients with suspected radioresistance.