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Radiotherapy is prescribed to more than 50% of cancer patients during their treatment schedule. Due to intrinsic factors, individual variation in response exists, which will result in side effects or toxicity in a number of patients. Therefore, development of an assay or biomarker for the prediction and assessment of radiosensitivity among cancer patients undergoing radiotherapy would be beneficial. Such an assay would limit toxicities and facilitate dose-escalation for those patients who require it. Assays for predicting intrinsic cellular radiosensitivity remains as the established G2 chromosomal radiosensitivity and most promising, γH2AX foci assay. They can be applied to blood samples from donors and are sensitive enough to detect individual radiosensitivity. Therefore, both assays were applied to normal control cohorts compared to ‘radiosensitive’ cells to assess their efficacy as potential predictive assays for the clinic. Different low doses and energies of Linac radiation was applied to cells to assess their impact on patient intrinsic radiosensitivity and the most radiosensitive dose was confirmed at 0.5Gy (6MV photon beam) Linac radiation in cells. In addition to this, intrinsic radiosensitivity which could be measured at initial diagnosis and treatment planning stages for patients was investigated. The assays were applied to patients sampled at various time-points throughout a course of their radiotherapy treatment. The time-points included pre-treatment, post hormone treatment, last day of radiotherapy and the 2 and 8 month follow ups. Both assays were capable of depicting a dose response and differences between treatment visits. The DNA damage based assays indicated that cell cycle regulation through the DNA damage response (DDR) activated by radiation was central to the underlying mechanistic response. Therefore, the molecular mechanisms of radiosensitivity were studied with an emphasis of genes related to the cell cycle and DDR. Furthermore, genetic targets that emerged from this work could potentially be biomarkers of radiosensitivity that could also be incorporated into the clinic. Following from the emergence of cell cycle and DDR genes, potential biomarkers for predicting radiosensitivity was analysed in a collaboration with Public Health England. This was done using the most sensitive genes which were found from bio dosimetry microarray studies carried out by the group (P21, PCNA, SESN1 and FDXR). Again this work was done on blood from healthy controls, prostate cancer patients and radiosensitive cells from Ataxia Telangiectasia donors. The genes in combination were able to depict a clear difference in the cohorts analysed in which expression was collectively highest in the healthy controls, less expression was observed in the Prostate cancer cohort and the least expression was observed in the radiosensitive cells from Ataxia Telangiectasia donors. Finally, investigation of the miRNA composition of exosomes in healthy cells and cells from Ataxia telangiectasia donors was done to identify novel biomarkers for radiosensitivity prediction, in a collaboration with Trinity College Dublin. A subgroup of the let-7 family of miRNA’s was among the top 88 expressed miRNA’s in this chapter. Additionally, most miRNA’s were not as highly expressed in radiosensitive cells compared to normal healthy cells. This work forms the basis for future work on prostate cancer patient samples.
White, L. (2016) Predictive biomarkers of cellular radiosensitivity for clinical radiotherapy treatment. Doctoral Thesis. Technological University Dublin. doi:10.21427/D70W2X