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Title: Radiation biology of uveal melanoma
Author: Hussain, Rumana
ISNI:       0000 0004 9358 4366
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2020
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Uveal melanoma (UM) is a rare cancer with an annual incidence of approximately 5-8/million, but is the most common primary intraocular malignancy in adults. Treatment of this condition is generally successful with local primary tumour control being at 90-95%; localised radiotherapy in the form of plaque brachytherapy or proton beam radiotherapy are the most utilised in the UK, with primary enucleation still contributing to around a third of cases. Although the response to radiation treatment tends to be excellent, the basic mechanisms of radiation response, DNA repair and tissue reactions have not been well documented or established. The aim of this thesis was to investigate the DNA repair mechanisms in response to exogenous radiation sources (both x-rays and protons) in UM cell lines to determine the basic radiation sensitivity of these cells as well as the pathways involved in DNA repair; such pathways have been utilised in multiple other malignancies as targets for treatment strategies. Chapter 2 investigates this in detail and describes the differences in the radiosensitivities of different UM cell lines, which can be correlated with an upregulation in the ATM-checkpoint pathway involved in DNA repair in more radioresistant lines (OMM2.5 and Mel 270). The use of ATM inhibitors demonstrates this further with a disruption in both x-ray and proton-exposed cell culture analysis regarding both clonogenic assays for cell viability and comet assays for DNA repair response efficiency. Furthermore, tumour responses to radiation, although previously described, have not been correlated to these specific pathways. Chapter 3 describes the cellular and tissue responses in UM after radiotherapy (i.e. following both ruthenium-106 and proton exposure) with a time-independent marked inflammatory and necrotic reaction. The immunohistochemistry of these tissues with ATM demonstrated no significant differences in sample types, but may have been underpowered to do so, and should be investigated in future studies with fresh tissues. The thesis also aims to address the dilemmas in managing patients with UM with regards to reliability of prognostic genetic analysis of tumour biopsies following radiation, as well as the structural and subsequent visual sequelae following exposure to these forms of radiation. Chapter 4 shows the reliability of DNA-based prognostic analyses with regards to estimation of patient mortality from metastatic disease following radiotherapy. However, the reliability of these tests is time-limited with those samples taken many months after radiation treatments demonstrating anomalous results. The recommendation is therefore to aim for UM sample analysis for prognostication within 4 weeks of treatment. Structural radiation effects on local tissues has also been addressed in Chapter 5 with OCT assessment of retinal tissues following both ruthenium-106 and proton beam exposure. Brachytherapy leads to a rapid atrophic response with outer retinal layer disruption and destruction evident within 6 months in the majority of cases; proton beam exposure however shows a significantly different reaction and timeline with minimal outer retinal layer changes in the first 2 years. Visual outcomes following radiation exposure of essential structures for central vision, such as the fovea, therefore demonstrate rapid deterioration following plaque brachytherapy but much less pronounced over a longer time period in proton beam treated patients. This determines the form of treatment utilised for these patients in the medium and long term. In conclusion, this thesis has described the basic radiosensitivity linked with the DNA repair response and time efficiencies of UM cell lines, the UM tissue responses in response to radiation exposure, the structural changes in the tissues surrounding treatments and demonstrated the genetic reliability of post irradiation biopsies. Although answering many questions, it has formed the basis for future work, which may be carried on into more advanced models such as 3D spheroids, and into tissues examining a shorter term response to radiation exposure.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral