Forsøksdyr: PROCCA: Late effects of oral x-ray irradiation (pilot)

Godkjenningsdato 20.04.2020

Godkjenningsperiode 20.04.2020-20.04.2022

Damage to normal tissue following radiotherapy of head and neck (H&N) cancers causes severe early and late effects and reductions in quality of life. Side effects include salivary hypofunction, swallowing dysfunction, oral mucositis, skin toxicity, soft tissue necrosis, pathologic fractures, and osteoradionecrosis. This may lead to unplanned interruptions in treatment, and potentially treatment failure.

Proton therapy (PT) is a radiotherapy technique that will be available to patients in Norway in 2023. PT reduces the dose to healthy tissues compared with conventional X-ray therapy (RT), and may thus cause fewer side effects. Although PT is already applied to H&N cancer patients abroad, clinical studies are limited. Late effects are well documented for both PT and RT, however, important questions regarding the mechanisms and cellular signaling pathways culminating in this damage remain unanswered. Knowledge of these mechanisms is vital for early detection of patients at risk and the development of strategies for mitigation. Such studies are not possible in human patients, and we therefore require the use of animals.

The purpose of this pilot is to make an exploratory investigation of the mechanisms of x-ray-induced damage to normal tissues of the H&N region, as a baseline for later studies on PT. We will explore MR imaging metrics and screen for cytokines (proinflammatory/profibrotic/proangiogenic) as potential biomarkers for early and late toxicities.

We apply for a total of 18 C57BL/6 mice. This study will use a fractionated RT design, which is clinically more relevant compared with the single-fraction irradiation employed in many pre-clinical studies. Biological responses to x-ray irradiation will be characterized and related to clinical symptoms. Irradiated animals may develop acute erythema/inflammation/ulceration of skin/mucosa, xerostomia, dysphagia, anorexia and general malaise. Salivary hypofunction is expected to persist. Animals will be longitudinally monitored by saliva/blood sampling. A subset of animals will be examined by MRI for monitoring structural radiation-induced alterations and optimization of imaging protocols for future studies.

Generating a (radiation-induced) H&N normal tissue response mouse model in this pilot will facilitate future research aimed at investigating and understanding radiation-induced normal tissue injury after RT and PT. It will serve as a first exploratory cytokine screen, gauge dose/fractionation response in this particular mouse strain, and inform optimal sample size (e.g. establish endpoint variability, tolerance to radiotherapy) for more extensive studies on normal tissue damage following conventional X-ray RT (future study I) and PT (future study II), and potential drug interventions (future study III).

The multidisciplinary nature of the project ensures maximum data extraction per mouse, and knowledge gained in this pilot will minimise the number of animals expended in future studies. The longitudinal design with non-/minimally invasive experimental assessment (imaging, saliva, blood) also avoids the use of satellites, improving statistical quality of data and reducing the total number of animals needed. Refinement: Animal welfare will be ensured through close monitoring during and post radiotherapy, with strict compliance with humane endpoints. Analgesia and alternative fodder will be provided to alleviate symptoms and ease feeding/maximise nutrition.