Regeneration in damaged microenvironments: mitigation of radiation-induced salivary gland damage through antioxidant-loaded electrospun scaffolds

Abstract

Cancer is one of the leading causes of mortality worldwide, attributing to almost 10 million (nearly one in six) deaths annually across the globe. Due to modern advances in both medicine and research, the mortality rate of cancer has seen significant improvement, but at the same time, incidences of cancer diagnoses have increased to a point where it is believed that one in two of the world’s population will receive a cancer diagnosis in their lifetime. Head and neck cancer is the seventh most prevalent cancer worldwide (Global Cancer Statistics, 2020). It is most often diagnosed at an advanced stage, complicating treatment and leading to poorer clinical outcomes. The most common treatment method for head and neck cancers is radiotherapy. Radiotherapy edectively destroys cancer cells but also causes subsequent damage to surrounding healthy cells and tissue. This leads to an increase in the levels of reactive oxygen species (ROS), increasing oxidative stress within, and causing alterations and damage to, the tumor microenvironment. As a result of this, tissue function can be severely impaired. The damaged environment means that the likelihood of tissue regeneration and the potential for tissue function to be restored is significantly reduced, as new healthy cells struggle to survive in this harsh environment. In the salivary glands, acinar cells – the primary cells responsible for saliva secretion – are particularly sensitive to radiation-induced damage, resulting in a marked loss of glandular function. In head and neck cancer patients, this can lead to radiation-induced xerostomia – a permanent reduction of salivary gland function that can cause issues with day-to-day activities, such as digestion, speech, dental hygiene, and sleep. This can significantly impede a patient’s quality of life. To date there is no preventative nor curative treatment, only surface level palliative care. As there is an increase in the number of cancer survivors, there is subsequently an increase in the number of patients left sudering from the long-term side edects and reduced quality of life, highlighting the need for more edective treatment options as opposed to the palliative level of care currently odered. One such treatment approach that can remediate these high ROS levels in attempt to prevent further microenvironmental damage is through tissue engineering, in particular, scadold-based approaches. Tissue engineering approaches are a modern approach being used to mimic tissue microenvironments. These scadold structures are also being used as drug delivery systems and can be modified to include bioactive compounds that are capable of mediating the damaged environment to bring it closer to a state of homeostasis. The research presented within this thesis sought to produce polycaprolactone (PCL) electrospun scadolds capable of mediating the harsh microenvironment through the antioxidant properties of retinyl acetate, a vitamin A derivative, and to provide a platform capable of supporting the delivery, and subsequent survival and proliferation of new, healthy cells into the previously damaged environment. This was achieved by considering two main factors: optimisation of the scadolds, which included optimising the concentration of retinyl acetate within the scadolds, the edects of scadold topography modifications, and long-term functionality and degradation of the scadolds; and the edect of the microenvironment, which included consideration of the harsh irradiated environment and its recovery, and preliminary investigations into the compatibility of the scadold with primary submandibular gland cells. Following scadold characterisation, which included scanning electron microscopy imaging, water contact angle, tensile testing, and measuring the antioxidant activity, scadolds were seeded with human submandibular gland (HSG) cells and the biological response of the cells to the scadolds was assessed. Tests including viability, DNA content, gene analysis and staining were performed to measure the response of the cells to the diderent environments. The studies presented herein successfully prove that retinyl acetate can be incorporated into electrospun PCL fibres and were able to promote the survival and proliferation of HSG cells under normal cell culture, high-level ROS mimicking environment, and irradiated conditions, whilst producing an antioxidant edect that was able to mediate the harsh environment. Overall, this provides encouraging evidence to support the potential use of such antioxidant tissue engineering approaches for use in restoring the damaged microenvironment post-radiation treatment, returning it to a state capable of supporting the survival and proliferation of healthy cells that are re-introduced to the environment, with the aim of repairing the damaged tissue and ultimately restoring salivary gland function.