Exploring strategies for enhancing type I interferon responses to radiotherapy by modulating cGAS-dependent and -independent mechanisms

Thesis

The potential of inducing anti-tumour immunity after radiotherapy, especially type I interferon (IFN) production that can facilitate immune cell recruitment, has recently been explored in different cancer contexts to enhance therapeutic efficacy. The cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway has been regarded as one of the major routes in detecting cytosolic DNA as a result of DNA damage caused by radiotherapy. However, the possible formation of micronuclei (MN) harbouring highly condensed nucleosomal DNA post-radiation has been thought to hinder cGAS/STING pathway activation, and hence reduce type I IFN production. This study thus aimed to investigate whether type I IFN production induced by radiation could be promoted by altering cGAS-independent pathways such as suppressing glycogen synthase kinase-3 beta (GSK3β), or by boosting activation of the cGAS/STING pathway itself through histone deacetylase (HDAC) inhibition to amplify the pro-immunogenic effects of radiotherapy and increase therapeutic effectiveness. Results demonstrated that repression of GSK3β either by administration of GSK3β inhibitors or siRNA knockdown did not increase interferon-beta (IFN-β) production post-radiation. HDAC inhibition with vorinostat increased histone acetylation and, at moderate concentrations, possibly increased cGAS binding to MN and nuclear interferon regulatory factor-3 (IRF-3) levels shown by immunofluorescence. However, effects were not sustained at higher concentrations and were not corroborated by bulk assays, suggesting that more evidence was required to further support these exploratory findings. Taken together, neither approach was sufficient to robustly enhance IFN-β induction post-radiation. Although the interventions did not yield strong effects, this study delineates key methodological constraints and the biological complexity of IFN regulation. It clarifies the limits of indirect modulation and points towards alternative and more direct approaches.

Authors: Lee, W

• DOI: 10.5287/ora-gppyvdnz9
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: micronuclei; immune responses; cGAS/STING; type I interferons; radiotherapy; interferons
• Subjects: Cancer; Oncology