Identifying potential genetic, phenotypic and epigenetic predictive markers in the Toll-like receptor/Interleukin-1 domain innate immune signalling pathway for severe gastrointestinal toxicity risk following 5-Fluorouracil-based therapy

Abstract

Severe gastrointestinal (GI) toxicity symptoms such as diarrhoea, mucositis, nausea and vomiting are adverse side effects following 5-fluorouracil (5-FU)-based therapy. Current supportive care measures for the treatment of severe GI toxicity are limited, with many patients requiring treatment intervention or hospitalisation to help manage and relieve symptoms. The presence of severe GI toxicity not only compromises patient clinical outcomes but, is also a financial burden on the health care system. Most importantly, the presence of severe GI toxicity symptoms decreases a patients’ quality of life whilst receiving 5-FU-based therapy. A predictive marker for severe GI toxicity risk is urgently required to identify patients at most risk of developing severe GI toxicity prior to receiving 5-FU-based therapy. This would not only allow at risk patients to be closely monitored whilst receiving 5-FU-based therapy but, improve resource utilisation and patient education, reducing the severity of GI toxicity experienced by at risk patients. Current predictive markers for severe GI toxicity, such as single nucleotide polymorphisms (SNPs) in 5-FU drug biotransformation genes, lack clinical utility, sensitivity and specificity. As such, the gap in the knowledge is a new predictive marker(s) for severe GI toxicity risk needs to be identified. A clinical pilot study conducted in my laboratory highlighted the potential of the Toll-like Receptor/Interleukin-1 (TIR) domain innate immune signalling pathway to be predictive for severe GI toxicity risk. The TIR domain pathway is one of the key mediating pathways in the development of GI toxicity and consists of membrane bound Toll-like Receptors (TLRs), adapter proteins, transcription factors and proinflammatory cytokines such as interleukin 1 beta (IL-1β) and tumour necrosis factor alpha (TNF-⍺). Based on the results of the pilot study, I firstly investigated the association of 21 SNPs within the TIR domain innate immune signalling pathway with severe GI toxicity risk in 155 participants who received 5-FU-based therapy. Secondly, in a subset of 34 participants, I also examined TLR2- and TLR4-stimulated IL-1β and TNF-⍺ secretion from isolated peripheral blood mononuclear cells to determine a phenotypic marker for severe GI toxicity risk. Both these studies were retrospective. Lastly, I considered whether administration of 5-FU could induce DNA methylation within the TIR domain innate immune signalling pathway in vitro, to identify a potential epigenetic predictive marker for severe GI toxicity risk. The results of my thesis point to no concordant genetic, phenotypic or epigenetic predictive marker for severe GI toxicity risk within the TIR domain innate immune signalling pathway. However, observations made throughout my thesis highlight the importance of using risk prediction modelling to encompass all potential predictive factors, such as demographic, clinical, genetic, phenotypic and epigenetic, to create a truly personalised risk prediction strategy for patients receiving 5-FU-based therapy.