Effect of Pelvic Radiotherapy on the Intestinal Microbiome and Metabolome

Background 80% of patients develop GI-toxicity during pelvic radiotherapy and half develop chronic GI-toxicity. This manifests as diarrhoea, pain, bleeding and incontinence. Unlike many diseases, the triggering event, i.e. radiotherapy, is known, enabling the identification of specific pathophysiological changes. The metabolomic and microbiomic profile of patients undergoing pelvic radiotherapy and the link with GI-toxicity has not been fully explored. Studies suggest radiation alters the gut microbiome, altering microbial diversity. Higher pre-radiotherapy diversity has been seen in those with no GI symptoms with reducing diversity as GI-toxicity increases and an association between low microbial diversity and severity of chronic GI-toxicity. Dietary change can alter microbial composition. Faecal VOCs are chemicals that exist in the gaseous phase at ambient temperature and form the faecal metabolome, the result of the interaction between the gut microbiota and cell metabolism. VOCs can be identified using established techniques and unique VOCs patterns have been identified in specific GI diseases. Early data suggest differences in VOCs between patients with high vs low levels of GI-toxicity. Metabolomic and microbiomic profiling and manipulation has the potential to advance understanding of disease-related pathways to predict, prevent and treat GI-toxicity.

Rationale GI-toxicity is a significant cause of morbidity both during and after pelvic radiotherapy to the extent that it adversely affects quality of life. There is a paucity of research into this condition. The metabolomic and microbiomic profile of patients undergoing pelvic radiotherapy and the link with GI-toxicity has not been fully explored. Studies suggest radiation alters the gut microbiome, altering microbial diversity. Higher pre-radiotherapy diversity has been seen in those with no GI symptoms with reducing diversity as GI-toxicity increases and an association between low microbial diversity and severity of chronic GI-toxicity. Dietary change can alter microbial composition. Unique VOCs patterns have been identified in specific GI diseases. Early data suggest differences in VOCs between patients with high vs low levels of GI-toxicity. Metabolomic and microbiomic profiling and manipulation has the potential to advance understanding of disease-related pathways to predict, prevent and treat GI-toxicity.

By comparing samples collected pre and post radiotherapy the investigators aim to identify potential biomarkers. They are going to integrate metadata indicating a negative GI response to the therapy, i.e. GI toxicity symptoms from validated questionnaires, with microbial community data and VOCs data in order to identify markers (VOCs or bacteria) that increase with symptoms. They will also identify which species make patients more susceptible to negative outcomes by analysing the community pre-treatment.

Previous literature using culture based methods showed an increase in E. coli and Staphylococcus spp. and the investigators will determine whether they can confirm this. In terms of VOCs, they will look for markers of inflammation, e.g. aldehydes. It has been proposed that there are similarities between radiation-induced GI-toxicity and IBD, particularly Crohn's disease, therefore it would be interesting to see whether there is a similar dysbiosis of the microbial community and VOCs profile to that observed in Crohn's disease, i.e. whether decreased species diversity, increased Bacteroides species and Enterobacteriaceae coupled with a decrease in Faecal bacterium are also observed in patients with severe GI toxicity symptoms.

Potential interventions to modify the gut microbiome, e.g. diet, pre/probiotics, synthetic faecal microbiota transplantation, are in wide clinical research use currently in other related clinical areas, e.g. inflammatory bowel disease, and would be the types of interventions that may be indicated by information from this work and the subsequent definitive study.

The objectives of the subsequent definitive study are as follows:

• Determine the differences in VOC profile/microbiome in patients with the most severe vs least severe GI-toxicity at 4 weeks and 6 months.
• Determine the differences in VOC profile/microbiome at baseline in patients who develop the most severe vs least severe GI-toxicity at 4 weeks and 6 months.
• Characterise disease-related pathways for GI-toxicity to identify potential therapeutic targets, including dietary.

Inclusion criteria

• Pelvic radiotherapy-cervix/endometrial/bladder cancer.
• ≥18 years.
• Able to consent.
• Able to complete questionnaires.

Exclusion criteria

• Pre-existing GI disease
• Abdominopelvic surgery within preceding 4 weeks