Defining a mechanism for Heligmosomoides polygyrus bakeri exacerbation of colorectal cancer development

Reed, Ella 2025. Defining a mechanism for Heligmosomoides polygyrus bakeri exacerbation of colorectal cancer development. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Around 10-15% of patients with inflammatory bowel disease (IBD) develop colitis-associated colorectal cancer (CAC). Recent findings indicate that a diet high in linoleic acid (ω-6) and infection with the small intestinal nematode Heligmosomoides polygyrus bakeri increase the risk of CAC separately, with the combination resulting in further exacerbation of disease. In a murine CAC model, inhibition of cyclooxygenase (COX) metabolites, products of linoleic acid, and subsequent prostaglandin signalling, significantly reduced tumour formation in H. polygyrus infected mice. Notably, activating COX-derived prostaglandin E2 (PGE2) receptors EP2 and EP4 prior to disease onset enhanced tumour formation, similar to the effect of H. polygyrus infection. This thesis demonstrates that H. polygyrus infection activates EP2 and EP4 receptors in the colon in vivo, and that excretory/secretory products (HES) increase cell permeability in vitro via EP2 and EP4 signalling. Biochemical analysis identified a heat-stable, non-protease molecule between 10,000-50,000 MW in HES responsible for this effect. The H. polygyrus genome revealed 17 proteins similar to human secretory phospholipase A2 (PLA2), with proteomic analysis confirming the presence of three in the 10-50,000 MW fraction. Among these, HPOL_0000384601 showed the highest similarity to human PLA2G1B active sites. Using an in vitro fluorescence assay, PLA2 activity was confirmed in HES. With commercial inhibitors of human and murine PLA2G1B showing no effect against H. polygyrus PLA2G1B, a structure-based design approach was taken to identify novel compounds to inhibit its activity. Using a crystal model of H. polygyrus PLA2G1B generated through protein threading, a known inhibitor was docked into the active site, and important ligand interactions used to identify compounds that interact with these residues. Testing of the IC50 of the best ten compounds based on in silico visual inspection revealed AF-3999/14183760 as having the highest potency, and addition of this compound along with HES in vitro resulted in a reduction in the ability of HES to increase cell permeability, suggesting H. polygyrus PLA2G1B plays a central role in HES-mediated increase in cell permeability. To explore the mechanisms by which H. polygyrus may exacerbate CAC, transcriptomic analysis of infected mice colons revealed upregulation of inflammatory and oncogenic pathways, alongside downregulation of cell cycle regulatory and tumour suppressor pathways. These findings offer new insights into H. polygyrus-driven CAC progression and open avenues for further functional studies.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	8 May 2025
Last Modified:	09 May 2025 16:14
URI:	https://orca.cardiff.ac.uk/id/eprint/178157

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