Summary
Chronic inflammation may drive development of cancer as observed in inflammation‐induced colorectal cancer (CRC). Though immune cells can infiltrate the tumour microenvironment, cancer cells seem to evade anti‐tumour responses, which is one of the established hallmarks of cancer. Targeting the programmed cell death protein‐1 (PD‐1)/PD‐L1 signalling pathway is currently at the forefront in the development of anti‐tumour immunity‐based therapies for multiple malignancies. By blocking the immune‐checkpoint of activated T‐cells, it is possible to rewire the adaptive resistance induced by the PD‐1 ligands expressed in the tumour microenvironment. However, adverse immunotherapy‐modulated events could complicate the treatment of individuals with preexisting chronic inflammatory conditions. In this study, we investigated the expression of different systemic and mucosal T‐cell subsets during the course of azoxymethane (AOM)/dextran sulphate sodium (DSS)‐induced colitis and colitis‐associated CRC. In addition, we examined the expression of PD‐1 and its ligands PD‐L1 and PD‐L2 as well as other molecular targets related to T‐cell exhaustion. We found a significant increase in PD‐1 expression on all examined mucosal T‐cell subsets of the colon and the ileum, which correlated with disease progression. We also observed an upregulation of PD‐L1 and PD‐L2 mRNA expression throughout the AOM/DSS regime. Blocking PD‐1 signalling with an anti‐PD1 antibody did not affect the tumour burden in the AOM/DSS‐treated mice, but did potentiate the weight loss in the third DSS cycle, indicating possible immune‐mediated toxicity. This raises a concern for patients with colitis‐associated CRCs and should be further investigated.
Cytoglobin (Cygb) is a member of the hemoglobin family and is thought to protect against cellular hypoxia and oxidative stress. These functions may be particularly important in inflammation-induced cancer, e.g., in patients with ulcerative colitis (UC). In this study, we investigated the development of inflammation and tumors in a murine model of inflammation-induced colorectal cancer using a combined treatment of azoxymethane and dextran sulfate sodium. A bioinformatics analysis of genome-wide expression data revealed increased colonic inflammation at the molecular level accompanied by enhanced macroscopic tumor development in Cygb-deficient mice. Moreover, the expression of the UC-associated gene neurexophilin and PC-esterase domain family member 4 (Nxpe4) depended on the presence of Cygb in the inflamed colonic mucosa. Compared to wild type mice, RT-qPCR confirmed a 14-fold (p = 0.0003) decrease in Nxpe4 expression in the inflamed colonic mucosa from Cygb-deficient mice. An analysis of Cygb protein expression suggested that Cygb is expressed in fibroblast-like cells surrounding the colonic crypts. Histological examinations of early induced lesions suggested that the effect of Cygb is primarily at the level of tumor promotion. In conclusion, in this model, Cygb primarily seemed to inhibit the development of established microadenomas.
Rectal insulin therapy could potentially be a novel treatment, targeting the epithelial layer to enhance mucosal healing in ulcerated areas. Our findings open up new possibilities for combination treatments to synergize with the existing anti-inflammatory therapies.
Dextran sulfate sodium (DSS)-induced colitis is the most commonly used animal model for inflammatory bowel diseases. However, the precise molecular action of DSS, in particular its initial effect on the epithelial tissue permeability, is still poorly understood. In the present work, organ culture of mouseand pig colon explants were performed for 1-2 h in the presence/absence of 2% DSS together with polar-and lipophilic fluorescent probes. Probe permeability was subsequently assessed by fluorescence microscopy. DSS rapidly increased paracellular permeability of 70-kDa dextran without otherwise affecting the overall epithelial integrity. FITC-conjugated DSS likewise permeated the epithelial barrier and strongly accumulated in nuclei of cells scattered in the lamina propria. By immunolabeling, plasma cells, T cells, macrophages, mast cells, and fibroblasts were identified as possible targets for DSS, indicating that accumulation of the polyanion in nuclei was not confined to a particular type of cell in the lamina propria. In contrast, colonocytes were rarely targeted by DSS, but as visualized by transmission electron microscopy, it induced the formation of vacuole-like structures in the intercellular space between adjacent epithelial cells. Nuclei of various cell types in the lamina propria, including both cells of the innate and adaptive immune system, are novel targets for a rapid action of DSS, and from previous in vitro studies, polyanions like DSS are known to disrupt nucleosomes by binding to the histones. We therefore propose that nuclear targeting is one way whereby DSS exerts its inflammatory action as a colitogen in animal models of inflammatory bowel diseases.
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