Just as the organs within an individual must communicate to function as a whole, the interactions of the microbiota with the host define local and systemic physiology. Within the intestine, pattern recognition receptors sense and respond to microbial products to promote tolerance or drive inflammation. In animal models and human patients with colorectal cancer, this innate immune sensing system fundamentally fails, leading to a highly inflammatory state and a tumorigenic environment. However, there is little known about the spatial and temporal distribution of the microbial products that signal through pattern recognition receptors within the tissue and how this relates to the immunological influence on tumor formation and progression.
We present an interdisciplinary approach utilizing bioorthogonal click chemistry (i.e. reactions that can be performed in living organisms) to label and track components of commensal organisms. We have used this method to successfully label the capsular polysaccharide A (PSA) of the important human commensal, Bacteroides fragilis. Since PSA can signal through TLR-2 to stimulate regulatory T cells and protect mice against experimental colitis, this molecule serves as an excellent model to decipher commensal-host communication. After administration of fluorescently labeled B. fragilis to the murine host, we can trace PSA into specific host immune cells in the intestine to define the pathways by which protective or inflammatory responses develop. We are also using this approach to visualize the spatial and temporal changes in bacterial product acquisition within diseased tissue. In mouse models of colitis associated colorectal cancer, we observe differences in distinct leukocyte subsets associated with PSA in the gut-associated mesenteric lymph nodes. We are currently characterizing the role that these identified leukocytes may play in PSAs immunomodulatory activity and why this changes during colorectal cancer.
We have also expanded on our chemical labeling approach by incorporating additional non-natural sugars and amino acids into the bacterial cell wall to fluorescently label lipopolysaccharide (LPS), capsular polysaccharide (CPS), and peptidoglycan (PGN). Employing this cutting-edge chemistry with modern methods in immunology and microscopy allows us to simultaneously track Toll-like receptor ligands (LPS, CPS) and NOD-like receptor ligands (PGN) from living commensal bacteria within host tissue. We are currently using this system to investigate whether certain cell types associate with distinct commensal molecules and how those pathways affect colorectal cancer progression.
J.E.H. is supported by a Cancer Research Institute Irvington postdoctoral fellowship.
Citation Format: Jason Hudak, Naama Geva-Zatorsky, Dennis L. Kasper. Tracking microbial sensing in colorectal cancer using bioorthogonal click chemistry. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr PR004.
- ©2016 American Association for Cancer Research.