Dysfunctional mucus structure in cystic fibrosis increases vulnerability to colibactin-mediated DNA adducts in the colon mucosa

Abstract

Colibactin is a recently characterized pro-carcinogenic genotoxin produced by pks+ Escherichia coli. We hypothesized that cystic fibrosis (CF)-associated dysfunctional mucus structure increases the vulnerability of host mucosa to colibactin-induced DNA damage. In this pilot study, we tested healthy-appearing mucosal biopsy samples obtained during screening and surveillance colonoscopies of adult CF and non-CF patients for the presence of pks+ E. coli, and we investigated the possibility of detecting a novel colibactin-specific DNA adduct that has not been yet been demonstrated in humans. While CF patients had a lower incidence of pks+ E. coli carriage (~8% vs 29%, p = 0.0015), colibactin-induced DNA adduct formation was detected, but only in CF patients and only in those who were not taking CFTR modulator medications. Moreover, the only patient found to have colon cancer during this study had CF, harbored pks+ E. coli, and had colibactin-induced DNA adducts in the mucosal samples. Larger studies with longitudinal follow-up should be done to extend these initial results and further support the development of colibactin-derived DNA adducts to stratify patients and their risk.

Keywords: colibactin; colon cancer; cystic fibrosis; microbiota; pks+ E. coli.

Figure 1.

The abundance of pks+ E. coli in positive mucosal biopsy samples from CF and non-cf control patients was estimated by (a) ratio of clbB to 16S rRNA gene copies, (b) ratio of clbB to b-actin gene copies, (c) the copy number of clbB gene copies per µl of extracted DNA. The red squares identify samples positive for DNA adducts. The differences between CF and non-cf samples did not reach statistical significance.

Figure 2.

MS extracted ion chromatograms of m/z 540.1765 [M+H]⁺ and the fragmentation ions m/z 229.0972 [M+H]⁺, m/z 387.1110 [M+H]⁺, and m/z 344.1057 [M+H]⁺ obtained from the analysis of the colibactin-DNA adducts synthetic standard (panel a), a pks- non-cystic fibrosis patient (panel b), and the two pks+ cystic fibrosis subjects (panel c and d).