Engineered Probiotic Saccharomyces boulardii Reduces Colitis-Associated Colorectal Cancer Burden in Mice.

Background: Individuals with inflammatory bowel diseases experience an elevated risk of colorectal cancer driven by chronic inflammation. Current systemic immunosuppressive therapies often cause severe side effects. Live oral biotherapeutics are an emerging treatment modality that directly target the intestines. We have engineered a probiotic Saccharomyces boulardii strain that expresses targeting ligands to bind fibronectin on inflamed mucosa and secretes anti-tumor necrosis factor nanobodies locally to reduce inflammation. We previously demonstrated that engineering S. boulardii to bind fibronectin enhanced colonization and reduced inflammation in a DSS colitis model.

Aims: Here, we tested the anti-cancer potential of engineered S. boulardii using a well-established model of IBD-associated CRC, azoxymethane-treated interleukin 10-deficient (AOM/Il10^-/-) mice. These mice develop inflammation and invasive tumors that model those found in inflammatory bowel disease.

Methods: Mice were orally administered engineered S. boulardii at two dosing frequencies, unmodified S. boulardii, or placebo throughout the 18-week model. Colons were harvested for gross, histological, and molecular evaluation for inflammation and tumorigenesis.

Results: Histological colon inflammation was reduced by twice weekly dosing of engineered and unmodified S. boulardii. Engineered S. boulardii reduced gross tumor number in a dose-dependent manner, with median tumor counts reduced from 7.5 to 2 per mouse (p < 0.0002 vs. placebo). Unmodified S. boulardii similarly reduced gross tumor number. Colonization studies revealed that engineered S. boulardii failed to colonize for greater time or density vs. unmodified S. boulardii.

Conclusion: Together our data indicate that engineering S. boulardii does not reduce its ability to decrease inflammation-associated tumorigenesis, and that further host-binding target optimization is required to enhance colonization and anti-cancer effects.