Inflammatory bowel diseases (IBD) affect over 1.5 million individuals in the United States and over 2 million in Europe. These individuals have an increased risk of colorectal cancer (CRC) driven by chronic inflammation. Current medical therapies include systemic infusions of antibodies targeting proinflammatory cytokines, which increases the risk of opportunistic infections, among other side effects such as infusion reactions. Live biotherapeutics are an emerging treatment modality that offers local rather than systemic treatment that may limit systemic side effects. Our group has engineered an orally deliverable Saccharomyces boulardii strain that not only expresses targeting ligands capable of binding to inflamed tissues but also possesses the capability to secrete anti-inflammatory molecules. We used a well-established model of IBD-associated CRC to test the anti-cancer potential of our engineered S. boulardii. Germ-free Il10^-/- mice were colonized with a specific-pathogen free fecal microbiota transplant to initiate inflammation and then were injected with azoxymethane to induce colonic carcinogenesis. To test the hypothesis that engineered S. boulardii can effectively reduce tumor burden, mice were treated with engineered S. boulardii via oral gavage at two dosing frequencies (n=20 once weekly, n=17 twice weekly), unmodified S. boulardii (n=15 twice weekly), or placebo (n=18) until the end of the 18-week model. Stools were collected one week post-colonization and at harvest to non-invasively assess intestinal inflammation by fecal lipocalin (Lcn2) ELISA. Colonic tissues were collected at harvest for gross, histological, and molecular analysis of inflammation and tumorigenesis. Fecal Lcn2 ELISA revealed that all groups developed intestinal inflammation over time. Both engineered S. boulardii and unmodified S. boulardii reduced gross tumor number in a dose dependent manner with median tumor counts equal to 7.5 per mouse in the placebo group, 5 in mice treated with engineered S. boulardii once weekly, 3 in the group treated with engineered S. boulardii twice weekly (p=0.0046 versus placebo), and 2 in the group treated with unmodified S. boulardii twice weekly (p=0.0002 versus placebo). Distal colonic Il12b, Il23a, and Tgfb expression were decreased in a dose-dependent manner in mice treated with engineered S. boulardii. Histological inflammation and tumor invasion were not different between placebo and once weekly S. boulardii. Histological scoring of twice weekly S. boulardii administration cohorts are in process. Together, our data suggest that S. boulardii may reduce colorectal cancer tumor burden with associated changes in the inflammatory milieu.

Mairead Heavey

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