TOXICOLOGICAL FINDINGS OF A RECOMBINANT CHOLERA TOXIN B SUBUNIT VARIANT WITH THERAPEUTIC POTENTIAL IN ULCERATIVE COLITIS

Abstract

Abstract Background The cholera toxin B subunit (CTB) is the nontoxic and homopentameric component of the holotoxin. Upon binding to GM1 ganglioside on the surface of epithelial cells, CTB mediates entry and retrograde transport through the endomembrane system and disengages the catalytic A subunit in the endoplasmic reticulum (ER). EPICERTIN (EPT) is a recombinant variant of CTB with a non-native C-terminal extension harboring an ER-retention motif, KDEL. We have found that increased ER-retention time resulting from this modification allowed EPT to induce an unfolded protein response and TGF-β signaling in colon epithelial cells, triggering wound healing activity in preclinical colitis models. The unique epithelial repair activity of EPT hints at its therapeutic potential in ulcerative colitis. Objective We aim to develop data supporting a first-in-human clinical trial with an EPT enema indicated for ulcerative colitis. Here, we evaluated the efficacy and toxicity of intrarectal (IR) administration of EPT in preclinical rodent models. Results IR administration of EPT at 0.1 and 1 µM to female C57/BL6 mice (0.6 and 6.1 μg/animal) with acute dextran sodium sulfate (DSS)-induced colitis resulted in decreased disease activity index scores and increased body weight recovery, supporting a target therapeutic dose of ≤1 µM for clinical administration. A dose-escalation study was performed following a single IR exposure at 1, 2 and 5 µM (61.4, 122.8 and 307 μg/animal) in male and female Sprague Dawley rats. No drug-related adverse effects were evident in clinical observations, including clinical pathology and gross necropsy, even at the highest dose tested. A pharmacokinetics study was performed in male and female mice dosed with a 1 or 10 µM (6.1 and 61.4 μg/animal) IV bolus of EPT. Plasma samples were collected periodically for up to 24 h postdose. EPT concentrations were highest at first collection and decreased steadily until unquantifiable by 4 h. The elimination phase half-life was 0.26 to 0.3 h. When healthy and DSS-induced colitic mice (n = 72) were dosed with 1 or 10 µM EPT IR, marginal amounts of EPT were found in only 4 plasma samples scattered across groups and time points, suggesting that systemic exposure after IR administration is negligible. Conclusion These data support further development of EPT as a potential therapeutic for ulcerative colitis.