Cholera toxin B subunit (CTB), a non-toxic homopentameric component of Vibrio cholerae holotoxin, is an oral cholera vaccine antigen that induces an anti-toxin antibody response. Recently, we demonstrated that a recombinant CTB variant with a Lys-Asp-Glu-Leu (KDEL) endoplasmic reticulum retention motif (CTB-KDEL) exhibits colon mucosal healing effects that have therapeutic implications for inflammatory bowel disease (IBD). Herein, we investigated the feasibility of CTB-KDEL for the treatment of chronic colitis. We found that weekly oral administration of CTB-KDEL, dosed before or after the onset of chronic colitis, induced by repeated dextran sodium sulfate (DSS) exposure, could significantly reduce disease activity index scores, intestinal permeability, inflammation, and histological signs of chronicity. To address the consequences of immunogenicity, mice (C57BL/6 or C3H/HeJ strains) were pre-exposed to CTB-KDEL then subjected to DSS colitis and CTB-KDEL treatment. While the pre-dosing of CTB-KDEL elicited high-titer anti-drug antibodies (ADAs) of the immunoglobin A (IgA) isotype in the intestine of C57BL/6 mice, the therapeutic effects of CTB-KDEL were similar to those observed in C3H/HeJ mice, which showed minimal ADAs under the same experimental conditions. Thus, the immunogenicity of CTB-KDEL does not seem to impede the protein’s mucosal healing efficacy. These results support the development of CTB-KDEL for IBD therapy.

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The novel wound-healing biologic EPICERTIN, a recombinant analog of cholera toxin B subunit, is in early development for the management of ulcerative colitis. This study established for the first time the pharmacokinetics (PK), bioavailability (BA) and acute safety of EPICERTIN in healthy and dextran sodium sulfate-induced colitic mice and healthy rats. For PK and BA assessments, single administrations of various concentrations of EPICERTIN were given intravenously (iv) or intrarectally (ir) to healthy and colitic C57BL/6 mice and to healthy Sprague Dawley rats. After iv administration to healthy animals, the drug's plasma half-life (t 1/2 ) for males and females was 0.26 and 0.3 h in mice, and 19.4 and 14.5 h in rats, respectively. After ir administration, drug was detected at very low levels in only 4 samples of mouse plasma, with no correlation to colon epithelial integrity. No drug was detected in rat plasma. A single ir dose of 0.1 µM (0.6 µg/mouse) EPICERTIN significantly facilitated the healing of damaged colonic epithelium as determined by disease activity index and histopathological scoring, while 10-fold higher or lower concentrations showed no effect. For acute toxicity evaluation, healthy rats were given a single ir administration of various doses of EPICERTIN with sacrifice on Day 8, recording body weight, morbidity, mortality, clinical pathology and gross necropsy observations. There were no drug-related effects of toxicological significance. The NOAEL (ir) in rats was determined to be 5 µM (307 µg/animal, or 5.2 µg drug/cm 2 of colorectal surface area), which is 14-times the anticipated ir-delivered clinical dose.