Colon-Specific Delivery of Probenecid Enhances Therapeutic Activity of the Uricosuric Agent Against Rat Colitis

Background/Objectives: Probenecid (PBN) is a uricosuric agent that facilitates the excretion of uric acid and is used to treat gout. Here, a colon-targeted prodrug of PBN was designed to facilitate repositioning as a treatment for inflammatory bowel disease (IBD). Methods: The carboxylic group in PBN was amide-conjugated with the amine groups of acidic amino acids to yield aspartic acid-conjugated PBN (PBN-AA) and glutamic acid-conjugated PBN (PBN-GA). Conjugation with amino acids increased the hydrophilicity of PBN and decreased cell permeability across the Caco-2 cell monolayer. While remaining intact in buffers (pH 1.2, 6.8) and in the small intestinal contents of rats, the conjugates were cleaved to release PBN from the cecal contents of rats, with a significant difference in the maximal conversion percentage between PBN-AA (12%) and PBN-GA (74%). Results: Upon oral gavage, PBN-GA accumulated a much greater amount of PBN in the cecum than PBN alone, thus verifying the in vitro colon specificity of PBN-GA. Oral PBN-GA enhanced the anticolitis effectiveness in dinitrobenzene sulfonic acid-induced rat colitis and limited the systemic absorption of PBN, thus reducing the risk of systemic adverse effects ascribed to PBN. Moreover, PBN-GA therapeutically surpassed sulfasalazine, a currently used anti-IBD drug, in rat colitis. Conclusions: These results suggest that amide conjugation with GA can be used to design a colon-targeting prodrug for PBN. Colon-targeted PBN may not only enhance therapeutic effectiveness but also improve the safety of PBN repositioned for the treatment of IBD and may be a pharmacological alternative for current small-molecule anti-IBD drugs with low efficacy or serious adverse effects with long-term use.