Colon-Targeted β₃-Adrenoceptor Agonist Mirabegron Enhances Anticolitic Potency of the Drug via Potentiating the Nrf2-HO-1 Pathway

The selective agonist of β₃-adrenergic receptor mirabegron (MBG), clinically used to treat overactive bladders, exerts beneficial effects in animal models of colitis. Here, we aimed to enhance the therapeutic activity and safety of MBG as an anticolitic drug by implementing colon-targeted drug delivery using a prodrug approach. MBG was azo-linked with salicylic acid (SA) to yield SA-conjugated MBG (MAS), which was conjugated with aspartic acid (Asp) and glutamic acid (Glu) to yield more hydrophilic derivatives: Asp-conjugated MAS (MAS-Asp) and Glu-conjugated MAS (MAS-Glu). MBG derivatives reduced the distribution coefficient and cell permeability of MBG, which were greater with the amino acid-conjugated MAS than with MAS. MBG derivatives were cleaved to release MBG in the cecal contents. Upon oral gavage, compared with MBG, MBG derivatives delivered greater amounts of MBG to the cecum while limiting the systemic absorption of MBG, and the amino acid-conjugated MAS exhibited a greater performance than MAS. In a rat colitis model, MBG derivatives were more effective than MBG in ameliorating colonic damage and inflammation, and the amino acid-conjugated MAS was more potent than MAS. MAS-Glu was therapeutically superior to sulfasalazine, a current drug to treat inflammatory bowel disease, against rat colitis. Moreover, MBG activated the anti-inflammatory nuclear factor erythroid 2-related factor 2 (Nrf2)-hemeoxygenase (HO)-1 pathway in inflamed colonic tissue, and the MAS-Glu-mediated amelioration of colitis was significantly compromised by an HO-1 inhibitor. Taken together, colon-targeted delivery of MBG may enhance the anticolitic activity, reduce the risk of systemic side effects of MBG, and elicit the therapeutic effects, at least partly by activating the Nrf2-HO-1 pathway.