Jaejeong Kim

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.

Background/Objectives: In addition to oncological applications, poly(ADP-ribose) polymerase (PARP) inhibitors have potential as anti-inflammatory agents. Colon-targeted delivery of PARP inhibitors has been evaluated as a pharmaceutical strategy to enhance their safety and therapeutic efficacy against gut inflammation. Methods: Colon-targeted PARP inhibitors 5-aminoisoquinoline (5-AIQ) and 3-aminobenzamide (3-AB) were designed and synthesized by azo coupling with salicylic acid (SA), yielding 5-AIQ azo-linked with SA (AQSA) and 3-AB azo-linked with SA (ABSA). Additional conjugation of AQSA with acidic amino acids yielded glutamic acid-conjugated AQSA (AQSA-Glu) and aspartic acid-conjugated AQSA, which further increased the hydrophilicity of AQSA. Results: The distribution coefficients of PARP inhibitors were lowered by chemical modifications, which correlated well with drug permeability via the Caco-2 cell monolayer. All derivatives were effectively converted to their corresponding PARP inhibitors in the cecal contents. Compared with observations in the oral administration of PARP inhibitors, AQSA-Glu and ABSA resulted in the accumulation of much greater amounts of each PARP inhibitor in the cecum. ABSA accumulated mesalazine (5-ASA) in the cecum to a similar extent as sulfasalazine (SSZ), a colon-targeted 5-ASA prodrug. In the DNBS-induced rat colitis model, AQSA-Glu enhanced the anticolitic potency of 5-AIQ. Furthermore, ABSA was more effective against rat colitis than SSZ or AQSA-Glu, and the anticolitic effects of AQSA-Glu were augmented by combined treatment with a colon-targeted 5-ASA prodrug. In addition, the colon-targeted delivery of PARP inhibitors substantially reduced their systemic absorption. Conclusions: Colon-targeted PARP inhibitors may improve the therapeutic and toxicological properties of inhibitors and synergize the anticolitic effects of 5-ASA.

In our previous study, riluzole azo-linked to salicylic acid (RAS) was prepared as a colon-targeted prodrug of riluzole (RLZ) to facilitate the repositioning of RLZ as an anticolitic drug. RAS is more effective against rat colitis than RLZ and sulfasalazine, currently used as an anti-inflammatory bowel disease drug. The aim of this study is to further improve colon specificity, anticolitic potency, and safety of RAS. N-succinylaspart-1-ylRLZ (SAR) and N-succinylglutam-1-ylRLZ (SGR) were synthesized and evaluated as a “me-better” colon-targeted prodrug of RLZ against rat colitis. SAR but not SGR was converted to RLZ in the cecal contents, whereas both conjugates remained intact in the small intestine. When comparing the colon specificity of SAR with that of RAS, the distribution coefficient and cell permeability of SAR were lower than those of RAS. In parallel, oral SAR delivered a greater amount of RLZ to the cecum of rats than oral RAS. In a DNBS-induced rat model of colitis, oral SAR mitigated colonic damage and inflammation and was more potent than oral RAS. Moreover, upon oral administration, SAR had a greater ability to limit the systemic absorption of RLZ than RAS, indicating a reduced risk of systemic side effects of SAR. Taken together, SAR may be a “me-better” colon-targeted prodrug of RLZ to improve the safety and anticolitic potency of RAS, an azo-type colon-targeted prodrug of RLZ.

We designed colon-targeted trans-cinnamic acid (tCA) and synthesized its conjugates with glutamic acid (tCA-GA) and aspartic acid (tCA-AA). We evaluated the anti-colitic activity of colon-targeted tCA using a dinitrobenzenesulfonic acid-induced rat colitis model. The conjugates lowered the distribution coefficient and Caco-2 cell permeability of tCA and converted to tCA in the cecum, with higher rates and percentages with tCA-GA than with tCA-AA. Following oral gavage, tCA-GA delivered a higher amount of tCA to the cecum and exhibited better anti-colitic effects than tCA and sulfasalazine (SSZ), which is the current treatment for inflammatory bowel disease. In the cellular assay, tCA acted as a full agonist of GPR109A (EC50: 530 µM). The anti-colitic effects of tCA-GA were significantly compromised by the co-administration of the GPR109A antagonist, mepenzolate. Collectively, colon-targeted tCA potentiated the anti-colitic activity of tCA by effectively activating GPR109A in the inflamed colon, enabling tCA to elicit therapeutic superiority over SSZ.

Dapsone (DpS) is an antimicrobial and antiprotozoal agent, especially used to treat leprosy. The drug shares a similar mode of action with sulfonamides. Additionally, it possesses anti-inflammatory activity, useful for treating autoimmune diseases. Here, we developed a “me-better” alternative to sulfasalazine (SSZ), a colon-specific prodrug of mesalazine (5-ASA) used as an anti-inflammatory bowel diseases drug; DpS azo-linked with two molecules of 5-ASA (AS-DpS-AS) was designed and synthesized, and its colon specificity and anti-colitic activity were evaluated. AS-DpS-AS was converted to DpS and the two molecules of 5-ASA (up to approximately 87% conversion) within 24 h after incubation in the cecal contents. Compared to SSZ, AS-DpS-AS showed greater efficiency in colonic drug delivery following oral gavage. Simultaneously, AS-DpS-AS substantially limited the systemic absorption of DpS. In a dinitrobenzene sulfonic acid-induced rat colitis model, oral AS-DpS-AS elicited better efficacy against rat colitis than oral SSZ. Moreover, intracolonic treatment with DpS and/or 5-ASA clearly showed that combined treatment with DpS and 5-ASA was more effective against rat colitis than the single treatment with either DpS or 5-ASA. These results suggest that AS-DpS-AS may be a “me-better” drug of SSZ with higher therapeutic efficacy, owing to the combined anti-colitic effects of 5-ASA and DpS.