Objective(s): 4-aminosalicylic acid (4-ASA) is an isomer of mesalazine that has recently been shown to be effective against inflammatory bowel disease (IBD), and more specifically, ulcerative colitis. However, the majority of orally administered 4-ASA is readily and extensively absorbed from the stomach and small intestine, so only a small amount is transported to the colon. A mutual ester and AZO PRODRUG of 4-ASA was synthesized with polyethylene glycol (PEG) and dimethylaniline, respectively, to overcome this issue. Materials and Methods: The 4-ASA PRODRUG was synthesized via a two-step process and then characterized by 1H-NMR. The stability of the PRODRUG was evaluated in simulated gastric fluid (pH 1. 2). Furthermore, the in vitro release profiles of the drug conjugate was evaluated at pH 1. 2, as well as pH 6. 8 in the absence or presence of rat cecal content. Results: The prepared PRODRUG was stable at pH 1. 2, indicating that it could be protected from the acidic environment of the stomach. Also, the results of drug release at pH 6. 8 showed that the amount of 4-ASA released was 63% within 12 hr in the absence of rat cecal content, while in the presence of rat cecal content, 97% of 4-ASA was released from the PRODRUG in 6 hr. Conclusion: Overall, the synthesized PEGylated AZO-based 4-ASA PRODRUG could be a potential candidate for targeted drug delivery to the inflamed gut tissue in IBD.

The protective and anti-inflammatory effects of AZO and AZO-linked polymeric PRODRUGs of 5-aminosalicylic acid (5-ASA) on acetic acid induced colitis in rats were investigated. Three AZO PRODRUGs; 4,4 -dihydroxy-AZObenzene-3-carboxilic acid (AZO compound I), 4-hydroxy-AZObenzene-3,4-dicarboxilic acid (AZO compound II), 4,4-dihydroxy-3-formyl-AZObenzene-3-carboxylic acid (AZO compound III) and their polyethylene glycol (PEG 6000) derivatives were synthesized. Rats were pretreated orally (1 hour prior to induction of colitis) with sulfasalazin (300 mg/kg), AZO compounds I, II, III and polyethylene glycol conjugates of AZO compounds II and III in doses which had the same amount of 5-ASA as sulfasalazin contains. The colonic damage was examined 24 hours later and characterized by gross microscopic injury and colonic edema. Among PRODRUGs only AZO compound III (215 mg/kg) produced a significant (p<0.01) protective effect against colonic injury comparable with sulfasalazin. Doubling the dose (430 mg/kg) showed more anti-colitis effects. Polyethylene glycol conjugate of AZO compounds II and III also showed reduction in the extent of the cell death and tissue disorganization similar to sulfasalazin. While neither sulfasalazin, nor AZO compound II and its PEG polymer produced anti-edema effects, both AZO compound III and its PEG polymer decreased colon edema significantly (p<0.05). Histological examinations also indicated a marked reduction in tissue injury and inhibition in neutrophil infiltration in rats treated with AZO compound III and PEG conjugates of AZO compounds II and III. Results of this investigation provide experimental evidence supporting new cytoprotective, anti-inflammatory and anti-edema properties of the AZO derivatives of 5-ASA and their PEGylated PRODRUGs.