Synthesis and release studies on amylose-based ester prodrugs of fenamic acid NSAIDs

<b>Aim:</b> To achieve colon-targeted release of mefenamic acid from its ester-linked amylose prodrugs. <b>Materials &amp; methods:</b> The prodrug was characterized by 1H NMR and IR spectroscopy. Drug activation and release profile was studied in enzyme enriched simulated physiological media via UV-vis spectroscopy and was validated with HPLC analysis. ELISA assay was employed for evaluating the % inhibition of COX-1 and COX-2 inhibition at different concentrations of the prodrug preincubated with ester and/ or amylose hydrolyzing enzymes. SEM studies further validated the performance of the prodrug under simulated physiological conditions. <b>Results:</b> Pancreatin was essential for the prodrug activation in SIM to make the ester bonds in prodrug vulnerable to hydrolysis by esterase. This evidence was confirmed by drug release studies, HPLC analysis, ELISA assay and SEM investigation where the ester conjugated prodrug showed marked stability in physiological media only to get activated in the presence of amylose degrading enzyme. <b>Conclusion:</b> Ester linked amylose-mefenamic acid conjugate showed both enzyme responsive activation and release in SIM. Development of enzyme sensitive, amine linked amylose-based prodrugs of mefenamic acid. 1H NMR and IR spectroscopy was employed to characterize amylose-mefenamic acid conjugates. Drug activation and its release from the prodrug was appraised in simulated physiological media via UV-vis spectroscopy. ELISA assay was performed to evaluate the % inhibition of COX-1 and COX-2 inhibition in the presence of free mefenamic acid, and its amylose-based prodrug conjugate at different concentrations after preincubating with pancreatin followed by treatment with esterase. SEM studies were conducted to observe the performance of the prodrug under simulated physiological conditions. HPLC experiments were conducted to validate the pancreatin-mediated prodrug activation and esterase-responsive drug release. 1H NMR suggested the participation of primary -CH2(OH) at C6 position and secondary -CH(OH) at C2 position of amylose unit toward esterification with mefenamic acid. Ester linked amylose-mefenamic acid prodrug shows stability toward degradation in simulated gastric and simulated intestinal media due to shielding effect of the macromolecule which prevents hydrolysis of ester linkage via esterase enzymes. The prodrug undergoes enzyme-responsive activation in the presence of pancreatin which degrades macromolecular backbone of amylose to cause relaxation in the shielding effect. Drug release from the prodrug was achieved in the presence of esterase, which was sustained for 20 h in SIM only after its activation by pancrelipase. Amide-linked amylose-mefenamic acid prodrug conjugate showed pancreatin-responsive activation and esterase-responsive release. Drug release from the prodrug was not achieved without preincubating the system with pancreatin, suggesting that the macromolecular structure of amylose was responsible for blocking the hydrolytic action of esterase on the ester linkers in the prodrug. This phenomenon also explains the stability of the prodrug conjugate under simulated gastric and simulated intestinal media.