Design, Synthesis, and Biological Characterization of Macromolecular Ester Prodrugs of a Selective Cyclooxygenase-2...

Owing to the importance of tracing new routes in the development of macromolecular prodrugs, in the present work, two potential macromolecular ester prodrugs (i.e., 12a and 13a) of selective cyclooxygenase-2 (COX-2) inhibitor 7b are designed and synthesized. In the design, two different oligo(ethylene glycol)-based spacers are linked through a ferulate residue to the backbone hyaluronic acid (HA) showing a medium molar mass value (i.e., Mw = 270 kDa). The spacers are designed to differ in the sensitivity to the hydrolytic conditions so that the chemical hydrolysis of ferulate ester bond in 12a is assumed to produce the corresponding ferulic acid derivative 12b. On the other hand, the same reaction in 13a leading to ferulate derivative 13b could be accompanied by the hydrolysis of the second ester bond with the release of the selective COX-2 inhibitor 7b. The COX inhibitory activity of the newly synthesized compounds is evaluated in vitro, and macromolecular ester prodrugs 12a and 13a are found to be completely inactive together with hydrolysis product 12b. Conversely, these in vitro studies reveal the intriguing COX-2 inhibitory activity and selectivity of ferulate derivative 13b related to macromolecular ester prodrug 13a. Therefore, to obtain information on the hydrolysis process in different environments, hydrolysis studies are performed on macromolecular ester prodrug 13a by using ¹H NMR and UHPLC-MS techniques. These studies show that severe hydrolytic conditions (i.e., aqueous NaOH solutions) promote the rapid release of potent and selective COX-2 inhibitor 7b, whereas in ammonium acetate buffer the release is slower. Overall, these results lead to envision possible applications of the design approach to the development of macromolecular ester prodrugs of all the drug molecules bearing hydroxyl groups in their structures.