Design of Poly-Catechol Biodynamers for Potentiation of Antibiotic Efficacy against Drug-Resistant Bacteria

Catechol-modified polymers, such as DOPA-functionalized systems, have recently gained significant interest for a variety of biomedical applications, particularly in their role as antibacterial adjuvants due to their oxidative activity and ability to generate reactive oxygen species (ROS). Current catechol-functionalized polymers, however, often suffer from a restricted number of catechol groups, limited biocompatibility and solubility, and low stability due to the rapid oxidation under physiological conditions. In this study, we developed a water-soluble, biocompatible DOPA-modified biodynamer (DOPA-BD), leveraging the principles of constitutional dynamic chemistry (CDC). DOPA-BD was synthesized via polycondensation of DOPA-hydrazide and the hexaethylene glycol-conjugated carbazole dialdehyde (CA-HG), forming dynamic imine and acylhydrazone linkages between the monomers. As a result of its dynamic covalent backbone, DOPA-BD exhibits biodegradability and undergoes pH-responsive degradation under mildly acidic conditions typically found at infection sites, leading to a more than 3-fold increase in DOPA-hydrazide release compared to physiological pH. Interestingly, driven by CDC, DOPA-BD folds into a nanorod structure with a hydrodynamic diameter of ∼7.8 nm, surrounded by HG chains that offer water solubility and biocompatibility. Moreover, the incorporation of the DOPA-derivative in each repeating unit yields a polymer with exceptionally high catechol content, which remains stable and resistant to oxidation for 72 h in physiological buffer conditions. Regarding its antibacterial applicability, DOPA-BD demonstrated synergistic antibacterial activity with Azithromycin (AZM) against AZM-resistant E. coli, enhancing the antibiotic's efficacy by 4-fold. Our study indicates that DOPA-BD induces ROS production in the respective bacterial strain, suggesting ROS generation as one of the possible mechanisms contributing to the observed synergy. Overall, DOPA-BD represents a promising alternative strategy to potentiate antibacterial activity against resistant strains, holding strong potential for future antibacterial applications.