AB2-type amphiphilic block copolymer containing a pH-cleavable hydrazone linkage for targeted antibiotic delivery

A novel AB2-type amphiphilic block copolymer [OA-CN-NH-(PEG)₂] with hydrazone linkage was synthesized and explored for pH-triggered antibiotic delivery. Vancomycin (VCM) loaded micelles of the polymer [OA-CN-NH-(PEG)₂-VCM] were spherical in shape with size, polydispersity index, zeta potential and entrapment efficiency of 130.33 ± 7.36 nm, 0.163 ± 0.009, -4.33 ± 0.55 mV and 39.61 ± 4.01% respectively. The dilution stability study exhibited no significant change in the size distribution of OA-CN-NH-(PEG)₂-VCM micelles up to 320-fold dilution. An in vitro drug release assay confirmed greater release of VCM from OA-CN-NH-(PEG)₂-VCM at pH 6, compared to pH 7.4. An in vitro antibacterial activity evaluation of OA-CN-NH-(PEG)₂-VCM showed 2-fold enhancement in antibacterial activity of VCM after 54 h of incubation against Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA) at acidic pH compared to physiological pH. An in vivo antibacterial activity of OA-CN-NH-(PEG)₂-VCM further proved the enhanced activity of OA-CN-NH-(PEG)₂-VCM against MRSA. In conclusion, micelles from pH-responsive OA-CN-NH-(PEG)₂ could be utilized for site-specific delivery of VCM at the infection site.