Thermoresponsive Polymer-Antibiotic Conjugates Based on Gradient Copolymers of 2-Oxazoline and 2-Oxazine

A polymer–antibiotic conjugate with thermoresponsive properties near body temperature is presented. The backbone polymer is a copolymer of 2-n-propyl-2-oxazine (PropOzi) and methoxycarbonylethyl-2-oxazoline (C₂MestOx) which is conjugated with the broad-spectrum antibiotic, cefazolin, via modification of the methyl ester group of C₂MestOx. The resulting polymer–antibiotic conjugate has a cloud point temperature near body temperature, meaning that it can form a homogenous solution if cooled, but when injected into a skin-mimic at 37 °C, it forms a drug depot precipitate. Cleavage of the ester linker leads to quantitative release of the pristine cefazolin (with some antibiotic degradation observed) and redissolution of the polymer. When Escherichia coli were treated with polymer–antibiotic conjugate total clearance is observed within 12 h. The power of this approach is the potential for localized antibiotic delivery, for example, at a specific tissue site or into infected phagocytic cells.