Enzymatic synthesis of PEG–poly(amine-co-thioether esters) as highly efficient pH and ROS dual-responsive nanocarriers for anticancer drug delivery

Novel multifunctional drug nanocarriers have been successfully fabricated from a new type of enzymatically synthesized, biodegradable block copolymer, PEG–poly(ω-pentadecalactone-co-N-methyldiethyleneamine-co-3,3′-thiodipropionate) (PEG–PPMT), which was responsive to tumor-relevant acidic pH (5.0–6.5) and intracellular reactive oxygen species (ROS) of tumor cells. The PEG–PPMT copolymers could self-assemble to form nano-scaled particles in aqueous solutions, which are stable in physiological solutions, but swell substantially upon reducing the pH from 7.4 to 5.0 and/or in the presence of ROS on account of the protonation of the tertiary amino groups and oxidation of the thioether groups, causing a hydrophobic to hydrophilic transition in the nanoparticle cores. Consistently, docetaxel (DTX) encapsulated in PEG–PPMT nanoparticles can be triggered in a synergistic manner by acidic pH and a high-ROS environment in tumor cells to release the hydrophobic drug at accelerated rates for efficient tumor growth inhibition. In particular, DTX encapsulated in PEG–PPMT–11% PDL and PEG–PPMT–28% PDL nanoparticles exhibit extraordinarily enhanced potency (95% and 93% tumor-inhibiting efficiency, respectively) in inhibiting the growth of ROS-rich CT-26 tumors xenografted in mice. Importantly, biosafety analyses show minimal toxicity of DTX-loaded PEG–PPMT nanoparticles toward normal organs including liver and kidneys during the in vivo antitumor treatments. These results demonstrate that the PEG–PPMT nanoparticles are promising pH and ROS dual-responsive multifunctional nanocarriers for tumor site specific, controlled release of anticancer drugs to treat ROS-rich tumors.