Stepwise dual targeting and dual responsive polymer micelles for mitochondrion therapy.

Methods to selectively destroy mitochondria of tumor cells and induce cell apoptosis with nanomedicine constitute challenges in cancer therapy. In the present study, we develop cell membrane/mitochondria dual targeting and pH/redox dual responsive nanoparticles for mitochondrion therapy. The nanoparticles are fabricated by the self-assembly of triphenylphosphonium (TPP) grafted poly(ethylene glycol)(PEG)-poly(d,l-lactide)(PLA) copolymers (TPP-PEG-ss-PLA) using disulfide bonds as the intermediate linkers. To shield the surface positive charge of the nanoparticles from TPP composition, chondroitin sulfate (CS) is employed to coat the nanoparticles, and this prolongs blood circulation while endowing an active targeting ability to the cell membrane. In acidic lyso-somes/endosomes, the negatively charged CS layer falls away to expose the TPP component. Subsequently, in the cyto-plasm, the nanoparticles can anchor to the mitochondrial outer membrane by TPP-mediated targeting, thereby inducing a decrease in the membrane potential and opening of the permeability transition pore. Thus, the overproduction of ROS in the mitochondria promotes cell apoptosis. The released DOX directly diffuse into the mitochondria, thereby resulting in mito-chondrial DNA damage. Therefore, the nanoparticles exhibit significant potential in terms of a new avenue for mitochondrion therapy in cancer treatment.