Drug -driven self-assembly of pH-sensitive nano-vesicles with high loading capacity and anti-tumor efficacy.

The in vivo delivery of nanomedicine is severely hampered by the limited enhanced permeability and retention effect (EPR) in tumors. Aiming at overcoming this limitation and achieving high anti-tumor effect of chemotherapeutics, we specially addressed an available strategy from a viewpoint of increasing the drug loading of nano-carriers. Here, we constructed a novel pH-responsive polymersome based on the drug-driven self-assembly of amphiphilic polyphosphazenes PAP containing the ortho ester group ABD and mPEG2000. Due to the non-covalent attractive forces between PAP and doxorubicin hydrochloride (DOX·HCl), DOX·HCl can induce the self-assembly of PAP via embedding itself in the lamella to form vesicles and the subsequent location in the center aqueous chamber of the resultant nano-vesicles, which resulted in the high drug loading content of 35.77 wt%. In addition, with the incorporation of cholesteryl hemisuccinate (CholHS), the premature leakage of DOX·HCl was significantly inhibited under physiological conditions. Meanwhile, the pH-sensitive drug release occurred at pH 5.5 by the advantage of the pH-sensitive biodegradation of ABD in PAP. Consequently, this CholHS-incorporated DOX·HCl-driven PAP vesicle achieved excellent anti-tumor effect with tumor growth inhibition up to 82.4% in S180 tumor-bearing mice. Taken together, our newly developed drug-driven vesicles may promote the development of efficient drug delivery systems for application in cancer therapy.