Doxorubicin-Incorporated Nanoparticles Composed of Ce6-Conjugated Hyaluronic Acid-b-poly(ethylene glycol) Copolymer for Overcoming Doxorubicin Resistance of Breast Cancer Cells

Oxidative stress in the tumor microenvironment, which is its own intrinsic property, is frequently utilized to deal with the drug-targeting issue in the nanoparticle drug delivery system. For this purpose, reactive oxygen species (ROS)-sensitive nanoparticles encapsulating doxorubicin (DOX) and chlorin e6 (Ce6) were synthesized for treatment of MDA-MB-231 breast cancer cells. Hyaluronic acid (HA) with a reductive end was conjugated with methoxy poly(ethylene glycol) (PEG) using thioketal diamine (ThdNH2) linkage (HA-b-PEG copolymer). Then, Ce6 were conjugated to the carboxylic acid group of HA via ThdNH2 (HA(Ce6)-b-PEG copolymer). DOX was physically incorporated to make DOX-incorporated HA(Ce6)-b-PEG copolymer nanoparticles (DOX-NP). HA(Ce6)-b-PEG copolymer nanoparticles (empty NP) and DOX-NP have a tiny particle size, less than 200 nm, with spherical morphology. They were responsively disintegrated according to the hydrogen peroxide (H2O2) concentration, then the release rate of Ce6 or DOX was accelerated, indicating that empty NP and DOX-NP have ROS sensitivity. DOX-resistant MDA-MB-231 cells were prepared by continuous treatment of DOX for three months. DOX-NP were efficiently internalized into the cells while intra-cellular delivery of DOX itself was inhibited. DOX-NP has higher anticancer activity against DOX-resistant MDA-MB-231 cells than that of DOX itself since cells were resistant to DOX itself. Under light irradiation, DOX-NP significantly decreased the viability of DOX-resistant MDA-MB-231 cells while DOX itself did not properly affect cell viability. Empty NP also efficiently inhibited cell viability rather than that of Ce6 itself while both of them did not affect the cell viability in the absence of light irradiation. Furthermore, empty NP showed higher ROS generation than that of Ce6 itself. DOX-NP more efficiently induced apoptosis/necrosis than DOX itself. In DOX-resistant MDA-MB-231 cell-bearing mice, DOX-NP was efficiently delivered to tumor tissue. DOX-NP greatly inhibited the growth of tumors under light irradiation, more than that of DOX itself or empty NP. In conclusion, DOX-NP showed promising antitumor activity against DOX-resistant MDA-MB-231 cells.