Reduction Responsive Self-Assembled Nanoparticles Based on Disulfide-Linked Drug-Drug Conjugate with High Drug Loading and Antitumor Efficacy.

Most anticancer drugs are poorly soluble and nonspecific, which restricts their clinical application. Drug conjugates, as a prodrug strategy, provide the possibility to overcome these shortcomings, especially combined with nanotechnology. Drug conjugate nanoparticles possess the advantages of high drug loading capacity and passive tumor targeting ability. Here, we prepared doxorubicin drug-drug conjugate nanoparticles (DOX-SS-DOX NPs) based on disulfide-linked doxorubicin drug-drug conjugate (DOX-SS-DOX). Dynamic light scattering (DLS) and transmission electron microscope (TEM) characterization indicated that DOX-SS-DOX NPs were spherical with a uniform size distribution around 89 nm. DLS and in vitro release experiment revealed that DOX-SS-DOX NPs possessed reduction responsive activity. In vitro cellular uptake studies reflected that DOX-SS-DOX NPs could increase the uptake level substantially compared with DOX liposomes. Endocytosis mechanism assay demonstrated that DOX-SS-DOX NPs internalized into cells through a clathrin-mediated endocytosis pathway in an energy-dependent manner. In this manner, the amidase in lysosomes could break the amide bond to release free DOX, which would be helpful to antitumor activity. The in vitro cytotoxicity of DOX-SS-DOX NPs was a bit weaker than that of DOX liposomes, which might be the result of the slow cleavage of the disulfide bridge; but the antitumor efficacy of DOX-SS-DOX NPs evaluated in MCF-7 bearing mice was demonstrated to be higher than that of DOX liposomes. This might be because of the long lasting effect resulting from the slow cleavage of the disulfide bond. In summary, DOX-SS-DOX NPs, prepared nearly totally with drug, provide a good strategy for cancer therapy.