A Two-Step Precise Targeting Nanoplatform for Tumor Therapy via the Alkyl Radicals Activated by the Microenvironment of Organelles

ABSTRACT With the in-depth research of organelles, the microenvironment characteristics of their own, such as the acid environment of lysosomes and the high temperature environment of mitochondria, could be used as a natural and powerful condition for tumor therapy. Based on this, we constructed a two-step precise targeting nanoplatform which can realize the drug release and drug action triggered by the microenvironment of lysosomes (endosomes) and mitochondria, respectively. To begin with, the mesoporous silica nanoparticles (MSNs) were modified with triphenylphosphonium (TPP) and loaded with 2,2’-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH). Then, folic acid (FA) targeted pH-sensitive liposomes containing docetaxel (Lipo/DTX-FA) were prepared by thin-film dispersion method, and the core-shell AIPH/MSN-TPP@Lipo/DTX-FA nanoparticles were constructed by self-assembly during the hydration of the liposomes. When this nanoplatform entered into the tumor cells through FA receptor-mediated endocytosis, the pH-sensitive liposomes were destabilized in the lysosomes, resulting in the release of DTX and AIPH/MSN-TPP nanoparticles. After that, AIPH was delivered to mitochondria by AIPH/MSN-TPP, and the alkyl radicals produced by AIPH under the high temperature environment can cause oxidative damage to mitochondria. Not only that, the DTX could enhance the anti-tumor effect of AIPH by downregulating the expression of anti-apoptotic Bcl-2 protein. The in vitro and in vivo results demonstrate that this delivery system could induce apoptosis based on organelles’ s own microenvironment, which provides a new approach for tumor therapy.