To address the limitations of conventional nanotechnology-based drug delivery systems, this work developed enzyme and reduction dual-responsive polymeric micelles. These micelles were synthesized with copolymers composed of TPGS₃₃₅₀-PVGLIG-DOX (TPD) and FA-SS-DOX (FSD), which endow them with tumor-targeted drug delivery capabilities. TPGS₃₃₅₀ contributes to extending the circulation of micelles in body, augmenting their accumulation in tumor tissues via the enhanced permeability and retention (EPR) effect. Upon localized the tumor site, matrix metalloproteinase 2 (MMP2) cleaves the PVGLIG peptide moiety within the micelles, thereby releasing TPGS₃₃₅₀ and exposing the targeting ligand of folate. This approach enables the subsequent internalization of the micelles by tumor cells through folate receptor-mediated endocytosis. After internalization, the high intracellular concentration of glutathione (GSH) triggers the reduction of the disulfide bond within the FA-SS-DOX, leading to the release of the anticancer-drug doxorubicin (DOX), which promotes apoptosis in the tumor cells and enhances the efficacy of chemotherapy.

Recently, the incidence of cancer keeps increasing, seriously endangers human health, and has evolved into the main culprit of human death. Conventional chemotherapeutic drugs, such as paclitaxel and doxorubicin (DOX), have some disadvantages, including low therapeutic effect, poor water solubility, high toxic side effects, short blood circulation time in the body, and so on. To improve the anti-tumor effect of the drug in vivo and reduce its side effects on the body, researchers have designed and developed a variety of responsive nanocarriers. In this work, we synthesized D-α-tocopherol polyethylene glycol 3350 succinate (TPGS₃₃₅₀)-Gly-Pro-Leu-Gly-Val-Arg (GPLGVR)-DOX (TPD) prodrugs in response to extracellular enzymes of matrix metalloproteinase (MMP-9) in the tumor microenvironment and FA-Asp-Glu-Val-Asp (DEVD)-DOX (FPD) prodrugs responsive to intracellular enzymes of caspase-3. Then, intracellular and extracellular enzyme-responsive TPD&FPD micelles with DOX (TPD&FPD&D) were successfully prepared through dialysis method. The outer layer of TPGS₃₃₅₀ can prolong the blood circulation time of micelles in vivo, followed by accumulation of micelles at tumor tissue through enhanced permeability and retention (EPR) effect. The peptide of GPLGVR can be cleaved by MMP-9 enzymes to remove the outer layer of TPGS₃₃₅₀, exposing the targeting molecule of folate, and then the micelles are engulfed by tumor cells through folate receptor-mediated endocytosis. After entering the tumor cells, the free DOX loaded in the micelles is released, which induces tumor cell apoptosis to activate caspase-3 in the cells, cutting the peptide DEVD to accelerate the intracellular release of the DOX, which further enhances cytotoxicity to improve antitumor effect.