Legumain enzyme is a well-conserved lysosomal
cysteine protease and is over-expressed in many
tumor cells and
tumor stromal cells and exhibits higher
protease activity under acidic conditions, such as in lysosomes and endosomes.
Legumain enzyme-triggered drug delivery systems have demonstrated potential therapeutic values in
cancer targeted
therapy. To realize a more efficient delivery of anticancer therapeutic agents, we herein report a
legumain/pH dual-responsive drug delivery system for enhancing site-specific controlled release of
antitumor drugs. The carrier (named "DS-NA") is a hybrid vector constituting PEG-b-PBLA
polymers, pH-responsive OAPI
polymers, and
legumain-sensitive
peptide-
doxorubicin prodrug decorated fluorescent
carbon dots (CDs-C9-AANL-DOX). In
tumor cells, DS-NA could disassemble rapidly in acidic environments, and then release
doxorubicin through
legumain digestion. Except as a
drug vector, the drug release process from DS-NA could also be dynamically monitored by CLSM as the DOX was released from the surface of CDs through the AANL
peptide linker digested by
legumain, then transferred into the cell nucleus and exerted cytotoxicity, while the CDs themselves remained in the cytoplasm. As a control, the CDs-C9-DOX, which did not contain the AANL
peptide linker, also still resided in the cytoplasm. Furthermore, in vivo studies show that DS-NA had a stronger inhibitory effect on
tumor tissue with attenuated side effects to normal tissues than control nanoparticles or free drugs, which may be due to comprehensive effects including pH/
legumain dual-triggered drug release, long blood circulation periods, and EPR effects. Together, a combination strategy of
acid sensitivity and
legumain enzyme sensitivity used for site-specific controlled release of drugs provides a novel method for enhanced and precise antitumor
chemotherapy.