Tumor microenvironment, such as the lowered tumor extracellular pH (pHe) and matrix metalloproteinase 2 (MMP2), has been extensively explored, which promotes the development of the microenvironment-responsive drug delivery system. Utilizing these unique features, an activatable cell-penetrating peptide (designated as dtACPP) that is dual-triggered by the lowered pHe and MMP2 has been constructed, and a smart nanoparticle system decorating with dtACPP has been successfully developed, which could dual-load gene drug and chemotherapeutics simultaneously. After systemic administration, dtACPP-modified nanoparticles possess passive tumor targetability via the enhanced permeability and retention effect. Then dtACPP would be activated to expose cell-penetrating peptide to drive the nanoparticles' internalization into the intratumoral cells. As angiogenesis and tumor cells might be mutually improved in tumor growth, so combining antiangiogenesis and apoptosis is meaningful for oncotherapy. Vascular endothelial growth factor (VEGF) is significant in angiogenesis, and anti-VEGF therapy could decrease blood vessel density and delay tumor growth obviously. Chemotherapy using doxorubicin (DOX) could kill off tumor cells efficiently. Here, utilizing dtACPP-modified nanoparticles to co-deliver plasmid expressing interfering RNA targeting VEGF (shVEGF) and DOX (designated as dtACPPD/shVEGF-DOX) results in effective shutdown of blood vessels and cell apoptosis within the tumor. On the premise of effective drug delivery, dtACPPD/shVEGF-DOX has demonstrated good tumor targetability, little side effects after systemic administration, and ideal antitumor efficacy.

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The purpose of this work was to evaluate the potential of HAIYPRH (T7) peptide as a ligand for constructing tumor-targeting drug delivery systems. T7 could target to transferrin-receptor (TfR) through a cavity on the surface of TfR and then transport into cells via endocytosis with the help of transferrin (Tf). In this study, T7-conjugated poly(ethylene glycol) (PEG)-modified polyamidoamine dendrimer (PAMAM) (PAMAM-PEG-T7) was successfully synthesized and further loaded with doxorubicin (DOX), formulating PAMAM-PEG-T7/DOX nanoparticles (NPs). In vitro, almost 100% of DOX was released during 2 h in pH 5.5, while only 55% of DOX was released over 48 h in pH 7.4. The cellular uptake of DOX could be significantly enhanced when treated with T7-modified NPs in the presence of Tf. Also, the in vitro antitumor effect was enhanced markedly. The IC(50) of PAMAM-PEG-T7/DOX NPs with Tf was 231.5 nM, while that of NPs without Tf was 676.7 nM. T7-modified NPs could significantly enhance DOX accumulation in the tumor by approximately 1.7-fold compared to that of unmodified ones and by approximately 5.3-fold compared to that of free DOX. For in vivo antitumor studies, tumor growth of mice treated with PAMAM-PEG-T7/DOX NPs was significantly inhibited compared to that of mice treated with PAMAM-PEG/DOX NPs and saline. The study provides evidence that PAMAM-PEG-T7 can be applied as a potential tumor-targeting drug delivery system. T7 may be a promising ligand for targeted drug delivery to the tumor.

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This work provides a practical non-viral gene vector for long-term gene therapy of chronic neurodegenerative disorders.