| Podophyllotoxin (PPT) is a natural aryltetralin lignin isolated from plant of podophyllum. Recent studies have shown that PPT and its derivatives have significant antitumor and antiviral properties. PPT is used as the lead compound for the synthesis of the well-known anticancer agents including etoposide and teniposide, which show good clinical effects against Wilms tumors, genital tumors, lung cancers and non-Hodgkin lymphomas. Compared to its derivatives, PPT has higher antitumor activity and broader antitumor spectrum. However, the possible clinical utility of PPT as an antitumour agent has been abandoned because of its water insolubility and side effects. Targeted drug delivery system allows chemotherapeutic drugs selectively concentrated in the cancer tissue through appropriate nanocarrier, which provides an important approach to improve bioavailability and clinical efficacy of similar compounds with PPT. In our study, we used two targeted drug delivery systems to investigate the antitumor application of PPT. It is expected that these systems are suitable for the potential compounds with similar characteristics. The details were as follows:(1) Functionalized graphene nanocarrier to deliver PPT via physical adsorption:PPT was loaded on chemically modified graphene by physical adsorption which has become a hot spot of research at the interlace of na note chno logy and biomedicine. Firstly, GO was prepared via modified Hummer’s method. In order to improve its water solubility and biocompatibility, 6-armed PEG with amine end groups was grafted onto GO via an amidation process. The successful synthesis of PEGylated graphene oxide (GO-PEG) nanocarrier was confirmed by Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). TGA data indicated there are 52.7 wt% of PEG in GO-PEG. By dynamic light scattering (DLS) and atomic force microscopy (AFM), the size distribution of the nanoparticles were shown to be 60-200 nm. The size was suitable for using as a drug carrier according to the enhanced permeability and retention (EPR) effect. Cytotoxicity assay of empty carrier demonstrated that GO-PEG did not show obvious toxicity (relative cell viability>90%) even at high concentration of 25 mg/L, Furthermore, a complex by loading PPT onto GO-PEG (GO-PEG/PPT) via π-π stacking and hydrophobic interactions was investigated. The drug loading ratio was determined to be 10%. It was demonstrated that GO-PEG/PPT showed remarkably high cytotoxicity compared to free PPT in both the human cervical adenocarcinoma HeLa cell line and human hepatoma SMMC-7721 cell line.(2) Targeted tumor cells release (GSH-sensitive) drug delivery system:Based on the high tumor GSH concentration environment, we have conjugated PPT with a dicyanomethylene-4H-pyran derivative as the NIR fluorophore via a GSH cleavable disulfide linker to obtain prodrug (DCM-S-PPT). Firstly, we characterized the structure of DCM-S-PPT via1H NMR spectrum,13C NMR spectrum and HRMS spectrum. In vitro experiments indicated that GSH can active DCM-S-PPT resulting in the PPT release and concomitantly significant NIR fluorescence turn-on at 665 nm (five-fold). The cytotoxicity experiment showed reduced cytotoxicity for prodrug and the extra GSH can recover the toxicity to the free PPT levels. It indicated that intracellular GSH can also activate DCM-S-PPT leading to release of PPT and exhibit fluorescence. The fluorescence can be used for cell imaging. DCM-S-PPT has been successfully utilized for in situ tracking of drug release in living animals by NIR fluorescence. After being intravenously injected into tumor-bearing nude mouse, DCM-S-PPT exhibited excellent tumor-activatable performance. Furthermore, we have demonstrated that mPEG-DSPE as nanocarrier loading with DCM-S-PPT (mPEG-DSPE /DCM-S-PPT) showed even higher tumor-target performance than DCM-S-PPT owing to EPR effect. |
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