Introduction: Spatially restricted gene expression circumvents the gene expression and gene vector problem by enabling localized amplification. The objective of this study is to construct a spatially restricted gene expression for liver cancer therapy based upon the MFH-absorbing properties of PEI- Mn_0.5zn_0.5Fe₂o₄, gene therapy and radiation.
Methods: Mn_0.5zn_0.5Fe₂O₄ (MZF) magnetic nanoparticles were prepared by an improved chemical co-precipitation method, modified by polyethylene imine (PEI), and then the structure, modification characters, biocompatibility, temperature rise and control ability and binding efficiency of the plasmid were characterized. Then, the dual-promoter plasmid PCDNA3.1-EGR1-HSP70-HSVTK was constructed. The recombinant vectors were identified by enzyme digestion analysis and DNA sequencing. The TK gene expression level was detected by realtime-PCR assay in HEK293 cells. Also, the HSV-TK gene expression was detected in SMMC7721 cells with the help of PEI-Mn_0.5Zn_0.5Fe₂O₄. In vitro anti-tumor experiment, MTT assay and flow cytometry were used to evaluate the therapeutic effects of the cultured SMMC7721 cells treated by different ways. In vivo anti-tumor experiment, the xenografted mice were treated by different ways for three times to detect the antitumor effect.
Results: The Mn_0.5Zn_0.5Fe₂O₄ magnetic nanoparticles could be successfully prepared through improved co-precipitation process and showed good biocompatibility. And PEI had been coated on MZF complex. The modified PEI-MZF presented favorable dispensability, responsibility to magnetism, good loading capability and transfect capability. Also, pCDNA3.1-Egr1-Hsp70-HSVTK plasmid had been constructed successfully and could be induced by heat and irradiation. It would be used for further target gene therapy research. The antitumor results in vitro showed: The therapeutic effects of nanosized PEI-MZF-HSV-TK complex could significantly inhibit the proliferation of cultured liver cancer cells (SMC7721), induce cell apoptosis and had a prominent cell cycle disturbance in the S phase in vitro. The results in vivo showed: The combined therapy induced by PEI-MZF-HSV-TK could inhabit the growth of hepatocellular carcinoma xenografts by killing and inhabiting the proliferation of the tumor cells.
Conclusion: The novel site-directed heat/radiation-inducible expression system based upon the hyperthermia (by MFH) and radiation possessed superior antitumor effect in vivo and in vitro.
Keywords: radiation, magnet-induced heating, dual sensitive, magnetic nano vector