Methods: The structure of CRD-PEG-T7 was determined and the cellular uptake efficacy, gene transfection efficacy, cytotoxicity, and the targeting effect of the CRD-PEG-T7–plasmid DNA complex were examined. 

Results: The results demonstrated that the CRD-PEG-T7–plasmid DNA complex was nanosized and had a positively charged surface, good cellular uptake efficacy, minimal cytotoxicity, and a dual-targeting effect as compared with the CRD-PEG–plasmid DNA complex. The peptide T7-modifed new delivery system was able to target the highly expressed transferrin receptor (TfR) on tumor cells with an efficiency four-fold higher than that of the non-modified system. 
Conclusion: The results above indicatd that the CRD-PEG-T7–plasmid DNA complex may prove to be a promising gene delivery system targeting bone-metastatic tumor.
Keywords: arginine peptide, aspartic acid peptide, tumor targeting, DNA delivery, bone metastasis prostate cancer