Int J Biol Sci 2010; 6(2):151-162. doi:10.7150/ijbs.6.151 This issue

Research Paper

Tumors Induced in Mice by Direct Inoculation of Plasmid DNA Expressing Both Activated H-ras and c-myc

Li Sheng-Fowler1, Fang Cai1,4, Haiqing Fu1,5, Yong Zhu1,6, Brian Orrison1, Gideon Foseh1, Don G. Blair2,7, Stephen H. Hughes2, John M. Coffin2,3, Andrew M. Lewis Jr1, Keith Peden1

1. Division of Viral Products, OVRR, CBER, FDA, Bethesda, MD 20892, USA
2. Frederick Cancer Research Facility, National Cancer Institute, Frederick, MD 21702, USA
3. Present address: Center for Drug Evaluation and Research, White Oak, MD, USA
4. Present address: National Cancer Institute, Bethesda, MD, USA
5. Present address: University of Texas, Galveston, TX, USA
6. Present address: National Institutes of Health, Rockville, MD, USA
7. Tufts University, Boston, MA 02111, USA

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Sheng-Fowler L, Cai F, Fu H, Zhu Y, Orrison B, Foseh G, Blair DG, Hughes SH, Coffin JM, Lewis Jr AM, Peden K. Tumors Induced in Mice by Direct Inoculation of Plasmid DNA Expressing Both Activated H-ras and c-myc. Int J Biol Sci 2010; 6(2):151-162. doi:10.7150/ijbs.6.151. Available from

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Vaccines contain residual DNA derived from the cells used to produce them. As part of our investigation to assess the risk of this cellular DNA, we are developing a quantitative in vivo assay to assess the oncogenicity of DNA. In an earlier study, we had generated expression plasmids for two oncogenes - human activated T24-H-ras and murine c-myc - and had shown that these two plasmids, pMSV-T24-H-ras and pMSV-c-myc, could act in concert to induce tumors in mice, although the efficiency was low. In this study, we took two approaches to increase the oncogenic efficiency: 1) both oncogene-expression cassettes were placed on the same plasmid; 2) transfection facilitators, which increase DNA uptake and expression in vitro, were tested. The dual-expression plasmid, pMSV-T24-H-ras/MSV-c-myc, is about 20-fold more efficient at tumor induction in newborn NIH Swiss mice than the separate expression plasmids, with tumors being induced with 1 µg of the dual-expression plasmid DNA. However, none of the transfection facilitators tested increased the efficiency of tumor induction. Based on these data, the dual-expression plasmid pMSV-T24-H-ras/MSV-c-myc will be used as the positive control to develop a sensitive and quantitative animal assay that can be used to assess the oncogenic activity of DNA.

Keywords: H-ras, c-myc, oncogenes