ABSTRACT
<p><b>OBJECTIVE</b>To study the effect of X-ray on gene transfer and the antitumoral effect of X-ray combined with suicide gene therapy on colorectal carcinoma cells.</p><p><b>METHODS</b>Green fluorescent protein (GFP) was seen under fluorescent microscope. GFP gene was used for reporting gene to learn gene transfer efficiency and gene expressing time under the influence of radiation. G418 was used to select cytosine deaminase (CD) positive neoplasm cells and CD gene transfer efficiency was tested by cloning efficiency. Antitumoral effect of X-ray combined with CD and 5-FC on colorectal carcinoma cells was tested by MTT.</p><p><b>RESULTS</b>4 Gy radiation could improve supercoiled plasmid DNA transfer efficiency for about 2 - 4 times and 30 times for linearized plasmid DNA. The mean durations of GFP gene expression treated with 4 Gy radiation were 14 d for supercoiled plasmid and 21 and for linearized plasmid, while in control group, the time was 12 d. Middle-dose radiation combined with CD and 5-FC could kill 99 percent of colorectal carcinoma cells, while in the control group, 5-FC only killed 15 percent of colorectal carcinoma cells which were transduced with CD gene.</p><p><b>CONCLUSIONS</b>X-Ray combined with suicide gene therapy may be used as a promising method for treating colorectal neoplasm.</p>