Experimental Study Of Ionizing Radiation Combining Liposome-mediated Cytosine Deaminase Gene Delivery On The Treatment Of Rectal Cancer

Despite advances in both diagnosis and treatment, the annual numuber of rectal cancer -related deaths has not decreased during the past 60 years. The limitation of conventional cancer therapy derives from the imitis on their inability to ablate cancer without excessively damaging the patien. So improving the effectiveness of a treatment is of no clinical value if there is no significant increase in differential response between tumor and normal tissue. Thereby cytosine deaminase (CD) gene, one of the suicide genes, is becoming a hotspot for the cancer trerapy.However, the safety and the transfection efficiency are two very important puzzles faced by gene trepapy. Our research is to slolve these problems. Objective To investigate the effect of ionizing radiation on liposome-mediated gene delivery and the radiosensitization of CD/5-FC. If the two effects can be observed, we also want to eximine whether liposome-mediated CD gene delivery repeatedly combining radiation therapy can enhance killing of rectal cancer HR-8348 cells xenografts in nude mouse. Methods (1)Prior to liposome transfection, HR-8348 cells were irradiated at doses of 0,2,4,8Gy selected according to the surviving fraction line of HR-8348 cells after different dosage of radiation. After 36 hours of liposome transfection, green fluorocytes were counted. The transfection efficiency was figured out and compared with each other. (2) After lipofectin transducted CD gene into HR-8348 cells and exposed to 5-FC 100ug/ml for 72h, the cells were irradiated at the dose of 2Gy, a dosage often used by clinician. Flowcytometry monitored the ratio of apoptosis after irradiation for 72h. (3) HR-8348 cells were used as xenografts in nude mouse. Tumors were delivered with liposome-mediated CD gene repeatedly (at the day of 0, 4, 8, 12 ) and treated with fractionated radiation at a dose of 2Gy/day to a total dose of 30Gy. At the same time, mice were injected i.p.with 800mg/kg/day of 5-FC for 12 days. Three control groups, blank control, radiation only and CD/5-FC only, were set up respectively. Ten mice are in each group. Results (1)The transfection efficiency of liposome-mediated gene delivery was 34.91%,62.17%,68%,77.78% at the dosage of 0,2,4,8Gy respectively. The more of the dosage of the irradiation, the more is the transfection efficiency. The combination of radiation and liposome-mediated gene delivery can achieve the approximate transfection efficiency of virus vector. (2) The ratio of apoptosis of the blank control, radiation only, CD/5-FC and CD/5-FC plus radiation were 0.72%, 6.22%, 11.82%, 29.21% respectively. The tumors grew very slowly and tumors regression reached to 78.69% of the weight of the blank control and 81.5% of the volume of the blank control. Conclusion Ionizing radiation can improve the transfection efficiency of liposome-mediated gene delivery markedly .CD/5-FC has the effect of radiosensitization. The results suggest the combination of CD/5-FC and radiation therapy lead to pronounced anticancer effect without any notable toxicity.