Search

5-Flucytosine (5-FC) could be changed to 5-fluorouracil (5-FU) by cytosine deaminase (CD), the latter is able to kill cancer cells. However, there is no efficient method to deliver the CD gene into the tumor cells, which hampers the application of the suicide gene system. In this experiment, for the first time, the NDV has been utilized as a vector to deliver the CD gene into the cancer cells, the virus can infect the cancer cells specifically, replicate and assemble, while the cytosine deaminase is expressed. Then the CD converts the prodrug 5-FC into 5-FU to achieve the purpose of inhibiting tumor. Firstly, the whole genome of E. coli JM109 was extracted, and the CD gene was obtained by cloning method. Then the CD and IRES-EGFP were ligated into the pEE12.4 expression vector to become a recombinant pEE12.4IE-CD eukaryotic expression plasmid. The human liver cancer cells were transfected with the plasmid. The cells were treated with different concentrations of 5-FC, MTT method was used to determine the killing effect of CD/5-FC system on the human liver cancer cells. The cell deaths were 18.07%, 42.98% and 62.20% respectively when the concentrations of prodrug were at 10, 20 and 30 mmol x L(-1). In 5-FC acute toxicity experiment, Kunming mice were injected with different concentrations of 5-FC at intervals of 1:0.5. The LD50 of 5-FC through iv injection was determined by improved Karber's method, the LD50 was 507 mg x kg(-1) and the 95% confidence limit was 374-695 mg x kg(-1). According to the maximum LD0 dose of the LD50, the maximum safe dose was 200 mg x kg(-1). Body weight and clinic symptoms of the experimental animals were observed. These results laid the foundation to verify the antitumor effect and safety of CD/5-FC system in animal models. The CD gene was ligated into the NDV (rClone30) carrier, then the tumor-bearing animal was established to perform the tumor inhibiting experiment. The result showed that the recombinant rClone30-CD/5-FC system has a high antitumor activity in vivo. To summarize, CD gene has been cloned and its bioactivity has been confirmed in the mammalian cells. It is the first time in this study to utilize the recombinant NDV to deliver the CD gene into the tumor cells; our result proves the rClone30-CD/5-FC system is a potential method for cancer therapy.

Objective: To investigate the killing effects of cytosine deaminase/5-fluorocytosine (CD/5-FC) suicide gene therapy system on human malignant glioma cells in vitro., Methods: The pCMVCD plasmid was transfected into the U251 human malignant glioma cells using Lipofectamine 2000-mediated method. Resistant clones (named U251/CD cells) were isolated by screening with G418 presence. U251/CD cells were incubated with 5-FC in different concentrations to determine the number of viability cells (or cytotoxicity assay), and measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The concentrations of 5-fluorouracil (5-FU) in the media were measured by the high-performance liquid chromatography (HPLC) analysis., Results: The untreated U251 cells were insensitive to 5-FC, with the IC50 about 6 500 micromol/L. After the transfection, the IC50 was dramatically reduced to about 10 micromol/L. Therefore, gene transfection made G418-resistant clones (U251/CD cells) highly sensitive to 5-FC. HPLC analysis showed that 5-FU was detected in U251/CD cell medium., Conclusion: The killing effects of U251 cells modified by CD gene were induced by 5-FC, and the CD/5-FC system was feasible to treat glioma.

Objective: To elucidate the killing activity of yeast cytosine deaminase/5-fluorocytosine (YCD/5-FC) gene therapy system on gene-transferred tumorigenic cell line K562B in vivo., Method: K562B cell was infected with high titer virus and a gene transferred cell clone, YCD-K562B, was selected. Twelve male SCID mice of 4 week old were divided into 2 groups at random and both YCD-K562B and K562B cells were implanted to each mice. 5-FC or saline was given i. p for 10 days after tumor developed, and relative tumor volume was measured every 3 days. At the end of experiment, animals were sacrificed and the specimens were processed for histopathological examination., Results: At the end of experiment (21 days after tumor cell implantation), the relative tumor volume of the 4 groups were: YCD-K562B + 5-FC 2.922 +/- 0.581, YCD-K562B + saline 24.434 +/- 4.790, K562B + 5-FC 22.701 +/- 2.350 and K562B + saline 24.460 +/- 1.670; t-test analysis showed that 5-FC could kill cells (YCD-K562B) in vivo (P = 0.0001), but had no effect on the growth of gene-untransferred cells (K562B) (P = 0.096). In YCD-K562B + 5-FC group, relative tumor volume reduced in 3 approximately 6 days after treatment (the minimum was 0.681). Necrosis around artery could be found in the tumor of YCD-K562B + 5-FC group., Conclusion: YCD/5-FC suicide gene therapy system has a significant in vivo killing activity to gene-transferred tumorigenic YCD-K562B cell.