Suicide gene therapy consists of transferring into tumor cells a viral or bacterial gene encoding for an enzyme which converts a non-toxic product into a lethal drug.
Study aim: To analyze the therapeutic potential of vaccination with tumor cells expressing the bacterial cytosine deaminase (CD) gene and 5-fluorocytosine (5-FC) treatment in a rat liver metastasis model.
Material and method: We used a rat colon carcinoma cell line which, after subcapsular or intraportal injection in syngenic animals, generates single or multiple experimental liver metastases, respectively. We have shown that introduction of a vector expressing the CD gene in this colon carcinoma cell line results in 5-FC sensitivity (PRObCD).
Results: Intrahepatic subcapsular injection of PRObCD tumor cells, followed by 5-FC treatment, induces total regression of a wild-type tumor pre-established in the contralateral liver lobe in 45% of animals with a 96% decrease in mean volume (p < 0.0001), demonstrating the existence of a distant bystander effect. This vaccination significantly increased the survival of rats with single (log-rank p < 0.0001) or multiple (log-rank p = 0.01) liver metastasis
Conclusions: These results suggest that suicide gene-modified tumor cells can act as potent therapeutic vaccines against liver metastasis from colon carcinoma.