Anti-tumoral Effect of Recombinant Vaccinia Virus through US Guided Injection in a Rabbit Model of Hepatic VX2 Carcinoma

ABSTRACT

PURPOSE: The purpose of this study was to evaluate the anti-tumoral effect of recombinant vaccinia virus (rVV) (Thymidine kinase (-)/GM-CSF (+)) that was administered as a US guided intratumoral injection in a rabbit model of hepatic VX2 carcinoma. MATERIALS AND METHODS: VX2 carcinoma was implanted in the livers of 12 rabbits. US was performed at every week interval to detect hepatic mass after the implantation of VX2 carcinoma. The accurate tumor size and volume was evaluated with CT when the tumor was detected on US. US guided injection of rVV (109 pfu/ml) was preformed in three rabbits, intravenous injection of the same dose of rVV was done in two rabbits and another seven rabbits that were without any treatment were selected as a control group. We evaluated the change of the hepatic tumor size and extrahepatic metastasis on serial CT. Tumor specimens were harvested from rabbits that were killed at 8 weeks after VX2 implantation. These tissues were histoimmuopathologically compared to each other (the virus injection group and the control group). The differences between these groups were statistically assessed with student t-tests. RESULTS: Tumor growth was significantly suppressed in the US guided injection group compared with the intravenous injection group or the control group (p< 0.01). The intravenous injection group showed statistically significant tumor suppression compared to the control group (p< 0.01) until 2 weeks after virus injection. Quantification of the pulmonary metastatic nodules was performed in view of both the number and volume. The average number or volume of the pulmonary metastatic nodules in the US injection group was much smaller than these in the control group. Histopathologically, the tumors of the US guided injection group showed less extensive necrosis than those of the control group. Immunohistochemically, the tumor of the US guided injection group showed more prominent infiltration of CD4 (+) and CD8 (+) lymphocytes than did the tumors of the other group. CONCLUSION: rVV was markedly effective in suppressing hepatic tumor growth and extrahepatic metastasis in a rabbit model of hepatic VX2 carcinoma. US guided intra-tumoral injection was more effective than systemic intravenous injection.