A murine model for retroperitoneal neuroblastoma was established with viable neuroblastoma cells. A green fluorescent protein (GFP—Clontech, Palo Alto, CA) gene was inserted into our attenuated Salmonella species via electroporation. Fourteen days after retroperitoneal injection, the Salmonella typhimurium-pGFP construct was administered and studied. In separate experiments, the antitumor effect against neuroblastoma was studied in controls, Salmonella lacking an interleukin 2 (IL-2) gene (Sal-NG), and Salmonella containing an IL-2 gene (Salmonella-pIL2).
Consistent with previous reports, 74 % of mice injected were found to have recognizable tumors. Salmonella was present within tumor cells. Average tumor volumes for control, Sal-NG, and Salmonella-pIL2 mice were 2024.3, 749.5, and 332.4 mm3, respectively (P < .0001). Tumor weights for control, Sal-NG, and Salmonella-pIL2 mice were 2.218, 0.880, and 0.377 g, respectively (P < .0001).
Attenuated Salmonella species can now be tracked via fluorescent microscopy within tumor cells. Furthermore, an 84 % reduction in tumor burden was observed in those animals gavage fed Salmonella with the IL-2 gene.