Tumor-targeting salmonella typhimurium A1-R inhibits osteosarcoma angiogenesis in the in vivo Gelfoam^® assay visualized by color-coded imaging

Background: We previously developed a color-coded imaging model that can quantify the length of nascent blood vessels using Gelfoam^® implanted in nestin-driven green fluorescent protein (ND-GFP) nude mice. In this model, nascent blood vessels selectively express GFP. We also previously showed that osteosarcoma cells promote angiogenesis in this assay. We have also previously demonstrated the tumor-targeting bacteria Salmonella typhimurium A1-R (S. typhimurium A1-R) can inhibit or regress all tested tumor types in mouse models. The aim of the present study was to determine if S. typhimurium A1-R could inhibit osteosarcoma angiogenesis in the in vivo Gelfoam^® color-coded imaging assay. Materials and Methods: Gelfoam^® was implanted subcutaneously in ND-GFP nude mice. Skin flaps were made 7 days after implantation and 143B-RFP human osteosarcoma cells expressing red fluorescent protein (RFP) were injected into the implanted Gelfoam. After establishment of tumors in the Gelfoam^®, control-group mice were treated with phosphate buffered saline via tail-vein injection (iv) and the experimental group was treated with S. typhimurium A1-R iv Skin flaps were made at day 7, 14, 21, and 28 after implantation of the Gelfoam^® to allow imaging of vascularization in the Gelfoam^® using a variable-magnification small-animal imaging system and confocal fluorescence microscopy. Results: Nascent blood vessels expressing ND-GFP extended into the Gelfoam^® over time in both groups. However, the extent of nascent blood-vessel growth was significantly inhibited by S. typhimurium A1-R treatment by day 28. Conclusion: The present results indicate S. typhimurium A1-R has potential for anti-angiogenic targeted therapy of osteosarcoma.