Timing and Targeting of Cell-Based VEGF¹⁶⁵ Gene Expression in Ischemic Tissue

Background: Therapeutic angiogenesis has become a key technology in experimental and clinical medicine. Only few data are available on the effects of timing and targeting of therapeutic proteins after cell-based gene transfer. This work investigates such effects after temporary expression of vascular endothelial growth factor 165 (VEGF¹⁶⁵), the most commonly used angiogenic protein for therapeutic purposes. Methods: We established a cell-based gene-transfer model using fibroblasts to temporarily produce VEGF¹⁶⁵. Cells were implanted into 40 rats. Protein expression and angiogenic effects were measured by PCR, immunohistology, and microangiography. To determine an improvement for survival of ischemically challenged tissue, cells were implanted in an ischemic flap model at different locations and time points. Results: After implantation of modified cells, a temporary increase was found in the target tissue for VEGF¹⁶⁵, endothelial cell counts, and capillary network formations. Four wk later, histological alterations in the target tissue area were not different from controls. Implantation of modified cells into flap plus wound margin 1 wk before surgery showed significant improvement of tissue survival demonstrated by planimetric measurements and blood vessels counting in the target tissue. Conclusion: In our model, temporary expression of VEGF¹⁶⁵ induces therapeutically relevant angiogenesis and improves blood supply only if applied 1 wk before ischemia. It is essential to include the surrounding area for induction of angiogenesis in this model. In contrast, the angiogenic effects are not effective in the target area and its surrounding tissue, if therapeutic gene expression is started during onset of ischemia or 2 wk before ischemia in this model.