Expression of thymidine kinase mediated by a novel non-viral delivery system under the control of vascular endothelial growth factor receptor 2 promoter selectively kills human umbilical vein endothelial cells

Figure 6 Fluorescent microscopy showed EGFP expression 48 h after pEGFP-KDR-TK transfection. A: Shows no obvious EGFP expression in cells without microbubbles and ultrasound (× 200); B: 1.7% cells exposed to ultrasound only shows EGFP expression (× 200); C, D: Significant increase in EGFP expression in HUVECs exposed to both the ultrasound and SonoVue (C: × 200, D: × 400). About 20.3% HUVECs had EGFP expression.