Therapeutic efficacy of the suicide gene driven by the promoter of vascular endothelial growth factor gene against hypoxic tumor cells

We examined whether herpes simplex virus thymidine kinase (HSV-TK) gene exp ression driven by the promoter of the vascular endothelial growth factor (V EGF) gene that is activated by hypoxia is effective in killing highly metas tatic Lewis lung carcinoma All cells under hypoxic conditions. We isolated the promoter region encompassing the hypoxia response element (HRE) of the mouse VEGF gene. To assess the hypoxia responsiveness of the VEGF promoter, All cells were transiently transfected with luciferase reporter plasmids, Exposure of the transfectants to hypoxia resulted in a 2-3-fold induction o f luciferase activity. Deletion of the HRE site abolished VEGF promoter act ivity under both normoxic and hypoxic conditions. We constructed a retrovir al vector harboring the HSV-TK or green fluorescence protein (GFP) gene und er the control of the VEGF promoter. All cells transfected with vector harb oring the VEGF promoter fused to the HSV-TK gene [A11(HRE/TK) cells] were m ore sensitive to ganciclovir than cells transfected with the control vector harboring the VEGF promoter alone, and the sensitivity of the A11(HRE/TK) cells was increased by exposure to hypoxia followed by reoxygenation, Cultu ring All cells transfected with vector harboring the VEGF promoter fused to the GFP gene under hypoxic conditions resulted in an increase in the expre ssion of GFP. Monitoring GFP expression and vascularity in the All transfec tant tumors revealed up-regulation of GFP expression in poorly vascularized regions. Administration of ganciclovir to mice bearing s.c. tumors formed by A11(HRE/TK) cells resulted in regression of the tumors. These results su ggest a possible application of the suicide gene driven by the VEGF promote r to cancer gene therapy that efficiently targets hypoxic tumor cells.