Characterization of the cyclooxygenase-2 promoter in an adenoviral vector and its application for the mitigation of toxicity in suicide gene therapy of gastrointestinal cancers

The application of adenoviral molecular chemotherapy for systemic malignant disease using herpes simplex virus thymidine kinase has been limited by ec topic transgene expression in the liver due to the vector hepatotropism. Th e aim of this study was to mitigate this hepatotoxicity using the promoter of cyclooxygenase-2 inactive in liver but active in many gastrointestinal c ancers. To analyze the specificity of transgene expression driven by cycloo xygenase-2 (cox-2) promoters, promoters of two different lengths were incor porated into adenoviral vectors to drive luciferase expression. The specifi c cytocidal effect and in vivo toxicity were analyzed with thymidine kinase expression vectors. The specificity of the cox-2 promoter was well preserv ed in the adenoviral vector. In vivo, the cox-2 promoter (-1432/+59) showed very little activity in the liver but attained high activity, comparable t o that of the cytomegalovirus promoter, in cyclooxygenase-2-positive subcut aneous tumors. The cox-2 promoter-driven thymidine kinase-expressing vector s showed a cytocidal effect specifically in cyclooxygenase-2-positive cells . When mice were treated with the thymidine kinase-expressing vector and ga nciclovir, the cox-a promoter successfully mitigated the fatal hepatotoxici ty, which was observed with the cytomegalovirus promoter-driven vector. The cox-2 promoter successfully mitigated the adverse effects of adenoviral su icide gene therapy by minimizing transgene expression in the liver.