The application of adenoviral molecular chemotherapy for systemic malignant disease using herpes simplex virus thymidine kinase has been limited by ectopic transgene expression in the liver due to the vector hepatotropism. The aim of this study was to mitigate this hepatotoxicity using the promoter of cyclooxygenase-2, inactive in liver but active in many gastrointestinal cancers. To analyze the specificity of transgene expression driven by cyclooxygenase-2 (cox-2) promoters, promoters of two different lengths were incorporated into adenoviral vectors to drive luciferase expression. The specific cytocidal effect and in vivo toxicity were analyzed with thymidine kinase expression vectors. The specificity of the cox-2 promoter was well preserved in the adenoviral vector. In vivo, the cox-2 promoter (-1432/+59) showed very little activity in the liver but attained high activity, comparable to that of the cytomegalovirus promoter, in cyclooxygenase-2-positive subcutaneous tumors. The cox-2 promoter-driven thymidine kinase-expressing vectors showed a cytocidal effect specifically in cyclooxygenase-2-positive cells. When mice were treated with the thymidine kinase-expressing vector and ganciclovir, the cox-2 promoter successfully mitigated the fatal hepatotoxicity, which was observed with the cytomegalovirus promoter-driven vector. The cox-2 promoter successfully mitigated the adverse effects of adenoviral suicide gene therapy by minimizing transgene expression in the liver.
Bibliographical noteFunding Information:
This work was supported by grants from the National Institutes of Health (N01-CO-97110, R01 CA74242-04, R01 CA68245-01, R01 CA83821), the Juvenile Diabetes Foundation International, and the Cap Cure Research Award. The authors thank Drs. H. Inoue and T. Tanabe of the National Cardiovascular Center Research Institute, Suita, Japan, for providing plasmid phPES2 containing the cox-2 promoter; Julia Davydova for excellent technical assistance; Drs Cristina Balague and Kaori Suzuki for excellent advice; and Drs. Joanne Douglas and Candace Coolidge for critically reading the manuscript.