Enzyme/prodrug gene therapy for human colon cancer cells using adenovirus-mediated transfer of the Escherichia coli cytosine deaminase gene driven bya CAG promoter associated with 5-fluorocytosine administration

Escherichia coli cytosine deaminase (CD), which is a prokaryotic enzyme, co nverts nontoxic prodrug 5-fluorocytosine (5-FC) into the toxic chemotherape utic agent 5-fluorouracil (5-FU). To investigate an enzyme/prodrug gene the rapy for colorectal cancer, using adenoviral gene transfer of the E. coli C D gene associated with administration of 5-FC, we constructed replication-d efective adenovirus vectors expressing the E. coli CD gene or lacZ gene dri ven by a CAG promoter (composed of a cytomegalovirus immediate early enhanc er and a chicken beta-actin promotor). The present study demonstrated that an adenoviral gene transfer system using a CAG promoter induced sufficient gene expression of CD to confer the cytotoxicity of 5-FC to HT29 human colo n cancer cells by converting it into 5-FU even at an moi of one. Furthermor e, experimental gene therapy using intratumoral injection of the CD-express ing adenovirus with systemical administration of 5-FC successfully suppress ed the growth of established HT29 subcutaneous tumors in nude mice. These r esults suggest that enzyme/prodrug gene therapy using the adenoviral gene t ransfer of the E. coli CD gene with concomitant administration of 5-FC may be an effective strategy in the local control of colorectal cancer.