Adenovirus-mediated prodrug-enzyme therapy for CEA-producing colorectal cancer cells

Carcinoembryonic antigen expression is increased in more than 80% of patients with colorectal cancer. Values are especially higher in patients with advanced stage disease. Virus directed prodrug/enzyme therapy (VDEPT) using genetically engineered viral vectors has been considered as one of the more notable cancer gene therapies for the transduction of various enzymes into cancer cells. We made adenovirus vectors under the control of a CEA promoter that included the HSV-tk gene and investigated its usefulness to specifically target human CEA-producing colorectal cancer cells.

An adenovirus vector with the lacZ or HSV-tk gene under the control of a CAG or CEA promoter was designed for the VDEPT experiment. Human colorectal cancer cell lines were used for in vitro experiments to assure the transduction efficacy of the inserted genes by these vectors. To conduct the in vivo experiment, liver metastases of the cell line were created in CB17 SCID mouse. We then performed intrasplenic injections of adenovirus vectors and intraperitoneal injections of the prodrug, ganciclovir.

RCM-1, the CEA-producing human rectal cancer cell line, was more strongly stained by X-gal staining. Furthermore, COLO320 was faintly stained secondary to a shortage of CEA production. The in vivo VDEPT experiment with RCM-1 and the adenovirus vector driven by the CEA promoter revealed attenuation of liver metastases in the treatment group.

Adenovirus vectors under the control of the CEA promoter can transduce inserted genes effectively into targeted human colorectal cancer cells according to the amount of expressed CEA protein. We anticipate the future use of VDEPT of the HSV-tk/GCV system using this vector in the treatment of advanced colorectal cancers.