Immunogene approach toward cancer therapy using erythrocyte growth factor receptor-mediated gene delivery

In this article we describe an improved method to produce a conjugate of anti- erythrocyte growth factor (EGF) receptor monoclonal antibody with polylysine via thio-ether bonds. The resulting antibody/polylysine conjugate was found to be a much more stable DNA (gene) carrier than the previous conjugate formed via disulfide bonds. We designated the conjugate as an ''immunoporter'' and the immunoporter/DNA (gene) complex as an ''immunogene.'' The fluorescent microscopic observation showed that the immunoporter as well as immunogene bound specifically to the EGF receptors on the cell surface, and the loaded reporter gene, such as beta-galactosidase (P-GAL), was detected in the cell nucleus al 2 hours after transfection. The enzyme activity from the beta-GAL gene was detected at 12 hours and increased for 3 to 5 days. Similar kinetics were obtained for another reporter gene, chloramphenicol acetyltransferase. Furthermore, the immunoporter delivered the herpes simplex virus thymidine kinase gene and induced substantial suicide effects on tumor cells when gancyclovir or acyclovir was added. Thus, the immunogene approach was successful in delivering therapeutic genes to EGF receptor overexpressing tumor cells. Further technical refinement may prove useful as a supplementary treatment of patients with squamous cell carcinomas.