CANCER GENE-THERAPY BY DIRECT TUMOR INJECTIONS OF A NONVIRAL T7 VECTOR ENCODING A THYMIDINE KINASE GENE

Previously, we described a nonviral cytoplasmic gene therapy vector sy stem based on the T7 autogene concept, This system has been shown to a chieve rapid and high levels of gene expression in a variety of animal cells and tissues, To test the utility of the system in vivo tumor ab lation, a T7 cancer gene therapy plasmid vector, pT7T7/T7TK, was const ructed, This nonviral vector contains a T7 autogene, T7T7, and a human herpes simplex virus thymidine kinase (HSV-TK) gene driven by a secon d T7 promoter (T7TK), When co-transfected with T7 RNA polymerase (T7 R NAP) into cultured human osteosarcoma 143B cells, abut 10-20% of the c ells were found to express HSV-TK, and more than 90% of the cells were killed in the presence of 1 mu M ganciclovir (GCV) within 4 days afte r DNA transfection. The increase in killing above the transfection fre quency is due to a ''bystander'' effect among transfected and untransf ected 143B cells, Direct injections of pT7T7/T7TK into 143B tumors gro wn in nude mice resulted in TK gene expression in tumor cells located near the injection sites as revealed by the immunohistochemical staini ng, Repeated tumor injections of the pT7T7/T7TK vector and intraperito neal (i.p.) injections of GCV resulted in inhibition of tumor growth a nd in tumor shrinkage in 6 out of 10 treated nude mice, Three of those six tumors fully regressed shortly after the end of the GCV injection s, All of the full tumor regressions were found to be permanent and no apparent tumor relapses were observed for the rest of the lives of th e treated nude mice after the initial tumor ablations, These results, combined with the nonviral and rapid cytoplasmic gene expression featu res, suggest that the T7 vector may be a good candidate for cancer gen e therapy and other medical and biological applications.