DIRECT INTRATUMORAL GENE-TRANSFER OF THE HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE WITH DNA-LIPOSOME COMPLEXES - GROWTH-INHIBITION OF TUMORS AND LACK OF LOCALIZATION IN NORMAL-TISSUES

To constitute the site-specific expression of the herpes simplex virus thymidine-kinase (HSV-TK) gene in tumor cells, we have assessed the p romoter function of the simian virus 40 (SV40) promoter and the 5' fla nking region of c-erbB-2 gene using a luciferase-expressing reporter p lasmid. After the transfection of the luciferase plasmid directed by t he promoter region of c-erbB-2 gene, a large amount of luciferase acti vity was observed in c-erbB-2-expressing cells (Colo201, MCF-7, and HE C1-A), while none was detected in cells with no expression of c-erbB-2 protein (HRA and KF cells). On the other hand, a high level of lucife rase activity was detected in all tumor cell lines tested, when the tr ansfection was performed with SV40 promoter. The repeated transfection of the liposome-conjugated HSV-TK gene regulated by the SV40 promoter or by the promoter region of c-erbB-2 gene with cultivation in 100 mu g/ml of aciclovir for 5 days in vitro resulted in growth inhibition f or all four cell Lines examined or for only c-erbB-2-expressing cells in the presence of SV40 promoter or c-erbB-2 promoter, respectively. F inally, direct injection of the DNA-liposome complex into established tumors in the presence of 50 mg/kg of aciclovir led to significant tum or volume reduction in all three tumors tested when SV40 promoter was employed. However, this anti-tumor effect was noted only in c-erbB-2-p ositive cells (Colo201 cells) upon intratumoral injection of HSV-TK ge ne regulated by c-erbB-2 promoter. In the case of intratumoral gene tr ansfer, foreign DNA was detected in only one of seven mice by polymera se chain reaction (PCR) analysis performed 7 days following injection. When PCR analysis Has carried out at 14 or 21 days following injectio n, no DNA signal Has found at all. However, DNA was detected in severa l normal tissues at all three times tested in the case of intravenous injection. No abnormalities were seen in histologic examinations of no rmal tissues or in serum biochemical parameters following DNA liposome delivery. These results suggest that the direct gene transfer of HSV- TK gene regulated by tumor-specific transcriptional units may be one o f the most clinically promising of the selective genetic strategies ag ainst cancer.