INHIBITION OF TUMOR-GROWTH BY DIRECT INTRATUMORAL GENE-TRANSFER OF HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE WITH DNA-LIPOSOME COMPLEXES

To establish the expression of the herpes simplex virus thymidine kina se (HSV-TK) gene in tumor cells, we analyzed the promoter function of the SV40 promoter and the nucleotide sequence (CACGTG) to which Myc-Ma x heterodimers (Myc/Max) were capable of binding in four kinds of cell lines: COLO320 DM, A-431, KF, and Nakajima. When luciferase reporter plasmid under the control of SV40 promoter was transfected into tumor cells in vitro, a high level of luciferase activity was observed in al l kinds of cell lines. However, by transfection of the luciferase gene promoted by the Myc/Max binding sequence, accelerated luciferase expr ession was observed in COLO320 DM and A-431 cells with high expression of c-myc, but not in KF and Nakajima cells, which showed low expressi on of c-myc. The repeated transfection of the liposome-conjugated HSV- TK gene regulated by the SV40 promoter and cultivation in 100 mu g/ml of aciclovir for 5 days in vitro demonstrated growth inhibition for al l four kinds of cell lines. However, cell toxicity was observed only i n COLO320 DM and A-431 cells when the HSV-TK gene promoted by the Myc/ Max binding sequence was introduced. (The survival rate to 100 mu g/ml of aciclovir concentration in COLO320 DM, A-431, KF, and Nakajima cel ls was 59%, 53%, 74%, and 79%, respectively.) In vivo direct injection of the liposome-conjugated HSV-TK gene regulated by the SV40 promoter into established tumors and aciclovir administration for 10 days into the mice resulted in significant tumor volume reduction in three test ed tumor cells. However, injection of the HSV-TK gene promoted by the Myc/Max binding sequence and aciclovir administration into mice could achieve significant tumor regression only in COLO320 DM and A-431 cell s. These results suggest that gene therapy using the HSV-TK gene promo ted by the Myc/Max binding sequence can be an attractive approach for treatment against tumor cells expressing high levels of c-myc.