INDUCED EXPRESSION OF THE CONDITIONALLY CYTOTOXIC HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE BY MEANS OF A PARVOVIRAL REGULATORY CIRCUIT

As a step toward the achievement of targeted expression of toxic genes , we have established a model system using the selective trans-activat ion of the late promoter P-38 of Minute Virus of Mice (MVMp) by the pa rvoviral nonstructural protein NS-1. The conditionally toxic herpes si mplex virus type 1 thymidine kinase (tk) gene (HSV1-tk) was cloned und er the control of the P-38 promoter and transfected into NIH-3T3 TK- c ells. Treatment of the stably transfected cells with acyclovir (ACV) f ollowed by infection with MVMp reduced cell survival by 3.5- to 5-fold compared to the toxic effects of ACV or MVMp alone. These results ind icate that it should be possible to combine the genuine cytopathic act ion of parvoviruses with a specific activation of toxic genes driven b y parvoviral promoters, to achieve the targeted destruction of parvovi rus-expressing (in particular tumor) cells.