Specific tumor-cell killing with adenovirus vectors containing the apoptingene

Specificity is an essential prerequisite for cancer gene therapy Recently w e described that apoptin, a protein of 121 amino acids which is derived fro m the chicken anemia virus, induces programmed cell death or apoptosis in t ransformed and malignant cells, but not in normal, diploid cells (Danen-van Oorschot AAAM et al, Proc Natl Acad Sci USA 1997; 94: 5843-5847). This pro tein has an intrinsic specificity that allows if to selectively kill tumor cells, irrespective of the p53 or Bcl-2 status of these cells. Hence, it is attractive ive to explore the use of the apoptin gene for therapeutic appl ications, viz cancer gene therapy. In this paper, we describe the generatio n and characterization of an adenovirus vector, AdMLPvp3 for the expression of apoptin. Despite the fact that apoptin ultimately induces apoptosis in the helper cells, which are transformed by the adenovirus type 5 early regi on I (El), the propagation kinetics and yields of AdMLPvp3 are similar to t hose of control vectors. Infection with AdMLPvp3 of normal rat hepatocytes in cell culture did not increase the frequency of apoptosis. in contrast, i n the hepatoma cell lines HepG2 and Hep3b, infection with AdMLPvp3! but not with control vectors, led to a rapid induction of programmed cell death. E xperiments in rats demonstrated that AdMLPvp3 could be safely administered by intraperitoneal, subcutaneous or intravenous injection. Repeated intrave nous doses of AdMLPvp3 were also well tolerated, indicating that the apopti n-expressing virus can be administered without severe adverse effects. In a preliminary experiment, a single intratumoral injection of AdMLPvp3 into a xenogeneic tumor (HepG2 cells in Balb/C-nu/nu mice) resulted in a signific ant reduction of tumor growth. Taken together, our data demonstrate that ad enovirus vectors for the expression of the apoptin gene may constitute a po werful tool for the treatment of solid tumors.