Stereotactic delivery of a recombinant adenovirus into a c6 glioma cell line in a rat brain tumor model

THE DISMAL RESULTS of conventional therapy for primary malignant brain tumors has justified exploring gene therapy approaches for this disease. Transduction of animal brain tumor models in vivo has been reported previously with retroviruses and herpes viruses. Because adenoviruses have the advantage of transducing quiescent and actively dividing tumor cells, they may prove to be more effective in such therapy. We used a replication-deficient recombinant adenovirus bearing the Escherichia coli β-galactosidase gene in a rat C6 glioma tumor model. Transduced cells were detected by X-5-bromo-4-chloro-3-indolyl β-D-galactoside staining to reveal β-galactosidase activity. Initial experiments in vitro showed 50% and 90% transduction at vector titers of approximately 10⁷ and 10⁸ plaque-forming units/ml, respectively. Although no cytopathic effects were seen at 10⁷ plaque-forming units/ml, more than 50% reduction in tumor cell growth was noted at 10⁸ plaque-forming units/ml both in vitro and in vivo. Stereotactic delivery of the recombinant adenovirus into the frontal lobe of normal rat brains resulted in intense staining of all cell types, that is, neurons, astrocytes, and ependymal cells. Stereotactic injection into C6 glioma brain tumors in rats stained 25 to 30% of the tumor cells. We conclude that adenovirus vectors can be used to transfer genes to central nervous system tumors in vivo. Using stereotactic delivery, adenovirus vectors can transfer genes into the central nervous system intended for tumor therapy.