GENE-THERAPY FOR MALIGNANT GLIOMAS USING REPLICATION INCOMPETENT RETROVIRAL AND ADENOVIRAL VECTORS ENCODING THE CYTOCHROME-P450 2B1 GENE TOGETHER WITH CYCLOPHOSPHAMIDE

Cyclophosphamide is an inactive prodrug which is converted by hepatic cytochrome P450 2B1 to cytotoxic metabolites which produce interstrand DNA cross-linking in a cell cycle-independent fashion. The limited ab ility of these metabolites to cross the blood-brain barrier contribute s to the poor activity of cyclophosphamide against brain tumors. In th is study we demonstrate that replication deficient retroviral and aden oviral vector-mediated gene transfer of cytochrome P450 2B1 into 9L gl ioma cells significantly increases the sensitivity of these tumor cell s to cyclophosphamide in vitro, and prolongs the survival of animals b earing intracerebral 9L tumors treated with cyclophosphamide in vivo. Attempts to improve the effectiveness of retrovirally mediated transdu ction of the P450 2B1 gene by increasing the concentration cyclophosph amide delivered to the tumors using intracarotid and intratumoral inje ctions did not prolong animal survival, although survival was increase d when a second treatment with P450-expressing retroviral vectors and cyclophosphamide was administered These results suggest that in situ t ransduction of firmer cells with the P450 281 gene using retroviral an d adenoviral vectors increases their sensitivity to cyclophosphamide a nd may have a potential role in the therapy of malignant gliomas.