For most patients with malignant brain tumors conventional chemoradiotherapy is highly toxic and only prolongs survival by months. There is an urgent need for more effective and less-toxic treatment. This has contributed to the excessive optimism surrounding human gene therapy for these neoplasms. This optimism has overshadowed the need to bridge major gaps in knowledge about effects on tumor physiology and overcome the hurdle of developing suitable delivery systems. The goal of this application is to address these overlooked issues. The applicant's laboratory has developed and begun testing potent anti-oncogenic constructs. These are replication-defective adenoviruses that enable ectopic overexpression of myc-family oncogene antagonists (Mad, Mxil, and RepMax, a chimera containing the repression domain of MYC-antagonists linked to MAX) and cyclin dependent kinase inhibitors (CDKIs) p21 WAFI/CIPI and p27KIPI). These genes were chosen because they are both anti-proliferative and are well studied biochemically and at the cellular level in vitro. The hypothesis is that ectopic overexpression of these genes will inhibit proliferation of post-surgical microscopic residual malignant human brain tumor cells without damaging adjacent normal nondividing post-mitotic brain. The objective is to test this hypothesis by investigating the effects of these reagents on the physiology of normal brain and of malignant brain tumors in animal models. These in vitro studies are of primary importance since events that occur in cell culture do not necessarily reflect what happens in vivo. An integral part of this objective will be to optimize the adenoviral vector delivery system. This will be accomplished by: 1) refining the adenovirus system via incorporation of a tetracycline-repressible promoter system, reduction of immunogenicity, and the addition of glial tumor-specific promoter elements, 2) determining the effects of ectopic overexpression of these genes on normal brain, and 3) determining the effects of ectopic overexpression of these genes on brain tumor physiology in vivo using intracerebral brain tumor xenografts in both immunodeficient and immunocompetent animals.
