PRECLINICAL TESTING OF RECOMBINANT ADENOVIRAL HERPES-SIMPLEX VIRUS THYMIDINE KINASE GENE-THERAPY FOR CENTRAL-NERVOUS-SYSTEM MALIGNANCIES

OBJECTIVES: Adenoviral gene transfer and killing efficiency using the thymidine kinase (TK)/ganciclovir (GCV) mechanism was evaluated in hum an cancer cells occurring as central nervous system tumors. The effect iveness of this approach was tested in vitro and in experimental model s for brain tumor and leptomeningeal metastases in rats in vivo. Recom binant adenoviruses with different promoters were compared. METHODS: A denoviral vectors harboring a marker (lacZ) or a TK gene were construc ted. Transcription of genes was under the control of either the adenov irus Type 2 major late promoter (MLP) or the human cytomegalovirus (CM V) immediate early gene promoter. lacZ expression and GCV killing effi ciency after TK gene transfer in several human tumor cells was evaluat ed in vitro. The 9L rat brain tumor and leptomeningeal metastases mode ls were used to determine the effectiveness of adeno-TK and subsequent GCV treatment in vivo. MLP and CMV containing adenoviral vectors were compared. RESULTS: Gene expression and the killing of tumor cells wer e very efficient in all human tumor cell lines tested. The adenovirus containing the CMV promoter showed cytopathic effects in cultured tumo r cells at high multiplicity of infections but also greater cell killi ng efficiency after TK/GCV treatment, as compared to the MLP promoter. Although both the MLP and CMV vectors showed a significant dose-depen dent therapeutic effect, animals treated with recombinant adenovirus c ontaining the CMV promoter showed significantly longer survival time ( brain tumors) or symptom-free periods (leptomeningeal metastases). CON CLUSION: This study demonstrates the therapeutic efficiency and feasib ility of the TK/GCV approach in experimental brain tumors and leptomen ingeal metastases. It also demonstrates that the promoter driving the transgene in an adenoviral vector influences toxicity and efficiency o f treatment.