APOPTOSIS BY RETROVIRUS-MEDIATED AND ADENOVIRUS-MEDIATED GENE-TRANSFER OF FAS LIGAND TO GLIOMA-CELLS - IMPLICATIONS FOR GENE-THERAPY

Astrocytic tumors frequently express Fas/APO-1 (Fas), in sharp contras t to surrounding normal brain cells, providing a potential window thro ugh which selective killing of tumor cells could be pursued. To assess this possibility, we transduced Fas into U251, a glioma cell line res istant to anti-Fas antibody-mediated apoptosis, and obtained transfect ants with high levels of Fas expression, Anti-Fas antibody showed sign ificantly enhanced cytotoxicity for the transfectants, suggesting that U251 cells maintained an intercellular cascade of Fas-mediated apopto sis. When U251 transfectants with high-level Fas expression were trans duced with Fas ligand-encoding gene via retrovirus, they were unaffect ed by exposure to anti-Fas antibody or Eas ligand adenovirus (Adeno-FL ). Thus, retroviral induction of Fas ligand into the glioma cells with high levels of Fas led to the selection of cells that were resistant to Fas-dependent apoptosis. These resistant U251 transfectants were su sceptible to FADD adenovirus (Adeno-FADD)-induced apoptosis, indicatin g that a cascade of death signals was blocked at the steps between Fas ligand and FADD. As for adenoviral transduction of Fas ligand into gl iomas, gliomas with a relatively high level of expression of Fas were remarkably sensitive to Adeno-FL-induced apoptosis. Besides, Adeno-FAD D induced pronounced apoptosis in all glioma cells. Our data suggest t he possibility of using adenovirus-mediated transduction of Fas ligand and FADD genes as a therapeutic approach to target gliomas.