TRANSDUCTION OF CYTOSINE DEAMINASE GENE MAKES RAT GLIOMA-CELLS HIGHLYSENSITIVE TO 5-FLUOROCYTOSINE

To investigate the potential use of E. coil cytosine deaminase (CD) ge ne instead of the commonly used HSV-TK gene in the gene therapy of bra in tumors, we constructed a retrovirus vector carrying the CD gene, We then transduced a rat glioma cell line C6 with CD gene by the retrovi rus vector. Transduction of the CD gene made C6 cells become highly se nsitive to the anti-fungi drug 5-fluorocytosine (5FC). IC50 for 5FC wa s 6,000 mu M in CD-negative cells, while it was 3 mu M in CD-positive cells. Mixed cellular assay showed that CD-positive cells had a strong ''bystander effect'' on CD-negative cells when exposed to 5FC. Signif icant anti-tumor effects were observed in nude mice bearing s.c. tumor s derived from CD-positive cells when these animals were given 250 mg/ kg 5FC twice a day for 20 consecutive days. A marked decrease in tumor weight occurred when a mixture containing 50% CD-positive and 50% CD- negative C6 cells was injected s.c., followed by 5FC treatment, sugges ting the bystander effect in vivo, Concerning the pharmacokinetics of 5FC, especially its high oral bio-availability and good penetration in to cerebrospinal fluid, we suppose that the combination of CD-gene tra nsfer and 5FC oral administration may have potential use in the gene t herapy of brain tumors. (C) 1997 Wiley-Liss, Inc.