Enzyme/prodrug gene therapy: comparison of cytosine deaminase/5-fluorocytosine versus thymidine kinase/ganciclovir enzyme/prodrug systems in a human colorectal carcinoma cell line.
We have been developing an enzyme/prodrug gene therapy approach for the treatment of primary and metastatic tumors in the liver. This system uses the cytosine deaminase/5-fluorocytosine (CD/5-FCyt) enzyme/prodrug combination. Another system that has received considerable attention is the herpes simplex virus thymidine kinase/ganciclovir (HSV-TK/GCV) enzyme/prodrug combination. The purpose of the present study was to compare these two enzyme/prodrug systems. The human colorectal tumor cell line, WiDr, was genetically modified to express either the CD gene (WiDr/CD) or the HSV-TK gene (WiDr/TK). The IC50 (concentration of drug producing 50% inhibition of cell growth) for GCV was approximately 3.4 microM in WiDr/TK cells, while the IC50 for 5-FCyt was approximately 27 microM in WiDr/CD cells. In vivo antitumor studies were conducted using high but nontoxic levels of GCV (50 mg/kg/day) or 5-FCyt (500 mg/kg/day). When tumor xenografts were composed of 100% of cells expressing either HSV-TK or CD, 100% tumor-free animals were observed after GCV or 5-FCyt treatment, respectively. However, when only 10% of the tumor cells expressed HSV-TK, no antitumor effect by GCV treatment could be observed. In contrast, when tumors were composed of 4% of the cells expressing CD, 60% of the animals were tumor-free after 5-FCyt treatment. Transmission electron microscopy of the WiDr solid tumors revealed the presence of desmosomes but no gap junctions.
Trinh
Q T
QT
Division of Cell Biology, Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709, USA.
Austin
E A
EA
Murray
D M
DM
Knick
V C
VC
Huber
B E
BE
D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics / Q000627:therapeutic use*; D001483:Base Sequence; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D043525:Cytosine Deaminase; D004354:Drug Screening Assays, Antitumor; D005437:Flucytosine / Q000493:pharmacokinetics / Q000627:therapeutic use*; D015774:Ganciclovir / Q000493:pharmacokinetics / Q000627:therapeutic use*; D015316:Genetic Therapy; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009368:Neoplasm Transplantation; D009700:Nucleoside Deaminases / Q000235:genetics* / Q000378:metabolism*; D011355:Prodrugs / Q000493:pharmacokinetics / Q000627:therapeutic use*; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000235:genetics* / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000964:Antimetabolites, Antineoplastic; D011355:Prodrugs; D005437:Flucytosine; D013937:Thymidine Kinase; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase; D015774:Ganciclovir