Regression of experimental brain tumors with 6-thioxanthine and Escherichia coli gpt gene therapy.
The identification of transgenes with antitumor activity is critical to the development of gene therapy of cancer. Retrovirus-mediated transfer of the Escherichia coli gpt gene into rat C6 glioma cells without subsequent selection still inhibited the proliferation of this mixed polyclonal population upon addition of the prodrug, 6-thioxanthine, with an ID50 of 4.1 microM, whereas parental C6 cells were not affected at a concentration of 500 microM. In a time-course assay, effects of the prodrug on the mixed polyclonal cell proliferation required at least 10 days of exposure. In mixed co-cultures, a bystander effect was not present over the first 4 days of prodrug exposure, but required trypsinization of the co-cultures and replating at lower densities. This "modified" bystander assay thus revealed a 50% decrease in C6 cell proliferation, even when the initial ratio of gpt-expressing to parental C6 cells was as low as 1:19. In a nude mouse model of subcutaneous tumors, co-grafts of C6 glioma and gpt-retrovirus producer cells displayed retarded growth upon exposure to 6-thioxanthine (6-TX). In a nude mouse model of intracerebral tumors, grafting of the gpt-retrovirus producer cells leads to an 80% reduction in intracerebral tumor volumes after 6-TX treatment. This reduction results in a 28% increase in the mean time of survival of animals that harbor intracerebral tumors (p < 0.0005). These antitumor effects indicate that the gpt/6-TX enzyme/prodrug pair is a promising alternative to the thymidine kinase gene and ganciclovir combination in the gene therapy of cancer.
Ono
Y
Y
Department of Surgery & Molecular Neurooncology Laboratory, Massachusetts General Hospital, Boston 02114, USA.
Ikeda
K
K
Wei
M X
MX
Harsh
G R
GR
Tamiya
T
T
Chiocca
E A
EA
D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use* / Q000633:toxicity; D001932:Brain Neoplasms / Q000188:drug therapy / Q000628:therapy*; D004195:Disease Models, Animal; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005069:Evaluation Studies as Topic; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D005910:Glioma / Q000188:drug therapy / Q000628:therapy*; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D011355:Prodrugs / Q000627:therapeutic use*; D014407:Tumor Cells, Cultured; D014970:Xanthines / Q000627:therapeutic use* / Q000633:toxicity
D000964:Antimetabolites, Antineoplastic; D011355:Prodrugs; D014970:Xanthines; C054700:6-thioxanthine; D007041:Hypoxanthine Phosphoribosyltransferase