title: Gene-directed enzyme prodrug therapy: quantitative bystander cytotoxicity and DNA damage induced by CB1954 in cells expressing bacterial nitroreductase.
abstract: Clones of human colon carcinoma (WiDr), ovarian carcinoma (SK-OV-3), and Chinese hamster V79 cells expressing the nitroreductase enzyme (NR) from E. coli B were 52-, 225- and 177-fold respectively more sensitive to a 24-h incubation with the prodrug 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB1954) than the parent lines. The IC50s of non-NR-expressing bystander cells were measured in the presence of differing proportions of NR-expressing cells. The shift in IC50 was used to calculate a value for the bystander effect, termed the transmission efficiency (TE), which is the decrease in IC50 due to bystander effect as a percentage of the maximum decrease possible. The percentage of NR-expressing cells for which the TE was 50%, (the TE50) is a single datum of bystander efficacy. WiDr and V79 cell lines, had a similar TE50 of approximately 2%. SK-OV-3 gave a lower value of 0.3%. These TE50 correlate with concentrations of cytosolic NR activity, which is distinguished from endogenous DT diaphorase activity by kinetic differences. A novel method is described which enables both DNA crosslinks and drug-induced single-strand breaks to be simultaneously quantified in a sedimentation assay. Using this technique, bystander DNA damage was demonstrated in V79 cells, of approximately 50% of that in activator cells.
authors.affiliation: Cancer Research Campaign Centre for Cancer Therapeutics, Institute of Cancer Research, Sutton, UK.
authors.forename: F
authors.initials: F
authors.lastname: Friedlos
authors.forename: S
authors.initials: S
authors.lastname: Court
authors.forename: M
authors.initials: M
authors.lastname: Ford
authors.forename: W A
authors.initials: WA
authors.lastname: Denny
authors.forename: C
authors.initials: C
authors.lastname: Springer
mesh_terms: D001388:Aziridines / Q000627:therapeutic use*; D004249:DNA Damage; D004926:Escherichia coli / Q000201:enzymology; D015870:Gene Expression; D015316:Genetic Therapy / Q000379:methods*; D006801:Humans; D009369:Neoplasms / Q000628:therapy*; D009601:Nitroreductases / Q000235:genetics*; D011355:Prodrugs / Q000627:therapeutic use; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D001388:Aziridines; D011355:Prodrugs; C100099:tretazicar; D009601:Nitroreductases