Sensitisation of human carcinoma cells to the prodrug CB1954 by adenovirus vector-mediated expression of E. coli nitroreductase.
Weedon SJ., Green NK., McNeish IA., Gilligan MG., Mautner V., Wrighton CJ., Mountain A., Young LS., Kerr DJ., Searle PF.
The enzyme nitroreductase from E. coli can reduce the weak, monofunctional alkylating agent 5-(aziridin-1-yl)-2, 4-dinitrobenzamide (CB1954) to a potent cytotoxic species that generates interstrand crosslinks in DNA. Nitroreductase therefore has potential as a "suicide enzyme" for cancer gene therapy, as cells that express nitroreductase become selectively sensitive to the prodrug CB1954. We have incorporated a nitroreductase expression cassette into a replication-defective adenovirus vector (Ad-CMV-ntr), which allowed efficient gene transfer to SK-OV-3 or IGROV-1 ovarian carcinoma cells. Nitroreductase levels increased in line with multiplicity of infection, and this was reflected in increasing sensitisation of the cells to CB1954, reaching an optimum (approx. 2, 000-fold sensitisation) with 25-50 p.f.u. per cell. Similar Ad-CMV-ntr-dependent sensitisation to CB1954 was seen in 3 of 6 low-passage primary ovarian tumour lines. Cells grown at low-serum concentration to inhibit proliferation remained equally susceptible to the Ad-CMV-ntr-dependent cytotoxicity of CB1954, indicating a distinct advantage over retroviral gene delivery and other popular enzyme-prodrug systems for human tumours with a low rate of cell proliferation. Additionally, cisplatin-resistant cells were sensitised towards CB1954 by Ad-CMV-ntr as efficiently as the parental cells, indicating that the system could be effective in patients with cisplatin-resistant tumours. In a murine xenograft model for disseminated peritoneal carcinomatosis with ascites, treatment of nude mice bearing intraperitoneal SUIT2 tumours with Ad-CMV-ntr and CB1954 almost doubled the median survival from 14 to 26 days (p < 0.0001).