Sensitisation of human carcinoma cells to the prodrug CB1954 by adenovirusvector-mediated expression of E-coli nitroreductase

The enzyme nitroreductase from E. coli can reduce the weak, monofunctional alkylating agent 5-(aziridin-1-yl)-2,4-dinitrobenzamide (CB1954) to a poten t cytotoxic species that generates interstrand crosslinks in DNA. Nitroredu ctase therefore has potential as a "suicide enzyme" for cancer gene therapy , as cells that express nitroreductase become selectively sensitive to the prodrug CB 1954. 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-I ovarian carcinoma cells. Nitr oreductase levels increased in line with multiplicity of infection, and thi s was reflected in increasing sensitisation of the cells to CB1954, reachin g 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 lo w-passage primary ovarian tumour lines. Cells grown at low-serum concentrat ion to inhibit proliferation remained equally susceptible to the Ad-CMV-ntr -dependent cytotoxicity of CB1954, indicating a distinct advantage over ret roviral gene delivery and other popular enzyme-prodrug systems for human tu mours with a low rate of cell proliferation. Additionally, cisplatin-resist ant cells were sensitised towards CB 1954 by Ad-CMV-ntr as efficiently as t he parental cells, indicating that the system could be effective in patient s with cisplatin-resistant tumours. In a murine xenograft model for dissemi nated peritoneal carcinomatosis with ascites, treatment of nude mice bearin g intraperitoneal SUIT2 tumours with Ad-CMV-ntr and CB1954 almost doubled t he median survival from 14 to 26 days (p < 0.0001). Int. J. Cancer 86:848-8 54, 2000. (C) 2000 Wiley-Liss, Inc.