title: Virus directed enzyme prodrug therapy for ovarian and pancreatic cancer using retrovirally delivered E. coli nitroreductase and CB1954.
abstract: Expression of the E. coli enzyme nitroreductase (NTR) in tumour cells enables them to activate the prodrug CB1954 (5-(aziridin-1-yl)-2,4-dinitrobenzamide), leading to interstrand DNA crosslinking and cell death. Using transfected or retrovirally transduced SKOV3 ovarian carcinoma cell clones, we show a strong correlation between sensitivity to CB1954 and level of NTR enzyme activity. Importantly for clinical application in ovarian cancer, a cisplatin-resistant ovarian tumour cell line remains as susceptible to the NTR-dependent cytotoxicity of CB1954 as parental cells. In mixed populations of NTR-expressing and non-expressing cells, we observe a marked 'bystander killing' effect with this system. The use of NTR-encoding retroviruses from clonal producer cell lines at titres of 5 x 10(5) c.f.u./ml to transduce either established or low passage primary ovarian carcinoma lines only achieves an average 10-fold sensitisation of the cultures at gene transfer efficiencies of 15-25%. Concentration of the retrovirus to 3 x 10(7) c.f.u./ml elevates gene transfer to 80-90% in a single exposure to target cells, resulting in up to 500-fold sensitisation of the entire, unselected SKOV3 population to CB1954. In an initial investigation of NTR/CB1954 for the treatment of tumours in vivo, we observe regression of tumours expressing NTR following administration of CB1954, resulting in significantly increased median survival.
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001388:Aziridines / Q000627:therapeutic use; D005260:Female; D018014:Gene Transfer Techniques; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D051379:Mice; D008807:Mice, Inbred BALB C; D009601:Nitroreductases / Q000235:genetics*; D010051:Ovarian Neoplasms / Q000628:therapy*; D010190:Pancreatic Neoplasms / Q000628:therapy*; D011355:Prodrugs / Q000627:therapeutic use; D012190:Retroviridae