title: Nitroreductase: a prodrug-activating enzyme for cancer gene therapy.
abstract: 1. The prodrug CB1954 (5-(aziridin-1-yl)-2,4-dinitrobenzamide) is activated by Escherichia coli nitroreductase (NTR) to a potent DNA-crosslinking agent. 2. Virus-mediated expression of NTR in tumour cells sensitizes them to CB1954 in vitro and in vivo, providing the basis for a strategy of cancer gene therapy. 3. A phase I trial of CB1954 in cancer patients has been completed, documenting the pharmacokinetics and establishing an acceptable dose. Subsequent trials of the replication-defective adenovirus CTL102 in patients with resectable tumours have documented expression of NTR in injected colorectal liver metastases, hepatocellular carcinoma, head and neck cancer and prostate cancer. Trials combining CTL102 and CB1954 are underway. 4. An oncolytic (replication-competent) adenovirus vector allowed increased expression of NTR in vitro and in a mouse tumour model, resulting in a greater reduction in tumour growth when combined with CB1954 treatment. 5. Alternative prodrugs may eventually prove superior to CB1954; a nitroaryl phosphoramide mustard prodrug activated by NTR shows a greater therapeutic index than CB1954 in a human ovarian carcinoma. 6. The crystal structure of NTR provided the basis for site-directed mutagenesis, which has identified a number of mutants with improved kinetics of CB1954 activation. These can provide improved cell sensitization to CB1954. Combinations of these are being tested. 7. The basis for a positive selection for improved NTR variants has been demonstrated.
authors.affiliation: Cancer Research UK Institute for Cancer Studies, University of Birmingham, Edgbaston, Birmingham. P.F.SEARLE@bham.ac.uk
authors.forename: Peter F
authors.initials: PF
authors.lastname: Searle
authors.forename: Ming-Jen
authors.initials: MJ
authors.lastname: Chen
authors.forename: Longqin
authors.initials: L
authors.lastname: Hu
authors.forename: Paul R
authors.initials: PR
authors.lastname: Race
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Lovering
authors.forename: Jane I
authors.initials: JI
authors.lastname: Grove
authors.forename: Chris
authors.initials: C
authors.lastname: Guise
authors.forename: Mansooreh
authors.initials: M
authors.lastname: Jaberipour
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: James
authors.forename: Vivien
authors.initials: V
authors.lastname: Mautner
authors.forename: Lawrence S
authors.initials: LS
authors.lastname: Young
authors.forename: David J
authors.initials: DJ
authors.lastname: Kerr
authors.forename: Andrew
authors.initials: A
authors.lastname: Mountain
authors.forename: Scott A
authors.initials: SA
authors.lastname: White
authors.forename: Eva I
authors.initials: EI
authors.lastname: Hyde
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001388:Aziridines / Q000627:therapeutic use; D001711:Biotransformation; D002986:Clinical Trials as Topic; D003131:Combined Modality Therapy; D005818:Genetic Engineering; D015316:Genetic Therapy; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy / Q000628:therapy*; D009601:Nitroreductases / Q000378:metabolism*; D011355:Prodrugs / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D001388:Aziridines; D011355:Prodrugs; C100099:tretazicar; D009601:Nitroreductases