The bystander effect of the nitroreductase/CB1954 enzyme/prodrug system is due to a cell-permeable metabolite

Hum Gene Ther. 1997 Apr 10;8(6):709-17. doi: 10.1089/hum.1997.8.6-709.


The bystander effect is an important part of tumor kill using gene-directed enzyme prodrug therapy (GDEPT). Recently, we have described a novel enzyme prodrug system using bacterial nitroreductase and the prodrug CB1954 (NTR/CB1954). We demonstrate here the presence of a cell-permeable cytotoxic activity in the conditioned growth medium of nitroreductase (NTR)-transduced cells treated with CB1954 and show that its appearance corresponds to the appearance of two metabolites of CB1954 previously identified (Friedlos et al., 1992). The degree of bystander effect and the degree of transferred cytotoxicity correlates with the level of NTR enzyme expression. Two other prodrugs for NTR show little bystander killing and do not produce detectable cell permeable metabolites. The elucidation of the mechanism of the bystander effect may allow the more effective use of NTR/CB1954.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3T3 Cells
  • Animals
  • Anti-Infective Agents / metabolism
  • Antineoplastic Agents / metabolism*
  • Antineoplastic Agents / therapeutic use
  • Aziridines / metabolism*
  • Aziridines / therapeutic use
  • Blotting, Western
  • Cell Membrane Permeability
  • Cell Survival / drug effects
  • Culture Media, Conditioned
  • Gene Transfer Techniques
  • Genetic Therapy* / methods
  • Metronidazole / metabolism
  • Mice
  • Nitrofurantoin / metabolism
  • Nitroreductases / genetics*
  • Nitroreductases / metabolism
  • Prodrugs / metabolism*
  • Prodrugs / therapeutic use


  • Anti-Infective Agents
  • Antineoplastic Agents
  • Aziridines
  • Culture Media, Conditioned
  • Prodrugs
  • Metronidazole
  • tretazicar
  • Nitrofurantoin
  • Nitroreductases