There is ample evidence for the presence of reducing enzymes in hypoxic tumors, including but not limited to enzymes able to reduce nitroaromatic compounds . For example a nitroreductase enzyme has been isolated from Walker 256 rat carcinoma cells, which can convert CB 1954 to a cytotoxic DNA interstrand crosslinking agent by reduction of its 4-nitro group to the corresponding hydroxylamino species . Interestingly, inhibition of drug reduction by oxygen through redox cycling mechanism was first demonstrated for nitro compounds and was subsequently shown to be responsible for the hypoxia-selective cytotoxicity of nitroimidazole. In the current study we have worked with a bacterial enzyme (NTR from E. coli), since it is well-known mimic of hypoxic conditions.