Directed enzyme prodrug therapies (DEPT) are cunently being clinically trialled, the aim being to localise cytotoxic compounds at cancer sites; enzymes are either expressed or delivered to solid tumours so that non-toxic prodrugs are activated to cytotoxic derivatives exclusively at cancer cells. Nitroreductases (NTRs) have been clinically trialled in DEPT with the prodrug CB1954 (5-[aziridin-1-yl]-2,4-dinitrobenzamide), however the rate of tumour transduction and subsequent over-expression of the NTR was relatively low for effective cancer treatment, as was the activity of the enzyme with the prodrug.
This research details the assay of a series of NTRs as yet untested with CB1954 to measure activity with the prodrug and evaluate their potential suitability for application in the therapy. The enzymes were assayed in a range of environmental conditions and their kinetic parameters with CB1954 determined and compared to other NTRs reported in the literature. The nfrA2 NTR from Bacillus licheniformis was identified as having a higher catalytic efficiency (Kcat/Km) to the much studied nfnB from Escherichia coli which has been used in phase I/II clinical trials and is currently the leading candidate for application in DEPT.
Magnetic nanoparticles were synthesised which behave superparamagnetically at room temperature and coated with gold using an aqueous, low cost, non-toxic synthesis. The gold coated magnetic nanoparticles were characterised by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDAX), x-ray diffraction (XRD) and ultraviolet-visible (UV-vis) spectrometry, indicating successful Au surface coating producing 38 nm ± 6 nm nanoparticles, which separated under exposure to an applied magnetic field of 1.28 T and readily redispersed upon agitation. 
The genetically modified NTRs self-assembled onto Au surfaces and could do so via the introduced cysteine sequence, meaning the enzymes can be immobilised with controlled orientation.