The properties of interest in the radiosensitization of a metal comple
x, nickel lapachol, are compared with those of the 2-nitroimidazole, m
isonidazole. These very different comPounds were found to be surprisin
gly similar in terms of their reduction potential (- 370 mV), enhancem
ent ratios for killing of hypoxic Chinese hamster ovary cells by X-irr
adiation, and enhancement of DNA breaks in hypoxia. For nitroimidazole
s, the sensitization depends on 'electron affinity', reduction of the
nitro group; for nickel lapachol it is the metal which is necessary fo
r reduction, yet the sensitization efficiencies are remarkably close.
However, the metal complex has additional activities (some sensitizati
on in aerobic cells; increased sensitization with preincubation) which
are as yet unexplained but are assumed to be related to the nature of
the naphthoquinone ligand, rather than to the reduction of the metal.