Radiosensitization by Metal Salts

The early studies on metal salts, including some chosen for their oxidizing ability, mostly used bacterial systems and, since no uniform parameter of activity was adopted, no real mechanistic pointers emerged from these 

The above example of reduction-enhanced cytotoxicity is of particular relevance because of the role of copper as an essential trace element and its function in many intracellular redox processes. The arguments for an overall mechanism of radiobiological action invoking copper participation have, in fact, been presented [35] and will be summarized later. 

The fact that the ferricenium ion (FeCpJ) is an effective radiosensitizer, DMF = 2.0 at 100 juM, is of interest because of its good oxidizing power and stability. The analogous Co complex is inactive, no difference between effects on hypoxic and oxygenated cells was found in this study [40]. The 

Another metal complex which may be mentioned here is platinum-thymine blue (see Chapter 4), which, because of its mixed-valent nature, may well involve reduction in its as yet undefined mechanism of sensitizing action [45]. 

The more recent results on the interaction of these substitution inert complexes with DNA (see Chapter 1), and especially the photosensitized cleavage of DNA by Co(III) complexes [46], may well be relevant to these biological results, especially as a 1,10-phenanthroline chelate, cis-[Co(phen)2(N02)2], is also claimed to be an efficient sensitizer. Differing activities have been observed in isomeric forms of [Co(NH3)4X2], X = Cl, NO2. Abrams et al. [40] have observed that all active complexes show a reduction potential of 260 mV, which represents a cut-off point as there is no strict correspondence between reduction potential and OER. No selectivity is apparent for these complexes in hypoxic cells. The hexam-mine and pentammine complexes originally reported [36] are essentially 

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