Radiosensitization by Thiol Depletion

The radioprotecting properties of thiols and aminothiols have been known for some time and this is generally attributed to their quenching of radiation-induced radicals such as Oj. Compounds which remove endogenous thiols thus increase radical lifetime and can have sensitizing properties. This mechanism contributes to the action of, for instance, A-ethylmaleimide [90] and any thiol depletion by artificial means should indeed produce enhancement of sensitization [91]. 

The known use of ferricyanide as a thiol labelling group also prompted its examination, and excellent sensitization in bacteria was found [42] and attributed to the reaction  

As stated earlier, the number of possibilities for reaction of these species with radiation-induced radicals is large and the exact mechanism may be different from that suggested by the above reaction. In recent results the in vitro sensitizing action of rhodium carboxylates has been attributed to their thiol binding capacity [58], and this is of interest in view of their known affinity for sulfur-containing cellular constituents (see Chapter 6). The in vitro sensitizing efficiency of the carboxylates follows the order butyrate propionate acetate methoxyacetate, which parallels the antitumour effect and is related to the intracellular uptake. The sensitiza- 

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