Radiation Chemical and Physical Mechanisms of Radiosensitization of Single Cell Systems by Iothalamate

Summary

The radiosensitizing effect of iothalamate (ITA) has been investigated in bacterial and mammalian cells in order to obtain a better understanding of the physical and radiation chemical mechanisms of sensitization displayed by the drug. In order to distinguish between the two, Escherichia coli B/r cells were irradiated with 9 MeV electrons, which allow only the radiation chemical mechanism to operate, and V79 cells with 250 KVp X-rays, which instead make possible the occurrence of both mechanisms.

It has been shown that: (a) Maximum sensitization already occurs in bacteria with 10⁻² mol dm⁻³ ITA (enhancement ratio (ER) 11·2 in oxygen, 2·7 in nitrogen), while in mammalian cells a concentration higher by a factor of 10 is required (ER 2·2 both in air and nitrogen). (b) ITA sensitization is inhibited when bacteria are irradiated in growth medium instead of buffer. Such inhibition does not occur with V79 cells. (c) Cysteine and glycerol completely cancel the sensitizing effect of ITA on bacterial cells in both gas phases. Dimethylsulphoxide (DMSO) does the same in nitrogen, while in oxygen it only reduces ITA sensitization to about 50 per cent of the level observed in control conditions. With mammalian cells, all the three scavengers do not modify significantly the enhancement produced by ITA, either in air or in nitrogen. The experimental results are consistent with both postulated mechanisms of sensitization.

• iothalamate
• bacterial cells
• mammalian cells