On the Radiomimetic Effects of Cupferron and Potassium Cyanide

Cupferron, the ammonium salt of N-nitro-sophenylhydroxylamine, enhances the frequencies of structural chromosome changes produced by x-rays in the root tips of the broad bean, Vicia faba (7, 4-6). The enhancement produced at low oxygen pressures (0.3 to 5 per cent 02 in the gas phase) is particularly striking and appears to be a result of the inhibitory action of cupferron on oxygen consumption (4-6). The enhancing agent itself is not cupferron but oxygen, which, in the presence of the respiratory inhibitor is able to diffuse into the root meristem. As expected, a similar enhancement of the radio-sensitivity at low oxygen pressures is obtained with other respiratory inhibitors (9, 8, 4, 6). In addition to their ability to enhance x-ray sensitivity , the two best studied of these inhibitors, cupferron and potassium cyanide (KCN), have radiomimetic effects; i.e., they are able to produce structural chromosome changes in the absence of radiation (9, 8, 3). Studies on the radiomimetic effects of KCN (3) have shown that the effect is strongest 24 to 36 hours after the treatment, which indicates that KCN does not produce chromosome aberrations in cells which are in the second half of the mitotic cycle during the treatment. The frequencies of aberrations produced by KCN are independent of the temperature during the treatment , but are markedly affected by the concentration of oxygen. Concentrations of oxygen varying between 0 and 100 per cent were tested for their ability to influence the effect of KCN, and it was found that the higher the oxygen concentration, the stronger the radiomimetic effect. The radiomimetic effect of cupferron appeared to be much weaker than that of KCN (3), and in contrast to the effect of KCN, it was found to be unaffected by variations in the concentration of oxygen. More differences between the radiomimetic effects of cupferron and KCN appear from the experiments described below. The experimental material in these experiments consisted of lateral roots of the broad bean, Vicia faba. The methods of treatment and preparation of slides were the same in these experiments as in those described previously (3). It appears from Table I that the radiomimetic effect of cupferron is strongly influenced by the pH and the temperature of the treatment solution. The effect increases when the temperature during the treatment is increased or when the pH of the solution is lowered. The toxic effects of cupferron is also increased …