Radiosensitization of hypoxic cells by a nitrofuran; dose-modifying and shoulder effects

The radiosensitizer nifurpipone dihydrochloride (5-nitro-2-furaldehyde N-methyl piperazino acetyl hydrazone dihydrochloride) sensitizes hypoxic V79 mammalian cells by at least two mechanisms. Sensitization is by a reduction of ñ in addition to an increase in slope. Both these affects are absent under oxygenated conditions. When hypoxic V79 cells are irradiated in the presence of nifurpipone dihydrochloride combined with Ro-07-0582, sensitization greater than that due to air alone is observed; this effect is due to a reduction in ñ and an increased slope. Again this effect is absent under oxygenated conditions. Rapid-mix studies using Serratia marcescens show that full senitization occurs with a pre-irradiation contact time of 4 msec; this contrasts with data for V79 cells where a pre-irradiation contact time of 40 msec is insufficient for any sensitization to occur. This sensitizer also exerts a differential toxic effect, being more toxic to hypoxic cells than to oxygenated ones. It is concluded from these results that nifurpipone dihydrochloride sensitizes by at least two mechanisms, one of which resembles that of the electron-affinic type.