Study on the "toxic oxygen effect" of Janus green B in mouse ascites tumour cells

10(7) mouse ascites tumor cells/ml incubated at 37 degrees C in 0.5 to 1.0 X 10(-4) M Janus green B or in 1.0 X 10(-4) M phenazine methosulphate are destroyed in 100 per cent oxygen atmosphere but remain transplantable in nitrogen atmosphere. The "sensitizing" effect of oxygen can be substituted by SH inhibitors (iodoacetic acid, iodoacetamide and their spinlabelled variants) as well as by some nitroxide free radicals. The "oxygen effect" is blocked by mercaptoethanole or cooling. Compared with the spectrum of native cells a more symmetrical singlet of larger amplitude, approximately g = 2 value, arose in the ESR spectrum of Janus green B treated cells. The "oxygen effect" observed in the presence of Janus green B differs in several ways from the oxygen effect of ionizing radiation and from the "photodynamic" effect.