An unusual NAD(P)H-dependent O2-.-enerating redox system in hepatoma 22a nuclei.

Nuclear membranes from many tumors contain an unusual redox chain discovered originally in the Hepatoma 22a nuclear membranes which catalyzes superoxide dismutase-sensitive adrenaline oxidation to adrenochrome in the presence of either NADPH or NADH as electron donor, the reaction being inhibited by cyanide and azide. This redox chain can reduce anthracycline antitumor antibiotics adriamycin and carminomycin to their free radical states under anaerobic conditions. Evidence has been obtained for a higher stability of the carminomycin radical as compared to that of adriamycin. Operation of the nuclear membrane-bound redox chain can be a source of oxygen radical-mediated single strand breaks in DNA. The role of the nuclear membrane-associated electron transfer chain in augmenting the anticancer action of the anthracycline antibiotics is discussed.