On the formation of oxygenated radicals by fredericamycin A and implications to its anticancer activity: an ESR investigation.

It has been recently suggested that the exceptionally high antitumor and antibacterial activity of natural fredericamycin A (FMA) is related to its ability to spontaneously generate the superoxide anion (O2-) and hydroxyl (.OH) radicals in aerobic solutions [Hilton, B. D., Misra, R., & Zweier, J. L. (1986) Biochemistry 25, 5533]. With a view to understand the mechanistic details, attempts were made to reproduce earlier electron spin resonance (ESR) evidence for the oxygenated free radical formation in well-aerated solutions of natural FMA in dimethyl sulfoxide and dilute H2O2. Little or no evidence was obtained for the formation of the O2- and methoxy (.OCH3) radicals, while the detected formation of the .OH and methyl (.CH3) radicals was attributable largely to mechanisms not involving FMA. These results thus reopen the question regarding the mechanism of its exceptionally high tumoricidal-bacteriocidal activity.