A free radical scavenger role for daunomycin: inhibition of nonenzymatic oxidation of NADH

Mitochondria as subcellular targets for clinically useful anthracyclines

Due to the widespread use of anthracyclines as antitumor agents, a large number of investigations have been reported analyzing clinical and molecular aspects of these quinone antibiotics. While the high affinity of anthracyclines towards chromosomal DNA has been held responsible for their antitumor activity, an increasing amount of data is being accumulated showing that these drugs also target mitochondria thus interfering with major mitochondrial functions. Since this toxicity of anthracyclines towards mitochondria is associated with side effects significantly limiting their chemotherapeutic dose, the corresponding underlying mechanisms need to be understood. Bioenergetic failure, enzyme inhibitions, lipid peroxidations, induction of membrane disorders as well as the initiation of oxidative stress are being attributed to the accumulation of anthracyclines at or inside mitochondria. In this review the wide spectrum of possible mode of actions of these antibiotics leading to mitochondrial dysfunctions will be presented and discussed.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.