Molecular mechanisms of anthracycline activity.

On the basis of evidence that anthracyclines are DNA intercalating agents and DNA is the primary target,a large number of analogs and related intercalators have been developed. However, doxorubicin andclosely related anthracyclines still remain among the most effective antitumor agents. Multiple mechanismshave been proposed to explain their efficacy. They include inhibition of DNA-dependent functions, freeradical formation, and membrane interactions. The primary mechanism of action is now ascribed to drug interferencewith the function of DNA topoisomerase II. The stabilization of the topoisomerase-mediated cleavablecomplex results in a specific type of DNA damage (i.e., double-strand protein-associated DNA breaks).The drug-stabilized cleavable complex is a potentially reversible molecular event and its persistence,as a consequence of strong DNA binding, may be recognized as an apoptotic stimulus. Indirect evidencesupports the notion that the bioreductive processes of the quinone moiety generating the semiquinone radicalwith concomitant production of reactive oxygen species may contribute to the drug effects. The cellulardefense mechanisms and response to genotoxic/cytotoxic stress appear to be critical determinants of thetumor sensitivity to anthracyclines.