Are reduced quinones necessarily involved in the antitumour activity of quinone drugs?

Several studies have shown that the antitumour quinones, adriamycin, mitomycin C, mitozantrone and 3,6-diaziridinyl-2,5-bis (carboethoxyamino)-1,4-benzoquinone (AZQ) can form semiquinone radicals in vitro. The biophysical chemistry data for these reactions and the properties of the radical quinones are presented together with the proposed mechanisms for cytotoxicity. An attempt has been made to correlate the available in vitro data for the quinones with each other and with the available in vivo data. As a consequence of these correlations a number of conclusions have been proposed regarding the techniques of investigation and the evidence for the role of reduced quinones in antitumour activity.