Reductive activation of potential antitumor mitosene compounds.
The reductive activation of mitosene compounds was studied with cyclic voltammetry and HPLC analysis. Reduction of mitosenes, possessing good leaving groups at C-1 and C-10, was shown to result in loss of these groups at pH 7.0 and pH 6.0. The loss of leaving groups from mitosenes occurred faster at lower pH. Mitosenes without good leaving groups were found to be stable upon reduction. In the presence of acetoxy groups at C-1 and C-10, the C-10 site is the most reactive site upon reductive activation. This is opposite to the case of mitomycin C, where the C-1 site is the first to react upon reduction. At pH 6.0 without reduction, acid degradation also caused the loss of leaving groups of mitosenes, although at a very slow rate. In contrast to reductive activation, upon acid degradation of a diacetoxymitosene the C-1 group appeared to be lost faster. Electrochemical as well as dithionite reduction of a bifunctional (diacetoxy) mitosene compound in the presence of calf thymus DNA at pH 5.5 resulted in the formation of DNA interstrand cross-links. Depending on activation method, this diacetoxymitosene was at least as efficient in DNA cross-linking as mitomycin C under comparable conditions.