Induction of p53 by the concerted actions of aziridine and quinone moieties of diaziquone

The biologic functions attributed to the nucleophosphoprotein p53 have been increasing in recent years. Some studies suggested that wild type p53 is responsible for cell cycle arrest brought about as a response to exposure of mammalian cells to DNA-damaging agents. This cell cycle arrest occurs in order for cells to repair the damaged macromolecules. Extensively damaged cells are also thought to undergo apoptosis via the p53-dependent or -independent signal transduction pathways. In this study, we investigated the ability of diaziridinylbenzoquinones to increase p53 levels in the human breast cancer cell line MCF-7. Diaziquone (AZQ), an anticancer agent, and its derivatives, diaziridinequinone (DZQ) and methyldiaziridinequinone (MeDZQ), induced p53 in a dose-and time-dependent manner as measured by the electrophoretic mobility shift assay. Wild type p53 induction by AZQ was suppressed when DT-diaphorase activity was inhibited by pretreating the cells with dicumarol. Aside from their potent alkylating activity, these agents also undergo redox cycling as evidenced by oxygen consumption and the production of reactive oxygen species (ROS). Inhibition of ROS production by the antioxidant enzyme catalase reduced AZQ- and DZQ-mediated p53 induction by about 45%. Thiotepa, a non-quinone aziridine-containing agent, and 1,4-benzoquinone (p-BQ), a redox cycling quinone, increased p53 levels. The nonalkylator oxygen-radical-generating agent menadione (MD) caused p53 induction only when MCF-7 cells were allowed to recover in drug-free media. On the basis of these data, we propose that the bioreductive activation of AZQ is a prerequisite for p53 induction. Moreover, the induction of p53 by AZQ requires both the quinone and the aziridine moieties of the AZQ molecule. Although AZQ and its analogues increased p53 levels in MCF-7 cells, p53 induction in these cells may not be responsible for the apoptosis seen upon treatment of MCF-7 cells with these agents. The uncoupling of p53 induction and apoptosis is evidenced by the generation of nucleosomal DNA laddering in aziridinequinone-treated T47D cells, a breast cancer cell line bearing a p53 mutation.