BD-40, an ellipticine-related DNA intercalative agent induces DNA-protein bridges in vivo

The ability of BD-40, a DNA intercalative Ellipticine analogue, to induce DNA protein-cross links (DPLs) in mammalian cell DNA was studied by measuring DNA extractability with 0.5M KCl. Like Ellipticine, BD-40 was found to decrease the extractability of DNA, indicating the presence of DPLs, at inhibitory doses as well as at cytotoxic doses. Further analysis by alkaline sucrose gradient sedimentation of BD-40-induced DLPs indicated that the apparent size of DNA was not modified in comparison to that of control cell DNA. Abolition of DPLs by a prior proteinase K treatment of nuclear lysates resulted in DNA size reduction revealing the existence of hidden DNA strand breaks. In contrast, no proteolytic treatment was required to obtain a similar size reduction of DNA from Ellipticine-treated cells. These data suggest that BD-40 induced DPLs involve NaDodSO4+alkali-resistant DNA strand-protein bridges which maintain cohesiveness of adjacent DNA termini. Thus, BD-40 appears to be different from other DPL-inducing intercalative agents which have not been reported to induce DNA-protein bridges.