BINDING TO DNA, CELLULAR UPTAKE AND BIOLOGICAL-ACTIVITY OF A DISTAMYCIN ELLIPTICINE HYBRID MOLECULE

A hybrid molecule which conjugates the minor groove binding agent dist amycin and an ellipticine derivative was synthesized and evaluated for cytostatic and cytotoxic activities against L1210 leukaemia cells in vitro. The binding of the hybrid molecule, named 'Distel', to a range of natural DNAs and synthetic polynucleotides with different base pair arrangements was studied by electric linear dichroism. The interactio n with DNA simultaneously implicates binding of the distamycin part in the minor groove and intercalation of the ellipticine chromophore. Th e drug binds to DNA without any apparent preference for AT or GC polyn ucleotides, and can accommodate both homopolymeric and co-polymeric se quences as a binding site. However, the geometry of the drug-DNA compl ex varies depending on the targeted sequence. The lower activity of th e hybrid as compared to the ellipticine derivative cannot be explained in terms of DNA binding. Taking advantage of the fluorescence of the pyridocarbazole chromophore, fluorescence microscopy was used to map c ellular uptake of the hybrid molecule compared to the ellipticine deri vative. Both the conjugate and the ellipticine derivative preferential ly accumulate in the nuclei of HeLa cells rather than in the cytoplasm . Nuclei of ellipticine derivative-treated cells appear markedly more fluorescent than those of cells treated with the hybrid, which seems t o be preferentially located in the nucleoli. Therefore, we consider th e possibility that the difference in cytotoxicity between the two elli pticine-containing drugs is due to different intranuclear concentratio ns of these two compounds.