| Abstrakt: |
The interaction of Fe3+ with the anthracycline anticancer drug idarubicin (Ida) was studied by absorption, CD, Mössbauer, and EPR spectroscopy. The formation of two major Fe3+−Ida complexes, labeled I and II, was observed. In complex I, Fe3+ ion was bound to anthracycline at the {C(12)&dbd;O; C(11)−O-} coordination site. In complex II, two Fe3+ ions were bound at sites {C(5)&dbd;O; C(6)−O-} and {C(12)&dbd;O; C(11)−O-}, respectively. Complex I was an equimolar monomeric species with a 1:1 Fe3+:Ida stoichiometry (β1 = 4.8 × 1011 M-1), whereas in complex II the anthracycline ligand was bridging two metal ions, alternatively bound to both anthracycline ring chelating sites with the assumption that the ratio of Fe3+:Ida in complex II was 2:1 (β2 = 5.3 × 1024 M-2). Alternatively, complex II may be oligomeric with Fe3+:Ida = 1:1 and with each Fe3+ bridging two Ida molecules. Our findings could be important in understanding the biological effects of the anthracycline−ferric complexes. Thus, providing information about the nature of the Fe3+−Ida system, we suggest that the formal 1:3 Fe3+:anthracycline complexes, reported in the previous literature, could be a mixture of species I, II, and free ligand. |
