The interaction of two antitumor ruthenium(III) complexes,-Na[trans-RuCl4(DMSO)(Im)] and
Na[trans-RuCl4(DMSO)(Ind)]- with human serum apotransferrin (apoTf) was investigated through
a number of spectroscopic techniques such as UV-Vis absorption, CD and H1 NMR
spectroscopy. Interestingly, the hydrolysis profiles of these complexes in a physiological buffer
are markedly affected by the presence, in solution, of apoTf suggesting the occurrence of a
specific interaction of their respective hydrolysis products with the protein. The formation of
stable adducts with apotransferrin has been demonstrated by CD spectroscopy, and additional
information obtained through H1 NMR of the hyperfine shifted signals. The bound ruthenium(III)
species may be detached from these adducts by addition of excess citrate at low pH. The
behavior of the investigated ruthenium(III) complexes with apoTf is compared with that of the
recently described and strictly related ru-im and ru-ind antitumour complexes, and discussed in
the frame of general strategies of drug targeting.