Mitomycin antitumor compounds. 2. Interaction of transition metal ions with mitomycin C. Solution structure and biological activity of a Pd(2+)-MMC complex

Interactions of Cu(2+), Zn(2+), and Pd(2+) ions with the antitumor compound mitomycin C (MMC) have been investigated by UV-vis, circular dichroism, and (13)C NMR spectroscopy. While Zn(2+) and Cu(2+) neither interacted with MMC nor catalyzed the formation of mitosenes, Pd(2+) induced strong MMC spectral modifications, suggesting the formation of a major complex, in which MMC acted as a bidentate ligand through N(1) and N(4) atoms. The coordination mode in this complex was solvent dependent: in MeOH, the NH(2) of the carbamate function was also involved as a third coordination site whereas, in H(2)O, Pd(2+) hydrolysis was more effective, leading to the replacement of the carbamoyl NH(2) function with either H(2)O or OH(-) ligands. Although coordination of the indoline nitrogen prevented methanol elimination and consequent aziridino ring opening, Pd(2+) complexation maintained MMC biological activity against Cancer cells, as shown by IC(50) values. This suggests that alternative mechanisms in the biological activity of MMC should be explored.