Speciation in human blood of Metvan, a vanadium based potential anti-tumor drug.

The first report on the anti-cancer activity of the compound Metvan, [VIV O(Me2 phen)2 (SO4 )], where Me2 phen is 4,7-dimethyl-1,10-phenanthroline, dates back to 2001. Although it was immediately identified as one of the most promising multitargeted anti-cancer V compounds, no development on the medical experimentation was carried out. One of the possible reasons is the lack of information on its speciation in aqueous solution and its thermodynamic stability, factors which influence the transport in the blood and the final form which reaches the target organs. To fill this gap, in this work the speciation of Metvan in aqueous solution and human blood was studied by instrumental (EPR, electronic absorption spectroscopy, ESI-MS and ESI-MS/MS), analytical (pH-potentiometry) and computational (DFT) methods. The results suggested that Metvan transforms at physiological pH into the hydrolytic species cis-[VO(Me2 phen)2 (OH)]+ and that both citrate and proteins (transferrin and albumin in the blood serum, and hemoglobin in the erythrocytes) form mixed complexes, denoted [VO(Me2 phen)(citrH-1 )]2- and VO-Me2 phen-Protein with the probable binding of His-N donors. The measurements with erythrocytes suggest that Metvan is able to cross their membrane forming mixed species VO-Me2 phen-Hb. The redox stability in cell culture medium was also examined, showing that ca. 60% is oxidized to VV after 5 h. Overall, the speciation of Metvan in the blood mainly depends on the V concentration: when it is larger than 50 μM, [VO(Me2 phen)(citrH-1 )]2- and VO-Me2 phen-Protein are the major species, while for concentrations lower than 10 μM, (VO)(hTf) is formed and Me2 phen is lost. Therefore, it is plausible that the pharmacological activity of Metvan could be due to the synergic action of free Me2 phen, and VIV O and VV O/VV O2 species.