Spontaneous CO Release from RuII(CO)2-Protein Complexes in Aqueous Solution, Cells, and Mice

We demonstrate that Ru-II(CO)(2)-protein complexes, formed by the reaction of the hydrolytic decomposition products of [fac-RuCl((2)-H2NCH2CO2)(CO)(3)] (CORM-3) with histidine residues exposed on the surface of proteins, spontaneously release CO in aqueous solution, cells, and mice. CO release was detected by mass spectrometry (MS) and confocal microscopy using a CO-responsive turn-on fluorescent probe. These findings support our hypothesis that plasma proteins act as CO carriers after invivo administration of CORM-3. CO released from a synthetic bovine serum albumin (BSA)-Ru-II(CO)(2) complex leads to downregulation of the cytokines interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)- in cancer cells. Finally, administration of BSA-Ru-II(CO)(2) in mice bearing a colon carcinoma tumor results in enhanced CO accumulation at the tumor. Our data suggest the use of Ru-II(CO)(2)-protein complexes as viable alternatives for the safe and spatially controlled delivery of therapeutic CO invivo.