Nitric oxide photorelease from a trinuclear ruthenium nitrosyl complex and its in vitro cytotoxicity against melanoma cells.

In vitro cytotoxicity study of the [Ru3O(CH3COO)6(4-pic)2(NO)]PF6 triruthenium nitrosyl cluster (compound 1, 4-pic=4-methylpyridine) against B16F10 melanoma cell line was evaluated in the presence and absence of visible light irradiation. The nitrosyl cluster 1 showed a significant tumoricidal activity when irradiated at λ=532 nm, reducing cell viability up to 90% at a concentration of 62.5 μM. However, cell death of 60% is also observed in the dark which can be assigned to the NO release mediated by a redox reaction of the cluster in cell medium. This possibility was confirmed by amperometric detection of NO after the addition of ascorbic acid to compound 1 in phosphate buffer. A control experiment was performed with the solvated cluster [Ru3O(CH3COO)6(4-pic)2(CH3OH)]PF6 (compound 2) and no significant lowering of cell viability was observed. These results suggest that the nitrosyl cluster acts as a pro-drug, delivering NO, which is the actual active species.