UC Santa Barbara

The dinuclear ruthenium (Ru) compounds Ru265 and Ru360 are inhibitors of the mitochondrial calcium uniporter (MCU) and potential therapeutic agents for conditions associated with mitochondrial calcium (mt-Ca²⁺) dysregulation. The nitrido-bridged Ru265 offers improved cell permeability and redox stability relative to the oxo-bridged analogue, Ru360, while maintaining high selectivity and potency. In this study, extended X-ray absorption fine-structure (EXAFS) spectroscopy interrogated the stability of these compounds in buffer, saline/DMSO solutions, and human blood by probing the sensitive Ru─X─Ru scattering signal. Both dinuclear compounds remained intact in a pH 7.4 buffered solution, even in the presence of glutathione (5 mol equiv). Following addition to whole blood, EXAFS identified the presence of diaqua-capped Ru265', indicating axial ligand substitution but confirming stability of the Ru─N─Ru backbone during incubation (1 h, 37 °C). In contrast, Ru360' rapidly degraded in saline/DMSO at room temperature, as evidenced by the diminished intensity of the Ru···Ru peak at ∼3.65 Å in the EXAFS Fourier transform. Subsequently, the mononuclear Ru360' degradation products displayed negligible uptake into red blood cells. These findings support previous studies highlighting the improved stability of Ru265 and provide validation of the structure and coordination environment of the complex in an ex vivo human blood sample.