X-ray Absorption Near Edge Structure Spectroscopy to Resolve the in Vivo Chemistry of the Redox-Active Indazolium trans-[Tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019)

Abstract

Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (1, KP1019) and its analogue sodium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (2, KP1339) are promising redox-active anticancer drug candidates that were investigated with X-ray absorption near edge structure spectroscopy. The analysis was based on the concept of the coordination charge and ruthenium model compounds representing possible coordinations and oxidation states in vivo. 1 was investigated in citrate saline buffer (pH 3.5) and in carbonate buffer (pH 7.4) at 37 °C for different time intervals. Interaction studies on 1 with glutathione in saline buffer and apo-transferrin in carbonate buffer were undertaken, and the coordination of 1 and 2 in tumor tissues was studied too. The most likely coordinations and oxidation states of the compound under the above mentioned conditions were assigned. Microprobe X-ray fluorescence of tumor thin sections showed the strong penetration of ruthenium into the tumor tissue, with the highest concentrations near blood vessels and in the edge regions of the tissue samples.

Calpain-Mediated Integrin Deregulation as a Novel Mode of Action for the Anticancer Gallium Compound KP46

“…Indeed, Mg 2þ overload reduced KP46-induced detachment and cell death. On the contrary, KP46 has been demonstrated to be extremely stable in biologic environments (10,41), making the presence of substantial amounts of free ligand questionable. In addition, even the formation of small amounts of the 8-hydroxyquinoline Mg 2þ complex would not distinctly reduce the extracellular Mg 2þ concentration due to the high excess of Mg 2þ (400 mmol/L in the culture medium) compared with the used KP46 concentrations in the low mmol/L range.…”

“…KP46 was designed to optimize hydrolytic stability and membrane penetration abilities. A recent X-ray absorption study proved high stability under physiologic conditions in cell culture media and even in tissue samples of treated mice (10). Antihypercalcemic as well as antitumor effects were demonstrated in the Walker carcinosarcoma 256 model in rats (11).…”

Electronic State of Sodium trans-[Tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) in Tumor, Liver and Kidney Tissue of a SW480-bearing Mouse

“…The Ru L 3 - and L 2 -edge energies of 1 to 13 span a range of 1.5 eV and 1.4 eV, respectively, as compared to 6.1 eV at the Ru K-edge for an almost identical set of model compounds17. As reported for the Ru K-edges the edge energies at the Ru L 2,3 -edges increase as the Ru oxidation state changes from Ru II to Ru III and within the same Ru oxidation state the defined edges are shifted to higher energies with increasing electronegativity of the first shell atoms (see Table 1).…”

“…KP1019 and 7 were also investigated in tumor and liver tissue with dosages varying between 7.5–40 mg/kg. Ru K-edge spectroscopy did not allow to distinguish between Ru III Cl 3 N 2 (O/N) and Ru II ClN 2 (O/N) 3 as assigned coordination modes in the tissue samples17. A study on human hepatoma cells treated with KP1019 under cell culture conditions found, besides O/N binding from amine/imine and carboxylato groups of proteins, also indications of S donor atoms binding to Ru II/III that may originate from Cys residues of cytoplasmic enzymes such as cysteine proteases and thioredoxin reductase19.…”

“…X-ray absorption spectroscopy (XAS) has been proven to be successful in the study of metal complexes for cancer therapy in vivo and in vitro 1314151617181920. In contrast to the metal K-edge transitions (1 s →  n p), the metal L-edges transitions (2p → 4d) are very sensitive to changes in the oxidation state and the electronic environment, such as ligand dissociation and association in biological samples.…”