The Anticancer Agent Elesclomol Has Direct Effects on Mitochondrial Bioenergetic Function in Isolated Mammalian Mitochondria.

Elesclomol ((N-malonyl-bis(N'-methyl-N'-thiobenzoylhydrazide)); formerly STA-4783) is a mitochondria-targeted chemotherapeutic agent that has demonstrated efficacy in selective cancer cell killing in pre-clinical and clinical testing. The biologically active form of elesclomol is a deprotonated copper chelate (elesclomol:copper; E:C), which has been shown to enhance reactive oxygen species (ROS) production and induce a transcriptional gene profile characteristic of an oxidative stress response in vitro. Previous studies suggest that E:C interacts with the electron transport chain (ETC) to generate high levels of ROS within the organelle and ultimately induce cell death. The purpose of this study was to further explore the mechanism of cellular and mitochondrial toxicity of E:C by examining its direct effect on mitochondrial bioenergetic function. The results obtained indicate that E:C treatment in whole cells of non-tumorigenic origin at high concentrations (40 M and higher) induces a rapid and substantial increase in mitochondrial superoxide levels and dissipation of mitochondrial membrane potential. Furthermore, similar higher concentrations of E:C act as a direct uncoupler of oxidative phosphorylation and generalized inhibitor of electron transport activity in isolated, intact mitochondria, and induce a dose-dependent inhibition of mitochondrial NADH-ubiquinone oxidoreductase activity in freeze-thawed mitochondrial preparations. The results of this study are important in that they are the first to demonstrate a direct effect of the E:C chelate on bioenergetic function in isolated mammalian mitochondria, and suggest the possibility that the increase in ROS production and cytotoxicity induced by E:C may in part be due to uncoupling of mitochondrial oxidative phosphorylation and/or inhibition of electron transport activity. These results also provide important information about the mechanisms of mitochondrial and cellular toxicity induced by E:C and will ultimately contribute to a better understanding of the therapeutic potential of elesclomol as an anticancer compound.

γ-Carboxyethyl hydroxychroman, a metabolite of γ-tocopherol, preserves nitric oxide bioavailability in endothelial cells challenged with high glucose.

Endothelial dysfunction occurs when there are imbalances between factors that regulate the synthesis and degradation of nitric oxide (NO•), and has been reported in patients with hyperglycemia and insulin resistance. We reported that supplementation with γ-tocopherol (γ-T) in humans limits impairments in endothelial function otherwise induced by postprandial hyperglycemia. Given the rapid metabolism of γ-T into γ-carboxyethyl hydroxychroman (γ-CEHC), we hypothesized that the vasoprotective activities of γ-T could be attributed to its metabolite γ-CEHC. To test this, human aortic endothelial cells (HAECs) treated with 0 (vehicle control) or 3 µM γ-CEHC for 24 h prior to incubation with normal (5 mM) or high (25 mM) glucose for 48 h. High-glucose increased levels of uncoupled endothelial nitric oxide synthase (eNOS) as evidenced by reduced ( p < 0.05) eNOS dimer:monomer. High glucose also prevented insulin-stimulated increases in p-AktSer473: total Akt, p-eNOSSer1177: total eNOS, and NO• production. These adverse changes were accompanied by increased ( p < 0.05) reactive oxygen species and mRNA expression of inflammatory mediators (VCAM-1, E-selectin, IL-8). However, each deleterious response evoked by high glucose was prevented when HAECs were incubated with γ-CEHC prior to the high glucose challenge. Taken together, our data support the hypothesis that vascular protection provided by γ-T in vivo may be elicited through the bioactivity of its metabolite, γ-CEHC. Furthermore, it is possible that the antioxidant and anti-inflammatory activities of γ-CEHC may mediate this protective activity.