An impaired mitochondrial electron transport chain increases retention of the hypoxia imaging agent diacetylbis(4-methylthiosemicarbazonato)copper ^II

Abstract

Radiolabeleddiacetylbis4-methylthiosemicarbazonatocopper II [Cu II atsm] is an effective positron-emission tomography imaging agent for myocardial ischemia, hypoxic tumors, and brain disorders with regionalized oxidative stress, such as mitochondrial myopathy, encephalopathy, and lactic acidosis with stroke-like episodes (MELAS) and Parkinson's disease. An excessively elevated reductive state is common to these conditions and has been proposed as an important mechanism affecting cellular retention of Cu from Cu II atsm. However, data from whole-cell models to demonstrate this mechanism have not yet been provided. The present study used a unique cell culture model, mitochondrial xenocybrids, to provide whole-cell mechanistic data on cellular retention of Cu from Cu II atsm. Genetic incompatibility between nuclear and mitochondrial encoded subunits of the mitochondrial electron transport chain (ETC) in xenocybrid cells compromises normal function of the ETC. As a consequence of this impairment to the ETC we show xenocybrid cells upregulate glycolytic ATP production and accumulate NADH. Compared to control cells the xenocybrid cells retained more Cu after being treated with Cu II atsm. By transfecting the cells with a metal-responsive element reporter construct the increase in Cu retention was shown to involve a Cu II atsminduced increase in intracellular bioavailable Cu specifically within the xenocybrid cells. Parallel experiments using cells grown under hypoxic conditions confirmed that a compromised ETC and elevated NADH levels contribute to increased cellular retention of Cu from Cu II atsm. Using these cell culture models our data demonstrate that compromised ETC function, due to the absence of O 2 as the terminal electron acceptor or dysfunction of individual components of the ETC, is an important determinant in driving the intracellular dissociation of Cu II atsm that increases cellular retention of the Cu.sodium arsenite | energy metabolism | radiopharmaceutical P

Comparison of 18F-Fluoroazomycin-Arabinofuranoside and 64Cu-Diacetyl-Bis(N4-Methylthiosemicarbazone) in Preclinical Models of Cancer

“…Differences in expression or activity of the heavy metal exporter ATP7B or a dual-phase uptake mechanism have been suggested to have a role in the cell line dependence of 64 Cu-ATSM redistribution (20)(21)(22)(23)(24). However, other factors, such as pH changes, oxidative stress, and the activity of the mitochondrial electron transport chain, seem to influence the cellular trapping of 64 Cu-ATSM (25).…”

64Cu-ATSM Reflects pO2 Levels in Human Head and Neck Cancer Xenografts but Not in Colorectal Cancer Xenografts: Comparison with 64CuCl2

“…The mechanism responsible for 64 Cu-ATSM retention is not completely understood, but in vitro studies have indicated that the 64 Cu-ATSM complex undergoes reduction by free diffusion after entering the cells (27)(28)(29). In normoxic cells, 64 Cu-ATSM is rapidly reoxidized and consequently able to leave the cell again by free diffusion.…”

Precise Evaluation of Striatal Oxidative Stress Corrected for Severity of Dopaminergic Neuronal Degeneration in Patients with Parkinson’s Disease: A Study with ⁶²Cu-ATSM PET and ¹²³I-FP-CIT SPECT

“…Thus, 62 Cu-ATSM is retained in sites with an over-reductive state in the delayed phase (10–20 min) [7, 18-20]. A higher accumulation of Cu-ATSM observed in cell lines with increased levels of biological reductant NADH due to hypoxia or mitochondrial respiratory failure than that in the parental cells under normoxic conditions supports the retention mechanism of this ligand [8, 21, 22]. …”