Copper Bis(thiosemicarbazonato)-stilbenyl Complexes That Bind to Amyloid-ß Plaques.

Alzheimer's disease is characterized by the presence of extracellular amyloid-ß plaques. Positron emission tomography (PET) imaging with tracers radiolabeled with positron-emitting radionuclides that bind to amyloid-ß plaques can assist in the diagnosis of Alzheimer's disease. With the goal of designing new imaging agents radiolabeled with positron-emitting copper-64 radionuclides that bind to amyloid-ß plaques, a family of bis(thiosemicarbazone) ligands with appended substituted stilbenyl functional groups has been prepared. The ligands form charge-neutral and stable complexes with copper(II). The new ligands can be radiolabeled with copper-64 at room temperature. Two lead complexes were demonstrated to bind to amyloid-ß plaques present in post-mortem brain tissue from subjects with clinically diagnosed Alzheimer's disease and crossed the blood-brain barrier in mice. The work presented here provides strategies to prepare compounds with radionuclides of copper that can be used for targeted brain PET imaging.

Metal complexes designed to bind to amyloid-ß for the diagnosis and treatment of Alzheimer's disease.

Alzheimer's disease is the most common form of age-related neurodegenerative dementia. The disease is characterised by the presence of plaques in the cerebral cortex. The major constituent of these plaques is aggregated amyloid-ß peptide. This review focuses on the molecular aspects of metal complexes designed to bind to amyloid-ß. The development of radioactive metal-based complexes of copper and technetium designed as diagnostic imaging agents to detect amyloid burden in the brain is discussed. Separate sections of the review discuss the use of luminescent metal complexes to act as non-conventional probes of amyloid formation and recent research into the use of metal complexes as inhibitors of amyloid formation and toxicity.

Diagnostic imaging agents for Alzheimer's disease: copper radiopharmaceuticals that target Aß plaques.

One of the pathological hallmarks of Alzheimer's disease is the presence of amyloid-ß plaques in the brain and the major constituent of these plaques is aggregated amyloid-ß peptide. New thiosemicarbazone-pyridylhydrazine based ligands that incorporate functional groups designed to bind amyloid-ß plaques have been synthesized. The new ligands form stable four coordinate complexes with a positron-emitting radioactive isotope of copper, (64)Cu. Two of the new Cu(II) complexes include a functionalized styrylpyridine group and these complexes bind to amyloid-ß plaques in samples of post-mortem human brain tissue. Strategies to increase brain uptake by functional group manipulation have led to a (64)Cu complex that effectively crosses the blood-brain barrier in wild-type mice. The new complexes described in this manuscript provide insight into strategies to deliver metal complexes to amyloid-ß plaques.

Inhibition of TDP-43 accumulation by bis(thiosemicarbazonato)-copper complexes.

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, motor neuron disease with no effective long-term treatment options. Recently, TDP-43 has been identified as a key protein in the pathogenesis of some cases of ALS. Although the role of TDP-43 in motor neuron degeneration is not yet known, TDP-43 has been shown to accumulate in RNA stress granules (SGs) in cell models and in spinal cord tissue from ALS patients. The SG association may be an early pathological change to TDP-43 metabolism and as such a potential target for therapeutic intervention. Accumulation of TDP-43 in SGs induced by inhibition of mitochondrial activity can be inhibited by modulation of cellular kinase activity. We have also found that treatment of cells and animal models of neurodegeneration, including an ALS model, with bioavailable bis(thiosemicarbazonato)copper(II) complexes (Cu(II)(btsc)s) can modulate kinase activity and induce neuroprotective effects. In this study we examined the effect of diacetylbis(-methylthiosemicarbazonato)copper(II) (Cu(II)(atsm)) and glyoxalbis(-methylthiosemicarbazonato)copper(II) (Cu(II)(gtsm)) on TDP-43-positive SGs induced in SH-SY5Y cells in culture. We found that the Cu(II)(btsc)s blocked formation of TDP-43-and human antigen R (HuR)-positive SGs induced by paraquat. The Cu(II)(btsc)s protected neurons from paraquat-mediated cell death. These effects were associated with inhibition of ERK phosphorylation. Co-treatment of cultures with either Cu(II)(atsm) or an ERK inhibitor, PD98059 both prevented ERK activation and blocked formation of TDP-43-and HuR-positive SGs. Cu(II)(atsm) treatment or ERK inhibition also prevented abnormal ubiquitin accumulation in paraquat-treated cells suggesting a link between prolonged ERK activation and abnormal ubiquitin metabolism in paraquat stress and inhibition by Cu. Moreover, Cu(II)(atsm) reduced accumulation of C-terminal (219-414) TDP-43 in transfected SH-SY5Y cells. These results demonstrate that Cu(II)(btsc) complexes could potentially be developed as a neuroprotective agent to modulate neuronal kinase function and inhibit TDP-43 aggregation. Further studies in TDP-43 animal models are warranted.

The hypoxia imaging agent CuII(atsm) is neuroprotective and improves motor and cognitive functions in multiple animal models of Parkinson's disease.

Parkinson's disease (PD) is a progressive, chronic disease characterized by dyskinesia, rigidity, instability, and tremors. The disease is defined by the presence of Lewy bodies, which primarily consist of aggregated α-synuclein protein, and is accompanied by the loss of monoaminergic neurons. Current therapeutic strategies only give symptomatic relief of motor impairment and do not address the underlying neurodegeneration. Hence, we have identified Cu(II)(atsm) as a potential therapeutic for PD. Drug administration to four different animal models of PD resulted in improved motor and cognition function, rescued nigral cell loss, and improved dopamine metabolism. In vitro, this compound is able to inhibit the effects of peroxynitrite-driven toxicity, including the formation of nitrated α-synuclein oligomers. Our results show that Cu(II)(atsm) is effective in reversing parkinsonian defects in animal models and has the potential to be a successful treatment of PD.

An impaired mitochondrial electron transport chain increases retention of the hypoxia imaging agent diacetylbis(4-methylthiosemicarbazonato)copperII.

Radiolabeled diacetylbis(4-methylthiosemicarbazonato)copper(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)(atsm)-induced 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.

Diacetylbis(N(4)-methylthiosemicarbazonato) copper(II) (CuII(atsm)) protects against peroxynitrite-induced nitrosative damage and prolongs survival in amyotrophic lateral sclerosis mouse model.

Amyotrophic lateral sclerosis (ALS) is a progressive paralyzing disease characterized by tissue oxidative damage and motor neuron degeneration. This study investigated the in vivo effect of diacetylbis(N(4)-methylthiosemicarbazonato) copper(II) (CuII(atsm)), which is an orally bioavailable, blood-brain barrier-permeable complex. In vitro the compound inhibits the action of peroxynitrite on Cu,Zn-superoxide dismutase (SOD1) and subsequent nitration of cellular proteins. Oral treatment of transgenic SOD1G93A mice with CuII(atsm) at presymptomatic and symptomatic ages was performed. The mice were examined for improvement in lifespan and motor function, as well as histological and biochemical changes to key disease markers. Systemic treatment of SOD1G93A mice significantly delayed onset of paralysis and prolonged lifespan, even when administered to symptomatic animals. Consistent with the properties of this compound, treated mice had reduced protein nitration and carbonylation, as well as increased antioxidant activity in spinal cord. Treatment also significantly preserved motor neurons and attenuated astrocyte and microglial activation in mice. Furthermore, CuII(atsm) prevented the accumulation of abnormally phosphorylated and fragmented TAR DNA-binding protein-43 (TDP-43) in spinal cord, a protein pivotal to the development of ALS. CuII(atsm) therefore represents a potential new class of neuroprotective agents targeting multiple major disease pathways of motor neurons with therapeutic potential for ALS.

Mechanisms controlling the cellular accumulation of copper bis(thiosemicarbazonato) complexes.

Copper (Cu) bis(thiosemicarbazonato) metal complexes [Cu(II)(btsc)s] have unique tumor-imaging and treatment properties and more recently have revealed potent neuroprotective actions in animal and cell models of neurodegeneration. However, despite the continued development of Cu(II)(btsc)s as potential therapeutics or diagnostic agents, little is known of the mechanisms involved in cell uptake, subcellular trafficking, and efflux of this family of compounds. Because of their high lipophilicity, it has been assumed that cellular accumulation is through passive diffusion, although this has not been analyzed in detail. The role of efflux pathways in cell homeostasis of the complexes is also largely unknown. In the present study, we investigated the cellular accumulation of the Cu(II)(btsc) complexes Cu(II)(gtsm) and Cu(II)(atsm) in human neuronal (M17) and glial (U87MG) cell lines under a range of conditions. Collectively, the data strongly suggested that Cu(II)(gtsm) and Cu(II)(atsm) may be taken into these cells by combined passive and facilitated (protein-carrier-mediated) mechanisms. This was supported by strong temperature-dependent changes to the uptake of the complexes and the influence of the cell surface protein on Cu accumulation. We found no evidence to support a role for copper-transporter 1 in accumulation of the compounds. Importantly, our findings also demonstrated that Cu from both Cu(II)(gtsm) and Cu(II)(atsm) was rapidly effluxed from the cells through active mechanisms. Whether this was in the form of released ionic Cu or as an intact metal complex is not known. However, this finding highlighted the difficulty of trying to determine the uptake mechanism of metal complexes when efflux is occurring concomitantly. These findings are the first detailed exploration of the cellular accumulation mechanisms of Cu(II)(btsc)s. The study delineates strategies to investigate the uptake and efflux mechanisms of metal complexes in cells, while highlighting specific difficulties and challenges that need to be considered before drawing definitive conclusions.

Subcellular localization of a fluorescent derivative of CuII(atsm) offers insight into the neuroprotective action of CuII(atsm).

Copper complexes of bis(thiosemicarbazone) (Cu(II)(btsc)s) have been studied as potential anti-cancer agents and hypoxia imaging agents. More recently, Cu(II)(btsc)s have been identified as possessing potent neuroprotective properties in cell and animal models of neurodegenerative disease. Despite their broad range of pharmacological activity little is known about how cells traffic Cu(II)(btsc)s and how this relates to potential anti-cancer or neuroprotective outcomes. One method of investigating sub-cellular localization of metal complexes is through confocal fluorescence imaging of the compounds in cells. Previously we harnessed the fluorescence of a pyrene group attached to diacetyl-bis(N4-methylthiosemicarbazonato)copper(ii)) (Cu(II)(atsm)), (Cu(II)L(1)). We demonstrated that Cu(II)L(1) was partially localized to lysosomes in HeLa cancer epithelial cells. Here we extend these studies to map the sub-cellular localization of Cu(II)L(1) in M17 neuroblastoma cells. Treatment of M17 or HeLa cells led to rapid association of the Cu-complex into distinct punctate structures that partially co-localized with lysosomes as assessed by co-localization with Lysotracker and acridine orange. No localization to early or late endosomes, the nucleus or mitochondria was observed. We also found evidence for a limited association of Cu(II)L(1) with autophagic structures, however, this did not account for the majority of the punctate localization of Cu(II)L(1). In addition, Cu(II)L(1) revealed partial localization with ER Tracker and was found to inhibit ER stress induced by tunicamycin. This is the first report to comprehensively characterize the sub-cellular localization of a Cu(II)(atsm) derivative in cells of a neuronal origin and the partial association with lysosome/autophagic structures and the ER may have a potential role in neuroprotection.

A copper radiopharmaceutical for diagnostic imaging of Alzheimer's disease: a bis(thiosemicarbazonato)copper(II) complex that binds to amyloid-beta plaques.

A bis(thiosemicarbazonato)copper(ii) complex with an appended stilbene functional group binds to amyloid-beta plaques that are associated with Alzheimer's disease. The complex has the potential to be of use as a copper-64 radiopharmaceutical to assist in the diagnosis of Alzheimer's disease by positron emission tomography.

Copper and zinc bis(thiosemicarbazonato) complexes with a fluorescent tag: synthesis, radiolabelling with copper-64, cell uptake and fluorescence studies.

The synthesis of new copper(II) bis(thiosemicarbazonato) complexes with an appended pyrene chromophore and their zinc(II) analogues is reported. The new proligands and their copper(II) and zinc(II) complexes were characterised by a combination of NMR, EPR, high performance liquid chromatography, mass spectrometry, electronic spectroscopy and electrochemical measurements. The new copper(II) complexes are fluorescent as a consequence of an appended pyrene substituent that is separated from the sulphur coordinating to the metal ion by five bonds. The emission from the pyrene substituent is concentration- and solvent-dependent with characteristic formation of excimer aggregates. A radioactive (64)Cu complex has been prepared. Cell permeability, intracellular distribution and importantly the ability to cross the nuclear membrane to target DNA were investigated using confocal fluorescence microscopy in a human cancer cell line under normal oxygen conditions and hypoxic conditions. In both cases, there was no evidence of uptake of the copper(II) bis(thiosemicarbazonato) complexes in the area of the cell nucleus.