Alzheimer's Drug PBT2 Interacts with the Amyloid ß 1-42 Peptide Differently than Other 8-Hydroxyquinoline Chelating Drugs.

Although Alzheimer's disease (AD) was first described over a century ago, it remains the leading cause of age-related dementia. Innumerable changes have been linked to the pathology of AD; however, there remains much discord regarding which might be the initial cause of the disease. The "amyloid cascade hypothesis" proposes that the amyloid ß (Aß) peptide is central to disease pathology, which is supported by elevated Aß levels in the brain before the development of symptoms and correlations of amyloid burden with cognitive impairment. The "metals hypothesis" proposes a role for metal ions such as iron, copper, and zinc in the pathology of AD, which is supported by the accumulation of these metals within amyloid plaques in the brain. Metals have been shown to induce aggregation of Aß, and metal ion chelators have been shown to reverse this reaction in vitro. 8-Hydroxyquinoline-based chelators showed early promise as anti-Alzheimer's drugs. Both 5-chloro-7-iodo-8-hydroxyquinoline (CQ) and 5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline (PBT2) underwent unsuccessful clinical trials for the treatment of AD. To gain insight into the mechanism of action of 8HQs, we have investigated the potential interaction of CQ, PBT2, and 5,7-dibromo-8-hydroxyquinoline (B2Q) with Cu(II)-bound Aß(1-42) using X-ray absorption spectroscopy (XAS), high energy resolution fluorescence detected (HERFD) XAS, and electron paramagnetic resonance (EPR). By XAS, we found CQ and B2Q sequestered ∼83% of the Cu(II) from Aß(1-42), whereas PBT2 sequestered only ∼59% of the Cu(II) from Aß(1-42), suggesting that CQ and B2Q have a higher relative Cu(II) affinity than PBT2. From our EPR, it became clear that PBT2 sequestered Cu(II) from a heterogeneous mixture of Cu(II)Aß(1-42) species in solution, leaving a single Cu(II)Aß(1-42) species. It follows that the Cu(II) site in this Cu(II)Aß(1-42) species is inaccessible to PBT2 and may be less solvent-exposed than in other Cu(II)Aß(1-42) species. We found no evidence to suggest that these 8HQs form ternary complexes with Cu(II)Aß(1-42).

Dysregulation of Streptococcus pneumoniae zinc homeostasis breaks ampicillin resistance in a pneumonia infection model.

Streptococcus pneumoniae is the primary cause of community-acquired bacterial pneumonia with rates of penicillin and multidrug-resistance exceeding 80% and 40%, respectively. The innate immune response generates a variety of antimicrobial agents to control infection, including zinc stress. Here, we characterize the impact of zinc intoxication on S. pneumoniae, observing disruptions in central carbon metabolism, lipid biogenesis, and peptidoglycan biosynthesis. Characterization of the pivotal peptidoglycan biosynthetic enzyme GlmU indicates a sensitivity to zinc inhibition. Disruption of the sole zinc efflux pathway, czcD, renders S. pneumoniae highly susceptible to ß-lactam antibiotics. To dysregulate zinc homeostasis in the wild-type strain, we investigated the safe-for-human-use ionophore 5,7-dichloro-2-[(dimethylamino)methyl]quinolin-8-ol (PBT2). PBT2 rendered wild-type S. pneumoniae strains sensitive to a range of antibiotics. Using an invasive ampicillin-resistant strain, we demonstrate in a murine pneumonia infection model the efficacy of PBT2 + ampicillin treatment. These findings present a therapeutic modality to break antibiotic resistance in multidrug-resistant S. pneumoniae.

Copper(II) Binding to PBT2 Differs from That of Other 8-Hydroxyquinoline Chelators: Implications for the Treatment of Neurodegenerative Protein Misfolding Diseases.

PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) is a small Cu(II)-binding drug that has been investigated in the treatment of neurodegenerative diseases, namely, Alzheimer's disease (AD). PBT2 is thought to be highly effective at crossing the blood-brain barrier and has been proposed to exert anti-Alzheimer's effects through the modulation of metal ion concentrations in the brain, specifically the sequestration of Cu(II) from amyloid plaques. However, despite promising initial results in animal models and in clinical trials where PBT2 was shown to improve cognitive function, larger-scale clinical trials did not find PBT2 to have a significant effect on the amyloid plaque burden compared with controls. We propose that the results of these clinical trials likely point to a more complex mechanism of action for PBT2 other than simple Cu(II) sequestration. To this end, herein we have investigated the solution chemistry of Cu(II) coordination by PBT2 primarily using X-ray absorption spectroscopy (XAS), high-energy-resolution fluorescence-detected XAS, and electron paramagnetic resonance. We propose that a novel bis-PBT2 Cu(II) complex with asymmetric coordination may coexist in solution with a symmetric four-coordinate Cu(II)-bis-PBT2 complex distorted from coplanarity. Additionally, PBT2 is a more flexible ligand than other 8HQs because it can act as both a bidentate and a tridentate ligand as well as coordinate Cu(II) in both 1:1 and 2:1 PBT2/Cu(II) complexes.

Anti-Aß agents for mild to moderate Alzheimer's disease: systematic review and meta-analysis.

OBJECTIVE: To assess the efficacy and safety of Aß-targeting agents for mild to moderate Alzheimer's disease. METHODS: The MEDLINE, Embase, Cochrane Central Register of Controlled Trials, PsycINFO, ClinicalTrials.gov and the WHO's International Clinical Trials Registry Platform search portal were searched from their inception to April 2020. We generated pooled estimates using random effects meta-analyses. RESULTS: Nineteen randomised controlled trials, of which 17 had a low risk of bias, included 12 903 participants. The meta-analysis showed no difference in the cognitive subscale of Alzheimer's Disease Assessment Scale (ADAS-Cog) between anti-Aß drugs and placebo (mean difference (MD): 0.20, 95% CI -0.40 to 0.81; I 2=99.8%; minimal important difference 3.1-3.8 points, moderate-certainty evidence). For ADAS-Cog, results suggested that one drug that increases Aß clearance may differ in effect (MD: -0.96, 95% CI -0.99 to -0.92) from drugs that reduce Aß production (MD: 0.78, 95% CI 0.25 to 1.32) (interaction p<0.000001); this difference also existed in the outcome of MMSE and CDR-SOB. Compared with placebo, anti-Aß drug-related adverse events were as follows: anxiety, depression, diarrhoea, fatigue, rash, syncope and vomit. DISCUSSION: From current evidence, anti-Aß interventions are unlikely to have an important impact on slowing cognitive or functional decline. Although the subgroup analysis suggested possible benefits from Aß clearance drugs, the analysis has limited credibility, and a benefit from drugs that increase clearance, if real, is very small. TRIAL REGISTRATION NUMBER: PROSPERO registration number CRD42019126272.

In silico and in vitro analysis of FAK/MMP signaling axis inhibition by VO-clioquinol in 2D and 3D human osteosarcoma cancer cells.

The study of novel mechanisms of action of vanadium compounds is critical to elucidating the role and importance of these kinds of compounds as antitumor and antimetastatic agents. This work deals with in silico and in vitro studies of one clioquinol oxidovanadium(iv) complex [VO(clioquinol)2], VO(CQ)2, and its regulation of FAK. In particular, we focus on elucidating the relationship of the FAK inhibition, MMP activity and antimetastatic effects of the complex in human bone cancer cells.

Multiple Bactericidal Mechanisms of the Zinc Ionophore PBT2.

Globally, more antimicrobials are used in food-producing animals than in humans, and the extensive use of medically important human antimicrobials poses a significant public health threat in the face of rising antimicrobial resistance (AMR). The development of novel ionophores, a class of antimicrobials used exclusively in animals, holds promise as a strategy to replace or reduce essential human antimicrobials in veterinary practice. PBT2 is a zinc ionophore with recently demonstrated antibacterial activity against several Gram-positive pathogens, although the underlying mechanism of action is unknown. Here, we investigated the bactericidal mechanism of PBT2 in the bovine mastitis-causing pathogen, Streptococcus uberis In this work, we show that PBT2 functions as a Zn2+/H+ ionophore, exchanging extracellular zinc for intracellular protons in an electroneutral process that leads to cellular zinc accumulation. Zinc accumulation occurs concomitantly with manganese depletion and the production of reactive oxygen species (ROS). PBT2 inhibits the activity of the manganese-dependent superoxide dismutase, SodA, thereby impairing oxidative stress protection. We propose that PBT2-mediated intracellular zinc toxicity in S. uberis leads to lethality through multiple bactericidal mechanisms: the production of toxic ROS and the impairment of manganese-dependent antioxidant functions. Collectively, these data show that PBT2 represents a new class of antibacterial ionophores capable of targeting bacterial metal ion homeostasis and cellular redox balance. We propose that this novel and multitarget mechanism of PBT2 makes the development of cross-resistance to medically important antimicrobials unlikely.IMPORTANCE More antimicrobials are used in food-producing animals than in humans, and the extensive use of medically important human antimicrobials poses a significant public health threat in the face of rising antimicrobial resistance. Therefore, the elimination of antimicrobial crossover between human and veterinary medicine is of great interest. Unfortunately, the development of new antimicrobials is an expensive high-risk process fraught with difficulties. The repurposing of chemical agents provides a solution to this problem, and while many have not been originally developed as antimicrobials, they have been proven safe in clinical trials. PBT2, a zinc ionophore, is an experimental therapeutic that met safety criteria but failed efficacy checkpoints against both Alzheimer's and Huntington's diseases. It was recently found that PBT2 possessed potent antimicrobial activity, although the mechanism of bacterial cell death is unresolved. In this body of work, we show that PBT2 has multiple mechanisms of antimicrobial action, making the development of PBT2 resistance unlikely.

Neisseria gonorrhoeae Becomes Susceptible to Polymyxin B and Colistin in the Presence of PBT2.

Neisseria gonorrhoeae (N. gonorrhoeae) causes the sexually transmitted disease gonorrhea, which has a global incidence of 106 million cases per year. No vaccine is available to prevent the disease, and the emergence of multidrug resistant (MDR) strains makes N. gonorrhoeae an immediate public health threat. Here, we show that an ionophore, PBT2, can reverse the intrinsic resistance of N. gonorrhoeae to polymyxin B and colistin. These antibiotics administered in combination with PBT2 may be an effective path to treat MDR gonococcal infections.

WBQ5187, a Multitarget Directed Agent, Ameliorates Cognitive Impairment in a Transgenic Mouse Model of Alzheimer's Disease and Modulates Cerebral ß-Amyloid, Gliosis, cAMP Levels, and Neurodegeneration.

Previously, we designed, synthesized, and evaluated a series of quinolone-benzofuran derivatives as multitargeted anti-Alzheimer's disease (anti-AD) compounds, and we discovered that WBQ5187 possesses superior anti-AD bioactivity. In this work, we investigated the pharmacokinetics of this new molecule, as well as its therapeutic efficacy in restoring cognition and neuropathology, in the APP/PS1 mouse model of AD. Pharmacokinetic analyses demonstrated that WBQ5187 possessed rational oral bioavailability, metabolic stability, and excellent blood-brain barrier (BBB) permeability. Pharmacodynamics studies indicated that a 12-week treatment with the lead compound at doses of 40 mg/kg or higher significantly enhanced the learning and memory performance of the APP/PS1 transgenic mice, and the effect was more potent than that of clioquinol (CQ). Furthermore, WBQ5187 notably reduced cerebral ß-amyloid pathology, gliosis, and neuronal cell loss and increased the levels of cAMP in the hippocampus of these mice. The surrogate measures of emesis indicated that WBQ5187 had no effect at its cognitive effective doses. Overall, our results demonstrated that this compound markedly improves cognitive and spatial memory functions in AD mice and represents a promising pharmaceutical agent with potential for the treatment of AD.

Chemical Synergy between Ionophore PBT2 and Zinc Reverses Antibiotic Resistance.

The World Health Organization reports that antibiotic-resistant pathogens represent an imminent global health disaster for the 21st century. Gram-positive superbugs threaten to breach last-line antibiotic treatment, and the pharmaceutical industry antibiotic development pipeline is waning. Here we report the synergy between ionophore-induced physiological stress in Gram-positive bacteria and antibiotic treatment. PBT2 is a safe-for-human-use zinc ionophore that has progressed to phase 2 clinical trials for Alzheimer's and Huntington's disease treatment. In combination with zinc, PBT2 exhibits antibacterial activity and disrupts cellular homeostasis in erythromycin-resistant group A Streptococcus (GAS), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). We were unable to select for mutants resistant to PBT2-zinc treatment. While ineffective alone against resistant bacteria, several clinically relevant antibiotics act synergistically with PBT2-zinc to enhance killing of these Gram-positive pathogens. These data represent a new paradigm whereby disruption of bacterial metal homeostasis reverses antibiotic-resistant phenotypes in a number of priority human bacterial pathogens.IMPORTANCE The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, "On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you."

Targeting metals rescues the phenotype in an animal model of tauopathy.

Tauopathies are characterized by the pathological accumulation of the microtubule associated protein tau within the brain. We demonstrate here that a copper/zinc chaperone (PBT2, Prana Biotechnology) has rapid and profound effects in the rTg(tauP301L)4510 mouse model of tauopathy. This was evidenced by significantly improved cognition, a preservation of neurons, a decrease in tau aggregates and a decrease in other forms of "pathological" tau (including phosphorylated tau and sarkosyl-insoluble tau). Our data demonstrate that one of the primary mechanisms of action of PBT2 in this model may be driven by an interaction on the pathways responsible for the dephosphorylation of tau. Specifically, PBT2 increased protein levels of both the structural and catalytic subunits of protein phosphatase 2A (PP2A), decreased levels of the methyl esterase (PME1) that dampens PP2A activity, and increased levels of the prolyl isomerase (Pin1) that stimulates the dephosphorylation activity of PP2A. None of these effects were observed when the metal binding site of PBT2 was blocked. This highlights the potential utility of targeting metal ions as a novel therapeutic strategy for diseases in which tau pathology is a feature, which includes conditions such as frontotemporal dementia and Alzheimer's disease.

Clioquinol is a promising preventive morphological switching compound in the treatment of Candida infections linked to the use of intrauterine devices.

PURPOSE: Candida biofilm infections are frequently linked to the use of biomaterials and are of clinical significance because they are commonly resistant to antifungals. Clioquinol is an antiseptic drug and is effective against multidrug-resistant Candida. We investigated the effect of clioquinol and two other 8-hydroxyquinoline derivatives on Candida biofilm. METHODOLOGY: The ability to inhibit biofilm formation, inhibit preformed biofilm and remove established biofilms was evaluated using in vitro assays on microtitre plates. The action of clioquinol on biofilm in intrauterine devices (IUDs) was also investigated, describing the first protocol to quantify the inhibitory action of compounds on biofilms formed on IUDs. RESULTS: Clioquinol was found to be the most effective 8-hydroxyquinoline derivative among those tested. It prevented more than 90 % of biofilm formation, which can be attributed to blockade of hyphal development. Clioquinol also reduced the metabolic activity of sessile Candida but the susceptibility was lower compared to planktonic cells (0.031-0.5 µg ml-1 required to inhibit 50 % planktonic cells and 4-16 µg ml-1 to inhibit 50 % preformed biofilms). On the other hand, almost complete removal of biofilms was not achieved for the majority of the isolates. Candida spp. also showed the ability to form biofilm on copper IUD; clioquinol eradicated 80-100 % of these biofilms. CONCLUSION: Our results indicate a potential application in terms of biomaterials for 8-hydroxyquinoline derivatives. Clioquinol could be used as a coating to prevent morphological switching and thus prevent biofilm formation. Furthermore, clioquinol may have future applications in the treatment of Candida infections linked to the use of IUDs.

Metal Protein-Attenuating Compound for PET Neuroimaging: Synthesis and Preclinical Evaluation of [11C]PBT2.

Dyshomeostasis or abnormal accumulation of metal ions such as copper, zinc, and iron have been linked to the pathogenesis of multiple neurodegenerative disorders including Alzheimer's disease (AD) and Huntington's disease (HD). 5,7-Dichloro-2-((dimethylamino)methyl)quinolin-8-ol, PBT2, is a second generation metal protein-attenuating compound that has recently advanced in Phase II clinical trials for the treatment of AD and HD based on promising preclinical efficacy data. Herein, we report the first radiosynthesis and preclinical positron emission tomography (PET) neuroimaging evaluation of [11C]PBT2 in rodents and nonhuman primates. Carbon-11 labeled PBT2 was synthesized in 4.8 ± 0.5% (nondecay corrected) radiochemical yield (RCY) at end-of-synthesis, based upon [11C]CH3I (n = 6), with >99% radiochemical purity and 80-90 GBq/µmol molar activity (Am) from the corresponding normethyl precursor. In the nonhuman primate brain, [11C]PBT2 uptake was extensive with peak concentration SUVpeak of 3.2-5.2 within 2.5-4.5 min postinjection in all cortical and subcortical gray matter regions (putamen > caudate > cortex ≫ white matter) followed by rapid washout from normal brain tissues. Furthermore, it is shown that [11C]PBT2 binds specifically in AD human brain tissue in vitro. The results presented here, combined with the clinical data available for PBT2, warrant the evaluation of [11C]PBT2 as an exploratory PET radiotracer in humans.

Clioquinol-ruthenium complex impairs tumour cell invasion by inhibiting cathepsin B activity.

Over the past few years, the organometalled compounds, including ruthenium, gained a lot of attention as anticancer agents. We report on the clioquinol-ruthenium complex [Ru(η6-p-cymene)(Cq)Cl] as a potent inhibitor of cathepsin B, a lysosomal cysteine peptidase, involved in tumour cell invasion and metastasis. In the low micromolar concentration range, the clioquinol-ruthenium complex did not exhibit cytotoxic effects on MCF-10A neoT and U-87 MG cells; it did, however, significantly reduce their ability for extracellular matrix degradation and invasiveness in two independent cell-based models, measuring either electrical impedance in real time or the growth of multicellular tumour spheroids implanted in Matrigel, a model representing the extracellular matrix. These results establish ruthenium based organometallic compounds as promising candidates for further pre-clinical studies as anticancer therapeutics.

Possible role of metal ionophore against zinc induced cognitive dysfunction in D-galactose senescent mice.

Metal ionophores are considered as potential anti-dementia agents, and some are currently undergoing clinical trials. Many metals are known to accumulate and distribute abnormally in the aging brain. Alterations in zinc metal homeostasis in the glutaminergic synapse could contribute to ageing and the pathophysiology of Alzheimer's disease (AD). The present study was designed to investigate the effect of metal ionophores on long term administration of zinc in D-galactose induced senescent mice. The ageing model was established by combined administration of zinc and D-galactose to mice for 6 weeks. A novel metal ionophore, PBT-2 was given daily to zinc-induced d-galactose senescent mice. The cognitive behaviour of mice was monitored using the Morris Water Maze. The anti-oxidant status and amyloidogenic activity in the ageing mouse was measured by determining mito-oxidative parameters and deposition of amyloid ß (Aß) in the brain. Systemic administration of both zinc and D-galactose significantly produced memory deficits, mito-oxidative damage, heightened acetylcholinesterase enzymatic activity and deposition of amyloid-ß. Treatment with PBT-2 significantly improved behavioural deficits, biochemical profiles, cellular damage, and curbed the deposition of APP in zinc-induced senescent mice. These findings suggest that PBT-2, acting as a metal protein attenuating compound, may be helpful in the prevention of AD or alleviation of ageing.

New Hydroxyquinoline-Based Derivatives as Potent Modulators of Amyloid-ß Aggregations.

Copper and zinc have been found to contribute to the burden of amyloid-ß (Aß) aggregations in neurodegenerative Alzheimer's disease (AD). Dysregulation of these metals leads to the generation of reactive oxygen species (ROS) and eventually results in oxidative damage and accumulation of the Aß peptide, which are the key elements of the disease. Aiming to pursue the discovery of new modulators for the disease, we here rationally focused on conjugating the core hydroxyquinoline of the metal-protein attenuating compound PBT2 and the N-methylanilide analogous moiety of the Aß imaging agent to build a new type of multi-target modulators of Aß aggregations. We found that the N,N-dimethylanilinyl imines 7a, 8a, and the corresponding amines 7b, 8b exerted efficient inhibition of Cu(2+) - or Zn(2+) -induced Aß aggregations and significant disassembly of metal-mediated Aß aggregated fibrils. Further, 7a and 7b also exhibited significant ROC scavenging effects compared to PBT2. The results suggested that 7a and 7b are promising lead compounds for the development of a new therapy for AD.

Design, Synthesis, and Evaluation of Orally Available Clioquinol-Moracin M Hybrids as Multitarget-Directed Ligands for Cognitive Improvement in a Rat Model of Neurodegeneration in Alzheimer's Disease.

A novel series of clioquinol-moracin hybrids were designed and synthesized by fusing the pharmacophores of clioquinol and moracin M, and their activities as multitarget-directed ligands against Alzheimer's disease were evaluated. Biological activity results demonstrated that these hybrids possessed significant inhibitory activities against phosphodiesterase 4D (PDE4D) and Aß aggregation as well as remarkable antioxidant effects and excellent blood-brain barrier permeability. The optimal compound, 18d (WBQ5187), exhibited excellent PDE4D inhibitory potency (IC50 = 0.32 µM), significant antioxidant effects, appropriate biometal chelating functions, and interesting properties that modulated self- and metal-induced Aß aggregation. Two-dimensional NMR studies revealed that 18d had significant interactions with Aß1-42 at the R5, H6, H14, Q15, and F20 residues. Furthermore, this typical hybrid possessed preeminent neuroprotective effects against inflammation in microglial cells. Most importantly, oral administration of 18d·HCl demonstrated marked improvements in cognitive and spatial memory in a rat model of Alzheimer's disease and protected hippocampal neurons from necrosis.

PBT2 inhibits glutamate-induced excitotoxicity in neurons through metal-mediated preconditioning.

Excitotoxicity is the pathological process by which neuronal death occurs as a result of excessive stimulation of receptors at the excitatory synapse such as the NMDA receptor (NMDAR). Excitotoxicity has been implicated in the acute neurological damage from ischemia and traumatic brain injury and in the chronic neurodegeneration in Alzheimer's disease (AD) and Huntington's disease (HD). As a result NMDAR antagonists have become an attractive therapeutic strategy for the potential treatment of multiple neurodegenerative diseases. However NMDAR signaling is dichotomous in nature, with excessive increases in neuronal intracellular calcium through excessive NMDAR activity being lethal but moderate increases to intracellular calcium levels during normal synaptic function providing neuroprotection. Subsequently indiscriminant inhibition of this receptor is best avoided as was concluded from previous clinical trials of NMDAR antagonists. We show that the metal chaperone, PBT2, currently in clinical trials for HD, is able to protect against glutamate-induced excitotoxicity mediated through NMDARs. This was achieved by PBT2 inducing Zn(2+)-dependent increases in intracellular Ca(2+) levels resulting in preconditioning of neurons and inhibition of Ca(2+)-induced neurotoxic signaling cascade involving calpain-activated cleavage of calcineurin. Our study demonstrates that modulating intracellular Ca(2+) levels by a zinc ionophore is a valid therapeutic strategy to protect against the effects of excitotoxicity thought to underlie both acute and chronic neurodegenerative diseases.

Stabilization of nontoxic Aß-oligomers: insights into the mechanism of action of hydroxyquinolines in Alzheimer's disease.

The extracellular accumulation of amyloid ß (Aß) peptides is characteristic of Alzheimer's disease (AD). However, formation of diffusible, oligomeric forms of Aß, both on and off pathways to amyloid fibrils, is thought to include neurotoxic species responsible for synaptic loss and neurodegeneration, rather than polymeric amyloid aggregates. The 8-hydroxyquinolines (8-HQ) clioquinol (CQ) and PBT2 were developed for their ability to inhibit metal-mediated generation of reactive oxygen species from Aß:Cu complexes and have both undergone preclinical and Phase II clinical development for the treatment of AD. Their respective modes of action are not fully understood and may include both inhibition of Aß fibrillar polymerization and direct depolymerization of existing Aß fibrils. In the present study, we find that CQ and PBT2 can interact directly with Aß and affect its propensity to aggregate. Using a combination of biophysical techniques, we demonstrate that, in the presence of these 8-HQs and in the absence of metal ions, Aß associates with two 8-HQ molecules and forms a dimer. Furthermore, 8-HQ bind Aß with an affinity of 1-10 µm and suppress the formation of large (>30 kDa) oligomers. The stabilized low molecular weight species are nontoxic. Treatment with 8-HQs also reduces the levels of in vivo soluble oligomers in a Caenorhabditis elegans model of Aß toxicity. We propose that 8-HQs possess an additional mechanism of action that neutralizes neurotoxic Aß oligomer formation through stabilization of small (dimeric) nontoxic Aß conformers.

Metal chaperones prevent zinc-mediated cognitive decline.

Zinc transporter-3 (ZnT3) protein is responsible for loading zinc into presynaptic vesicles and consequently controls the availability of zinc at the glutamatergic synapse. ZnT3 has been shown to decline with age and in Alzheimer's disease (AD) and is crucially involved in learning and memory. In this study, we utilised whole animal behavioural analyses in the ZnT3 KO mouse line, together with electrophysiological analysis of long-term potentiation in brain slices from ZnT3 KO mice, to show that metal chaperones (clioquinol, 30 mg/kg/day for 6weeks) can prevent the age-dependent cognitive phenotype that characterises these animals. This likely occurs as a result of a homeostatic restoration of synaptic protein expression, as clioquinol significantly restored levels of various pre- and postsynaptic proteins that are critical for normal cognition, including PSD-95; AMPAR and NMDAR2b. We hypothesised that this clioquinol-mediated restoration of synaptic health resulted from a selective increase in synaptic zinc content within the hippocampus. While we demonstrated a small regional increase in hippocampal zinc content using synchrotron x-ray fluorescence microscopy, further sub-region analyses are required to determine whether this effect is seen in other regions of the hippocampal formation that are more closely linked to the synaptic plasticity effects observed in this study. These data support our recent report on the use of a different metal chaperone (PBT2) to prevent normal age-related cognitive decline and demonstrate that metal chaperones are efficacious in preventing the zinc-mediated cognitive decline that characterises ageing and disease.

Safety, tolerability, and efficacy of PBT2 in Huntington's disease: a phase 2, randomised, double-blind, placebo-controlled trial.

BACKGROUND: PBT2 is a metal protein-attenuating compound that might reduce metal-induced aggregation of mutant huntingtin and has prolonged survival in a mouse model of Huntington's disease. We aimed to assess the safety, tolerability, and efficacy of PBT2 in patients with Huntington's disease. METHODS: In this 26-week, randomised, double-blind, placebo-controlled trial, adults (≥25 years old) with early-stage to mid-stage Huntington's disease were randomly assigned (1:1:1) by a centralised interactive response system to once daily PBT2 250 mg, PBT2 100 mg, or placebo. Randomisation was stratified by site with a block size of three. Participants, carers, the steering committee, site investigators, study staff, and the study sponsor were masked to treatment assignment. Primary endpoints were safety and tolerability. The safety population consisted of all participants who were randomly assigned and had at least one dose of study drug. The principal secondary endpoint was cognition, measured by the change from baseline to week 26 in the main composite Z score of five cognitive tests (Category Fluency Test, Trail Making Test Part B, Map Search, Symbol Digit Modalities Test, and Stroop Word Reading Test) and scores on eight individual cognitive tests (the five aforementioned plus the Trail Making Test Part A, Montreal Cognitive Assessment, and the Speeded Tapping Test). The intention-to-treat population comprised participants who were randomly assigned and had at least one efficacy assessment after administration of study drug. This trial is registered with ClinicalTrials.gov, NCT01590888. FINDINGS: Between April 18, 2012, and Dec 14, 2012, 109 participants were randomly assigned to PBT2 250 mg (n=36), PBT2 100 mg (n=38), or placebo (n=35) at 19 research centres in Australia and the USA. 32 (89%) individuals on PBT2 250 mg, 38 (100%) on PBT2 100 mg, and 34 (97%) on placebo completed the study. Six serious adverse events (acute coronary syndrome, major depression, pneumonia, suicide attempt, viral infection, and worsening of Huntington's disease) occurred in five participants in the PBT2 250 mg group, three (fall with subdural haematoma, suicide attempt, and hospital admission for stabilisation of Huntington's disease) occurred in two participants in the PBT2 100 mg group, and one (increasing aggression) occurred in a participant in the placebo group. The site investigators deemed all, except the worsening of Huntington's disease, as unrelated to study drug. 32 (89%) participants on PBT2 250 mg, 30 (79%) on PBT2 100 mg, and 28 (80%) on placebo had at least one adverse event. Compared with placebo, neither PBT2 100 mg (least-squares mean 0·02, 95% CI -0·10 to 0·14; p=0·772) nor PBT2 250 mg (0·07, -0·05 to 0·20; p=0·240) significantly improved the main composite cognition Z score between baseline and 26 weeks. Compared with placebo, the Trail Making Test Part B score was improved between baseline and 26 weeks in the PBT2 250 mg group (17·65 s, 0·65-34·65; p=0·042) but not in the 100 mg group (0·79 s improvement, -15·75 to 17·32; p=0·925); neither dose significantly improved cognition on the other tests. INTERPRETATION: PBT2 was generally safe and well tolerated in patients with Huntington's disease. The potential benefit on executive function will need to be confirmed in a larger study. FUNDING: Prana Biotechnology Limited.