[11C]MODAG-001-towards a PET tracer targeting α-synuclein aggregates.

PURPOSE: Deposition of misfolded alpha-synuclein (αSYN) aggregates in the human brain is one of the major hallmarks of synucleinopathies. However, a target-specific tracer to detect pathological aggregates of αSYN remains lacking. Here, we report the development of a positron emission tomography (PET) tracer based on anle138b, a compound shown to have therapeutic activity in animal models of neurodegenerative diseases. METHODS: Specificity and selectivity of [3H]MODAG-001 were tested in in vitro binding assays using recombinant fibrils. After carbon-11 radiolabeling, the pharmacokinetic and metabolic profile was determined in mice. Specific binding was quantified in rats, inoculated with αSYN fibrils and using in vitro autoradiography in human brain sections of Lewy body dementia (LBD) cases provided by the Neurobiobank Munich (NBM). RESULTS: [3H]MODAG-001 revealed a very high affinity towards pure αSYN fibrils (Kd = 0.6 ± 0.1 nM) and only a moderate affinity to hTau46 fibrils (Kd = 19 ± 6.4 nM) as well as amyloid-ß1-42 fibrils (Kd = 20 ± 10 nM). [11C]MODAG-001 showed an excellent ability to penetrate the mouse brain. Metabolic degradation was present, but the stability of the parent compound improved after selective deuteration of the precursor. (d3)-[11C]MODAG-001 binding was confirmed in fibril-inoculated rat striata using in vivo PET imaging. In vitro autoradiography showed no detectable binding to aggregated αSYN in human brain sections of LBD cases, most likely, because of the low abundance of aggregated αSYN against background protein. CONCLUSION: MODAG-001 provides a promising lead structure for future compound development as it combines a high affinity and good selectivity in fibril-binding assays with suitable pharmacokinetics and biodistribution properties.

Anle138b modulates α-synuclein oligomerization and prevents motor decline and neurodegeneration in a mouse model of multiple system atrophy.

BACKGROUND: MSA is a fatal neurodegenerative disease characterized by autonomic failure and severe motor impairment. Its main pathological hallmark is the accumulation of α-synuclein in oligodendrocytes, leading to glial and neuronal dysfunction and neurodegeneration. These features are recapitulated in the PLP-hαSyn mouse model expressing human α-synuclein in oligodendrocytes. At present, there is no effective disease-modifying therapy. Previous experiments have shown that the aggregation inhibitor, anle138b, reduces neurodegeneration and behavioral deficits in mouse models of other proteinopathies. OBJECTIVES: To test the therapeutic potential of anle138b in a mouse model of MSA. METHODS: Two-month-old PLP-hαSyn mice were fed over a period of 4 months with pellets containing anle138b at two different doses (0.6 and 2 g/kg) and compared to healthy controls and PLP-hαSyn mice fed with placebo pellets. At the end of the treatment, behavioral and histological analyses were performed. RESULTS: We observed a reversal of motor function to healthy control levels when PLP-hαSyn mice were treated with both doses of anle138b. Histological and molecular analyses showed a significant reduction in α-synuclein oligomers and glial cytoplasmic inclusions in animals fed with anle138b compared to nontreated mice. These animals also present preservation of dopaminergic neurons and reduction in microglial activation in SN correlating with the α-synuclein reduction observed. CONCLUSIONS: Anle138b reduces α-synuclein accumulation in PLP-hαSyn mice, leading to neuroprotection, reduction of microglial activation, and preservation of motor function supporting the use of anle138b in a future clinical trial for MSA. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Photophysics of diphenyl-pyrazole compounds in solutions and α-synuclein aggregates.

BACKGROUND: Recently diphenyl-pyrazole (DPP) compounds and especially anle138b were found to reduce the aggregation of α-synuclein or Tau protein in vitro as well as in a mouse model of neurodegenerative diseases [1,2]. Direct interaction of the DPPs with the fibrillar structure was identified by fluorescence spectroscopy. Thereby a strong dependence of the fluorescence on the surroundings could be identified [3]. METHODS: Stationary and time-resolved emission experiments were performed on DPP compounds substituted by different halogens. RESULTS: The compounds reveal a pronounced dependence of the fluorescence on the surrounding solvent. In non-polar solvents they show strong emission in the blue part of the spectrum while in polar and proton donating solvents, such as water or acetic acid a dual fluorescence can be observed where a red-shifted emission points to a charge transfer in the excited state with large dipole moment. Non-radiative processes including photochemical reactions are observed for DPP substituted with heavy halogens. Upon binding of anle138b and its derivatives to protein fibrils in aqueous buffer, strong enhancement of the fluorescence at short wavelengths is found. CONCLUSION: The investigations of the DPPs in different surroundings lead to a detailed model of the fluorescence characteristics. We propose a model for the binding in fibrils of different proteins, where the DPP is located in a hydrophobic groove independent of the specific sequence of the amino acids. GENERAL SIGNIFICANCE: These investigations characterize the binding site of the DPP anle138b in protein aggregates and contribute to the understanding of the therapeutic mode of action of this compound.

Atp23 biogenesis reveals a chaperone-like folding activity of Mia40 in the IMS of mitochondria.

Mia40 is a recently identified oxidoreductase in the intermembrane space (IMS) of mitochondria that mediates protein import in an oxidation-dependent reaction. Substrates of Mia40 that were identified so far are of simple structure and receive one or two disulphide bonds. Here we identified the protease Atp23 as a novel substrate of Mia40. Atp23 contains ten cysteine residues which are oxidized during several rounds of interaction with Mia40. In contrast to other Mia40 substrates, oxidation of Atp23 is not essential for its import; an Atp23 variant in which all ten cysteine residues were replaced by serine residues still accumulates in mitochondria in a Mia40-dependent manner. In vitro Mia40 can mediate the folding of wild-type Atp23 and prevents its aggregation. In these reactions, the hydrophobic substrate-binding pocket of Mia40 was found to be essential for its chaperone-like activity. Thus, Mia40 plays a much broader role in import and folding of polypeptides than previously expected and can serve as folding factor for proteins with complex disulphide patterns as well as for cysteine-free polypeptides.

Reducing tau aggregates with anle138b delays disease progression in a mouse model of tauopathies.

Pathological tau aggregation leads to filamentous tau inclusions and characterizes neurodegenerative tauopathies such as Alzheimer's disease and frontotemporal dementia and parkinsonism linked to chromosome 17. Tau aggregation coincides with clinical symptoms and is thought to mediate neurodegeneration. Transgenic mice overexpressing mutant human P301S tau exhibit many neuropathological features of human tauopathies including behavioral deficits and increased mortality. Here, we show that the di-phenyl-pyrazole anle138b binds to aggregated tau and inhibits tau aggregation in vitro and in vivo. Furthermore, anle138b treatment effectively ameliorates disease symptoms, increases survival time and improves cognition of tau transgenic PS19 mice. In addition, we found decreased synapse and neuron loss accompanied by a decreased gliosis in the hippocampus. Our results suggest that reducing tau aggregates with anle138b may represent an effective and promising approach for the treatment of human tauopathies.

Biogenesis of mitochondrial proteins.

Depending on the organism, mitochondria consist approximately of 500-1,400 different proteins. By far most of these proteins are encoded by nuclear genes and synthesized on cytosolic ribosomes. Targeting signals direct these proteins into mitochondria and there to their respective subcompartment: the outer membrane, the intermembrane space (IMS), the inner membrane, and the matrix. Membrane-embedded translocation complexes allow the translocation of proteins across and, in the case of membrane proteins, the insertion into mitochondrial membranes. A small number of proteins are encoded by the mitochondrial genome: Most mitochondrial translation products represent hydrophobic proteins of the inner membrane which-together with many nuclear-encoded proteins-form the respiratory chain complexes. This chapter gives an overview on the mitochondrial protein translocases and the mechanisms by which they drive the transport and assembly of mitochondrial proteins.

Safety, tolerability and pharmacokinetics of the oligomer modulator anle138b with exposure levels sufficient for therapeutic efficacy in a murine Parkinson model: A randomised, double-blind, placebo-controlled phase 1a trial.

BACKGROUND: Synucleinopathies such as Parkinson ́s disease (PD), Dementia with Lewy bodies (DLB) and Multiple System Atrophy (MSA) are characterized by deposition of misfolded and aggregated α-synuclein. Small aggregates (oligomers) of α-synuclein have been shown to be the most relevant neurotoxic species and are targeted by anle138b, an orally bioavailable small molecule compound which shows strong disease-modifying effects in animal models of synucleinopathies. METHODS: Anle138b was studied in a single-centre, double-blind, randomised, placebo-controlled single ascending dose (SAD) and multiple ascending dose (MAD) study in healthy subjects. Eligible participants were randomly assigned (1:1 for sentinel subjects and 1:5 for main group) to placebo or anle138b (dose range 50 mg to 300 mg per day), respectively. In addition, the effect of food on the pharmakokinetics of anle138b in healthy subjects was examined in doses of 150 mg per day. Participants were randomized to treatment sequence (fed→fasted) or (fasted→fed). Treatment was administered orally in hard gelatine capsules containing either 10 mg or 30 mg of anle138b or excipient only. The primary endpoints were safety and tolerability, the secondary endpoint was pharmakokinetics. Data from all randomized individuals were evaluated. CLINICALTRIALS: gov-identifier: NCT04208152. EudraCT-number: 2019-004218-33. FINDINGS: Between December 17th, 2019 and June 27th, 2020 196 healthy volunteers were screened and 68 participants were enrolled. Of these, all completed the study per protocol. There were no major protocol deviations. Adverse events in this healthy volunteer trial were mostly mild and all fully recovered or resolved prior to discharge. From baseline to completion of the trial no medically significant individual changes were observed in any system organ class. Already at multiple doses of 200 mg, exposure levels above the fully effective exposure in the MI2 mouse Parkinson model were observed. INTERPRETATION: The favourable safety and PK profile of anle138b in doses resulting in exposures above the fully effective plasma level in a mouse Parkinson model warrant further clinical trials in patients with synucleinopathies. FUNDING: This study was funded by MODAG GmbH and by the Michael J. Fox foundation for Parkinson's Research.

The rubella virus capsid protein inhibits mitochondrial import.

The rubella virus (RV) capsid is an RNA-binding protein that functions in nucleocapsid assembly at the Golgi complex, the site of virus budding. In addition to its role in virus assembly, pools of capsid associate with mitochondria, a localization that is not consistent with virus assembly. Here we examined the interaction of capsid with mitochondria and showed that this viral protein inhibits the import and processing of mitochondrial precursor proteins in vitro. Moreover, RV-infected cells were found to contain lower intramitochondrial levels of matrix protein p32. In addition to inhibiting the translocation of substrates into mammalian mitochondria, capsid efficiently blocked import into yeast mitochondria, thereby suggesting that it acts by targeting a highly conserved component of the translocation apparatus. Finally, mutation of a cluster of five arginine residues in the amino terminus of capsid, though not interfering with its binding to mitochondria, abrogated its ability to block protein import into mitochondria. This is the first report of a viral protein that affects the import of proteins into mitochondria.

Potential sources of interference with the highly sensitive detection and quantification of alpha-synuclein seeds by qRT-QuIC.

Parkinson's disease (PD) is a progressive neurodegenerative disease which is histologically characterized by loss of dopaminergic neurons in the substantia nigra and deposition of aggregated alpha-synuclein (aSyn) in the brain. The detection of aSyn in well accessible fluids has been one of the central approaches in the development of biomarkers for PD. Recently, real-time quaking-induced conversion (RT-QuIC) has been successfully adapted for use with aSyn seeds. Here, we systematically analysed parameters potentially impacting the reliability of this assay by using quantitative real-time quaking-induced conversion (qRT-QuIC) with in vitro-formed aSyn seeds. Seeds diluted in cerebrospinal fluid (CSF) accelerated the seeding reaction and slightly increased the sensitivity without affecting specificity. Repeated freeze-thaw cycles decreased the apparent lag times of seeds diluted in ddH2 O but did not alter the seeding activity of seeds diluted in CSF. High levels of artificial contamination with blood resulted in prolonged apparent lag times, while sensitivity and specificity were unaffected. Altogether, qRT-QuIC with aSyn seems to be robust concerning sensitivity and specificity in our model system, but quantitative interpretation might be limited under certain conditions.

Tau-induced mitochondrial membrane perturbation is dependent upon cardiolipin.

Misfolding and aggregate formation by the tau protein has been closely related with neurotoxicity in a large group of human neurodegenerative disorders, which includes Alzheimer's disease. Here, we investigate the membrane-active properties of tau oligomers on mitochondrial membranes, using minimalist in vitro model systems. Thus, exposure of isolated mitochondria to oligomeric tau evoked a disruption of mitochondrial membrane integrity, as evidenced by a combination of organelle swelling, efflux of cytochrome c and loss of the mitochondrial membrane potential. Tau-induced mitochondrial dysfunction occurred independently of the mitochondrial permeability transition (mPT) pore complex. Notably, mitochondria were rescued by pre-incubation with 10-N-nonyl acridine orange (NAO), a molecule that specifically binds cardiolipin (CL), the signature phospholipid of mitochondrial membranes. Additionally, NAO prevented direct binding of tau oligomers to isolated mitochondria. At the same time, tau proteins exhibited high affinity to CL-enriched membranes, whilst permeabilisation of lipid vesicles also strongly correlated with CL content. Intriguingly, using single-channel electrophysiology, we could demonstrate the formation of non-selective ion-conducting tau nanopores exhibiting multilevel conductances in mito-mimetic bilayers. Taken together, the data presented here advances a scenario in which toxic cytosolic entities of tau protein would target mitochondrial organelles by associating with their CL-rich membrane domains, leading to membrane poration and compromised mitochondrial structural integrity.

11 C Radiolabeling of anle253b: a Putative PET Tracer for Parkinson's Disease That Binds to α-Synuclein Fibrils in†vitro and Crosses the Blood-Brain Barrier.

There is an urgent clinical need for imaging of α-synuclein (αSyn) fibrils, the hallmark biomarker for Parkinson's disease, in neurodegenerative disorders. Despite immense efforts, promising tracer candidates for nuclear imaging of αSyn are rare. Diphenyl pyrazoles are known modulators of αSyn aggregation and thus bear potential for non-invasive detection of this biomarker in vivo. Here we demonstrate high-affinity binding of the family member anle253b to fibrillar αSyn and present a high-yielding site-selective radiosynthesis route for 11 C radiolabeling using in-situ generated [11 C]formaldehyde and reductive methylation. Radio-HPLC of the tracer after incubation with rat serum in vitro shows excellent stability of the molecule. Positron emission tomography in healthy animals is used to assess the pharmacokinetics and biodistribution of the tracer, showing good penetration of the blood-brain barrier and low background binding to the non-pathological brain.

Iron-mediated aggregation and toxicity in a novel neuronal cell culture model with inducible alpha-synuclein expression.

Parkinson's disease (PD) represents an increasing problem in society. The oligomerization of alpha-synuclein (αSyn) is a suggested key event in its pathogenesis, yet the pathological modes of action remain to be fully elucidated. To identify potential disease-modifying therapeutics and to study αSyn-mediated toxic mechanisms, we established cell lines with inducible overexpression of different αSyn constructs: αSyn, αSyn coupled to the fluorescence protein Venus (αSyn-Venus), and αSyn coupled to the N-terminal or C-terminal part of Venus (V1S and SV2, respectively) for a bimolecular fluorescence complementation assay (BiFC). Inducibility was achieved by applying modified GAL4-UAS or Cre-loxP systems and addition of tebufenozide or 4-OH-tamoxifen, respectively. Expression constructs were stably integrated into the host genome of H4 neuroglioma cells by lentiviral transduction. We here demonstrate a detailed investigation of the expression characteristics of inducible H4 cells showing low background expression and high inducibility. We observed increased protein load and aggregation of αSyn upon incubation with DMSO and FeCl3 along with an increase in cytotoxicity. In summary, we present a system for the creation of inducibly αSyn-overexpressing cell lines holding high potential for the screening for modulators of αSyn aggregation and αSyn-mediated toxicity.

Methods to study the biogenesis of membrane proteins in yeast mitochondria.

The biogenesis of mitochondrial membrane proteins is an intricate process that relies on the import and submitochondrial sorting of nuclear-encoded preproteins and on the synthesis of mitochondrial translation products in the matrix. Subsequently, these polypeptides need to be inserted into the outer and the inner membranes of the organelle where many of them assemble into multisubunit complexes. In this chapter we provide established protocols to study these different processes experimentally using mitochondria of budding yeast. In particular, methods are described in detail to purify mitochondria, to study mitochondrial protein synthesis, to follow the import of radiolabeled preproteins into isolated mitochondria, and to assess membrane association and the aggregation of mitochondrial proteins by fractionation. These protocols and a list of dos and don'ts shall enable beginners and experienced scientists to address the targeting and assembly of mitochondrial membrane proteins.