Do We Need Anti-Prion Compounds to Treat Alzheimer’s Disease?

While phase III clinical trials for the treatment of Alzheimer’s disease (AD) keep failing regardless of the target, more and more data suggest that the toxic protein assemblies of amyloid-beta protein (Aβ) and tubulin binding protein (TAU) behave like prions. Irrespective of the question of whether AD is theoretically or practically contagious, the presence of a self-replicating toxic etiologic agent in the brains of AD patients must have decisive consequences for drug development programs and clinical trial designs. Objectives: We intend to challenge the hypothesis that the underlying etiologic agent of AD is behaving prion-like. We want to discuss whether the outcome of clinical trials could have been predicted based on this hypothesis, and whether compounds that directly disassemble the toxic prion could be more beneficial for AD treatment. Method: We collected publicly accessible pre-clinical efficacy data of Aβ targeting compounds that failed or still are in phase III clinical trials. We describe the desired properties of an anti-prion compound and compare it the properties of past and current phase III drug candidates. Results: We could not find convincing and reproducible pre-clinical efficacy data of past and current phase III drug candidates on cognition other than in preventive treatment settings. The desired properties of an anti-Aβ-prionic compound are fulfilled by the drug candidate RD2, which has been developed to directly disassemble toxic Aβ oligomers. Conclusion: RD2 is the first anti-prion drug candidate. It is able to enhance cognition and impede neurodegeneration in three different transgenic AD mouse models, even under truly non-preventive conditions and even when applied orally. In addition, it is safe in humans

Characterization of D-enantiomeric peptides binding to monomeric Amyloid beta (1-42) identified by a competitive mirror image phage display

Alzheimer's disease (AD) is the most prominent type of dementia in elderly people. Until now there is no curative therapy available.Amyloid beta (Aβ) is assumed to play a major role in the development and progression of the disease. Freely diffusible, toxic Aβ oligomers seem to have a major toxicological impact

Toward the Mode of Action of the Clinical Stage All- d -Enantiomeric Peptide RD2 on Aβ42 Aggregation

The aggregation of amyloid-β (Aβ) into oligomers and fibrillary structures is critical for the pathogenesis of Alzheimer’s disease (AD). Recently, research effort has been focused on developing novel agents that can preferentially suppress Aβ oligomer mediated toxicities, for example, by directly targeting these toxic assemblies. The compound RD2 has been developed and optimized for Aβ42 monomer binding and stabilization of the monomer in its native intrinsically disordered conformation. It has been demonstrated to improve and even reverse the cognitive and behavioral deficits in AD mouse models, while the detailed mechanism of action is not fully clarified. Here we focused on exploring the interaction between RD2 and Aβ42 monomers and its consequences for the fibrillation of Aβ42. RD2 binds to Aβ42 monomers with nanomolar affinities, according to microscale thermophoresis and surface plasmon resonance measurements. Complexes between RD2 and Aβ42 monomers are formed at 1:1 and other stoichiometries, as revealed by analytical ultracentrifugation. At substoichiometric levels, RD2 slows down the secondary structure conversion of Aβ42 and significantly delays the fibril formation. Our research provides experimental evidence in supporting that RD2 eliminates toxic Aβ assemblies by stabilizing Aβ monomers in their native intrinsically disordered conformation. The study further supports the promising application of RD2 in counteracting Aβ aggregation related pathologies

D-peptides developed to be therapeutically active against beta-amyloid oligomers show promising pharmakokinetic properties

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Surprisingly high stability of the Aβ oligomer eliminating all-d-enantiomeric peptide D3 in media simulating the route of orally administered drugs

The aggregation of the amyloid β protein (Aβ) plays an important role in the pathology of Alzheimer's disease. Previously, we have developed the all-d-enantiomeric peptide D3, which is able to eliminate neurotoxic Aβ oligomers in vitro and improve cognition in a transgenic Alzheimer's disease mouse model in vivo even after oral administration. d-Peptides are expected to be more resistant against enzymatic proteolysis compared to their l-enantiomeric equivalents, and indeed, a pharmacokinetic study with tritiated D3 revealed the oral bioavailability to be about 58%. To further investigate the underlying properties, we examined the stability of D3 in comparison to its corresponding all-l-enantiomeric mirror image l-D3 in media simulating the gastrointestinal tract, blood and liver. Potential metabolization was followed by reversed-phase high-performance liquid chromatography. In simulated gastric fluid, D3 remained almost completely stable (89%) within 24 h, while 70% of l-D3 was degraded within the same time period. Notably, in simulated intestinal fluid, D3 also remained stable (96%) for 24 h, whereas l-D3 was completely metabolized within seconds. In human plasma and human liver microsomes, l-D3 was metabolized several hundred times faster than D3. The remarkably high stability may explain the high oral bioavailability seen in previous studies allowing oral administration of the drug candidate. Thus, all-d-enantiomeric peptides may represent a promising new compound class for drug development

Characterization of D-enatiomeric peptides derived from D3 for treatment of Alzheimer`s disease

Alzheimer's disease (AD) is the most prominent neurodegenerative disease affecting more than 24 million people worldwide. Currently, it is the sixth-leading cause of death, but until now there is no causal therapy available. The amyloid-beta (Aβ) peptide plays an important role in the pathology of the disease. Especially the soluble, most harmful neurotoxic oligomers of Aβ are discussed to be responsible for the development and progression of the disease. In our group we identified the D-enantiomeric peptide D3 via mirror image phage display, which reduces the formation of Aβ oligomers in vitro [1-3]

Oral Treatment with <span style="font-variant: small-caps">d</span>-RD2RD2 Impedes Early Disease Mechanisms in SOD1*G93A Transgenic Mice but Does Not Prolong Survival

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting upper and lower motor neurons, thus, progressing to complete muscle loss until the patient dies from respiratory arrest. The disease is not curable, and patients die approximately 2–5 years after diagnosis. Studying the underlying disease mechanisms to get access to new treatment options is, therefore, essential for patients’ benefit. However, so far, only three drugs that alleviate the symptoms have been approved by the U.S. Food and Drug Administration (FDA). A new drug candidate for the treatment of ALS is the all-d-enantiomeric peptide RD2RD2. In this study, we investigated the therapeutic effect of RD2RD2 in two setups. First, we analyzed disease progression and survival in 7 week-old B6.Cg-Tg(SOD1*G93A)1Gur/J mice. Second, we confirmed the result of the survival analysis in the B6SJL-Tg(SOD1*G93A)1Gur/J mouse line. Shortly before disease onset, the mice were treated daily with an oral dose of 50 mg/kg body weight. Treatment with RD2RD2 led to a delayed disease onset and reduced motor phenotype as shown using the SHIRPA test, the splay reflex test, and the pole test, but did not affect survival. In conclusion, RD2RD2 has the ability to delay the onset of symptoms

Development of an α-synuclein fibril and oligomer specific tracer for diagnosis of Parkinson's disease, dementia with Lewy bodies and multiple system atrophy

The development of specific disease-associated PET tracers is one of the major challenges, the realization of which in neurodegenerative diseases would enable not only the efficiency of diagnosis but also support the development of disease-modifying therapeutics. Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by neuronal fibrillary inclusions composed of aggregated α-synuclein (α-syn). However, these deposits are not only found in PD, but also in other related diseases such as multiple system atrophy (MSA) and dementia with Lewy bodies (DLB), which are grouped under the term synucleinopathies. In this study, we used NGS-guided phage display selection to identify short peptides that bind aggregated α-syn. By surface plasmon resonance (SPR)-based affinity screening, we identified the peptide SVLfib-5 that recognizes aggregated α-syn with high complex stability and sequence specificity. Further analysis SPR showed that SVLfib-5 is not only specific for aggregated α-syn, but in particular recognizes fibrillary and oligomeric structures. Moreover, fluorescence microscopy of human brain tissue sections from PD, MSA, and DLB patients with SVLfib-5 allowed specific recognition of α-syn and a clear discrimination between diseased and non-diseased samples. These findings provide the basis for the further development of an α-syn PET tracer for early diagnosis and monitoring of disease progression and therapy progress

Aβ oligomer concentration in mouse and human brain and its drug-induced reduction ex vivo

The elimination of amyloid beta (Aβ) oligomers is a promising strategy for therapeutic drug development of Alzheimer’s disease (AD). AD mouse models that develop Aβ pathology have been used to demonstrate in vivo efficacy of compounds that later failed in clinical development. Here, we analyze the concentration and size distribution of Aβ oligomers in different transgenic mouse models of AD and in human brain samples by surface-based fluorescence intensity distribution analysis (sFIDA), a highly sensitive method for detecting and quantitating protein aggregates. We demonstrate dose- and time-dependent oligomer elimination by the compound RD2 in mouse and human AD brain homogenates as sources of native Aβ oligomers. Such ex vivo target engagement analyses with mouse- and human-brain-derived oligomers have the potential to enhance the translational value from pre-clinical proof-of-concept studies to clinical trials

Oral absorption enhancement of the amyloid-β oligomer eliminating compound RD2 by conjugation with folic acid

Amyloid-β (Aβ) plays a central role in the development and progression of Alzheimer’s disease (AD) with Aβ oligomers representing the most toxic species. The all-D-enantiomeric peptide RD2, which recently successfully completed clinical phase I, specifically eliminates Aβ oligomers in vitro as well as in vivo and improves cognitive deficits in various transgenic AD mouse models even after oral administration. To further enhance the oral absorption of RD2, folic acid has been conjugated to the D-peptide promoting an endocytosis-mediated uptake via a folate receptor located in the colon and rectum. Two different conjugation strategies were selected to obtain prodrugs with folic acid being cleaved after intestinal absorption releasing unmodified RD2 in order to enable RD2’s unaltered systemic efficacy. Both conjugates remained stable in simulated gastrointestinal fluids. But only one of them was suitable as prodrug as it was cleaved to RD2 in vitro in human blood plasma and liver microsomes and in vivo in mice after intravenous injection leading to a systemic release of RD2. Furthermore, the conjugate’s permeability after oral administration was strongly enhanced compared to unconjugated RD2 demonstrating the prodrug’s functionality. However, the conjugate seemed to have impaired the mice’s wellbeing shortly after oral administration