People with Parkinson’s disease have treatment options, but none directly tackle the underlying pathology of misfolded and aggregated α-synuclein. That may be poised to change, with numerous approaches targeting the protein now in the pipeline, including two immunotherapies in the clinic. At the 12th International Conference on Alzheimer’s and Parkinson’s Diseases, held March 18–22 in Nice, France, researchers at Prothena Biosciences of South San Francisco, California, presented topline Phase 1 data from their anti-α-synuclein antibody. It’s early days, but at first glance, at least, the treatment appears safe in healthy volunteers and squelches serum levels of the protein. Researchers will have to wait for the results of an ongoing trial in Parkinson’s patients to learn how the treatment behaves in the central nervous system. Meanwhile, an active vaccine under investigation by the Austrian company AFFiRiS, Vienna, has cleared Phase 1.

Published in 1892, this photograph shows the characteristic posture of a patient with Parkinson’s disease.

Other speakers described different preclinical strategies to normalize α-synuclein. Overall, the AD/PD talks showcased a field that has placed α-synuclein squarely in its sights even while some crucial questions remain unanswered. Chief among these is determining exactly what its toxic form is. “It’s exciting to see clinical progress made toward α-synuclein-lowering biologics,” Clemens Scherzer at Harvard Medical School wrote to Alzforum.

Why the emphasis on targeting α-synuclein now? In short, because researchers finally can. Alpha-synuclein has drawn intense interest ever since the late 1990s, when the first α-synuclein missense mutation was identified as a cause of familial Parkinson’s and the protein soon after turned out to be the main constituent of Lewy bodies. But α-synuclein has been an obstreperous target because it has been slow to give up its secrets about what it does normally and in disease. Finally, this year, some basic knowledge and tools are in hand, and companies developing immunotherapies against α-synuclein include, besides Prothena and AFFiRiS, AstraZeneca, BioArctic, Biogen, Genentech, and Lundbeck.

In animals, researchers know that suppressing toxic forms of the protein reverses cognitive and motor deficits (Jul 2011 newsNuber et al., 2013). Also in mice, antibodies can stop the transfer of misfolded α-synuclein from cell to cell, improving neuron survival as well as motor function (Jun 2014 news). A therapy against pathological α-synuclein would benefit not only PD patients, but also people who have dementia with Lewy bodies (DLB) or multiple system atrophy (MSA), and perhaps even some Alzheimer’s patients, noted Eliezer Masliah of the University of California, San Diego.

Immunotherapy approaches are currently closest to the clinic. At AD/PD, Wagner Zago, who leads Prothena’s research division, said his team has been working on an antibody for human use since 2003. Prothena is an outgrowth of Athena Neurosciences and Élan Corporation. Some of its employees, notably Dale Schenk, originally developed immunotherapy for Alzheimer’s disease, such as the first active vaccine, AN-1792, and the antibody bapineuzumab.

In preclinical work, the researchers found that targeting different epitopes of α-synuclein gave varying efficacy. “Most of the antibodies we tested failed,” Zago noted. Those that recognized the C-terminus of α-synuclein performed best. Cell culture experiments suggested that these antibodies somehow prevented the protease calpain-1 from cleaving the C-terminal end of extracellular α-synuclein, Zago said. Accumulation of cleaved forms in particular correlates with aggregation and toxicity (Mishizen-Eberz et al., 2003; Li et al., 2005; Dufty et al., 2007).

A Lewy body and neurite from Parkinson's brain containing α-synuclein (green=full length; red=cleaved) and proximal to nuclei (purple). [Image courtesy of Prothena Biosciences Inc.]

The winning antibody from preclinical studies was 9E4, and its humanized version became PRX002. It is an IgG1 monoclonal that binds better to aggregated forms than to monomers, Zago reported. In mice, it lowered α-synuclein deposits and gliosis, while improving spatial memory and motor skills (Games et al., 2014).

The findings led Prothena to start Phase 1 trials in collaboration with Hoffmann-La Roche in Basel, Switzerland. At AD/PD, Zago presented data from a single-ascending-dose study in 40 healthy volunteers. The study tested intravenously administered doses of 0.3, 1, 3, 10, and 30 mg/kg in six participants each, with the remaining 10 volunteers receiving placebo. Most importantly, Zago said, this first experiment with an anti-α-synuclein antibody was safe and well-tolerated at all doses tested. The antibody had favorable pharmacokinetic properties. It appeared to engage its target in the periphery, because it caused free α-synuclein in the blood to plummet by as much as 96 percent, Zago said. The reductions were dose-dependent, he said in answer to an audience query, though he stayed mum on details. A March 19 press release from Prothena noted that the main adverse events were headache and pain at the injection site.

Some audience members worried whether antibodies interfered with the cellular and synaptic functions of normal α-synuclein in the brain. Zago answered that Prothena’s preclinical studies found no change in the levels of monomeric α-synuclein levels in the brain during antibody therapy. In a panel discussion, Masliah, who has collaborated with Prothena on preclinical studies, noted that α-synuclein participates in synaptic fusion and neurotransmitter release. These functions continued normally in cell cultures after treatment with PRX002, he said.

Scherzer wrote to Alzforum that this trial does not yet answer the key question. “The reported reduction of free serum α-synuclein levels … is really intriguing and shows that there is a peripheral pharmacodynamic effect. However, α-synuclein is selectively and highly expressed in red blood cells … We don’t know yet whether the target was engaged centrally,” he wrote. The answer should be forthcoming. PRX002 is currently in a Phase 1 multiple-ascending-dose study in 60 Parkinson’s patients. That study includes cerebrospinal fluid (CSF) collection. “In this first trial we were mostly concerned to show that the antibody engages α-synuclein and that that is a safe thing to do. Everything else we still need to show,” Zago told Alzforum.

AFFiRiS’ active vaccine PD01A recently completed Phase 1 testing of multiple doses in 32 Parkinson’s patients (Mandler et al., 2014). A poster at AD/PD reported the treatment as being safe and producing antibodies in 15 of the 24 participants who received the vaccine. According to a July 2014 press release, a follow-up Phase 1 study is still ongoing. A second poster noted that AFFiRiS is also testing the vaccine in a Phase 1 trial of MSA patients. In this disease, α-synuclein accumulates in oligodendrocytes, leading to demyelination and movement problems. In a mouse model, treatment with PD01A mopped up α-synuclein aggregates in oligodendrocytes, activated microglia, and preserved myelination and neuron health, the scientists reported.

In Nice, Masliah outlined other ways to go after α-synuclein. They include blocking aggregation, promoting degradation, stabilizing non-toxic forms, or preventing toxicity by targeting receptors. “Different therapies will be applicable to different stages of the disease,” Masliah predicted.

Blocking aggregation has been popular with researchers, and several such inhibitors are inching their way toward the clinic. The Seattle-area company ProteoTech plans to take its aggregation inhibitor Synuclere, which is administered subcutaneously, into Phase 1 trials for MSA. The compound busts up α-synuclein deposits and improves motor skills in old Parkinson’s model mice, ProteoTech’s Alan Snow reported at AD/PD (Apr 2011 conference news). Snow told Alzforum that he is seeking collaborations with pharma companies. He is working on an oral formulation of the compound before moving into PD trials.

Armin Giese at Ludwig-Maximilians Universität, Munich, and Christian Griesinger at the Max Planck Institute in Göttingen formed the company MODAG GmbH in Wendelsheim, Germany, to develop the general aggregation inhibitor Anle138b. They plan to start clinical trials within the year (Apr 2011 conference newsAug 2014 conference news). At AD/PD, Michal Wegrzynowicz of Cambridge University in England presented new data on the compound’s efficacy in a mouse that expresses truncated human α-synuclein. Dopamine levels drop in these animals at six months of age, and by 12 months, dopaminergic neurons are dying. In contrast, animals that ate Anle138b in their chow from 9 to 12 months of age maintained their neurons, and levels of the neurotransmitter rebounded, Wegrzynowicz reported. The result complements recent work from Giese and Griesinger, which found that treatment with Anle138b prolonged survival of year-old, symptomatic mice that model PD by about 2 months (Levin et al., 2014).

Even though some α-synuclein therapeutics are in, or within reach of, clinical trials, researchers acknowledge a pressing need for better biomarkers to gauge their efficacy. Gene Kinney, who spun out with Prothena from Élan, told Alzforum that, as in the AD field, early trials will include a plethora of candidate biomarkers to find those that track most closely with clinical improvement. At AD/PD, Mark Frasier of the Michael J. Fox Foundation discussed the organization’s efforts to help in this regard. The MJFF has invested $100 million in biomarker discovery and validation, Frasier noted (Oct 2010 news seriesMar 2014 conference news). Foundation projects are attempting to standardize research-grade serum and CSF assays of α-synuclein, improve their sensitivity and dynamic range, and move promising “home brews” toward mass production, Frasier said. One such assay, developed by Michael Schlossmacher and Brit Mollenhauer and then mass-produced by BioLegend, is commercially available and being used in the Parkinson’s Progression Markers Initiative; Prothena is developing in-house assays with Roche to use with PRX002.

Kinney noted that trial results in Alzheimer’s have shown the importance of screening participants for trials to make sure they have the pathology being targeted by the investigational drug. Screening is done with CSF or amyloid PET. A research consortium funded by MJFF to develop PET tracers for detecting the protein in living brains (Bagchi et al., 2013) remains a ways off from human trials. One challenge in finding a high-affinity tracer—and even just sufficiently robust and specific antibodies—is that they tend to bind other amyloids in brain tissue, which in many α-synucleinopathies comprise a mixture of misfolded protein deposits. “For Parkinson’s, we need even better biomarkers than for Alzheimer’s, because the mixed pathologies are a bigger problem in PD than AD. People enter the clinic with movement disorders and not everything is due to α-synuclein,” said Lars Lannfelt of Uppsala University, who works on a similar antibody to Prothena’s with the company BioArctic.

Not everything is more complex in Parkinson’s, however. One consolation is that α-synuclein does not form extracellular deposits on blood vessels, so sides effects such as ARIA are unlikely to be a concern.

One burning issue flared up in many talks: The pathological species of α-synuclein remains unknown. A similar narrative as in AD has unfolded over the years: a native synaptic protein of mysterious function, various misfolded/aggregated/secreted species ranging from oligomers to fibrils, but no consensus on which is most important, if indeed there even is a single toxic species. The next frontier will be to answer this question, Frasier said. To address it, MJFF is funding mass spectrometry research to compare the forms of the protein detected by different commercial assays. This may help pin down post-translational modifications associated with toxicity, Frasier said.—Madolyn Bowman Rogers and Gabrielle Strobel


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News Citations

  1. Targeting α-Synuclein, Glucocerebrosidase May Work for LBD
  2. Synuclein Snatch: Antibodies Snag Protein En Route to Next Neuron
  3. Barcelona: Parkinson’s Treatments on the Horizon
  4. Therapies Take Aim at Tau
  5. Prodromal Initiative to Identify Biomarkers for Parkinson’s

Therapeutics Citations

  1. Bapineuzumab

Series Citations

  1. Michael J. Fox Foundation Launches Big PD Biomarker Study

Paper Citations

  1. . A progressive dopaminergic phenotype associated with neurotoxic conversion of α-synuclein in BAC-transgenic rats. Brain. 2013 Feb;136(Pt 2):412-32. PubMed.
  2. . Distinct cleavage patterns of normal and pathologic forms of alpha-synuclein by calpain I in vitro. J Neurochem. 2003 Aug;86(4):836-47. PubMed.
  3. . Aggregation promoting C-terminal truncation of alpha-synuclein is a normal cellular process and is enhanced by the familial Parkinson's disease-linked mutations. Proc Natl Acad Sci U S A. 2005 Feb 8;102(6):2162-7. Epub 2005 Jan 31 PubMed.
  4. . Calpain-cleavage of alpha-synuclein: connecting proteolytic processing to disease-linked aggregation. Am J Pathol. 2007 May;170(5):1725-38. PubMed.
  5. . Reducing C-terminal-truncated alpha-synuclein by immunotherapy attenuates neurodegeneration and propagation in Parkinson's disease-like models. J Neurosci. 2014 Jul 9;34(28):9441-54. PubMed.
  6. . Next-generation active immunization approach for synucleinopathies: implications for Parkinson's disease clinical trials. Acta Neuropathol. 2014 Jun;127(6):861-79. Epub 2014 Feb 14 PubMed.
  7. . The oligomer modulator anle138b inhibits disease progression in a Parkinson mouse model even with treatment started after disease onset. Acta Neuropathol. 2014 Mar 11; PubMed.
  8. . Binding of the radioligand SIL23 to α-synuclein fibrils in Parkinson disease brain tissue establishes feasibility and screening approaches for developing a Parkinson disease imaging agent. PLoS One. 2013;8(2):e55031. PubMed.

Other Citations

  1. AN-1792

External Citations

  1. single-ascending-dose study
  2. press release
  3. Phase 1
  4. Phase 1
  5. press release
  6. Phase 1 study
  7. Phase 1 trial
  8. research consortium

Further Reading