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SFN Annual Meeting

Access daily, concise peer-reviewed reports from the SFN Annual Meeting selected by the Neurology Today editors.

Wednesday, October 21, 2015

CHICAGO—Scientists at the University of British Columbia’s Centre for Molecular Medicine and Therapeutics (CMMT) have identified eight of the most common genetic variations of the huntingtin (HTT) gene associated with Huntington’s disease (HD) and tested specialized antisense oligonucleotides (ASOs) in blood cells derived from patients with HD to assess whether the drugs can silence, or turn off, the mutated gene and reduce levels of the toxic huntingtin protein.

 

The results could lead to a combination therapy that could potentially benefit more patients with HD, said Nicholas Caron, PhD, a postdoctoral fellow in the CMMT laboratory of Michael Hayden, MD, PhD, who described the research here on Tuesday at the Society for Neuroscience annual meeting.

 

ASOs work by binding to the messenger RNA and inducing degradation of the transcript, preventing synthesis of the mutant protein, Dr. Caron explained in an interview with the Neurology Today Conference Reporter.

 

The Hayden laboratory has performed genetic analyses on thousands of patients with HD (and healthy controls) to identify variations on the HTT gene that are common among patients with HD. With these specific variations in hand, they developed ASOs that target each one of these genetic sequences and delivered a combination of ASO molecules to HD animals to see whether they work to reduce the toxic huntingtin protein. The normal huntingtin protein, critical for brain cells throughout life, is not targeted in this approach.

 

“We identified eight single nucleotide polymorphisms (SNPs) that are enriched on the mutant allele,” said Dr. Caron. “We wanted maximum coverage for HD patients. The panel of ASOs we are now identifying and testing could ultimately help treat up to 85 percent of the HD population. We hope we can identify ASOs for each haplotype so we can tailor the medicine for an individual patient.”

 

Dr. Caron added: “We design ASOs to bind to that specific sequence on the allele and only silence the mutant copy. The difference in our approach to what is now being developed for clinical trials is that other ASOs target the wild-type and mutant alleles. But the wild-type protein is important for neuronal health.”

 

Dr. Hayden’s team is developing a panel of ASOs targeting HD SNPs specific to the three most common HD HTT haplotypes and are using a potent and well tolerated ASO to see if one of the HD SNPs they identified is effective at reducing the mutant huntingtin protein.

 

Lowering mutant huntingtin in animal models of HD has proven effective at reducing the motor and behavioral symptoms, as well as the neuropathology observed in the brain. RNA interference methods are also being developed by other groups to reduce the huntingtin protein.

 

The first clinical trial using a non-selective HTT silencing approach (targeting wild-type and the mutant gene) is now underway. The trial is sponsored by ISIS Pharmaceuticals and Roche and will enroll a few dozen early stage patients with HD in several sites across Canada and Europe.

 

Commenting on the research, Willeke van Roon-Mom, PhD, an assistant professor and head of the Huntington’s Disease Research Group at Leiden University Medical Center in the Netherlands, said: “I think this strategy will work, and these kinds of approaches make a lot of sense. Scientists can design a drug that only targets the sequence in which they are interested.”

 

But, Dr. van Roon-Mom, added, “You always have patients who don’t have the common SNPs, so other strategies are needed, too.”

 

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·        Kay C, et al. Huntingtin haplotypes provide prioritized target panels for allele-specific silencing in Huntington disease patients of European ancestry. Mol Ther 2015; Epub 2015 Jul 23: http://1.usa.gov/1MBFye4

Wednesday, October 21, 2015

BY JAMIE TALAN

 

CHICAGO—Scientists at the University of Texas Medical Branch in Galveston have successfully engineered an anti-tau antibody that only targets tau oligomer aggregates of the protein. The antibody was powerful enough to reverse severe cognitive and motor symptoms in an alpha-synuclein animal model, they reported here on Tuesday at the Society for Neuroscience annual meeting.

 

The researchers said the strategy could be used to treat Parkinson’s disease (PD) and Lewy body dementia (LBD), as well as other neurodegenerative conditions.

 

Describing the experiments at the meeting, Julia Gerson, a doctoral student in the laboratory of Rakez Kayed, PhD, who led the experiments, said they designed the monoclonal antibody to target only toxic tau and not harm the normal tau that is required to support microtubules, the highways of the cells.

 

She and colleagues injected seven-month-old mice overexpressing the mutated alpha-synuclein with either a tau oligomer-specific antibody (TOMA), an antibody targeting all forms of tau, or a control (immunoglobulin G) antibody. Healthy (wild-type) mice were injected with saline. Two weeks later, they conducted a battery of tests assessing cognitive and motor function, and found that the severe phenotype (motor and cognitive deficits) were reversed in the mice that had received TOMA.

 

Following the testing, half of the mice in each group were sacrificed and collected for biochemical and immunohistochemical analysis. The researchers found decreased levels of toxic tau oligomers in the brains of TOMA-treated mice and elevated levels of dopamine and the synaptic protein synapsin 1.

 

The remaining living mice were tested again at 12 months. The researchers observed that the severe movement and cognitive problems were reversed in the animals that had received the TOMA, while the phenotype appeared to be exacerbated in mice treated with the antibody for all forms of tau.

 

Dr. Kayed, an associate professor in the departments of neurology and cell biology and neuroscience, told the Neurology Today Conference Reporter that the research team is now in discussions with pharmaceutical companies to test the TOMA in clinical trials. He said he hopes that this will be a viable therapeutic strategy for treating all forms of tauopathies. Immunization against toxic forms of tau could also protect against memory and movement symptoms, he said.

 

Dr. Kayed said he believes that toxic forms of alpha-synuclein trigger the aggregation of tau, which then leads to cell death in PD and LBD.

 

“We will likely need to have several different monoclonal antibodies that target toxic tau in different diseases,” he said. “There could be differences in tau aggregates that are formed from one disease to another. We are developing new antibodies that are disease specific.”

 

The researchers are now trying to better understand the interaction between toxic tau and alpha-synuclein and how the antibody works to reverse the phenotype.

 

Commenting on the study, Chad Dickey, PhD, an associate professor and vice chair of molecular medicine at University of South Florida Health Morsani College of Medicine, said: “This study shows that neurodegenerative diseases share common pathologies, and each of these can be targeted for treatment.

 

“Although clinicians might think it best to treat a Parkinson’s patient carrying an A53T synuclein with anti-synuclein treatment, anti-tau treatment may also be effective,” he said. “It seems increasingly clear that for many neurodegenerative diseases, all it takes is for one protein to develop a structural abnormality (such as a mutation or post-translational modification) for it to then set off a cascade that corrupts other proteins, such as tau or even possibly TDP-43, creating an overall proteotoxic environment contributed to by many toxic intermediates.”

 

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·        Castillo-Carranza DL, et al. Passive immunization with tau oligomer monoclonal antibody reverses tauopathy phenotypes without affecting hyperphosphorylated neurofibrillary tangles. J Neurosci 2014; 34(12):4260-4272: http://1.usa.gov/1OQ65J2

Wednesday, October 21, 2015

BY JAMIE TALAN                                     

 

CHICAGO—Researchers have developed a strategy to prevent the formation of amyloid-beta (Abeta) with a compound that blocks the dimerization of the amyloid precursor protein (APP), according to a study described here on Monday at the annual meeting of the Society for Neuroscience.

 

Previous research has shown that inducing dimerization — the biochemical reaction that joins two molecules into a single dimer — increases Abeta, the researchers, led by Carmela R. Abraham, PhD, a professor of biochemistry and pharmacology at Boston University School of Medicine, and her colleagues explained in their abstract. In their study, they wanted to determine what would happen if they inhibited dimerization.

 

The findings, which build on research first published in 2012, could provide a new therapeutic target, said Dr. Abraham, whose colleague, Ella Zeldich, PhD, a post-doctoral fellow, presented the results at the meeting.

 

“There are a lot of companies working on inhibiting beta secretase and gamma secretase, the two enzymes that carve Abeta from its precursor, APP, or they are trying to clear the brain of Abeta using immunotherapy,” said Dr. Abraham. “I think it is important to stop Abeta from being made in the first place.”

 

She and her colleagues conducted a high-throughput screening of 77,140 small molecules — using 200 plates with 384 wells on each one — to determine if any of them could inhibit the dimerization of APP. They genetically engineered the APP molecules with firefly luciferase gene. When APP bound to another APP in the well, the two terminals of the firefly luciferase gene became luminescent. Then they added tens of thousands of different small molecules to each of the wells and waited to see which cells emitted light.

 

Only one substance in the panel, which they called Y, was able to stop the formation of a dimer between two APP molecules.  The researchers observed that the substance was similar to other kinase inhibitors. When they tested the compound against select kinases, they found that it only inhibited a tyrosine kinase called cKit.  And when they inhibited cKit, they observed an increase in the phosphorylation of APP and a decrease in Abeta.

 

“This is a whole pathway that has never been discovered that leads to the formation of Abeta,” said Dr. Abraham. “We don’t think that cKit directly induces the phosphorylation of APP, but the pathway definitely has a role in the cleavage of APP to generate Abeta.”

 

There are still many unanswered questions, including what needs to happen first, dimerization or phosphorylation. “We are not sure yet,” said Dr. Abraham. “But right now, what matters is that there is much less Abeta forming.”

 

Dennis J. Selkoe, MD, FAAN, the Vincent and Stella Coates professor of neurologic diseases at Harvard Medical School and Brigham and Women’s Hospital, said that the findings are quite interesting. “It is a novel mechanism that focuses on the dimerization of APP,” he said. “It is not known what percentage of APP forms dimers. But the key is to lower Abeta, which they have shown it does.”

 

Benjamin Wolozin, MD, PhD, a professor of pharmacology at Boston University added that “scientists now know how to get rid of Abeta using antibody approaches. The field has been looking beyond Abeta for new ways to treat Alzheimer’s. Still, people are not using phosphorylation to reduce Abeta. This definitely is a new approach that might impact the disease process.”

 

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·        So PP, et al. Lowering of amyloid beta peptide production with a small molecule inhibitor of amyloid dimerization. Am J Neurodegener Dis 2012;1(1)75-87: http://1.usa.gov/1W3x1ej

Wednesday, October 21, 2015

CHICAGO—Scientists at the Institute for Regenerative Cures and the Genome Center at the University of California, Davis are using transcription-like effectors (TALEs) in human Huntington’s disease (HD) fibroblasts and neurons to see if they can reduce mutant huntingtin.

 

Based on results of quantitative assays that measured how much transcription of the mutated gene occurred, they reported that the technique lowered the expression of the mutant gene to near-normal levels. The expression of the healthy gene was not affected by the treatments.

 

The findings, reported here on Tuesday at the Society for Neuroscience annual meeting, demonstrate the potential of this gene-modifying technique for treating HD.

 

TALEs are DNA-binding molecules that can be designed to target single nucleotide polymorphisms (SNPs) in the mutant allele. The TALE molecules recognize sequences in DNA and make a double-stranded cut, which collapses the CAG length down to a non-disease stage, causing transcriptional repression to the mutant allele.

 

Kyle Fink, PhD, a postdoctoral fellow, explained that his group tested the TALEs in human HD fibroblasts and induced neurons made from these skin cells. In previous research, they have reported overproduction of reactive oxygen species (ROS) and oxidative damage (altered mitochondria function), neuronal dysfunction, and cell death in the HD cell lines.

 

In the study reported here, they treated human HD fibroblasts with each TALE-specific SNP or TALE-Fok1, which was developed by fusing TALEs to a snippet of the Fok1 endonuclease. Both TALE strategies targeted specific sites within only the mutant huntingtin gene, Dr. Fink told the Neurology Today Conference Reporter.

 

“It has been thought that reducing mutant huntingtin through protein interference or conditional gene knockout could prove to be an effective therapy for patients and reduce the associated downstream effects,” said Dr. Fink. “We showed that the TALE-SNP and the TALE-Fok1 that is delivered into the HD fibroblasts or HD neurons led to a significant reduction in aggregated proteins and mutant allele repression.”

 

The scientists are now trying to figure out the best way to deliver TALEs in an in vivo delivery system for use in humans. “We are looking for ways to deliver TALEs with a higher efficiency,” Dr. Fink said. The technique we are now using is not feasible for human trials.”

 

Since the HD mutant gene involves a triplet repeat expansion, it is difficult to develop an intervention that targets the mutated allele without affecting the wild-type allele, explained Christopher Ross, MD, PhD, a professor of psychiatry, neurology, pharmacology, and neuroscience at Johns Hopkins University School of Medicine and director of the Baltimore Huntington's Disease Center at Johns Hopkins.

 

“One strategy is to target other parts of the HD message whose sequence is specific to the mutant allele,” Dr. Ross said. “This strategy is attempting to correct the gene defect, and another difficulty is that you need to get every cell, or at least a significant number of them. Delivery of these therapeutic agents into relevant areas of the brain is very challenging.  You use these technologies to edit the mutant gene and thereby disrupt its ability to transcribe mRNA to make mutant protein.”

 

He added: “These are still very early days, but the gene editing strategy is still tremendously exciting and novel. A few years ago no one would have imagined gene editing technology, so who knows what will come in the future. The difficulty is to image a viral delivery system that would target all the relevant cells in the HD brain.”

 

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·         More on the use of TALEs for HD: http://bit.ly/TALE-HD

Tuesday, October 20, 2015

BY JAMIE TALAN

 

CHICAGO—A change in a single enzyme, histone deacetylase 3 (HDAC3), seems to play a role in restoring memory in older mice, according to a study described here on Sunday at the annual meeting of the Society for Neuroscience.

 

Janine L. Kwapis, PhD, a post-doctoral researcher at the University of California, Irvine, and colleagues have been studying the role of epigenetic mechanisms — changes in gene expression that occur through alterations in chromatin structure — in age-related memory loss. In their research, they found that a major epigenetic mechanism important for memory is histone acetylation, in which acetyl groups are added or removed from histone tails by acetyltransferases or histone deacetylases, respectively.

 

In the brain, Dr. Kwapis explained, HDAC3-mediated deacetylation works like a molecular brake pad, restricting gene expression until a learning event occurs. When learning happens, HDAC3 is inhibited and acetyl groups are added, paving the way for gene expression. But DNA requires a flexible system and there may be disruptions in this system as the brain ages.

 

Dr. Kwapis completely depleted the HDAC3 protein from the dorsal hippocampus in 18-month-old mice, and observed that the older mice were learning tasks — and not forgetting them — as if they were younger. She introduced the animals to an object in a particular environment one day and then brought them back the next day, having moved the object to a different location. Moving the object to a different location allowed the scientists to measure what the animals had learned the day before. Young mice learn this task easily, she said, while older mice normally have a harder time. 

 

The researchers found that memory was enhanced in the mice, and they observed a change in a critical cellular component of synaptic plasticity and long-term memory: long-term potentiation (LTP).

 

“We restored LTP in these older mice,” said Dr. Kwapis. She and her colleagues looked at the expression of three genes known to be associated with learning — cFos, Arc, and Nr4a2 — to see if there were any differences in the expression of these genes in younger and older animals and in the animals with depleted HDAC3. Dr. Kwapis reported at the meeting that it was only the Nr4a2 expression that changed in the brains of older mice without HDAC3.

 

“This makes us believe that Nr4a2 is critical to aging, and expressing it in the aging brain may be enough to strengthen learning,” she said. “It suggests that we may be able to disrupt HDAC3 and restore a more normal epigenetic state to prolong normal cognition in old age.”

 

The scientists are now working with pharmaceutical companies to identify compounds that selectively block HDAC3.

 

“This work adds yet another promising avenue for therapeutic treatment options for reversing memory deficits with normal aging,” said Farah Lubin, PhD, an associate professor in the department of neurobiology and director of the National Institute of Neurological Disorders and Stroke Neuroscience Roadmap Scholar Program at the University of Alabama.

 

“Specifically, epigenetic mechanisms, such as regulation of HDAC3 activity, represents an innovative locus that can be targeted to influence the process of memory storage with age,” he said. “By increasing our knowledge of these types of molecular processes, we are closer to developing therapeutic interventions and possibly a cure for age-related dementias like Alzheimer's.”

 

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·        Kwapis JL, et al. Does PKM(zeta) maintain memory? Brain Res Bull 2014; 105:36-45: http://1.usa.gov/1LInHFI