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A research group in Spain is planning a clinical trial to explore if biotin and thiamine supplementation may help treat motor symptoms of Huntington’s Disease. This strategy emerged from their observations that some protein changes in both mice and people with the HD gene mutation resembled those seen in another rare brain disorder, biotin-thiamine responsive basal ganglia disease (BTBGD). Like HD, BTBGD affects a part of the brain called the striatum and causes movement problems. Daily biotin and thiamine vitamin supplementation is an approved treatment for BTBGD, and has been used with success for individuals with this condition. A recent publication provides some evidence that this treatment could be worth a try in HD, too, but a rigorous clinical trial in people with HD would be needed first.

Approaching Huntington’s disease treatment from a new angle

Individuals with Huntington’s Disease (HD) have a mutation in a gene called huntingtin, which creates an expanded, longer-than-normal huntingtin protein. The protein builds up in the brain and is thought to be toxic to brain cells, leading to the symptoms of HD. Research on HD treatment has largely focused on targeting the huntingtin gene and protein itself. Many of these treatments and therapies aim to lower huntingtin protein levels through various methods, and several current clinical trials, both past and present, have been developed with this goal in mind.

However, the field of HD research is diverse, and scientists are exploring other treatment targets from different angles. Recently a group of HD researchers in Spain has investigated the role of a family of proteins called CPEBs in neurodegenerative diseases. The research group’s work was published in Science Translational Medicine in September of 2021 and presented by Dr. Jose Lucas on Day 1 of the CHDI HD Therapeutics conference in March 2022.

The basic job of CPEB proteins in cells is to modify the genetic RNA message molecule in a way that affects the size and the amount of the proteins the RNA message produces. CPEBs affect protein creation by lengthening or shortening a part of the RNA message called the poly-A tail. This tail can be placed in slightly different locations, allowing one gene to make different “recipes” to produce proteins of multiple lengths. When a poly-A tail is very short, this signals that the RNA recipe should be destroyed. Therefore, the actions and amounts of CPEBs can significantly affect the lengths and levels of important protein molecules in cells.

From CPEBs to vitamin deficiency

CPEB proteins are known to play a role in brain development and in adult nerve cells. Changes in the actions and levels of CPEB proteins have been seen while studying autism and epilepsy, but CPEB proteins had not yet been looked at closely in neurodegenerative diseases like HD. In this recent study, Lucas’s team observed changes in CPEB levels in the brains of humans and mice with the HD gene. This led them to look more closely at how that affected the levels of other RNA messages and proteins related to HD and other brain diseases.

One of the genes affected by changes in CPEB levels was a gene identified in biotin-thiamine-responsive basal ganglia disease (BTBGD). This is a very rare genetic disorder (one in a million) that usually strikes in early childhood and hinders the brain’s ability to use dietary thiamine (also known as vitamin B1). Like HD, BTBGD causes damage to a part of the brain called the striatum, which leads to problems with movement, mood, and thinking. But unlike HD, there is a treatment that can do more than manage symptoms. With daily oral administration of biotin and thiamine, complete clinical recovery from BTBGD is typically reported if treatment is started soon after noticing symptoms, and if lifelong treatment is maintained. The clinical similarities between BTBGD and HD and their genetic findings prompted Lucas’s group to explore whether thiamine deficiency could also be occurring in HD, and if vitamin supplementation could be a way to treat it.

Indeed, the researchers found that mice with HD showed BTBGD-like bloodwork, including thiamine deficiency, and human HD brain tissue also showed signs of thiamine deficiency. This led them to move forward with testing a combination of high-dose biotin and thiamine in two types of mice with HD. The treatment prevented deficiency in brain thiamine, improved brain health, and decreased the rate of loss of nerve cells, in comparison to untreated mice. Based on these observations, the researchers think it’s possible that individuals with HD might also benefit from thiamine and biotin vitamin supplementation.

Moving findings in mice into people?

These promising results in mice don’t mean that individuals HD should start taking large quantities of biotin and thiamine from the grocery store. The research done in mouse models was limited to the motor symptoms of HD and did not evaluate the cognitive and psychiatric symptoms of HD. As we’ve learned many times over, animals and cells in a dish can provide valuable insight into HD and a starting point for testing therapies, but the only way to test safety and effectiveness of new treatments is to conduct clinical trials. To date, promising vitamin-based therapies (CoQ10, for example) have not panned out in human trials.

Despite these limitations, a randomized trial based in Spain to use biotin and thiamine to treat people with HD is being designed, with the hope that the combined oral therapy might be able to modify the progression of HD in people with HD in the early-to-middle stages. Clinical testing may be a logical next step, though some researchers and clinicians have questioned why the design of the trial does not include a placebo group for comparison. Nevertheless, vitamin supplementation is easily implementable, and high dose combination treatment of biotin and thiamine has already been proven safe. Furthermore, both vitamins are approved by various regulatory agencies and are available at a low cost. We are encouraged by the knowledge that this type of therapy is evidence to be well-tolerated, safe, and effective for patients with BTBGD and look forward to hearing more news about the upcoming trial in people with HD.

Scientists at Novartis and The Children’s Hospital of Philadelphia have recently published a paper detailing how the drug branaplam, originally developed for the neurological disease spinal muscular atrophy (SMA), could be repurposed to treat Huntington’s disease. Branaplam can lower levels of the huntingtin protein and is now being tested in the clinic in a phase IIb study, VIBRANT-HD.

Huntingtin-lowering therapies are being pursued by lots of companies

Despite setbacks with some recent clinical trials, many experts in the field agree that huntingtin-lowering remains an attractive strategy for treating HD. Every person with HD has an expansion in their huntingtin gene which means they will make an expanded form of the huntingtin protein. This expanded form of the protein seems to be toxic and is thought to cause to the signs and symptoms of HD. If we can reduce the amount of this toxic form of the protein, researchers hope we might slow or stop the progression of HD.

Lots of companies are testing huntingtin-lowering drugs in the clinic, including Roche, Wave Life Sciences, and uniQure, all of whom are using slightly different approaches to target the genetic message which is made into the huntingtin protein. The drugs they have developed cannot easily spread through the body, so they are given to patients through spinal tap or direct injection into the brain. While this means the drug can get to the parts of the body most badly affected by HD, these procedures are demanding for patients and very expensive. These are also not treatment options which could be trivially rolled out to the global community of people with HD due to healthcare access issues and prohibitive costs.

Repurposing an SMA drug to try to treat HD

What scientists call “small molecule therapies” are an attractive option to treat diseases affecting the brain. This type of drug can often be formulated so it can be taken orally as a pill or syrup, which is much easier for patients, and these drugs have a better likelihood of crossing from the bloodstream into the brain so patients can avoid onerous procedures. For a long time, it was a pipedream for many folks in the HD community that a small molecule huntingtin-lowering therapy could ever be made and then, two independent companies did just that! Very similar drugs developed by both Novartis and PTC Therapeutics can lower huntingtin – we recently wrote about a paper which describes the PTC drug on HDBuzz. Now we have more details about the Novartis drug, called branaplam.

Branaplam targets machinery in our cells which processes genetic messages, called splicing machinery. Each genetic message can be thought of like a story book, and when the story is over, the final part of the message reads the genetic equivalent of “the End” to tell the cell that the sequence for that message is complete. Drugs like branaplam rejig the pages of the story book so “The End” is read before it makes sense. When this happens, the cell will destroys the message and won’t make the associated protein, similar to how you might get rid of a book that had a premature ending which made no sense.

Branaplam was originally developed for a fatal childhood disorder called SMA because it also changes the levels of a protein called SMN2, which underlies that disease. Scientists at Novartis discovered that branaplam also changed the levels of the huntingtin protein so switched gears to test if branaplam would be a good treatment for people with HD and have now published their findings which we’ll digest for you here.

Working out how branaplam lowers levels of the huntingtin protein

First, the research team treated cells in a dish with branaplam and looked at how the genetic messages in the cells were affected. They found that a signature in the huntingtin genetic message, which is normally chopped out by the splicing machinery, called a pseudoexon, was kept in the message molecule in branaplam treated cells. The scientists went on to show that this reduced the amount of the huntingtin genetic message because keeping in the pseudoexon genetic code, targets the huntingtin message to the trash bin of the cell. When the branaplam treated cells were no longer treated with the drug, this effect was reversed, and the levels of the huntingtin message bounced back to normal.

Whilst changes to the huntingtin message are a good sign, what we are really interested in is the levels of the huntingtin protein. The team measured huntingtin protein levels when different amounts of branaplam was dosed in cells in a dish and showed that the more drug was given, the more the level of huntingtin protein was lowered. The team next tested if this finding held true for cells in a dish derived from people with HD i.e. folks who have the Huntington’s disease mutation. They showed that the levels of huntingtin message and protein were also reduced by branaplam in these cells too.

Insights from branaplam in HD animal models and SMA patients

Next, the scientists went on to see how branaplam performed in a mouse model of HD. Mice were given different oral doses of branaplam and then the levels of the huntingtin message were measured in different areas of the brain. In four different brain regions, they showed that the level of the huntingtin message including the pseudoexon was increased the more drug that was administered. This was matched by a decrease in the levels of the huntingtin protein. The scientists found that if mice were no longer treated with branaplam, the effect was reversed and huntingtin levels bounced back.

Lowering the levels of huntingtin is all well and good, but what the research team really wanted to know is if this improved symptoms in the HD mouse model. Next, they tested the motor skills of the HD mice who had been treated with branaplam and compared them to HD mice which hadn’t be treated as well as regular lab mice. The scientists suggest that the branaplam treated mice are more like the regular mice but the presented data is fairly limited.

The team finally looked at the levels of the huntingtin message in blood from branaplam treated SMA infant patients. Patients in the open-label extension of the SMA branaplam trial received weekly doses of branaplam for over 2 years. After over 900 days, a sustained decrease in the levels of the huntingtin message in these blood samples could still be seen, showing ~40% decrease at this timepoint in the study. The Novartis team believes this indicates that the drug was having the desired effect over a long period of time in people.

What’s next for branaplam?

We recently heard from scientists at Novartis at the recent CHDI therapeutics meeting who gave us updates on their branaplam program. Dr Beth Borowsky gave us details of a now completed phase I study, where the drug was tested for the first time in adults to figure out a safe amount and frequency of dosing. As branaplam was originally developed to treat SMA in infants, figuring out a safe dose for adult patients is an important first step.

The next step for branaplam is a phase IIb study called VIBRANT-HD. This will be the first time branaplam is tested in adults with HD and this study will work out what dose of the drug needs to be administered to lower huntingtin. Branaplam will be given as an oral liquid, like cough medicine, that people in the trial will drink once a week. Different patients will be given different doses of branaplam so Novartis can work out what dose will work best for a second phase of the trial. Lots of different clinical measurements will be collected from participants in the trial, including levels of various biomarkers, like huntingtin and neurofilament. Recruitment for this trial is underway and hopefully we’ll hear updates on how the trial is proceeding soon.

Good morning! Today is the 3rd and final day of the #CHDI HD Therapeutics Conference in Palm Springs. Follow our feed today to get live updates!

Biomarkers and clinical tools

The fourth session of research talks will cover biomarkers and clinical tools for diagnosing, tracking, and treating HD. It is being introduced by Dr. Edith Monteagudo of CHDI and Dr. Niels Skotte, of University of Copenhagen.

Biomarkers Task Force!

The first talk is by Dr. Cristina Sampaio & Dr. Robert E Pacifici, both from CHDI. They’ll be discussing CHDI’s Biomarker Task Force, focused on developing a strategy for moving biomarkers for HD forward.

Biomarkers are critical for drug development. They allow researchers to track how patients are progressing as their disease advances. They’ll also be critical as the field moves forward with treatments, because they’ll allow researchers to determine if patients are getting better. CHDI and other organizations are committed to making biomarker data (and many other types of data) available in a way that can benefit the entire HD research and family community, not just an individual company. CHDI is focused on advancing biomarkers related to imaging (such as MRI scans), blood, and spinal fluid.

One molecule that didn’t turn out to be a great biomarker in blood is expanded huntingtin. Even though it’s directly involved in causing HD, it turns out it doesn’t track well with disease progression. It seems like imaging is a strong bet in the biomarker field. Identifying biomarkers that can be assessed using imaging would give researchers a non-invasive way to continually track HD patients over time. Another key component of defining biomarkers is to find those that change with very early HD progression. This will allow researchers to start monitoring disease at the very earliest stages, before symptoms appear – a time when some think treatment needs to begin.

The lengthening of CAG repeats in some cells over time, known as somatic repeat expansion, is not only gaining interest because of the effects it has on age of disease onset, but it may also be useful as a biomarker. There are also ways to take advantage of “wearables” – digital devices, like watches, that people with HD can wear to gather lots of data in real time. These devices could track movement, sleep habits, and other metrics. CHDI has a 2-year goal for defining some of these important biomarkers and is eager to collaborate with the entire HD research community for this important project.

Biomarker discovery – the future is bright!

The next speaker is Dr. Jim Rosinski from CHDI. He’ll be sharing his work using large datasets that will help profile people with HD for biomarker discovery. He feels “the future is bright!”

We are in a new age of data where scientists are able to measure thousands of changes in genetic messages and protein over time in many individuals. Using powerful analysis techniques, sorting through this data can be very valuable for drug development. Doing this requires a strong “pipeline,” from being able to collect blood and spinal fluid samples from many people with HD, to developing the skills and software to understand the data. This is where observational studies like Enroll-HD and HDClarity come into play.

Samples donated by HD families who participate in these studies are essential for the many different types of analyses that can be made, by looking at how genes turn on and off, and examining changes in levels of different forms of RNA and protein. Looking at changes in protein levels across a brain area, organism, or group of people with a disease is known as proteomics. Using spinal fluid samples donated through the HDClarity study, researchers can link clinical data from Enroll HD with protein changes.
Dr. Rosinski shared some exciting preliminary data tracking many proteins in a large group of HDClarity participants. Looking at each individual protein alongside clinical data will help define biomarkers for disease progression and identify routes for drug design.

One biomarker that’s been defined in HD is neurofilament light – NfL. It turns out, it’s a really great biomarker! Dr. Rosinski found that just looking at this one protein can predict HD status! Wow! They also identified a few other proteins that are predictive of where a person might be in their HD symptoms. Ultimately, combining these findings could power more individualized care and treatment in HD.

The future is bright! Instead of scientists talking about IF we’ll have a treatment for HD, they’re focused on WHEN we get a treatment, we need biomarkers that will help us track how patients are doing. We’ve come a long way!

Next up is Dr. Aline Delva from KU Leuven. Dr. Delva will be describing her work using a type of imaging called PET. We recently wrote about it here: https://en.hdbuzz.net/319

PET ligands allow scientists and clinicians to visualize things inside the body or brain. This particular ligand is designed to stick to huntingtin and make it light up in a brain scanner, so levels can be tracked over time, and eventually during treatment.
Dr. Delva is sharing new data from a human study where the PET ligand sticks to synapses, connection points between brain cells, to track their health over time, especially in areas of the brain that are most vulnerable to HD.

It appears that these PET ligands can detect changes even in premanifest HD patients! This is great news because it gives researchers a tool to determine if a treatment is making a patient better before there are even noticeable HD-related changes.
Next, Dr. Delva described her work looking at PET ligands that examined the huntingtin protein itself. The goal of this study was to determine if huntingtin could be used to track disease progression using PET technology. After testing the PET ligands in mouse and primate models, they did a small study in humans, and were able to figure out the best one to use, and find a safe and effective dose.

The results from the study showed that the PET ligand is useful for lighting up the cortex and striatum – brain regions that are particularly vulnerable in HD. While this is expected, it’s exciting because it shows that this tool could work well for studying HD! A major advantage of these PET ligands is that they are examined using noninvasive, painless imaging techniques – similar to an MRI. So they can be done relatively easily and frequently on HD patients to track disease progression. All great qualities for a biomarker!

Next steps will be to expand these studies by testing the PET ligands in a larger group of people with HD. Such tools are now widely used and accepted in the Alzheimer’s disease field, which sets a good precedent for their development in HD.
We’re taking a break, but will be back shortly after refueling with some coffee! Stay tuned!

Digital Monitoring of HD

Up next is an exciting update from Drs. Peter McColgan and Jonas Dorn from Roche are here to provide an update from the GENERATION-HD1 trial of Tominersen. Appropriately, Dr. McColgan begins with an acknowledgement of the disappointment of HD families and thanks them for their incredible contributions to these studies.

The specific update for this talk is a discussion of some results from the digital monitoring platform – digital tools used to track HD progression in participants in Roche’s various studies with tominersen. The trial participants had a smartphone to track measurements of HD-relevant symptoms, such as movement and cognitive changes. These are do-it-at-home versions of the kinds of tasks that physicians use to track HD in clinics.

Data was collected from 784 patients, with more than 350,000 days of tests recorded. That’s a lot of information to process! Each participant spent 30-60 minutes per day, on average, conducting tasks on their phones. Many of the tasks reveal clear changes between HD patients and controls, including a speeded tapping task. This requires participants to quickly and repetitively tap a button, which becomes more difficult as HD progresses.

Because at-home testing is new, the team compared results for tests done at home, then repeated in a formal clinical setting. This resulted in excellent consistency – so collecting data at home seems feasible. Surprisingly simple tasks – including the speeded tapping – show very clear worsening during the course of the trial. This suggests these measures could be useful for future trials, and potentially save participants and families having to do so much in a clinic.

Dr. Dorn explains that there are some complexities in the digital data. For example, people who were doing worse on some tasks were more likely to stop completing the tasks early. Perhaps because those are the people with more severe symptom progression? For some of the tasks, including a “draw a shape” task, trial participants were clearly learning how to do the task faster. This is called a “practice effect,” and it makes it tricky to generate useful data over a long time for those tasks.

A lot of work remains to digest these huge sets of data from the participants in Roche’s tominersen trials. Expect to hear more from Roche as they continue to dive into the data.

In the next talk, Dr. Sarah Tabrizi (UCL) and Dr. Jeff Long (University of Iowa) will talk about the development of a staging system to help better define where a person is in their HD journey. This will be important for planning trials in people who haven’t yet shown symptoms.

Staging systems are very important for grouping people with similar disease characteristics so they can be properly treated based on their current symptoms. This has been very helpful in fields like cancer treatment. HD needs this kind of staging system because it is still mainly diagnosed based on chorea, which can occur much later than other thinking and mood changes. By analyzing tens of thousands of data sets from people with HD, a large consortium of researchers has been able to create a system with stages 0 through 3. This demonstrates the power of participating in studies like Enroll-HD.

At the scale’s most basic level, 0 means the person has the gene but nothing else has changed, 1 is when biomarker changes can be detected (like in blood or brain images), 2 is changes measured in clinical tests, and 3 is when HD begins to affect day to day function.

Creating a scale for use by the entire clinical and research community is important for ensuring that care and research are consistent and we can learn as much as possible from every trial. The research community is now building powerful new tools around this existing scale. One example is a program to help determine whether an individual is a good fit for a clinical trial by taking into account their CAG repeat number, their age, and the results of many tests and brain images.

Combining and analyzing many measurements – brain images, tests of movement and thinking, shifts in abilities at home and work, potential changes in blood and spinal fluid – is a very powerful way to track progression and determine response to a drug.
As with many aspects of HD, there can be a lot of variability within the four stages, and researchers are tackling ways to further define them based on things like age, genetics, and findings from exams in the clinic.

This is an even more refined way to help recruit the right people for trials than current methods, which use clinical scores (you may have heard of CAP or PIN). This conference is a great venue for presenting novel tools like this because so many players in HD research are present.

It’s lunch time for us here in sunny CA. We’ll be back after the break to share exciting updates from various HD clinical trials. Tune back in soon!

Clinical and Human data

We’re back for the last session of the conference! We’ll be sharing exciting talks focused on recent clinical trials.

Up first are Dr. Jamie Hamilton and Dr. Mark Guttman from University of Toronto who will be introducing this clinical session. Dr. Guttman is acknowledging the resilience of the HD community over the past few years and the continued hope to be found in clinical trials.

Tominersen in the spotlight

The first talk this afternoon is from Dr Peter McColgan and Dr Lauren Boak from Roche. They will be giving us an update on tominersen, the huntingtin-lowering drug under investigation in the Phase III GENERATION HD1 study. Lauren is kicking things off – she has shared the slides of the Roche presentation through this link if you want to follow along or look at these later: https://bit.ly/3sH1faG

Roche has several approaches for lowering huntingtin. They’re not just using tominersen to lower total huntingtin, but they also have programs to specifically reduce levels of the expanded huntingtin copy and other tools they’re exploring. It’s encouraging to hear that Roche is committed to HD. But today Lauren will just be focusing on what they learned in GENERATION-HD1 with their tominersen program. The final analysis of the data from this trial is ongoing.

There are in fact 3 different trials Roche is conducting where data analysis is not yet complete – the Natural history study, GEN-PEAK study and GENERATION HD1 but today the focus will be on the halted phase 3 GENERATION HD1 study. Lauren is now recapping the data from animal models which informed the trial. These were used to determine the dose of tominersen in the GENERATION HD1 study – 120 mg every 8 or 16 weeks which Roche predicted would lower huntingtin by 25-45%.

Now Peter will tell us about the analysis they’ve done so far of the data from GENERATION-HD1. Levels of expanded huntingtin were reduced in both the 8 and 16 week groups as predicted. This suggests tominersen was engaging the target. However, when they looked at certain scores that measured overall how participants were doing, people who were treated with tominersen did worse than people who were treated with placebo, particularly when treated every 8 weeks.

Peter shares that more adverse events (side effects) were seen for folks who got the drug more frequently, fitting with the trend we see with the overall scores for patients in the different drug groups. Our previous session taught us a lot about biomarkers for HD. One biomarker we learned about was NfL. Unexpectedly, Roche found that NfL levels went up after tominersen dosing. They’re still not sure why this is.

Tominersen lowered huntingtin levels but the trial did not reach its endpoints and did not improve symptoms in patients. Scientists are now working hard to understand why.

Roche have been looking at the data collected from patients in the trial after they stopped taking tominersen. 84% of patients stayed in the trial even after dosing was halted which is very helpful for Roche scientists to try and figure out what happened.
The number of patients that stayed in the trial following the dosing halt is a true testament to HD patients. From this it’s evident that the HD community is passionate about participating in research and contributing to finding a treatment.

Changes in brain structure were reported for patients in the trial with bigger changes seen for patients who took the drug more frequently. Peter suggested there may be some recovery of the brain structure after dosing was stopped, but analysis of this data is ongoing. Roche scientists used a common clinical measurement called UHDRS which looks at lots of different signs and symptoms of HD. Looking at this score after dosing was halted, no significant difference was seen between people who did or did not receive the drug in the trial.

A similar pattern is seen in another clinical measurement called total functional capacity, which measures daily function in activities at home and work. There was no statistically significant difference between patients after dosing was stopped. Roche wanted to divide people in the trial into groups to see whether severity of symptoms might have played a role in how they responded to the drug. This was done after the trial was designed, known as a post-hoc analysis – so all results must be taken with a pinch of salt.

As we previously wrote, Roche thinks that younger participants who had less advanced symptoms of HD might have done somewhat better in the trial than older more advanced ones. https://en.hdbuzz.net/316

BUT! This is not a statistically significant finding and is the subject of heated debate by scientists in the field. Roche have sliced and diced the data in lots of different ways to work out if the drug was beneficial for a subgroup of patients. Another factor is how much drug the patients were exposed to which they work out by measuring the drug in spinal fluid.

Peter is now sharing data which suggests people in the trial exposed to less of the drug might have fared slightly better, but, again, there are not enough people to power these statistical analyses. A lot of folks working on making medicines for HD will learn from this trial to help inform the design of future clinical trials, including which types of drugs, dosing, and delivery might work best. The data seem to indicate that younger less advanced HD patients might be better candidates for huntingtin lowering, and that lower drug doses may be more beneficial. This doesn’t mean it couldn’t help a wider population, but it’s useful for designing the next trial.

In a new phase II study, Roche plans to enroll younger people with HD, with less advanced symptoms, and to use 2 new doses. These were not disclosed in the talk, but they would be lower than the doses used in the GENERATION-HD1 study. Peter is now talking us through how this younger cohort fits into the new HD-ISS staging which was described in the talk by Prof. Tabrizi earlier in the day. This new system will be important to help define exactly which people might benefit from huntingtin-lowering drugs like tominersen.

The Q&A is lively and technical! No details have been shared yet about the potential Phase II trial, but it will once again rely on the strength and enthusiasm of future participants and their families.

Gene therapy for early stage HD

Next up is neurosurgeon Dr David Cooper from uniQure who will give us an update on the gene therapy trials, HD-GeneTRX-1 and HD-GeneTRX-2, for their one shot drug called AMT-130 which they are testing to treat early-stage HD. Dr. Cooper describes the structure of the drug – a harmless virus particle filled with instructions to make a set of RNA that leads to the lowering in of the Huntigntin gene into regions it is injected into. In this case, deep brain structures.

UniQure did a lot of studies of their drug in a range of different HD models including cells in a dish as well as monkeys and pigs. These studies informed their studies now underway in people with HD. The deep parts of the brain impacted most in HD – the “striatum” – are tricky to reach, and hard to infuse with uniQure’s viral particles. Decades of work have led to procedures for infusing brain structures to maximize how much is treated with drug.

AMT-130 lowers total huntingtin – the normal and the expanded forms of the protein. uniQure’s goal isn’t 100% reduction of huntingtin, but to significantly lower levels, for life, after a single injection. There are two studies – one in Europe and one in the US, with 15 and 26 patients respectively. There will be patients with low dose, higher doses, or placebo.

The primary objective of both studies is to establish whether the treatment is safe and tolerated. Additional objectives include trying to understand if – as predicted by the mouse work done – the therapy is persistent for years after a single injection
As with many trials, there are limitations in who can participate in the study. For example, participants must be able to handle anesthesia. Given the ongoing pandemic, this means that people must be 8-12 weeks past any COVID infection so omicron has made things more tricky.

The current goals are to include people with at relatively early stages of HD, and people whose deep brain regions are preserved enough to safely inject them with the drug. This is the first gene therapy for HD, and the first time anyone has done as many brain injections as uniQure is planning to do – 6! This gives them the best chance to cover the whole striatum with a single surgical procedure. Each surgery is reviewed by a team of neurosurgeons, who must all agree that the planned surgeries are likely to be safe.

No two brains are exactly the same, so each patient’s brain scans have to be carefully analyzed before surgery.
A harmless contrast agent is injected along with the AMT-130 which helps the surgeons see exactly where the injected material spreads to. This allows the surgeons to confirm successful delivery of the drug across the entire targeted region. In the first 4 patients treated, all left the hospital the next day without any serious complications. Similarly, no bad changes were observed in brain imagery during this first year after the patients were treated with AMT-130.

Despite the challenges posed by the pandemic, the US cohort is nearly completely treated, and the first few patients in Europe have been treated. UniQure are now fine-tuning the surgical procedures which are needed to inject the AMT-130 into the brain, to make sure that the drug is going to the right regions every single surgery and that the surgery is not taking too long to do.
What they’ve learned about the surgical procedure will help inform a planned third trial group (cohort) in the US in the near future.

We’re taking a quick break before we head into the final talks of the conference, covering updates from some of the other clinical trials underway right now.

Innovations that led to SELECT-HD

First up after the break is Dr. Michael A Panzara from Wave Life Sciences. Dr Panzara will be telling us about the phase 1b/2a clinical trial called SELECT-HD, which is testing an expanded huntingtin-specific lowering therapy. Wave makes anti-sense oligonucleotides or ASOs which target the huntingtin “message” molecule in the cell, to lower levels of huntingtin protein. This is similar to the approach Roche took with Tominersen except their drug only targets expanded huntingtin.

PRECISION-HD1 and PRECISION-HD2 were trials testing two ASOs against expanded huntingtin. Although the drugs were safe, they did NOT lower huntingtin as expected. Both trials used drugs which were specific to expanded huntingtin as they target genetic signatures called SNPs (“snips”) – parts of genetic code that differ between gene copies – only found on the expanded huntingtin gene.

Wave have since developed another ASO drug called WVE-003 that targets a different SNP and has updated chemistry. This drug can be tested in some of the HD animal models as they also have the SNP targeted by WVE-003 and the results so far are promising. Wave is hopeful that this new approach will allow for more effective lowering of harmful huntingtin at lower doses of ASO, while leaving the healthy form of huntingtin intact. It is being tested now in a new trial called SELECT-HD.

When Wave tested their new and (hopefully) improved drug in HD mouse models, the drug lowered levels of expanded huntingtin by at least 50% and this effect was sustained for about 3 months. The scientists at Wave also checked if unexpanded huntingtin was affected by this new drug. HD mouse models treated with the drug did not have any significant change in their unexpanded huntingtin levels – good news! Wave also tested their drug in monkeys to see how it dispersed in the brain. They wanted to ensure that all of the important regions would get a sufficient dose of the drug – these data were also very encouraging.

In order for people with HD to be enrolled in the SELECT-HD clinical trial, they must have the SNP which the drug targets, so Wave have developed a diagnostic test to check thiss. Wave are designing the trial to be “adaptive” – this means that based on the data, they might change the dose or frequency of dosing of the drug while the trial is ongoing. But these changes won’t affect results since they’re being planned for in the beginning.

Deep brain stimulation in HD

Next up is Dr. Jan Vesper, from Heinrich Heine University in Düsseldorf to discuss HD-DBS. This is a proposed pilot trial for deep brain stimulation in people with HD. Deep brain stimulation is a procedure that uses electrical signals to stimulate the brain. A pilot trial was conducted nearly 10 years ago now which showed that some HD movement symptoms were reduced when people with HD were treated with deep brain stimulation.

A much larger trial called HD-DBS was then run across multiple sites around the world, which looked to measure lots of different clinical signs and symptoms of HD in participants who received the treatment or the placebo. To ensure participant safety, the inclusion and exclusion criteria were extensive, so it took a pretty long time to recruit people for the trial, but eventually 48 participants were recruited from Germany, Austria, and France, and about half received the placebo treatment. All data were collected in January of this year and analysis is ongoing. Today we will hear some of the preliminary findings.

For both groups in the trial, those treated with the deep brain stimulation and those who received placebo, some people improved but others got worse. So it doesn’t seem that this treatment is especially promising for folks with HD. Some patients did improve in the trial but its not clear why this might have been and there were no significant differences between those who received the treatment or placebo. Despite the disappointing outcome, researchers developed and refined surgical techniques in this trial that could be applied to future studies in HD and other diseases.

Now we are onto the development of oral huntingtin-lowering drugs! Two companies are working on these treatments for HD. Presenting first is Brian Beers, from PTC Therapeutics. He will be telling us about PTC518, a huntingtin lowering drug which can be taken by mouth.

PTC518 – Update!

In mouse models of HD, PTC518 has been shown to effectively lower the levels of total huntingtin and preclinical data looked very promising. PTC tested their drug in healthy volunteers and showed the drug was having the desired genetic effect of messing with the huntingtin recipe, known as RNA splicing. They were also able to determine a safe and tolerable dose of PTC-518. The scientists also looked at what happened when they stopped treating with the drug and showed that the effects could be rapidly reversed. This is great news if the data suggests dosing of the participants need to be stopped for any reason.

They are sharing the new study design, which will involve two groups of participants who will get either a low or a high dose for 12 weeks. 162 patients will be recruited in this trial which they aim to begin in the first quarter of 2022. PIVOT-HD will be the new phase II clinical trial, which aims to demonstrate that PTC518 works to reduce huntingtin levels in people with HD and they will track important biomarkers to see how the drug is working. PTC will look at the safety of the drug as well as changes to the levels of huntingtin protein, the biomarker NfL, different clinical measurements of HD signs, and symptoms.

The trial is about to get going in the US, UK, France, Germany and Australia. Hopefully we will be hearing updates from PTC soon!

Branaplam – an oral HTT lowering molecule

The final talk of the conference will be from Dr Beth Borowsky, from Novartis Pharmaceuticals. We will hear some updates about the VIBRANT-HD, a phase 2b trial investigating the huntingtin lowering drug, branaplam.

Dr Borowsky explains how taking a drug by mouth has a lot of benefits for patients compared to other therapies delivered by more taxing routes, such as spinal injections or brain surgery. A pill can also work on the whole body, rather than just the brain, and the effects can be reversed!

Branaplam was originally developed for a fatal childhood disorder called SMA, but in an amazing twist of science was found to also lower huntingtin, so Novartis redirected their efforts towards HD. Branaplam targets machinery which processes genetic messages, called splicing machinery. Changing how messages are spliced can affect how much protein is made from the message, so drugs that modify splicing can change the levels of proteins in the cell.

In a phase I study, the drug was tested for the first time in adults to figure out a safe amount and frequency of dosing. This was important because branaplam was developed to treat SMA in children. VIBRANT-HD is a phase IIb study which will test branaplam for the first time in adults with HD to work out what dose of the drug needs to be administered to lower huntingtin.

Branaplam is given as an oral liquid that patients drink once per week. Different patients will be given different doses so Novartis can work out what dose will work best for a second phase of the trial.

Lots of clinical measurements will be collected from participants in the trial, including levels of various biomarkers, like huntingtin and NfL. Recruitment for this trial is underway and hopefully we’ll hear updates on how the trial is proceeding soon!

That’s all folks! Thanks so much for following along. You can read our daily reports for the CHDI conference at https://hdbuzz.net

Good morning from sunny Palm Springs! After a 2-year hiatus because of COVID, the HD Therapeutics Conference is back in person this year – the biggest annual gathering of HD researchers! Our Twitter updates are compiled below. Continue to follow live updates for the rest of the conference with the hashtag #HDTC2022.

Day 1 is focused on research updates from some of the top HD labs around the world.

Huntingtin protein building blocks

Dr. Paolo Beuzer (CHDI) and Dr. Vanessa Wheeler (MGH) are introducing the first session of research talks, which will focus on ways to study and potentially manipulate CAG repeats in huntingtin DNA and RNA.

CAG repeats – more complex than they seem

The first speaker of the day is Darren Monckton from the University of Glasgow. The Monckton lab researches the repeats in the DNA sequence in diseases like Huntington’s disease.

While the CAG repeat seems simple because it’s so short, it’s actually quite complicated. The size of the CAG repeat alone doesn’t account for the age that someone will develop HD symptoms. CAG codes for the protein building block glutamine. But other protein letters can also code for glutamine. One of those is CAA, which can also contribute to the polyglutamines in HD. These CAA interruptions can also affect the age at which someone gets symptoms.
Having a CAA interruption, which is rare, causes an earlier age of onset compared to HD individuals who only have pure CAG repeats.
Changes in the “purity” of the CAG repeat tract i.e. whether it has these interruptions or not, could affect a process called somatic instability which we wrote about here: https://en.hdbuzz.net/291

The EnrollHD database from which these observations are made, is biased with data from lots of European and North American people, but not from other parts of the world. The Monckton lab decided to tackle this by teaming up with a group in South Africa.
In this South African population, the Monckton lab saw a very similar distribution of the different types of CAG tracts, with or without these interruptions. However there were some differences in another part of the HTT gene…

After the CAGs, the HTT protein contains letters, CCG, that make up a protein building block called proline. The Monckton lab sequenced how many prolines HD patients in South Africa had and found this area of the protein differs from HD patients with European descent.
They used this data to look at how the number of proline repeats and the letters that make up those proline repeats affect age of onset.
People with HD whose prolines who had a slightly different spelling had a 10 year earlier onset of HD symptoms. Tracking the way these protein building blocks are spelled can help improve diagnosis or prediction of age at disease onset.
Overall, what this means is that other changes in the huntingtin genetic recipe can affect the disease – HD genetics is proving to be much more pesky and complex than it first seems. Understanding these variations which lead to earlier or later symptom onset might help researchers find new ways to make medicines for people with HD – that’s the hope.

The researchers conclude that these other changes in the huntingtin recipe are not affecting somatic instability but perhaps are affecting the message made from the huntingtin recipe. The mRNA message molecule structure might be changing. Interestingly, none of the changes we’ve just described change the huntingtin protein itself. They only change the spelling of the gene or “recipe”. This suggests that it’s not protein-related changes that are affecting disease, but rather changes at the RNA-level. Altering the spelling of the RNA can change the way the molecule folds. No one yet knows what those folding changes mean, but they could be leveraged to develop therapeutics.

Dr. Monckton concludes, even though it all seems so simple – that people with HD have increased CAG repeats – it’s actually very complicated! But research like this gets at how we can take advantage of this complexity to design new drugs.

Examining how HD affects individual cells in the brain

Next up is Steve McCarroll who is affiliated with the Harvard Medical School and Broad Institute. Steve will be telling us about his research on understanding HD at the level of single cells in the brain.

The brain is made up of lots of different cell types that perform specific functions. Dr. McCarroll highlights the need to understand how these many different types of cells are affected by HD. His lab uses specialized techniques to separate out different types of cells and understand their genetics. They are committed to sharing the methodology widely to benefit the entire HD research community.

Dr McCarroll has found a way to speed up his analysis – he combines human brain samples from HD patients together, then separates the data out after. Getting data faster is a big advantage because it allows researchers to get their answers as fast as possible.
These types of large scale analyses are made possible through brain donations after a person with HD passes. Brain donations to HD research are a major way the field can get answers about HD in the only organism we care about curing HD in – people.

The McCarroll lab is applying these techniques to understand how the proportion of different kinds of cells in the brain changes as HD symptoms progress. His lab has defined these changes as the disease progresses, which helps us understand the cellular composition of the brain in people with HD.
In most people with HD, there is significant loss of cells called medium spiny neurons. Researchers have known this for a while, but Dr McCarroll has also shown there are cellular changes in many other cell types in the brain.
The loss of cells is accompanied by changes in which genes turn on and off. Dr. McCarroll has mapped these changes in these genes in each cell type as the disease progresses – wow!

These types of data can identify different genes within specific cells that modify the disease. One of those disease-related modifications is associated with expansion of the CAG repeat as a person with HD ages.

Certain people with HD have an increase in their CAG repeats over time, particularly in the brain. These expansions can increase the age of onset for HD patients. Understanding what causes these expansions could help develop medicines to delay disease onset.
Other genes, known as genetic modifiers, affect whether and how much a person’s CAG repeats will expand over time. McCarroll’s lab is looking at these modifiers within individual cells in many people!

Knowing how these processes change at such a small level produces a LOT of data that will give tons of information about how CAG expansion is changing in various cell types and how that affects disease progression. Interestingly, he found these CAG expansions happen to a much greater extent in medium spiny neurons, which are one of the most affected cell types by HD. This could be one of the reasons why this particular cell type is so vulnerable in HD.
He’s also defined these changes in different cell types of the brain as well as different areas of the brain. Depending where in the brain a certain cell type is can also affect CAG expansion in that cell type. So it’s not just cell identity, but also cell location that matters!
Understanding why both cell type and “neighborhood” in the brain affect CAG expansion will be an important next step towards developing therapies to combat it.
This data from the McCarroll lab is hot off the presses and reflects recent breakthroughs in laboratory and analysis techniques. They plan to apply these techniques to more samples from people with various stages of HD.

HD mouse models

The next speaker is Dr. William Yang from the University of California, Los Angeles who will be telling us about his new mouse model, which his lab recently developed. We recently wrote about this new model: https://en.hdbuzz.net/318

No HD mouse model is perfect for studying HD, but different types can capture different aspects of the disease and allow for different types of experiments. For many years the Yang lab has specialized in creating mouse models to answer specific questions about HD.
Choosing the right model for specific experiments is critical, since some mouse models only have certain features of HD – like altered gene expression or protein aggregation.
The main innovation of the

Yang lab’s new mouse model is that it shows somatic instability, the growth of CAG repeats in certain cells over time. This allows researchers to understand the consequences of expansion to the health and behavior of the mice.
In these mice, the more CAG repeats expand, the more their behavior and brain cell health are affected, confirming for the first time in animals what we have suspected based on data from human blood, spinal fluid, and brain donations.
The lab is now using their new mouse model to better understand how unstable, expanding CAG repeats affect the huntingtin recipe and protein and the harm they may be doing in cells.

Dr. Yang also shared data from a different type of HD mouse model which is allowing them to study how genes get turned on and off over the course of HD. It’s great to see this question approached from multiple angles (along with the McCarroll lab and others).
We’re taking a quick break now but will be back shortly with updates from the rest of this morning’s speakers. Stay tuned!

Processing the huntingtin message

Our next speaker is Dr. Gillian Bates from Queen Square Institute of Neurology, University College London. Dr. Bates will be updating us on how the huntingtin gene is processed and how we can perhaps use this information to develop therapeutics.

The huntingtin gene gets “spliced” to remove small bits of genetic information that sit between the code. The gene then gets put back together before the protein is made. This process is typically used to give cells diversity in the information they can create from a single gene.
But this process can go wrong in HD. In HD, the huntingtin gene is used to create a very small fragment of a protein – called “exon 1”. This exon 1 contains the CAG repeats and is very toxic to cells.

Dr. Bates looked at the amounts of exon 1 in HD mouse models and in different areas of brains from people with HD. She found that with longer CAG repeats, the splicing process making the exon1 protein happened more frequently.
The Bates lab is experimenting with ways to detect and distinguish between different forms and pieces of the huntingtin protein created by splicing. They do this using different combinations of antibodies, a way to detect different parts of the protein.
This work suggests the exon 1 fragment is the site of protein aggregation creation. Understanding how this process occurs can give us lots of clues about how to reduce these protein clumps.

The Bates lab specializes in innovative ways to try and see different forms of the protein under a microscope or in an assay, like creating novel mice and treating the tissue with different chemicals.
They made a special mouse model where the splicing pattern is altered, and the exon1 fragment of the huntingtin protein should no longer be made.
In these mice the lab looked at the levels of toxic protein clumps which are made compared to regular HD mouse models. In the new mouse model there were a lot less clumps suggesting the exon1 fragment is important for making the clumps.
Next steps will involve exploring how differences in huntingtin clumping could change mouse behavior and the pattern of communication between brain cells.
Sometimes huntingtin clumps show up near the cell’s nucleus – the part of the cell that houses genetic material. The Bates lab used multiple models to show that this only happens with human huntingtin, not mouse huntingtin.
These data suggest there’s something unique about human huntingtin that leads to these pathogenic protein clumps. This may be a clue to why humans are the only species to naturally get HD!

Understanding which forms of huntingtin are most toxic and why will help us design drugs to combat its negative effects in (human!) brain cells.

Cellular handling of the huntingtin protein

Next up is Dr. Judith Frydman from Stanford University. She’ll be talking about why CAG repeat expansions can lead to problems with “trash tagging and disposal” systems in brain cells.

While we know the cause of HD, researchers don’t truly know the “normal” function of the huntingtin protein. What they do know is that it participates in a variety of different biological processes – kind of like a swiss army knife of the cell.
Because of this, researchers debate if HD is a disease caused by disruption of other genes or a disruption of other proteins. Dr. Frydman’s work argues that HD, at least in part, results from disruption at the protein level.

Dr Frydman’s research focuses on understanding how the huntingtin message molecule, called mRNA, is turned into the protein molecule, through a process called translation.
Stresses on cells (things like viral infection, reduced availability of protein building blocks, and changes in how the cell’s machinery works) can alter the way translation occurs.
Researchers know that cells from people or animal models with HD have increased amounts of cellular stress. Dr Frydman’s lab have shown in their models, that under these conditions of stress, more huntingtin protein is made.
When cells are making the huntingtin protein by translation, they use machinery called ribosomes. Frydman and colleagues show that when cells make mutated huntingtin, the ribosomes collide and cause a traffic jam on the huntingtin message.
When the Frydman lab looked at what genes were altered on the message with and without the traffic jam, they found that many of those genes were involved in protein cleanup in cells.

One protein, called eIF5A, is depleted in HD models. eIF5A is important for helping the ribosomes to clear the traffic jams, so if less of this protein is around in HD, there will be more problems making new protein molecules and clearing away the old ones.
Together, Dr. Frydman’s work suggests that a whole host of molecular disruptions that result from HD occur at the level of both the RNA message and the huntingtin protein, each contributing to the signs and symptoms of HD we see in patients and in HD models.

Disease effects caused by huntingtin

The second session is hosted by Dr. Balajee Somalinga (CHDI) and Dr. Ali Brivanlou (The Rockefeller University) and it will focus mainly on the huntingtin message and protein and their roles in health and disease.

Early effects caused by huntingtin

The first speaker of this session is Sandrine Humbert from INSERM, who will be talking to us about her research on the role of the huntingtin protein during brain development.
The huntingtin protein has lots of jobs in the cell, one of which is to move different molecules around the cell. One of the molecules huntingtin helps transport in nerve cells is BDNF, which is important for supporting the health of brain cells.
Both the normal and expanded forms of the huntingtin protein are made by cells in the very early stages of life. The Humbert lab thinks that errors made by the expanded form of the protein in people with HD may be responsible for the symptoms they suffer later in life.
The Humbert lab has discovered that huntingtin is important for many functions in nerve cell development, including how these cells are originally formed, their final structure and how they ultimately work and connect with other nerve cells.
In HD mouse models which the Humbert lab work on, this development doesn’t happen properly which may account for the neurodegeneration seen later in life for these mice. We wrote about this work previously here: https://en.hdbuzz.net/290
Dr. Humbert hypothesizes that the change in the way the cells in an HD brain connect sets them up to be vulnerable later in life when HD patients would typically develop symptoms.

Her lab’s latest work continues to explore huntingtin’s roles in health and in HD, including how HD affects nerve cell growth, structure, and movement.
Creating more stability within the structure of the neurons, similar to supportive scaffolding on a building, seems to have positive effects on their health later on.

In summary, it seems that even though nerve cell development is different in HD models, the nerve cells are very resilient and symptoms can still take decades to present themselves.

Huntingtin in other species

Next up is Dr. Raffaele Iennaco from the University of Milan & Istituto Nazionale di Genetica Molecolare. His work uses stem cells to understand how the structure of the huntingtin exon1 fragment affects function.

Dr. Iennaco works with Dr. Elena Cattaneo’s lab, where he focuses on the use of special forms of stem cells known as “induced pluripotent stem cells” or iPSCs. These cells, derived from HD patients, enable the team to study the very beginning of the Huntingtin protein.
This small piece reflects just a tiny bit of the Huntingtin protein – maybe 3% or so of the full protein. But this tiny bit plays an outsized role in Huntingtin’s jobs in the cell – particularly how it moves around the cell.

To better understand this small bit of the Huntingtin protein, Iennaco’s team determined the exact sequence of this region in 209 different animal species! This dramatically increases the numbers of species for which we have this kind of information.

The number of CAG’s across species varies quite a lot – in fish it always seems to be 4 CAGs, in lizards 5, whereas humans without HD have 17-20 CAG repeats. Why different species need different amounts of CAGs is a big mystery that Iennaco is interested in understanding.
Other evidence from Iennaco’s work suggests that the huntingtin gene is unable to accept mutations – there are many fewer changes to huntingtin’s genetic code than would be expected by chance. Additional evidence for the importance of the huntingtin gene.
In marmosets – go google that for a very cute monkey experience – there are actually two Huntingtin genes! This isn’t the case in any other species studied, but it suggests the power of looking at more than 200 species to find examples of rare genetic events to better understand the Huntingtin gene.
Using their stem cells growing in the lab, Iennaco’s team could study the exact link between the length of the CAG repeat region and the ability of those cells to develop into brain cells called neurons. These experiments help us understand the importance of all the genetic diversity identified in their sequencing studies.

Next, Iennaco and team focused on the comparison of mouse and human Huntingtin. Strangely, while they are very similar, the human Huntingtin gene has been found to be more toxic than the mouse version, but we’ve not known why.
The team is able to coax their stem cells grown in dishes to begin going through the very earliest phases of brain development. This allows them to study the importance of small changes (in CAG length or across species) and to measure their impact on brain development.
Using a very cool automated system, the team took images of approximately 5,000 different mini-brains in the lab to better understand the impact of tiny changes in Huntingtin’s sequence.

Many of the aspects of new brain cell growth they measured were more impacted by human Huntingtin rather than mouse Huntingtin. This suggests that there’s something about the human sequence that sets it apart, in its ability to be toxic to newly born brain cells.
The team has narrowed in on a very specific region of the Huntingtin gene that they think explains why human versions of the HD gene are more toxic than those from mice. This supports the importance of genetic studies like this in animals.

Effects caused by huntingtin in astrocytes

Next up is a talk from Prof. Baljit Khakh, from UCLA. His lab is interested in a specific type of support cell – called an astrocyte – in HD. These aren’t the most vulnerable cells in HD – that’s neurons – but astrocytes job in life is to support neurons.
While astrocytes don’t die early in HD, they definitely express the HD gene, and they show a number of changes in their shape and function when they express a mutant copy of the HD gene. Khakh’s lab wants to know whether these changes in astrocytes impact HD.
Khakh’s lab began their work by looking at huge data sets generated from the brains of HD patients and animal models showing which genes were turned on and off, to look for hints that astrocytes might be working poorly. This seemed to be the case.
There are changes in astrocytes in the brains of HD patients, but do they matter for the progression of HD, or are they just reflecting changes in other cell types?

A very cool Huntingtin-lowering tool called a “zinc finger” can shut down expression of the mutant Huntingtin gene. We’ve written about ZFPs before at Buzz, which you can read about here: https://en.hdbuzz.net/275

The UCLA team was able to develop viruses that deliver these Huntingtin-lowering payloads to different cell types in the brain, including neurons or astrocytes. This enables them to lower the Huntingtin gene in different types of cells.
These new viruses very nicely reduce levels of the Huntingtin gene only in the targeted cell type, so the team is able to ask specific questions about the relationship between Huntingtin expression in particular cells, and HD-like symptoms in mice.
Shutting down mutant Huntingtin in each cell type rescued many of the changes found in that cell type. When mutant huntingtin is shut down in neurons (the sick cell type in HD), they saw improvements in the astrocytes – the support cells!
This is weird! It suggests that there’s some kind of feedback loop happening between sick support cells and sick neurons in the HD brain. It also shows the power of manipulating specific cell types – things aren’t always as we assume.
The team then asked the question – what happens to HD-like symptoms in HD mice if Huntingtin is lowered in astrocytes or neurons using a ZFP?
Many of the symptoms they investigated were improved by knocking down the mutant huntingtin gene in neurons, but less so when they knocked it down in astrocytes.

This is important – Khakh loves astrocytes, and wanted to understand if they drive HD symptoms. They did a very good set of experiments and find that astrocytes are changed, but that changes in neurons remain the most important factor, in light of their results.

Processing the huntingtin message

Next up is Jose Lucas from Center for Molecular Biology Severo Ochoa (CBMSO) who will be speaking about how the huntingtin message is processed and how this differs in people with HD.

The process by which gene messages are processed is called splicing. This topic has cropped up in a few earlier talks that also looked at this process, and splicing is thought to create the toxic exon1 fragment of huntingtin.
Splicing goes wrong in various other diseases, so understanding the similarities in this process between diseases could help answer questions about HD and the symptoms we see in patients such as loss of nerve cells. Lucas and colleagues looked to see which genes are affected by changes in the splicing process in HD. If a gene’s message is spliced incorrectly, this will often mean that less of the full protein product of that message will be made.
Scientists in the Lucas lab showed that if they switched on a gene called RBFOX1 artificially, they could improve the symptoms in a HD mouse model by helping correct the splicing mistakes. Maybe this idea could be used to help make new medicines to treat HD?

Gene messages are also processed to remove a “tail” in their genetic code sequence which is made up of lots of the letter A repeating over and over. It turns out that in HD models, lots of messages keep their tails longer than they should, which will affect how they are turned into their protein products.
One of the most affected proteins discovered in this research led the scientists to find out that people with HD have less of a vitamin called thiamine. They confirmed this by measuring the thiamine levels in the spinal fluid, showing reduced levels.
The scientists are now pursuing the answers to two different questions in the clinic: Could thiamine levels be used as a biomarker for progression of HD? And can thiamine treatment improve symptoms in people with HD?

While these are commonly available vitamins the Lucas group is looking at, tightly controlled clinical trials are required for conclusive answers. Hopefully we will have updates for you soon on how this possible treatment might be working in people with HD.

Controling huntingtin protein degradation

Wrapping up the talks for today, Dr. Michael Rapé from Howard Hughes Medical Institute, University of California, Berkeley will discuss his work on how huntingtin is degraded in the cell and how it might be used to treat HD.
The Rapé lab is looking for small molecules that can be used to target the huntingtin protein so the cell’s machinery will break it down and remove it, a process known as protein degradation.

There are certain proteins in the cell that tag other proteins for degradation. So if you can control this process, you could control which proteins the cell degrades. This would be great for a disease like HD where we want to reduce or get rid of a harmful protein!
One challenge with therapeutics for brain diseases is getting past the blood-brain barrier – the selective barrier that protects the brain from harmful things in the blood. The drugs the Rapé lab are developing are small compared to ASOs (like those developed by Roche and Wave) but are still big compared to most drug molecules.

Luckily scientists have shown that small molecule degraders can pass from the bloodstream into the brain which is great news for researchers looking to make degraders to treat diseases like HD.

Our cells make lots of different proteins, called E3 ligases, which are used to “tag the trash” in the cell and target it for degradation. If we could find an E3 that tags the huntingtin protein, we could harness it to develop a degrader molecule.
The Rapé lab developed a screen that would allow them to identify E3 ligases that would be good targets. They identified an E3 ligase called RNF126 which seems to have all of the desired characteristics for developing of the huntingtin degrader molecule, harnessing RNF126.
Next they tested if RNF126 could specifically degrade the huntingtin protein. They found that when expression of RNF126 was increased, it led to degradation of harmful huntingtin in cells!

But these experiments were done with just a fragment of harmful, expanded huntingtin. What happens when the same experiment is done with full-length huntingtin protein with an expanded CAG repeat? The results replicated!
Together, these data suggest that they were able to find this needle in a haystack – the perfect enzyme that binds to huntingtin to naturally allow for its degradation in cells to prevent protein aggregation that causes disease.

The next steps are to move RNF126 forward in drug development to try and identify a compound called a molecular glue which forces RNF126 to help degrade huntingtin protein. We’ll be anxiously waiting to see what the next steps are for this exciting molecule!

Stay tuned for more updates!

That’s all for today, folks. We’re breaking for the night, but will be back tomorrow morning to continue with research updates focused on innovative approaches for HD therapeutics!

Good morning and welcome to Day 2 of HDBuzz coverage of the CHDI HD Therapeutics conference!

Innovative approaches for HD therapeutics

Chairing the third session of HD research talks is Dr. Michael Finley (CHDI) and Dr. William Martin (Janssen R&D, LLC) are chairing the third session of HD research talks, which will cover innovative approaches for HD therapeutics.

Our first talk is from Dr. Beverly L Davidson from The Children’s Hospital of Philadelphia & University of Pennsylvania, who will discuss her work on improving gene therapies for HD.

Improving gene therapies for HD

The Davidson lab works on making gene therapies to treat genetic illnesses like HD. She’s focused on what part of the huntingtin gene to target and how best to get drugs to the brain. Researchers want to make sure they’re doing this as efficiently as possible. As we learned yesterday, there are small toxic fragments of huntingtin that exist at the beginning of the code – exon1. The Davidson lab is focused on making sure this part of the huntingtin gene is targeted by the therapies they’re developing.

The Davidson lab is working with CRISPR – this is a very precise tool which can edit specific letters in the DNA code. The lab aims to take advantage of unique genetic signatures, called SNPs (“snips”), to target the expanded huntingtin gene. Using this approach, researchers identify SNPs that are only on expanded huntingtin. This allows their potential therapeutics to specifically target only harmful huntingtin, leaving “normal” huntingtin alone. In a mouse model of HD, they showed that their CRISPR tool reduced the levels of huntingtin protein by about 50% – the magic number researchers think we need to lower huntingtin by to improve symptoms of HD.

Next the Davidson lab focused on how to improve the way that these tools are delivered to cells. They want to make sure they’re effective and safe. The Davidson lab used a neat genetic trick to allow precise tuning to the expression level of the gene of interest, which you can think of like a dimmer switch. We previously wrote about this cool new tool here: https://en.hdbuzz.net/311

This molecular dimmer switch could be really powerful for HD research – it could allow precise control of huntingtin levels, it gets directly to the right places in the brain, and leaves the body of the mouse quickly after they stop delivering it. The Davidson lab have now refined this tool for use in HD models and showed that they can fine tune huntingtin levels – the more drug they treat with, the more the dimmer switch is lowered.

Moving forward, they’re focused on improving the way this CRISPR tool is delivered and testing it in other types of animals, including monkeys.
They delivered this tool to the monkeys through a spinal injection and found that even very low doses reached lots of different areas in the brain, including those most affected by HD.

Overall, the Davidson lab has developed an exciting new tool that targets only the expanded huntingtin copy and can reach many areas of the brain. This occurs even at low doses and can be precisely controlled. We’re excited to see where this goes next!

RNA-targeting CRISPR

Next up is Gene Yeo, from the University of California, San Diego, who will also be talking about CRISPR technology and testing genetic treatments in different animal models of HD. The Yeo lab is focused on understanding proteins that bind to the genetic message – RNA. They’re trying to target these RNA-binding proteins to develop therapeutics.

RNA-binding proteins (RBPs) can control expression of other genes. The Yeo lab wants to know where RBPs bind, and have developed tools that let them learn this in individual cells – wow!

Many experiments look at changes in whole tissues, or samples created from many cells. Looking at individual cells lets researchers zoom in on subtle but potentially important changes. A recent publication from the Yeo lab showed that they could use RBPs to bind to certain RNAs to “chew them up”. This would be great for destroying the huntingtin message to treat HD!

Most recently, they have shown a decrease in the huntingtin message by delivering RBPs that specifically target CAG repeats. They can do this in multiple models, including human neurons created from stem cells. When the CAG repeats in the huntingtin message were destroyed, they were able to reverse some changes in cells caused by HD! One change they noticed was that expression of genes associated with brain cell health went back to normal. But they wanted to know what happens when they use this therapy in mice – does destroying the CAG repeats with their cool tool make the HD mice better?

Yes! The mice did better on performance tests, had reduced huntingtin protein clumps, and improvements in brain structures seen by MRI. Also important, this genetic approach didn’t seem to affect other genes. This cool new tool still needs some validation but has lots of promise for many diseases, most excitingly, for HD!

SHIELD HD – supporting clinical and biomarker development!

Our next speakers are Drs. Irina Antonijevic & Peter Bialek from Triplet Therapeutics. They’ll be discussing the SHIELD HD trial, a study that followed HD patients over time to try to find clinical differences and identify biomarkers.

Triplet is researching therapies to combat the expansion of CAG repeats in brain cells over time, a process known as somatic instability. This may be an important driver of symptom onset in people with HD. By looking at data from all the genetic information from individuals with HD, researchers identified changes in genes that control somatic instability that modify the age that HD patients develop HD. One of those genes is called MSH3. While Triplet is developing a therapy that targets MSH3, they are also keen to better understand when best to treat patients and which patients would benefit most from the MSH3 targeting therapy.

To better understand how CAG repeat expansion relates to HD symptoms, we need to follow people over time. SHIELD-HD is known as a natural history study – it does not involve a drug, but it is monitoring people with the HD gene who have very early symptoms.

They followed HD patients for over 2 years and took various samples, including blood and CSF. They also analyzed the patients’ brains using MRI scans.
They found that different regions of the brain, called the caudate and ventricles, changed their size over time during the 48 week period of the SHIELD-HD study. This is as we would expect as symptoms progress in people with HD.

The study also looked at another measurement called the total motor score to see how this changed over time in people in the trial. As expected, this also decreased over time, and more so for patients at the later stages of HD. While these changes are expected in HD patients, the SHIELD-HD trial provides researchers with a comprehensive dataset that can be used to better make predictions about the course of HD. These types of datasets could help expedite finding the right type of clinical trial for patients based on where they are during their disease.

Next, Triplet will share updates about their drug that targets the gene MSH3. They did experiments in monkeys to see how reducing MSH3 levels affected their CAG repeats. By lowering MSH3 by 50% in the monkeys, they found that somatic expansion was stopped! If this translates to HD patients, this might significantly delay the age at which patients start to develop symptoms.

Triplet is also interested in measuring MSH3 levels to track HD disease progression and how well the treatment is working. But they ran into a challenge since it’s difficult to detect this gene in brain tissue. To get around this problem, the team at Triplet looked at expression of MSH3 in spinal fluid from participants with HD who were in the SHIELD-HD trial. They had to develop a very sensitive technique. They are continuing to experiment with different ways to collect samples from the spinal fluid and brain in monkeys, as well as testing the drug they are developing, called TTX-3360.

They looked at levels of MSH3 in the CSF of patients at various disease stages. They found no difference in these levels between individuals without HD and those with HD who had no symptoms or were very early in their disease. This finding is important because it gives researchers at Triplet a baseline reading of MSH3 to follow for when they move TTX-3360 to a Phase 1 clinical trial and look to see how the levels of MSH3 change with treatment.
Observational trials like SHIELD-HD not only collect lots of valuable data from HD patients over time, but they also allow researchers to develop new potential treatments like those described by Triplet today. Cool stuff!

Time for a break! We’ll be back shortly for the rest of this mornings presentations. Stay tuned!

New biological insights

Next up is Dr. Beth Stevens from Boston Children’s Hospital and the Broad Institute, who will be talking about her research that could provide insight for moving treatments toward the clinic. Dr. Stevens studies yet another specialized brain cell, called microglia, which act as the immune system of the brain, protecting it from invaders, and helping clean up debris left over from damaged brain cells.

Microglia are tiny (thus the “micro”), and make up about only about 10% of the cells of the brain. But when they encounter damage, or invading bacteria, they get activated and go to work cleaning up the mess. This activation of these key helper cells is normally a good thing for the brain, but in a range of diseases – including HD – it has long been thought that they might be a little too active.

Stevens is a world expert on the role of microglia in health and disease. Stevens has shown that one of the roles of microglia in the brain is to eat up synapses – the bulb-like links between communicating brain cells called neurons. Synapses are good, but need to be cleared to to encode new information into the brain.

There’s a cell-to-cell communication system called the “complement system” that tells microglia to eat, or not to eat, a given synapse or cell. Years ago, Stevens’ team discovered that this complement system is used in the brain by microglia to decide which brain bits need to be digested. In many brain diseases – including HD – this complement system becomes over-active, eating bits clearly labeled with a “don’t eat me” signal for the complement system. The team is interested in understanding whether the complement system plays a key role in the loss of synapses known to happen in HD.

They’ve developed very sophisticated microscope tricks to identify specific populations of synapses in brain regions impacted by HD. In HD mice, there’s a very specific pattern of synapse loss that worsens during aging. Similar changes are seen in HD patient brains. As they’d seen in other diseases, these same vulnerable synapses were decorated with “eat me” signals for the complement system. That suggests that microglia in HD mice and patients might help remove these critical synapses from the brain, potentially contributing to disease progression.

In brains donated by HD patients, Stevens’ team found clear evidence of angry, activated, microglia. They then turned back to mice, where they can manipulate this system to see what role it plays in disease progression. A company – Annexon Biosciences – has developed a drug that blocks complement activation. This allows us to ask whether blocking this hyper-active “eat me” activity contributes to the development of HD-like symptoms in HD model mice. Treating HD mice with this drug did what it was supposed to do – it reduced the “eat me” label from being placed onto critical brain regions. This allows us to ask whether this synapse removal is good or bad in diseases like HD. Using another approach – a genetic change to the mice to fully block the complement system – the team is studying the relationship between complement activation and symptoms. Excitingly, they see protection from some HD-like symptoms in HD model mice.

But what about HD patients, do similar things happen in the brains of real patients? Using Clarity, the team was able to get access to cerebrospinal fluid from HD patients. This fluid, which bathes the brain, can be a non-invasive way to sample brain proteins. Consistent with their predictions, there were clear signs of increased activation of the complement system in the spinal fluid from HD patients. A small human study in HD patients is being conducted currently by Annexon.

Very cool to see how seemingly very basic biological studies can be quickly translated to trials in HD patients!

Stem cell research!

Dr. Leslie Thompson, from UC Irvine, is up next. Thompson has been a long-time leader in the field using stem cells to understand and treat HD. Stem cells are very special cells that can be coaxed to become any other cell type in the body, including the brain cells that are vulnerable in HD.

Historically, these cells had to be isolated from human embryos, but more recently researchers have learned to coax regular cells from adult humans to become stem cells. These “induced pluripotent stem cells” are an amazing tool, allowing researchers to generate real brain cells in the lab.

Dr. Thompson represents a large consortium – called Stem Cells for HD (SC4HD) – who are coordinating efforts to develop potential cell-replacement treatments for HD. They’ve carried out huge studies to develop stem cell lines as a potential source for transplant studies into people with HD. Cells are complicated! The team has carried out a huge amount of standardization to make a very well-characterized source of donor cells.
They’re using these human stem cell lines in experiments in HD mouse models to see whether transplanting cells into the brain improves HD-like symptoms in mice. Excitingly, transplantation of human stem cells leads to significant improvements. This is a proof of concept to show that implanting stem cells can lead to some improvements in HD-relevant symptoms in mice. Understanding the underpinnings of these improvements might allow the team to predict what symptoms to go after in HD patients.

Long-term mouse studies show quite striking improvement in the movement symptoms of an HD mouse model treated with human stem cell transplants. Excitingly, the team has been able to refine their procedures to increase the survival of transplanted cells.

Thompson outlines the consortium’s clinical studies to meet all the requirements of regulators for trials in humans. An obvious concern with stem cells is making sure they don’t grow into unexpected cell types, or cause tumors. These enabling studies are underway – including testing the surgical approaches needed to implant stem cells into the right place in the HD brain. We don’t want transplants into the wrong spot!

That wraps up an exciting series of talks focused on novel treatments for HD. This afternoon is a featured speaker, David Baker, from the University of Washington. We’ll not tweet that talk – so stay tuned for more exciting updates tomorrow!