At 23:30 on the 3rd August 2017, the results of a phase II clinical trial investigating the use of a Glucagon-like peptide-1 receptor (GLP-1R) agonist called Exenatide (Bydureon) in Parkinson’s were published the Lancet journal website.
The findings of the study were very interesting.
And after years of failed trials, the Parkinson’s community finally had a drug that appeared to be ‘doing something’. Naturally these results got many in the Parkinson’s community very excited.
Over the last couple of weeks, further research related to this topic has been published. In today’s post we will review some of this new research and ask some important questions regarding how to move forward with these results.
Dr John Eng. Source: Health.USnews
The Award was created in 2012 to celebrate researchers whose seemingly odd or obscure federally funded research turned out to have a significant and positive impact on society.
This week a research report was published in the journal Nature Medicine that expanded on the work of Dr Eng (some 25 years after his big discovery).
And it could be very important to the Parkinson’s community.
Sounds intriguing. What did Dr Eng do?
In the 1980’s, Dr Eng became really interested in some studies (such as this one) that described the effects that certain types of venom had on cells in the pancreas.
The pancreas is the organ that produces the chemical insulin which is critical for maintaining normal glucose levels in our bodies. Having worked with diabetic people who do not produce enough insulin, Dr Eng started wondering if venom may contain chemicals that could help people with diabetes. But rather than injecting diabetic people with venom, he started looking at all the chemicals that make up the venom from different poisonous creatures.
Venom looks like great fun. Source: Cen
What did he find?
This charming creature is a Gila monster.
The Gila monster. Source: Californiaherps
Some interesting facts about the Gila (pronounced ‘Hila’) monster:
- They are named after the Gila River Basin of New Mexico and Arizona (where these lizards are found)
- They are protected by State law
- They are venomous, but very sluggish creatures
- They spend 95 percent of their time underground in burrows.
In 1992, Dr Eng identified the two proteins that he had isolated from the venom of the Gila monster. One of them was called exendin-4 and it bore a striking similarity -structurally and functionally – to a human protein, called glucagon like peptide-1 (GLP-1).
What is GLP-1?
Insulin instructs cells to take in and use glucose from the blood. This has the effect of lowering blood sugar. The hormone Glucagon has the opposite effect – it tells the body to release glucose into the blood to raise sugar levels.
GLP-1 is a hormone that stimulates insulin production while blocking glucagon release.
The function of GLP-1. Source: Wikipedia
Unfortunately, naturally produced GLP-1 in your body is rapidly deactivated by a circulating enzyme called dipeptidyl peptidase IV. Exendin-4, however, was found to be resistant to this deactivation, meaning that could last longer in the body stimulating insulin production and blocking glucagon release. Dr Eng quickly realised that there was enormous medicinal potential for exendin-4 as a drug for people with diabetes. He patented the idea and soon afterwards a biotech company called Amylin Pharmaceuticals to begin the work of turning exendin-4 into a drug for diabetes.
That drug was eventually called Exenatide.
In April 2005, Byetta (the commercial name for Exenatide) was approved by the FDA for clinical use in the treatment of Type 2 diabetes. On the 27th January 2012, the FDA gave approval for a new formulation of Exenatide called Bydureon, as the first weekly treatment for Type 2 diabetes. In July of 2012, Bristol-Myers Squibb announced it would acquire Amylin Pharmaceuticals for $5.3 billion, and one year later AstraZeneca purchased the Bristol-Myers Squibb share of the diabetes joint venture.
Interesting, but what does any of this have to do with Parkinson’s?
In 2008, this report was published:
Title: Peptide hormone exendin-4 stimulates subventricular zone neurogenesis in the adult rodent brain and induces recovery in an animal model of Parkinson’s disease.
Authors: Bertilsson G, Patrone C, Zachrisson O, Andersson A, Dannaeus K, Heidrich J, Kortesmaa J, Mercer A, Nielsen E, Rönnholm H, Wikström L.
Journal: J Neurosci Res. 2008 Feb 1;86(2):326-38.
In this study, Exendin-4 (the protein very similar to exenatide) was tested in a rat model of Parkinson’s. Five weeks after giving the neurotoxin (6-hydroxydopamine) to the rats, the investigators began treating the animals with exendin-4 over a 3 week period. Despite the delay in starting the treatment, the researchers found behavioural improvements and a reduction in the number of dying dopamine neurons.
And this first result was followed a couple of months later by a similar report with a very similar set of results:
Title: Glucagon-like peptide 1 receptor stimulation reverses key deficits in distinct rodent models of Parkinson’s disease.
Authors: Harkavyi A, Abuirmeileh A, Lever R, Kingsbury AE, Biggs CS, Whitton PS.
Journal: J Neuroinflammation. 2008 May 21;5:19. doi: 10.1186/1742-2094-5-19.
PMID: 18492290 (This study is OPEN ACCESS if you would like to read it)
The scientists in this study tested exendin-4 on two different rodent models of Parkinson’s (6-hydroxydopamine and lipopolysaccaride), and they found similar results to the previous study. The drug was given 1 week after the animals developed the motor features, but the investigators still reported positive effects on both motor performance and the survival of dopamine neurons.
This was a lot of positive results for this little protein.
How is Exendin-4/Exenatide having this positive effect?
Exendin-4 and exenatide are both GLP-1 receptor agonists.
What does that mean?
On the surface of cells there are small proteins called receptors, which act like switches for certain biological processes. Receptors will wait for another protein to come along and activate them or alternatively block them.
The proteins that activate the receptors are called agonists, while the blockers are called antagonists.
Agonist vs antagonist. Source: Psychonautwiki
Exendin-4 and exenatide are agonists, so they activate the GLP-1 receptor.
Activation of the GLP-1 receptor by a GLP-1 receptor agonist like exendin-4 or exenatide results in the activation of many different biological pathways within a cell:
The GLP-1 signalling pathway. Source: Sciencedirect
Of particular importance is that GLP-1 receptor activation inhibits cell death pathways, reduces inflammation, reduces oxidative stress, and increases neurotransmitter release. All pretty positive stuff really. For a recent and very good OPEN ACCESS review of the GLP-1-related Parkinson’s research field, click here.
And all of these research reports with positive results led to and supported the idea of clinically testing exenatide in people with Parkinson’s.
What happened in the first clinical trial?
The first clinical trial of exenatide in Parkinson’s was a phase I trial to determine if the drug was safe to use in people with Parkinson’s. The results of the trial were published in 2013:
Title: Exenatide and the treatment of patients with Parkinson’s disease.
Authors: Aviles-Olmos I, Dickson J, Kefalopoulou Z, Djamshidian A, Ell P, Soderlund T, Whitton P, Wyse R, Isaacs T, Lees A, Limousin P, Foltynie T.
Journal: J Clin Invest. 2013 Jun;123(6):2730-6.
PMID: 23728174 (This study is OPEN ACCESS if you would like to read it)
The researchers gave exenatide (the Byetta formulation which is injected twice per day) to a group of 21 people with moderate Parkinson’s and evaluated their progress over a 14 month period. They compared those participants to 24 additional subjects with Parkinson’s who acted as control (they received no treatment). Exenatide was well tolerated by the participants, although there was some weight loss reported among many of the subjects (one subject could not complete the study due to weight loss).
Importantly, the exenatide-treated subjects demonstrated improvements in their Parkinson’s movement symptoms (as measured by the Movement Disorders Society Unified Parkinson’s Disease Rating Scale (or MDS-UPDRS)), while the control patients continued to decline.
Interestingly, in a two year follow up study – which was conducted 12 months after the subjects stopped receiving exenatide – the researchers found that participants previously exposed to exenatide demonstrated a significant improvement (based on a blind assessment) in their motor features when compared to the control subjects involved in the study.
It is important to remember, however, that this trial was an ‘open-label study’ – that is to say, the participants knew that they were receiving the exenatide treatment so there is the possibility of a placebo effect explaining the improvements. And this necessitated the testing of the efficacy of exenatide in a phase II double blind clinical trial.
And the results of that trial were published last August (2017):
Title: Exenatide once weekly versus placebo in Parkinson’s disease: a randomised, double-blind, placebo-controlled trial
Authors: Athauda D, Maclagan K, Skene SS, Bajwa-Joseph M, Letchford D, Chowdhury K, Hibbert S, Budnik N, Zampedri L, Dickson J, Li Y, Aviles-Olmos I, Warner TT, Limousin P, Lees AJ, Greig NH, Tebbs S, Foltynie T
Journal: Lancet 2017 Aug 3. pii: S0140-6736(17)31585-4.
In the study, the investigators recruited 62 people with Parkinson’s (average time since diagnosis was approximately 6 years) and they randomly assigned them to one of two groups, exenatide (the Bydureon formulation which is injected once per week) or placebo (32 and 30 people, respectively). The treatment was given for 48 weeks (in addition to their usual medication) and then the participants were followed for another 12-weeks without exenatide (or placebo) in a ‘washout period’.
It is important to remember that in this trial everyone was blind. Both the investigators and the participants. This is referred to as a double-blind clinical trial and is considered the gold standard for testing the efficacy of a new drug.
The researchers found a statistically significant difference in the motor scores of the exenatide-treated group verses the placebo group (p=0·0318). As the placebo group continued to have an increasing (worsening) motor score over time, the exenatide-treated group demonstrated improvements, which remarkably remained after the treatment had been stopped for 3 months (weeks 48-60 on the graph below).
Reduction in motor scores in Exenatide group. Source: Lancet
Brain imaging (DaTscan) also suggested a trend towards reduced rate of decline in the exenatide-treated group when compared with the placebo group. Interestingly, the researchers found no significant differences between the exenatide and placebo groups in scores of cognitive ability or depression – suggesting that the positive effect of exenatide may be specific to the dopamine or motor regions of the brain.
Given that these results were coming from a randomised, double-blind clinical trial, the Parkinson’s community got very excited about them (Click here to read a previous SoPD post about this particular trial).
This is very positive stuff. What has been published more recently?
So very recently, the researchers who conducted the Phase II exenatide trial published some follow up results which looked deeper into the data and found some interesting trends:
Title: What Effects Might Exenatide have on Non-Motor Symptoms in Parkinson’s Disease: A Post Hoc Analysis
Authors: Athauda D, Maclagan K, Budnik N, Zampedri L, Hibbert S, Skene S, Chowdhury K, Aviles-Olmos I, Limousin P, Foltynie T
Journal: Journal of Parkinson’s Disease, 2018, Pre-press, pp. 1-12.
In this study, the investigators collected all of the data that had been collected during the exenatide clinical trial, and they went through the painstaking process of trying to find interesting trends in the data that were not large enough to be picked up in the initial analysis.
And as they analysed all of the data, the researchers noticed something interesting.
Compared to the placebo-treated group, participants treated with exenatide appeared to have improvements in individual domains assessing mood and depression. While the trends were not always significant, they were apparent across all observer-rated outcome measures that were collected after 48 weeks.
These changes were not associated with changes in motor severity or other factors, which the investigator proposed may suggest that exenatide could be having an independent effect on mood.
BUT, we have to be very careful in how we interpret these results.
And the researchers have stressed throughout the report that these new results are based on a post hoc analysis, which in no way should be interpreted as evidence of efficacy (irrespective of any statistical threshold).
This type of analysis is only conducted for hypothesis generating purposes (especially on such a small sample of participants – just 32 people treated with exenatide).
Having said that, the results of this new analysis may also be very useful in the planning of outcome measures in the next exenatide (or other future GLP1 agonist) clinical trials.
Very interesting. So summing up, what does it all mean?
Not just yet.
We aren’t finished.
There is more to discuss.
Earlier this week a research report was published on the website of the journal Nature Medicine, which may help to explain how exenatide could be having an effect on Parkinson’s… and it may also provide another GLP-1 receptor agonist to add to the arsenal of new treatments for PD.
Here is the report:
Title: Block of A1 astrocyte conversion by microglia is neuroprotective in models of Parkinson’s disease
Authors: Yun SP, Kam TI, Panicker N, Kim S, Oh Y, Park JS, Kwon SH, Park YJ, Karuppagounder SS, Park H, Kim S, Oh N, Kim NA, Lee S, Brahmachari S, Mao X, Lee JH, Kumar M, An D, Kang SU, Lee Y, Lee KC, Na DH, Kim D, Lee SH, Roschke VV, Liddelow SA, Mari Z, Barres BA, Dawson VL, Lee S, Dawson TM, Ko HS
Journal: Nature Medicine, 2018, 11 June. [Epub ahead of print]
(Before we start here, I just want to say: This report is a beast! It is massive – so much work has been done! Congrats to the investigators on an impressive volume of work).
In this study, the researchers were investigating the use of a drug called NLY01 in models of Parkinson’s. NLY01 is new GLP-1 receptor agonist being developed by a company called Neuraly Inc, which is also developing novel brain penetrant c-Abl inhibitors for Parkinson’s (Click here to read more about this).
The investigators started their analysis by treating normal mice and primates with the drug.
NLY01 had a very impressive half-life of 38 hours in mice and 88 hours (in primates). This is impressive compared to Exenatide (Byetta) which has a half-life of 2.5 hours in primates. The half-life of a drug is the time required for the concentration of the drug to decrease by half in the body.
NLY01 also did not increase the risk of hypoglycemia (or low blood sugar) when administered in the animals. And it reached the brain very efficiently – having no issues with the blood brain barrier (the protective membrane surrounding the brain).
Next, the researchers tested the drug on two different mouse models of Parkinson’s:
- the alpha synuclein preformed fibril model
- the hA53T genetically engineered mouse
What are alpha synuclein preformed fibrils?
As regular readers will be aware alpha synuclein is considered to be one of the main trouble makers in Parkinson’s. It may sound like a distant galaxy, but it is an extremely abundant protein in our brains – making up about 1% of all the proteins floating around in each neuron.
When alpha synuclein is produced by a cell, it normally referred as a ‘natively unfolded protein’, in that is does not really have a defined structure. Alone, it will look like this:
Alpha synuclein. Source: Wikipedia
By itself, alpha synuclein is considered a monomer, or a single molecule that can bind to other molecules. When it does bind to other alpha synuclein proteins, they form an oligomer (a collection of a certain number of monomers in a specific structure). In Parkinson’s, alpha synuclein also aggregates to form what are called ‘fibrils’.
Microscopic images of Alpha Synuclein (AS) monomers, oligomers and fibrils. Source: Brain
And over the last few years research labs have been taking alpha synuclein and turning them into fibrils, and then using those ‘preformed fibrils’ in models of Parkinson’s. For example:
Title: Pathological α-synuclein transmission initiates Parkinson-like neurodegeneration in nontransgenic mice.
Authors: Luk KC, Kehm V, Carroll J, Zhang B, O’Brien P, Trojanowski JQ, Lee VM.
Journal: Science. 2012 Nov 16;338(6109):949-53.
PMID: 23161999 (This report is OPEN ACCESS if you would like to read it)
In this study, when the researchers injected preformed fibrils of alpha synuclein into the mice, they started to observed alpha synuclein protein aggregation in the brain approximately one month later, and the mice started to exhibit motor problems 3-6 months later.
In the NLY01 study, the researchers injected their preformed fibrils into mice and they waited one month before initiating treatment of the mice with either NLY01 or a placebo treatment. They treated the mice for twice per week for 5 months.
The results found that NLY01 treatment significantly reduced the amount of alpha synuclein aggregating and also reduced the loss of dopamine neurons. The drug also rescued the motor deficits across a range of behaviour tests.
Next the researchers tested NLY01 on the hA53T genetically engineered mouse.
And what is the hA53T genetically engineered mouse?
There is a region of your DNA that provides the instructions for making alpha syncuclein. That region of DNA is called SNCA. And there are several genetic variations (or mutations) inside of SNCA that are associated with an increased risk of developing Parkinson’s.
A53T is the name of one of those genetic variations.
As you can see in the image below, A53T lies in the red (Amphipathic) region of SNCA along with several other genetic variants, such as A30P and E46K:
Mice have been genetically engineered to carry the SNCA gene with the A53T genetic mutation (Click here to read the original report). These mice exhibit hyperactivity and then start to display signs of alpha synuclein protein aggregation at about four to six months of age. They also pass away earlier than normal mice (12-14 months of age, compared to 20+ months for normal mice).
In the NLY01 study, the investigators started treating the A53T mice at 6 months of age with either NLY01 or a placebo control, and they reported that NLY01 significantly prolonged the lifespan of the A53T mice by over 3 months. In addition to this prolonged survival, the researchers also found a reduction in levels of aggregated alpha synuclein in the brains of the NLY01-treated A53T mice.
Next, the researchers wanted to try and determine how NLY01 was having this effect (the ‘mechanism of action’), and they started by labelling GLP-1 receptors in cell cultures of difference types of brain cells (astrocytes, microglia and neurons) and then they looked to see where GLP-1 was most abundant.
Interestingly, they found that microglia cells have the highest levels of GLP-1 receptors.
Microglia are some of the helper cells in the brain. They act as the resident immune cells. When infection or damage occurs, the microglia become ‘activated’ and start cleaning up the area.
Different types of cells in the brain. Source: Dreamstime
Also of interest: the researcher reported that treating the cells with preformed fibrils of alpha synuclein decrease GLP-1 levels in neurons and increased GLP-1 levels almost two fold in microglia. And when they looked at postmortem tissue, the investigators found a 10x increase in the levels of GLP-1 in the substantia nigra of people who passed away with Parkinson’s (compared to healthy controls samples). The substantia nigra is the region of the brain where the dopamine neurons reside, and it is badly affected in Parkinson’s.
The finding that microglia have higher levels of GLP-1 protein led the researchers to test the idea that perhaps NLY01 was having its effect via the microglia cells rather than the neurons. So they treated cultures of just dopamine neurons with preformed fibrils of alpha synuclein and the investigators found that NLY01 treatment had no protective effect on the cells.
Dopamine neurons (green) in cell culture. Source: Axolbio
Previously the researchers conducting this study had demonstrated that activation of microglia can cause them to release all sorts of nasty, inflammatory chemicals. They do this to alert other microglia to a potential problem. But these chemicals can also cause astrocytes to shift from a neutral state to a highly reactive state (Click here to read more about this).
An astrocyte. Source: Wikipedia
Astrocytes, like microglia, are helper cells in the brain. They provide nutrients to neurons and make sure the environment surrounding the neurons is balanced and supportive. When astrocytes shift from a neutral state to a reactive state, however, it can be very bad news for any neurons nearby. And given this scenario, the researchers began to wonder whether the interactions between microglial cells and astrocytes could be involved in the neuroprotective effects of NLY01.
They decided to test this idea by firstly treating microglia with preformed fibrils of alpha synuclein. This got the microglia nice and activated, and the researchers then split the microglia in to two groups: one group was treated with NLY01 and the other group was not. Next the investigators collected the solutions from these two groups of microglia cultures, and they applied those solutions to two groups of astrocytes in cell culture. Astrocytes given the NLY01-treated microglial solution did not become reactive.
And subsequent experiments demonstrated that this reduction in reactive astrocytes was neuroprotective for dopamine neurons when they were grown in culture solution from the NLY01-treated activated microglia and reactive astrocytes.
I hope all of this makes a little bit of sense.
Long story short/the take home message:
- Preformed fibrils of alpha synuclein activate microglia
- Activated microglia spit out nasty, inflammatory chemicals
- Astrocytes exposed to those chemicals get reactive
- Reactive astrocytes are bad news for nearby neurons
And NLY01 limits the activated microglia from spitting out too much of the nasty, inflammatory chemicals, thus lowering the number of reactive astrocytes.
NLY01 appears to be having its effect via the microglial cells.
Interestingly, when the researchers removed astrocytes from the equation by exposing the neurons to solution collected from activated microglia, there is some cell death in the neuronal population, but it is not as much as that seen in the cultures including reactive astrocyte solution.
Thus, reactive astrocytes seem to be critical to the neuronal cell death.
And when the researchers looked at the brains of the ‘preformed fibrils of alpha synuclein’ injected mice that had been treated with NLY01 for 5 months (which we discussed above), they found a reduced number of activated microglia.
These results led the researchers to conclude that “NLY01 exhibits protective effects primarily through microglial GLP1R“. And because of this specific mechanism, the investigators suggest that “NLY01 may have broad neuroprotective properties in a variety of neurodegenerative disorders and neurologic injuries“, beyond just Parkinson’s.
All of this data sounds fantastic. So why the negative title to this post?!? Exenatide doesn’t sound like a problem.
Ah, but it is.
In several ways.
(and if you are not interested in academic arguments, you can turn off here)
Let’s me ask you this: With all the hype and excitement in the Parkinson’s community surrounding Exenatide, how can we possibly conduct an un-biased phase III clinical trial?
And this is a very serious question.
Massive resources (millions of dollars and hundreds of people) are potentially going to be marshaled in a phase III clinical trial of this drug. Multiple research centres are going to be involved. It would be a major investment.
But expectations are already extremely high (and websites like the SoPD are obviously not helping!).
We have been to this rodeo before (think of all the GDNF approaches to PD – they had high expectations). With such high expectations, the risk of a placebo response (that is, the experiencing of beneficial effect where no pharmacological cause is apparent) is a very real possibility. And the placebo effect is a major issue in Parkinson’s research (Click here to read a previous post on the placebo effect in PD).
Imagine conducting a massive (200+ participant) clinical trial and at the end of the 2 years period of the study finding that many participants in the placebo control group demonstrated a placebo response (that is, they had beneficial effects despite only taking the the inert treatment).
Thus, we return to the question: With all the hype and excitement in the Parkinson’s community surrounding Exenatide, how can we possibly conduct an un-biased phase III clinical trial?
Your thoughts on this matter in the comment section below would be greatly appreciated.
And then, if we do run “Exenatide III” and the results are positive, will we face the ‘Dilemma of success‘? That is, if we have a semi-neuroprotective drug that everyone wants to take, how will we develop future neuroprotective therapies for Parkinson’s?
As I have said before, “these are good problems to have“, but they do keep me awake at night!
So what does it all mean?
These are really interesting times for Parkinson’s research. And it is hard not to be excited – it is a very human response when there are some positive results after a long period of negative outcomes. We may be standing on the edge of a new age with regards to Parkinson’s, where sufferers may be provided with more than just treatments that cover up the symptoms.
But it is important for readers to understand that we are not there yet.
The results coming from the GLP-1 agonist research are very interesting and encouraging, but we must not read too much from them. The deep analysis of the Phase II clinical trial ‘suggest’ that exenatide may be having an effect that goes beyond the previously reported motor results, but all of these results need to be tested in a larger cohort and over a longer period of time. There is still so mush that we don’t know. For example, we have no idea what impact long term exenatide treatment has in Parkinson’s (diabetes yes, but PD may be different – we simply do not know).
One of the ‘long-term use’ concerns with the exenatide approach to Parkinson’s is the weight loss issue. A lot of people that take exenatide lose their appetite. And this was evident in the phase II exenatide study, in which at the 48 weeks time point, the exenatide group had lost an average of 2·6 kg, while the control group had lost only 0·6 kg. In the phase I trial one subject could not complete the study due to weight loss.
Thus, there is still a lot of work to be done, but the results are looking very encouraging.
EDITOR’S NOTE: The information provided by the SoPD website is for information and educational purposes only. Under no circumstances should it ever be considered medical or actionable advice. It is provided by research scientists, not medical practitioners. Any actions taken – based on what has been read on the website – are the sole responsibility of the reader. Any actions being contemplated by readers should firstly be discussed with a qualified healthcare professional who is aware of your medical history. While some of the information discussed in this post may cause concern, please speak with your medical physician before attempting any change in an existing treatment regime.
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