Prothena reports Phase 1b results for Parkinson’s immunotherapy

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This week the biotech company Prothena released the results of their phase 1b clinical trial for their treatment, PRX002 (also known as RG7935).

This is one of the first immuno-therapies being tested in Parkinson’s disease, and the results indicate that the treatment was active and well tolerated.

In this post we will review the press release and what it tells us regarding this clinical trial.


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Antibodies binding to proteins. Source: AXS

When your body is infected by a foreign agent, it begins to produce some things called antibodies. In most cases, these are Y-shaped proteins that binds to the un-wanted invader and act as a beacon for the immune system. It is a very effective system, allowing us to go about our daily business without getting sick on a regular basis. Antibodies allow us to build up immunity, or resistance of an organism to infection or disease.

Scientist have harnessed the power of this natural process, and they have use it to develop methods of helping our bodies fight off disease.

The first approach is called Acquired Immunity (or adaptive immunity), and it is based on the idea that exposure of the immune system to a pathogen (disease/damage causing agent) creates an ‘immunological memory’ within our immune system, and this leads to an enhanced response to subsequent future encounters with that same pathogen.

Scientists have used the idea of acquired immunity to develop what we call vaccines – which are simply small, neutral fragments of specific pathogen that help the immune system to build up immunity (or resistance) before the body is attacked by the disease-causing pathogen itself.

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Vaccination. Source: WebMD

The second approach is called Passive Immunity.

Passive immunisation is simply the sharing of antibodies. And that might sound a bit disturbing, but it is actually a naturally occurring process. For example, a mother’s antibodies are transferred to her baby in the womb via the placenta.

And again, scientists have devised ways of producing passive immunisation artificially. And recently researchers have been using this approach to attack many medical conditions (particularly cancer), in an area of medicine called immunotherapy.

Think of it as simply boosting the immune system by supplementing the supply of antibodies. Scientists can produce high levels of antibodies that specifically target a particular pathogen and then transfer those antibodies to affected people via an intravenous injection.

How is this being used for Parkinson’s disease?

Well, we have previously discussed the idea of a vaccine for Parkinson’s disease (click here to read that post), and we have been closely following the progress of an Austrian company, AffiRis, who are leading the vaccination approach (Click here for that post).

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Source: AffiRis

The vaccine approach is targeting the Parkinson’s disease associated protein, Alpha synuclein. It is believed that a bad kind of alpha synuclein is causing the spread of the condition, by being passed from cell to cell. The goal of the vaccine is to capture and remove all of the alpha synuclein being passed between cells and thus (hopefully) halt the progress of – or at least slow down – the disease.

And this week, another company – Prothena – has reported the results of their phase 1 trial for a passive immunity approach to Parkinson’s disease. They have been injecting subjects in the trial with a treatment called PRX002.

(Remember that a phase 1 trial simply tests the safety of a treatment in humans, it is not required to test efficacy of the treatment. Efficacy comes with phases 2 & 3 trials)

What is PRX002?

PRX002 is a monoclonal antibody. The scientists at the biotech company Prothena have artificially produced large amounts of antibodies to alpha synuclein and these have been injected into people with Parkinson’s disease.

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Monoclonal antibodies. Source: Astrazeneca

Prothena provide a short video explaining this concept (click here to view the video).

So what were the results of the Prothena study?

The study was conducted in collaboration the pharmaceutical company Roche. It was a double-blind (so both the researchers and subjects did not know what they were receiving until the conclusion of the study), placebo-controlled study involving 80 people with Parkinson’s disease. The subjects were randomly assigned to one of six groups, which received either PRX002 or a placebo. There were six doses of PRX002 tested in the study (0.3, 1, 3, 10, 30 or 60 mg/kg).

The study was conducted over six-month, during which patients received three once-a-month injections of either PRX002 or placebo. The subjects were then followed for an observational period of three months.

According to the press release, no serious treatment-related adverse events were reported in PRX002 treated patients. Mild treatment-related adverse events (greater than anything experienced within the placebo group) were noted in 4 of the 12 subjects in the highest dosage group of PRX002, including constipation and diarrhoea.

Importantly, the investigators reported that thePRX002 antibodies were crossing the blood brain barrier and entering the brain. This resulted in a rapid reduction of alpha-synuclein levels (in some cases by up to 97 percent after a single dose!).

The follow-on Phase 2 clinical study is expected to begin in 2017.

What is the difference between the vaccine and the passive immunity approaches?

Basically, it comes down to levels of control. With a vaccination, once you have injected the vaccine and the immune system is activated, there isn’t much you can do to control the response of the body. And that immune memory is going to last a long time. The passive immunity response, on the other hand, requires regular injections of antibodies which can be stopped if adverse effects are noted.

Plus – and forgive me if I sound a little bit cynical here – drug companies prefer a regular treatment approach (which they can charge for each visit) compared to a one-shot cure. It’s simply a better business model.

What happens next?

In both cases – the vaccine and the passive immunity approaches – phase 2 trials are being set up by the respective companies and we will wait to see have affective these treatments are at slowing down Parkinson’s disease.

If they are affective, expect big headlines in the media and plans for adults everywhere to start being vaccinated. If they fail,…. well, we will have to re-address our understanding of the role of alpha synuclein in Parkinson’s disease.

Interesting times lie ahead.


The banner for todays post was sourced from Prothena

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6 comments

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