A recently completed clinical trial for a new drug being developed by Prothena Corporation (PRTA 1.00%) is sparking excitement within the Parkinson's community. The drug, PRX-002 demonstrated a key ability to reduce the presence of an enzyme thought to be associated with causing Parkinson's disease, and if that results in an ability to slow disease progression, it could mark an important turning point in the treatment of this vexing indication.

Source: Prothena Corporation.

First, a bit of background
Parkinson's disease is a tough-to-treat neurological disease that affects up to 1 million Americans. More than 60,000 new cases of Parkinson's disease are diagnosed every year in the United States, and treatment options remain limited. Globally, it is estimated that there are between 7 and 10 million people living with Parkinson's disease.

Typically, Parkinson's disease patients' symptoms are treated with levodopa. While levodopa isn't a cure, it does help patients control their tremors and muscle stiffness. Additional drugs used in the treatment of Parkinson's symptoms include medicines that help mimic dopamine activity, ones that prevent dopamine levels from falling, and drugs that block the neurotransmitter acetylcholine in the nervous system.

While these drugs do help reduce patient symptoms early on, they fall short of tackling the disease head-on and preventing disease progression. As a result, considerable effort has been focused in the past decade on developing new therapies that can more directly attack Parkinson's at the root of its cause.

Innovating treatment
Research indicates that Parkinson's, as well as other neurodegenerative diseases, could be caused by a build-up of alpha-synuclein, a protein that is found in neurons in the brain and helps neurotransmitters send messages to one another. Although alpha-synuclein's role isn't fully understood, the protein also has a role in dopamine regulation.

In Parkinson's patients, aggregating alpha-synuclein can cause neurodegeneration. Importantly, there's evidence that suggests that these unnatural build-ups can spread from neuron to neuron, causing disease progression.

Prothena, with the help of co-developer Roche Holdings (RHHBY 1.45%), thinks PRX-002 may be able to change that. PRX-002 is a monoclonal antibody that targets alpha-synuclein. The immunotherapy is designed to slow or reduce the spreading of neurodegeneration caused by alpha-synuclein.

Although PRX-002 remains in the very earliest of human clinical trials, an initial look at results from a phase 1 study show that PRX-002 leads to an average reduction in free serum alpha-synuclein levels of up to 96%. That was statistically significantly better than what was seen in the placebo group. Additionally, and importantly, there were no significant adverse events reported by patients in the study, suggesting that PRX-002 appears to be safe.

Looking forward
The study is intriguing because it could lead to a significant advancement in the treatment of this disease; however, investors should remember that 90% of drugs entering phase 1 trials fail, and that the PRX-002 phase 1 trial involved just 40 Parkinson's disease patients. Also, it's uncertain if more complete results from an ongoing trial that is expected to offer up data next year will support or refute these early findings.

While those reasons should make investors cautious, there's a lot to like about Prothena, including the fact that its well-heeled partner, Roche, has extensive experience in monoclonal antibodies like PRX-002. 

Under an agreement with Roche that was inked in December 2013, Prothena has already received $45 million in payments, and Prothena could receive up to another $555 million in milestones over time from this deal. Investors should also know that Prothena has a track record of success. The company was spun-off by Elan Plc, the company that, alongside Biogen, created the blockbuster MS drug Tysabri.

Given that backdrop, investors willing to take on some risk in their portfolios might want to keep an eye on this one.