The urgent need for disease-modifying treatments for Parkinson's disease (PD) has driven significant innovation in the clinical trial pipeline. While current therapies primarily address symptoms, researchers are now pursuing multiple promising approaches that may slow or halt the underlying neurodegenerative processes. Five particularly noteworthy candidates are advancing through clinical development, each with unique mechanisms that could transform PD treatment paradigms.
Ambroxol: Repurposing a Cough Suppressant for Neuroprotection
Ambroxol, originally developed as a cough medication, has emerged as a potential disease-modifying therapy for PD through its novel mechanism as a molecular chaperone. The compound enhances lysosomal glucocerebrosidase (GCase) activity, improving the clearance of cellular waste including α-synuclein aggregates that are hallmarks of PD pathology.
The GRoningen Early-PD Ambroxol Treatment (GREAT) trial is currently evaluating high-dose ambroxol in Europe, specifically targeting patients with early-stage PD who carry GBA gene mutations—a known risk factor for PD. The trial (NCT05830396) will measure changes in both motor and non-motor symptoms over 12 months.
"Lysosomal dysfunction appears to be a fundamental mechanism in Parkinson's pathogenesis, not just in patients with GBA mutations," explains Dr. Stephen Mullin, a neurologist involved in ambroxol research. "By enhancing lysosomal function, ambroxol could potentially benefit the broader PD population."
Earlier open-label studies have already confirmed that ambroxol crosses the blood-brain barrier, increases cerebrospinal fluid GCase levels, and demonstrates a favorable safety profile at therapeutic doses.
NLRP3 Inflammasome Inhibitors: Targeting Neuroinflammation
Chronic neuroinflammation is increasingly recognized as a key driver of PD progression. Several compounds targeting the NLRP3 inflammasome—a protein complex that triggers inflammatory responses in microglia—are advancing through clinical trials.
Inzomelid (formerly known as Emlenoflast) from Biohaven has shown robust IL-1β suppression in preclinical models. Phase 1 studies in healthy volunteers demonstrated both safety and target engagement, suggesting potential for disease modification.
NT-0796, developed by NodThera, recently completed a combined Phase 1b/2a trial in PD patients. This brain-penetrant NLRP3 inhibitor showed dose-dependent reductions in blood IL-1β and neuroinflammatory markers, supporting its continued development.
Two additional NLRP3 inhibitors are also advancing: VTX3232 (Zomagen Biosciences) in a Phase 2a study (NCT06556173) and VENT-02 (Ventus Therapeutics) in Phase 1b (NCT06822517).
"If chronic neuroinflammation truly accelerates disease progression, as mounting evidence suggests, NLRP3 blockade could represent an entirely new disease-modifying strategy," notes Dr. Maria Trujillo, a neuroinflammation specialist at University Medical Center.
AAV2-GDNF: Gene Therapy for Continuous Neuroprotection
AAV2-GDNF represents a pioneering gene therapy approach to PD treatment. This investigational therapy uses an adeno-associated virus serotype 2 (AAV2) vector to deliver the gene encoding glial cell line-derived neurotrophic factor (GDNF) directly into the putamen, a brain region severely affected in PD.
GDNF is a naturally occurring protein that supports the survival and function of dopaminergic neurons. By introducing the GDNF gene into specific brain regions, this therapy aims to stimulate long-term production of this neuroprotective factor at the site of neurodegeneration.
An initial Phase 1 trial (NCT01621581) demonstrated that the surgical delivery approach was safe and well-tolerated, with evidence of widespread vector distribution in the brain. Building on these promising results, a Phase 2 trial (NCT06285643) is now underway to evaluate safety, biodistribution, and exploratory efficacy in patients with moderately advanced PD.
"Gene therapy approaches like AAV2-GDNF could fundamentally change how we treat neurodegenerative diseases," explains Dr. James Richardson, a neurosurgeon involved in the clinical trials. "Rather than requiring daily medication, a single procedure could provide continuous, localized production of therapeutic proteins within the brain for years."
Solangepras: A Novel Non-Dopaminergic Approach
Solangepras (CVN-424) represents an innovative approach to symptom management through a non-dopaminergic mechanism. This oral small molecule acts as an inverse agonist of G-protein coupled receptor 6 (GPCR6), which is predominantly expressed in the striatum—a brain region integral to motor control.
A completed Phase 2 trial (NCT04191577) evaluated Solangepras as an adjunctive treatment to levodopa in PD patients experiencing motor fluctuations. Results were encouraging, with the 150 mg dose significantly reducing daily OFF-time by 1.3 hours compared to placebo.
Based on these positive findings, a Phase 3 trial (NCT06553027) is now assessing the efficacy of Solangepras as a stand-alone monotherapy in PD patients with motor fluctuations.
"By targeting a non-dopaminergic pathway, Solangepras may provide symptomatic relief without the dyskinesias and other complications we see with traditional dopaminergic therapies," says Dr. Caroline Tanner, movement disorders specialist. "This could significantly improve quality of life for patients struggling with motor fluctuations."
Glovadalen: Fine-Tuning Dopamine Signaling
Glovadalen (UCB0022) takes a sophisticated approach to enhancing dopaminergic function. This orally active, brain-penetrating compound acts as a positive allosteric modulator (PAM) of the dopamine D1 receptor. Unlike direct agonists, Glovadalen enhances the receptor's response to endogenous dopamine, amplifying D1 receptor signaling only when dopamine is present.
After successfully completing a Phase 1 trial (NCT04867642) that established safety and tolerability in healthy individuals, UCB has recently concluded a Phase 2 trial (NCT06055985) evaluating efficacy, safety, tolerability, and pharmacokinetics in participants with advanced PD.
"The beauty of a PAM like Glovadalen is that it works with the brain's natural dopamine release patterns rather than overriding them," explains Dr. Robert Chen, neurologist and clinical researcher. "This could potentially provide more physiological motor control with fewer side effects than traditional approaches."
Transforming the PD Treatment Landscape
These five therapeutic candidates represent diverse approaches to addressing both the symptoms and underlying pathology of Parkinson's disease. From enhancing cellular waste disposal with ambroxol to reducing neuroinflammation with NLRP3 inhibitors, from providing continuous neuroprotection with gene therapy to improving motor function through novel receptor modulation, each approach offers unique advantages.
While all these therapies remain investigational, their progress through the clinical pipeline offers hope for meaningful advances in PD treatment. As these and other innovative approaches continue development, the therapeutic landscape for Parkinson's disease may soon expand beyond symptomatic management to include truly disease-modifying strategies.
"We're witnessing a renaissance in Parkinson's research," notes Dr. Kevin McFarthing, a biochemist and person with Parkinson's who maintains The Parkinson's Hope List tracking compounds in development. "The diversity of approaches in clinical trials today reflects our deeper understanding of PD pathophysiology and offers multiple paths toward better treatments."
