Background

This is a negative allosteric modulator of the mGluR5 metabotropic glutamate receptor, taken by mouth. It is being developed for the treatment of levodopa-induced dyskinesia (LID) associated with Parkinson’s disease. Dyskinesias are uncontrollable, sometimes disabling, muscle contractions brought on by therapeutic doses of levodopa. Dipraglurant reduces the abnormal glutamate signaling that contributes to dyskinesia. The only drug approved to treat LID is amantadine, which also blocks glutamate signaling.

In preclinical work, dipraglurant rendered LID less severe in a macaque model of PD, without reducing levodopa’s efficacy (Bezard et al., 2014). Dipraglurant also reduced involuntary muscle contractions in a mouse model of dystonia, by restoring brain synaptic plasticity (Sciamanna et al., 2014; Martella et al., 2021). The drug improved symptoms in rodent models mimicking non-motor symptoms of anxiety, depression, and obsessive behaviors (Epping-Jordan et al., 2023).

MGluR5 antagonists are of interest in Alzheimer’s, as well, because the receptor is involved in neuron and astrocyte responses to Aβ (Renner et al., 2010; Um et al., 2013; Shrivastava et al., 2013). In mouse models of AD, mGluR5 inhibitors protect memory and reduce amyloid deposition (Hamilton et al., 2016). MGluR5 has also been reported to mediate α-synuclein-induced cognitive impairments in an α-synuclein transgenic mouse model of PD (Ferreira et al., 2017).

In the 2000s, at least three companies besides Addex were developing mGluR5 negative allosteric modulators for indications including Fragile X syndrome, anxiety, major depression, and LID. The programs were stopped for lack of efficacy, dose-limiting side effects, or liver toxicity.

Findings

Addex completed a Phase 2a trial for Parkinson’s Disease LID in 2012. Conducted in the U.S. and Europe, it enrolled 76 people with moderate to severe LID, who received dipraglurant for 28 days, taken at the same time as levodopa. The dose was titrated from 50 mg once daily to 100 mg three times daily over 21 days, and fixed at 100 mg for the last seven days. The primary endpoint was safety. Clinical endpoints included severity of dyskinesia rated on the modified Abnormal Involuntary Movement Scale on days one, 14, and 28, plus the Unified Parkinson Disease Rating Scale, Clinical Global Impression of Change (CGIC), and patient diaries.

The trial met its primary endpoints of safety and tolerability. The treatment group had more severe adverse events than the placebo group; two participants discontinued due to adverse events at 100 mg. Most common were dizziness, nausea, fatigue, and worsening dyskinesia between doses. On clinical endpoints, the treated group saw a 30 percent improvement of dyskinesia compared to placebo. The difference was statistically significant on days one and 14, but not 28. No differences were observed on UPRDS or patient-reported outcomes. The CGIC was improved in 71.2 percent of the treated group compared to 49.9 percent in placebo. Results are published (Tison et al., 2016).

In 2015, the company conducted a Phase 1 PET study to measure mGluR5 receptor occupancy kinetics in 12 healthy adults. According to an April 2016 press release, dipraglurant receptor binding was dose-proportional, with 27 percent occupancy after a 100 mg dose, 44.4 percent after 200 mg, and 53.5 percent after 300 mg. A range of 50 to 70 percent occupancy is claimed to give an optimal anti-dyskinetic effect.

In January 2016, dipraglurant received orphan drug designation from the U.S. FDA for the treatment of LID (press release).

In August 2021, Addex began a three-month Phase 2b/3 trial in PD patients with LID. The 140 participants were to take 150 mg per day for one week, then 300 mg daily for the rest of the study, or placebo. The study included a 12-month open-label extension. The primary endpoint was change in the Unified Dyskinesia Rating scale, a measure developed specifically to assess LID. Secondary endpoints were ON and OFF time based on patient diaries. Completion was slated for August 2023. In June 2022, the company stopped the trial, citing slow recruitment due to the COVID-19 pandemic (company release).

The company also conducted a Phase 2 feasibility study in 15 people with blepharospasm, a form of dystonia that affects the eyelid muscles and can cause vision problems. In a May 2022 press release, Addex said the study was inconclusive.

For details on dipraglurant trials, see clinicaltrials.gov.