Addex Therapeutics, a leading company pioneering allosteric modulation-based drug discovery and development, has reported positive preclinical data for its mGlu5 negative allosteric modulator (NAM) oral small molecule, dipraglurant, in a validated rodent model of dystonia, a spectrum of disorders, that includes several rare diseases and is characterised by debilitating involuntary muscle contractions and body movements. This is an area of high unmet medical need where many patients are left inadequately treated with the current standard of care.

Dipraglurant demonstrated a robust and dose-dependent reduction in severity of a dystonia-like attack, induced by caffeine in the tottering mouse model. These data are consistent with earlier reported Addex findings in a phase II a clinical trial measuring levodopa-induced dyskinesia in Parkinson's patients as well as a non-human primate model of Parkinson's-related dystonia.

"The effects of dipraglurant in the mouse model are very compelling. They provide additional support for further exploration of mGlu5 inhibitors as a novel treatment for dystonia and also open new therapeutic avenues," said Professor Ellen Hess at Emory University (USA) in whose laboratory the study was performed.

The validation of the tottering mouse model in the laboratory of Professor Hess has been funded in part by the Bachmann-Strauss Dystonia and Parkinson Foundation. The model recapitulates key genetic and phenotypic features of so called episodic neurological disorders, that involve aberrant calcium channel functioning and susceptibility to neurological attacks in response to stress, alcohol or caffeine. In the study, acute, oral administration of dipraglurant (10, 30, 50 mg/kg) resulted in dose-dependent reductions of dystonia scores, achieving significant reductions at the highest dose in comparison to vehicle treatment. In a sub-group of experimental animals, dipraglurant fully blocked the onset of dystonia. These results demonstrate the potential of mGlu5 inhibition as a novel approach for the treatment of multiple types of dystonias, as well as other rare neurological conditions including familial hemiplegic migraine type 1, episodic ataxia type 2, and periodic paralysis.

Bharatt Chowrira, CEO at Addex said, "We are pleased that we continue to see broad therapeutic application for dipraglurant.” He further added, "As we continue to seek a partner to advance dipraglurant in Parkinson's levodopa-induced-dyskinesia, we see great opportunity to take the compound forward in several rare disease indications including certain forms of dystonias. We look forward to starting phase II clinical testing in the second half of 2013 with this potentially important movement disorder therapeutic.”

Dipraglurant is an oral, small molecule allosteric modulator that inhibits selectively the metabotropic glutamate receptor 5 (mGlu5), a Class C G-Protein Coupled Receptor (GPCR), with potential to be used in combination with levodopa or dopamine agonists or as a standalone treatment for Parkinson's disease levodopa-induced dyskinesia (PD-LID), motor and non-motor symptoms of Parkinson's disease and other movement disorders. Data from a recent phase II a show that dipraglurant met the primary objective of the study by exhibiting a good safety and tolerability profile. Dipraglurant also demonstrated a statistically significant reduction in LID severity with both 50 and 100 mg doses. Dipraglurant appears to reduce dystonia severity in addition to chorea, the two major LID components.

In a double-blind, placebo-controlled study conducted in the US and Europe, the primary objective was to demonstrate safety and tolerability in PD-LID patients. In addition, the trial was designed to evaluate exploratory efficacy as a secondary objective. Efficacy was measured using the modified Abnormal Involuntary Movement Scale (mAIMS), patient diaries documenting "off-time" (impaired voluntary movement), "on-time" (with or without dyskinesia) and sleep. Additional endpoints include the Unified Parkinson's Disease Rating Scale (UPDRS), the Clinician & Patient Global Impression of Change (CGIC & PGIC), and an evaluation of the patients' mood using the Hospital Anxiety & Depression Score. The trial was supported by a grant from The Michael J Fox Foundation for Parkinson's Research.

There is increasingly convincing evidence that mGlu5 inhibition may be a valuable new strategy for treating a number of important diseases and conditions, such as Parkinson's disease, Parkinson's disease levodopa-induced dyskinesia (PD-LID), anxiety, depression, pain, tardive dyskinesia, dystonia, addiction, autism and Fragile X syndrome. With regards to Parkinson's disease, recent clinical and preclinical evidence suggest that mGlu5 inhibition may have an effect on parkinsonian motor symptoms as well as dyskinesia.

MGlu5 is found in regions of the brain considered to be key control points in the neuronal movement circuits affected by abnormal signaling by the neurotransmitter glutamate in Parkinson's disease. Perturbations in glutamate signaling (along with disruptions in dopaminergic signaling) are believed to be an underlying cause of movement disorders like Parkinson's disease. As such, inhibiting mGlu5 could act to re-establish normal movement via a non-dopaminergic mechanism. Separately, preclinical findings also suggest that mGlu5 inhibitors may be neuroprotective and may, therefore, hold potential as disease modifying agents that can slow or prevent progression of Parkinson's disease.

Dystonia is a movement disorder that causes the muscles to contract and spasm involuntarily, according to the Dystonia Medical Research Foundation. The involuntary muscle contractions force the body into repetitive and often twisting movements as well as awkward, irregular postures. There are approximately 13 forms of dystonia, and dozens of diseases and conditions include dystonia as a major symptom. Dystonia may affect a single body area or be generalized throughout multiple muscle groups. Dystonia affects men, women, and children of all ages and backgrounds. Dystonia causes varying degrees of disability and pain, from mild to severe. There is presently no cure, and, although many drugs are utilized to try to treat dystonia, the leading treatment is botox injections and many patients are left with inadequate efficacy. Dipraglurant has been shown to effectively reduce dystonia in both a clinical study and preclinical models of Parkinson's disease levodopa-induced dyskinesia (PD-LID). The neurophysiology of different forms of dystonia is thought to be similar and recent preclinical data in dystonia - suggesting that dipraglurant may also work for non-parkinsonian forms of dystonia.