Researchers from four countries have reported success in a phase II clinical trial of the metabotropic glutamate receptor antagonist mavoglurant in cocaine use disorder. When taking it, participants consumed significantly less cocaine and alcohol compared with placebo. The report is published in the journal Science Translational Medicine.
Glutamate is the main excitatory neurotransmitter. Its rapid effects are mediated by ionotropic NMDA and AMPA receptors, and its slow effects are mediated by G-protein-coupled metabotropic receptors mGluR, of which there are eight known types. Preclinical studies have shown that pharmacological inhibition of metabotropic glutamate receptors type 5 (mGluR5) suppresses cocaine seeking and self-administration in animals, and knockout of the gene for this receptor eliminates the reinforcing and stimulating effects of the substance. Mavoglurant (AFQ056) binds to the allosteric site of mGluR5 in a dose-dependent manner and acts as a selective non-competitive antagonist of these receptors.
Fabrizio Gasparini of Novartis Pharma and colleagues in Argentina, Spain, the United States and Switzerland conducted double-blind, randomized, placebo-controlled phase II trials in three countries. They enrolled 68 patients (82.4 percent men) with cocaine use disorder. Thirty-one of them took mavoglurant at a dose of up to 200 milligrams (individually titrated over the first two weeks) twice daily for 98 days; the remaining 37 took placebo.
When assessing the number of days of cocaine use by self-report on a retrospective time scale, the post-hoc probability of reducing cocaine use was at least 99 percent for a between-group difference of less than zero percent and at least 36.6 percent for a difference of less than 10 percent (p = 0.021). Moreover, the proportion of days of cocaine use in the main group significantly decreased over the course of treatment (p = 0.042 in the second month and p = 0.003 in the third). Mavoglurant also reduced cocaine use as measured by urine tests for its metabolite benzoylecgonine (p = 0.025) and alcohol use as measured by self-report on a retrospective time scale (p = 0.072).
Clinical improvement according to the CGI scale by the end of the trial was achieved by 90.9 percent of the participants in the main group versus 46.6 percent of the control group. Complete abstinence from cocaine use in the last three weeks of work was 41.4 versus 16.7 percent according to self-reports (p = 0.027) and 27.6 versus 8.3 percent according to urine tests (p = 0.040). Similar abstinence from alcohol use was 31.0 versus 11.1 percent. Hair analysis for cocaine and alcohol metabolites (benzoylecgonine, norcocaine, cocaethylene, and ethyl glucuronide) confirmed their more pronounced reduction when taking the active drug. The profile of adverse events was comparable in the main and control groups.
In summary, in a multicenter but relatively small and short-term trial, the mGluR5 antagonist mavoglurant significantly reduced cocaine and alcohol use in cocaine use disorder. The clinical significance of this effect will need to be clarified in larger, longer-term trials.
Previously, American researchers showed that the availability of mGluR5 to its ligand in several brain regions can serve as a biomarker of suicidal tendencies in post-traumatic stress disorder.