Group II metabotropic glutamate receptor agonists and positive allosteric modulators as novel treatments for schizophrenia.

Schizophrenia is a devastating chronic psychotic disorder characterized by positive, negative, and cognitive symptoms. Although the positive symptoms are relatively well controlled by current monoamine-based treatments for schizophrenia, these agents provide only modest efficacy against the negative and cognitive symptoms of the disease. Furthermore serious adverse events have been reported during treatment with antipsychotic drugs. Therefore, novel treatment strategies are needed that provide improved efficacy across the multiple symptom domains of schizophrenia and have improved tolerability/safety profiles. Glutamate is the primary excitatory neurotransmitter in the mammalian central nervous system (CNS) and plays an important role in physiological and pathological processes of the CNS. Group II metabotropic glutamate receptors (mGlu receptors), in particular, have been shown to modulate glutamatergic activity in brain synapses thought to be involved in the pathophysiology of schizophrenia. In recent years a number of selective mGlu2/3 receptor agonists and mGlu2 positive allosteric modulators have been disclosed with demonstrated efficacy in multiple animal models for schizophrenia. Consistent with predictions from pre-clinical animal studies, LY2140023 monohydrate, an mGlu2/3 receptor agonist prodrug, recently demonstrated evidence for antipsychotic activity in phase II proof of concept study. Although additional efficacy and safety studies are needed to understand the therapeutic potential of LY2140023, emerging preclinical and clinical data suggest that activation of group II mGlu receptors is a mechanistically novel and promising approach for the treatment of schizophrenia.