Effect of the mGlu₂ positive allosteric modulator biphenyl‐indanone A as a monotherapy and as adjunct to a low dose of L‐DOPA in the MPTP‐lesioned marmoset

Activation of metabotropic glutamate 2 (mGlu 2 ) receptors is a potential novel therapeutic approach for the treatment of parkinsonism. Thus, when administered as monotherapy or as adjunct to a low dose of L‐3,4‐dihydroxyphenylalanine (L‐DOPA), the mGlu 2 positive allosteric modulator (PAM) LY‐487,379 alleviated parkinsonism in 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐lesioned primates. Here, we sought to investigate the effect of biphenyl‐indanone A (BINA), a highly selective mGlu 2 PAM whose chemical scaffold is unrelated to LY‐487,379, to determine if a structurally different mGlu 2 PAM would also confer anti‐parkinsonian benefit. In monotherapy experiments, MPTP‐lesioned marmosets were injected with either vehicle, L‐DOPA/benserazide (15/3.75 mg/kg, positive control) or BINA (0.1, 1, 10 mg/kg). In adjunct to a low L‐DOPA dose experiments, MPTP‐lesioned marmosets were injected with L‐DOPA/benserazide (7.5/1.875 mg/kg) in combination with vehicle or BINA (0.1, 1, 10 mg/kg). Parkinsonism, dyskinesia and psychosis‐like behaviours (PLBs) were then quantified. When administered alone, BINA 1 and 10 mg/kg decreased parkinsonism severity by ~22% ( p < 0.01) and ~47% ( p < 0.001), when compared with vehicle, which was comparable with the global effect of a high L‐DOPA dose. When administered in combination with a low L‐DOPA dose, BINA 1 and 10 mg/kg decreased global parkinsonism by ~38% ( p < 0.001) and ~53% ( p < 0.001). BINA 10 mg/kg decreased global dyskinesia by ~94% ( p < 0.01) and global PLBs by ~92% ( p < 0.01). Our results provide additional evidence that mGlu 2 positive allosteric modulation elicits anti‐parkinsonian effects. That this benefit is not related to a particular chemical scaffold suggests that it may be a class effect rather than the effect of a specific molecule.