Anti-parkinsonian effect of the mGlu positive allosteric modulator LY-487,379 as monotherapy and adjunct to a low L-DOPA dose in the MPTP-lesioned marmoset.

In previous experiments, we have discovered that positive allosteric modulation of metabotropic glutamate 2 (mGlu) receptors enhances the anti-parkinsonian action of an optimal dose of L-3,4-dihydroxyphenylalanine (L-DOPA). Whether selective mGlu positive allosteric modulation would also alleviate parkinsonian disability as monotherapy or as adjunct to a sub-optimal dose of L-DOPA has not been determined. Here, we assessed the anti-parkinsonian effect of mGlu positive allosteric modulation as monotherapy and adjunct to a sub-optimal dose of L-DOPA in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets. The highly selective positive allosteric modulator (PAM) LY-487,379 was utilised to activate mGlu receptors. When administered as monotherapy, LY-487,379 10 mg/kg diminished global parkinsonism by 48% (P < 0.001) and increased duration of on-time by 7-fold, when compared to vehicle treatment (P < 0.05). When added to a sub-optimal dose of L-DOPA, LY-487,379 10 mg/kg decreased global parkinsonism by 44% (P < 0.001) and extended duration of on-time by 2.5-fold (P < 0.01). Our results indicate that selective mGlu positive allosteric modulation elicits anti-parkinsonian benefits as monotherapy and as adjunct to sub-optimal dose of L-DOPA paradigms, potentially suggesting that mGlu PAMs may have a therapeutic niche early in the treatment of PD as DOPA-sparing agents.