Pharmacology of mavoglurant, a metabotropic glutamate receptor 5 negative allosteric modulator

Kirstie A Bennett, John A Christopher, Alastair JH Brown, Fiona H Marshall. Heptares Therapeutics Ltd, Welwyn Garden City, UK

Metabotropic glutamate receptors (mGlu1-8) are expressed throughout the central nervous system where they act to modulate neurotransmission. Mavoglurant is a negative allosteric modulator (NAM) of the mGlu5 receptor which is in phase III trials for the treatment of Fragile X syndrome. Here we characterise the binding (in vitro and ex vivo) of mavoglurant.

To measure mavoglurant affinity in vitro, HEK293 cell membranes transiently expressing human mGlu5 (2.5 μg per well) were incubated (1 h at 25 °C) in assay buffer (50 mM HEPES (pH 7.4), 150 mM NaCl) with ~1.5 nM of [3H]M-MPEP, cold mavoglurant (0.5 nM - 10 µM) and 0.1 mM MPEP to define non-specific binding. Reactions were terminated by rapid filtration through GF/B filter plates pre-soaked with 0.1% polyethyleneimine. Plates were washed 5 x 0.5 mL in water, dried and bound radioactivity measured using scintillation spectroscopy. To measure exposure of mavoglurant PK was performed in male Sprague-Dawley (SD) rats (220-250g) following a 2 mg/kg po and a 1 mg/kg iv dose (vehicle 10 % DMAC, 10 % solutol HS15 + 80 % saline) (ChemPartner, Shanghai, China). Ex vivo receptor occupancy experiments were performed at RenaSci (Nottingham,UK). Briefly, SD rats (250-300 g) were dosed with vehicle (10 % DMAC, 10 % solutol HS15 + 80 % saline) or mavoglurant (3, 10 or 30 mg/kg) po. After 1 h rats were culled and whole brains removed. Three adjacent slices were cut from the CA3 region of the hippocampus. Two slices were incubated (10 min; 25 °C) in buffer (50 mM HEPES, 150 mM NaCl, pH7.4) containing 2 nM [3H]M-MPEP and the third slice incubated as before with 10 µM fenobam included to define non-specific binding. Slices were washed 4 x 5 min before radioactivity bound was determined using a β-imager (16 h). Brain and plasma exposure was determined.

In vitro mavoglurant exhibited pKi ± S.D of 7.97 ± 0.25. Mavoglurant showed CNS exposure and at 30 min a concentration of 4 ng/mL was measured in the CSF. Based on these PK data, the predicted receptor occupancy (RO) at 3, 10 and 30 mg/kg po was calculated to be 65, 86 and 95 % respectively. In ex vivo binding experiments, mavoglurant exposure increased linearly with dose (brain 0.64, 2.01 and 4.72 µM and plasma 0.40, 1.46 and 3.14 µM at 3, 10 and 30 mg/kg po doses respectively). Mavoglurant significantly reduced [3H]M-MPEP binding at all doses tested (p<0.001 compared to control using one-way ANOVA with William’s post-hoc test). Based on ex vivo binding data RO values were calculated to be 45, 73 and 83 % for 3, 10 and 30 mg/kg po doses respectively generating an ED50 of 3.59 mg/kg po.

Mavoglurant has high affinity for the mGlu5 receptor. In ex vivo binding experiments, following oral administration significant displacement of [3H]M-MPEP could be measured. Exposure and occupancy was linear across doses allowing an ED50 to be calculated.