A human PET study of [¹¹C]HMS011, a potential radioligand for AMPA receptors

α-Amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor is a primary mediator of fast glutamatergic excitatory signaling in the brain and has been implicated in diverse neuropsychiatric diseases. We recently developed a novel positron emission tomography (PET) ligand, 2-(1-(3-([¹¹C]methylamino)phenyl)-2-oxo-5-(pyrimidin-2-yl)-1,2-dihydropyridin-3-yl) benzonitrile ([¹¹C]HMS011). This compound is a radiolabelled derivative of perampanel, an antiepileptic drug acting on AMPA receptors, and was demonstrated to have promising in vivo properties in the rat and monkey brains. In the current study, we performed a human PET study using [¹¹C]HMS011 to evaluate its safety and kinetics. Four healthy male subjects underwent a 120-min PET scan after injection of [¹¹C]HMS011. Arterial blood sampling and metabolite analysis were performed to obtain parent input functions for three of the subjects using high-performance liquid chromatography. Regional distribution volumes (V _Ts) were calculated based on kinetic models with and without considering radiometabolite in the brain. The binding was also quantified using a reference tissue model with white matter as reference.

Brain uptake of [¹¹C]HMS011 was observed quickly after the injection, followed by a rapid clearance. Three hydrophilic and one lipophilic radiometabolites appeared in the plasma, with notable individual variability. The kinetics in the brain with apparent radioactivity retention suggested that the lipophilic radiometabolite could enter the brain. A dual-input graphical model, an analytical model designed in consideration of a radiometabolite entering the brain, well described the kinetics of [¹¹C]HMS011. A reference tissue model showed small radioligand binding potential (BP*_ND) values in the cortical regions (BP*_ND = 0-0.15). These data suggested specific binding component of [¹¹C]HMS011 in the brain.

Kinetic analyses support some specific binding of [¹¹C]HMS011 in the human cortex. However, this ligand may not be suitable for practical AMPA receptor PET imaging due to the small dynamic range and metabolite in the brain.