Comparative studies of AMPA receptor positive allosteric modulators PF‐04958242 and PF‐04531686

Abstract

Fast excitatory transmission in the central nervous system is mediated by α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors responding to the endogenous neurotransmitter L‐glutamate. Dysfunction of AMPA receptors has been associated with various neurological and neuropsychiatric disorders, but therapeutic targeting of these channels has proved difficult due to the preponderance of side effects associated with AMPA receptor agonists. Positive allosteric modulators (PAMs) of AMPA receptors are thus conceptually attractive therapeutics because they rely on endogenous glutamate signaling to potentiate excitatory signaling. The objective of this work is to study the effects of two PAMs, PF‐04958242 and PF‐04531686, on the biophysical properties of recombinant and native AMPA receptors, with the expectation that the comparative data will prove informative for pro‐cognitive preclinical or clinical studies with these small molecules.We expressed a wide variety of AMPA receptor constructs with and without auxiliary subunits in HEK293T/17 cells, and characterized the effects of PAMs on currents elicited by fast‐application of glutamate. Both PAMs increased glutamate‐evoked current amplitudes and completely eliminated desensitization of all AMPA receptors containing the flip splice isoform, whereas desensitization of currents from flop‐containing receptors was slowed to differing degrees. At saturating PAM concentrations, PF‐04531686 slowed deactivation of GluA1 and GluA4 receptors to a greater degree than PF‐04958242.Comparable effects were seen on deactivation of excitatory synaptic currents (EPSCs) recorded from hippocampal CA1 neurons in slice preparations from wildtype mice. Application (1 mM) of PF‐04531686 slowed both evoked and spontaneous EPSC decays by 3‐fold; in contrast, PF‐04958242 slowed EPSCs 1.5‐fold. At a lower concentration (300 nM), EPSCs were also slowed by PF‐04531686, but not PF‐04958242. There was no effect on paired‐pulse ratio at any concentration of either PAM. These results show that both PAMs slow the decay of EPSCs, resulting from their pharmacological actions on AMPA receptor decay rates. We predict from these data that both PAMs will impact cognition, but that PF‐04958242 might have less risk of unwanted mechanism‐mediated side‐effects due to its more modest modulatory action on synaptic AMPA receptor function.Support or Funding InformationThis project was supported by a contract from Pfizer Neuroscience.