Functional characterization of AMPA receptor positive allosteric modulators PF-04958242 and LY-451395

抄録

Background: Fast excitatory transmission in the central nervous system is mediated by 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 LY-451395, 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.

Methods: We expressed a 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. In addition, we recorded from hippocampal CA1 neurons and cerebellar granule cells in slice preparations from wildtype mice.

Results: 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, LY-451395 slowed deactivation of GluA receptors to a greater degree than PF-04958242. AMPA receptors incorporating stargazin were slowed to a significant extent by PAMs compared to receptors complexed with the g8 auxiliary protein. Comparable effects were seen in slice preparations. Application of both PAMs slowed evoked and spontaneous EPSC decays. LY-451395 prolonged decay of AMPA receptor currents to a greater extent than PF-04958242, and EPSCs at CA1 pyramidal cell synapses were slowed to a lesser degree by the PAMs than granule cell's EPSCs.

Conclusions: These results show that both PAMs slow the decay of EPSCs, and the PAMs efficacy were most sensitive to stargazin incorporated into AMPA receptor complexes. 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.