Virginia Research Day 2021

Graduate Student Research Biomedical

01 Pharmacology of a Novel Biased Allosteric Modulator for NMDA Receptors

Lina Kwapisz 1 ; Brittney Merhkens 2 ; Blaise Costa 2,3 Corresponding author: linak@vt.edu

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor plays a crucial role in brain physiology like memory, synaptic formation and mood control. Functional diheteromeric NMDA receptors (GluN2A, GLuN2B, GluN2C and GluN2D) are widely expressed in the brain across different stages of development, some diheteromeric receptors exhibit predisposition towards certain brain regions like the GluN2B subunit in Cortex and the GluN2C subunit in cerebellum. Glutamate concentration is highly diverse in the CNS and synapse specific. NMDAR normally function under glutamate physiologic concentrations, however, when the receptor is hyperactivated due to excessive glutamate several conditions like Alzheimer’s disease, Huntington’s disease, stroke and acute brain injuries can arise. On the other hand, when there is not enough NMDAR expression 1 Virgnia-Maryland College of Veterinary Medicine, Virginia Tech 2 Center for One Health Research, Virginia Tech 3 Via College of Osteopathic Medicine-Virginia Campus

normal brain function its altered being liked with conditions like Schizophrenia, Autism Spectrum Disorder and anti-NMDAR encephalitis. Furthermore, proper regulation of glutamate function through the NMDA receptors is crucial to enhance normal brain physiology. Several compounds like agonist and antagonist have been described to target NMDAR but they exhibit undesired side effects. There is a need to find a compound that can be able to selectively tune the normal receptor function based on glutamate concentration without producing glutamate- mediated excitotoxicity. In the present study, using two-electrode voltage clamp electrophysiology, we have characterized a compound (CNS4), which is an agonist concentration dependent allosteric

modulator which effects is based on subunit type and glutamate concentration. It also exhibits a non- voltage dependent activity at the current voltage plot (I-V) and does not seem to block the NMDAR channel. Next, we were able to study CNS4 activity on primary rat brain neurons demonstrating its effect on hyperactivated neurons from different brain regions. In an induced excitotoxic environment, CNS4 increased Ca2+ influx in neurons when applied with agonist and did not further increase cellular death. When used alone, CNS4 did not alter cellular metabolic activity being non-toxic for neurons. Overall, CNS4 serves as a potential lead compound that can modulate NMDA receptors based on glutamate (agonist) concentration and its activity differs based on NMDA diheteromeric receptor subtype.

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