NAALADase (GCP II) inhibition as a novel therapeutic target for neuropathic pain, diabetic neuropathy, and ALS

Abstract

NAALADase (N‐acetylated‐α‐linked‐acidic dipeptidase; also termed glutamate carboxypeptidase II) is an enzyme that catalyzes hydrolysis of the abundant brain peptide N‐acetyl‐aspartyl‐glutamate (NAAG) to N acetyl‐aspartate (NAA) and glutamate. We have synthesized many potent and selective NAALADase inhibitors from distinct chemical classes. In rodents, selective inhibitors have been shown to increase NAAG and decrease glutamate extracellularly and provide therapeutic benefits in animal models of neurological diseases where excess glutamate neurotransmission has been implicated. Specifically, NAALADase inhibitors exhibit neuroprotection in rats following transient middle cerebral artery occlusion, attenuate neuropathic pain following chronic constrictive injury, prevent nerve conduction velocity deficits and sural nerve degeneration following chronic diabetes in STZ and BB/W rats, and delay clinical symptoms and mortality in the mouse SOD transgenic model of ALS. These biological effects are likely mediated by increases in extracellular NAAG and decreases in extracellular glutamate as a consequence of NAALADase inhibition. NAALADase inhibition may be useful in neurological disorders in which excessive excitatory amino acid transmission is pathogenic. Also, NAALADase inhibition may represent a novel glutamate regulating strategy devoid of the side‐effects that have hampered development of postsynaptic glutamate receptor antagonists. A lead NAALADase inhibitor termed GPI 5693 is currently completing Phase I clinical testing.