Development of GCPII inhibitors for the treatment of age-related cognitive disorders

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Project Summary The goal of this research proposal is to develop brain-penetrant inhibitors of glutamate carboxypeptidase II (GCPII) as a new therapeutic strategy to improve cognition and reduce risk of late-onset Alzheimer's Disease (AD). GCPII (EC 3.4.17.21) is a membrane-bound zinc metallopeptidase that cleaves the C-terminal glutamate from N-acetylaspartylglutamate (NAAG) producing N-acetylaspartate and glutamate. NAAG is known to act as an endogenous agonist at metabotropic glutamate receptor type 3 (mGluR3) and we have recently found that NAAG can enhance memory-related neuronal firing in monkeys through stimulation of Gi/Go-mediated regulation of postsynaptic cAMP-PKA-calcium signaling. Therefore, GCPII inhibition may offer a new therapeutic approach to the cognitive impairments by increasing extracellular NAAG levels and controlling cAMP-PKA-calcium signaling dysregulated in the aging brain. In the absence of mGluR3-selective agonists and positive allosteric modulators, this approach is particularly attractive as a number of structurally diverse and potent GCPII inhibitors have been developed and preclinically evaluated in a variety of neurological disorders with a robust efficacy and an excellent side effect profile. Indeed, our preliminary data show cognitive enhancement upon treatment with 2-MPPA, a clinically tested GCPII inhibitor, in aged rats and monkeys. To date, however, efforts on clinical translation of GCPII inhibitors have been substantially limited despite the significant therapeutic potential. This prompted us to propose a broad range of pharmacological approaches to the development of brain-penetrant GCPII inhibitors. We are poised to seize this therapeutic opportunity for the treatment of age-related cognitive disorders by executing the following three Specific Aims: (Aim 1) Design and synthesis of GCPII inhibitors and their prodrugs; (Aim 2) Evaluate the pharmacokinetic (PK) profile of GCPII inhibitors in rats and monkeys; (Aim 3) Assess the effects GCPII inhibitors on cognitive function in aged rats and monkeys. The successful execution of this project will lead to a novel therapeutic strategy with greater feasibility for clinical translation to address the main healthcare needs of the growing elderly population.