Selective CNS Uptake of the GCP-II Inhibitor 2-PMPA following Intranasal Administration

Abstract

Glutamate carboxypeptidase II (GCP-II) is a brain metallopeptidase that hydrolyzes the abundant neuropeptide N-acetyl-aspartyl-glutamate (NAAG) to NAA and glutamate. Small molecule GCP-II inhibitors increase brain NAAG, which activates mGluR3, decreases glutamate, and provide therapeutic utility in a variety of preclinical models of neurodegenerative diseases wherein excess glutamate is presumed pathogenic. Unfortunately no GCP-II inhibitor has advanced clinically, largely due to their highly polar nature resulting in insufficient oral bioavailability and limited brain penetration. Herein we report a non-invasive route for delivery of GCP-II inhibitors to the brain via intranasal (i.n.) administration. Three structurally distinct classes of GCP-II inhibitors were evaluated including DCMC (urea-based), 2-MPPA (thiol-based) and 2-PMPA (phosphonate-based). While all showed some brain penetration following i.n. administration, 2-PMPA exhibited the highest levels and was chosen for further evaluation. Compared to intraperitoneal (i.p.) administration, equivalent doses of i.n. administered 2-PMPA resulted in similar plasma exposures (AUC0-t, i.n./AUC0-t, i.p. = 1.0) but dramatically enhanced brain exposures in the olfactory bulb (AUC0-t, i.n./AUC0-t, i.p. = 67), cortex (AUC0-t, i.n./AUC0-t, i.p. = 46) and cerebellum (AUC0-t, i.n./AUC0-t, i.p. = 6.3). Following i.n. administration, the brain tissue to plasma ratio based on AUC0-t in the olfactory bulb, cortex, and cerebellum were 1.49, 0.71 and 0.10, respectively, compared to an i.p. brain tissue to plasma ratio of less than 0.02 in all areas. Furthermore, i.n. administration of 2-PMPA resulted in complete inhibition of brain GCP-II enzymatic activity ex-vivo confirming target engagement. Lastly, because the rodent nasal system is not similar to humans, we evaluated i.n. 2-PMPA also in a non-human primate. We report that i.n. 2-PMPA provides selective brain delivery with micromolar concentrations. These studies support intranasal delivery of 2-PMPA to deliver therapeutic concentrations in the brain and may facilitate its clinical development.

Enhanced Brain Delivery of 2-(Phosphonomethyl)pentanedioic Acid Following Intranasal Administration of Its γ-Substituted Ester Prodrugs

“…24 Briefly, standard curves were prepared in naive plasma and brain tissues ranging from 10 to 50,000 nM. For extraction of 2-PMPA, plasma samples were thawed on ice, and then 50 μ L of the calibration standard or sample was transferred into silanized vials.…”

“…24 Briefly, samples and standards were reconstituted in 100 μ L of acetonitrile with vortex mixing followed by 50 μ L of MTBSTFA and were set to react at 60 °C in a water bath for 30 min. Upon completion of the reaction the samples were then centrifuged again at 10,000 rpm at 5 °C for 2 min.…”

“…22 Indeed, low oral bioavailability ( F < 2%) and brain penetration (brain/plasma ratio < 2%) of 2-PMPA 23,24 necessitate very high systemic doses or direct brain injection for efficacy. Previous structure–activity relationship (SAR) efforts by our group and others have demonstrated that the potency of 2-PMPA is dependent upon the zinc-chelating properties of the phosphonate side chain combined with the core glutarate structure that mimics glutamate in the active site and promotes high affinity GCPII binding.…”

“…To more closely reflect human nasal anatomy, nonhuman primates were used to confirm the rodent findings using a brain targeted IN device. 24 …”

Glutamate carboxypeptidase II (GCPII) inhibitor 2-PMPA reduces rewarding effects of the synthetic cathinone MDPV in rats: a role for N-acetylaspartylglutamate (NAAG)

“…On the other hand, the greater efficacy of NAAG may stem from improved brain penetration achieved with nasal versus intraperitoneal drug administration (Lochhead and Thorne 2012). Indeed, Rais and colleagues (2015) recently showed that nasal delivery of 2-PMPA resulted in significantly higher concentrations of the drug in brain tissue compared to an equivalent dose given by intraperitoneal injection. Certainly, it would be of interest to determine whether nasal relative to intraperitoneal administration of 2-PMPA has greater efficacy against the behavioral effects of MDPV, as well as other psychostimulants.…”