D-DOPA Is a Potent, Orally Bioavailable, Allosteric Inhibitor of Glutamate Carboxypeptidase II

Abstract

Glutamate carboxypeptidase-II (GCPII) is a zinc-dependent metalloenzyme implicated in numerous neurological disorders. The pharmacophoric requirements of active-site GCPII inhibitors makes them highly charged, manifesting poor pharmacokinetic (PK) properties. Herein, we describe the discovery and characterization of catechol-based inhibitors including L-DOPA, D-DOPA, and caffeic acid, with sub-micromolar potencies. Of these, D-DOPA emerged as the most promising compound, with good metabolic stability, and excellent PK properties. Orally administered D-DOPA yielded high plasma exposures (AUCplasma = 72.7 nmol·h/mL) and an absolute oral bioavailability of 47.7%. Unfortunately, D-DOPA brain exposures were low with AUCbrain = 2.42 nmol/g and AUCbrain/plasma ratio of 0.03. Given reports of isomeric inversion of D-DOPA to L-DOPA via D-amino acid oxidase (DAAO), we evaluated D-DOPA PK in combination with the DAAO inhibitor sodium benzoate and observed a >200% enhancement in both plasma and brain exposures (AUCplasma = 185 nmol·h/mL; AUCbrain = 5.48 nmol·h/g). Further, we demonstrated GCPII target engagement; orally administered D-DOPA with or without sodium benzoate caused significant inhibition of GCPII activity. Lastly, mode of inhibition studies revealed D-DOPA to be a noncompetitive, allosteric inhibitor of GCPII. To our knowledge, this is the first report of D-DOPA as a distinct scaffold for GCPII inhibition, laying the groundwork for future optimization to obtain clinically viable candidates.

Glutamate carboxypeptidase II

“…To overcome the limitations associated with poor oral bioavailability and negligible brain penetration of "traditional" GCP II inhibitors, recently, catechol-based inhibitors were developed. In particular D-DOPA offered a non-competitive mode of inhibition with an excellent pharmacokinetic profile which can be enhanced by co-administration with the DAAO inhibitor sodium benzoate, resulting in robust target engagement in the brain [108].…”

Chirality: a key parameter in chemical probes

“… 7 Hence, it is vital to ensure that a chiral molecule's absolute stereochemistry is correctly assigned and indeed this is a basic premise in synthetic organic chemistry. As early as undergraduate level, chemists are taught about stereochemistry and its consequences in a medicinal context: 8 l -, not d -, Dopa is an anti-Parkinson's drug, 9 and thalidomide was administered as a morning sickness drug in racemic form, with terrible consequences ( Fig. 1 ).…”