Interactions between Human Glutamate Carboxypeptidase II and Urea-Based Inhibitors: Structural Characterization

Abstract

Urea-based, low molecular weight ligands of glutamate carboxypeptidase II (GCPII) have demonstrated efficacy in various models of neurological disorders and can serve as imaging agents for prostate cancer. To enhance further development of such compounds, we determined X-ray structures of four complexes between human GCPII and urea-based inhibitors at high resolution. All ligands demonstrate an invariant glutarate moiety within the S1′ pocket of the enzyme. The ureido linkage between P1 and P1′ inhibitor sites interacts with the active-site Zn12+ ion and the side chains of Tyr552 and His553. Interactions within the S1 pocket are defined primarily by a network of hydrogen bonds between the P1 carboxylate group of the inhibitors and the side chains of Arg534, Arg536, and Asn519. Importantly, we have identified a hydrophobic pocket accessory to the S1 site that can be exploited for structure-based design of novel GCPII inhibitors with increased lipophilicity.

Glu-Ureido–Based Inhibitors of Prostate-Specific Membrane Antigen: Lessons Learned During the Development of a Novel Class of Low-Molecular-Weight Theranostic Radiotracers

“…Such modifications are well tolerated by PSMA because of the fact that, unlike the constricted S19 glutamate recognition pocket, the entrance funnel is quite spacious and can accommodate many diverse chemical groups (43,(48)(49)(50). Typically, a flexible aminohexanoyl moiety is used as the proximal segment of the linker.…”

“…Additionally, it facilitates the engagement of these moieties with structurally defined pockets in the entrance funnel (e.g., the S1 accessory hydrophobic pocket or the arene-binding site), thus contributing to the increased affinity of such bivalent ligands for PSMA ( Fig. 6) and allowing for the structure-assisted design of the next generation of ligands (48,(51)(52)(53)(54)(55).…”

PSMA-Targeted Radionuclide Therapy of Metastatic Castration-Resistant Prostate Cancer with 177Lu-Labeled PSMA-617

“…1). All used PSMA ligands share the Glu-urea motif for binding to the proteolytic domain and a lipophilic chelate or linker region to interact with the hydrophobic accessory pocket proposed by Bařinka et al (13). 177 Lu-PSMA-617 was offered as surrogate therapy in accordance with the updated Declaration of Helsinki, paragraph-37 "Unproven Interventions in Clinical Practice," and in accordance with German regulations for "compassionate use," which includes priority of all approved treatments (without contraindications) and confirmation of the indication by both a nuclear medicine physician and an external expert in urology or oncology.…”

99mTc-Labeled Small-Molecule Inhibitors of Prostate-Specific Membrane Antigen for Molecular Imaging of Prostate Cancer

“…Analysis of the crystal structure of PSMA has aided in understanding of the critical interactions of potent inhibitors within the active site of the enzyme and has led to the design and synthesis of several classes of NAALADase inhibitors that are substrate or transition state analogs (11,12).…”