Inhibitor-GCPII Interaction: Selective and Robust System for Targeting Cancer Cells with Structurally Diverse Nanoparticles.

Glutamate carboxypeptidase II (GCPII) is a membrane protease overexpressed by prostate cancer cells and detected in the neovasculature of most solid tumors. Targeting GCPII with inhibitor-bearing nanoparticles can enable recognition, imaging, and delivery of treatments to cancer cells. Compared to methods based on antibodies and other large biomolecules, inhibitor-mediated targeting benefits from the low molecular weight of the inhibitor molecules, which are typically stable, easy-to-handle, and able to bind the enzyme with very high affinity. Although GCPII is established as a molecular target, comparing previously reported results is difficult due to the different methodological approaches used. In this work, we investigate the robustness and limitations of GCPII targeting with a diverse range of inhibitor-bearing nanoparticles (various structures, sizes, bionanointerfaces, conjugation chemistry, and surface densities of attached inhibitors). Polymer-coated nanodiamonds, virus-like particles based on bacteriophage Qß and mouse polyomavirus, and polymeric poly(HPMA) nanoparticles with inhibitors attached by different means were synthesized and characterized. We evaluated their ability to bind GCPII and interact with cancer cells using surface plasmon resonance, inhibition assay, flow cytometry, and confocal microscopy. Regardless of the diversity of the investigated nanosystems, they all strongly interact with GCPII (most with low picomolar Ki values) and effectively target GCPII-expressing cells. The robustness of this approach was limited only by the quality of the nanoparticle bionanointerface, which must be properly designed by adding a sufficient density of hydrophilic protective polymers. We conclude that the targeting of cancer cells overexpressing GCPII is a viable approach transferable to a broad diversity of nanosystems.

Label-free determination of prostate specific membrane antigen in human whole blood at nanomolar levels by magnetically assisted surface enhanced Raman spectroscopy.

Prostate cancer is one of the most common cancers among men and can in its later stages cause serious medical problems. Due to the limited suitability of current diagnostic biochemical markers, new biomarkers for the detection of prostate cancer are highly sought after. An ideal biomarker should serve as a reliable prognostic marker, be applicable for early diagnosis, and be applicable for monitoring of therapeutic response. One potential candidate is glutamate carboxypeptidase II (GCPII), also known as prostate specific membrane antigen (PSMA), which has a promising role for direct imaging. GCPII is considerably over-expressed on cancerous prostatic epithelial cells; its analysis typically follows radiological or spectrophotometric principles. Its role as a biomarker present in blood has been recently investigated and potential correlation between a concentration of GCPII and prostate cancer has been proposed. The wider inclusion of GCPII detection in clinical praxis limits mainly the time and cost per analysis. Here, we present a novel analytical nanosensor applicable to quantification of GCPII in human whole blood consisted of Fe3O4@Ag magnetic nanocomposite surface-functionalized by an artificial antibody (low-molecular-weight GCPII synthetic inhibitor). The nanocomposite allows a simple magnetic isolation of GCPII using external magnetic force and its consecutive determination by magnetically assisted surface enhanced Raman spectroscopy (MA-SERS) with a limit of detection 6 pmol. L-1. This method enables a rapid determination of picomolar concentrations of GCPII in whole human blood of healthy individuals using a standard addition method without a complicated sample pre-treatment.

Design of highly potent urea-based, exosite-binding inhibitors selective for glutamate carboxypeptidase II.

We present here a structure-aided design of inhibitors targeting the active site as well as exosites of glutamate carboxypeptidase II (GCPII), a prostate cancer marker, preparing potent and selective inhibitors that are more than 1000-fold more active toward GCPII than its closest human homologue, glutamate carboxypeptidase III (GCPIII). Additionally, we demonstrate that the prepared inhibitor conjugate can be used for sensitive and selective imaging of GCPII in mammalian cells.

Rational design of urea-based glutamate carboxypeptidase II (GCPII) inhibitors as versatile tools for specific drug targeting and delivery.

Glutamate carboxypeptidase II (GCPII), also known as prostate specific membrane antigen (PSMA), is an established prostate cancer marker and is considered a promising target for specific anticancer drug delivery. Low-molecular-weight inhibitors of GCPII are advantageous specific ligands for this purpose. However, they must be modified with a linker to enable connection of the ligand with an imaging molecule, anticancer drug, and/or nanocarrier. Here, we describe a structure-activity relationship (SAR) study of GCPII inhibitors with linkers suitable for imaging and drug delivery. Structure-assisted inhibitor design and targeting of a specific GCPII exosite resulted in a 7-fold improvement in Ki value compared to the parent structure. X-ray structural analysis of the inhibitor series led to the identification of several inhibitor binding modes. We also optimized the length of the inhibitor linker for effective attachment to a biotin-binding molecule and showed that the optimized inhibitor could be used to target nanoparticles to cells expressing GCPII.