Stereoselective inhibition of glutamate carboxypeptidase by organophosphorus derivatives of glutamic acid

Non-Canonical Amino Acids in Analyses of Protease Structure and Function

All known organisms encode 20 canonical amino acids by base triplets in the genetic code. The cellular translational machinery produces proteins consisting mainly of these amino acids. Several hundred natural amino acids serve important functions in metabolism, as scaffold molecules, and in signal transduction. New side chains are generated mainly by post-translational modifications, while others have altered backbones, such as the β- or γ-amino acids, or they undergo stereochemical inversion, e.g., in the case of D-amino acids. In addition, the number of non-canonical amino acids has further increased by chemical syntheses. Since many of these non-canonical amino acids confer resistance to proteolytic degradation, they are potential protease inhibitors and tools for specificity profiling studies in substrate optimization and enzyme inhibition. Other applications include in vitro and in vivo studies of enzyme kinetics, molecular interactions and bioimaging, to name a few. Amino acids with bio-orthogonal labels are particularly attractive, enabling various cross-link and click reactions for structure-functional studies. Here, we cover the latest developments in protease research with non-canonical amino acids, which opens up a great potential, e.g., for novel prodrugs activated by proteases or for other pharmaceutical compounds, some of which have already reached the clinical trial stage.

Evaluation of radioiodinated protein conjugates and their potential metabolites containing lysine-urea-glutamate (LuG), PEG and closo-decaborate(2-) as models for targeting astatine-211 to metastatic prostate cancer

INTRODUCTION

The use of lysine-urea-glutamate (LuG) for targeting the PSMA antigen on prostate cancer (PCa) is a promising method for delivering the alpha particle-emitting radionuclide astatine-211 (211At) to metastatic PCa. High kidney localization has been a problem with radiolabeled LuG derivatives, but has been adequately addressed in radiometal-labeled DOTA-LuG derivatives by linker optimization. Herein, we report an investigation of an alternate approach to diminishing the kidney concentrations of radiolabeled LuG-containing compounds.

METHODS

Our approach involves PEGylated LuG moieties and closo-decaborate (2-) moieties conjugated to streptavidin (SAv) or human serum albumin (HSA). After preparing the LuG conjugates, SAv and HSA conjugates were succinylated to decrease their kidney localization and radioiodinated for evaluation in athymic mice bearing C4-2B osseous PCa tumor xenografts.

RESULTS

Covalently attaching LuG to succinylated SAv and HSA significantly reduced kidney localization, but unfortunately succinylation resulted in decreased tumor concentrations. In contrast, a potential metabolite [131I]16b, an unconjugated LuG derivative containing a dPEG4® linker, provided tumor concentrations of ~15% ID/g at 4 h pi. A second unconjugated LuG derivative with a similar structure, but containing a dPEG12® linker, [131I]16a had tumor concentrations of ~4%ID/g at 4 h pi. Those results suggest that long PEG linkers also affect tumor localization in a negative manner.

CONCLUSION

Conjugation of PEGylated LuG derivatives to proteins can be an effective approach to diminishing kidney localization of radiolabeled LuG reagents, but the protein, linker and the method of linkage need to be further studied. Additionally, modification of the unconjugated 16b to decrease kidney localization may provide PCa targeting agents for use with radiohalogens, including 211At. Advances in knowledge and implications for patient care: This study is the first to evaluate PEGylated LuG and closo-decaborate (2-) moieties conjugated to proteins as potential methods for diminishing the kidney concentrations of radiolabeled LuG-containing compounds.

Investigating the generation of hydrogen sulfide from the phosphonamidodithioate slow-release donor GYY4137

A two-step hydrolytic decomposition pathway has been elucidated for the slow-release hydrogen sulfide donor GYY4137.

The diverse pharmacology and medicinal chemistry of phosphoramidates – a review

Promising examples of the phosphoramidates, which possess antiviral, antitumor, antibacterial, antimalarial and anti-protozoal as well as enzyme inhibitor activity are reviewed.

Assessment of an 18F-labeled phosphoramidate peptidomimetic as a new prostate-specific membrane antigen-targeted imaging agent for prostate cancer

Prostate-specific membrane antigen (PSMA) is a transmembrane protein commonly found on the surface of late-stage and metastatic prostate cancer and a well-known imaging biomarker for staging and monitoring therapy. Although (111)In-labeled capropmab pendetide is the only approved agent available for PSMA imaging, its clinical use is limited because of its slow distribution and clearance that leads to challenging image interpretation. A small-molecule approach using radiolabeled urea-based PSMA inhibitors as imaging agents has shown promise for prostate cancer imaging. The motivation of this work is to explore phosphoramidates as a new class of potent PSMA inhibitors to develop more effective prostate cancer imaging agents with improved specificity and clearance properties.

METHODS

N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) was conjugated to S-2-((2-(S-4-amino-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (Phosphoramidate (1)), yielding S-2-((2-(S-4-(4-(18)F-fluorobenzamido)-4-carboxybutanamido)-S-2-carboxyethoxy)hydroxyphosphorylamino)-pentanedioic acid (3). In vivo studies were conducted in mice bearing either LNCaP (PSMA-positive) or PC-3 (PSMA-negative) tumors. PET images were acquired at 1 and 2 h with or without a preinjection of a nonradioactive version of the fluorophosphoramidate. Tissue distribution studies were performed at the end of the 2 h imaging sessions.

RESULTS

Phosphoramidate (1) and its fluorobenzamido conjugate (2) were potent inhibitors of PSMA (inhibitory concentration of 50% [IC(50)], 14 and 0.68 nM, respectively). PSMA-mediated tumor accumulation was noted in the LNCaP versus the PC-3 tumor xenografts. The LNCaP tumor uptake was also blocked by the administration of nonradioactive (2) prior to imaging studies. With the exception of the kidneys, tumor-to-tissue and tumor-to-blood ratios were greater than 5:1 at 2 h. The strong kidney uptake may be due to the known PSMA expression in the mouse kidney, because significant reduction (>6-fold) in kidney activity was seen in mice injected with (2).

CONCLUSION

(18)F-labeled phosphoramidate (3) is a representative of a new class of PSMA targeting peptidomimetic molecules that shows great promise as imaging agents for detecting PSMA+ prostate tumors.

Design and synthesis of a siderophore conjugate as a potent PSMA inhibitor and potential diagnostic agent for prostate cancer

A siderophore conjugate was designed as a potential PSMA inhibitor and diagnostic agent for prostate cancer. A semi-rigid spacer was incorporated to avoid competitive participation of iron binding by the enzyme inhibitor relative to the siderophore component. Biological test results showed that, even with the extended scaffold, this compound is a potent PSMA inhibitor with an IC50 of 4 nM. This siderophore conjugate may be useful for detection of prostate-derived cancer cells by magnetic resonance imaging (MRI).

Double dearomatization of bis(diphenylphosphinamides) through anionic cyclization. A facile route of accessing multifunctional systems with antitumor properties

The sequential one-pot double dearomatization of bis(N-benzyl-P,P-diphenylphosphinamides) via anionic cyclization is described for the first time. Protonation and alkylation of the dearomatized dianions provide bis(tetrahydro-2,1-benzazaphospholes) in good yield and with very high regio- and stereocontrol. Acid-catalyzed methanolysis of the bisheterocycles affords bis(methyl gamma-aminophosphinates) stereospecifically. The doubly phosphorylated systems proved to be active against a series of cancer cell lines.

Design, synthesis and pharmacological activity of novel enantiomerically pure phosphonic acid-based NAALADase inhibitors

Inhibitors of NAALADase have shown promise for a variety of diseases associated with glutamate excitotoxicity, and could be useful for the diagnosis and therapy of prostate cancer. A series of novel enantiomerically pure 2-(phosphonomethyl)pentanedioic acid (2-PMPA) based NAALADase inhibitors were synthesized. These compounds were prepared from previously reported (S)-2-(hydroxyphosphinoylmethyl)pentanedioic acid benzyl ester . Biological test results showed that the new compounds are good to outstanding NAALADase inhibitors. Compounds and showed activity similar to the known potent inhibitor (S)-2-PMPA. Fluorescently labeled inhibitor may potentially be used to study binding to prostate cancer cells by fluorescence microscopy, and siderophore-containing inhibitor may be useful for detection of prostate-derived cancer cells by magnetic resonance imaging (MRI).

Tight binding inhibitors of N-acyl amino sugar and N-acyl amino acid deacetylases

Very potent inhibitors were synthesized for the enzymatic deacetylation of N-acetyl-d-glucosamine-6-phosphate (NagA) and N-acetyl-d-glutamate (DGD). The methyl phosphonamidate derivative of d-glucosamine-6-phosphate bound to N-acetyl-d-glucosamine-6-phosphate deacetylase with an equilibrium dissociation constant of 34 +/- 5 nM at pH 7.5 and an association rate constant of 6.1 x 103 M-1 s-1. The inhibition constant is 4000-fold lower than the Michaelis constant for the substrate N-acetyl-d-glucosamine-6-phosphate. N-Acetyl-d-glutamate deacetylase was inhibited by the methyl phosphonamidate derivative of d-glutamate with an inhibition constant of 460 +/- 70 pM at pH 7.6. The inhibitor bound to the enzyme 500 000-fold tighter than the Michaelis constant for N-formyl-d-glutamate. These compounds mimic the putative tetrahedral intermediate formed upon nucleophilic attack of an activated water molecule on the amide bond of the target substrate. These inhibitors should prove useful in the elucidation of the enzyme-substrate interactions for enzymes within the amidohydrolase superfamily.