High-Throughput Microscopy Analysis of Mitochondrial Membrane Potential in 2D and 3D Models.

Recent proteomic, metabolomic, and transcriptomic studies have highlighted a connection between changes in mitochondria physiology and cellular pathophysiological mechanisms. Secondary assays to assess the function of these organelles appear fundamental to validate these -omics findings. Although mitochondrial membrane potential is widely recognized as an indicator of mitochondrial activity, high-content imaging-based approaches coupled to multiparametric to measure it have not been established yet. In this paper, we describe a methodology for the unbiased high-throughput quantification of mitochondrial membrane potential in vitro, which is suitable for 2D to 3D models. We successfully used our method to analyze mitochondrial membrane potential in monolayers of human fibroblasts, neural stem cells, spheroids, and isolated muscle fibers. Moreover, by combining automated image analysis and machine learning, we were able to discriminate melanoma cells from macrophages in co-culture and to analyze the subpopulations separately. Our data demonstrated that our method is a widely applicable strategy for large-scale profiling of mitochondrial activity.

Comparison among Neuroblastoma Stages Suggests the Involvement of Mitochondria in Tumor Progression.

Neuroblastoma (NB) is the most common extracranial tumor of early childhood and accounts for 15% of all pediatric cancer mortalities. However, the precise pathways and genes underlying its progression are unknown. Therefore, we performed a differential gene expression analysis of neuroblastoma stage 1 and stage 4 + 4S to discover biological processes associated with NB progression. From this preliminary analysis, we found that NB samples (stage 4 + 4S) are characterized by altered expression of some proteins involved in mitochondria function and mitochondria-ER contact sites (MERCS). Although further analyses remain necessary, this review may provide new hints to better understand NB molecular etiopathogenesis, by suggesting that MERCS alterations could be involved in the progression of NB.

Mitochondria and Central Nervous System Disorders.

Mitochondria are semi-autonomous, membrane-bound organelles present in the cytoplasm of nearly all eukaryotic cells [...].

Chemical Modulation of Mitochondria-Endoplasmic Reticulum Contact Sites.

Contact sites between mitochondria and endoplasmic reticulum (ER) are points in which the two organelles are in close proximity. Due to their structural and functional complexity, their exploitation as pharmacological targets has never been considered so far. Notwithstanding, the number of compounds described to target proteins residing at these interfaces either directly or indirectly is rising. Here we provide original insight into mitochondria-ER contact sites (MERCs), with a comprehensive overview of the current MERCs pharmacology. Importantly, we discuss the considerable potential of MERCs to become a druggable target for the development of novel therapeutic strategies.

GCPII and its close homolog GCPIII: from a neuropeptidase to a cancer marker and beyond.

Glutamate carboxypeptidases II and III (GCPII and GCPIII) are highly homologous di-zinc metallopeptidases belonging to the M28 family. These enzymes are expressed in a variety of tissues, including the brain, prostate, kidney, testis and jejunum. GCPII has been recognized as a neuropeptidase in the central nervous system, as a folate hydrolase participating in absorption of folates in the jejunum and, most importantly, as a prostate-specific membrane antigen that is highly expressed in prostate adenocarcinoma. Furthermore, it has been identified in the neovasculature of most human solid tumors. In contrast, GCPIII has not been associated with any specific physiological function or pathology, and its expression, activity and inhibition have not been as well-studied. In this review, we provide an overview of the current understanding of the structure, enzymatic activity, substrate specificity, and tissue distribution of these two homologous enzymes. We discuss their potential physiological functions and describe the available animal models, including genetically modified mice. We also review the potential use of specific monoclonal antibodies and small-molecule inhibitors recognizing GCPII/III for diagnosis, imaging and experimental therapy of human cancers and other pathologies.

Identification of Protein Targets of Bioactive Small Molecules Using Randomly Photomodified Probes.

Identifying protein targets of bioactive small molecules often requires complex, lengthy development of affinity probes. We present a method for stochastic modification of small molecules of interest with a photoactivatable phenyldiazirine linker. The resulting isomeric mixture is conjugated to a hydrophilic copolymer decorated with biotin and a fluorophore. We validated this approach using known inhibitors of several medicinally relevant enzymes. At least a portion of the stochastic derivatives retained their binding to the target, enabling target visualization, isolation, and identification. Moreover, the mix of stochastic probes could be separated into fractions and tested for binding affinity. The structure of the active probe could be determined and the probe resynthesized to improve binding efficiency. Our approach can thus enable rapid target isolation, identification, and visualization, while providing information required for subsequent synthesis of an optimized probe.

Mouse glutamate carboxypeptidase II (GCPII) has a similar enzyme activity and inhibition profile but a different tissue distribution to human GCPII.

Glutamate carboxypeptidase II (GCPII), also known as prostate-specific membrane antigen (PSMA) or folate hydrolase, is a metallopeptidase expressed predominantly in the human brain and prostate. GCPII expression is considerably increased in prostate carcinoma, and the enzyme also participates in glutamate excitotoxicity in the brain. Therefore, GCPII represents an important diagnostic marker of prostate cancer progression and a putative target for the treatment of both prostate cancer and neuronal disorders associated with glutamate excitotoxicity. For the development of novel therapeutics, mouse models are widely used. However, although mouse GCPII activity has been characterized, a detailed comparison of the enzymatic activity and tissue distribution of the mouse and human GCPII orthologs remains lacking. In this study, we prepared extracellular mouse GCPII and compared it with human GCPII. We found that mouse GCPII possesses lower catalytic efficiency but similar substrate specificity compared with the human protein. Using a panel of GCPII inhibitors, we discovered that inhibition constants are generally similar for mouse and human GCPII. Furthermore, we observed highest expression of GCPII protein in the mouse kidney, brain, and salivary glands. Importantly, we did not detect GCPII in the mouse prostate. Our data suggest that the differences in enzymatic activity and inhibition profile are rather small; therefore, mouse GCPII can approximate human GCPII in drug development and testing. On the other hand, significant differences in GCPII tissue expression must be taken into account when developing novel GCPII-based anticancer and therapeutic methods, including targeted anticancer drug delivery systems, and when using mice as a model organism.

Inhibitor-Decorated Polymer Conjugates Targeting Fibroblast Activation Protein.

Proteases are directly involved in cancer pathogenesis. Expression of fibroblast activation protein (FAP) is upregulated in stromal fibroblasts in more than 90% of epithelial cancers and is associated with tumor progression. FAP expression is minimal or absent in most normal adult tissues, suggesting its promise as a target for the diagnosis or treatment of various cancers. Here, we report preparation of a polymer conjugate (an iBody) containing a FAP-specific inhibitor as the targeting ligand. The iBody inhibits both human and mouse FAP with low nanomolar inhibition constants but does not inhibit close FAP homologues dipeptidyl peptidase IV, dipeptidyl peptidase 9, and prolyl oligopeptidase. We demonstrate the applicability of this iBody for the isolation of FAP from cell lysates and blood serum as well as for its detection by ELISA, Western blot, flow cytometry, and confocal microscopy. Our results show the iBody is a useful tool for FAP targeting in vitro and potentially also for specific anticancer drug delivery.

DNA-linked Inhibitor Antibody Assay (DIANA) for sensitive and selective enzyme detection and inhibitor screening.

Human diseases are often diagnosed by determining levels of relevant enzymes and treated by enzyme inhibitors. We describe an assay suitable for both ultrasensitive enzyme quantification and quantitative inhibitor screening with unpurified enzymes. In the DNA-linked Inhibitor ANtibody Assay (DIANA), the target enzyme is captured by an immobilized antibody, probed with a small-molecule inhibitor attached to a reporter DNA and detected by quantitative PCR. We validate the approach using the putative cancer markers prostate-specific membrane antigen and carbonic anhydrase IX. We show that DIANA has a linear range of up to six logs and it selectively detects zeptomoles of targets in complex biological samples. DIANA's wide dynamic range permits determination of target enzyme inhibition constants using a single inhibitor concentration. DIANA also enables quantitative screening of small-molecule enzyme inhibitors using microliters of human blood serum containing picograms of target enzyme. DIANA's performance characteristics make it a superior tool for disease detection and drug discovery.

iBodies: Modular Synthetic Antibody Mimetics Based on Hydrophilic Polymers Decorated with Functional Moieties.

Antibodies are indispensable tools for biomedicine and anticancer therapy. Nevertheless, their use is compromised by high production costs, limited stability, and difficulty of chemical modification. The design and preparation of synthetic polymer conjugates capable of replacing antibodies in biomedical applications such as ELISA, flow cytometry, immunocytochemistry, and immunoprecipitation is reported. The conjugates, named "iBodies", consist of an HPMA copolymer decorated with low-molecular-weight compounds that function as targeting ligands, affinity anchors, and imaging probes. We prepared specific conjugates targeting several proteins with known ligands and used these iBodies for enzyme inhibition, protein isolation, immobilization, quantification, and live-cell imaging. Our data indicate that this highly modular and versatile polymer system can be used to produce inexpensive and stable antibody substitutes directed toward virtually any protein of interest with a known ligand.

Detection and quantitation of glutamate carboxypeptidase II in human blood.

BACKGROUND: Glutamate carboxypeptidase II (GCPII) is a transmembrane enzyme that cleaves N-acetyl-L-aspartyl-L-glutamate (NAAG) in the brain. GCPII is highly expressed in the prostate and prostate cancer and might be associated with prostate cancer progression. Another exopeptidase, plasma glutamate carboxypeptidase (PGCP), was reported to be similar to GCPII and to share its NAAG-hydrolyzing activity. METHODS: We performed a radioenzymatic assay with [(3) H]NAAG as a substrate to detect and quantify the enzymatic activity of GCPII in plasma. Using a specific antibody raised against native GCPII (2G7), we immunoprecipitated GCPII from human plasma. We also cloned two PGCP constructs, expressed them in insect cells, and tested them for their NAAG-hydrolyzing activity. RESULTS: We detected GCPII protein in human plasma and found that its concentration ranges between 1.3 and 17.2 ng/ml in volunteers not diagnosed with prostate cancer. Recombinant PGCP was enzymatically active but exhibited no NAAG-hydrolyzing activity. CONCLUSION: GCPII is present in human blood, and its concentration within a healthy population varies. Recombinant PGCP does not hydrolyze NAAG, suggesting that GCPII alone is responsible for the NAAG-hydrolyzing activity observed in human blood. The potential correlation between GCPII serum levels and the disease status of prostate cancer patients will be further investigated.