Identification of c-Met as a novel target of γ-glutamylcyclotransferase

γ-Glutamylcyclotransferase (GGCT) is highly expressed in multiple types of cancer tissues and its knockdown suppresses the growth of cancer cells in vitro and in vivo. Although GGCT is a promising target for cancer therapy, the mechanisms underlying the antitumor effects remain unclear. The knockdown of GGCT inhibited the MEK-ERK pathway, and activated the tumor suppressor retinoblastoma gene (RB) at the protein level in cancer cell lines. c-Met was down-regulated by the knockdown of GGCT in cancer cells and its overexpression attenuated the dephosphorylation of RB and cell cycle arrest induced by the knockdown of GGCT in lung cancer A549 cells. STAT3 is a transcription factor that induces c-Met expression. STAT3 phosphorylation and its nuclear expression level were decreased in GGCT-depleted A549 and prostate cancer PC3 cells. The simultaneous knockdown of AMPK and GGCT restored the down-regulated expression of c-Met, and attenuated the dephosphorylation of STAT3 and MEK-ERK-RB induced by the knockdown of GGCT in PC3 cells. An intraperitoneal injection of a GGCT inhibitor decreased c-Met protein expression in a mouse xenograft model of PC3 cells. These results suggest that the knockdown of GGCT activates the RB protein by inhibiting the STAT3-c-Met-MEK-ERK pathway via AMPK activation.

Identification of U83836E as a γ-glutamylcyclotransferase inhibitor that suppresses MCF7 breast cancer xenograft growth

γ-Glutamylcyclotransferase (GGCT) is involved in glutathione homeostasis, in which it catalyzes the reaction that generates 5-oxoproline and free amino acids from γ-glutamyl peptides. Increasing evidence shows that GGCT has oncogenic functions and is overexpressed in various cancer tissues, and that inhibition of GGCT activity exerts anticancer effects in vitro and in vivo. Here, we demonstrate that U83836E ((2R)-2-[[4-(2,6-dipyrrolidin-1-ylpyrimidin-4-yl)piperazin-1-yl]methyl]-3,4-dihydro-2,5,7,8,-tetramethyl-2H-1-benzopyran-6-ol, dihydrochloride), a lazaroid that inhibits lipid peroxidation, inhibits GGCT enzymatic activity. U83836E was identified from a high-throughput screen of low molecular weight compounds using a fluorochrome-conjugated GGCT probe. We directly quantified that U83836E specifically inhibited GGCT by measuring the product of a fluorochrome-conjugated GGCT substrate assay, and showed that U83836E inhibited GGCT activity in extracts of NIH3T3 cells overexpressing GGCT. Moreover, U83836E significantly inhibited tumor growth in a xenograft model that used immunodeficient mice orthotopically inoculated with MCF7 human breast cancer cells. These results indicate that U83836E may be a useful GGCT inhibitor for the development of potential cancer therapeutics.

Resorufin-based responsive probes for fluorescence and colorimetric analysis

The fluorescence imaging technique has attracted increasing attention in the detection of various biological molecules in situ and in real-time owing to its inherent advantages including high selectivity and sensitivity, outstanding spatiotemporal resolution and fast feedback. In the past few decades, a number of fluorescent probes have been developed for bioassays and imaging by exploiting different fluorophores. Among various fluorophores, resorufin exhibits a high fluorescence quantum yield, long excitation/emission wavelength and pronounced ability in both fluorescence and colorimetric analysis. This fluorophore has been widely utilized in the design of responsive probes specific for various bioactive species. In this review, we summarize the advances in the development of resorufin-based fluorescent probes for detecting various analytes, such as cations, anions, reactive (redox-active) sulfur species, small molecules and biological macromolecules. The chemical structures of probes, response mechanisms, detection limits and practical applications are investigated, which is followed by the discussion of recent challenges and future research perspectives. This review article is expected to promote the further development of resorufin-based responsive fluorescent probes and their biological applications.

Supramolecular optimization of the visual contrast for colorimetric indicator assays that release resorufin dye

A tetralactam macrocycle acts as a novel supramolecular adjuvant to capture a released resorufin dye and create a higher contrasting yellow/blue color change for enhanced naked eye interpretation of a colorimetric indicator assay.

γ-Glutamyl cyclotransferase contributes to endometrial carcinoma malignant progression and upregulation of PD-L1 expression during activation of epithelial-mesenchymal transition

Recent increases in the incidence of endometrial carcinoma represent a significant risk to women's health. We found that γ-glutamyl cyclotransferase (GGCT) was significantly up-regulated in endometrial carcinoma tissues and cells, which suggested that it may be a potential target for treatment of endometrial carcinoma. Furthermore, the impact of GGCT on proliferation, migration, and invasion of endometrial carcinoma has been demonstrated in vitro and in vivo using GGCT silencing and overexpression techniques. In addition, the epithelial-mesenchymal transition (EMT) was significantly inhibited in response to GGCT knockdown, which indicated that GGCT may contribute endometrial carcinoma malignancy during activation of the EMT. We also found that GGCT regulated PD-L1 expression during EMT activation. Furthermore, co-culture of endometrial carcinoma cells with CD8⁺ T lymphocytes showed that downregulation of PD-L1 expression following GGCT knockdown contributed to the killing activity of CD8⁺ T lymphocytes on endometrial carcinoma cells. In conclusion, our study showed that GGCT contributed to malignant progression and upregulation of PD-L1 expression of endometrial carcinoma, and may be a potential target for treatment of endometrial carcinoma.

HAP-01, the first chromogenic substrate forAspergillus oryzaeacid protease

HAP-01 was developed as an activity-based probe forA. oryzaeacid protease important for production ofsake, a Japanese rice wine.

Mechanisms of Tumor Growth Inhibition by Depletion of γ-Glutamylcyclotransferase (GGCT): A Novel Molecular Target for Anticancer Therapy

γ-Glutamylcyclotransferase (GGCT), which is one of the major enzymes involved in glutathione metabolism, is upregulated in a wide range of cancers—glioma, breast, lung, esophageal, gastric, colorectal, urinary bladder, prostate, cervical, ovarian cancers and osteosarcoma—and promotes cancer progression; its depletion leads to the suppression of proliferation, invasion, and migration of cancer cells. It has been demonstrated that the suppression or inhibition of GGCT has an antitumor effect in cancer-bearing xenograft mice. Based on these observations, GGCT is now recognized as a promising therapeutic target in various cancers. This review summarizes recent advances on the mechanisms of the antitumor activity of GGCT inhibition.

A Novel Prodrug of a γ-Glutamylcyclotransferase Inhibitor Suppresses Cancer Cell Proliferation in vitro and Inhibits Tumor Growth in a Xenograft Mouse Model of Prostate Cancer

γ-Glutamylcyclotransferase (GGCT) depletion inhibits cancer cell proliferation. However, whether the enzymatic activity of GGCT is critical for the regulation of cancer cell growth remains unclear. In this study, a novel diester-type cell-permeable prodrug, pro-GA, was developed based on the structure of N-glutaryl-l-alanine (GA), by structure optimization using temporary fluorophore-tagged prodrug candidates. The antiproliferative activity of pro-GA was demonstrated using GGCT-overexpressing NIH-3T3 cells and human cancer cells including MCF7, HL-60, and PC3 cells. By contrast, normal cells were not significantly affected by pro-GA treatment. Moreover, pro-GA administration exhibited anticancer effects in a xenograft model using immunocompromised mice inoculated with PC3 cells. These results indicate that the enzymatic activity of GGCT accelerates tumor growth and that GGCT inhibition is a promising therapeutic strategy for the treatment of GGCT-overexpressing tumors.

Gamma-Glutamylcyclotransferase: A Novel Target Molecule for Cancer Diagnosis and Treatment

Gamma-glutamylcyclotransferase (GGCT) is one of the major enzymes involved in glutathione metabolism. However, its gene locus was unknown for many years. Recently, the gene for GGCT was found to be identical to C7orf24, which is registered as a hypothetical protein. Orthologs have been found in bacteria, plants, and nematodes as well as higher organisms, and the GGCT gene is highly preserved among a wide range of species. GGCT (C7orf24) was also reported as an upregulated protein in various cancers. Although the function of GGCT in cancer cells has not been determined, the following important activities have been reported: (1) high expression in various cancer tissues and cancer cell lines, (2) low expression in normal tissues, (3) inhibition of cancer cell proliferation via anti-GGCT RNAi, (4) inhibition of cancer cell invasion and migration via anti-GGCT RNAi, (5) an epigenetic transcriptional regulation in cancer cells, and (6) an antitumor effect in cancer-bearing xenograft mice. Therefore, GGCT is promising as a diagnostic marker and a therapeutic target for various cancers. This review summarizes these interesting findings.