Recent advances in the discovery and development of glyoxalase I inhibitors

Development of pathway-oriented screening to identify compounds to control 2-methylglyoxal metabolism in tumor cells

Controlling tumor-specific alterations in metabolic pathways is a useful strategy for treating tumors. The glyoxalase pathway, which metabolizes the toxic electrophile 2-methylglyoxal (MG), is thought to contribute to tumor pathology. We developed a live cell-based high-throughput screening system that monitors the metabolism of MG to generate D-lactate by glyoxalase I and II (GLO1 and GLO2). It utilizes an extracellular coupled assay that uses D-lactate to generate NAD(P)H, which is detected by a selective fluorogenic probe designed to respond exclusively to extracellular NAD(P)H. This metabolic pathway-oriented screening is able to identify compounds that control MG metabolism in live cells, and we have discovered compounds that can directly or indirectly inhibit glyoxalase activities in small cell lung carcinoma cells.

Glyoxalase 1 inhibitor BBGC suppresses the progression of chronic lymphocytic leukemia and promotes the efficacy of Palbociclib

Chronic lymphocytic leukemia (CLL) is a highly heterogeneous disease. Despite recent tremen-dous progress in managing CLL, the disease remains incurable with clinical therapies, and relapse is inevitable. To overcome this, new diagnostic and prognostic markers need to be investigated. We thus screened through the public database for genes with diagnostic, prognostic, and therapeutic implications in CLL. We further performed RT-qPCR and Western blot analysis to measure the candidate gene and protein expression levels, respectively, in peripheral blood mononuclear cells. Our results indicated that Glyoxalase 1 (GLO1) expression was significantly higher in patients with CLL than in healthy controls. Furthermore, cell proliferation, apoptosis, and cell cycle assay results together indicated that S-p-bromobenzylglutathione cyclopentyl diester (BBGC), an effective inhibitor of GLO1, suppresses the progression of CLL. Bioinformatics analysis revealed that GLO1 expression is closely associated with CDK4 expression in a wide variety of cancer types, and inhibition of CDK4 through silencing of genes or inhibitors can downregulate GLO1 expression. Subsequent validation experiments demonstrated that GLO1 protein levels were downregulated in MEC-1 and Jurkat cell lines after palbociclib exposure, and combination treatment of palbociclib with GLO1 inhibitor BBGC effectively delayed the growth of tumor cell lines.

Glyoxalase I Assay as a Possible Tool for Evaluation of Biological Activity of Antioxidant-Rich Plant Extracts

The health-promoting properties of natural plant bioactive compounds are mainly attributable to their ability to counteract oxidative stress. This is considered a major causative factor in aging and aging-related human diseases, in which a causal role is also ascribed to dicarbonyl stress. This is due to accumulation of methylglyoxal (MG) and other reactive dicarbonyl species, leading to macromolecule glycation and cell/tissue dysfunction. The glyoxalase (GLYI) enzyme, catalyzing the rate-limiting step of the GSH-dependent MG detoxification pathway, plays a key role in cell defense against dicarbonyl stress. Therefore, the study of GLYI regulation is of relevant interest. In particular, GLYI inducers are important for pharmacological interventions to sustain healthy aging and to improve dicarbonyl-related diseases; GLYI inhibitors, allowing increased MG levels to act as proapoptotic agents in tumor cells, are of special interest in cancer treatment. In this study, we performed a new in vitro exploration of biological activity of plant bioactive compounds by associating the measurement of their antioxidant capacity (AC) with the evaluation of their potential impact on dicarbonyl stress measured as capability to modulate GLYI activity. AC was evaluated using TEAC, ORAC, and LOX-FL methods. The GLYI assay was performed using a human recombinant isoform, in comparison with the recently characterized GLYI activity of durum wheat mitochondria. Different plant extracts were tested, obtained from plant sources with very high phytochemical content ('Sun Black' and wildtype tomatoes, black and 'Polignano' carrots, and durum wheat grain). Results showed high antioxidant properties of the tested extracts, associated with different modes (no effect, activation, and inhibition) and effectiveness in modulating both GLYI activity sources. Overall, results indicate the GLYI assay as an advisable and promising tool for researching plant foods as a source of natural antioxidant compounds acting as GLYI enzymatic regulators to be used for dietary management associated the treatment of oxidative/dicarbonyl-promoted diseases.

Current Fragment-to-lead Approaches Starting from the 7-azaindole: The Pharmacological Versatility of a Privileged Molecular Fragment

Fragment-based drug discovery is one of the most powerful paradigms in the recent context of medicinal chemistry and is being widely practiced by academic and industrial researchers. Currently, azaindoles are among the most exploited molecular fragments in pharmaceutical innovation projects inspired by fragment-to-lead strategies. The 7-azaindole is the most prominent representative within this remarkable family of pyrrolopyridine fragments, as it is present in the chemical structure of several approved antitumor drugs and also of numerous therapeutic candidates. In this paper, a brief overview on existing proofs of concept in the literature will be presented, as well as some recent works that corroborate 7-azaindole as a privileged and pharmacologically versatile molecular fragment.

Understanding the Contribution of Lactate Metabolism in Cancer Progress: A Perspective from Isomers

Lactate mediates multiple cell-intrinsic effects in cancer metabolism in terms of development, maintenance, and metastasis and is often correlated with poor prognosis. Its functions are undertaken as an energy source for neighboring carcinoma cells and serve as a lactormone for oncogenic signaling pathways. Indeed, two isomers of lactate are produced in the Warburg effect: L-lactate and D-lactate. L-lactate is the main end-production of glycolytic fermentation which catalyzes glucose, and tiny D-lactate is fabricated through the glyoxalase system. Their production inevitably affects cancer development and therapy. Here, we systematically review the mechanisms of lactate isomers production, and highlight emerging evidence of the carcinogenic biological effects of lactate and its isomers in cancer. Accordingly, therapy that targets lactate and its metabolism is a promising approach for anticancer treatment.

Crystal structures of human glyoxalase I and its complex with TLSC702 reveal inhibitor binding mode and substrate preference

Human glyoxalase I (hGLO I) is an enzyme for detoxification of methylglyoxal (MG), and has been considered an attractive target for the development of new anti-cancer drugs. In our previous report, the GLO I inhibitor TLSC702 induced apoptosis in tumor cells. Here, we determined the crystal structures of hGLO I and its complex with TLSC702. In the complex, the carboxy O atom of TLSC702 is coordinated to Zn²⁺ , and TLSC702 mainly shows van der Waals interaction with hydrophobic residues. In the inhibitor-unbound structure, glycerol, which has similar functional groups to MG, was bound to Zn²⁺ , indicating that GLO I can easily bind to MG. This study provides a structural basis to develop better anticancer drugs.

Glyoxalase 1 Expression as a Novel Diagnostic Marker of High-Grade Prostatic Intraepithelial Neoplasia in Prostate Cancer

Glyoxalase 1 (GLO1) is an enzyme involved in the detoxification of methylglyoxal (MG), a reactive oncometabolite formed in the context of energy metabolism as a result of high glycolytic flux. Prior clinical evidence has documented GLO1 upregulation in various tumor types including prostate cancer (PCa). However, GLO1 expression has not been explored in the context of PCa progression with a focus on high-grade prostatic intraepithelial neoplasia (HGPIN), a frequent precursor to invasive cancer. Here, we have evaluated GLO1 expression by immunohistochemistry in archival tumor samples from 187 PCa patients (stage 2 and 3). Immunohistochemical analysis revealed GLO1 upregulation during tumor progression, observable in HGPIN and PCa versus normal prostatic tissue. GLO1 upregulation was identified as a novel hallmark of HGPIN lesions, displaying the highest staining intensity in all clinical patient specimens. GLO1 expression correlated with intermediate-high risk Gleason grade but not with patient age, biochemical recurrence, or pathological stage. Our data identify upregulated GLO1 expression as a molecular hallmark of HGPIN lesions detectable by immunohistochemical analysis. Since current pathological assessment of HGPIN status solely depends on morphological features, GLO1 may serve as a novel diagnostic marker that identifies this precancerous lesion.

Addition of hydrophobic side chains improve the apoptosis inducibility of the human glyoxalase I inhibitor, TLSC702

Glyoxalase I (GLO I) is a known therapeutic target in cancer. Even though TLSC702, a GLO I inhibitor that we discovered, induces apoptosis in tumor cells, exceptionally higher doses are required compared with those needed to inhibit GLO I activity in vitro. In this work, structure-activity optimization studies were conducted on four sections of the TLSC702 molecule to determine the partial structural features necessary for the inhibition of GLO I. Herein, we found that the carboxy group in TLSC702 was critical for binding with the divalent zinc at the active site of GLO I. In contrast, the side chain substituents in the meta- and para- positions of the benzene ring had little influence on the in vitro inhibition of GLO I. The CLogP values of the TLSC702 derivatives showed a positive correlation with the antiproliferative effects on NCI-H522 cells. Thus, two derivatives of TLSC702, which displayed either high or low lipophilicity due to the types of substituents at the phenyl position, were selected. Even though both derivatives showed comparable inhibitory effects as that of their parent compound, the derivative with the high CLogP value was distinctly more antiproliferative than TLSC702. In contrast, the derivative with the low CLogP value did not decrease cell viability in NCI-H522 and HL-60 cells. These findings suggested that structural improvements, such as the addition of hydrophobic moieties to the phenyl group, enhanced the ability of TLSC702 to induce apoptosis by increasing cell membrane permeability.