A compound-based proteomic approach discloses 15-ketoatractyligenin methyl ester as a new PPARγ partial agonist with anti-proliferative ability

Cladosporols and PPARγ: Same Gun, Same Bullet, More Targets

Several natural compounds have been found to act as PPARγ agonists, thus regulating numerous biological processes, including the metabolism of carbohydrates and lipids, cell proliferation and differentiation, angiogenesis, and inflammation. Recently, Cladosporols, secondary metabolites purified from the fungus Cladosporium tenuissimum, have been demonstrated to display an efficient ability to control cell proliferation in human colorectal and prostate cancer cells through a PPARγ-mediated modulation of gene expression. In addition, Cladosporols exhibited a strong anti-adipogenetic activity in 3T3-L1 murine preadipocytes, preventing their in vitro differentiation into mature adipocytes. These data interestingly point out that the interaction between Cladosporols and PPARγ, in the milieu of different cells or tissues, might generate a wide range of beneficial effects for the entire organism affected by diabetes, obesity, inflammation, and cancer. This review explores the molecular mechanisms by which the Cladosporol/PPARγ complex may simultaneously interfere with a dysregulated lipid metabolism and cancer promotion and progression, highlighting the potential therapeutic benefits of Cladosporols for human health.

Role of 4-Thiazolidinone-Pyrazoline/Indoline Hybrids Les-4369 and Les-3467 in BJ and A549 Cell Lines

Cancer is one of the most important problems of modern societies. Recently, studies have reported the anticancer properties of rosiglitazone related to its ability to bind peroxisome proliferator receptor γ (PPARγ), which has various effects on cancer and can inhibit cell proliferation. In this study, we investigated the effect of new 4-thiazolidinone (4-TZD) hybrids Les-4369 and Les-3467 and their effect on reactive oxygen species (ROS) production, metabolic activity, lactate dehydrogenase (LDH) release, caspase-3 activity, and gene and protein expression in human foreskin fibroblast (BJ) cells and lung adenocarcinoma (A549) cells. The ROS production and caspase-3 activity were mainly increased in the micromolar concentrations of the studied compounds in both cell lines. Les-3467 and Les-4369 increased the mRNA expression of PPARG, P53 (tumor protein P53), and ATM (ATM serine/threonine kinase) in the BJ cells, while the mRNA expression of these genes (except PPARG) was mainly decreased in the A549 cells treated with both of the tested compounds. Our results indicate a decrease in the protein expression of AhR, PPARγ, and PARP-1 in the BJ cells exposed to 1 µM Les-3467 and Les-4369. In the A549 cells, the protein expression of AhR, PPARγ, and PARP-1 increased in the treatment with 1 µM Les-3467 and Les-4369. We have also shown the PPARγ modulatory properties of Les-3467 and Les-4369. However, both compounds prove weak anticancer properties evidenced by their action at high concentrations and non-selective effects against BJ and A549 cells.

Enhanced detection of ligand-PPARγ binding based on surface plasmon resonance through complexation with SRC1- or NCOR2-related polypeptide

A previous study reported the use of a biosensing technique based on surface plasmon resonance (SPR) for the ligand binding detection of peroxisome proliferator activator receptor gamma (PPARγ). This detection was designed based on the structural properties of PPARγ. Because of cross-linked protein inactivation and the low molecular weight of conventional ligands, direct ligand binding detection based on SPR has low stability and repeatability. In this study, we report an indirect response methodology based on SPR technology in which anti-His CM5 chip binds fresh PPARγ every cycle, resulting in more stable detection. We developed a remarkable improvement in ligand-protein binding detectability in vitro by introducing two coregulator-related polypeptides into this system. In parallel, a systematic indirect response methodology can reflect the interaction relationship between ligands and proteins to some extent by detecting the changes in SA-SRC1 and GST-NCOR2 binding to PPARγ. Rosiglitazone, a PPARγ agonist with strong affinity, is a potent insulin-sensitizing agent. Some ligands may be competitively exerted at the same sites of PPARγ (binding rosiglitazone). We demonstrated using indirect response methodology that selective PPARγ modulator (SPPARM) candidates of PPARγ can be found by competing for the binding of the rosiglitazone site on PPARγ, although they may have no effect on polypeptides and PPARγ binding.

Synthetic Derivatives of Natural ent-Kaurane Atractyligenin Disclose Anticancer Properties in Colon Cancer Cells, Triggering Apoptotic Cell Demise

The antitumor activity of different ent-kaurane diterpenes has been extensively studied. Several investigations have demonstrated the excellent antitumor activity of synthetic derivatives of the diterpene atractyligenin. In this research, a series of new synthetic amides and their 15,19-di-oxo analogues obtained from atractyligenin by modifying the C-2, C-15, and C-19 positions were designed in order to dispose of a set of derivatives with different substitutions at the amidic nitrogen. Using different concentrations of the obtained compounds (10-300 μM) a reduction in cell viability of HCT116 colon cancer cells was observed at 48 h of treatment. All the di-oxidized compounds were more effective than their alcoholic precursors. The di-oxidized compounds had already reduced the viability of two colon cancer cells (HCT116 and Caco-2) at 24 h when used at low doses (2.5-15 μM), while they turned out to be poorly effective in differentiated Caco-2 cells, a model of polarized enterocytes. The data reported here provide evidence that di-oxidized compounds induced apoptotic cell death, as demonstrated by the appearance of condensed and fragmented DNA in treated cells, as well as the activation of caspase-3 and fragmentation of its target PARP-1.

Cytotoxic activity of several ent-kaurane derivatives of atractyligenin. Synthesis of unreported diterpenic skeleton by chemical rearrangement

Atractyloside, carboxyatractyloside, their aglycon atractyligenin, and several synthetic derivatives were tested and found to be active against a panel of human tumor cell lines. Atractyligenin was subjected to oxidation, bromination, and elimination reactions, obtaining several compounds. A singular skeleton was synthesized by chemical rearrangement starting from 3β-bromo-2,15-diketoatractyligenin methyl ester. The synthesized compounds resulted active against all cell lines tested. In particular, 15-ketoatractyligenin methyl ester and 3β-bromo-2,15-diketoatractyligenin methyl ester resulted the most active with IC50 values of 0.427 and 0.723 μM against A375 melanoma cell line. Excellent results were also obtained against the colon cancer cell line CaCo2, with slightly lower antiproliferative activity. An interesting extension of the study should be to analyze the atractyligenin derivatives also as target for human melanoma and human colon cancer cells.

Thiazolidinedione "Magic Bullets" Simultaneously Targeting PPARγ and HDACs: Design, Synthesis, and Investigations of their In Vitro and In Vivo Antitumor Effects

Monotargeting anticancer agents suffer from resistance and target nonspecificity concerns, which can be tackled with a multitargeting approach. The combined treatment with HDAC inhibitors and PPARγ agonists has displayed potential antitumor effects. Based on these observations, this work involves design and synthesis of molecules that can simultaneously target PPARγ and HDAC. Several out of 25 compounds inhibited HDAC4, and six compounds acted as dual-targeting agents. Compound 7i was the most potent, with activity toward PPARγ EC50 = 0.245 μM and HDAC4 IC50 = 1.1 μM. Additionally, compounds 7c and 7i were cytotoxic to CCRF-CEM cells (CC50 = 2.8 and 9.6 μM, respectively), induced apoptosis, and caused DNA fragmentation. Furthermore, compound 7c modulated the expression of c-Myc, cleaved caspase-3, and caused in vivo tumor regression in CCRF-CEM tumor xenografts. Thus, this study provides a basis for the rational design of dual/multitargeting agents that could be developed further as anticancer therapeutics.

Structural mechanism underlying ligand binding and activation of PPARγ

Ligands bind to an occluded orthosteric ligand-binding pocket within the nuclear receptor ligand-binding domain. Molecular simulations have revealed theoretical ligand entry/exit pathways to the orthosteric pocket; however, it remains unclear whether ligand binding proceeds through induced fit or conformational selection mechanisms. Here, using nuclear magnetic resonance spectroscopy, isothermal titration calorimetry, and surface plasmon resonance analysis, we provide evidence that structurally distinct agonists bind peroxisome proliferator-activated receptor γ (PPARγ) via a two-step induced fit mechanism involving an initial fast kinetic step followed by a slow conformational change. The agonist encounter complex binding pose is suggested in crystal structures where ligands bind to a surface pore suggested as a ligand entry site in molecular simulations. Our findings suggest an activation mechanism for PPARγ whereby agonist binding occurs through an initial encounter complex followed by a transition of the ligand into the final binding pose within the orthosteric pocket, inducing a transcriptionally active conformation.

A Series of Ferulic Acid Amides Reveals Unexpected Peroxiredoxin 1 Inhibitory Activity with in vivo Antidiabetic and Hypolipidemic Effects

Insulin resistance is a major pathophysiological feature in the development of type 2 diabetes (T2DM). Ferulic acid is known for attenuating the insulin resistance and reducing the blood glucose in T2DM rats. In this work, we designed and synthesized a library of new ferulic acid amides (FAA), which could be considered as ring opening derivatives of the antidiabetic PPARγ agonists Thiazolidinediones (TZDs). However, since these compounds displayed weak PPAR transactivation capacity, we employed a proteomics approach to unravel their molecular target(s) and identified the peroxiredoxin 1 (PRDX1) as a direct binding target of FAAs. Interestingly, PRDX1, a protein with antioxidant and chaperone activity, has been implied in the development of T2DM by inducing hepatic insulin resistance. SPR, mass spectrometry-based studies, docking experiments and in vitro inhibition assay confirmed that compounds VIe and VIf bound PRDX1 and induced a dose-dependent inhibition. Furthermore, VIe and VIf significantly improved hyperglycemia and hyperlipidemia in streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats as confirmed by histopathological examinations. These results provide guidance for developing the current FAAs as new potential antidiabetic agents.

N6-Isopentenyladenosine Inhibits Colorectal Cancer and Improves Sensitivity to 5-Fluorouracil-Targeting FBXW7 Tumor Suppressor

N6-isopentenyladenosine has been shown to exert potent in vitro antitumor activity on different human cancers, including colorectal cancer. Although some potential biochemical targets have been identified, its precise mechanism of action remains unclear. We found that N6-isopentenyladenosine affects colorectal cancer proliferation in in vitro models carrying different mutational status of FBXW7 and TP53 genes, and in HCT116 xenografts in SCID mice, by increasing the expression of the well-established tumor suppressor FBXW7, a component of the SCF-E3 ubiquitin ligase complex that promotes degradation of various oncoproteins and transcription factors, such as c-Myc, SREBP and Mcl1. Corroborating our previous studies, we identified for the first time the FBXW7/SREBP/FDPS axis as a target of the compound. Pull down of ubiquitinated proteins, immunoprecipitation and luciferase assays, reveal that through the increase of FBXW7/c-Myc binding, N6-isopentenyladenosine induces the ubiquitination of c-Myc, inhibiting its transcriptional activity. Moreover, in FBXW7- and TP53-wild type cells, N6-isopentenyladenosine strongly synergizes with 5-Fluorouracil to inhibit colon cancer growth in vitro. Our results provide novel insights into the molecular mechanism of N6-isopentenyladenosine, revealing its multi-targeting antitumor action, in vitro and in vivo. Restoring of FBXW7 tumor-suppressor represents a valid therapeutic tool, enabling N6-isopentenyladenosine as optimizable compound for patient-personalized therapies in colorectal cancer.

Discovery of Immunoproteasome Inhibitors Using Large-Scale Covalent Virtual Screening

Large-scale virtual screening of boronic acid derivatives was performed to identify nonpeptidic covalent inhibitors of the β5i subunit of the immunoproteasome. A hierarchical virtual screening cascade including noncovalent and covalent docking steps was applied to a virtual library of over 104,000 compounds. Then, 32 virtual hits were selected, out of which five were experimentally confirmed. Biophysical and biochemical tests showed micromolar binding affinity and time-dependent inhibitory potency for two compounds. These results validate the computational protocol that allows the screening of large compound collections. One of the lead-like boronic acid derivatives identified as a covalent immunoproteasome inhibitor is a suitable starting point for chemical optimization.

Novel Benzylidene Thiazolidinedione Derivatives as Partial PPARγ Agonists and their Antidiabetic Effects on Type 2 Diabetes

Peroxisome proliferator-activated receptor γ (PPARγ) has received significant attention as a key regulator of glucose and lipid homeostasis. In this study, we synthesized and tested a library of novel 5-benzylidene-thiazolidin-2,4-dione (BTZD) derivatives bearing a substituent on nitrogen of TZD nucleus (compounds 1a-1k, 2i-10i, 3a, 6a, and 8a-10a). Three compounds (1a, 1i, and 3a) exhibited selectivity towards PPARγ and were found to be weak to moderate partial agonists. Surface Plasmon Resonance (SPR) results demonstrated binding affinity of 1a, 1i and 3a towards PPARγ. Furthermore, docking experiments revealed that BTZDs interact with PPARγ through a distinct binding mode, forming primarily hydrophobic contacts with the ligand-binding pocket (LBD) without direct H-bonding interactions to key residues in H12 that are characteristic of full agonists. In addition, 1a, 1i and 3a significantly improved hyperglycemia and hyperlipidaemia in streptozotocin-nicotinamide (STZ-NA)-induced diabetic rats at a dose of 36 mg/kg/day administered orally for 15 days. Histopathological investigations revealed that microscopic architecture of pancreatic and hepatic cells improved in BTZDs-treated diabetic rats. These findings suggested that 1a, 1i and 3a are very promising pharmacological agents by selectively targeting PPARγ for further development in the clinical treatment of type 2 diabetes mellitus.

Identification of a specific agonist of human TAS2R14 from Radix Bupleuri through virtual screening, functional evaluation and binding studies

Bitter taste receptors (TAS2Rs) have attracted a great deal of interest because of their recently described bronchodilator and anti-inflammatory properties. The aim of this study was to identify natural direct TAS2R14 agonists from Radix Bupleuri that can inhibit mast cell degranulation. A ligand-based virtual screening was conducted on a library of chemicals contained in compositions of Radix Bupleuri, and these analyses were followed by cell-based functional validation through a HEK293-TAS2R14-G16gust44 cell line and IgE-induced mast cell degranulation assays, respectively. Saikosaponin b (SSb) was confirmed for the first time to be a specific agonist of TAS2R14 and had an EC₅₀ value of 4.9 μM. A molecular docking study showed that SSb could directly bind to a TAS2R14 model through H-bond interactions with Arg160, Ser170 and Glu259. Moreover, SSb showed the ability to inhibit IgE-induced mast cell degranulation, as measured with a β-hexosaminidase release model and real-time cell analysis (RTCA). In a cytotoxicity bioassay, SSb showed no significant cytotoxicity to HEK293 cells within 24 hours. This study demonstrated that SSb is a direct TAS2R14 agonist that inhibit IgE-induced mast cell degranulation. Although the target and in vitro bioactivity of SSb were revealed in this study, it still need in vivo study to further verify the anti-asthma activity of SSb.