Search for Bioactive Natural Products Targeting Cancer-Related Signaling Pathways

Screening for natural products that affect Wnt signaling activity

Wnt signaling has been implicated in numerous aspects of development, cell biology, and physiology. When aberrantly activated, Wnt signaling can also lead to the formation of tumors. Thus, Wnt signaling is an attractive target for cancer therapy. Based on our screening program targeting Wnt signaling activity using a cell-based luciferase screening system assessing TCF/β-catenin transcriptional activity, we isolated a series of terpenoids and heterocyclic aromatic compounds that affect the Wnt signaling pathway at different points. Here, we describe our recent results in screening for natural products that inhibit or activate Wnt signaling.

Evaluation of WO2014207069 A1: Multitarget Hedgehog pathway inhibitors and uses thereof

In recent years, the involvement of the Hedgehog (Hh) signaling pathway in various human diseases and dysfunctions has been clearly demonstrated. Smoothened (Smo), one of the upstream signal transducers, has been the most druggable target of the Hh pathway. However, the emergence of resistance to Smo inhibitors and the identification of Smo-independent activation of the Hh pathway led to the need to find new chemical entities able to interfere with downstream components, such as Gli. For this purpose, two different computational approaches have been applied to a small-sized library of natural compounds. As a result, an isoflavone derivative that showed ability to inhibit both Smo and Gli1 has been identified; namely, Glabrescione B. A new synthetic approach has been planned for this compound and its derivatives. Biological evaluation demonstrated the mechanism of action and showed a promising preclinical profile.

Prenylated flavonoids and resveratrol derivatives isolated from Artocarpus communis with the ability to overcome TRAIL resistance

In a screening program on natural products that can abrogate tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resistance, four new prenylated flavonoid and resveratrol derivatives (1-4) were isolated from Artocarpus communis, together with eight known prenylflavonoids (5-12). The structures of 1-4 were elucidated spectroscopically. Pannokin D [corrected] (1) (2 μM) and artonin E (5) (3 μM) potently exhibited the ability to overcome TRAIL resistance. Artonin E (5) induced caspase-dependent apoptosis in combination with TRAIL, increased caspase 3/7 activity, and enhanced the protein levels of p53 and DR5. Moreover, this substance decreased cell viability in combination with TRAIL and enhanced the protein levels of DR5, and these effects were mediated by increases in the production of ROS (reactive oxygen species). Thus, artonin E (5) was found to induce extrinsic apoptotic cell death by the ROS- and p53-mediated up-regulation of DR5 expression in AGS cells.

Prenylflavonoids isolated from Artocarpus champeden with TRAIL-resistance overcoming activity

In a screening program for bioactive natural products which can overcome Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-resistance, three prenylflavonoids, named pannokin A-C, were isolated from a MeOH extract of Artocarpus champeden (Moraceae) roots, together with three known prenylflavonoids. The structures of pannokin A-C were elucidated by spectroscopic analysis. These of the prenylflavonoids in combination with TRAIL, showed cytotoxic activity in sensitizing TRAIL-resistant human gastric adenocarcinoma (AGS) cells. Of these compounds, heterophyllin increased caspase 3/7 activity when combined with TRAIL in AGS cells, and enhanced the expression of DR4 and DR5 mRNA. Moreover, heterophyllin up-regulated mRNA expression of CCAAT/enhancer-binding protein-homologous protein (CHOP) which was reported to be an important regulator of DR5 expression. Thus, heterophyllin was presumed to cause a CHOP-dependent up-regulation of DR5 expression resulting in apoptosis in AGS cells.

Xylogranin B: a potent Wnt signal inhibitory limonoid from Xylocarpus granatum

Xylogranin B (2) was isolated from Xylocarpus granatum (Meliaceae) leaves, by use of a cell-based luciferase screening system targeting a Wnt signaling pathway. Compound 2 inhibited TCF/β-catenin transcriptional activity (IC50 48.9 nM) and exhibited strong cytotoxicity against colon cancer cell lines. Compound 2 significantly decreased β-catenin protein levels in nuclei but not in the cytosol. These results indicated that a decrease in β-catenin levels in nuclei by 2 resulted in the Wnt signal inhibitory effects of 2.

Eudesmane-type sesquiterpenoid and guaianolides from Kandelia candel in a screening program for compounds to overcome TRAIL resistance

In a screening program for natural products that can overcome TRAIL resistance, a new eudesmane-type sesquiterpenoid (1), three new guaianolides, mehirugins A-C (2-4), and two known guaianolides (5 and 6) were isolated from a MeOH extract of Kandelia candel leaves. Compounds 1 and 3-6 in combination with TRAIL showed cytotoxic activity in sensitizing TRAIL-resistant human gastric adenocarcinoma cells.

Phorbol Esters with Wnt Signal-Augmenting Effects Isolated from

A screening of natural products using a luciferase assay targeting the Wnt signaling pathway was carried out, and the bioassay-guided fractionation of Excoecaria indica (Euphorbiaceae) collected from Bangladesh afforded three phorbol esters (1 – 3). These compounds exhibited Wnt signal-augmenting effects with 1 causing a 25-fold increase in TCF/β-catenin (TOP) transcriptional activity at 95 nM.

New pyranonaphthoquinones and a phenazine alkaloid isolated from Streptomyces sp. IFM 11307 with TRAIL resistance-overcoming activity

Four new pyranonaphthoquinones (1-4) were isolated from the liquid culture of Streptomyces sp. IFM 11307. Additionally, one new phenazine derivative (5), along with the known phenazine-1,6-dicarboxylic acid (6) were identified. The chemical structure of compounds 1-6 was elucidated by 1D and 2D NMR spectroscopy together with CD spectral analysis. Compounds 1-4 significantly overcame tumor necrosis factor-related apoptosis-inducing ligand resistance in human gastric adenocarcinoma cell lines.

Izumiphenazine D, a new phenazoquinoline N-oxide from Streptomyces sp. IFM 11204

A new phenazine derivative named izumiphenazine D (1), together with three known metabolites, 1-hydroxyphenazine (2), phenazine-1-carboxylic acid (3) and 6-hydroxyphenazine-1-carboxylic acid (4) has been isolated from the ethyl acetate extract of culture of Streptomyces sp. IFM 11204. The structure of 1 was established via spectroscopic methods, including 1D- and 2D-NMR measurements.

Cycloartane triterpenes isolated from Combretum quadrangulare in a screening program for death-receptor expression enhancing activity

In our screening program for natural products that increase DR5 (death-receptor 5) expression, nine new cycloartane triterpenes, combretanones A-G (1-7), combretic acid A (8), and combretic acid B (9), were isolated from a MeOH extract of Combretum quadrangulare leaves. The known oleanane triterpenes (10, 11) and six known flavonols (12-17) were also isolated. The structures of 1-9 were elucidated by spectroscopic studies. Compounds 7, 9, 12, 16, and 17 enhanced DR5 expression, and 16 showed TRAIL-resistance abrogating activity.

2-methoxy-1,4-naphthoquinone isolated from Impatiens balsamina in a screening program for activity to inhibit Wnt signaling

A screening study using a luciferase assay to identify natural products which inhibit Wnt signaling was carried out. The bioassay-guided fractionation of aerial parts of a plant, Impatiens balsamina, led to the isolation of 2-methoxy-1,4-naphthoquinone (1) as an active compound. Compound 1 inhibited the TCF/β-catenin (TOP) transcriptional activity (IC(50) 2.9 µM), while it decreased the transcriptional activity of FOP (mutated TCF-binding site)-transfected cells at >5 µM.

Search for bioactive natural products from medicinal plants of Bangladesh

In our continuous search for bioactive natural products from natural resources, we explored medicinal plants of Bangladesh, targeting cancer-related tumor necrosis factor-related apoptosis-inducing ligand-signaling pathway, along with some other biological activities such as prostaglandin inhibitory activity, 1,1-diphenyl-2-picrylhydrazyl free-radical-scavenging activity, and cell growth inhibitory activity. Along with this, we describe a short field study on Sundarbans mangrove forests, Bangladesh, in the review.

Total synthesis of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin: powerful new inhibitors of beta-catenin/TCF4- and E2F-mediated gene transcription

Herein we describe our asymmetric total syntheses of (+)-A83586C, (+)-kettapeptin and (+)-azinothricin. We also demonstrate that molecules of this class powerfully inhibit beta-catenin/TCF4- and E2F-mediated gene transcription within malignant human colon cancer cells at low drug concentrations.