Isolation and evaluation of cardenolides from Lansium domesticum as Notch inhibitors.

Since Notch signaling plays important roles in cell proliferation and differentiation, aberrant activation of this signaling contributes to cancer progression. In neural stem cells, Notch signaling inhibits differentiation by activating HES1 expression. Therefore, Notch signaling inhibitors may be candidates for new anticancer drugs or have applications in neural regenerative medicine. In this study, six naturally occurring Notch inhibitors were isolated from the methanol (MeOH) extract of Lansium domesticum using our novel cell-based assay. Hongherin (2), a cardiac glycoside, demonstrated potent Notch inhibitory activity with an IC50 of 0.62 µM and was found to be cytotoxic in HPB-ALL human T cell acute lymphoblastic leukemia cells. Hongherin (2) also induced the differentiation of C17.2 neural stem cells to neurons, causing a 65% increase in differentiation compared to the control. Mechanistically, hongherin (2) reduced the amount of Notch1 (full length) and mastermind-like protein (MAML). This indicates that hongherin (2) inhibits Notch signaling through a dual mechanism involving the reduction of both Notch1 and MAML protein levels.

Cadinane sesquiterpenoids isolated from Santalum album using a screening program for Wnt signal inhibitory activity.

Upon screening compounds having Wnt signal inhibitory activity through evaluating TCF/ß-catenin transcriptional (TOP) activity, eight cadinane sesquiterpenoids, including three new compounds (1-3), were isolated from wood extracts of Santalum album (Santalaceae). Structures of compounds 1-3 were elucidated by spectral data to have a cadinane skeleton with an aromatic ring. Of the eight compounds isolated, compound 4, identified as mansonone I, was found to be active against TOP, having an IC50 of 1.2 µM.

The Notch Inhibitors Isolated from Nerium indicum.

Notch signaling plays a crucial role in differentiation and cell maintenance, but once aberrantly activated, it contributes to cancer progression. Notch inhibitors were isolated from plant extracts and tested using an originally constructed cell-based assay system. We isolated eight compounds from Nerium indicum that showed inhibition of the Notch signaling pathway. HES1 and HES5 are target genes of the Notch signaling pathway, and oleandrin (1) decreased the protein levels of HES1 and HES5 in assay cells. Oleandrin (1) showed potent cytotoxicity against HPB-ALL cells and decreased HES1 and the Notch intracellular domain in these cells. The main mechanism of action of 1 appears to be inhibition of Notch signaling by acceleration of Notch intracellular domain degradation.

ß-Sitosterol and flavonoids isolated from Bauhinia malabarica found during screening for Wnt signaling inhibitory activity.

Screening with a cell-based luciferase assay was conducted to identify bioactive natural products which inhibit Wnt signaling activity-guided separation of an MeOH extract of Bauhinia malabarica (Caesalpiniaceae) leaves yielded five compounds, which were identified as ß-sitosterol (1), quercetin (2), 6,8-C-dimethyl kaempferol-3-O-rhamnopyranoside (3), hyperin (4), and 6,8-C-dimethyl kaempferol-3-methyl ether (5). The tested compounds 1, 3, and 5 exhibited Wnt signaling inhibitory activity, with IC50 values of 0.77, 0.74, and 16.6 µM, respectively.

Naturally occurring Ngn2 promoter activators from Butea superba.

Neurogenin2 (Ngn2), an activator-type bHLH transcriptional factor, promotes differentiation of neural stem cells into neurons by transcription of pro-neural genes. To find neural stem cell accelerators from the extract library of natural resources, we used a two-step screening including a Ngn2 promoter reporter gene screening and differentiation assay screening of neural stem cells. A reporter gene assay that can detect Ngn2 promoter activity by luciferase expression was constructed using C3H10T1/2 cells. Using this primary cell-based screening, Butea superba was found to include Ngn2 promoter activators from our tropical plant extract libraries. Bioassay-guided fractionation of this plant extract led to the isolation of 18 natural products, including pterocarpans and isoflavonoids. Dehydromaackiain (1), formononetin (6), ()-variabilin (13), ()-medicarpin (14), rothindin (17) and ononin (18) showed 1.8­2.8 times higher Ngn2 promoter activity at 5 mM compared with control. Of active natural compounds, 30-methoxydaidzein (3) showed promotion of neurite outgrowth of C17.2 in a secondary screen. 30-Methoxydaidzein (3) increased mRNA expression of pro-neural transcriptional factors (Ngn2, Ngn1, NeuroD2), a mature neuron-specific enzyme GAD1 and a pro-neural neurotrophic growth factor neurotrophin 3 (NT3) in C17.2 neural stem cells.

Cycloartane triterpenes and ingol diterpenes isolated from Euphorbia neriifolia in a screening program for death-receptor expression-enhancing activity.

In our screening program for natural products that increase death-receptor 5 expression, seven new cycloartane triterpenes, euphonerins A-G (1-7), and 3-O-acetyl-8-O-tigloylingol (8), a new ingol diterpene, were isolated from the MeOH extract of Euphorbia neriifolia leaves, together with 3,12-di-O-acetyl-8-O-tigloylingol (9), (24R)-cycloartane-3ß,24,25-triol (10), and three known flavonols (11-13). The structures of 1-8 were elucidated by spectroscopic analysis. Among these compounds, 1-11 showed death-receptor 5 expression enhancing activity.

Inhibition of lysenin-induced hemolysis by all-E-lutein derived from the plant Dalbergia latifolia.

Lysenin is a pore-forming toxin derived from coelomic fluid of the earthworm Eisenia foetida. The model of lysenin-induced hemolysis includes the specific binding of lysenin to sphingomyelin, oligomerization of the pore proteins, and pore formation. Although the mechanism of lysenin-induced hemolysis is unique, its precise mechanism of action and its inhibitors are poorly understood. In the present study, we screened for inhibitors of lysenin-induced hemolysis by using an optimized screening system and found a methanolic extract of Dalbergia latifolia leaves to be a potential candidate. After isolation and identification, all-E-lutein was identified as the hemolysis inhibitor with an effective dose of 0.025-2.5 ng/mL without any toxicity. The inhibition by all-E-lutein is likely to occur during the receptor binding and/or pore-forming protein oligomerization.

Acoschimperoside P, 2'-acetate: a Hedgehog signaling inhibitory constituent from Vallaris glabra.

Complete (1)H and (13)C NMR assignments of acoschimperoside P, 2'-acetate (1) and a new cardiac glycoside (2), isolated from the leaves of Vallaris glabra, are described. Compound 1 was active in the assay for Hedgehog signaling inhibition. In further experiments, this compound showed a strong cytotoxicity against human pancreatic (PANC1) and human prostate (DU145) cancer cells. The expression of GLI-related proteins (PTCH and BCL-2) in a dose-dependent manner was also inhibited by 1.

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/ß-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.

Activity of mangosteen xanthones and teleocidin a-2 in death receptor expression enhancement and tumor necrosis factor related apoptosis-inducing ligand assays.

A screening study using a luciferase assay to identify natural products that enhance death receptor 5 (DR5) expression was carried out, and bioassay-guided fractionation of two organisms, the pericarp of Garcinia mangostana (mangosteen) and actinomycete CKK609 strain, led to the isolation of eight xanthone derivatives (1-8) and teleocidin A-2 (9). Among them, compounds 1, 2, and 5, isolated from G. mangostana, and 9, from the actinomycete, showed potent DR5 promoter activity. Furthermore, we revealed that combined treatment with gartanin (5) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) showed a potentiation effect in sensitizing TRAIL-resistant human gastric adenocarcinoma (AGS) cells. Thus, the present results suggested that 5 has the ability to overcome TRAIL resistance via the up-regulation of DR5 and may be an effective sensitizer of TRAIL-resistant cells.

Death receptor 5 promoter-enhancing compounds isolated from Catimbium speciosum and their enhancement effect on TRAIL-induced apoptosis.

The TRAIL/death-receptor signaling pathway has been considered a promising target for selective cancer therapy, although some malignant tumors exhibit TRAIL resistance. We previously found that isoflavonoid enhanced TRAIL-induced apoptosis in TRAIL-resistant cells, which is achieved through up-regulation of death receptor 5 (DR5). In our screening program targeting DR5 promoter enhancement activity, activity-guided fractionations of the extract of Catimbium speciosum led to the isolation of six compounds. Of the isolates, cardamomin (6), the most potent compound, enhanced the expressions of DR5 and DR4 and decreased the Bcl-xL level in TRAIL-resistant DLD1 cells. The combination of 6 and TRAIL synergistically enhanced TRAIL-induced apoptosis against TRAIL-resistant cells upon the activation of caspase-8, 9, and 3. In addition, enhancement of apoptosis by 6 was inhibited by human recombinant DR5/Fc and DR4/Fc chimera proteins, TRAIL-neutralizing fusion proteins, indicating that 6 sensitize TRAIL-resistant cells to TRAIL through the induction of DR5 and DR4. Also, up-regulation of DR5 by 6 paralleled that of CCAAT/enhancer-binding protein-homologous protein (CHOP).

Cardenolide glycosides of Thevetia peruviana and triterpenoid saponins of Sapindus emarginatus as TRAIL resistance-overcoming compounds.

A screening study for TRAIL resistance-overcoming activity was carried out, and activity-guided fractionations of Thevetia peruviana and Sapindus emarginatus led to the isolation of four cardenolide glycosides (1-4) and four triterpenoid saponins (5-8), respectively. In particular, cardenolide glycosides (1 and 2) from T. peruviana were shown to have a significant reversal effect on TRAIL resistance in human gastric adenocarcinoma cells, and real-time PCR showed that thevefolin (2) enhanced mRNA expression of death receptor 4 (DR4) and DR5. In addition, 1H and 13C NMR characterizations are shown for thevefolin (2) for the first time.

New Wnt/beta-catenin signaling inhibitors isolated from Eleutherine palmifolia.

Aberrant Wnt/beta-catenin signaling has recently been implicated in tumorigenesis. On the basis of our screening program targeting inhibition of TCF/beta-catenin transcriptional activity, a plant extract of Eleutherine palmifolia was selected as a hit sample. Activity-guided fractionations led to the isolation of 15 naphthalene derivatives (1-15), including 4 new glucosides, eleutherinosides B-E (1-4), and 10 of the 15 compounds showed strong activities with high viability among 293T cells. Our data showed that 2 and 9 inhibited the transcription of TCF/beta-catenin in SW480 colon cancer cells in a dose-dependent manner. These two compounds also showed selective cytotoxicity against three colorectal cancer cell lines. In addition, treatment with 9 led to a significant decrease in the level of nuclear beta-catenin protein, suggesting this reduction to have resulted in the inhibitory effect of 9 on the transcription of TCF/beta-catenin.

Hedgehog/GLI-mediated transcriptional inhibitors from Zizyphus cambodiana.

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. By screening tropical plant extracts by using our screening system, Zizyphus cambodiana was found to include Hh/GLI signaling inhibitors. Bioassay-guided fractionation of this plant extract led to the isolation of three active pentacyclic triterpenes, colubrinic acid (1), betulinic acid (2) and alphitolic acid (3), as potent inhibitors. The inhibition of GLI-related protein expression with 1 or 2 was observed in HaCaT cells with exogenous GLI1, or human pancreatic cancer cells (PANC1), which express Hh/GLI components aberrantly. The expressions of GLI-related proteins PTCH and BCL2 were clearly inhibited by 1 or 2. We also examined the cytotoxicity of these active compounds against PANC1, human prostate cancer cells (DU145) and mouse embryo fibroblast cells (C3H10T1/2). The cytotoxicity against cancer cells (PANC1 and DU145) by 1 or 2 would be caused by inhibition of the expression of the anti-apoptosis protein BCL2. These pentacyclic triterpene inhibitors showed an important relationship between Hh/GLI signaling inhibition, the decrease of BCL2, and cytotoxicity against cancer cells.

Acylated triterpenoid saponins from Schima noronhae and their cell growth inhibitory activity.

Two new acylated triterpenoid saponins were isolated from the branches of Schima noronhae by bioassay-guided purification. Their chemical structures were established on the basis of spectroscopic analysis and chemical means as 3-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-galactopyranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl 22-O-angeloyl-A1-barrigenol (1) and 3-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-galactopyranosyl-(1-->3)-[beta-D-glucopyranosyl-(1-->2)]-beta-D-glucuronopyranosyl 22-O-angeloylerythrodiol (2). Compounds 1 and 2 showed cell growth inhibitory activity against both HeLa and DLD1 cells at a concentration of less than 10 microM.

Naturally occurring small-molecule inhibitors of hedgehog/GLI-mediated transcription.

The aberrant hedgehog (Hh)/GLI signaling pathway causes the formation and progression of a variety of tumors. To search for Hh/GLI inhibitors, we screened for naturally occurring inhibitors of the transcriptional activator GLI1 by using a cell-based assay. We identified zerumbone (1), zerumbone epoxide (2), staurosporinone (9), 6-hydroxystaurosporinone (10), arcyriaflavin C (11) and 5,6-dihydroxyarcyriaflavin A (12) as inhibitors of GLI-mediated transcription. In addition, we isolated physalins F (17) and B (18) from Physalis minima, which are also potent inhibitors. These compounds also inhibited GLI2-mediated transactivation. Semiquantitative RT-PCR and Western blotting analysis further revealed that 1, 9, 17, and 18 decreased Hh-related component expressions. We also show that inhibitors of GLI-mediated transactivation reduce the level of the antiapoptosis Bcl2 expression. Finally, these identified compounds were cytotoxic to PANC1 pancreatic cancer cells, which express Hh/GLI components. These results strongly suggest that the cytotoxicity of the compounds to PANC1 cells correlates with their inhibition of GLI-mediated transcription.

Biologically active aspidofractinine alkaloids from Kopsia singapurensis.

Ten new indole alkaloids of the aspidofractinine type, in addition to several recently reported indole alkaloids and 20 other known alkaloids, were obtained from the leaf and stem-bark extract of the Malayan Kopsia singapurensis, viz., kopsimalines A-E (1-5), kopsinicine (6), kopsofinone (7), and kopsiloscines H-J (8-10). The structures of these alkaloids were determined using NMR and MS analysis. Kopsimalines A (1), B (2), C (3), D (4), and E (5) and kopsiloscine J (10) were found to reverse multidrug-resistance in vincristine-resistant KB cells, with 1 showing the highest potency.

Quinic acid esters from Pluchea indica with collagenase, MMP-2 and MMP-9 inhibitory activities.

Investigation of collagenase inhibitory natural components afforded two quinic acid esters (1 and 2) and quercetin (3) from the leaves of Pluchea indica (Compositae). Of these, compounds 1 and 2 exhibited collagenase inhibitory activity (IC(50)) at a concentration of less than 10 microm, and 1 showed matrix metalloproteinase (MMP)-2 and -9 inhibitory activity (IC(50)) at 2.5 and 6.4 microm, respectively.

Biologically active aspidofractinine, rhazinilam, akuammiline, and vincorine alkaloids from Kopsia.

Eleven new indole alkaloids, in addition to the previously reported rhazinal (1), and 14 other known alkaloids, were obtained from the Malayan Kopsia singapurensis, viz., kopsiloscines A-F (2-7), 16-epikopsinine (8), kopsilongine- N-oxide (9), 16-epiakuammiline (10), aspidophylline A (11), and vincophylline (12). The structures of these alkaloids were determined using NMR and MS analyses. Rhazinal (1), rhazinilam (17), and rhazinicine (18) showed appreciable cytotoxicity toward drug-sensitive as well as vincristine-resistant KB cells, while kopsiloscines A (2), B (3), and D (5) and aspidophylline A (11) were found to reverse drug-resistance in drug-resistant KB cells.

Mangiferin identified in a screening study guided by neuraminidase inhibitory activity.

A screening study on neuraminidase inhibitory constituents was carried out, and activity-guided fractionations of three plants, Gouania obtusifolia, Zizyphus cambodiana, and Mangifera odorata, led to the isolation of eleven compounds (1-11). Mangiferin was identified as a significant neuraminidase inhibitor.