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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.

B-Cell-specific Moloney murine leukemia virus insertion region 1 (BMI1) is a core component of the polycomb repressive complex 1 (PRC1). Abnormal expression of BMI1 is associated with a number of human malignances and cancer stem cells (CSCs), which cause chemotherapy resistance. Therefore, small molecules that inhibit BMI1 expression are potential candidates for cancer therapy. In this study, a cell-based reporter gene assay was developed that allowed BMI1 promoter activity to be measured in 293T human embryonic kidney cells based on luciferase expression levels. Using this screening assay, the methanol-soluble extracts of Beaumontia murtonii and Eugenia operculata were selected as leads. Bioassay-guided fractionation of the extracts led to the isolation of three known cardenolides (1-3) and one new compound (4) from B. murtonii and two known triterpenoids (5 and 6) and one new compound (7) from E. operculata. These seven compounds inhibited BMI1 promoter activity (IC 50 range 0.093-23.0 μM), and the most active compound, wallichoside (1), was further evaluated. Western blot analysis revealed that wallichoside (1) decreases BMI1 protein levels in HCT116 human colon carcinoma cells, and flow cytometry analysis showed that it significantly reduced levels of the CSC biomarker epithelial cell adhesion molecule. Wallichoside (1) also inhibited sphere formation of Huh7 human hepatocellular carcinoma cells, indicating that it diminished the self-renewal capability of CSCs.

A new bis-aporphine alkaloid, cerasoidine (1), was isolated from the root extract of Polyalthia cerasoides together with the known bis-aporphine bidebiline E (2) during screening for compounds with Wnt signal inhibitory activities. The structure of cerasoidine (1) was established by X-ray analysis and shown by chiral HPLC analyses and electronic circular dichroism to be a 57:43 mixture of R(-)- and S(+)-atropisomers. Bidebiline E (2) exhibited inhibition of transcriptional activity of TCF/β-catenin with an IC50 value of 20.2 μM and was also found to inhibit Wnt signaling by decreasing nuclear β-catenin.

TRAIL is a potent and selective inducer of apoptosis in most cancer cells while sparing normal cells, which makes it an attractive target for the development of new cancer therapies. In a screening program on natural resources with the ability to abrogate TRAIL resistance, the bioassay-guided fractionation of Boesenbergia pandurata rhizomes resulted in the isolation of 17 pimarane diterpenes and a monoterpene. Among these, compounds 1-8, named boesenberols A-H, are new pimarane diterpenes. All compounds exhibited TRAIL-resistance-overcoming activity in TRAIL-resistant AGS cells. Subtoxic doses of the major compound 9 sensitized AGS cells to TRAIL-induced apoptosis by up-regulating apoptosis-inducing proteins, such as DR4, DR5, p53, Fas, CHOP, Bak, and cleaved caspases-3, -8, and -9, and down-regulating the levels of cell survival proteins, such as Bcl-2, c-FLIP, and GSK-3β, in TRAIL-resistant AGS cells. Furthermore, compound 9 did not decrease the viability of noncancerous (HEK293) cells at concentrations up to 30 μM.

Wnt signaling regulates various processes such as cell proliferation, differentiation, and embryo development. However, numerous diseases have been attributed to the aberrant transduction of Wnt signaling. We screened a plant extract library targeting TCF/β-catenin transcriptional modulating activity with a cell-based luciferase assay. Activity-guided fractionation of the MeOH extract of the E. longifolia root led to the isolation of 9-hydroxycanthin-6-one (1). Compound 1 exhibited TCF/β-catenin inhibitory activity. Compound 1 decreased the expression of Wnt signal target genes, mitf and zic2a, in zebrafish embryos. Treatment of SW480 cells with 1 decreased β-catenin and increased phosphorylated β-catenin (Ser 33, 37, Tyr 41) protein levels. The degradation of β-catenin by 1 was suppressed by GSK3β-siRNA, while compound 1 decreased β-catenin even in the presence of CK1α-siRNA. These results suggest that 1 inhibits Wnt signaling through the activation of GSK3β independent of CK1α.

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.

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.

Overexpression of glioma-associated oncogene 1 (GLI1), which has been characterized as a terminal effector and a target gene of the Hedgehog (Hh) signaling pathway, is associated with the development of cancer. A cellular screen was applied utilizing of a GLI-dependent luciferase reporter in human keratinocyte cells (HaCaT) and identified two terpenoids (1 and 2) and a flavonoid glycoside (5) from Acacia pennata as Hh/GLI inhibitors. Compounds 1, 2, and 5 exhibited selective cytotoxicity against human pancreatic (PANC1) and prostate (DU145) cancer cells with no toxic effect on normal cells. This result was consistent with a dose-dependent reduction of the protein levels of antiapoptotic BCL-2 and the tumor suppressor patched 1 protein (PTCH). Additionally, treatment of 1 downregulated mRNA expression of Ptch in PANC1, suggesting that the compound has an inhibitory effect on the transcription of Hh/GLI.

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.

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.

Two new cadinane sesquiterpenes (1 and 2) were isolated from Curcuma parviflora, and their structures were elucidated by spectroscopic data. Compound 1, 4alpha-acetoxycadina-2,9-diene-1,8-dione, possesses two conjugated enone chromophores, while compound 2, 1alpha,3alpha,4beta-trihydroxy-9-cadinen-8-one, has an enone moiety with three hydroxy groups. Isolation of these cadinane monomers may reasonably suggest that parviflorenes are biogenetically classified as cadinane dimers.

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.

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.

In a screening study for natural products with tumor-selective apoptosis-inducing properties, six new isoflavonoids (1- 6), named brandisianins A-F, respectively, have been isolated from a MeOH extract of the dried leaves of Millettia brandisiana, together with five known compounds. The structures of the new compounds were elucidated by spectroscopic data interpretation. Among these compounds, brandisianin D (4) exhibited death-receptor 5 expression enhancement activity in a luciferase assay based in DLD-1/ SacI cells. The results suggest that brandisianin D (4) might overcome TRAIL-resistance by an increase in DR5 expression.

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.

Nine new indole alkaloids, rhazinoline (1), 19(S)-methoxytubotaiwine (2), 19(R)-methoxytubotaiwine (3), kopsamidine A (4), kopsamidine B (5), kopsinidine A (6), kopsinidine B (7), paucidactine C (8), and pericine N-oxide (9), in addition to several recently reported novel indoles and 34 other known ones, were obtained from the stem-bark extract of the Malayan Kopsia arborea. The structures were determined using NMR and MS analysis. Valparicine (12) showed pronounced cytotoxic effects against KB and Jurkat cells (IC(50) 13.0 and 0.91 microM, respectively).

Two new quinic acid esters (1 and 2) were isolated from the extract of Ipomoea pes-caprae together with six known quinic acid esters (3-8). The structures of compounds 1 and 2 were elucidated by spectroscopic data interpretation. These new compounds exhibited collagenase inhibitory activity and showed almost no cytotoxicity.

Two new sesquiterpenoid esters (1 and 2) were isolated from the extract of Blumea balsamifera, a tropical Compositae plant. Compound 2 proved to be weakly cytotoxic when tested against Jurkat human T-cell leukemia cells. Nine known flavonoids, of which two showed plasmin-inhibitory activity, were also isolated.

Three new natural onoceranoid triterpenes, lansionic acid (1), 3beta-hydroxyonocera-8(26),14-dien-21-one (2), and 21alpha-hydroxyonocera-8(26),14-dien-3-one (3), were isolated from the fruit peel of Lansium domesticum together with two known triterpenoids (4 and 5), and their structures were elucidated from spectral data. These triterpenoids exhibited mild toxicity against brine shrimp (Artemia salina).

Three new 12beta-hydroxymultiflorane triterpenoid acids, sandorinic acids A-C (1-3), were isolated from the stem bark of Sandoricum indicum together with five known triterpenes (4-8). The structures of 1-3 were elucidated by spectral data interpretation. Compounds 1-8 were evaluated for their inhibiting activity against several tumor cell lines and for their effects on lymphocyte proliferation.

The EtOH extract of the leaves of Holarrhena curtisii yielded five new steroidal alkaloids: 17-epi-holacurtine (3), 17-epi-N-demethylholacurtine (4), holacurtinol (5), 3alpha-amino-14beta-hydroxypregnan-20-one (7), and 15alpha-hydroxyholamine (8), in addition to the known compounds, holacurtine (1), N-demethylholacurtine (2), and holamine (6). All eight compounds showed significant cytotoxic and leishmanicidal activities.

In the course of screening for Ras function inhibitors, rocaglaol (1) and the related compounds, the known pyrimidinone (2) and the novel aglaiastatin (3), were isolated from a CHCI3 extract of the leaves of Aglaia odorata. The structure of 3 was elucidated as a novel cyclopentabenzofuran on the basis of its NMR spectroscopic data and by X-ray crystallographic analysis. These compounds (1-3) were potent inhibitors of the growth of K-ras-NRK cells, with IC50 values of 1-10 ng/mL, and induced normal morphology in K-ras-NRK cells at 10-30 ng/mL. They also specifically inhibited protein synthesis. Aglaiastatin (3) was slightly more potent than 1 and 2 in inhibiting cell growth. Aglaiastatin (3) reduced the amount of Ras, possibly by inhibiting its de novo synthesis.