Cytotoxic constituents of Glycosmis ovoidea collected in Vietnam.

Compounds derived from natural sources have been major contributors to the area of cancer chemotherapy for decades. As part of an ongoing effort to discover anticancer drug leads from tropical plants, a large-scale collection of Glycosmis ovoidea Pierre (Rutaceae), was made at Nui Chua National Park, Vietnam. Activity-guided fractionation of the chloroform-soluble fractions led to the isolation of nine coumarins, including the new compound, 1-(7-methoxy-2-oxo-2H-chromen-8-yl)-3-methyl-1-oxobut-2-en-2-yl (S)-2-methylbutanoate (1). An close analogue of 1, namely, kincuongin (2), was deemed as non-cytotoxic (IC50 > 10 µM) against five different cancer cell lines. However, co-administration of kimcuongin (2) showed an approximately 100 times potentiation of the MCF-7 breast cancer cell cytotoxicity of the previously reported flavonoid, 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (10). To provide a mechanistic basis for the cancer cell line inhibition enhancement observed, an initial in silico study on compound 10 indicated that it interacts with isoforms of the NF-κB complex. In a confirmatory western blot experiment conducted, kimcuongin (2) was found to potentiate the effects of flavone 10 in inhibiting both NF-κB and PARP-1. In vivo investigations using a zebrafish (Danio rerio) model showed that compounds 2, 3, 5, and 6 did not exhibit any discernible toxicity at concentrations up to 50 µM.

Spermidine alkaloid and glycosidic constituents of Vietnamese Homalium cochinchinensis.

Phytochemical investigation of the aerial parts of Homalium cochinchinensis led to the isolation of secondary metabolites belonging to the spermidine alkaloid, glycoside, depsidone and phenol classes. Of the eleven secondary metabolites isolated in this study, two spermidine alkaloids, dovyalicins H (1) and I (2), which belong to a rare group among this class, and six glycosides (3-8) are previously undescribed. The structures of all new isolates were determined by interpretation of spectroscopic and spectrometric data. In this report, the structural elucidation of these unprecedented secondary metabolites (1-8) is described.

A pentamethoxylated flavone from Glycosmis ovoidea promotes apoptosis through the intrinsic pathway and inhibits migration of MCF-7 breast cancer cells.

The rare flavone 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone (PMF) has been isolated from several plant species, and its cytotoxic activity has been reported against many types of cancer cells. In this study, PMF was purified from Glycomis ovoidea collected in Vietnam, and its antiproliferative effects and underlying mechanism of action were investigated against MCF-7 cells. PMF inhibited growth in MCF-7 > MCF-10A > MDA-MB-231 cells after 72 hr treatment, with IC50 values of 1.5, 1.9, and 8.6 µg/ml, respectively. Further experiments conducted with this compound in MCF-7 cells, showed the loss of mitochondrial membrane potential, reactive oxygen species overproduction, upregulation of BAX, cytochrome c, caspase-3 and PARP-1 and down-regulation of BCL-2 proteins as well as an increase in caspase-3/-7 activity, suggesting induction of the apoptotic intrinsic pathway. Furthermore, PMF increased cell cycle arrest in the G1 phase, which correlated with increments in the p53 and p21 levels. Additionally, MCF-7 cell migration was inhibited, which could be related to NF-κB p65 downregulation. Finally, PMF did not show toxicity in vivo in a zebrafish (Danio rerio) model. In conclusion, PMF induces cell death in MCF-7 cells through regulation of the BCL-2 protein family and may be proposed as a lead as a potential alternative for breast cancer therapy.

Caspase-Dependent Apoptosis in Prostate Cancer Cells and Zebrafish by Corchorusoside C from Streptocaulon juventas.

Corchorusoside C (1), isolated from Streptocaulon juventas collected in Vietnam, was found to be nontoxic in a zebrafish ( Danio rerio) model and to induce cytotoxicity in several cancer cell lines with notable selective activity against prostate DU-145 cancer cells (IC50 0.08 µM). Moreover, corchorusoside C induced DU-145 cell shrinkage and cell detachment. In CCD-112CoN colon normal cells, 1 showed significantly reduced cytotoxic activity (IC50 2.3 µM). A preliminary mechanistic study indicated that 1 inhibits activity and protein expression of NF-κB (p50 and p65), IKK (α and ß), and ICAM-1 in DU-145 cells. ROS concentrations increased at 5 h post-treatment, and MTP decreased in a dose-dependent manner. Moreover, decreased protein expression of Bcl-2 and increased expression of PARP-1 was observed. Furthermore, corchorusoside C increased both the activity and protein levels of caspases 3 and 7. Additionally, 1 induced sub-G1 population increase of DU-145 cells and modulated caspases in zebrafish with nondifferential morphological effects. Therefore, corchorusoside C (1) induces apoptosis in DU-145 cells and targets the same pathways both in vitro and in vivo in zebrafish. Thus, the use of zebrafish assays seems worthy of wider application than is currently employed for the evaluation of potential anticancer agents of natural origin.

Cytotoxic and NF-κB and mitochondrial transmembrane potential inhibitory pentacyclic triterpenoids from Syzygium corticosum and their semi-synthetic derivatives.

Syzygium is a large genus of flowering plants, with several species, including the clove tree, used as important resources in the food and pharmaceutical industries. In our continuing search for anticancer agents from higher plants, a chloroform extract of the leaves and twigs of Syzygium corticosum collected in Vietnam was found to be active toward the HT-29 human colon cancer cell line. Separation of this extract guided by HT-29 cells and nuclear factor-kappa B (NF-κB) inhibition yielded 19 known natural products, including seven triterpenoids, three ellagic acid derivatives, two methylated flavonoids, a cyclohexanone, four megastigmanes, a small lactone, and an aromatic aldehyde. The full stereochemistry of (+)-fouquierol (2) was defined for the first time. Biological investigations showed that (+)-ursolic acid (1) is the major cytotoxic component of S. corticosum, which exhibited also potent activities in the NF-κB and mitochondrial transmembrane potential (MTP) inhibition assays conducted, with IC50 values of 31 nM and 3.5 µM, respectively. Several analogues of (+)-ursolic acid (1) were synthesized, and a preliminary structure-activity relationship (SAR) study indicated that the C-3 hydroxy and C-28 carboxylic acid groups and 19,20-dimethyl substitution are all essential in the mediation of the bioactivities observed for this triterpenoid.

Cardiac Glycoside Constituents of Streblus asper with Potential Antineoplastic Activity.

Three new (1-3) and two known (4 and 5) cytotoxic cardiac glycosides were isolated and characterized from a medicinal plant, Streblus asper Lour. (Moraceae), collected in Vietnam, with six new analogues and one known derivative (5a-g) synthesized from (+)-strebloside (5). A preliminary structure-activity relationship study indicated that the C-10 formyl and C-5 and C-14 hydroxy groups and C-3 sugar unit play important roles in the mediation of the cytotoxicity of (+)-strebloside (5) against HT-29 human colon cancer cells. When evaluated in NCr nu/nu mice implanted intraperitoneally with hollow fibers facilitated with either MDA-MB-231 human breast or OVCAR3 human ovarian cancer cells, (+)-strebloside (5) showed significant cell growth inhibitory activity in both cases, in the dose range 5-30 mg/kg.

Isolation of Bioactive Rotenoids and Isoflavonoids from the Fruits of Millettia caerulea.

Three new rotenoids (1-3), two new isoflavonoids (4 and 5), and six known analogues (6-11) were isolated from an n-hexane partition of a methanol extract of the fruits of Millettia caerulea, with the structures of the new compounds elucidated by analysis of their spectroscopic data. The relative configurations of the rotenoids were determined by interpretation of their NMR spectroscopic data, and their absolute configurations were established using electronic circular dichroism spectra and specific rotation values. All compounds isolated were evaluated for their cell growth inhibitory activity against the HT-29 human colon cancer cell line, and the known compounds, (-)-3-hydroxyrotenone (6) and (-)-rotenone (7), were found to be potently active. When tested in an NF-κB inhibition assay, compound 6 showed activity. This compound, along with the new compound, (-)-caeruleanone D (1), and the known compound, ichthynone (8), exhibited K-Ras inhibitory potency. Further bioactivity studies showed that the new compounds, (-)-3-deoxycaeruleanone D (2) and (-)-3-hydroxycaeruleanone A (3), and the known compounds 8 and 11 induced quinone reductase in murine Hepa 1c1c7 cells.

New Bioactive Lupane Triterpene Coumaroyl Esters Isolated from Buxus cochinchinensis.

Five new lupane triterpene coumaroyl esters (1-5), together with betulin (6) and a known Buxus alkaloid, N-3-benzoyldihydrocyclomicrophylline F (7), were isolated from a CHCl3-soluble partition of a methanol extract of Buxus cochinchinensis Pierre ex Gagnep. (Buxaceae) collected in Vietnam. Isolation work was monitored using human colon cancer cells (HT-29). The structures of the new compounds (1-5) were determined on the basis of spectroscopic data interpretation. In addition to their cytotoxicity against HT-29 cells and nuclear factor-kappa B (p65) inhibitory activity in an enzyme-linked immunosorbent assay, all isolates as well as two semisynthetic compounds derived from betulin and 5, respectively, were also evaluated for their in vitro antiplasmodial activities against the drug-resistant Dd2 strain of Plasmodium falciparum and antifungal effects on the growth of the pathogenic yeast Candida albicans. The new lupane triterpene coumaroyl esters (1-5), along with a betulin derivative and the known Buxus alkaloid, were found to show significant in vitro antimalarial activities, with IC50 values ranging from 0.26 to 2.07 µM.

Cytotoxic and natural killer cell stimulatory constituents of Phyllanthus songboiensis.

A dichapetalin-type triterpenoid and a dibenzylbutyrolactone-type lignan, together with five known lignans, a known aromatic diterpenoid, and a known acylated phytosterol, were isolated from the aerial parts of Phyllanthus songboiensis, collected in Vietnam. Their structures were determined by interpretation of the spectroscopic data, and the inhibitory activity toward HT-29 human colon cancer cells of all isolates was evaluated by a cytotoxicity assay. The known arylnaphthalene lignan, (+)-acutissimalignan A, was highly cytotoxic toward HT-29 cells, with an IC50 value of 19 nM, but this compound was inactive as a DNA topoisomerase IIα (topo IIα) poison. The known phytosterol, (-)-ß-sitosterol-3-O-ß-D-(6-O-palmitoyl)glucopyranoside, was found to stimulate natural killer (NK) cells at a concentration of 10µM in the presence of interleukin 12 (IL-12).

Investigation of Vietnamese plants for potential anticancer agents.

Higher plants continue to afford humankind with many new drugs, for a variety of disease types. In this review, recent phytochemical and biological progress is presented for part of a collaborative multi-institutional project directed towards the discovery of new antitumor agents. The specific focus is on bioactive natural products isolated and characterized structurally from tropical plants collected in Vietnam. The plant collection, identification, and processing steps are described, and the natural products isolated from these species are summarized with their biological activities.

Potent cytotoxic arylnaphthalene lignan lactones from Phyllanthus poilanei.

Two new (1 and 2) and four known arylnaphthalene lignan lactones (3-6) were isolated from different plant parts of Phyllanthus poilanei collected in Vietnam, with two further known analogues (7 and 8) being prepared from phyllanthusmin C (4). The structures of the new compounds were determined by interpretation of their spectroscopic data and by chemical methods, and the structure of phyllanthusmin D (1) was confirmed by single-crystal X-ray diffraction analysis. Several of these arylnaphthalene lignan lactones were cytotoxic toward HT-29 human colon cancer cells, with compounds 1 and 7-O-[(2,3,4-tri-O-acetyl)-α-L-arabinopyranosyl)]diphyllin (7) found to be the most potent, exhibiting IC50 values of 170 and 110 nM, respectively. Compound 1 showed activity when tested in an in vivo hollow fiber assay using HT-29 cells implanted in immunodeficient NCr nu/nu mice. Mechanistic studies showed that this compound mediated its cytotoxic effects by inducing tumor cell apoptosis through activation of caspase-3, but it did not inhibit DNA topoisomerase IIα activity.

Caeruleanone A, a rotenoid with a new arrangement of the D-ring from the fruits of Millettia caerulea.

Caeruleanone A (1), a novel rotenoid with an unprecedented arrangement of the D-ring, was isolated with another two new analogues, caeruleanones B (2) and C (3), together with 11 known rotenoids from the fruits of Millettia caerulea. The structures of the new compounds were determined by spectroscopic data analysis, with that of 1 being confirmed by single-crystal X-ray diffraction. Compounds 2 and 3 displayed potent mitochondrial transmembrane potential inhibitory and quinone reductase induction activities.

Bioactive indole alkaloids isolated from Alstonia angustifolia.

Bioassay-guided fractionation was conducted on a CHCl3-soluble extract of the stem bark of Alstonia angustifolia (Apocynaceae) collected in Vietnam using the HT-29 human colon cancer cell line, and led to the isolation of a new sarpagine-type indole alkaloid (1), together with nine known alkaloids, including four macroline-derived alkaloids (2-5), a sarpagine-type alkaloid (6), and four macroline-pleiocarpamine bisindole alkaloids (7-10). The structure of the new compound (1) was determined on the basis of spectroscopic data interpretation. Compounds 1-10 were evaluated in vitro for their NF-κB (p65) inhibitory activity against the Hela cells in an ELISA assay. The new sarpagine alkaloid, N(4)-methyltalpinine (1), was found to show significant NF-κB inhibitory activity (ED50 = 1.2 µM). Furthermore, all the isolates (1-10) were evaluated in vitro for their antileishmanial activity, and compounds (1-4, 6 and 8-10) exhibited leishmaniacidal activity against promastigotes of Leishmania mexicana.

Bioactive constituents of Indigofera spicata.

Four new flavanones, designated as (+)-5″-deacetylpurpurin (1), (+)-5-methoxypurpurin (2), (2S)-2,3-dihydrotephroglabrin (3), and (2S)-2,3-dihydrotephroapollin C (4), together with two known flavanones (5 and 6), three known rotenoids (7-9), and one known chalcone (10) were isolated from a chloroform-soluble partition of a methanol extract from the combined flowers, fruits, leaves, and twigs of Indigofera spicata, collected in Vietnam. The compounds were obtained by bioactivity-guided isolation using the HT-29 human colon cancer, 697 human acute lymphoblastic leukemia, and Raji human Burkitt's lymphoma cell lines. The structures of 1-4 were established by extensive 1D- and 2D-NMR experiments, and the absolute configurations were determined by the measurement of specific rotations and CD spectra. The cytotoxic activities of the isolated compounds were tested against the HT-29, 697, Raji, and CCD-112CoN human normal colon cells. Also, the quinone reductase induction activities of the isolates were determined using the Hepa 1c1c7 murine hepatoma cell line. In addition, cis-(6aß,12aß)-hydroxyrotenone (7) was evaluated in an in vivo hollow fiber bioassay using HT-29, MCF-7 human breast cancer, and MDA-MB-435 human melanoma cells.

Bioactive flavaglines and other constituents isolated from Aglaia perviridis.

Eight new compounds, including two cyclopenta[b]benzopyran derivatives (1, 2), two cyclopenta[b]benzofuran derivatives (3, 4), three cycloartane triterpenoids (5-7), and an apocarotenoid (8), together with 16 known compounds, were isolated from the chloroform-soluble partitions of separate methanol extracts of a combination of the fruits, leaves, and twigs and of the roots of Aglaia perviridis collected in Vietnam. Isolation work was monitored using human colon cancer cells (HT-29) and facilitated with an LC/MS dereplication procedure. The structures of the new compounds (1-8) were determined on the basis of spectroscopic data interpretation. The Mosher ester method was employed to determine the absolute configurations of 5-7, and the absolute configuration of the 9,10-diol unit of compound 8 was established by a dimolybdenum tetraacetate [Mo2(AcO)4] induced circular dichroism procedure. Seven known rocaglate derivatives (9-15) exhibited significant cytotoxicity against the HT-29 cell line, with rocaglaol (9) being the most potent (ED50 0.0007 µM). The new compounds 2-4 were also active against this cell line, with ED50 values ranging from 0.46 to 4.7 µM. The cytotoxic compounds were evaluated against a normal colon cell line, CCD-112CoN. In addition, the new compound perviridicin B (2), three known rocaglate derivatives (9, 11, 12), and a known sesquiterpene, 2-oxaisodauc-5-en-12-al (17), showed significant NF-κB (p65) inhibitory activity in an ELISA assay.

Alkaloids from Microcos paniculata with cytotoxic and nicotinic receptor antagonistic activities.

Microcos paniculata is a large shrub or small tree that grows in several countries in South and Southeast Asia. In the present study, three new piperidine alkaloids, microgrewiapines A-C (1-3), as well as three known compounds, inclusive of microcosamine A (4), 7'-(3',4'-dihydroxyphenyl)-N-[4-methoxyphenyl)ethyl]propenamide (5), and liriodenine (6), were isolated from cytotoxic fractions of the separate chloroform-soluble extracts of the stem bark, branches, and leaves of M. paniculata. Compounds 1-6 and 1a (microgrewiapine A 3-acetate) showed a range of cytotoxicity values against the HT-29 human colon cancer cell line. When evaluated for their effects on human α3ß4 or α4ß2 nicotinic acetylcholine receptors (nAChRs), several of these compounds were shown to be active as nAChR antagonists. As a result of this study, microgrewiapine A (1) was found to be a selective cytotoxic agent for colon cancer cells over normal colon cells and to exhibit nicotinic receptor antagonistic activity for both the hα3ß4 and hα4ß2 receptor subtypes.

Isolation, structure elucidation, and biological evaluation of 16,23-epoxycucurbitacin constituents from Eleaocarpus chinensis.

Eight new 16,23-epoxycucurbitacin derivatives, designated as elaeocarpucins A-H (1-8), and five known cucurbitacins (9-13) were isolated from the chloroform-soluble partitions of separate methanol extracts of the fruits and stem bark of Elaeocarpus chinensis collected in Vietnam. Isolation work was facilitated using a LC/MS dereplication procedure, and bioassay-guided fractionation was monitored using HT-29 human cancer cells. The structures of compounds 1-8 were determined on the basis of spectroscopic data interpretation, with the absolute configurations of isomers 1 and 2 established by the Mosher ester method. Compounds 1-13 were evaluated in vitro against the HT-29 cell line and using a mitochondrial transmembrane potential assay. Elaeocarpucin C (3), produced by partial synthesis from 16α,23α-epoxy-3ß,20ß-dihydroxy-10αH,23ßH-cucurbit-5,24-dien-11-one (13), was found to be inactive when evaluated in an in vivo hollow fiber assay using three different cancer cell types (dose range 0.5-10 mg/kg/day, i.p.).

Bioassay-guided isolation of constituents of Piper sarmentosum using a mitochondrial transmembrane potential assay.

Bioassay-guided fractionation was conducted on a chloroform-soluble extract of the aerial parts of Piper sarmentosum collected in Vietnam, monitored by a mitochondrial transmembrane potential assay using HT-29 human colon cancer cells. This led to the isolation of four new C-benzylated dihydroflavones, sarmentosumins A-D (1-4), as well as 14 known compounds. The structures of the new compounds were elucidated on the basis of spectroscopic data interpretation. Among these compounds, 1-4 as well as five known C-benzylated dihydroflavones (5-9) and a piperamide, pipercallosine (11), were found to induce apoptosis in HT-29 cells by moderately reducing the mitochondrial transmembrane potential (ΔΨm), with ED50 values ranging from 1.6 to 13.6 µM. Furthermore, 7-methoxydichamanetin (8) and pinocembrin (10) exhibited proteasome inhibitory activities in a human 20S proteasome bioassay with IC50 values of 3.45±0.18 and 2.87±0.26 µM, respectively. This is the first time that C-benzylated dihydroflavones have been reported to demonstrate an apoptotic effect associated with disruption of the mitochondrial transmembrane potential.

Cytotoxic and NF-κB inhibitory constituents of the stems of Cratoxylum cochinchinense and their semisynthetic analogues.

A new caged xanthone (1), a new prenylxanthone (2), seven known xanthones, and a known sterol glucoside were isolated from the stems of Cratoxylum cochinchinense, collected in Vietnam. Compounds 1 and 2 were determined structurally by analysis of their spectroscopic data. In addition, five new (10 and 16-19) and eight known prenylated xanthone derivatives were synthesized from the known compounds α-mangostin (3) and cochinchinone A (6). Several of these substances were found to be cytotoxic toward HT-29 human colon cancer cells, with the most potent being 3,6-di-O-acetyl-α-mangostin (8, ED50, 1.0 µM), which was tested further in an in vivo hollow fiber assay, but found to be inactive at the highest dose used (20 mg/kg; ip). Of the substances evaluated in a NF-κB p65 inhibition assay, 1,3,7-trihydroxy-2,4-diisoprenylxanthone (5) exhibited the most potent activity (IC50, 2.9 µM). In a mitochondrial transmembrane potential assay, two new compounds, 1 (IC50, 3.3 µM) and 10 (IC50, 1.4 µM), and two known compounds, 3 (α-mangostin, IC50, 0.2 µM) and 11 (3,6-di-O-methyl-α-mangostin, IC50, 0.9 µM), were active. A preliminary analogue development study showed that 3,6-diacetylation and 6-benzoylation both slightly increased the cytotoxicity of α-mangostin (3), whereas methylation reduced such activity. In contrast, neither acetylation, benzoylation, nor methylation enhanced the cytotoxicity of cochinchinone A (6).

Bioactivity-guided isolation of cytotoxic constituents of Brucea javanica collected in Vietnam.

Five new triterpenoids (1-5), together with two known quassinoids, bruceantin (6) and bruceine A (7), and a known flavonolignan, (-)-hydnocarpin (8), were isolated from the chloroform-soluble subfraction of a methanol extract of the combined twigs, leaves, and inflorescence of Brucea javanica collected in Vietnam. The structures of the new compounds 1-5 were established on the basis of spectroscopic methods. All isolates were evaluated for cytotoxicity against a small panel of human cancer cell lines. Quassinoids 6 and 7 were found to be highly active against these cell lines. (-)-Hydnocarpin (8) showed a potentiating effect when combined with both 6 and 7, during cytotoxicity testing using the MCF-7 human breast cancer cell line.