A systematic review of spirostanol saponins and anticancer natural products isolated from Tacca plantaginea (Hance) Drenth.

The plant genus Tacca comprises twenty species including Tacca plantaginea, essentially distributed in the Indo-China region. Medicinal preparations from the rhizomes are used traditionally to treat gastrointestinal ailments, stomach aches and inflammatory disorders. A variety of bioactive molecules have been isolated from T. plantaginea, including potent anticancer steroids such as the taccanolides which interfere with microtubules dynamic. Other efficient anticancer natural products have been isolated from the plant, in particular a series of diosgenin/yamogenin-type sapogenins including taccaoside (monodesmosidic) and taccaoside A (bidesmosidic). Taccaoside A displays marked anticancer properties through two complementary mechanisms: a direct action on cancer stem cells via HRas and Pi3K/Akt signaling and an indirect immunomodulatory action via activation of cytotoxic T cells. A similar mechanism of action has been invoked with a total saponin extract from Schizocapsa plantaginea Hance (synonym to T. plantaginea) and the saponin SSPH 1. This saponin reduced tumor growth in mice through stimulation of cytotoxic T lymphocytes. Other bioactive products have been isolated from T. plantaginea, including withanolide-type steroids (plantagiolides, chantriolides), diarylheptanoids (plantagineosides) and different saponins (diosbulbisides, lieguonins). The discussion centers around the mechanism of action of spirostanol saponins, with the objective to promote their study as immuno-active anticancer agents.

Chantriolides F-P, Highly Oxidized Withanolides with Hepatoprotective Activity from Tacca chantrieri.

Eleven highly oxidized withanolides, chantriolides F-P (1-11), together with six known analogues (12-17), were isolated from the rhizomes of Tacca chantrieri. Their structures were established on the basis of comprehensive spectroscopic data analysis and comparison with published NMR data, and their absolute configurations were further confirmed by experimental ECD data and single crystal X-ray diffraction analysis. The structures of compounds 5-8 contained a chlorine atom substituted at C-3. Compounds 1 and 12 are a pair of epimers isomerized at C-24 and C-25, while compounds 9 and 16 are isomerized at C-1, C-7, C-24, and C-25. Next, the hepatoprotective effect of all the isolates was evaluated on tert-butyl hydroperoxide (t-BHP)-injured AML12 hepatocytes. Compounds 5-11 and 16 significantly enhanced cell viability. Compound 8 decreased reactive oxygen species accumulation and increased glutathione level in t-BHP injured AML12 hepatocytes through promoting nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2).

Taccachatrones A-G, Highly Oxidized Steroids from the Rhizomes of Tacca chantrierii and Their Cytotoxicity Assessment.

Seven highly oxidized steroids, taccachatrones A-G (1-7), together with four known taccalonolides (8-11), were characterized from the rhizomes of Tacca chantrieri. The structures of 1-7 were established on the basis of spectroscopic data analysis, while the absolute configurations were determined by single-crystal X-ray diffraction. Compounds 1-4 may be derived from taccalonolide derivatives by the degradation of three carbon atoms. Compounds 7, 8, 10, and 11 exhibited cytotoxicity to human cancer cell lines, indicating that the presence of a lactone moiety, as well as a double bond between C-22 and C-23, might play key roles in mediating their cytotoxicity.

Taccalonolide Microtubule Stabilizers.

Microtubule stabilizers are a mainstay in the treatment of many solid cancers and continue to find utility in combination therapy with molecularly targeted anticancer agents and immunotherapeutics. However, innate and acquired resistance to microtubule stabilizers can limit their clinical efficacy. The taccalonolides are a unique class of microtubule stabilizers isolated from plants of Tacca that circumvent clinically relevant mechanisms of drug resistance. Although initial reports suggested that the microtubule-stabilizing activity of the taccalonolides was independent of direct tubulin binding, additional studies have identified that potent C-22, C-23 epoxidized taccalonolides covalently bind the Aspartate 226 residue of ß-tubulin and that this interaction is critical for their microtubule-stabilizing activity. The taccalonolides have distinct properties as compared to other microtubule stabilizers with regard to their biochemical effects on tubulin structure and dynamics that promote distinct cellular phenotypes. Some taccalonolides have demonstrated in vivo antitumor efficacy in drug-resistant tumor models with exquisite potency and long-lasting antitumor efficacy as a result of their irreversible target engagement. The recent identification of a site on the taccalonolide scaffold that is amenable to modification has provided evidence of the specificity of the taccalonolide-tubulin interaction. This also affords an opportunity to further optimize the targeted delivery of the taccalonolides to further improve their anticancer efficacy and potential for clinical development.

Neuroprotective and Anti-inflammatory Ditetrahydrofuran-Containing Diarylheptanoids from Tacca chantrieri.

Three new dimeric diarylheptanoids, taccachanfurans A-C (1-3), a new monomeric diarylheptanoid, taccachannoid A (4), and four known diarylheptanoids (5-8) were isolated from the EtOH extract of the rhizomes of Tacca chantrieri. Their structures were established on the basis of comprehensive spectroscopic data analysis. The absolute configuration of taccachanfuran A (1) was confirmed by single-crystal X-ray diffraction. All the diarylheptanoid dimers contain a ditetrahydrofuran moiety, which has not been described previously for diarylheptanoid compounds. A plausible biosynthetic pathway for the diarylheptanoid dimers is proposed. Compounds 2-4 showed significant neuroprotective activity against Aß25-35-induced damage in SH-SY5Y cells at the concentrations of 10 and 1 µM. Compounds 3, 4, 6, 7, and 8 showed anti-inflammatory activity in LPS-stimulated murine microglial BV-2 cells at the concentrations of 10 and 1 µM.

Saponins isolated from Schizocapsa plantaginea inhibit human hepatocellular carcinoma cell growth in vivo and in vitro via mitogen-activated protein kinase signaling.

The underground cane of Schizocapsa plantaginea (Hance) has long been used by Chinese ethnic minority as a constituent of anti-cancer formulae. Saponins are abundant secondary metabolic products located in the underground cane of this plant. The potential therapeutic effects of total saponins isolated from Schizocapsa plantaginea (Hance) (SSPH) on human hepatocellular carcinoma (HCC) were tested in vitro in human liver cancer cell lines, SMMC-7721 and Bel-7404. Apoptosis and cell cycle arrest were determined using flow cytometry, caspase activation was determined by ELISA, and PARP, cleaved PARP, mitogen-activated protein kinase (MAPK) expression and phosphorylation were measured using Western blotting analysis. In vivo anti-HCC effects of SSPH were verified in nude mouse xenograft model. SSPH exerted markedly inhibitory effect on HCC cell proliferation in time- and concentration-dependent manner. Moreover, SSPH significantly induced apoptosis through caspase-dependent signaling and arrested cell cycle at G2/M phase. These anti-proliferation effects of SSPH were associated with up-regulated phosphorylation of extracellular signal-regulated kinase-1/2 (Erk1/2) and c-jun-NH2-kinase-1/2 (JNK1/2) and reduced phosphorylation of p38MAPK. Furthermore, inhibitors of ERK, UO126, and JNK, SP600125 inhibited the anti-proliferation effects by SSPH, suggesting that Erk and JNK were the effector molecules in SSPH induced anti-proliferative action. During in vivo experiments, SSPH was found to inhibit xenograft tumor growth in nude mice, with a similar mechanism in vitro. Our study confirmed that SSPH exerted antagonistic effects on human liver cancer cells both in vitro and in vivo. Molecular mechanisms underlying SSPH action might be closely associated with MAPK signaling pathways. These results indicated that SSPH has potential therapeutic effects on HCC.

Taccalonolide Microtubule Stabilizers Generated Using Semisynthesis Define the Effects of Mono Acyloxy Moieties at C-7 or C-15 and Disubstitutions at C-7 and C-25.

The taccalonolides are a unique class of microtubule stabilizers isolated from Tacca spp. that have efficacy against drug-resistant tumors. Our previous studies have demonstrated that a C-15 acetoxy taccalonolide, AF, has superior in vivo antitumor efficacy compared to AJ, which bears a C-15 hydroxy group. With the goal of further improving the in vivo efficacy of this class of compounds, we semisynthesized and tested the biological activities of 28 new taccalonolides with monosubstitutions at C-7 or C-15 or disubstitutions at C-7 and C-25, covering a comprehensive range of substituents from formic acid to anthraquinone-2-carbonyl chloride. The resulting taccalonolide analogues with diverse C-7/C-15/C-25 modifications exhibited IC50 values from 2.4 nM to >20 µM, allowing for extensive in vitro structure-activity evaluations. This semisynthetic strategy was unable to provide a taccalonolide with improved therapeutic window due to hydrolysis of substituents at C-7 or C-15 regardless of size or steric bulk. However, two of the most potent new taccalonolides, bearing isovalerate modifications at C-7 or C-15, demonstrated potent and highly persistent antitumor activity in a drug-resistant xenograft model when administered intratumorally. This study demonstrates that targeted delivery of the taccalonolides to the tumor could be an effective, long-lasting approach to treat drug-resistant tumors.

Taccaoside induces apoptosis in hepatocellular carcinoma cell lines.

Objective Taccaoside, a steroidal saponin, has been shown to be cytotoxic, although the mechanism of cytotoxicity remains unclear. This study examined the effect of taccaoside on the human hepatocellular carcinoma (HCC) cell lines SMMC-7721 and Bel-7404. Methods The antiproliferative effect of taccaoside were measured using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. Cells were stained with Hoechst 33258 to observe morphology. Cell cycle and apoptosis were analysed by flow cytometry. Caspase activation was detected using specific assays, and PARP, Bax and Bcl-2 expression were analysed using western blotting. Results Taccaoside showed antiproliferative effect on HCC cell lines growth in a concentration- and time-dependent manner. Taccaoside arrested cell cycle in the G2/M phase and induced caspase-dependent apoptosis. Western blotting indicated that taccaoside upregulated Bax expression and downregulated Bcl-2 expression. PARP cleavage was observed following taccaoside treatment. Conclusions This study showed that taccaoside may inhibit HCC cell proliferation by inducing apoptosis.

Antitrypanosomal Activity of a Novel Taccalonolide from the Tubers of Tacca leontopetaloides.

INTRODUCTION: Several taccalonolides with various bioactivities have been isolated from Tacca species but no studies to isolate taccalonolides with anti-trypanosomal activity from Tacca leontopetaloides have been reported. OBJECTIVES: To analyse extracts of the roots of Tacca leontopetaloides, purify the extracts by column chromatography and identify isolated compounds by spectroscopic methods. The compounds and fractions will be tested for antitrypanosomal activity in vitro against Trypanosoma brucei brucei. MATERIAL AND METHODS: Dried roots or tubers of Tacca leontopetaloides, chromatographic separation and spectroscopic identification. RESULTS: A novel taccalonolide A propanoate and some known taccalonolides were isolated and their structures were determined by NMR and mass spectrometry CONCLUSION: Several taccalonolides were isolated from Tacca leontopetaloides and were found to have in vitro antitrypanosomal activity against Trypanosoma brucei brucei and EC50 values for the isolated compounds were from 0.79 µg/mL. Copyright © 2016 John Wiley & Sons, Ltd.

Spirostanol saponins from Tacca vietnamensis and their anti-inflammatory activity.

Using various chromatographic methods, five new steroidal saponins named taccavietnamosides A-E (1-5) and three known, (24S,25R)-spirost-5-en-3ß,24-diol 3-O-α-l-rhamnopyranosyl-(1→2)-[α-l-rhamnopyranosyl-(1→3)]-ß-d-glucopyranoside (6), (24S,25R)-spirost-5-en-3ß,24-diol 3-O-α-l-rhamnopyranosyl-(1→2)-[ß-d-glucopyranosyl-(1→4)-α-l-rhamnopyranosyl-(1→3)]-ß-d-glucopyranoside (7), and chantrieroside A (8) were isolated from the rhizomes of Tacca vietnamensis Thin et Hoat. Their chemical structures were elucidated by physical and chemical methods. All compounds were evaluated for the inhibitory activities of nitric oxide production in LPS-stimulated RAW 264.7 macrophages and BV2 cells. As the results, compounds 3-5 showed moderate inhibition on NO production in LPS-stimulated BV2 cells and RAW 264.7 macrophages with the IC50 values ranging from 37.0 to 60.7µM.

Steroidal Glucosides from the Rhizomes of Tacca chantrieri and Their Inhibitory Activities of NO Production in BV2 Cells.

Two new steroidal glucosides, chantriolides D and E (1 and 2), along with four known compounds, chantriolide A (3), chantriolide B (4), chantriolide C (5), and (25S)-spirost-5-en-3-ol 3-O-α-L-rhamnopyranosyl-(1-->2)-O-[α-L-rhamnopyranosyl-(1-->3)]-ß-D-glucopyranoside (6) were isolated from the rhizomes of Tacca chantrieri. Their structures were determined by 1D and 2D NMR spectroscopic and HR-ESI-MS data, as well as by comparison with reported data. Compounds 1 and 2 were found to show strong inhibitory NO effect in BV2 cells, with IC50 values of 12.45 and 59.03 µM, respectively.

Bioactive spirostane glycosides from Tacca plantaginea.

Eight new spirostane glycosides, taccaosides E-L (2-7, 11, and 14), along with 7 known spirostane glycosides were isolated from the extract of the whole plants of Tacca plantaginea (Hance) Drenth. Their structures were established on the basis of physical data, spectroscopic analysis (MS, 1D and 2D NMR), and chemical methods. The cytotoxicities of the isolates were evaluated in vitro against two human cancer cell lines (HEK293 and HepG2). The results showed that compound 1 had the strongest cytotoxic activity with IC50 values of 1.7 µM and 1.2 µM against the two cancer cell lines, respectively. Furthermore, the spirostane glycosides with 17α-hydroxyl group at their aglycones (10, 12, and 15) were tested for the induced platelet aggregation activity.

The protective effect of Trillin LPS-induced acute lung injury by the regulations of inflammation and oxidative state.

Inflammation response and oxidative stress have been reported to be involved in the pathogenesis of acute lung injury (ALI). Accordingly, anti-inflammatory treatment is proposed to be a possible efficient therapeutic strategy for ALI. The purpose of our present study was to evaluate the anti-inflammatory efficacy of trillin (Tr) on ALI induced by lipopolysaccharide (LPS) in mice and explore the underlying mechanism. BALB/c mice received Tr (50, 100 mg/kg) intraperitoneally 1 h prior to the intratracheal instillation of lipopolysaccharide (LPS) challenge. Pretreatment with Tr at the dose of 50, 100 mg/kg markedly ameliorated lung wet-to-dry weight (W/D) ratio, myeloperoxidase (MPO) activity and pulmonary histopathological conditions. In addition, the protective efficacy of Tr might be attributed to the down-regulations of neutrophil infiltration, malondialdehyde (MDA), inflammatory cytokines and the up-regulations of super-oxide dismutase (SOD), catalase(CAT), glutathione(GSH), Glutathione Peroxidase(GSH-Px) in bronchoalveolar lavage fluid (BALF). Meanwhile, our study revealed some correlations between (NF-E2-related factor 2) Nrf2/heme oxygenase (HO)-1/nuclear factor-kappa B (NF-κB) pathways and the beneficial effect of Tr, as evidenced by the significant up-regulations of HO-1 and Nrf2 protein expressions as well as the down-regulations of p-NF-κB and p-inhibitor of NF-κB (IκB) in lung tissues. Taken together, our results indicated that Tr exhibited protective effect on LPS-induced ALI by the regulations of related inflammatory events via the activations of Nrf2, HO-1 and NF-κB pathway. The current study indicated that Tr could be a potentially effective candidate medicine for the treatment of ALI.

[Discovery of Novel Biologically Active Compounds of Natural Origin, with a Focus on Anti-tumor Activity].

Numerous clinically valuable medicines, including anticancer drugs, have been developed from biologically active natural compounds and their structurally related derivatives. This review discusses novel natural compounds with promising biological activities and those with novel chemical structures. Glaziovianin A, an isoflavone isolated from the leaves of Ateleia glazioviana (Legminosae), inhibited cell cycle progression at the M-phase with an abnormal spindle structure. AU-1 and YG-1, 5ß-steroidal glycosides isolated from the whole plants of Agave utahensis and the underground parts of Yucca glauca (Agavaceae), induced apoptosis of HL-60 cells via caspase-3 activation. Lycolicidinol, an alkaloid isolated from the bulbs of Lycoris albiflora (Amaryllidaceae), induced transient autophagy and morphological changes in mitochondria in the early stage of the apoptotic cell death process in HSC-2 cells. Taccasterosides isolated from the rhizomes of Tacca chantrieri (Taccaceae) and stryphnosides isolated from the pericarps of Stryphnodendron fissuratum (Legminosae) are steroidal and triterpene glycosides with unique chemical structures having novel sugar sequences.

Plantagiolides K-N, three new withanolides and one withanolide glucoside from Tacca plantaginea.

Phytochemical investigation of the whole plants of Tacca plantaginea led to the isolation of 3 new withanolides and one new withanolide glucoside, named plantagiolides K-N (1-4), together with one known withanolide, 4 known withanolide glucosides, and 2 known taccalonolides. Their structures were elucidated by extensive spectroscopic analysis. Compound 4 is the first withanolide glycoside which the sugar moiety is attached at C-7. The effects of the some of isolates on TNFα-induced NF-κB transcriptional activity and cytotoxicity were evaluated.

Cytotoxic taccalonolides and withanolides from Tacca chantrieri.

Six new taccalonolides, taccalonolides AT-AY (1-6), and two new withanolides, chantriolides D and E (7 and 8), together with ten known compounds (9-18), have been isolated from whole plants of Tacca chantrieri. The structures, including the absolute configurations of some of the compounds, were determined by spectroscopic and chemical methods. All compounds were evaluated for their in vitro cytotoxicity against five tumor cell lines. Compounds 9, 10, 13-15, and 17 exhibited cytotoxic activity, with IC50 values of 1.13-5.71 µM, while compound 7 showed selective cytotoxicity. The results indicated that taccalonolides with a six-membered lactone moiety located at C-15 and C-24 were devoid of cytotoxicity against five tumor cell lines (> 10 µM).

Synthetic reactions with rare taccalonolides reveal the value of C-22,23 epoxidation for microtubule stabilizing potency.

The taccalonolides are microtubule stabilizers isolated from plants of the genus Tacca. Taccalonolide AF is 231 times more potent than the major metabolite taccalonolide A and differs only by the oxidation of the C-22,23 double bond in A to an epoxy group in AF. In the current study, 10 other rare natural taccalonolides were epoxidized and in each case epoxidation improved potency. The epoxidation products of taccalonolide T and AI were the most potent, with IC50 values of 0.43 and 0.88 nM, respectively. These potent taccalonolides retained microtubule stabilizing effects, and T-epoxide demonstrated antitumor effects in a xenograft model of breast cancer. Additional reactions demonstrated that reduction of the C-6 ketone resulted in an inactive taccalonolide and that C-22,23 epoxidation restored its activity. These studies confirm the value of C-22,23 epoxidation as an effective strategy for increasing the potency of a wide range of structurally diverse taccalonolide microtubule stabilizers.

Structure-activity relationships of retro-dihydrochalcones isolated from Tacca sp.

Several biologically active compounds have been identified from Tacca species, including glycosides, diarylheptanoids, saponins, withanolides, and the taccalonolide class of microtubule stabilizers. More recently, two cytotoxic retro-dihydrochalcones named evelynin A (7) and taccabulin A (6) were isolated and their biological activities characterized, including the finding that taccabulin has microtubule destabilizing effects. Here we describe the identification and characterization of five new retro-chalcones, named taccabulins B-E (1-4) and evelynin B (5) from Tacca sp. extracts. Their structures were determined using 1D and 2D NMR as well as mass spectroscopic data and modeled into the colchicine binding site of tubulin. The antiproliferative and microtubule effects of each compound were determined experimentally and found to be well correlated with modeling studies. The isolation and biological characterization of several retro-dihydrochalcones facilitated preliminary structure-activity relationships for this compound class concerning its antiproliferative and microtubule depolymerizing activities.

The bat flower: a source of microtubule-destabilizing and -stabilizing compounds with synergistic antiproliferative actions.

The biosynthesis of secondary metabolites provides higher plants with mechanisms of defense against microbes, insects, and herbivores. One common cellular target of these molecules is the highly conserved microtubule cytoskeleton, and microtubule-targeting compounds with insecticidal, antifungal, nematicidal, and anticancer activities have been identified from plants. A new retro-dihydrochalcone, taccabulin A, with microtubule-destabilizing activity has been identified from the roots and rhizomes of Tacca species. This finding is notable because the microtubule-stabilizing taccalonolides are also isolated from these sources. This is the first report of an organism producing compounds with both microtubule-stabilizing and -destabilizing activities. A two-step chemical synthesis of taccabulin A was performed. Mechanistic studies showed that taccabulin A binds within the colchicine site on tubulin and has synergistic antiproliferative effects against cancer cells when combined with a taccalonolide, which binds to a different site on tubulin. Taccabulin A is effective in cells that are resistant to many other plant-derived compounds. The discovery of a natural source that contains both microtubule-stabilizing and -destabilizing small molecules is unprecedented and suggests that the synergistic action of these compounds was exploited by nature long before it was discovered in the laboratory.