Inhibition of cellular proliferation by diterpenes, topoisomerase II inhibitor

The Role of Ingenane Diterpenes in Cancer Therapy: From Bioactive Secondary Compounds to Small Molecules

Diterpenes are a class of critical taxonomic markers of the Euphorbiaceae family, representing small compounds (eg, molecules) with a wide range of biological activities and multi-target therapeutic potential. Diterpenes can exert different activities, including antitumor and multi-drug resistance-reversing activities, and antiviral, immunomodulatory, and anti-inflammatory effects, mainly due to their great structural diversity. In particular, one polycyclic skeleton has been highlighted: ingenane. Besides this natural diterpene, promising polycyclic skeletons may be submitted to chemical modification—by in silico approaches, chemical reactions, or biotransformation—putatively providing more active analogs (eg, ingenol derivatives), which are currently under pre-clinical investigation. This review outlines the current mechanisms of action and potential therapeutic implications of ingenol diterpenes as small cancer molecules.

Therapeutic Effects of Methanol Extract from Euphorbia kansui Radix on Imiquimod-Induced Psoriasis

The roots of Euphorbia kansui, which belong to the family Euphorbiaceae, have been used as a traditional medicine for the treatment of various diseases such as diabetes, ascites, and leukemia. Recently, it was reported that the methylene chloride fraction of E. kansui radix (EKC) regulated the differentiation of Th17 cells and alleviated the symptoms of Th17-related inflammatory bowel disease. Imiquimod (IMQ), a TLR7/8 agonist, has been used to induce psoriasis in a mouse model. In this study, we evaluated the effect of EKC in an IMQ-induced psoriasis model. EKC effectively inhibited the production of interleukin-17A and interferon-γ in vitro. On this basis, EKC was administered to an animal model of psoriasis. Acanthosis and the infiltration of inflammatory cells into the dermis were significantly reduced by EKC. EKC also inhibited the expression of IL-17A, IL-22, IL-23, IL-12, and RAR-related orphan receptor gamma t (RORγt) in the spleen, skin-draining lymph nodes, and the skin. Additionally, EKC inhibited the activity of dendritic cells but not that of keratinocytes. In conclusion, EKC ameliorated the symptoms of psoriasis through inhibition of Th17 differentiation and activation of dendritic cells. These effects are expected to be beneficial in the treatment and prevention of psoriasis.

EVALUATION OF ANTICANCER POTENTIAL OF EIGHT VEGETAL SPECIES FROM THE STATE OF OAXACA

Background:

Eight plant species from Oaxaca, some of them used in traditional medicine, were subjected to screening of several biological activities to provide data regarding their anticancer potential, although no scientific information is available about their pharmacological effects.

Materials and methods:

Methanol extracts from stems or roots of the eight plants were tested for antioxidant activity by the DPPH- method. Antimicrobial activity was determined using the agar diffusion method and the minimal inhibitory concentration (MIC) was obtained by broth dilution method. Antitopoisomerase activity was assessed using mutant strains of Saccharomyces cerevisiae JN362a, JN394, JN394t_-1, JN394t₂.₄ and JN394t_2-5. The mutagenic activity was evaluated using the Ames test (Salmonella typhimurium TA1535).

Results:

No extract showed significant antioxidant activity. The best antimicrobial activity was observed for Salpianthus arenarius (MIC 56.25 μg/mL) and Lantana achyranthifolia (MIC 78.12 μg/mL) against Staphylococcus aureus. Extracts of Acalypha cuspidata, Alloispermum integrifolium and L. achyranthifolia stems showed antitopoisomerase II activity with JN394_t-1 growth of -30.88±0.0%, -38.11±4.95%, and -70.97±12.02% respectively. Galium mexicanum stem extract showed antitopoisomerase I activity with growth of 35.31±6.36% on the same mutant strain. All plant extracts were non-mutagenic. Fractionation of A. cuspidata extract led to identification of two subfractions with antitopoisomerase I and II activity at 154μg/mL (Positive controls 50 and 100μg/mL).

Conclusion:

Methanol extracts of A. cuspidata, A. integrifolium, G. mexicanum, and L. achyranthifolia stems showed antitopoisomerase and non-mutagenic activities, and consequently could be promising as a source of anticancer drugs.

Comparative study of the cytotoxicity and genotoxicity of kaurenoic acid and its semi-synthetic derivatives methoxy kaurenoic acid and kaurenol in CHO-K1 cells

The diterpene kaurenoic acid (KA) has vasorelaxant, antimicrobial, anti-tumoural and anti-leishmanial effects. Semi-synthetic derivatives were obtained to achieve more satisfactory responses. The assessment of genotoxicity is part of the toxicological evaluation of therapeutic compound candidates. The present study investigated the cytotoxicity and genotoxicity of KA and its semi-synthetic derivatives methoxy kaurenoic acid (MKA) and kaurenol (KRN) using the CHO-K1 cell line. The cytotoxicity evaluation demonstrated that treatments with 200 and 400 μM KA reduced cellular proliferation to 36.5 and 4.43%, respectively, and that 100 and 200 μM KA reduced the survival fraction (SF) to 48.1 and 5.5%, respectively. MKA and KRN at concentrations of 400 μM reduced proliferation to 81 and 86.8%, respectively, while 100 and 200 μM KRN reduced the SF to 50%, and 200 μM MKA reduced the SF to 74%. No genotoxicity was observed for KA or MKA. However, 100 μM KRN increased the DNA damage index, as detected by comet assay, although a micronucleus assay did not confirm these data. The results demonstrated that KA and its semi-synthetic derivative MKA were not genotoxic when tested at noncytotoxic concentrations, but KRN was genotoxic at the highest concentration that was tested, as demonstrated by the comet assay.

Therapeutic Potential of Essential Oils Focusing on Diterpenes

Among all plant derivates, essential oils (EOs) have gained the attention of many scientists. Diterpenes, a family of components present in some EO, are becoming a milestone in the EOs world. The goal of this review is to describe a scenario of diterpenes taking into health-consumption deportment. Previous studies revealed that diterpenes have antioxidant, antimicrobial, antiviral, antiprotozoal, cytotoxic, anticancer, antigenotoxic, antimutagenic, chemopreventive, antiinflammatory, antinociceptive, immunostimulatory, organoprotective, antidiabetic, lipid-lowering, antiallergic, antiplatelet, antithrombotic, and antitoxin activities. In conclusion, diterpenes may be an immense featuring concern in pharmaceutical consumption from a drug discovery point of view. Copyright © 2016 John Wiley & Sons, Ltd.

The Chemical and Biological Properties of Euphorbia kansui

Kansui, the root of Euphorbia kansui T.N. Liou ex T.P. Wang, is a well-known traditional Chinese medicine. This paper reviews advances in investigations of the botany, the phytochemistry, the analytical method, the pharmacology and the toxicology of kansui. Nearly 100 compounds have been isolated from kansui and identified, and diterpenes and triterpenes are considered to be the characteristic and bio-active constituents of kansui. They possess multiple pharmacological activities, including diuretic, purgation, and antitumor effects. However, they also have a degree of toxicity, and can cause skin, oral, and gastrointestinal irritation. In this paper, the toxicity-efficacy relationship, attenuation and incompatibility of kansui are further discussed. Several future investigations of kansui are also proposed, all of which would improve the identification of kansui and other toxic herbs, as well as further their utilization.

Ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry analysis of the impact of processing on toxic components of Kansui Radix

BACKGROUND

Kansui Radix (Gansui in Chinese), the dried tuber of Euphorbia kansui, is a Chinese medicinal herb commonly used for the treatment of oedema and ascites with dyspnea. Because of its toxic nature, the herb is usually processed with vinegar to reduce the toxicity. A report has shown that the contents of toxic terpenoids in Gansui decreased after processing with vinegar. However, comprehensive comparison of the chemical profiles between vinegar-processed and raw Gansui has not yet been conducted.

METHODS

An ultra-high-performance liquid chromatography in conjunction with ultra-high resolution quadrupole time-of-flight mass spectrometry (UHPLC UHD Q-TOF MS/MS) method was developed for the analysis of chemical profiles of vinegar-processed and raw Gansui in this study.

RESULTS

Results showed that processing with vinegar caused conspicuous chemical changes. Among the altered components, 11 toxic terpenoids, 3-O-benzoyl-13-O- dodecanoylingenol/20-O-benzoyl-13-O-dodecanoylingenol, kansuinine D, kansuinine A, 3-O-benzoyl-13-O-dodecanoylingenol/20-O-benzoyl-13-O-dodecanoylingenol, 3-O- benzoylingenol/20-O-benzoylingenol, 20-O-(2'E,4'Z-decadienoyl)ingenol/20-O-(2'E,4'E- decadienoyl)ingenol/3-O-(2'E,4'Z-decadienoyl)ingenol/3-O-(2'E,4'E-decadienoyl)ingenol, 3-O-(2'E,4'Z-decadienoyl)-20-deoxyingenol,3-O-(2'E,4'Z-,ecadienoyl)-5-O-acetylingenol,3-O-(2'E,4'Z-decadienoyl)-20-O-acetylingenol,3-O-(2,3-dimethylbutanoyl)-13-O-dodecanoylingenol, were tentatively identified. The contents of most of these terpenoids were obviously decreased after processing with reductions of 6.66-95.25%.

CONCLUSION

Our findings could help us understand the chemical basis for the toxicity reduction of Gansui afforded by processing with vinegar. Further investigations are warranted to establish the relationship between processing-induced chemical changes and the reduction of toxicity of Gansui.

3-O-(2'E,4'Z-decadienoyl)-20-O-acetylingenol induces apoptosis in intestinal epithelial cells of rats via mitochondrial pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia kansui is a traditional Chinese medicine widely used for the treatment of edema, ascite and asthma in China for centuries. However, its serious gastrointestinal toxicity restricted its safe clinical application. 3-O-(2'E,4'Z-decadienoyl)-20-O-acetylingenol (3EZ,20Ac-ingenol), a diterpenoid compound derived from kansui, has obvious gastrointestinal cytotoxicity in cells. Until now, its gastrointestinal cytotoxic mechanism is mostly unknown. This study focused on elucidating the cytotoxic mechanism of 3EZ,20Ac-ingenol in intestinal epithelial cells of rats (IEC-6 cells) to guide safer application of this herb in clinic.

MATERIALS AND METHODS

3EZ,20Ac-ingenol was isolated from the EtOAc extract of kansui. Cell morphology was detected by inverted phase contrast microscope and transmission electron microscope (TEM). Cell apoptosis was examined by Annexin V-FITC/PI dual-staining or Hoechst staining. ROS generation was detected with DCFH-DA staining by laser scanning confocal microscope. MMP change was examined with JC-1 staining by high content screening (HCS). Further, the release of cytochrome c, the expressions of Bax, Bcl-2, AIF and Apaf-1 were analyzed by western blot and the activities of caspase-3, 8, 9 were determined by ELISA. Additionally, cell cycle analysis was performed to detect the effects of 3EZ,20Ac-ingenol on cell cycle in IEC-6 cells by flow cytometry.

RESULTS

The study showed that 3EZ,20Ac-ingenol significantly reduced IEC-6 cells viability in a dose-dependent manner and the IC50 value was 5.74 μg/mL. Consistently, 3EZ,20Ac-ingenol could elevate reactive oxygen species (ROS), disrupt mitochondrial membrane potential (MMP), induce the release of cytochrome c from mitochondria to cytosol, enhance the expressions of Bax, AIF and Apaf-1, suppress the expression of Bcl-2, then activate caspase-3, 8, 9 cascade, and subsequently result in apoptosis. Additionally, 3EZ,20Ac-ingenol also could cause G2/M phase arrest in IEC-6 cells.

CONCLUSIONS

The results indicated that 3EZ,20Ac-ingenol induced the cytotoxicity of IEC-6 cells depends on induction of cell apoptosis via mitochondrial pathway and cell cycle arrest.

Cytotoxic and genotoxic effects of ethanolic extract of Euphorbia hyssopifolia L. on HepG2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia hyssopifolia L. is a weed with recognized antimicrobial potential employed in Indian, Asian and Latin-American popular medicine. However, little is known with regard to its toxic potential. The present study aimed to investigate the cytotoxic and genotoxic effects of ethanolic extract of E. hyssopifolia in HepG2 cell culture.

MATERIALS AND METHODS

Phytochemical screening of ethanolic extract was carried out to determine the presence of active secondary plant metabolites. Six concentrations (0.00001, 0.0001, 0.001, 0.01, 0.1 and 1.0mg/mL) of ethanolic extract were tested by the MTT assay to verify cytotoxicity. Then, genotoxic evaluations (alkaline comet assay and cytokinesis-block micronucleus assay - CBMN) were carried out in HepG2 cells with extract concentrations of 0.01, 0.1 and 1.0mg/mL.

RESULTS

Mono and sesquiterpenes, triterpenes and steroids, and flavonoids were the main classes found in the phytochemical screening. Extract concentrations used in the MTT assay showed no cytotoxic activity. On the other hand, genotoxic activity was verified at 0.1 and 1.0mg/mL in the alkaline comet assay. Additionally, the 1.0mg/mL concentration induced severe cell damage leading to death in the CBMN assay, indicating a cytotoxic effect for this concentration in the latter method.

CONCLUSION

The use of E. hyssopifolia extract for medicinal purposes should be avoided, because concentrations above 0.01mg/mL may pose risk to human health due to cytotoxic and/or genotoxic effects.

Recent Progress of Research on Herbal Products Used in Traditional Chinese Medicine: the Herbs belonging to The Divine Husbandman's Herbal Foundation Canon ( Shén Nóng Běn Cǎo Jīng)

This article will review selected herbal products from Chinese Materia Medica that are used in Traditional Chinese Medicine. The herbs come from the upper, middle, and lower class medicines as listed in The Divine Husbandman's Herbal Foundation Canon (神農本草經 Shén Nóng Běn Cǎo Jīng). The review will focus on the active constituents of the herbs and their bioactivities, with emphasis on the most recent progress in research for the period of 2003 to 2011.

Processing of kansui roots stir-baked with vinegar reduces kansui-induced hepatocyte cytotoxicity by decreasing the contents of toxic terpenoids and regulating the cell apoptosis pathway

Euphorbia kansui is a Traditional Chinese Medicine widely used for the treatment of oedema, ascites and asthma. However, its serious hepatotoxicity hinders its safe clinical application. The process of stir-baking with vinegar is regularly used to reduce the toxicity of kansui. Up till now, the exact mechanism of the reduction in hepatotoxicity of kansui stir-baked with vinegar has been poorly defined. In this study, decreased  contents of five diterpene and one triterpene in kansui (GS-1) after stir-baking with vinegar (GS-2) was investigated by UPLC-QTOF/MS. Flow cytometry and Hoechst staining were used to show that the stir-baking with vinegar process reduces kansui-induced cell apoptosis. Furthermore, the result also indicated that kansui stir-baked with vinegar protects LO2 cells from apoptosis by increasing the cell mitochondrial membrane potential (ΔΨm), decreasing the release of cytochrome c and inhibiting the activities of caspase-9 and caspase-3 as evidenced by means of high content screening (HCS), ELISA and western blotting. These results suggested that the stir-baking vinegar could reduce the hepatotoxicity of kansui by effectively decreasing the contents of toxic terpenoids and inhibiting the intrinsic pathway of hepatocyte cell apoptosis. In conclusion, the study provided significant data for promoting safer and better clinical use of this herb.

3EZ,20Ac-ingenol, a catalytic inhibitor of topoisomerases, downregulates p-Akt and induces DSBs and apoptosis of DT40 cells

We have previously reported that many ingenol compounds derived from Euphorbia kansui exhibit topoisomerase (topo) II inhibitory activity. Of these compounds, 3EZ,20Ac-ingenol inhibited topo I activity. Camptothecin, which inhibits the religation activity of topo I without interfering with the binding of topo I to DNA and induces topo I-mediated DNA cleavage, was used as a positive control. In this study, we found that 3EZ,20Ac-ingenol did not hamper the binding of topo I to DNA in the same manner as camptothecin but affected the inhibition of cleavage of one DNA strand. 3EZ,20Ac-ingenol inhibited cell proliferation by blocking cell cycle progression in the G2/M phase. To define the mechanism of inhibition of DT40 cell proliferation, the change in Akt activity was observed because Akt activity is regulated in response to DNA damage. Western blot analysis revealed that 3EZ,20Ac-ingenol downregulated the expression of p-Akt, and apoptosis was detected by the presence of DNA double-strand breaks and caspase 3 activation.

Bio-guided isolation of the cytotoxic terpenoids from the roots of Euphorbia kansui against human normal cell lines L-O2 and GES-1

The dried roots of Euphorbia kansui (kansui) have been used for centuries in China as a herbal medicine for edema, ascites, and asthma. The 95% ethanol extract showed a significant inhibition of cell proliferation against human normal cell lines L-O2 and GES-1. Bioassay-guided separation of the 95% ethanol extract from the roots of E. kansui led to the isolation of 12 diverse terpenoids whose structures were identified by ¹H, ¹³C NMR spectroscopy and ESI-MS as kansuinine A (1), kansuinine B (2), kansuinine C (3), kansuiphorin C (4), 3-O-(2′E,4′Z-decadienoyl)-20-O-acetylingenol (5), 3-O-(2′E,4′Edecadienoyl)-20-O-acetylingenol (6), 3-O-(2′E,4′Z-decadienoyl)-20-deoxyingenol (7), 3-O-benzoyl-20-deoxyingenol (8), 5-O-benzoyl-20-deoxyingenol (9), kansenone (10), epi-kansenone (11), euphol (12). All these 12 terpernoids were evaluated in vitro for cytotoxicity on L-O2 and GES-1 cell lines. Most ingenane-type diterpenoids and 8-ene-7-one triterpenoids (5–11) exhibited a relatively lower IC₅₀ value; therefore, these compounds had stronger cytotoxicity against human normal cell lines L-O2 and GES-1 with dose-dependent relationships. These results will be significantly helpful to reveal the mechanism of toxicity of kansui and to effectively guide safer clinical application of this herb.

Inhibition of topoisomerase II α activity and induction of apoptosis in mammalian cells by semi-synthetic andrographolide analogues

Topoisomerase II α enzyme plays a critical role in DNA replication process. It controls the topologic states of DNA during transcription and is essential for cell proliferation. Human DNA topoisomerase II α (hTopo II α) is a promising chemotherapeutic target for anticancer agents against a variety of cancer types. In the present study, andrographolide and its structurally modified analogues were investigated for their inhibitory activities on hTopo II α enzyme. Five out of nine andrographolide analogues potently reduced hTopo II α activity and inhibited cell proliferation in four mammalian cell lines (Hela, CHO, BCA-1 and HepG2 cells). IC50 values for cytotoxicity of analogues 3A.1, 3A.2, 3A.3, 1B and 2C were 4 to 7 μM. Structure-activity relationship studies revealed that both core structure of andrographolide and silicon based molecule of functional group were important for the inhibition of hTopo II α activity whereas position C-19 of analogues was required for anti-proliferation. In addition, the analogue 2C at 10 μM concentration inhibited hTopo II α, and induced apoptosis with nuclear fragmentation and formation of apoptotic bodies in HepG2 cells. The analogue 2C may, therefore, have a therapeutic potential as effective anticancer agent targeting the hTopo II α functions.

Analysis of inhibition of topoisomerase IIalpha and cancer cell proliferation by ingenolEZ

We previously reported that many ingenol compounds derived from Euphorbia kansui exhibit topoisomerase inhibitory activity and/or inhibitory activity of cell proliferation. The inhibitory effects of 20-O-(2'E,4'Z-decadienoyl) ingenol and 3-O-(2'E,4'Z-decadienoyl)-ingenol among these compounds on topoisomerase II activity and on the cell proliferative activity and arrest phase of the cell cycle were studied using a mouse breast cancer (MMT) cell line. Although 20-O-ingenolEZ exerted inhibitory effects on both topoisomerase II activity and cell proliferative activity, 3-O-ingenolEZ exerted inhibitory activity on neither. The 20-O-ingenolEZ-induced cell arrest of MMT-cell proliferation led to a cell cycle arrest in the G2/M phase. Topoisomerase II inhibition can be divided into the poison and catalytic inhibitor types. A checkpoint mechanism is activated when cells are treated with these topoisomerase II inhibitors. Poison-type inhibition occurs via induction of the DNA damage checkpoint and the catalytic-type inhibition occurs via induction of the DNA-decatenation checkpoint, suggestive of distinct checkpoint reactions. 20-O-ingenolEZ inhibited topoisomerase IIalpha activity through inhibition of ATPase, and induced DNA-decatenation checkpoint without signaling for phosphorylation of H2AX.

Secondary metabolites as DNA topoisomerase inhibitors: A new era towards designing of anticancer drugs

A large number of secondary metabolites like alkaloids, terpenoids, polyphenols and quinones are produced by the plants. These metabolites can be utilized as natural medicines for the reason that they inhibit the activity of DNA topoisomerase which are the clinical targets for anticancer drugs. DNA topoisomerases are the cellular enzymes that change the topological state of DNA through the breaking and rejoining of DNA strands. Synthetic drugs as inhibitors of topoisomerases have been developed and used in the clinical trials but severe side effects are a serious problem for them therefore, there is a need for the development of novel plant-derived natural drugs and their analogs which may serve as appropriate inhibitors with respect to drug designing. The theme for this review is how secondary metabolites or natural products inactivate the action of DNA topoisomerases and open new avenues towards isolation and characterization of compounds for the development of novel drugs with anticancer potential.

Bioassay-guided separation of the proinflammatory constituents from the roots of Euphorbia kansui

In view of the toxic inflammatory reaction induced by Euphorbia kansui roots, a traditional Chinese medicine used for the treatment of edema, ascites, and asthma, the 95% ethanol extract was found to have a significant stimulating effect on inflammatory cells. Bioassay-guided separation of the 95% ethanol extract from the roots of E. kansui led to the isolation of five diterpenoids whose structures were identified by (1)H, (13)C NMR spectroscopy and HR-ESI-MS as kansuinine B (1), kansuinine A (2), kansuiphorin C (3), 3-O-benzoyl-20-deoxyingenol (4), and 3-O-(2'E,4'Z-decadienoyl)-20-O-acetylingenol (5). The proinflammatory effect of compounds 1-5 was evaluated in vitro in models of inflammation using exoteric mice splenic lymphocytes (SPL) and rat peritoneal macrophages (PMphi). Compounds 1, 2, and 5 markedly promoted SPL proliferation and NO production by PMphi at concentrations from 0.78 to 12.50 microg/mL. Hence the three compounds are believed to be important proinflammatory components of the roots of E. kansui.