Nuclear factor kappaB-mediated down-regulation of adhesion molecules: possible mechanism for inhibitory activity of bigelovin against inflammatory monocytes adhesion to endothelial cells

Anticancer Targets and Signaling Pathways Activated by Britannin and Related Pseudoguaianolide Sesquiterpene Lactones

Sesquiterpene lactones (SLs) are abundant in plants and display a large spectrum of bioactivities. The compound britannin (BRT), found in different Inula species, is a pseudoguaianolide-type SL equipped with a typical and highly reactive α-methylene-γ-lactone moiety. The bioproperties of BRT and related pseudoguaianolide SLs, including helenalin, gaillardin, bigelovin and others, have been reviewed. Marked anticancer activities of BRT have been evidenced in vitro and in vivo with different tumor models. Three main mechanisms are implicated: (i) interference with the NFκB/ROS pathway, a mechanism common to many other SL monomers and dimers; (ii) blockade of the Keap1-Nrf2 pathway, with a covalent binding to a cysteine residue of Keap1 via the reactive α-methylene unit of BRT; (iii) a modulation of the c-Myc/HIF-1α signaling axis leading to a downregulation of the PD-1/PD-L1 immune checkpoint and activation of cytotoxic T lymphocytes. The non-specific reactivity of the α-methylene-γ-lactone moiety with the sulfhydryl groups of proteins is discussed. Options to reduce or abolish this reactivity have been proposed. Emphasis is placed on the capacity of BRT to modulate the tumor microenvironment and the immune-modulatory action of the natural product. The present review recapitulates the anticancer effects of BRT, some central concerns with SLs and discusses the implication of the PD1/PD-L1 checkpoint in its antitumor action.

Sesquiterpene lactone Bigelovin induces apoptosis of colon cancer cells through inducing IKK-β degradation and suppressing nuclear factor kappa B activation

Bigelovin, a sesquiterpene lactone extracted from plant Inula helianthus aquatica, exhibited multiple interesting biological activities, including anti-inflammation, antiangiogenesis and cytotoxic action against cancer cells. In the present study, we found that Bigelovin reduced the viability of human colon cancer cells and induced their apoptosis in a time- and dose-dependent manner, with an IC50-5 μM. RNAseq and luciferase reporter analyses revealed that the nuclear factor kappa B (NF-κB) signaling was one of the most significantly inhibited pathways after Bigelovin treatment. Further systemic examination showed that exposure to Bigelovin resulted in ubiquitination and degradation of inhibitor of kappa-B kinase-beta (IKK-β) and decrease of IκB-α and p65 phosphorylation, which led to the downregulation of NF-κB-regulated genes expression. Moreover, enforced expression of exogenous IKK-β attenuated Bigelovin-induced NF-κB suppression and cell viability reduction. These results indicated that Bigelovin exerts a cytotoxic action against colon cancer cells through the induction of IKK-β degradation and consequently the inhibition of NF-κB signaling. Given the abnormal activation of NF-κB signaling in colorectal cancer (CRC) cells and the critical role of chronic inflammation in CRC development, it is conceivable that at least some colorectal cancer cells are addictive to NF-κB activation and targeting the pathway is an effective anti-CRC strategy.

Natural small molecule bigelovin suppresses orthotopic colorectal tumor growth and inhibits colorectal cancer metastasis via IL6/STAT3 pathway

Bigelovin, a sesquiterpene lactone, has been demonstrated to induce apoptosis, inhibit inflammation and angiogenesis in vitro, but its potential anti-metastatic activity remains unclear. In the present study, two colon cancer mouse models, orthotopic tumor allografts and experimental metastatic models were utilized to investigate the progression and metastatic spread of colorectal cancer after bigelovin treatments. Results showed that bigelovin (intravenous injection; 0.3-3 mg/kg) significantly suppressed tumor growth and inhibited liver/lung metastasis with modulation of tumor microenvironment (e.g. increased populations of T lymphocytes and macrophages) in orthotopic colon tumor allograft-bearing mice. Furthermore, the inhibitory activities were also validated in the experimental human colon cancer metastatic mouse model. The underlying mechanisms involved in the anti-metastatic effects of bigelovin were then revealed in murine colon tumor cells colon 26-M01 and human colon cancer cells HCT116. Results showed that bigelovin induced cytotoxicity, inhibition of cell proliferation, motility and migration in both cell lines, which were through interfering IL6/STAT3 and cofilin pathways. Alternations of the key molecules including Rock, FAK, RhoA, Rac1/2/3 and N-cadherin, which were detected in bigelovin-treated cancer cells, were also observed in the tumor allografts of bigelovin-treated mice. These findings strongly indicated that bigelovin has potential to be developed as anti-tumor and anti-metastatic agent for colorectal cancer.

Bigelovin triggered apoptosis in colorectal cancer in vitro and in vivo via upregulating death receptor 5 and reactive oxidative species

Colorectal cancer (CRC) is the third most prevalent cancer and the third highest cancer-related mortality in the United States. Bigelovin, a sesquiterpene lactone isolated from Inula helianthus aquatica, has been proven to induce apoptosis and exhibit anti-inflammatory and anti-angiogenic activities. However, the effects of bigelovin on CRC and underlying mechanisms have not been explored. The present study demonstrated that bigelovin exhibited potent anti-tumor activities against CRC in vitro and in vivo. Bigelovin suppressed cell proliferation and colony formation and induced apoptosis in human colorectal cancer HT-29 and HCT 116 cells in vitro. Results also revealed that bigelovin activated caspases, caused the G2/M cell cycle arrest and induced DNA damage through up-regulation of death receptor (DR) 5 and increase of ROS. In HCT 116 xenograft model, bigelovin treatment resulted in suppression of tumor growth. Bigelovin at 20 mg/kg showed more significant tumor suppression and less side effects than conventional FOLFOX (containing folinic acid, 5-fluorouracil and oxaliplatin) treatment. In addition, in vivo data confirmed that anti-tumor activity of bigelovin in CRC was through induction of apoptosis by up-regulating DR5 and increasing ROS. In conclusion, these results strongly suggested that bigelovin has potential to be developed as therapeutic agent for CRC patients.

Positive effects of intermittent fasting in ischemic stroke

Intermittent fasting (IF) is a dietary protocol where energy restriction is induced by alternate periods of ad libitum feeding and fasting. Prophylactic intermittent fasting has been shown to extend lifespan and attenuate the progress and severity of age-related diseases such as cardiovascular (e.g. stroke and myocardial infarction), neurodegenerative (e.g. Alzheimer's disease and Parkinson's disease) and cancerous diseases in animal models. Stroke is the second leading cause of death, and lifestyle risk factors such as obesity and physical inactivity have been associated with elevated risks of stroke in humans. Recent studies have shown that prophylactic IF may mitigate tissue damage and neurological deficit following ischemic stroke by a mechanism(s) involving suppression of excitotoxicity, oxidative stress, inflammation and cell death pathways in animal stroke models. This review summarizes data supporting the potential hormesis mechanisms of prophylactic IF in animal models, and with a focus on findings from animal studies of prophylactic IF in stroke in our laboratory.

Metabolomic Profile of the Genus Inula

Plants have a long history as therapeutics in the treatment of human diseases and have been used as source of medicines for ages. Searching for new biologically active natural products, many plants and herbs are screened for natural products with pharmacological activities. In this field, the genus Inula, which comprises more than 100 species, several of them being used in traditional medicine, is very important, especially due to the finding that several of the isolated pure secondary metabolites proved to possess important biological activities. Inula species have been reported as rich sources of sesquiterpene lactones, including eudesmanes, germacranes, guaianes, and dimeric structures, and since 2006 ca. 400 secondary metabolites, including more than 100 new natural products, some of them with relevant pharmacological activities, have been identified. Herein, we critically compile and update the information regarding the types of secondary metabolites found in the genus Inula and the progress in their isolation.

Bigelovin inhibits STAT3 signaling by inactivating JAK2 and induces apoptosis in human cancer cells

AIM

To study the function and mechanism of bigelovin, a sesquiterpene lactone from the flower of Chinese herb Inula hupehensis, in regulating JAK2/STAT3 signaling and cancer cell growth.

METHODS

HepG2 cells stably transfected with the STAT3-responsive firefly luciferase reporter plasmid (HepG2/STAT3 cells), and a panel of human cancer cell lines were used to identify active compounds. Cell viability was measured using MTT assay. Western blotting was used to detect protein expression and phosphorylation. Kinase assays were performed and the reaction between bigelovin and thiol-containing compounds was analyzed with LC-MS.

RESULTS

Bigelovin (1-50 μmol/L) dose-dependently inhibited the IL-6-induced STAT3 activation in HepG2/STAT3 cells (IC50=3.37 μmol/L) and the constitutive STAT3 activation in A549 and MDA-MB-468 cells. Furthermore, bigelovin dose-dependently inhibited JAK2 phosphorylation in HeLa and MDA-MB-468 cells, as well as the enzymatic activity of JAK2 in vitro (IC50=44.24 μmol/L). Pretreatment of the cells with DTT (500 μmol/L) or GSH (500 μmol/L) eliminated the inhibitory effects of bigelovin on the IL-6-induced and the constitutive STAT3 activation. The results in LC-MS analysis suggested that bigelovin might react with cysteine residues of JAK2 leading to inactivation of JAK2. Bigelovin (5 and 20 μmol/L) had no effects on the signaling pathways of growth factors EGF, PDGF or insulin. Finally, bigelovin suppressed the cell viability and induced apoptosis in 10 different human cancer cell lines, particularly those with constitutively activated STAT3.

CONCLUSION

Bigelovin potently inhibits STAT3 signaling by inactivating JAK2, and induces apoptosis of a variety of human cancer cells in vitro.

The role of wogonin in controlling SOCS3 expression in neuronal cells

The mechanism underlying the wogonin-mediated increase in the expression of suppressor of cytokine signaling 3 (SOCS3) is unclear. Promoter deletion assay results revealed that wogonin-induced SOCS3 expression is dependent on the AP-1 consensus sequences and two STAT responsive elements (TTACAAGAA and TTCCAGGAA) in the 5'-flanking region of the SOCS3 gene in SH-SY5Y cells. Wogonin-induced SOCS3 expression was blocked by inhibitors of PI3K, Akt, Raf, p38, JNK, MEK, and STAT3, respectively. However, JAK2 inhibitors did not inhibit wogonin-induced SOCS3 expression. These results indicate that SOCS3-inducing effect of wogonin is caused by the activation of PI3K-mediated MAPK signaling pathways (Akt, ERK1/2, p38, and JNK), and the subsequent activation of AP-1 consensus sequences and STAT responsive elements in SH-SY5Y cells.

The genus Inula and their metabolites: from ethnopharmacological to medicinal uses

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Inula comprises more than one hundred species widespread in temperate regions of Europe and Asia. Uses of this genus as herbal medicines have been first recorded by the Greek and Roman ancient physicians. In the Chinese Pharmacopoeia, from the 20 Inula spp. distributed in China, three are used as Traditional Chinese medicines, named Tumuxiang, Xuanfuhua and Jinfeicao. These medicines are used as expectorants, antitussives, diaphoretics, antiemetics, and bactericides. Moreover, Inula helenium L. which is mentioned in Minoan, Mycenaean, Egyptian/Assyrian pharmacotherapy and Chilandar Medical Codex, is good to treat neoplasm, wound, freckles and dandruff. Many other Inula spp. are used in Ayurvedic and Tibetan traditional medicinal systems for the treatment of diseases such as bronchitis, diabetes, fever, hypertension and several types of inflammation. This review is a critical evaluation of the published data on the more relevant ethnopharmacological and medicinal uses of Inula spp. and on their metabolites biological activities. This study allows the identification of the ethnopharmacological knowledge of this genus and will provide insight into the emerging pharmacological applications of Inula spp. facilitating the prioritirization of future investigations. The corroboration of the ethnopharmacological applications described in the literature with proved biological activities of Inula spp. secondary metabolites will also be explored.

MATERIALS AND METHODS

The major scientific databases including ScienceDirect, Medline, Scopus and Web of Science were queried for information on the genus Inula using various keyword combinations, more than 180 papers and patents related to the genus Inula were consulted. The International Plant Name Index was also used to confirm the species names.

RESULTS

Although the benefits of Inula spp. are known for centuries, there are insufficient scientific studies to certify it. Most of the patents are registered by Chinese researchers, proving the traditional use of these plants in their country. Although a total of sixteen Inula species were reported in the literature to have ethnopharmacological applications, the species Inula cappa (Buch.-Ham. ex D.Don) DC., Inula racemosa Hook.f., Inula viscosa (L.) Aiton [actually the accepted name is Dittrichia viscosa (L.) Greuter], Inula helenium, Inula britannica L. and Inula japonica Thunb. are the most frequently cited ones since their ethnopharmacological applications are vast. They are used to treat a large spectrum of disorders, mainly respiratory, digestive, inflammatory, dermatological, cancer and microbial diseases. Fifteen Inula spp. crude extracts were investigated and showed interesting biological activities. From these, only 7 involved extracts of the reported spp. used in traditional medicine and 6 of these were studied to isolate the bioactive compounds. Furthermore, 90 bioactive compounds were isolated from 16 Inula spp. The characteristic compounds of the genus, sesquiterpene lactones, are involved in a network of biological effects, and in consequence, the majority of the experimental studies are focused on these products, especially on their cytotoxic and anti-inflammatory activities. The review shows the chemical composition of the genus Inula and presents the pharmacological effects proved by in vitro and in vivo experiments, namely the cytotoxic, anti-inflammatory (with focus on nitric oxide, arachidonic acid and NF-κB pathways), antimicrobial, antidiabetic and insecticidal activities.

CONCLUSIONS

Although there are ca. 100 species in the genus Inula, only a few species have been investigated so far. Eight of the sixteen Inula spp. with ethnopharmacological application had been subjected to biological evaluations and/or phytochemical studies. Despite Inula royleana DC. and Inula obtusifolia A. Kerner are being used in traditional medicine, as far as we are aware, these species were not subjected to phytochemical or pharmacological studies. The biological activities exhibited by the compounds isolated from Inula spp., mainly anti-inflammatory and cytotoxic, support some of the described ethnopharmacological applications. Sesquiterpene lactone derivatives were identified as the most studied class, being britannilactone derivatives the most active ones and present high potential as anti-inflammatory drugs, although, their pharmacological effects, dose-response relationship and toxicological investigations to assess potential for acute or chronic adverse effects should be further investigated. The experimental results are promising, but the precise mechanism of action, the compound or extract toxicity, and the dose to be administrated for an optimal effect need to be investigated. Also human trials (some preclinical studies proved to be remarkable) should be further investigated. The genus Inula comprises species useful not only in medicine but also in other domains which makes it a high value-added plant.

Small compound bigelovin exerts inhibitory effects and triggers proteolysis of E2F1 in multiple myeloma cells

Multiple myeloma (MM) is a currently incurable blood cancer. Here we tested the effects of a small compound bigelovin on MM cells, and reported that it caused cell cycle arrest and subsequently induced apoptosis. Bigelovin triggered proteolysis of E2F1, which could be inhibited by caspase inhibitor. To investigate the clinical relevance, the expression of E2F1 in MM specimens was tested, and the results showed that E2F1 was overexpressed in 25-57% of MM patients and was associated with higher International Staging System (ISS) stage. These results suggest that E2F1 may be important for MM pathogenesis, and bigelovin could serve as a lead compound for the development of E2F1 inhibitor.

Anti-angiogenesis and immunomodulatory activities of an anti-tumor sesquiterpene bigelovin isolated from Inula helianthus-aquatica

Bigelovin is a sesquiterpene lactone isolated from the plant Inula helianthus-aquatica which was traditionally used in cancer treatment in Yunnan, China. The potent apoptotic activities of bigelovin in human leukemia U937 cells were shown in our previous study. The present study investigated the anti-angiogenic and immunomodulatory effects of bigelovin using transgenic zebrafish Tg(fli1a:EGFP)y1 with fluorescent blood vessels and human peripheral blood mononuclear cells (PBMCs), respectively. Furthermore, the inhibitory activities of bigelovin on the human endothelial cell adhesion molecules (CAMs) were also examined. Our results showed that the growth of subintestinal vessels of the bigelovin-treated zebrafish embryos was significantly inhibited and the gene expressions in angiogenesis signaling pathways (e.g. Ang2 and Tie2) of the zebrafish were down-regulated after bigelovin treatment. Besides, the proliferation and Th1 cytokines productions (e.g. IFN-γ, IL-2 and IL-12) were suppressed in bigelovin-treated PBMCs. On the other hand, bigelovin was shown to significantly inhibit the human monocyte adhesion to human endothelial cells and the gene expressions of inflammation-related CAMs (e.g. ICAM-1, VCAM-1 and E-selectin) were significantly down-regulated in bigelovin-treated human endothelial cells. In summary, our data provide the first evidence that bigelovin possesses anti-angiogenic and immunomodulatory activities, suggesting bigelovin may exert multi-target functions against cancer in animal models.