Embelin

Embelin, a natural benzoquinone from plants of the genus Embelia, is an inhibitor of X-linked inhibitor of apoptosis protein (XIAP) with IC50 of 4.1 μM.
XIAP is a member of the inhibitor of apoptosis family of proteins. This protein modulates signaling pathways involved in cell apoptosis and stops cell apoptosis induced by viral infection or overproduction of caspases.
Embelin was shown to exhibit anti-tumor and anti-inflammatory activity in cells. For instance, embelin inhibits cell growth and activates caspases to promote apoptosis in cancer cells with high expression of XIAP [1]. Additionally, embelin was reported to prevent NF-κB activation by inhibiting IKK and thus resulted in suppression of NF-κB-regulated anti-apoptotic and metastatic gene expression [2].
Embelin has also been used extensively in various animal models to study the role of XIAP. In the azoxymethane/dextran sulfate sodium (AOM/DSS) induced colitis-associated cancer (CAC) model, embelin reduced both incidence and tumor size in mice by inhibiting proliferation of tumor epithelial cells and suppressing IL6 expression and IL6-activated STAT3 in vivo [3].
References
1.Nikolovska-Coleska Z, Xu L, Hu Z, Tomita Y, Li P, Roller PP, et al. Discovery of embelin as a cell-permeable, small-molecular weight inhibitor of XIAP through structure-based computational screening of a traditional herbal medicine three-dimensional structure database. J Med Chem 2004,47:2430-2440.
2.Ahn KS, Sethi G, Aggarwal BB. Embelin, an inhibitor of X chromosome-linked inhibitor-of-apoptosis protein, blocks nuclear factor-kappaB (NF-kappaB) signaling pathway leading to suppression of NF-kappaB-regulated antiapoptotic and metastatic gene products. Mol Pharmacol 2007,71:209-219.
3.Dai Y, Jiao H, Teng G, Wang W, Zhang R, Wang Y, et al. Embelin reduces colitis-associated tumorigenesis through limiting IL-6/STAT3 signaling. Mol Cancer Ther 2014,13:1206-1216.

The XIAP inhibitor Embelin enhances TRAIL-induced apoptosis in human leukemia cells by DR4 and DR5 upregulation.[Pubmed:25293521]

Tumour Biol. 2015 Feb;36(2):769-77.

The present study was designed to explore the effects of low-toxicity Embelin on TRAIL-induced apoptosis and its possible mechanism in human leukemia cells. Our study showed that low-toxicity Embelin enhanced TRAIL-induced apoptosis through DR4 and DR5 upregulation and caspase activation in HL-60 cells. Pan-caspase inhibitor Z-VAD-FMK inhibited cell apoptosis induced by TRAIL alone or combined with low-toxicity Embelin, which indicated the cytotoxic effect is mediated by caspase-dependent apoptosis. Although Embelin is an X chromosome-linked inhibitor-of-apoptosis protein (XIAP) inhibitor, an XIAP independent effect on cell death was detected in HL-60 cells exposed to low-toxicity Embelin and TRAIL. Low-toxicity Embelin upregulated DR4 and DR5 expression to enhance TRAIL-induced apoptosis. The sensitizing effects of Embelin on TRAIL-induced apoptosis were markedly attenuated when DR4/DR5 was knocked down. These data suggested that low-toxicity Embelin enhanced TRAIL-induced cell apoptosis through DR4 and DR5 upregulation, indicating that combination of low-toxicity Embelin and TRAIL may become as a potential antileukemia strategy.

Embelin sensitizes acute myeloid leukemia cells to TRAIL through XIAP inhibition and NF-kappaB inactivation.[Pubmed:25358405]

Cell Biochem Biophys. 2015 Jan;71(1):291-7.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) shows promising result in cancer therapy and induces apoptosis in a wide variety of tumor cells, without causing toxicity to normal cells. However, many tumor cells including acute myeloid leukemia (AML) showed certain degrees of resistance to TRAIL and the mechanism remains largely unknown. Embelin is a potent XIAP inhibitor which has been shown to inhibit the proliferation of tumor cells and cause cell apoptosis. In this study, we investigated the effects of Embelin on the TRAIL-induced apoptosis and the underlying mechanism. Here, we chose an adenovirus vector as the expression vector for TRAIL, which was named Ad-TRAIL. The results in vitro showed that the co-treatment of Embelin and Ad-TRAIL has synergistically suppressed the proliferation of AML cells. Embelin has the ability to enhance TRAIL-induced apoptosis and activate caspase pathway. More interestingly, we found that the underlying mechanism for these talent skills of Embelin is through reducing the TRAIL-mediated activation of NF-kappaB and decreasing its transcriptional activity. Furthermore, our results in vivo suggest that combined therapy of Embelin and Ad-TRAIL caused significant growth inhibition of HL-60 xenograft tumors. Our results suggested that Embelin could sensitize AML cell to TRAIL through the repression of NF-kappaB signal pathway in vitro and in vivo, and combined therapy of Ad-TRAIL and Embelin may be the attractive candidate for clinical application in treatment of AML.

Embelin inhibits pancreatic cancer progression by directly inducing cancer cell apoptosis and indirectly restricting IL-6 associated inflammatory and immune suppressive cells.[Pubmed:25128650]

Cancer Lett. 2014 Nov 28;354(2):407-16.

Pancreatic cancer is an aggressive malignancy and unresponsive to conventional chemotherapies. Here, the anti-inflammatory and anti-tumor effects of Embelin on pancreatic cancer were investigated. Embelin significantly attenuated cells invasion, proliferation and induced apoptosis through inhibition of STAT3 and activation of p53 signaling pathways. Embelin substantially reduced the tumorigenicity of pancreatic cancer cells in vivo, which was associated with reduced inflammatory cells and immune suppressive cells, IL-17A(+) Th17, GM-CSF(+) Th, MDSCs and Treg, through inhibition of IL-6 secretion. Moreover, Embelin decrease IL-6-induced STAT3 phosphorylation. In summary, Embelin represents a novel therapeutic drug candidate for the clinical treatment of pancreatic cancer.

Embelin inhibits TNF-alpha converting enzyme and cancer cell metastasis: molecular dynamics and experimental evidence.[Pubmed:25336399]

BMC Cancer. 2014 Oct 22;14:775.

BACKGROUND: Embelin, a quinone derivative, is found in the fruits of Embelia ribes Burm (Myrsinaceae). It has been shown to have a variety of therapeutic potentials including anthelmintic, anti-tumor, anti-diabetic, anti-bacterial and anti-inflammation. Inflammation is an immunological response to external harmful stimuli and is regulated by an endogenous pyrogen and pleiotropic pro-inflammatory cytokine, tumor necrosis factor alpha (TNF-alpha). TNF-alpha production has been implicated in a variety of other human pathologies including neurodegeneration and cancer. Several studies have shown that the anti-inflammatory activity of Embelin is mediated by reduction in TNF-alpha. The latter is synthesized as a membrane anchored protein (pro-TNF-alpha); the soluble component of pro-TNF-alpha is then released into the extracellular space by the action of a protease called TNF-alpha converting enzyme (TACE). TACE, hence, has been proposed as a therapeutic target for inflammation and cancer. METHODS: We used molecular docking and experimental approaches to investigate the docking potential and molecular effects of Embelin to TACE and human cancer cell characteristics, respectively. RESULTS: We demonstrate that Embelin is a potential inhibitor of TACE. Furthermore, in vitro studies revealed that it inhibits malignant properties of cancer cells through inactivation of metastatic signaling molecules including MMPs, VEGF and hnRNP-K in breast cancer cells. CONCLUSION: Based on the molecular dynamics and experimental data, Embelin is proposed as a natural anti-inflammatory and anticancer drug.

Probing p300/CBP associated factor (PCAF)-dependent pathways with a small molecule inhibitor.[Pubmed:23570531]

ACS Chem Biol. 2013;8(6):1311-23.

PCAF (KAT2B) belongs to the GNAT family of lysine acetyltransferases (KAT) and specifically acetylates the histone H3K9 residue and several nonhistone proteins. PCAF is also a transcriptional coactivator. Due to the lack of a PCAF KAT-specific small molecule inhibitor, the exclusive role of the acetyltransferase activity of PCAF is not well understood. Here, we report that a natural compound of the hydroxybenzoquinone class, Embelin, specifically inhibits H3Lys9 acetylation in mice and inhibits recombinant PCAF-mediated acetylation with near complete specificity in vitro. Furthermore, using Embelin, we have identified the gene networks that are regulated by PCAF during muscle differentiation, further highlighting the broader regulatory functions of PCAF in muscle differentiation in addition to the regulation via MyoD acetylation.

Discovery of embelin as a cell-permeable, small-molecular weight inhibitor of XIAP through structure-based computational screening of a traditional herbal medicine three-dimensional structure database.[Pubmed:15115387]

J Med Chem. 2004 May 6;47(10):2430-40.

The X-linked inhibitor of apoptosis (XIAP) is a promising new molecular target for the design of novel anticancer drugs aiming at overcoming apoptosis-resistance of cancer cells to chemotherapeutic agents and radiation therapy. Recent studies demonstrated that the BIR3 domain of XIAP where caspase-9 and Smac proteins bind is an attractive site for designing small-molecule inhibitors of XIAP. Through computational structure-based screening of an in-house traditional herbal medicine three-dimensional structure database of 8221 individual natural products, followed by biochemical testing of selected candidate compounds, we discovered Embelin from the Japanese Ardisia herb as a small-molecular weight inhibitor that binds to the XIAP BIR3 domain. We showed that Embelin binds to the XIAP BIR3 protein with an affinity similar to that of the natural Smac peptide using a fluorescence polarization-based binding assay. Our NMR analysis further conclusively confirmed that Embelin interacts with several crucial residues in the XIAP BIR3 domain with which Smac and caspsase-9 bind. Embelin inhibits cell growth, induces apoptosis, and activates caspase-9 in prostate cancer cells with high levels of XIAP, but has a minimal effect on normal prostate epithelial and fibroblast cells with low levels of XIAP. In stably XIAP-transfected Jurkat cells, Embelin effectively overcomes the protective effect of XIAP to apoptosis and enhances the etoposide-induced apoptosis and has a minimal effect in Jurkat cells transfected with vector control. Taken together, our results showed that Embelin is a fairly potent, nonpeptidic, cell-permeable, small-molecule inhibitor of XIAP and represents a promising lead compound for designing an entirely new class of anticancer agents that target the BIR3 domain of XIAP.

Antitumor, anti-inflammatory and analgesic property of embelin, a plant product.[Pubmed:7510605]

Chemotherapy. 1994 Mar-Apr;40(2):109-13.

Embelin, a plant-based benzoquinone derivative, has been found to exhibit significant antitumor activity in methylcholanthrene-induced fibrosarcoma in albino rats besides enhancing their survival time. The drug also has an appreciable action on pain and inflammation. The changes in DNA, RNA and protein levels in various organs in the tumor-bearing control and the drug-treated animals were also studied.