Inhibitory effect of flavonoids from citrus plants on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumors

5-Demethylnobiletin: Insights into its pharmacological activity, mechanisms, pharmacokinetics and toxicity

BACKGROUND

5-Demethylnobiletin (5DN) is a polymethoxyflavone (PMF) primarily found in citrus fruits. It has various health-promoting properties and hence has attracted significant attention from scholars worldwide.

PURPOSE

This review is the first to systematically summarize the recent research progress of 5DN, including its pharmacological activity, mechanism of action, pharmacokinetics, and toxicological effects. In addition, the pharmacological mechanism of action of 5DN has been discussed from a molecular biological perspective, and data from in vivo and in vitro animal studies have been compiled to provide a more thorough understanding of 5DN as a potential lead drug.

METHODS

Data were extracted from SciFinder, PubMed, ScienceDirect and China National Knowledge Infrastructure (CNKI) from database inception to January 2022.

RESULTS

5DN has broad pharmacological activities. It exerts anti-inflammatory effects, promotes apoptosis and autophagy, and induces melanogenesis mainly by regulating the JAK2/STAT3, caspase-dependent apoptosis, ROS-AKT/mTOR, MAPK and PKA-CREB signaling pathways. 5DN can be used for treating diseases such as cancer, inflammation-related diseases, rheumatoid arthritis, and neurodegenerative diseases. To date, there have been only a few toxicological studies on 5DN, and both in vitro and in vivo on 5DN have not revealed significant toxic side effects. Pharmacokinetic studies have revealed that the metabolites of 5DN are mainly 5,3'-didemethylnobiletin (M1); 5,4'-didemethylnobiletin (M2) and 5,3',4'-tridemethylnobiletin (M3), in either, glucuronide-conjugated or monomeric form. The pharmacokinetic products of 5DN, especially M1, possess better activity than 5DN for the treatment of cancer.

CONCLUSION

The anticancer effects of 5DN and its metabolites warrant further investigation as potential drug candidates, especially through in vivo studies. In addition, the therapeutic effects of 5DN in neurodegenerative diseases should be examined in more experimental models, and the absorption and metabolism of 5DN should be further investigated in vivo.

Sinensetin: An Insight on Its Pharmacological Activities, Mechanisms of Action and Toxicity

Sinensetin, a plant-derived polymethoxylated flavonoid found in Orthosiphon aristatus var. aristatus and several citrus fruits, has been found to possess strong anticancer activities and a variety of other pharmacological benefits and promising potency in intended activities with minimal toxicity. This review aims to compile an up-to-date reports of published scientific information on sinensetin pharmacological activities, mechanisms of action and toxicity. The present findings about the compound are critically analyzed and its prospect as a lead molecule for drug discovery is highlighted. The databases employed for data collection are mainly through Google Scholar, PubMed, Scopus and Science Direct. In-vitro and in-vivo studies showed that sinensetin possessed strong anticancer activities and a wide range of pharmacological activities such as anti-inflammatory, antioxidant, antimicrobial, anti-obesity, anti-dementia and vasorelaxant activities. The studies provided some insights on its several mechanisms of action in cancer and other disease states. However, more detail mechanistic studies are needed to understand its pharmacological effects. More in vivo studies in various animal models including toxicity, pharmacokinetic, pharmacodynamic and bioavailability studies are required to assess its efficacy and safety before submission to clinical studies. In this review, an insight on sinensetin pharmacological activities and mechanisms of action serves as a useful resource for a more thorough and comprehensive understanding of sinensetin as a potential lead candidate for drug discovery.

Epstein-Barr virus (EBV) reactivation and therapeutic inhibitors

Epstein-Barr virus (EBV) is a ubiquitous human virus which infects almost all humans during their lifetime and following the acute phase, persists for the remainder of the life of the individual. EBV infects B lymphocytes leading to their immortalisation, with persistence of the EBV genome as an episome. In the latent phase, EBV is prevented from reactivating through efficient cytotoxic cellular immunity. EBV reactivates (lytic phase) under conditions of psychological stress with consequent weakening of cellular immunity, and EBV reactivation has been shown to occur in a subset of individuals with each of a variety of cancers, autoimmune diseases, the autoimmune-like disease, chronic fatigue syndrome/myalgic encephalitis and under other circumstances such as being an inpatient in an intensive care unit. Chronic EBV reactivation is an important mechanism in the pathogenesis of many such diseases, yet is rarely tested for in immunocompetent individuals. This review summarises the pathogenesis of EBV infection, EBV reactivation and its role in disease, and methods which may be used to detect it. Known inhibitors of EBV reactivation and replication are discussed, including drugs licensed for treatment of other herpesviruses, licensed or experimental drugs for various other indications, compounds at an early stage of drug development and nutritional constituents such as vitamins and dietary supplements.

EBV reactivation as a target of luteolin to repress NPC tumorigenesis

Nasopharyngeal carcinoma (NPC) is a malignancy derived from the epithelial cells of the nasopharynx. Although a combination of radiotherapy with chemotherapy is effective for therapy, relapse and metastasis after remission remain major causes of mortality. Epstein-Barr virus (EBV) is believed to be one of causes of NPC development. We demonstrated previously that EBV reactivation is important for the carcinogenesis of NPC. We sought, therefore, to determine whether EBV reactivation can be a target for retardation of relapse of NPC. After screening, we found luteolin is able to inhibit EBV reactivation. It inhibited EBV lytic protein expression and repressed the promoter activities of two major immediate-early genes, Zta and Rta. Furthermore, luteolin was shown to reduce genomic instability induced by recurrent EBV reactivation in NPC cells. EBV reactivation-induced NPC cell proliferation and migration, as well as matrigel invasiveness, were also repressed by luteolin treatment. Tumorigenicity in mice, induced by EBV reactivation, was decreased profoundly following luteolin administration. Together, these results suggest that inhibition of EBV reactivation is a novel approach to prevent the relapse of NPC.

Inhibition of Epstein-Barr virus reactivation by the flavonoid apigenin

Background

Lytic reactivation of EBV has been reported to play an important role in human diseases, including NPC carcinogenesis. Inhibition of EBV reactivation is considered to be of great benefit in the treatment of virus-associated diseases. For this purpose, we screened for inhibitory compounds and found that apigenin, a flavonoid, seemed to have the ability to inhibit EBV reactivation.

Methods

We performed western blotting, immunofluorescence and luciferase analyses to determine whether apigenin has anti-EBV activity.

Results

Apigenin inhibited expression of the EBV lytic proteins, Zta, Rta, EAD and DNase in epithelial and B cells. It also reduced the number of EBV-reactivating cells detectable by immunofluorescence analysis. In addition, apigenin has been found to reduce dramatically the production of EBV virions. Luciferase reporter analysis was performed to determine the mechanism by which apigenin inhibits EBV reactivation: apigenin suppressed the activity of the immediate-early (IE) gene Zta and Rta promoters, suggesting it can block initiation of the EBV lytic cycle.

Conclusion

Taken together, apigenin inhibits EBV reactivation by suppressing the promoter activities of two viral IE genes, suggesting apigenin is a potential dietary compound for prevention of EBV reactivation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12929-016-0313-9) contains supplementary material, which is available to authorized users.

Flavones: an important scaffold for medicinal chemistry

Flavones have antioxidant, anti-proliferative, anti-tumor, anti-microbial, estrogenic, acetyl cholinesterase, anti-inflammatory activities and are also used in cancer, cardiovascular disease, neurodegenerative disorders, etc. Also, flavonoids are found to have an effect on several mammalian enzymes like protein kinases that regulate multiple cell signaling pathways and alterations in multiple cellular signaling pathways are frequently found in many diseases. Flavones have been an indispensable anchor for the development of new therapeutic agents. The majority of metabolic diseases are speculated to originate from oxidative stress, and it is therefore significant that recent studies have shown the positive effect of flavones on diseases related to oxidative stress. Due to the wide range of biological activities of flavones, their structure-activity relationships have generated interest among medicinal chemists. The outstanding development of flavones derivatives in diverse diseases in very short span of time proves its magnitude for medicinal chemistry research. The present review gives detail about the structural requirement of flavone derivatives for various pharmacological activities. This information may provide an opportunity to scientists of medicinal chemistry discipline to design selective, optimize as well as poly-functional flavone derivatives for the treatment of multi-factorial diseases.

Design, synthesis and experimental validation of novel potential chemopreventive agents using random forest and support vector machine binary classifiers

Compared to the current knowledge on cancer chemotherapeutic agents, only limited information is available on the ability of organic compounds, such as drugs and/or natural products, to prevent or delay the onset of cancer. In order to evaluate chemical chemopreventive potentials and design novel chemopreventive agents with low to no toxicity, we developed predictive computational models for chemopreventive agents in this study. First, we curated a database containing over 400 organic compounds with known chemoprevention activities. Based on this database, various random forest and support vector machine binary classifiers were developed. All of the resulting models were validated by cross validation procedures. Then, the validated models were applied to virtually screen a chemical library containing around 23,000 natural products and derivatives. We selected a list of 148 novel chemopreventive compounds based on the consensus prediction of all validated models. We further analyzed the predicted active compounds by their ease of organic synthesis. Finally, 18 compounds were synthesized and experimentally validated for their chemopreventive activity. The experimental validation results paralleled the cross validation results, demonstrating the utility of the developed models. The predictive models developed in this study can be applied to virtually screen other chemical libraries to identify novel lead compounds for the chemoprevention of cancers.

Semisynthesis of Polymethoxyflavonoids from Naringin and Hesperidin

Polymethoxyflavonoids (PMFs) possess important biological activities, notably as anticancer agents. Semisynthesis of a series of PMFs were performed by glycoside hydrolysis, dehydrogenation, bromination, aromatic nucleophilic substitution, O-methylation, dimethyldioxirane oxidation and regioselective demethylation, starting from abundant and inexpensive natural sources naringin and hesperidin. A new synthetic method for selective methylation using CuBr catalysed and microwave-assisted reaction was developed, and the dimethyl dioxirane oxidation of flavones to flavonols was much improved. The new semisynthetic route has the advantages of easy availability of starting materials, simple operation and good yields.

Sulfated small molecules targeting eBV in Burkitt lymphoma: from in silico screening to the evidence of in vitro effect on viral episomal DNA

Epstein-Barr virus (EBV) infects more than 90% of the world population. Following primary infection, Epstein-Barr virus persists in an asymptomatic latent state. Occasionally, it may switch to lytic infection. Latent EBV infection has been associated with several diseases, such as Burkitt lymphoma (BL). To date, there are no available drugs to target latent EBV, and the existing broad-spectrum antiviral drugs are mainly active against lytic viral infection. Thus, using computational molecular docking, a virtual screen of a library of small molecules, including xanthones and flavonoids (described with potential for antiviral activity against EBV), was carried out targeting EBV proteins. The more interesting molecules were selected for further computational analysis, and subsequently, the compounds were tested in the Raji (BL) cell line, to evaluate their activity against latent EBV. This work identified three novel sulfated small molecules capable of decreasing EBV levels in a BL. Therefore, the in silico screening presents a good approach for the development of new anti-EBV agents.

Greater intake of fruit and vegetables is associated with lower risk of nasopharyngeal carcinoma in Chinese adults: a case-control study

PURPOSE

The effect of fruit and vegetable intake on the risk of nasopharyngeal carcinoma (NPC) remains uncertain due to limited published evidence. We performed a matched case-control study to investigate the relationship between the intake of fruit and vegetables and the risk of NPC.

METHODS

Between July 2009 and March 2011, 600 (448 male, 152 female), NPC incident cases from a single hospital in Guangzhou, Guangdong Province, China, a high-incidence area, were enrolled in the study. 600 controls, matched by gender, age (± 3 years) and household type (urban/rural) were also enrolled. Face-to-face interviews were used to collect habitual dietary intakes and information on various covariates.

RESULTS

Multivariate conditional logistic regression analyses showed significant, dose-dependent inverse associations between the intake of vegetables, fruit or a combination of the two and the risk of NPC, even after adjustments for social-economic status, body mass index, dietary factors and other potential covariates. The adjusted odds ratios (95% confidence intervals) for NPC in the top quartile of vegetable intake, fruit intake or a combination of the two, as compared to the lowest quartile, were 0.33 (0.22-0.50), 0.70 (0.47-1.04) and 0.37 (0.25-0.55), respectively. Dark green leafy vegetables, carrots, peppers and tomatoes, citrus fruit and pome fruit showed much more pronounced benefits with regards to NPC than other types of fruit and vegetables. Interaction analyses demonstrated that the effects of total combined vegetable and fruit intake were much more significant in subjects with a higher education level (p interaction: 0.027), and the benefits of fruit were observed in males, but not in females (p interaction: 0.088).

CONCLUSION

Our findings suggest that a greater consumption of fruit and vegetables may lower the risk of NPC in Chinese adults.

Cancer preventive agents 11. Novel analogs of dimethyl dicarboxylate biphenyl as potent cancer chemopreventive agents(†)

CONTEXT

Dimethyl dicarboxylate biphenyl (DDB) is a clinically used hepatoprotectant and has also been found to have chemopreventive activity.

MATERIALS AND METHODS

Sixteen novel analogs (5-20) were designed, synthesized, and evaluated for their cancer preventive activity. The 2,2'-bismethyl ester (5-18) and ether (19, 20) DDB analogs were synthesized by insertion of various linear alkyl, short fatty acid, polar, and aromatic groups. All synthesized analogs were evaluated in an in vitro short-term 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced Epstein Barr virus early antigen (EBA-EA) activation assay. Three of the most potent compounds were also tested for inhibitory effects on skin tumor promotion in an in vivo two-stage mouse-skin carcinogenesis test using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter.

RESULTS

Compound 19 with bisprenyl ethers had the most significant cancer preventive activity (100% inhibition of activation at 1 × 10(3) mol ratio/TPA, 78.4%, 49.7%, and 10.9% inhibition at 5 × 10(2), 1 × 10(2), 1 × 10 mol ratio/TPA, respectively) in vitro. Compound 19 also exhibited a remarkable inhibitory effect on skin tumor promotion in the in vivo two-stage mouse-skin carcinogenesis test.

DISCUSSION AND CONCLUSIONS

Thus, DDB analog 19 could be a valuable candidate as a cancer preventive agent or as a lead for the development of new antitumor promoter drugs.

Identification and physiological evaluation of the components from citrus fruits as potential drugs for anti-corpulence and anticancer

On the basis of monitoring the prevention of accumulation of lipid droplets in mouse 3T3-L1 preadipocyte cells and inhibition of the proliferation of human colon cancer HT-29 cells, effective anti-corpulence and anticancer compounds were isolated from the peel of Citrus fruits. These bioactive components were identified as polymethoxyflavones and coumarin derivatives by spectroscopic analyses. 5-Hydroxy-6,7,8,3',4'-pentamethoxyflavone had the greatest anti-corpulence effects and 3,5,6,7,8,3',5'-heptamethoxyflavone had the greatest anticancer effects. Furthermore, distributions of those bioactive components in the peel of 10 species of Citrus fruits were demonstrated by HPLC analyses.

Isolation and syntheses of polymethoxyflavones and hydroxylated polymethoxyflavones as inhibitors of HL-60 cell lines

Fifteen polymethoxyflavones (PMFs) and hydroxylated PMFs were isolated from sweet orange (Citrus sinensis) peel extract and synthesized to investigate their biological activity. All obtained compounds were tested in HL-60 cancer cell proliferation and apoptosis induction assays. While some PMFs and hydroxylated PMFs had moderate anti-carcinogenic activities, 5-hydroxy-6,7,8,3',4'-pentamethoxyflavone and 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone showed strong inhibitory activities against the proliferation and induced apoptosis of HL-60 cell lines.

Efficient and scalable method in isolation of polymethoxyflavones from orange peel extract by supercritical fluid chromatography

Polymethoxyflavones (PMFs) from citrus genus are of particular interest because of their broad spectrum of biological activities, such as anti-inflammatory, anti-carcinogenic, and anti-atherogenic properties. Recently, the exploration into the beneficial health properties of PMFs in citrus fruits has dramatically increased. However, the supply of pure PMFs in the in vivo study is a limiting factor due to the difficulties in large-scale isolation of the interested PMFs. Therefore, the development of an efficient and a scalable separation method of PMFs is necessary and significant. In this paper, we report a newly developed method for efficient and relatively large-scale isolation of four PMFs from sweet orange (Citrus sinensis) peel by employing supercritical chromatography (SFC): nobiletin, tangeretin, 3,5,6,7,8,3',4'-heptamethoxyflavone and 5,6,7,4'-tetramethoxyflavone.

Chemical Study of Citrus Plants in the Search for Cancer Chemopreventive Agents

The constituents of Citrus plants were investigated to develop useful agents that are effective in cancer chemoprevention. We examined the roots and bark of the roots of various Citrus plants, resulting in the isolation of many novel compounds. Their structures were determined using spectroscopic methods, especially 2D-NMR spectra. The following new compounds of constituents were found: dimeric coumarins, dimeric acridone alkaloids, and acridone-coumarin dimers. Auraptene and nobiletin are known as useful constituents of the peel of Citrus plants for cancer chemoprevention. However, we found that 3,5,6,7,8,3',4'-heptamethoxyflavone (HPT) has both antitumor promotion and initiation activities and is more effective than auraptene and nobiletin. We synthesized pentaallyl quercetin (QPA), a useful antitumor compound that has the additional effects of a P-glycoprotein (P-gp) inhibitor. The inhibitory effects of QPA on P-gp were more effective than those of the typical P-gp inhibitors cyclosporin A and verapamil. Both HPT and QPA have antitumor promotion activity and are potential candidates for effective multidrug resistance agents in cancer chemotherapy.

Cancer chemopreventive activity of flavanones on Epstein-Barr virus activation and two-stage mouse skin carcinogenesis

To search for possible cancer chemopreventive agents from natural sources, we performed primary screening of ten flavanones isolated from plants belonging to Rutaceae and Leguminosae by examining their possible inhibitory effects on Epstein-Barr virus (EBV) early antigen activation induced by 12-O-tetradecanoylphorbol-13-acetate in Raji cells. All of the flavanones tested in this study showed inhibitory activity against EBV, without showing any cytotoxicity. Amorilin (3), which has three prenyl (3-methyl-2-butenyl) side-chains in the molecule, showed the most potent activity. Furthermore, lupinifolin (5) exhibited a marked inhibitory effect on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. These results indicate that some of these prenylated flavanones might be valuable as potential cancer chemopreventive agents (anti-tumor promoters).

Inhibitory effect of flavonoid derivatives on Epstein-Barr virus activation and two-stage carcinogenesis of skin tumors

To search for possible anti-tumor promoters, ten flavonoid derivatives (1-10) synthesized from morin and quercetin were examined for their inhibitory effects on the Epstein-Barr virus early antigen (EBV-EA) activation by a short-term in vitro assay. Of these compounds, pentaallyl ethers (9, 10) showed significant inhibitory effects on EBV-EA activation induced by the tumor promoter, 12-O-tetradecanoylphorbol 13-acetate. Further, quercetin pentaallyl ether (10) exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.

Isolation and identification of two new flavanones and a chalcone from Citrus kinokuni

Two new flavanones and one chalcone were isolated from the peel of Citrus kinokuni Hort. ex Tanaka and identified as (2S)-5,6,7,8,4'-pentamethoxyflavanone (1), (2S)-5,6,7,3',4'-pentamethoxyflavanone (2) and 2'-hydroxy-3,4,3',4',6'-pentamethoxychalcone (3). The structures of new compounds were elucidated by spectroscopic analysis.

Structural characterization of flavonoid glycosides by collisionally activated dissociation of metal complexes

Collisionally activated dissociation is used for structural characterization of a series of flavonoid glycosides. Dissociation of transition metal/flavonoid binary complexes of the type [MII(L - H+)]+ and transition metal/2,2'-bipyridine/flavonoid ternary complexes of the type [MII(L - H+)bpy]+ give fragmentation patterns that are complementary and more diagnostic than those of the protonated, deprotonated, or sodium-cationized flavonoids. Analysis of fragmentation patterns of the [MII(L - H+)bpy]- complexes permits determination of the disaccharide as a rutinose or neohesperidose and the relative placement of the disaccharide (i.e., 3 vs. 7 positions).

Cancer chemopreventive activity of 3,5,6,7,8,3',4'-heptamethoxyflavone from the peel of citrus plants

Nobiletin and 3,5,6,7,8,3',4'-heptamethoxyflavone (HPT), isolated from the peel of Citrus plants, were examined for the anti-tumor-initiating activity on two-stage carcinogenesis of mouse skin tumors induced by a nitric oxide donor, (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexenamide, as an initiator and 12-O-tetradecanoylphorbol-13-acetate as a promoter. HPT exhibited the remarkable anti-tumor-initiating effect on mouse skin and it suggested the possibility of HPT being a chemopreventive agent against nitric oxide (NO) carcinogenesis.