Activation of the Epstein-Barr virus lytic cycle by the latex of the plant Euphorbia tirucalli

The Role of Plant Latex in Virus Biology

At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on numerous occasions. With a few exceptions, latex is stored under pressure in specialized cells known as laticifers and is exuded upon injury, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infections has been well established. Latex also appears to have effects on viruses, and laticifers are a hostile environment for virus colonization. Only one example of successful colonization has been reported: papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2) in Carica papaya. In this review, a summary of studies that support both the pro- and anti-viral effects of plant latex compounds is provided. The latex components represent a promising natural source for the discovery of new pro- and anti-viral molecules in the fields of agriculture and medicine.

Natural Plant Compounds: Does Caffeine, Dipotassium Glycyrrhizinate, Curcumin, and Euphol Play Roles as Antitumoral Compounds in Glioblastoma Cell Lines?

Many plant-derived compounds are shown to be promising antitumor therapeutic agents by enhancing apoptosis-related pathways and cell cycle impairment in tumor cells, including glioblastoma (GBM) cell lines. We aimed to review four natural plant compounds effective in GBM cell lines as caffeine, dipotassium glycyrrhizinate (DPG), curcumin, and euphol. Furthermore, antitumoral effect of these plant compounds on GBM cell lines through microRNAs (miRs) modulation was investigated. However, only DPG and curcumin were found as effective on miR modulation. Caffeine arrests GBM cell cycle in G0/G1 phase by cyclin-dependent kinases (CDK) complex inhibition and by decreasing BCL-2 and increasing FOXO1 expression levels causing greater apoptotic activity. Caffeine can also directly inhibit IP3R3, p38 phosphorylation, and rho-associated protein kinase (ROCK), decreasing cell invasion and migration capacity or indirectly by inhibiting the tissue inhibitor metalloproteinase-1 (TIMP-1) and integrins β1 and β3, leading to lower matrix metalloproteinases, MMP-2 and MMP-9. DPG presents antitumoral effect in GBM cells related to nuclear factor kappa B (NF-κB) pathway suppression by IRAK2 and TRAF6-mediating miR-16 and miR-146a, respectively. More recently, it was observed that DPG upregulated miR-4443 and miR-3620, responsible for post-transcriptional inhibition of the NF-κB pathway by CD209 and TNC modulation, respectively leading to lower MMP-9 and migration capacity. Curcumin is able to increase miR-223-3p, miR-133a-3p, miR-181a-5p, miR-34a-5p, miR-30c-5p, and miR-1290 expression leading to serine or threonine kinase (AKT) pathway impairment and also it decreases miR-27a-5p, miR-221-3p, miR-21-5p, miR-125b-5p, and miR-151-3p expression causing p53-BCL2 pathway inhibition and consequently, cellular apoptosis. Interestingly, lower expression of miR-27a by curcumin action enhanced the C/EBP homologous protein(CHOP) expression, leading to paraptosis. Curcumin can inhibit miR-21 expression and consequently activate apoptosis through caspase 3 and death receptor (DR) 4 and 5 activation. Autophagy is controlled by the LC-3 protein that interacts with Atg family for the LC3-II formation and autophagy activation. Euphol can enhance LC3-II levels directly in GBM cells or inhibits tumor invasion and migration through PDK1 modulation.

In vitro screening of cytotoxic activity of euphol from Euphorbia tirucalli on a large panel of human cancer-derived cell lines

A large number of classic antineoplastic agents are derived from plants. Euphorbia tirucalli L. (Euphorbiaceae) is a subtropical and tropical plant, used in Brazilian folk medicine against many diseases, including cancer, yet little is known about its true anticancer properties. The present study evaluated the antitumor effect of the tetracyclic triterpene alcohol, euphol, the main constituent of E. tirucalli in a panel of 73 human cancer lines from 15 tumor types. The biological effect of euphol in pancreatic cells was also assessed. The combination index was further used to explore euphol interactions with standard drugs. Euphol showed a cytotoxicity effect against several cancer cell lines (IC₅₀ range, 1.41–38.89 µM), particularly in esophageal squamous cell (11.08 µM) and pancreatic carcinoma cells (6.84 µM), followed by prostate, melanoma, and colon cancer. Cytotoxicity effects were seen in all cancer cell lines, with more than half deemed highly sensitive. Euphol inhibited proliferation, motility and colony formation in pancreatic cancer cells. Importantly, euphol exhibited synergistic interactions with gemcitabine and paclitaxel in pancreatic and esophageal cell lines, respectively. To the best of our knowledge, this study constitutes the largest in vitro screening of euphol efficacy on cancer cell lines and revealed its in vitro anti-cancer properties, particularly in pancreatic and esophageal cell lines, suggesting that euphol, either as a single agent or in combination with conventional chemotherapy, is a potential anti-cancer drug.

Epstein-Barr virus: more than 50 years old and still providing surprises

It is more than 50 years since the Epstein-Barr virus (EBV), the first human tumour virus, was discovered. EBV has subsequently been found to be associated with a diverse range of tumours of both lymphoid and epithelial origin. Progress in the molecular analysis of EBV has revealed fundamental mechanisms of more general relevance to the oncogenic process. This Timeline article highlights key milestones in the 50-year history of EBV and discusses how this virus provides a paradigm for exploiting insights at the molecular level in the diagnosis, treatment and prevention of cancer.

Burkitt's Lymphoma

Endemic Burkitt's lymphoma (BL) remains the most prevalent pediatric cancer in sub-Saharan Africa even though it was the first human cancer with a viral etiology described over 50 years ago. Epstein-Barr virus (EBV) was discovered in a BL tumor in 1964 and has since been implicated in other malignancies. The etiology of endemic BL has been linked to EBV and Plasmodium falciparum malaria co-infection. While epidemiologic studies have yielded insight into EBV infection and the etiology of endemic BL, the modulation of viral persistence in children by malaria and deficits in EBV immunosurveillance has more recently been reified. Renewed efforts to design prophylactic and therapeutic EBV vaccines provide hope of preventing EBV-associated BL as well as increasing the ability to cure this cancer.

Eutirucallin, a RIP-2 type lectin from the latex of Euphorbia tirucalli L. presents proinflammatory properties

Lectins are carbohydrate-binding proteins that recognize and modulate physiological activities and have been used as a toll for detection and identification of biomolecules, and therapy of diseases. In this study we have isolated a lectin present in the latex of Euphorbia tirucalli, and named it Eutirucallin. The latex protein extract was subjected to ion exchange chromatography and showed two peaks with haemagglutinating activity. Polypeptides of 32 kDa protein extract strongly interacted with immobilized galactose (α-lactose > D-N-acetylgalactosamine). The Eutirucallin was obtained with a yield of 5.6% using the α-lactose column. The lectin domain has 32 kDa subunits and at least two of which are joined by disulfide bridges. The agglutinating capacity for human erythrocytes A(+), B(+) and O(+) is inhibited by D-galactose. The haemagglutinating activity of Eutirucallin was independent of Ca(2+) and maintained until the temperature of 55°C. Eutirucallin presented biological activities such as neutrophils recruitment and cytokine prodution by macrophages. The analysis of the trypsin-digested Eutirucallin by ms/ms in ESI-Q-TOFF resulted in nine peptides similar to type 2 ribosome-inactivating protein (type-2 RIP). It's partial sequence showed a similarity of 67.4 - 83.1% for the lectin domain of type-2 RIP [Ricin and Abrin (83.1%), Viscumin, Ebulin, Pulchellin, Cinnamomin, Volkensin and type-2 RIP Iris hollandica]. Our data suggest that Eutirucallin is a new member of type 2 ribosome-inactivating protein and presents biotechnological potential.

EBV Reactivation and Chromosomal Polysomies: Euphorbia tirucalli as a Possible Cofactor in Endemic Burkitt Lymphoma

Burkitt lymphoma is endemic in the Equatorial Belt of Africa, its molecular hallmark is an activated, MYC gene mostly due to a chromosomal translocation. Especially in its endemic clinical variant, Burkitt lymphoma is associated with the oncogenic Epstein-Barr virus (EBV), and holoendemic malaria acts as an amplifier. Environmental factors may also cooperate in Burkitt lymphomagenesis in the endemic regions, such as plants used as traditional herbal remedies. Euphorbia tirucalli, a plant known to possess EBV-activating substances, has a similar geographical distribution to endemic Burkitt's Lymphoma and is used as a hedge, herbal remedy and toy in the Lymphoma BeltI. In this study we aimed at determining if exposure to Euphorbia tirucalli could contribute to lymphomagenesis, and at which extent. Lymphoblastoid and cord blood-derived cell lines were treated with plant extracts, and the expression of EBV-coded proteins was checked, to assess EBV reactivation. The occurrence of chromosomal translocations was then investigated by FISH. Our preliminary results suggest that E. tirucalli is able to reactivate EBV and determine chromosomal alterations, which leads to c-MYC altered expression. The existence of genomic alterations might determine the accumulation of further genetic alteration, which could eventually lead to a transformed phenotype.

Burkitt's lymphoma

Burkitt's lymphoma is a highly aggressive B-cell non-Hodgkin lymphoma and is the fastest growing human tumour. The disease is associated with Epstein-Barr virus and was one of the first tumours shown to have a chromosomal translocation that activates an oncogene (c-MYC). Burkitt's lymphoma is the most common childhood cancer in areas where malaria is holoendemic. The incidence is very high in immunosuppressed patients in non-endemic areas, especially when associated with HIV infection. Outcome with intensive chemotherapy has improved and is now excellent in children, but the prognosis is poor in elderly adults. The success of intensive treatment relies on good supportive care. The therapy offered in oncology units in low-income countries is not as aggressive as in centres in high-income countries and outcomes are less successful. Adjuvant monoclonal antibody therapy with rituximab shows promise for improved outcomes and reduced toxic effects in the future.

A Role for RNA Viruses in the Pathogenesis of Burkitt's Lymphoma: The Need for Reappraisal

Certain infectious agents are associated with lymphomas, but the strength of the association varies geographically, suggesting that local environmental factors make important contributions to lymphomagenesis. Endemic Burkitt's Lymphoma has well-defined environmental requirements making it particularly suitable for research into local environmental factors. The Epstein-Barr virus and holoendemic Malaria are recognized as important cofactors in endemic Burkitt's Lymphoma and their contributions are discussed. Additionally, infection with Chikungunya Fever, a potentially oncogenic arbovirus, was associated with the onset of endemic Burkitt's Lymphoma in one study and also with space-time case clusters of the lymphoma. Chikungunya Virus has several characteristics typical of oncogenic viruses. The Flavivirus, Hepatitis C, a Class 1 Human Carcinogen, closely related to the arboviruses, Yellow Fever, and Dengue, is also more distantly related to Chikungunya Virus. The mechanisms of oncogenesis believed to operate in Hepatitis C lymphomagenesis are discussed, as is their potential applicability to Chikungunya Virus.

Infectious agents and lymphoma

In the past 25 years revelations on the genesis of human cancer have come at an increasing pace. Research on oncogenic infectious agents, especially viruses, has helped us to understand the process of malignant transformation of cells because the cellular events in viral-driven transformation mirror, often brilliantly, basic cellular processes that culminate in cancer, even those not associated with viruses. Infectious agents, especially viruses, account for several of the most common malignancies-up to 20% of all cancers. Some of these cancers are endemic, with a high incidence in certain geographic locations, but sporadic/lower incidence in other parts of the world. Lymphomas arise frequently in association with infectious agents such as Epstein-Barr virus, human immunodeficiency virus, human herpes virus 8, Helicobacter pylori, and hepatitis C virus. In this review, we will focus on the association between infectious agents and lymphomas, with a look at the molecular mechanisms they use to disturb cell regulation and eventually result in cancer.

Potential of Jatropha curcas as a source of renewable oil and animal feed

Jatropha curcas (L.) is a perennial plant of the spurge family (Euphorbiaceae). Recently, it has received much attention as a potential source of vegetable oil as a replacement for petroleum, and, in particular, the production of biodiesel. Despite the interest that is being shown in the large-scale cultivation of J. curcas, genetic resources remain poorly characterized and conserved and there has been very little plant breeding for improved traits. At present, the varieties being used to establish plantations in Africa and Asia are inedible. The meal obtained after the extraction of oil cannot, therefore, be used as a source of animal feed. Naturally existing edible varieties are, however, known to occur in Mexico. The toxic components of J. curcas seeds, the potential for plant breeding to generate improved varieties, and the suitability of J. curcas oil as a feedstock for biodiesel production are discussed.

Burkitt's lymphoma in Africa, a review of the epidemiology and etiology

Burkitt's lymphoma (BL) was first described in Eastern Africa, initially thought to be a sarcoma of the jaw. Shortly it became well known that this was a distinct form of Non Hodgkin's lymphoma. The disease has given insight in all aspects of cancer research and care. Its peculiar epidemiology has led to the discovery of Epstein Barr virus (EBV) and its importance in the cause of several viral illnesses and malignancies. The highest incidence and mortality rates of BL are seen in Eastern Africa. BL affects mainly children, and boys are more susceptible than girls. Evidence for a causal relationship between EBV and BL in the endemic form is fairly strong. Frequency of association between EBV and BL varies between different patient groups and different parts of the world. EBV may play a role in the pathogenesis of BL by deregulation of the oncogene c-MYC by chromosomal translocation. Although several studies suggest an association between malaria and BL, there has never been a conclusive population study in support of a direct role of malaria in causation of BL. The emergence of HIV and a distinct subtype of BL in HIV infected have brought a new dimension to the disease particularly in areas where both HIV and BL are endemic. BL has been reported as a common neoplasmin HIV infected patients, but not in other forms of immuno-depression, and the occurrence of BL seems to be higher amongst HIV positive adults, while the evidence of an association amongst children is still disputed. The role of other possible risk factors such as low socio-economical status, exposure to a plant species common in Africa called Euphorbiaceae, exposure to pesticies and to other infections such as schistosomiasis and arbovirus (an RNA virus transmitted by insect vectors) remain to be elucidated.

Mechanisms involved in Burkitt's tumor formation

Burkitt's lymphoma is a rapidly fatal tumor if untreated, but it is curable with intensive polychemotherapy. Unfortunately, the toxicities reported for its treatment in adults are poorly tolerated. Novel therapies aimed at specific molecular targets might prove to be less toxic. A better knowledge of the mechanisms involved in the pathogenesis of Burkitt's lymphoma would facilitate the identification of such targets. This review explores the current knowledge on the alterations found in the three main Burkitt's lymphoma variants.

Larvicidal activity of some Euphorbiaceae plant extracts against Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Larvicidal activity of ethyl acetate, butanol, and petroleum ether extracts of five species of Euphorbiaceae plants, Jatropha curcas, Pedilanthus tithymaloides, Phyllanthus amarus, Euphorbia hirta, and Euphorbia tirucalli, were tested against the early fourth instar larvae of Aedes aegypti L. and Culex quinquefasciatus (Say). The larval mortality was observed after 24 h of exposure. All extracts showed low larvicidal effects; however, the highest larval mortality was found in petroleum ether extract. The LC50 value of petroleum ether extracts of J. curcas, P. tithymaloides, P. amarus, E. hirta, and E. tirucalli were 8.79, 55.26, 90.92, 272.36, and 4.25 ppm, respectively, against A. aegypti and 11.34, 76.61, 113.40, 424.94, and 5.52 ppm, respectively, against C quinquefasciatus. Of the various ratios tested, the petroleum ether extracts of J. curcas and E. tirucalli were observed to be more efficient than the other plant extracts. It is, therefore, suggested that E. tirucalli can be applied as an ideal potential larvicide against A. aegypti and C. quinquefasciatus. This is an ideal ecofriendly approach for the control of the dengue vector, A. aegypti, and the lymphatic filariasis vector, C. quinquefasciatus.

Toxicological screening of Euphorbia tirucalli L.: developmental toxicity studies in rats

Euphorbia tirucalli (Euphorbiaceae family), an environmental risk factor for Burkitt's lymphoma, also presents pharmacological activities. In the northeast region of Brazil its latex is used as an antimicrobial, antiparasitic in the treatment of coughs, rheumatism, cancer and other maladies as folk remedy. The present work concerns its developmental toxicity in rats. Wistar rats on the first day post-coitum (dpc) were grouped as control (distilled water) and treated (latex aqueous solution) groups. Animals were treated by oral gavage from the 1st to the 4th (Experiment I) and from the 5th to 7th dpc (Experiment II) and killed on the 5th or 14th dpc, respectively. Maternal variables were: clinical signs of toxicity, body weight, ovaries, liver and kidneys weight and number of corpora lutea. The uterine tubes and cornua were washed for counting and identification of embryos. The embryos and placenta were weighed. Apart from the leucopenia and the higher placental weight observed in treated rats from Experiment II, there were no significant differences between the groups. It is possible to conclude that the latex aqueous solution of Euphorbia tirucalli did not interfere with tubaric embryo development or with implantation, but it seems to alter the placenta morphology.

Reactivation of Kaposi's sarcoma-associated herpesvirus by natural products from Kaposi's sarcoma endemic regions

Kaposi's sarcoma (KS) and its causative agent, Kaposi's sarcoma associated herpesvirus (KSHV/HHV-8), a gamma2 herpesvirus, have distinctive geographical distributions that are largely unexplained. We propose the "oncoweed" hypothesis to explain these differences, namely that environmental cofactors present in KS endemic regions cause frequent reactivation of KSHV in infected subjects, leading to increased viral shedding and transmission leading to increased prevalence of KSHV infection as well as high viral load levels and antibody titers. Reactivation also plays a role in the pathogenesis of KSHV-associated malignancies. To test this hypothesis, we employed an in vitro KSHV reactivation assay that measured increases in KSHV viral load in KSHV infected primary effusion lymphoma (PEL) cells and screened aqueous natural product extracts from KS endemic regions. Of 4,842 extracts from 38 countries, 184 (5%) caused KSHV reactivation. Extracts that caused reactivation came from a wide variety of plant families, and extracts from Africa, where KSHV is highly prevalent, caused the greatest level of reactivation. Time course experiments were performed using 28 extracts that caused the highest levels of reactivation. The specificity of the effects on viral replication was examined using transcriptional profiling of all viral mRNAs. The array data indicated that the natural extracts caused an ordered cascade of lytic replication similar to that seen after induction with synthetic activators. These in vitro data provide support for the "oncoweed" hypothesis by demonstrating basic biological plausibility.

Spatial clustering of endemic Burkitt's lymphoma in high-risk regions of Kenya

Endemic Burkitt's lymphoma (eBL), the most common childhood cancer in sub-Saharan Africa, occurs at a high incidence in western Kenya, a region that also experiences holoendemic malaria. Holoendemic malaria has been identified as a co-factor in the etiology of this cancer. We hypothesized that eBL may cluster spatially within this region. Medical records for all eBL cases diagnosed from 1999 through 2004 at Nyanza Provincial General Hospital were reviewed for case residential information to examine this hypothesis. Two cluster detection methods, Anselin's Local Moran test for spatial autocorrelation and a spatial scan test statistic, were applied to this residential data to determine whether statistically significant high- and low-risk areas were present in the Province. During the 6-year study period, 272 children were diagnosed with eBL, with an average annual incidence of 2.15 cases per 100,000 children. Using Empirical Bayes smoothed rates, the Local Moran test identified 1 large multi-centered area of low eBL risk (p-values < 0.01) and 2 significant multi-centered clusters of high eBL risk (p-values < 0.001). The spatial scan detected 3 small independent low-risk areas (p-values < 0.02) and 2 high-risk clusters (p-values = 0.001), both similar in location to those identified from the Local Moran analysis. Significant spatial clustering of elevated eBL risk in high-malaria transmission regions and of reduced incidence where malaria is infrequent suggests that malaria plays a role in the complex eBL etiology, but that additional factors are also likely involved.

Euphorbia tirucalli L. modulates myelopoiesis and enhances the resistance of tumour-bearing mice

Myelosuppression concomitant with increased numbers of spleen CFU-GM was observed in tumour-bearing mice. Treatment of these animals with Euphorbia tirucalli L. (ET) (125, 250 and 500 mg/kg) stimulated marrow myelopoiesis and reduced spleen colony formation, with no differences observed between the effects of the three doses. The changes produced by the tumour in total and differential marrow cell counts were restored by the treatment with ET. Prostaglandin E2 (PGE2) levels, which were dramatically increased in tumour bearers, was also abrogated by the treatment with the plant extract. Euphorbia tirucalli L. significantly enhanced survival and concurrently reduced tumour growth in the peritoneal cavity. We propose that the modulatory effect of Euphorbia tirucalli L. on myelopoietic response and on the levels of PGE2 may be related to its antitumour activity as a possible mechanism for the regulation of granulocyte and macrophage production and expression of functional activities.

Capacity building for the clinical investigation of AIDS malignancy in East Africa

PURPOSE

To build capacity in the resource-poor setting to support the clinical investigation and treatment of AIDS-related malignancies in a region of the world hardest hit by the AIDS pandemic.

METHODS

An initial MEDLINE database search for international collaborative partnerships dedicated to AIDS malignancies in developing countries failed to identify any leads. This search prompted us to report progress on our collaboration in this aspect of the epidemic. Building on the formal Uganda-Case Western Reserve University (Case) Research Collaboration dating back to 1987, established NIH-supported centers of research excellence at Case, and expanding activities in Kenya, scientific and training initiatives, research capital amongst our institutions are emerging to sustain a international research enterprise focused on AIDS and other viral-related malignancies.

RESULTS

A platform of clinical research trials with pragmatic design has been developed to further enhance clinical care and sustain training initiatives with partners in East Africa and the United States. An oral chemotherapy feasibility trial in AIDS lymphoma is near completion; a second lymphoma trial of byrostatin and vincristine is anticipated and a feasibility trial of indinavir for endemic Kaposi's sarcoma is planned.

CONCLUSIONS

In the absence of published reports of evolving international partnerships dedicated to AIDS malignancy in resource constrained settings, we feel it important for such progress on similar or related international collaborative pursuits to be published. The success of this effort is realized by the long-term international commitment of the collaborating investigators and institutions to sustain this effort in keeping with ethical and NIH standards for the conduct of research; the provision of formal training of investigators and research personnel on clinical problems our East African partners are faced with in practice and the development of pragmatic clinical trials and therapeutic intervention to facilitate technology transfer and enhance clinical practice.

Is endemic Burkitt's lymphoma an alliance between three infections and a tumour promoter?

Malaria and Epstein-Barr virus (EBV), recognised cofactors for endemic Burkitt's lymphoma, are ubiquitous within the lymphoma belt of Africa, and, unless other cofactors are involved, the tumour should be much more common than it is. Malaria and EBV alone cannot account for the occasional shifting foci and space-time case clusters of endemic Burkitt's lymphoma. Arboviruses and plant tumour promoters are other possible local cofactors that could explain such characteristics. The geographical and age distributions of endemic Burkitt's lymphoma parallel those of potentially oncogenic, mosquito-borne arboviruses. Arboviruses seem to be associated with case clusters of endemic Burkitt's lymphoma, and symptoms compatible with arbovirus infection have been seen immediately before the onset of the tumour. RNA and DNA viruses, including EBV, are promoted by extracts of a commonly used plant, Euphorbia tirucalli, the distribution of which coincides with the boundaries of the lymphoma belt. Extracts of E tirucalli are tumour promoters and can induce the characteristic 8;14 translocation of endemic Burkitt's lymphoma in EBV-infected cell-lines. They also activate latent EBV in infected cells, enhance EBV-mediated cell transformation, and modulate EBV-specific immunity.

Inhibition of the Epstein–Barr virus lytic cycle by Zta-targeted RNA interference

Epstein–Barr virus (EBV) reactivation into the lytic cycle plays certain roles in the development of EBV-associated diseases, so an effective strategy to block the viral lytic cycle may be of value to reduce the disease risk or to improve the clinical outcome. This study examined whether the EBV lytic cycle could be inhibited using RNA interference (RNAi) directed against the essential viral gene Zta. In cases of EBV reactivation triggered by chemicals or by exogenous Rta, Zta-targeted RNAi prevented the induction of Zta and its downstream genes and further blocked the lytic replication of viral genomes. This antiviral effect of RNAi was not likely to be mediated by activation of the interferon pathway, as phosphorylation of STAT1 was not induced. In addition, novel EBV-infected epithelial cells showing constitutive activation of the lytic cycle were cloned; such established lytic infection was also suppressed by Zta-targeted RNAi. These results indicate that RNAi can be used to inhibit the EBV lytic cycle effectively in vitro and could also be of potential use to develop anti-EBV treatments.