Burkitt lymphoma--a stalking horse for cancer research?

Metabolic Reprogramming and Potential Therapeutic Targets in Lymphoma

Lymphoma is a heterogeneous group of diseases that often require their metabolism program to fulfill the demand of cell proliferation. Features of metabolism in lymphoma cells include high glucose uptake, deregulated expression of enzymes related to glycolysis, dual capacity for glycolytic and oxidative metabolism, elevated glutamine metabolism, and fatty acid synthesis. These aberrant metabolic changes lead to tumorigenesis, disease progression, and resistance to lymphoma chemotherapy. This metabolic reprogramming, including glucose, nucleic acid, fatty acid, and amino acid metabolism, is a dynamic process caused not only by genetic and epigenetic changes, but also by changes in the microenvironment affected by viral infections. Notably, some critical metabolic enzymes and metabolites may play vital roles in lymphomagenesis and progression. Recent studies have uncovered that metabolic pathways might have clinical impacts on the diagnosis, characterization, and treatment of lymphoma subtypes. However, determining the clinical relevance of biomarkers and therapeutic targets related to lymphoma metabolism is still challenging. In this review, we systematically summarize current studies on metabolism reprogramming in lymphoma, and we mainly focus on disorders of glucose, amino acids, and lipid metabolisms, as well as dysregulation of molecules in metabolic pathways, oncometabolites, and potential metabolic biomarkers. We then discuss strategies directly or indirectly for those potential therapeutic targets. Finally, we prospect the future directions of lymphoma treatment on metabolic reprogramming.

Malaria Infection and Risk for Endemic Burkitt Lymphoma: A Systematic Review and Meta-Analysis

Background: Malaria infection is reportedly linked to endemic Burkitt lymphoma (eBL) in malaria-endemic areas. This study aimed to pool the overall risk (or odds) of eBL among children with previous or concurrent malaria infection. Methods: We searched PubMed, Web of Science, Scopus, and reference lists of publications for potentially relevant studies on malaria infection and eBL. The quality of the included studies was assessed using the Joanna Briggs Institute for case-control studies. Random-effects meta-analysis was used to summarize whether the odds of eBL can be increased by (1) malaria infection or (2) elevated titer of IgGs to malaria antigen. The level of heterogeneity was evaluated using Cochran’s Q statistic and I². The individual study data, pooled odds, and confidence interval (CI) were illustrated using the forest plot. Publication bias was assessed using funnel plots and Egger’s test. Results: Ten studies were included, reporting the number of malaria cases in eBL and non-eBL (5 studied malaria infection and the odds of eBL; five studied the burden of IgGs to malarial antigens and the odds of eBL). According to the meta-analysis results, the odds of eBL was not increased by malaria infection (p = 0.562, OR: 0.87, 95% CI: 0.54–1.39, I²: 93.5%, malaria in eBL: 604/1506 cases, malaria in non-eBL: 2117/4549 cases) and the elevated titer of IgGs to malaria antigen (p = 0.051, OR: 1.50, 95% CI: 1.00–2.25, I²: 89%, increased IgG titer in eBL: 1059/1736 cases, increased IgG titer in non-eBL: 847/1722 cases). In meta-regression analysis, sex was not a confounding factor for the effect size of malaria infection and eBL (p = 0.10) and that of increased IgGs and eBL (p = 0.80). Conclusions: Malaria infection and IgG titer elevation did not increase the risk for eBL among children. However, the included studies, which are only few, do not generally agree on this point. Therefore, the risk for eBL in children diagnosed with malaria should be investigated further by longitudinal studies to confirm our evidence-based approach.

Upregulation of the Chemokine Receptor CCR2B in Epstein‒Barr Virus-Positive Burkitt Lymphoma Cell Lines with the Latency III Program

CCR2 is the cognate receptor to the chemokine CCL2. CCR2–CCL2 signaling mediates cancer progression and metastasis dissemination. However, the role of CCR2–CCL2 signaling in pathogenesis of B-cell malignancies is not clear. Previously, we showed that CCR2B was upregulated in ex vivo peripheral blood B cells upon Epstein‒Barr virus (EBV) infection and in established lymphoblastoid cell lines with the EBV latency III program. EBV latency III is associated with B-cell lymphomas in immunosuppressed patients. The majority of EBV-positive Burkitt lymphoma (BL) tumors are characterized by latency I, but the BL cell lines drift towards latency III during in vitro culture. In this study, the CCR2A and CCR2B expression was assessed in the isogenic EBV-positive BL cell lines with latency I and III using RT-PCR, immunoblotting, and immunostaining analyses. We found that CCR2B is upregulated in the EBV-positive BL cells with latency III. Consequently, we detected the migration of latency III cells toward CCL2. Notably, the G190A mutation, corresponding to SNP CCR2-V64I, was found in one latency III cell line with a reduced migratory response to CCL2. The upregulation of CCR2B may contribute to the enhanced migration of malignant B cells into CCL2-rich compartments.

Viral Causes of Lymphoma: The History of Epstein-Barr Virus and Human T-Lymphotropic Virus 1

In 1964, Epstein, Barr, and Achong published a report outlining their discovery of viral particles in lymphoblasts isolated from a patient with Burkitt lymphoma. The Epstein-Barr virus (EBV) was the first human cancer virus to be described, and its discovery paved the way for further investigations into the oncogenic potential of viruses. In the decades following the discovery of EBV, multinational research efforts led to the discovery of further viral causes of various human cancers. Lymphomas are perhaps the cancer type that is most closely associated with oncogenic viruses: infection with EBV, human T-lymphotropic virus 1 (HTLV-1), human immunodeficiency virus (HIV), Kaposi sarcoma-associated herpesvirus/human herpesvirus 8, and hepatitis C virus have all been associated with lymphomagenesis. Lymphomas have also played an important role in the history of oncoviruses, as both the first human oncovirus (EBV) and the first human retrovirus (HTLV-1) were discovered through isolates taken from patients with unique lymphoma syndromes. The history of the discovery of these 2 key oncoviruses is presented here, and their impact on further medical research, using the specific example of HIV research, is briefly discussed.

Oculomotor nerve palsy as a preceding symptom of adult sporadic Burkitt lymphoma: A case report and review of the literature

Adult sporadic Burkitt lymphoma (BL) is a rare aggressive neoplasm and represents ~1-5% of all lymphomas diagnosed in adults. The disease exhibits an aggressive clinical manifestation, which frequently involves the central nervous system (CNS) in the early stages, and is usually accompanied by abnormalities in cerebrospinal fluid (CSF) examinations and/or neuroradiography. The current study describes the rare case of a 29-year-old man who presented with oculomotor nerve palsy without palpated masses, B symptoms, peripheral blood anomaly and abnormalities of the nervous system. The patient was initially misdiagnosed with abducens diplopia, but was subsequently confirmed to have BL with early CNS invasion. Epstein-Barr virus and human immunodeficiency virus infection were negative. Intensive systemic chemotherapy with hyperfractionated cyclophosphamide, vincristine, therarubicin and dexamethasone (hyper-CVAD, cyclophosphamide 600 mg/m² on days 2-4; vincristine 1.4 mg/m² on days 5 and 12, therarubicin 50 mg/m² on day 5 and dexamethasone 40 mg on days 2-5 and 12-15), including intrathecal chemotherapy with methotrexate (5 mg), arabinocytidine (5 mg) and dexamethasone (5 mg), was determined as an appropriate treatment. Rituximab (375 mg/m² on day 1) was administered alongside chemotherapy to increase treatment efficacy. The patient temporarily underwent complete remission, but subsequently relapsed as no suitable bone marrow donor was available. Adult sporadic BL with early CNS invasion, which traditional tests such as neuroradiography and CSF examination fail to identify, is uncommon. Therefore, appropriate diagnostic tests are critical for accurate diagnosis and must be performed immediately, particularly in patients that present with unusual image and laboratory manifestations.

Different Mechanisms of Regulation of the Warburg Effect in Lymphoblastoid and Burkitt Lymphoma Cells

Background

The Warburg effect is one of the hallmarks of cancer and rapidly proliferating cells. It is known that the hypoxia-inducible factor 1-alpha (HIF1A) and MYC proteins cooperatively regulate expression of the HK2 and PDK1 genes, respectively, in the Burkitt lymphoma (BL) cell line P493-6, carrying an inducible MYC gene repression system. However, the mechanism of aerobic glycolysis in BL cells has not yet been fully understood.

Methods and Findings

Western blot analysis showed that the HIF1A protein was highly expressed in Epstein–Barr virus (EBV)-positive BL cell lines. Using biochemical assays and quantitative PCR (Q-PCR), we found that—unlike in lymphoblastoid cell lines (LCLs)—the MYC protein was the master regulator of the Warburg effect in these BL cell lines. Inhibition of the transactivation ability of MYC had no influence on aerobic glycolysis in LCLs, but it led to decreased expression of MYC-dependent genes and lactate dehydrogenase A (LDHA) activity in BL cells.

Conclusions

Our data suggest that aerobic glycolysis, or the Warburg effect, in BL cells is regulated by MYC expressed at high levels, whereas in LCLs, HIF1A is responsible for this phenomenon.

Burkitt Lymphoma: beyond discoveries

First described in 1958 in Uganda, Burkitt lymphoma (BL) attracted interest worldwide following reports of its uneven geographic distribution and rapidly fatal clinical course. Both suggested infectious etiology and curability. Seminal discoveries followed in quick succession. Viral etiology - due to Epstein-Barr virus (EBV) - was confirmed. Chromosomal translocations, involving cellular MYC, a protooncogene, were discovered, shown to be a hallmark of BL, and central to the genetic basis of cancer. Cure of BL using combination chemotherapy was demonstrated. Unfortunately, civil disturbance in Africa disrupted BL research and blunted its impact on education and oncology care in Africa. Important questions went unanswered. The risk of BL due to malaria or EBV was not quantified. Efforts to answer whether BL could be prevented - by preventing malaria or early EBV infection - were abandoned. The mechanism of malaria in BL is unknown. In Africa, BL remains mostly fatal and diagnosis is still made clinically. Unprecedented advances in molecular, genomics and proteomic technologies, promising to unlock mysteries of cancers, have re-awakened interest in BL. With return of stability to Africa, the unanswered questions about BL are re-attracting global interest. This interest now includes exploiting the knowledge gained about genetics, proteomics, and bioinformatics to enable the development of targeted less toxic treatment for BL; and simpler methods to diagnose BL with high accuracy and sensitivity. The articles in the Burkitt Lymphoma (BL): Beyond Discoveries in Infectious Agents and Cancer highlight BL as priority. Authors explore etiology, pathology, pathogenesis of BL, and whether knowledge gained in the studies of BL can catalyze sustainable cancer services in one of the world's poorest served regions.

Endemic Burkitt lymphoma is associated with strength and diversity of Plasmodium falciparum malaria stage-specific antigen antibody response

Endemic Burkitt lymphoma (eBL) is linked to Plasmodium falciparum (Pf) infection geographically, but evidence from individual-level studies is limited. We investigated this issue among 354 childhood eBL cases and 384 age-, sex-, and location-matched controls enrolled in Ghana from 1965 to 1994. Immunoglobulin G1 (IgG1) and immunoglobulin G3 (IgG3) antibodies to antigens diagnostic of recent infection Pf histidine-rich protein-II (HRP-II) and 6NANP, Pf-vaccine candidates SE36 and 42-kDa region of the 3D7 Pf merozoite surface protein-1 (MSP-1), and tetanus toxoid were measured by indirect enzyme-linked immunoassay. Odds ratios (ORs) and 95% confidence intervals (CIs) for association with eBL were estimated using unconditional logistic regression. After adjustments, eBL was positively associated with HRP-IIIgG3 seropositivity (adjusted OR: 1.60; 95% CI 1.08-2.36) and inversely associated with SE36IgG1 seropositivity (adjusted OR: 0.37; 95% CI 0.21-0.64) and with tetanus toxoidIgG3 levels equal or higher than the mean (adjusted OR: 0.46; 95% CI 0.32-0.66). Anti-MSP-1IgG3 and anti-6NANPIgG3 were indeterminate. eBL risk was potentially 21 times higher (95% CI 5.8-74) in HRP-IIIgG3-seropositive and SE36IgG1-seronegative responders compared with HRP-IIIgG3-seronegative and SE36IgG1-seropositive responders. Our results suggest that recent malaria may be associated with risk of eBL but long-term infection may be protective.

Epstein-Barr virus patterns in US Burkitt lymphoma tumors from the SEER residual tissue repository during 1979-2009

Burkitt lymphoma (BL) occurs at all ages, but the patterns of Epstein-Barr virus (EBV) positivity in relation to human immunodeficiency virus (HIV), immunoprofiles and age have not been fully explored. BL tissues from residual tissue repositories, and two academic centers in the United States were examined by expert hematopathologists for morphology, immunohistochemistry, MYC rearrangement, EBV-encoded RNA (EBER), and diagnosed according to the 2008 WHO lymphoma classification. Analysis was done using frequency tables, Chi-squared statistics, and Student's t-test. Of 117 cases examined, 91 were confirmed as BL. The age distribution was 26%, 15%, 19%, and 29% for 0-19, 20-34, 35-59, 60+ years, and missing in 11%. MYC rearrangement was found in 89% and EBER positivity in 29% of 82 cases with results. EBER positivity varied with age (from 13% in age group 0-19 to 55% in age group 20-34, and fell to 25% in age group 60+ years, p = 0.08); with race (56% in Blacks/Hispanics vs 21% in Whites/Asians/Pacific Islanders, p = 0.006); and by HIV status (64% in HIV positive vs 22% in HIV negative cases, p = 0.03). EBER positivity was demonstrated in about one-third of tumors and it was strongly associated with race and HIV status, and marginally with age-group.

Burkitt lymphoma risk in U.S. solid organ transplant recipients

Case reports of Burkitt lymphoma (BL) in transplant recipients suggest that the risk is markedly elevated. Therefore, we investigated the incidence of BL in 203,557 solid organ recipients in the U.S. Transplant Cancer Match Study (1987-2009) and compared it with the general population using standardized incidence ratios. We also assessed associations with demographic and clinical characteristics, and treatments used to induce therapeutic immunosuppression. BL incidence was 10.8 per 100,000 person-years, representing 23-fold (95% confidence interval (CI) 19-28) greater risk than in the general population, and it peaked 3-8 years after the time of transplantation. In adjusted analyses, BL incidence was higher in recipients transplanted when <18 vs. ≥35 years (incidence rate ratio [IRR] 3.49, 95% CI 2.08-5.68) and in those transplanted with a liver (IRR 2.91, 95% CI 1.68-5.09) or heart (IRR 2.39, 95% CI 1.30-4.31) compared with kidney. BL incidence was lower in females than males (IRR 0.45, 95% CI 0.28-0.71), in blacks than whites (IRR 0.33, 95% CI 0.12-0.74), in those with a baseline Epstein-Barr virus (EBV)-seropositive versus EBV-seronegative status (IRR 0.34, 95% CI 0.13-0.93), and in those treated with azathioprine (IRR 0.56, 95% CI 0.34-0.89) or corticosteroids (IRR 0.48, 95% CI 0.29-0.82). Tumors were EBV-positive in 69% of 32 cases with results. EBV positivity was 90% in those aged <18 years and 59% in those aged 18+ years. In conclusion, BL risk is markedly elevated in transplant recipients, and it is associated with certain demographic and clinical features. EBV was positive in most but not all BL cases with results.

Pediatric, elderly, and emerging adult-onset peaks in Burkitt's lymphoma incidence diagnosed in four continents, excluding Africa

Burkitt's lymphoma (BL) in the general population and immunosuppressed persons with AIDS in the United States was characterized by three age-specific incidence peaks near 10, 40, and 70 years. We hypothesized that BL from different geographical areas may exhibit pediatric, adult, and elderly age incidence peaks. We investigated this hypothesis using data on 3,403 cases obtained from the International Agency for Research on Cancer (1963-2002). Data from Africa were sparse or incomplete, and thus were excluded. Age-standardized rates (ASRs) and age-specific incidence rates were calculated, supplemented with the calculations performed using age-period-cohort (APC) models. The ASR rose 5.3% (95% confidence interval [CI], 5.0-5.6) per year in males and 4.6% (95% CI, 4.5-4.8) in females. The ASR increased gradually in children, steeply in adults and most rapidly in the elderly both in males and in females. Overall, BL male/female ASR ratio was 2.5, but it declined from 3.1 (95% CI, 3.0-3.3) for pediatric BL to 2.3 (95% CI, 2.2-2.4) for adult BL and 1.5 (95% CI, 1.4-1.6) for elderly BL. Age-specific incidence peaks occurred near 10 and 70 years in all regions and periods. A peak near 40 years of age emerged in the mid-1990s, particularly in men. Findings using APC models confirmed those based on the standard analyses. Our findings, based on the international BL cases, support our hypothesis that BL is multimodal and that BL peaks at different ages may be clues to differences in the etiology and/or biology of BL at those ages.

E2F4 plays a key role in Burkitt lymphoma tumorigenesis

Sporadic Burkitt lymphoma (sBL) is a rapidly growing B-cell non-Hodgkin's lymphoma whose treatment requires highly aggressive therapies that often result severely toxic. Identification of proteins whose expression or function is deregulated in sBL and play a role in its formation could facilitate development of less toxic therapies. We have previously shown that E2F1 expression is deregulated in sBL. We have now investigated the mechanisms underlying E2F1 deregulation and found that the E2F sites in its promoter fail to repress its transcriptional activity in BL cells and that the transcriptional repressor E2F4 barely interacts with these sites. We also have found that E2F4 protein levels, but not those of its mRNA, are reduced in sBL cell lines relative to immortal B-cell lines. E2F4 protein expression is also decreased in 24 of 26 sBL tumor samples from patients compared with control tissues. Our data demonstrate that enforced E2F4 expression in BL cells not only diminishes E2F1 levels, but also reduces selectively the tumorigenic properties and proliferation of BL cells, while increasing their accumulation in G(2)/M. Our results therefore point to E2F4 as a target for developing novel and less toxic treatments for sBL.

African Burkitt lymphoma: age-specific risk and correlations with malaria biomarkers

African Burkitt lymphoma is an aggressive B-cell, non-Hodgkin lymphoma linked to Plasmodium falciparum malaria. Malaria biomarkers related to onset of African Burkitt lymphoma are unknown. We correlated age-specific patterns of 2,602 cases of African Burkitt lymphoma (60% male, mean ± SD age = 7.1 ± 2.9 years) from Uganda, Ghana, and Tanzania with malaria biomarkers published from these countries. Age-specific patterns of this disease and mean multiplicity of P. falciparum malaria parasites, defined as the average number of distinct genotypes per positive blood sample based on the merozoite surface protein-2 assessed by polymerase chain reaction, were correlated and both peaked between 5 and 9 years. This pattern, which was strong and consistent across regions, contrasted parasite prevalence, which peaked at 2 years and decreased slightly, and geometric mean parasite density, which peaked between 2 and 3 years and decreased sharply. Our findings suggest that concurrent infection with multiple malaria genotypes may be related to onset of African Burkitt lymphoma.

Infection, stem cells and cancer signals

The association of cancer with preceding parasitic infections has been observed for over 200 years. Some such cancers arise from infection of tissue stem cells by viruses with insertion of viral oncogenes into the host DNA (mouse polyoma virus, mouse mammary tumor virus). In other cases the virus does not insert its DNA into the host cells, but rather commandeers the metabolism of the infected cells, so that the cells continue to proliferate and do not differentiate (human papilloma virus and cervical cancer). Cytoplasmic Epstein Barr virus infection is associated with a specific gene translocation (Ig/c-myc) that activates proliferation of affected cells (Burkitt lymphoma). In chronic osteomyelitis an inflammatory reaction to the infection appears to act through production of inflammatory cytokines and oxygen radical formation to induce epithelial cancers. Infection with Helicobacter pylori leads to epigenetic changes in methylation and infection by a parasite. Clonorchis sinensis also acts as a promoter of cancer of the bile ducts of the liver (cholaniocarcinoma). The common thread among these diverse pathways is that the infections act to alter tissue stem cell signaling with continued proliferation of tumor transit amplifying cells.

AIDS-related Burkitt lymphoma in the United States: what do age and CD4 lymphocyte patterns tell us about etiology and/or biology?

Trimodal or bimodal age-specific incidence rates for Burkitt lymphoma (BL) were observed in the United States general population, but the role of immunosuppression could not be excluded. Incidence rates, rate ratios, and 95% confidence intervals for BL and other non-Hodgkin lymphoma (NHL), by age and CD4 lymphocyte count categories, were estimated using Poisson regression models using data from the United States HIV/AIDS Cancer Match study (1980-2005). BL incidence was 22 cases per 100 000 person-years and 586 for non-BL NHL. Adjusted BL incidence rate ratio among males was 1.6× that among females and among non-Hispanic blacks, 0.4× that among non-Hispanic whites, but unrelated to HIV-transmission category. Non-BL NHL incidence increased from childhood to adulthood; in contrast, 2 age-specific incidence peaks during the pediatric and adult/geriatric years were observed for BL. Non-BL NHL incidence rose steadily with decreasing CD4 lymphocyte counts; in contrast, BL incidence was lowest among people with ≤ 50 CD4 lymphocytes/μL versus those with ≥ 250 CD4 lymphocytes/μL (incidence rate ratio 0.3 [95% confidence interval = 0.2-0.6]). The bimodal peaks for BL, in contrast to non-BL NHL, suggest effects of noncumulative risk factors at different ages. Underascertainment or biological reasons may account for BL deficit at low CD4 lymphocyte counts.