Kaposi's Sarcoma Herpesvirus Research Articles

HHV-8 associated lymphoma.

The discovery of Kaposi sarcoma herpesvirus (KSHV) / human herpesvirus 8 (HHV-8) led to recognition of primary effusion lymphoma (PEL) as a distinct lymphoproliferative disorder. Subsequently, two other types of lymphoma have been shown to be associated with HHV-8 : HHV-8 positive diffuse large B cell lymphoma not otherwise specified and germinotropic lymphoproliferative disorder.The pathogenesis of PEL is unique as in most cases the HHV-8+ tumoral cells are coinfected with the Epstein-Barr virus (EBV), suggesting an interplay between these two herpesviruses. This article reviews advances in the field of characterization of the lymphomatous cells, pathogenesis, and targeted therapies. The gene expression profile analysis of PEL cells and the experimental coinfection of peripheral B cells with HHV-8 and EBV allow dissection of the mechanisms of lymphomagenesis and of the relative contribution of both viruses. Systemic chemotherapy regimen remains poorly effective but new therapeutic perspectives are open with the use of monoclonal antibodies, immunomodulatory drugs, and immunotherapy. HHV-8 associated lymphoma is a model for studying virus-induced lymphoproliferation and its relation with host immune response and PEL is a unique model to study the relative contribution of two herpesviruses to lymphomagenesis in coinfected cells.

Cancer care cost-effectiveness in low-income and middle-income countries: time to shift the burden of proof

Kaposi sarcoma is one of the most common cancers in sub-Saharan Africa and is associated with substantial morbidity and mortality.1 Kaposi sarcoma is caused by the Kaposi's sarcoma herpesvirus. Although Kaposi sarcoma was recognised in endemic form before the HIV epidemic, HIV has driven an epidemic, AIDS-associated form of the disease.2

The emerging fifth epidemiologic subtype of Kaposi sarcoma in HIV-negative men who have sex with men at a tertiary care center in NYC from 2000 to 2021.

11579 Background: Kaposi sarcoma (KS) is a vascular tumor caused by human herpesvirus 8, also known as Kaposi sarcoma herpesvirus. There are 4 widely accepted distinct epidemiologic subtypes of KS: classic, endemic, iatrogenic, and epidemic (HIV-associated) forms. An emerging 5th subtype is increasingly recognized: non-epidemic KS in men who have sex with men (MSM) who are HIV-negative and have no other known causes for immunodeficiency. Objectives: To characterize a cohort of non-epidemic KS seen at the Sarcoma Medical Oncology or Dermatology Clinics at Memorial Sloan Kettering Cancer Center in New York City from 2000 to 2021 to identify risk factors, presentation, treatment course, and prognosis of these patients. Methods: Following IRB approval, a retrospective observational study was performed. Eligible patients were identified through the Electronic Health Records (EHR). The patients were characterized based on age at presentation, sex, gender identity, comorbidities, coinfections, and treatments and outcomes amongst other factors. Study data were collected and managed using REDCap electronic data capture tools. Results: Seventy-two patients were identified. The median age at time of diagnosis was 58 (range: 32-83). At initial diagnosis, 46% (33/72) of patients underwent observation, 50% (36/72) received localized treatment (i.e. excision, cryotherapy or topical therapy), and 4% (3/72) received systemic treatment with chemotherapy. The median duration of follow-up was 22 months. In follow-up, 43% (31/72) of patients had progression of disease requiring recurrent treatment: 24% (17/72) received localized treatment while 18% (13/72) received chemotherapy. Patients who received chemotherapy, predominantly pegylated liposomal doxorubicin, received treatment for a median duration of 13 months (range: 2-72 months). By the end of the follow-up period, 7 patients had died, of which 2 deaths were attributed to KS. During follow up, 10% (7/72) of patients were diagnosed with a lymphoproliferative disorder. Conclusions: This study is the largest yet, to our knowledge, to characterize the non-epidemic KS subtype in HIV-negative MSM. It is important to recognize this KS subtype to identify these individuals, who despite not having HIV are at increased risk for KS. Accurate recognition of this subtype may also allay patient concerns regarding overall prognosis, given that the majority of these patients present with indolent disease and have favorable outcomes compared to the epidemic variant of KS. Additional research is needed to understand the potential increased risk of lymphoproliferative disorders.

Human Oncoviruses and Thoracic Tumors: Understanding the Imaging Findings.

Approximately 1.4 million virus-induced cancers occur annually, representing roughly 10% of the cancer burden worldwide. Seven oncogenic DNA and RNA viruses (ie, oncoviruses) are implicated in approximately 12%-25% of all human cancers owing to a variety of mechanisms as uncommon consequences of the normal viral life cycle. These seven well-recognized human oncoviruses are Epstein-Barr virus (EBV), human T-lymphotropic virus 1, hepatitis B virus, hepatitis C virus, HIV, human papilloma virus (HPV), and human herpesvirus 8 (HHV-8). Several viruses-namely, EBV, HPV, and Kaposi sarcoma herpesvirus or HHV-8-are increasingly being recognized as being related to HIV and/or AIDS, the growing number of transplant cases, and the use of immunosuppressive therapies. Infectious and inflammatory processes, and the accompanying lymphadenopathy, are great mimickers of human oncovirus-related tumors. Although it is often difficult to differentiate these entities, the associated clinical setting and radiologic findings may provide clues for an accurate diagnosis and appropriate management. Malignant lymphoid lesions are best evaluated with multidetector chest CT. The radiologic findings of these lesions are often nonspecific and are best interpreted in correlation with clinical data and histopathologic findings. ©RSNA, 2022.

Structural Insight into KsBcl-2 Mediated Apoptosis Inhibition by Kaposi Sarcoma Associated Herpes Virus.

Numerous large DNA viruses have evolved sophisticated countermeasures to hijack the premature programmed cell death of host cells post-infection, including the expression of proteins homologous in sequence, structure, or function to cellular Bcl-2 proteins. Kaposi sarcoma herpes virus (KSHV), a member of the gammaherpesvirinae, has been shown to encode for KsBcl-2, a potent inhibitor of Bcl-2 mediated apoptosis. KsBcl-2 acts by directly engaging host pro-apoptotic Bcl-2 proteins including Bak, Bax and Bok, the BH3-only proteins; Bim, Bid, Bik, Hrk, Noxa and Puma. Here we determined the crystal structures of KsBcl-2 bound to the BH3 motif of pro-apoptotic proteins Bid and Puma. The structures reveal that KsBcl-2 engages pro-apoptotic BH3 motif peptides using the canonical ligand binding groove. Thus, the presence of the readily identifiable conserved BH1 motif sequence “NWGR” of KsBcl-2, as well as highly conserved Arg residue (R86) forms an ionic interaction with the conserved Asp in the BH3 motif in a manner that mimics the canonical ionic interaction seen in host Bcl-2:BH3 motif complexes. These findings provide a structural basis for KSHV mediated inhibition of host cell apoptosis and reveal the flexibility of virus encoded Bcl-2 proteins to mimic key interactions from endogenous host signalling pathways.

Antibodies Targeting KSHV gH/gL Reveal Distinct Neutralization Mechanisms

Kaposi’s sarcoma herpesvirus (KSHV) is associated with a significant disease burden, in particular in Sub-Sahara Africa. A KSHV vaccine would be highly desirable, but the mechanisms underlying neutralizing antibody responses against KSHV remain largely unexplored. The complex made of glycoproteins H and L (gH/gL) activates gB for the fusion of viral and cellular membranes in all herpesviruses. KSHV gH/gL also interacts with cellular Eph family receptors. To identify optimal antigens for vaccination and to elucidate neutralization mechanisms, we primed mice with recombinantly expressed, soluble gH/gL (gHecto/gL) that was either wildtype (WT), lacking defined glycosylation sites or bearing modified glycosylation, followed by boosts with WT gHecto/gL. We also immunized with a gL-gHecto fusion protein or a gHecto-ferritin/gL nanoparticle. Immune sera neutralized KSHV and inhibited EphA2 receptor binding. None of the regimens was superior to immunization with WT gHecto/gL with regard to neutralizing activity and EphA2 blocking activity, the gL-gHecto fusion protein was equally effective, and the ferritin construct was inferior. gH/gL-targeting sera inhibited gB-mediated membrane fusion and inhibited infection also independently from receptor binding and gL, as demonstrated by neutralization of a novel KSHV mutant that does not or only marginally incorporate gL into the gH/gL complex and infects through an Eph-independent route.

AMC-070: Lenalidomide Is Safe and Effective in HIV-Associated Kaposi Sarcoma.

Kaposi sarcoma (KS), an endothelial cell tumor associated with KS herpesvirus (KSHV), remains among the most common malignancies occurring with HIV infection (HIV-KS). As an oral anti-inflammatory, antiangiogenic, and immunomodulatory agent, lenalidomide is potentially an attractive alternative to standard chemotherapy for KS. The primary objectives of this phase I/II trial were to determine the maximum tolerated dose (MTD) and response rates for lenalidomide in HIV-KS. Secondary objectives included correlating response with natural killer (NK) and T-cell subsets, plasma cytokines, viral copy number, and KSHV gene expression in biopsies. Four dose levels of oral lenalidomide taken 21 consecutive days of 28-day cycles were evaluated in adults with HIV-KS on antiretroviral therapy with controlled viremia. Fifteen and 23 participants enrolled in phases I and II, respectively, 76% of whom had received prior KS therapy. The MTD was not reached, declaring 25 mg as the recommended phase II dose (RP2D). The most frequent adverse events were neutropenia, fatigue, leukopenia, and diarrhea. Of the 25 evaluable participants receiving RP2D, 60% responded. Correlative studies performed in a subset of participants demonstrated a significant increase in proportions of blood T cells with T-regulatory phenotype, and plasma cytokines trended toward a less inflammatory pattern. Clinical response was associated with loss of KSHV transcription. Lenalidomide is active in HIV-KS. The most common adverse events were manageable. With 60% of participants receiving RP2D obtaining a partial response and <10% discontinuing due to adverse events, the response and tolerability to lenalidomide support its use in HIV-KS. See related commentary by Henry and Maki, p. 2485.

Selected Articles from This Issue

Kaposi sarcoma (KS) arises after Kaposi sarcoma herpesvirus infection and frequently develops in HIV-positive individuals. Ramaswami and colleagues conducted a clinical trial of pomalidomide, an oral immunomodulating thalidomide derivative, in patients with KS with or without HIV. The overall response rate was 71%, with 67% of HIV-positive patients and 80% of HIV-negative participants showing a response. Baseline IL-6 levels were higher in nonresponders compared with responders, although further assessment of IL-6 as a biomarker is warranted. Based on these results, the United Stated Food and Drug Administration granted accelerated approval to pomalidomide for the treatment KS.TIGIT is a novel target in the field of cancer immunotherapy. To explore the potential of anti-TIGIT immunotherapy, Mettu and colleagues conducted a phase 1a/b study to evaluate the safety, tolerability, and preliminary efficacy of the novel anti-TIGIT antibody etigilimab alone (phase 1a) and in combination with the anti-PD-1 nivolumab (phase 1b) in patients with refractory solid tumors. This first-in-human study showed etigilimab was well tolerated. Signs of anti-tumor activity were observed, with eight patients showing stable disease and one patient showing a partial response. Biomarker analyses demonstrated evidence of clear dose-dependent target engagement by etigilimab. These findings lay a foundation for future clinical trials targeting TIGIT.Detecting neuroendocrine prostate cancer (NEPC) in men with metastatic castration-resistant prostate cancer (mCRPC) has important prognostic and therapeutic implications but is challenging in clinical practice. To address this unmet need, Berchuck and colleagues developed a noninvasive biomarker, termed NEPC Risk Score, based on tissue-informed cell-free DNA (cfDNA) methylation analysis. Applying the NEPC Risk Score to cfDNA from two independent mCRPC cohorts discriminated between men with versus without NEPC with high accuracy. These data support the further clinical development of this cfDNA methylation-based biomarker to noninvasively identify men with NEPC who should be considered for platinum-based chemotherapy or clinical trials of NEPC-directed therapies.PD-1 blockade has provided benefit for some patients with advanced sarcomas. However, predicting response is not feasible currently. Furthermore, the relevance of hyperprogressive disease (HPD) is unclear. Klemen and colleagues performed a pooled analysis of prospective trials evaluating checkpoint inhibition in patients with sarcoma. In total, 134 patients were assessed, of which 16% had a complete or partial response, 36% had stable disease, 34% had progressive disease without HPD, and 11% with HPD. Patients with HPD and non-HPD progressive disease showed similarities in terms of disease subtype, clinical features, and genomic alterations. Interestingly, patients developing HPD had smaller tumors at baseline than patients who progressed without HPD. Additional clinical studies will be required to further understand HPD in patients with sarcoma.

Burden of Kaposi sarcoma according to HIV status: A systematic review and global analysis.

In 2020, over 34 000 cases of Kaposi sarcoma (KS) were estimated globally, all attributable to KS herpesvirus (KSHV). Prior to the HIV epidemic, KS already existed in KSHV endemic regions, notably in sub-Saharan Africa (SSA). The HIV epidemic has vastly increased the KS burden. We developed a methodology to provide global estimates of KS burden according to HIV status. A systematic review identified studies reporting HIV prevalence in consecutive KS series. Pooled estimates of HIV prevalence, by country or UN subregion, were used to calculate population-attributable fraction (PAF) and these were applied to IARC's GLOBOCAN 2020 to estimate burden and incidence of HIV-attributable and non-HIV-attributable KS. We identified 55 eligible studies, reporting HIV prevalence ranging from ≤5% to ≥95%. Approximately 80% of KS in SSA was estimated attributable to HIV, vs ~50% in the rest of the world. By applying PAFs to national GLOBOCAN estimates, an estimated 19 560 KS cases attributable to HIV were diagnosed in SSA in 2020 (~80% of the worldwide burden), vs 5064 cases of non-HIV-attributable KS (~60% of the worldwide burden). Incidence of HIV-attributable KS was highest in Southern Africa (6.0 cases per 100 000) and Eastern Africa (3.4), which were also the world regions with highest incidence of non-HIV-attributable KS (0.4 and 1.0 cases per 100 000, respectively). This first systematic effort to produce a global picture of KS burden stratified by HIV status highlights the continuing important burden of HIV-attributable KS in SSA, even in the era of combined antiretroviral therapy.

827. High KSHV Seroprevalence Among MSM with HIV Associated with Oral Intercourse and Methamphetamine Use in the Southern United States

BackgroundDespite a decrease in Kaposi’s sarcoma (KS) cases in much of the US, the incidence of KS and associated mortality is increasing in specific subpopulations, particularly young, African American men in the South. To further understand this disparity, we sought to describe the seroprevalence and risk factors associated with Kaposi’s sarcoma herpesvirus (KSHV) among men who have sex with men (MSM) and transgender women (TGW) with HIV in Dallas, Texas. MethodsWe enrolled MSM and TGW with HIV and without known KSHV-related disease from a large urban safety-net clinic in Dallas. Blood samples were collected from participants for IgG testing (K8.1 and ORF73), followed by KSHV PCR on blood and saliva samples for those with positive IgG results. We also collected demographics, sexual history, sexual practices, HIV history, substance use, and insurance status. Multivariate logistic regression modeling was performed to identify associations with KSHV seropositivity. ResultsOf 159 participants, 110 (69.2%) were seropositive for KSHV. Seroprevalence varied by race/ethnicity, with 27/34 (79.4%) Hispanic, 27/37 (73.0%) white, and 54/84 (64.3%) black participants testing positive for KSHV IgG, though this difference was not statistically significant. 31/104 (29.8%) seropositive participants had detectable KSHV in saliva and 10/104 (9.6%) seropositive participants had detectable KSHV in blood. Risk factors independently associated with KSHV seropositivity include oral-anal sex (OR 4.02, 95% CI 1.89 – 8.54), oral-penile sex (OR 3.66, 95% CI 1.16 – 11.57), and methamphetamine use (OR 2.73, 95% CI 1.23 – 6.04). Current CD4 count, HIV viral load, history of intravenous drug use, tobacco or alcohol use were not associated with KSHV seropositivity. Table 1. Patient Characteristics ConclusionWe found that over two-thirds of MSM and TGW with HIV in Dallas are KSHV seropositive, which is relatively high compared to other studies of US MSM with HIV (30-70%). In our study, KSHV was more common among Hispanic and white individuals, and was associated with higher rates of oral sex and methamphetamine use. Differences in KSHV seroprevalence alone are unlikely to explain racial disparities in the incidence of KS. Further study is needed to better understand drivers of KSHV infection and KSHV-related diseases in highly impacted groups in the US.Disclosures All Authors: No reported disclosures

Kaposi's sarcoma herpesvirus activates the hypoxia response to usurp HIF2α-dependent translation initiation for replication and oncogenesis.

SUMMARYKaposi’s sarcoma herpesvirus (KSHV) is an angiogenesis-inducing oncovirus whose ability to usurp the oxygen-sensing machinery is central to its oncogenicity. By upregulating the hypoxia-inducible factors (HIFs), KSHV reprograms infected cells to a hypoxia-like state, triggering angiogenesis. Here we identify a link between KSHV replicative biology and oncogenicity by showing that KSHV’s ability to regulate HIF2α levels and localization to the endoplasmic reticulum (ER) in normoxia enables translation of viral lytic mRNAs through the HIF2α-regulated eIF4E2 translation-initiation complex. This mechanism of translation in infected cells is critical for lytic protein synthesis and contributes to KSHV-induced PDGFRA activation and VEGF secretion. Thus, KSHV regulation of the oxygen-sensing machinery allows virally infected cells to initiate translation via the mTOR-dependent eIF4E1 or the HIF2α-dependent, mTOR-independent, eIF4E2. This “translation initiation plasticity” (TRIP) is an oncoviral strategy used to optimize viral protein expression that links molecular strategies of viral replication to angiogenicity and oncogenesis.

Castleman disease.

Castleman disease (CD), a heterogeneous group of disorders that share morphological features, is divided into unicentric CD and multicentric CD (MCD) according to the clinical presentation and disease course. Unicentric CD involves a solitary enlarged lymph node and mild symptoms and excision surgery is often curative. MCD includes a form associated with Kaposi sarcoma herpesvirus (KSHV) (also known as human herpesvirus 8) and a KSHV-negative idiopathic form (iMCD). iMCD can present in association with severe syndromes such as TAFRO (thrombocytopenia, ascites, fever, reticulin fibrosis and organomegaly) or POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal plasma cell disorder and skin changes). KSHV-MCD often occurs in the setting of HIV infection or another cause of immune deficiency. The interplay between KSHV and HIV elevates the risk for the development of KSHV-induced disorders, including KSHV-MCD, KSHV-lymphoproliferation, KSHV inflammatory cytokine syndrome, primary effusion lymphoma and Kaposi sarcoma. A CD diagnosis requires a multidimensional approach, including clinical presentation and imaging, pathological features, and molecular virology. B cell-directed monoclonal antibody therapy is the standard of care in KSHV-MCD, and anti-IL-6 therapy is the recommended first-line therapy and only treatment of iMCD approved by the US FDA and EMA.

KSHV/HHV8-Associated Lymphoproliferative Disorders: Lessons Learnt from People Living with HIV

In 1992, Kaposi sarcoma herpesvirus (KSHV/HHV8) was discovered and identified as the causative agent for Kaposi sarcoma. Subsequently, the presence of this virus has been detected in a number of lymphoproliferative disorders in people living with HIV (PLWH), including: KSHV-associated multicentric Castleman disease, primary effusion lymphoma, KSHV-positive diffuse large B-cell lymphoma, and germinotropic lymphoproliferative disorder. Each of these rare entities has subsequently been diagnosed in HIV-negative individuals. The recognition of some of these KSHV/HHV8-associated lymphoproliferative disorders has led to their inclusion in the WHO classification of lymphomas in 2008 and the revision of 2016; however, further revision is under way to update the classification. The relatively recent recognition of these lymphoproliferative disorders and their low incidence, particularly in the HIV-negative population, means that there is little published evidence and consensus on their clinical features and management. The publication of a new WHO classification of lymphomas should yield diagnostic clarity, providing an impetus for retrospective case series and prospective clinical trials in these KSHV/HHV8-associated lymphoproliferative disorders.

Real time, in-line optical mapping of single molecules of DNA

DNA optical mapping in nanochannels allows studying intact molecules and analyzing their long-range structure at the single-molecule level. Recent efforts have demonstrated that optical mapping can be used for various biomedical applications, such as bacteria identification, analysis of tumor cells, or whole-genome mapping. However, techniques for optical mapping are still slow and restricted to specialized labs. Here, we show a complete methodology for real-time DNA optical mapping on-chip, which is simple and offers high throughput. It does not require a microscope nor a high sensitivity camera to read the barcode, nor the use of external forces (like electrophoresis) to drive the molecules into the nanochannels. The DNA molecules are labelled with different methods, which allows barcoding known and unknown molecules. The barcoded DNA sample is analyzed in single-use, plastic nanoimprinted fluidic devices, which are versatile platforms to manipulate and stretch the molecules in nanochannels. And the fluorescent signal of the molecules is recorded in-line, in real time, with a laser system and a photon counter. With this methodology, we obtained barcodes of molecules with periodic sequences, where we marked one site per period. Furthermore, we barcoded the DNA of bacteriophages (Lambda and T4) and of a tumor virus (the Kaposi Sarcoma Herpesvirus, KSHV) by competitive binding, and obtained their unique fingerprints. Interestingly, this method succeeds in the correct detection (length and number) of highly repetitive structures such as the terminal repeat region of KSHV. These results show the versatility of the proposed methodology for fast (few milliseconds per molecule), low cost, high throughput (tens of molecules per minute) DNA analysis on-demand for biomedical applications. In particular, it can be used to analyze DNA with repeated sequences complementing other commercial techniques.

HHV-6 in the Lymphoma Microenvironment: Both Chicken and Egg?

HHV-6 in the Lymphoma Microenvironment: Both Chicken and Egg?

Treatment Outcomes and Prognostic Factors in 40 Patients with Primary Effusion Lymphoma

Background: Primary effusion lymphoma (PEL) is a rare, B cell non-Hodgkin lymphoma (NHL) caused by Kaposi sarcoma herpesvirus (KSHV), also known as human herpesvirus 8, that is strongly associated with HIV infection. PEL often presents as malignant body cavity effusions but can also present as extracavitary masses. Patients may also have concurrent Kaposi sarcoma (KS) or multicentric Castleman disease (MCD). 80% of PEL is also positive for EBV, and in a cohort of 20 patients we previously showed EBV + PEL had improved overall survival (OS) (Lurain et al. Blood 2019). PEL prognosis is poor compared to other HIV-associated NHL with median survival of 6-10 months. While patients are often treated with chemotherapy regimens used in other NHL, the optimal front-line and subsequent-line treatments are unknown. In this largest cohort of patients with PEL in the United States, we evaluated survival, prognostic markers, and second-line treatments in relapsed/refractory disease.Methods: We analyzed clinical records of all patients with PEL treated in the HIV and AIDS Malignancy Branch at the National Cancer Institute from 2000-2021. We collected demographics, disease characteristics, concurrent KS and MCD, EBV status of tumor by EBER staining, and laboratory data at diagnosis as well as at progression and subsequent lines of therapy. We calculated overall survival (OS) of all patients and progression-free survival (PFS) in those who received front-line EPOCH by Kaplan-Meier method. The survival of extracavitary vs. cavitary PEL was compared using an exact log-rank test. A univariate Cox proportional hazard model was performed to determine prognostic variables associated with OS.Results: We identified 40 patients with PEL: 38 cisgender men, 2 cisgender women; 18 non-Hispanic Black, 6 Hispanic, 16 non-Hispanic White; median age 41 years. At diagnosis of PEL, 29 patients had concurrent KS, and 7 had concurrent MCD. Eight patients had only extracavitary disease, and 5 had leptomeningeal disease. All but 1 had HIV, and all with HIV received antiretroviral therapy. At diagnosis, median HIV viral load (VL) was 50 (IQR: 27-8323) copies/mL, median CD4 + cell count was 100 (IQR:44-395) cells/µL, and median KSHV VL was 4147 copies/10 6 cells (IQR:178-68,526). One patient died prior to receiving treatment. Of the 39 patients who received front-line treatment, 38 received combination chemotherapy (EPOCH [36], CHOP [1], ICE [1]) with rituximab added in 34 patients to treat concurrent MCD or deplete the KSHV-infected B cell reservoir. One patient received pembrolizumab as up-front therapy due to concurrent progressive multifocal leukoencephalopathy. Twenty-three (57%) had complete remission (CR) by Lugano criteria. Median PFS after front-line EPOCH was 16.4 months (Figure 1a), and median OS in all patients was 35.6 months (Figure 1b), with 5-year OS of 44%. Median OS for patients with extracavitary disease was significantly higher than in patients with cavitary disease (p=0.023, Figure 1c). EBER-positive tumors (HR=0.21, p=0.005) were associated with improved survival, while concurrent KS, MCD, leptomeningeal disease, and baseline CD4 and KSHV VL were not associated with OS outcomes.Eleven patients with relapsed/refractory disease received second-line therapy, including combination chemotherapy (3); brentuximab (3); pembrolizumab (1); pembrolizumab and pomalidomide (1); interferon-alpha, ganciclovir, and bevacizumab (1); bortezomib, ganciclovir, and zidovudine (1); and radiation to pelvic lymph nodes (1). Five of these patients received subsequent treatment after disease progression, including 2 patients with leptomeningeal PEL, 1 who received daratumumab and 1 who received pomalidomide and pembrolizumab with ongoing CRs at 12 months and 33 months, respectively.Conclusion: Patients with PEL had a median OS of 35.6 months, which is improved from previous reports. Patients with extracavitary PEL appear to have improved OS, and we confirmed our prior study noting EBER-positive PEL is a positive prognostic marker. Promising chemotherapy-sparing treatment regimens in relapsed/refractory PEL, include pembrolizumab, pomalidomide, and daratumumab. [Display omitted] DisclosuresUldrick: Regeneron: Current Employment; Roche: Research Funding; Merck: Other: Receives study drug; Celgene: Research Funding. Yarchoan: Celgene: Research Funding; Merck: Other: Clinical Trial Support; EMD-Serano: Other: Clinical Trial Support; Eli Lilly: Other: Clinical Trial Support; CTI BioPharma: Other: Clinical Trial Support; Janssen Pharmaceuticals: Other: Clinical Trial Support; U.S. Dept of Health and Human Services: Patents & Royalties. Lurain: EMD-Serrono: Research Funding; BMS-Celgene: Research Funding; CTI Biopharma: Research Funding; Merck: Research Funding; Janssen: Research Funding.

Targeting Metabolic Vulnerabilities in Primary Effusion Lymphoma Using the Novel Nucleoside Analog 6-Eti

Although nucleoside analogues have been used effectively in the clinic for the treatment of a wide range of hematological malignancies, lack of response to currently available nucleoside analogues and drug resistance limit their utility. A rare but highly aggressive cancer is primary effusion lymphoma (PEL). Through high throughput screening, we have discovered a novel nucleoside analog, called 6-ethylthioinosine (6-ETI) as a potent and selective inhibitor of PEL, with little activity in other lymphomas tested. PEL is a rare B-cell non-Hodgkin's lymphoma characterized by lymphomatous effusions in body cavities. It is associated with Kaposi's sarcoma herpesvirus (KSHV/HHV-8) infection and occurs mainly in immunocompromised patients. PEL is known to frequently be resistant to conventional chemotherapy (CHOP and EPOCH) resulting in poor prognosis and a rather incurable disease. Our studies demonstrated that 6-ETI is a pro-drug activated by adenosine kinase (ADK), an enzyme that is overexpressed in PEL cell lines and primary PEL specimens, as well as other plasma cell malignancies, including plasmablastic lymphoma (PBL) and multiple myeloma (MM). The latter is also responsive to 6-ETI in vitro and in mouse models. 6-ETI induces S phase arrest and inhibits DNA synthesis. RNA sequencing of in vitro generated PEL resistant clones and CRISPR knock out of ADK (ADK KO), respectively, indicated that mutations or loss of expression of ADK renders cells resistant to treatment. This data demonstrates that ADK expression can be used as a predictive biomarker of response to 6-ETI, which can help identify which patients are more likely to respond to this treatment.We investigated which pathways are differentially regulated in sensitive and resistant cells to better delineate the mechanism of action of 6-ETI and to design effective combinatorial regimens and prevent resistance. We found that drug sensitivity was associated with AMPK activation and inhibition of PI3K/mTOR/p70S6K signaling. Little is known about the function of ADK in plasma cell neoplasms. Knock-out of this protein in PEL, or use of ADK chemical inhibitors, do not affect their viability. Thus, we used ADK KO cell lines to examine the role of ADK in these tumors and to determine if cells undergo adaptations that may contribute to 6-ETI resistance and represent potential vulnerabilities to combat it. We performed metabolic and transcriptomic profiling of wild type (WT) (6-ETI sensitive) and ADK KO (6-ETI resistant) cells to achieve a comprehensive assessment of all the metabolic perturbations and gene expression changes induced by knocking out ADK. We also treated these cells with 6-ETI to examine the effects in sensitive and resistant cells. This integrated analysis revealed that 6-ETI depletes sensitive PEL cells of their nucleotide pools accompanied by the downregulation of several genes in purine and pyrimidine biosynthesis pathways. We found that adenine supplementation rescues sensitive PEL cells from 6-ETI induced cytotoxicity, reverses p70S6K inhibition and restores DNA synthesis suggesting that purine metabolism is a critical mediator of 6-ETI induced cytotoxicity. Using seahorse bioenergetic assay, we show that ADK KO resistant cells have impaired mitochondrial respiration indicating that ADK plays a critical role in mitochondrial bioenergetics. Metabolic profiling of these ADK KO resistant cells showed that these cells have elevated levels of de novo pyrimidine metabolic intermediates. Metabolic flux through de novo pyrimidine is controlled by the rate limiting enzyme CAD. The activity of CAD is regulated by ribosomal protein S6 Kinase 1(S6K1) by phosphorylation at its (Ser1859) site. Using western blotting, we observed a striking increase of phosphorylation of CAD at its S6K1 site (Ser1859) in ADK KO cells compared to WT cells.This is the first to date study that characterizes the role of ADK in lymphomas. Our data indicates that ADK KO cells have undergone metabolic reprogramming to upregulate de novo pyrimidine biosynthesis and p70S6K signaling. Moreover, we found that 6-ETI synergizes with the pan PI3K inhibitor BKM120 highlighting nucleotide metabolism and PI3K/mTOR signaling as key therapeutic vulnerabilities targeted by this novel nucleoside analog. DisclosuresNo relevant conflicts of interest to declare.

DNA damage triggers an interplay between wtp53 and c-Myc affecting lymphoma cell proliferation and Kaposi sarcoma herpesvirus replication

The induction of DNA damage together with the interference with DNA repair represents a promising strategy in cancer treatment. Here we show that the PARP-1/2/3 inhibitor AZD2461 in combination with the CHK1 inhibitor UCN-01 altered the DNA damage response and reduced cell proliferation in PEL cells, an aggressive B cell lymphoma highly resistant to chemotherapies.AZD2461/UCN-01 combination activated p53/p21 and downregulated c-Myc in these cells, leading to a reduced expression level of RAD51, molecule involved in DNA repair. The effect of AZD2461/UCN-01 on c-Myc and p53/p21 was inter-dependent and, besides impairing cell proliferation, contributed to the activation of the replicative cycle of KSHV, carried in a latent state in PEL cells. Finally, we found that the pharmacological or genetic inhibition of p21 counteracted the viral lytic cycle activation and further reduced PEL cell proliferation, suggesting that it could induce a double beneficial effect in this setting. This study unveils that, therapeutic approaches, based on the induction of DNA damage and the reduction of DNA repair, could be used to successfully treat this malignant lymphoma.

Conquering the Host: Determinants of Pathogenesis Learned from Murine Gammaherpesvirus 68.

Gammaherpesviruses are an important class of oncogenic pathogens that are exquisitely evolved to their respective hosts. As such, the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV) do not naturally infect nonhuman primates or rodents. There is a clear need to fully explore mechanisms of gammaherpesvirus pathogenesis, host control, and immune evasion in the host. A gammaherpesvirus pathogen isolated from murid rodents was first reported in 1980; 40 years later, murine gammaherpesvirus 68 (MHV68, MuHV-4, γHV68) infection of laboratory mice is a well-established pathogenesis system recognized for its utility in applying state-of-the-art approaches to investigate virus-host interactions ranging from the whole host to the individual cell. Here, we highlight recent advancements in our understanding of the processes by which MHV68 colonizes the host and drives disease. Lessons that inform KSHV and EBV pathogenesis and provide future avenues for novel interventions against infection and virus-associated cancers are emphasized.

1543P Gemcitabine in classic Kaposi’s sarcoma: A pilot study

Kaposi’s Sarcoma (KS) is a rare multifocal neoplasm of lymphatic endothelium-derived cells, associated with infection by human herpes virus-8 (also called KS herpes virus). Four clinical subtypes are recognized: classic, endemic, epidemic (HIV-related), and iatrogenic. Classic KS typically occurs in elderly people of specific areas, such as the Mediterranean; it usually featured by skin lesions, often at lower limbs, without visceral involvement, and has a chronic course that requires systemic chemotherapy for locally aggressive extensive disease.