Hypoxia enhances the phosphorylation and cytotoxicity of ganciclovir and zidovudine in Kaposi's sarcoma-associated herpesvirus infected cells

HIV-associated cancers and lymphoproliferative disorders caused by Kaposi sarcoma herpesvirus and Epstein-Barr virus

SUMMARYWithin weeks of the first report of acquired immunodeficiency syndrome (AIDS) in 1981, it was observed that these patients often had Kaposi sarcoma (KS), a hitherto rarely seen skin tumor in the USA. It soon became apparent that AIDS was also associated with an increased incidence of high-grade lymphomas caused by Epstein-Barr virus (EBV). The association of AIDS with KS remained a mystery for more than a decade until Kaposi sarcoma-associated herpesvirus (KSHV) was discovered and found to be the cause of KS. KSHV was subsequently found to cause several other diseases associated with AIDS and human immunodeficiency virus (HIV) infection. People living with HIV/AIDS continue to have an increased incidence of certain cancers, and many of these cancers are caused by EBV and/or KSHV. In this review, we discuss the epidemiology, virology, pathogenesis, clinical manifestations, and treatment of cancers caused by EBV and KSHV in persons living with HIV.

The complete Kaposi sarcoma-associated herpesvirus genome induces early-onset, metastatic angiosarcoma in transgenic mice

Kaposi sarcoma (KS) is the most common cancer in persons living with HIV. It is caused by KS-associated herpesvirus (KSHV). There exists no animal model for KS. Pronuclear injection of the 170,000-bp viral genome induces early-onset, aggressive angiosarcoma in transgenic mice. The tumors are histopathologically indistinguishable from human KS. As in human KS, all tumor cells express the viral latency-associated nuclear antigen (LANA). The tumors transcribe most viral genes, whereas endothelial cells in other organs only transcribe the viral latent genes. The tumor cells are of endothelial lineage and exhibit the same molecular pattern of pathway activation as KS, namely phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR, interleukin-10 (IL-10), and vascular endothelial growth factor (VEGF). The KSHV-induced tumors are more aggressive than Ha-ras-induced angiosarcomas. Overall survival is increased by prophylactic ganciclovir. Thus, whole-virus KSHV-transgenic mice represent an accurate model for KS and open the door for the genetic dissection of KS pathogenesis and evaluation of therapies, including vaccines.

Pacritinib inhibits proliferation of primary effusion lymphoma cells and production of viral interleukin-6 induced cytokines

Primary effusion lymphoma (PEL) and a form of multicentric Castleman's disease (MCD) are both caused by Kaposi sarcoma herpesvirus (KSHV). There is a critical need for improved therapies for these disorders. The IL-6/JAK/STAT3 pathway plays an important role in the pathogenesis of both PEL and KSHV-MCD. We explored the potential of JAK inhibitors for use in PEL and KSHV-MCD, and found that pacritinib was superior to others in inhibiting the growth of PEL cell lines. Pacritinib induced apoptosis in PEL cells and inhibited STAT3 and NF-κB activity as evidenced by reduced amount of phosphorylated moieties. Pacritinib also inhibits FLT3, IRAK1, and ROS1; studies utilizing other inhibitors of these targets revealed that only FLT3 inhibitors exhibited similar cell growth inhibitory effects. FLT3's likely contribution to pacritinib's cell growth inhibition was further demonstrated by siRNA knockdown of FLT3. RNA sequencing and RT-PCR showed that many key host genes including cyclins and IL-6 were downregulated by pacritinib, while KSHV genes were variably altered. Finally, pacritinib suppressed KSHV viral IL-6-induced human IL-6 and IL-10 production in peripheral blood mononuclear cells, which may model an important step in KSHV-MCD pathogenesis. These results suggest that pacritinib warrants testing for the treatment of KSHV-MCD and PEL.

Hypoxia and hypoxia-inducible factors in Kaposi sarcoma-associated herpesvirus infection and disease pathogenesis

Kaposi sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi sarcoma and several other tumors and hyperproliferative diseases seen predominantly in human immunodeficiency virus-infected and other immunocompromised persons. There is an increasing body of evidence showing that hypoxia and hypoxia-inducible factors (HIFs) play important roles in the biology of KSHV and in the pathogenesis of KSHV-induced diseases. Hypoxia and HIFs can induce lytic activation of KSHV and KSHV can in turn lead to a hypoxic-like state in infected cells. In this review, we describe the complex interactions between KSHV biology, the cellular responses to hypoxia, and the pathogenesis of KSHV-induced diseases. We also describe how interference with HIFs can lead to decreased tumor growth and/or death of infected cells and KSHV-induced tumors. Finally, we show how these observations may lead to novel strategies for the treatment of KSHV-induced diseases.

KSHV Viral Protein Kinase Interacts with USP9X to Modulate the Viral Lifecycle

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy and one of the most common childhood cancers. Immunosuppressed patients, including HIV-infected patients, are more prone to KSHV-associated disease. KSHV encodes a viral protein kinase (vPK) that is expressed from ORF36. KSHV vPK contributes to the optimal production of infectious viral progeny and upregulation of protein synthesis. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used a bottom-up proteomics approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Subsequently, we validated this interaction using a co-immunoprecipitation assay. We report that both the ubiquitin-like and the catalytic domains of USP9X are important for association with vPK. To uncover the biological relevance of the USP9X/vPK interaction, we investigated whether the knockdown of USP9X would modulate viral reactivation. Our data suggest that depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Understanding how USP9X influences the reactivation of KSHV will provide insights into how cellular deubiquitinases regulate viral kinase activity and how viruses co-opt cellular deubiquitinases to propagate infection. Hence, characterizing the roles of USP9X and vPK during KSHV infection constitutes a first step toward identifying a potentially critical interaction that could be targeted by future therapeutics. IMPORTANCE Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi sarcoma (KS), the plasmablastic form of multicentric Castleman's disease, and primary effusion lymphoma. In sub-Saharan Africa, KS is the most common HIV-related malignancy. KSHV encodes a viral protein kinase (vPK) that aids viral replication. To elucidate the interactions of vPK with cellular proteins in KSHV-infected cells, we used an affinity purification approach and identified host protein ubiquitin-specific peptidase 9X-linked (USP9X) as a potential interactor of vPK. Depletion of USP9X inhibits both viral reactivation and the production of infectious virions. Overall, our data suggest a proviral role for USP9X.

DLX1008 (brolucizumab), a single-chain anti-VEGF-A antibody fragment with low picomolar affinity, leads to tumor involution in an in vivo model of Kaposi Sarcoma

Kaposi Sarcoma (KS) is among the most angiogenic cancers in humans and an AIDS-defining condition. KS-associated herpesvirus (KSHV) is necessary for KS development, as is vascular endothelial growth factor (VEGF-A). DLX1008 is a novel anti-VEGF-A antibody single-chain variable fragment (scFv) with low picomolar affinity for VEGF-A. In vivo imaging techniques were used to establish the efficacy of DLX1008 and to establish the mechanism of action; this included non-invasive imaging by ultrasound and optical fluorescence, verified by post-mortem histochemistry. The results showed that DLX1008 was efficacious in a KS mouse model. The NSG mouse xenografts suffered massive internal necrosis or involution, consistent with a lack of blood supply. We found that imaging by ultrasound was superior to external caliper measurements in the validation of the angiogenesis inhibitor DLX1008. Further development of DLX1008 against VEGF-dependent sarcomas is warranted.

Induction of Kaposi's Sarcoma-Associated Herpesvirus-Encoded Thymidine Kinase (ORF21) by X-Box Binding Protein 1

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent for Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD). Like other herpesviruses, it has latent and lytic repertoires. However, there is evidence that some lytic genes can be directly activated by certain cellular factors. Cells undergoing endoplasmic reticulum stress express spliced X-box binding protein 1 (XBP-1s). XBP-1s is also present in large amounts in germinal center B cells. XBP-1s can activate the KSHV replication and transcription activator (RTA) and lytic replication. It can also directly activate KSHV-encoded viral interleukin-6 (vIL-6) and, thus, contribute to the pathogenesis of KSHV MCD. KSHV thymidine kinase (TK), the ORF21 gene product, can enhance the production of dTTP and is important for lytic replication. It can also phosphorylate zidovudine and ganciclovir to toxic moieties, enabling treatment of KSHV-MCD with these drugs. We show here that XBP-1s can directly activate ORF21 and that this activation is mediated primarily through two XBP-response elements (XRE) on the ORF21 promoter region. Deletion or mutation of these elements eliminated XBP-1s-induced upregulation of the promoter, and chromatin immunoprecipitation studies provide evidence that XBP-1s can bind to both XREs. Exposure of PEL cells to a chemical inducer of XBP-1s can induce ORF21 within 4 hours, and ORF21 expression in the lymph nodes of patients with KSHV-MCD is predominantly found in cells with XBP-1. Thus, XBP-1s may directly upregulate KSHV ORF21 and, thus, contribute to the pathogenesis of KSHV-MCD and the activity of zidovudine and valganciclovir in this disease.IMPORTANCE Spliced X-box binding protein 1 (XBP-1s), part of the unfolded protein response and expressed in developing germinal center B cells, can induce Kaposi's sarcoma-associated herpesvirus (KSHV) lytic replication and directly activate viral interleukin-6 (vIL-6). We show here that XBP-1s can also directly activate KSHV ORF21, a lytic gene. ORF21 encodes KSHV thymidine kinase (TK), which increases the pool of dTTP for viral replication and enhances lytic replication. Direct activation of ORF21 by XBP-1s can enhance viral replication in germinal center B cells and contribute to the pathogenesis of KSHV multicentric Castleman disease (MCD). KSHV-MCD is characterized by systemic inflammation caused, in part, by lytic replication and overproduction of KSHV vIL-6 in XBP-1s-expressing lymph node plasmablasts. KSHV thymidine kinase can phosphorylate zidovudine and ganciclovir to toxic moieties, and direct activation of ORF21 by XBP-1s may also help explain the effectiveness of zidovudine and valganciclovir in the treatment of KSHV-MCD.

A viral protein kinase drug target for tumors?

The human gammaherpesviruses, Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV), are both associated with tumors. Standard antiviral therapies are ineffective at treating these tumors. A serine/threonine kinase important for viral replication is conserved across the herpesviruses. Expression of the KSHV protein kinase in transgenic mice under the control of a ubiquitin promoter was associated with B cell lymphoproliferative disease and lymphoma. If the viral protein kinase is important in the pathogenesis of KSHV lymphoproliferative disease or lymphoma, the kinase may present a very good target for pharmacologic therapies.

Human herpesvirus-encoded kinase induces B cell lymphomas in vivo

Kaposi's sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus that is the etiological agent of the endothelial cell cancer Kaposi's sarcoma (KS) and 2 B cell lymphoproliferative disorders, primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). KSHV ORF36, also known as viral protein kinase (vPK), is a viral serine/threonine kinase. We previously reported that KSHV vPK enhances cell proliferation and mimics cellular S6 kinase to phosphorylate ribosomal protein S6, a protein involved in protein synthesis. We created a mouse model to analyze the function of vPK in vivo. We believe this is the first mouse tumor model of a viral kinase encoded by a pathogenic human virus. We observed increased B cell activation in the vPK transgenic mice compared with normal mice. We also found that, over time, vPK transgenic mice developed a B cell hyperproliferative disorder and/or a high-grade B cell non-Hodgkin lymphoma at a greatly increased incidence compared with littermate controls. This mouse model shows that a viral protein kinase is capable of promoting B cell activation and proliferation as well as augmenting lymphomagenesis in vivo and may therefore contribute to the development of viral cancers.

Treatment of Kaposi Sarcoma Herpesvirus-Associated Multicentric Castleman Disease

Kaposi sarcoma herpesvirus (KSHV)-associated multicentric Castleman disease (MCD) is a rare, polyclonal lymphoproliferative disorder characterized by flares of inflammatory symptoms, edema, cytopenias, lymphadenopathy, and splenomegaly. Diagnosis requires a lymph node biopsy. Pathogenesis is related to dysregulated inflammatory cytokines, including human and viral interleukin-6. Rituximab alone or in combination with chemotherapy, such as liposomal doxorubicin, has led to an overall survival of over 90% at 5 years. Experimental approaches to treatment include virus activated cytotoxic therapy with high-dose zidovudine and valganciclovir and targeting human interleukin-6 activity. Despite successful treatment of KSHV-MCD, patients remain at high risk for developing non-Hodgkin lymphomas.

Hypoxia-inducible factor-1 alpha as a therapeutic target for primary effusion lymphoma

Primary effusion lymphoma (PEL) is an aggressive B-cell lymphoma with poor prognosis caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). Previous studies have revealed that HIF-1α, which mediates much of the cellular response to hypoxia, plays an important role in life cycle of KSHV. KSHV infection promotes HIF-1α activity, and several KSHV genes are in turn activated by HIF-1α. In this study, we investigated the effects of knocking down HIF-1α in PELs. We observed that HIF-1α knockdown in each of two PEL lines leads to a reduction in both aerobic and anaerobic glycolysis as well as lipid biogenesis, indicating that HIF-1α is necessary for maintaining a metabolic state optimal for growth of PEL. We also found that HIF-1α suppression leads to a substantial reduction in activation of lytic KSHV genes, not only in hypoxia but also in normoxia. Moreover, HIF-1α knockdown led to a decrease in the expression of various KSHV latent genes, including LANA, vCyclin, kaposin, and miRNAs, under both normoxic and hypoxic conditions. These observations provide evidence that HIF-1α plays an important role in PEL even in normoxia. Consistent with these findings, we observed a significant inhibition of growth of PEL in normoxia upon HIF-1α suppression achieved by either HIF-1α knockdown or treatment with PX-478, a small molecule inhibitor of HIF-1α. These results offer further evidence that HIF-1α plays a critical role in the pathogenesis of PEL, and that inhibition of HIF-1α can be a potential therapeutic strategy in this disease.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is an oncogenic herpesvirus that causes several malignancies including primary effusion lymphoma (PEL). PEL is an aggressive B-cell lymphoma that usually develops in a hypoxic environment. There is no standard treatment for PEL and it carries a poor prognosis. Previous studies have revealed that certain KSHV-encoded genes are activated by hypoxia-inducible factor 1 (HIF-1), an intracellular factor that mediates much of the cellular response to hypoxia. KSHV in turn can upregulate HIF-1, suggesting HIF-1 might play a substantial role in PEL oncogenesis. Here, we report for the first time the effects of suppressing HIF-1α, an oxygen-sensitive subunit of HIF-1, in PEL tumor cells. We demonstrate that suppressing HIF-1α can dramatically affect the oncogenic metabolic signature of PELs, replication of KSHV, expression of KSHV-encoded oncogenes, and the growth of PEL cells. Findings presented here not only provide new insights into the role of HIF-1α in KSHV-induced tumors but also provide a rationale for using anti-HIF-1α agents as a therapeutic strategy for PEL and potentially other KSHV-associated malignancies.

HIV-associated Kaposi sarcoma and related diseases

: The search for the etiologic agent for Kaposi sarcoma led to the discovery of Kaposi sarcoma-associated herpesvirus (KSHV) in 1994. KSHV, also called human herpesvirus-8, has since been shown to be the etiologic agent for several other tumors and diseases, including primary effusion lymphoma (PEL), an extracavitary variant of PEL, KSHV-associated diffuse large B-cell lymphoma, a form of multicentric Castleman disease, and KSHV inflammatory cytokine syndrome. KSHV encodes several genes that interfere with innate and specific immunity, thwart apoptosis, enhance cell proliferation and cytokine production, and promote angiogenesis, and these play important roles in disease pathogenesis. HIV is an important cofactor in Kaposi sarcoma pathogenesis, and widespread use of antiretroviral therapy has reduced Kaposi sarcoma incidence. However, Kaposi sarcoma remains the second most frequent tumor arising in HIV-infected patients in the United States and is particularly common in sub-Saharan Africa. KSHV prevalence varies substantially in different populations. KSHV is secreted in saliva, and public health measures to reduce its spread may help reduce the incidence of KSHV-associated diseases. Although there have been advances in the treatment of Kaposi sarcoma, KSHV-multicentric Castleman disease, and PEL, improved therapies are needed, especially those that are appropriate for Kaposi sarcoma in resource-poor regions.

Restoration of immune surface molecules in Kaposi sarcoma-associated herpes virus infected cells by lenalidomide and pomalidomide

Kaposi sarcoma-associated herpesvirus (KSHV) is the cause of several tumors, including Kaposi sarcoma and primary effusion lymphoma (PEL). Most viruses have evolved means of escaping immune recognition. KSHV downregulates MHC-I expression during lytic infection, and expression of ICAM-1 and B7-2 (CD86) during latent infection, allowing evasion of T cell and natural killer immunity respectively. These effects are largely mediated by two KSHV-encoded proteins, K3 and K5. We show here that lenalidomide (Len) and pomalidomide (Pom) prevent down-regulation of MHC-I during lytic activation, and restore ICAM-1 and B7-2 surface expression in latently infected PEL cells. Importantly, these changes occurred at clinically achievable concentrations and prior to any cytotoxic effects. Exploration of the mechanism revealed that Pom blocked lytic down-regulation of MHC-I induced by transfection with K3 but not K5. Although Pom alone did not significantly increase HLA mRNA expression in PEL cells, it did blunt the butyrate-induced decrease in MHC-I mRNA expression and decreased the upregulation of K3 mRNA in lytic cells. Virus-induced tumors express foreign antigens, but immunotherapy can be thwarted by viral strategies to evade immune recognition. The effects of Pom and Len described here can prevent these strategies and support the use of these drugs to treat KSHV-induced tumors.

A viral kinase mimics S6 kinase to enhance cell proliferation

Viruses depend upon the host cell for manufacturing components of progeny virions. To mitigate the inextricable dependence on host cell protein synthesis, viruses can modulate protein synthesis through a variety of mechanisms. We report that the viral protein kinase (vPK) encoded by open reading frame 36 (ORF36) of Kaposi's sarcoma-associated herpesvirus (KSHV) enhances protein synthesis by mimicking the function of the cellular protein S6 kinase (S6KB1). Similar to S6KB1, vPK phosphorylates the ribosomal S6 protein and up-regulates global protein synthesis. vPK also augments cellular proliferation and anchorage-independent growth. Furthermore, we report that both vPK and S6KB1 phosphorylate the enzyme 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 2 (PFKFB2) and that both kinases promote endothelial capillary tubule formation.

Kaposi sarcoma-associated herpesvirus-associated malignancies: epidemiology, pathogenesis, and advances in treatment

Kaposi sarcoma associated herpesvirus (KSHV), a γ2-herpesvirus, also known as human herpesvirus-8, is the etiologic agent of three virally associated tumors: Kaposi sarcoma, a plasmablastic form of multicentric Castleman disease (KSHV-MCD), and primary effusion lymphoma. These malignancies are predominantly seen in people with acquired immunodeficiencies, including acquired immunodeficiency syndrome and iatrogenic immunosuppression in the setting of organ transplantation, but can also develop in the elderly. Kaposi sarcoma (KS) is most frequent in regions with high KSHV seroprevalence, such as sub-Saharan Africa and some Mediterranean countries. In the era of combination antiviral therapy, inflammatory manifestations associated with KSHV-infection, including KSHV-MCD, a recently described KSHV-associated inflammatory cytokine syndrome and KS immune reconstitution syndrome also are increasingly appreciated. Our understanding of viral and immune mechanisms of oncogenesis continues to expand and lead to improved molecular diagnostics, as well as novel therapeutic strategies that employ immune modulatory agents, manipulations of the tumor microenvironment, virus-activated cytotoxic therapy, or agents that target interactions between specific virus-host cell signaling pathways. This review focuses on the epidemiology and advances in molecular and clinical research that reflects the current understanding of viral oncogenesis, clinical manifestations, and therapeutics for KSHV-associated tumors.

Viral profiling identifies multiple subtypes of Kaposi's sarcoma

Kaposi’s sarcoma (KS), caused by KS-associated herpesvirus (KSHV), is the most common cancer among HIV-infected patients in Malawi and in the United States today. In Malawi, KSHV is endemic. We conducted a cross-sectional study of patients with HIV infection and KS with no history of chemo- or antiretroviral therapy (ART). Seventy patients were enrolled. Eighty-one percent had T1 (advanced) KS. Median CD4 and HIV RNA levels were 181 cells/mm³ and 138,641 copies/ml, respectively. We had complete information and suitable plasma and biopsy samples for 66 patients. For 59/66 (89%) patients, a detectable KSHV load was found in plasma (median, 2,291 copies/ml; interquartile range [IQR], 741 to 5,623). We utilized a novel KSHV real-time quantitative PCR (qPCR) array with multiple primers per open reading frame to examine KSHV transcription. Seventeen samples exhibited only minimal levels of KSHV mRNAs, presumably due to the limited number of infected cells. For all other biopsy samples, the viral latency locus (LANA, vCyc, vFLIP, kaposin, and microRNAs [miRNAs]) was transcribed abundantly, as was K15 mRNA. We could identify two subtypes of treatment-naive KS: lesions that transcribed viral RNAs across the length of the viral genome and lesions that displayed only limited transcription restricted to the latency locus. This finding demonstrates for the first time the existence of multiple subtypes of KS lesions in HIV- and KS-treatment naive patients.

KS is the leading cancer in people infected with HIV worldwide and is causally linked to KSHV infection. Using viral transcription profiling, we have demonstrated the existence of multiple subtypes of KS lesions for the first time in HIV- and KS-treatment-naive patients. A substantial number of lesions transcribe mRNAs which encode the viral kinases and hence could be targeted by the antiviral drugs ganciclovir or AZT in addition to chemotherapy.

P2' benzene carboxylic acid moiety is associated with decrease in cellular uptake: evaluation of novel nonpeptidic HIV-1 protease inhibitors containing P2 bis-tetrahydrofuran moiety

GRL007 and GRL008, two structurally related nonpeptidic human immunodeficiency virus type 1 (HIV-1) protease inhibitors (PIs) containing 3(R),3a(S),6a(R)-bis-tetrahydrofuranylurethane (bis-THF) as the P2 moiety and a sulfonamide isostere consisting of benzene carboxylic acid and benzene carboxamide as the P2' moiety, respectively, were evaluated for their antiviral activity and interactions with wild-type protease (PR(WT)). Both GRL007 (Ki of 12.7 pM with PR(WT)) and GRL008 (Ki of 8.9 pM) inhibited PR(WT) with high potency in vitro. X-ray crystallographic analysis of PR(WT) in complex with GRL007 or GRL008 showed that the bis-THF moiety of both compounds has three direct polar contacts with the backbone amide nitrogen atoms of Asp29 and Asp30 of PR(WT). The P2' moiety of both compounds showed one direct contact with the backbone of Asp30' and a bridging polar contact with Gly48' through a water molecule. Cell-based antiviral assays showed that GRL007 was inactive (50% effective concentration [EC50] of >1 μM) while GRL008 was highly active (EC50 of 0.04 μM) against wild-type HIV-1. High-performance liquid chromatography (HPLC)/mass spectrometry-based cellular uptake assays showed 8.1- and 84-fold higher intracellular concentrations of GRL008 than GRL007 in human MT-2 and MT-4 cell extracts, respectively. Thus, GRL007, in spite of its favorable enzyme-inhibitory activity and protease binding profile, exhibited a lack of antiviral activity in cell-based assays, most likely due to its compromised cellular uptake associated with its P2' benzene carboxylic acid moiety. The anti-HIV-1 potency, favorable toxicity, and binding profile of GRL008 suggest that further optimization of the P2' moiety may improve its antiretroviral features.

Recent advances in Kaposi sarcoma herpesvirus-associated multicentric Castleman disease

PURPOSE OF REVIEW

The discovery of Kaposi sarcoma herpesvirus (KSHV) led to recognition of KSHV-associated multicentric Castleman disease (MCD) as a distinct lymphoproliferative disorder. The pathogenesis of KSHV-MCD is attributed to proliferation of KSHV-infected B cells, production of KSHV-encoded viral interleukin 6 by these cells, and dysregulation of human interleukin 6 and interleukin 10. This article reviews advances in the field of disease pathogenesis and targeted therapies.

RECENT FINDINGS

Our understanding of the pathogenesis of KSHV-MCD has increased in recent years and improved therapies have been developed. Recent studies demonstrate that the anti-CD20 monoclonal antibody, rituximab, as well as virus-activated cytotoxic therapy using high-dose zidovudine and valganciclovir, can control symptoms and decrease adenopathy. With treatment, 1-year survival now exceeds 85%. Interestingly, even in the absence of pathologic findings of MCD, KSHV-infected patients may have inflammatory symptoms, excess cytokine production, and elevated KSHV viral load similar to KSHV-associated MCD. The term KSHV-associated inflammatory cytokine syndrome has been proposed to describe such patients.

SUMMARY

Recent advances in targeted therapy have improved outcomes in KSHV-MCD, and decreased need for cytotoxic chemotherapy. Improved understanding of the pathogenesis of KSHV-MCD and KSHV-associated inflammatory cytokine syndrome is needed, and will likely lead to additional advances in therapy for these disorders.

Kaposi's sarcoma herpesvirus lytic replication compromises apoptotic response to p53 reactivation in virus-induced lymphomas

Primary effusion lymphomas (PELs) are aggressive Kaposi's sarcoma herpesvirus (KSHV)-induced malignancies with median survival time <6 months post-diagnosis. Mutations in the TP53 gene seldom occur in PELs, suggesting that genetic alterations in the TP53 are not selected during PEL progression. We have reported that p53 reactivation by an inhibitor of the p53-MDM2 interaction, Nutlin-3, induces selective and massive apoptosis in PEL cells leading to efficient anti-tumor activity in a subcutaneous xenograft model for PEL. Here, we show compelling anti-tumor activity of Nutlin-3 in the majority of intraperitoneal PEL xenografts in vivo. Interestingly, our results demonstrate that spontaneous induction of viral lytic replication in tumors could drastically attenuate the p53-dependent apoptotic response to Nutlin-3. Moreover, viral reactivation compromised p53-dependent apoptosis in PEL cells treated with genotoxic anti-cancer agents doxorubicin and etoposide. We have recently demonstrated that the Ser/Thr kinases Pim 1 and 3 are required to trigger induction of the lytic replication cascade of KSHV. We have now assessed the ability of a novel Pim kinase inhibitor to restore the Nutlin-3-induced cytotoxicity in lytic PEL cells. PEL cells induced to lytic replication by phorbol esters showed 50% inhibition of active viral replication following treatment with the Pim kinase inhibitor. Importantly, co-treatment of these cells with the kinase inhibitor and Nutlin-3 resulted in a robust restoration of the Nutlin-3-induced cell death. These results highlight the potential impact of activation of viral lytic replication on disease progression and response to treatment in KSHV-induced lymphomas.

Clinical Manifestations of Kaposi Sarcoma Herpesvirus Lytic Activation: Multicentric Castleman Disease (KSHV-MCD) and the KSHV Inflammatory Cytokine Syndrome

Soon after the discovery of Kaposi sarcoma (KS)-associated herpesvirus (KSHV), it was appreciated that this virus was associated with most cases of multicentric Castleman disease (MCD) arising in patients infected with human immunodeficiency virus. It has subsequently been recognized that KSHV–MCD is a distinct entity from other forms of MCD. Like MCD that is unrelated to KSHV, the clinical presentation of KSHV–MCD is dominated by systemic inflammatory symptoms including fevers, cachexia, and laboratory abnormalities including cytopenias, hypoalbuminemia, hyponatremia, and elevated C-reactive protein. Pathologically KSHV–MCD is characterized by polyclonal, IgM-lambda restricted plasmacytoid cells in the intrafollicular areas of affected lymph nodes. A portion of these cells are infected with KSHV and a sizable subset of these cells express KSHV lytic genes including a viral homolog of interleukin-6 (vIL-6). Patients with KSHV–MCD generally have elevated KSHV viral loads in their peripheral blood. Production of vIL-6 and induction of human (h) IL-6 both contribute to symptoms, perhaps in combination with overproduction of IL-10 and other cytokines. Until recently, the prognosis of patients with KSHV–MCD was poor. Recent therapeutic advances targeting KSHV-infected B cells with the anti-CD20 monoclonal antibody rituximab and utilizing KSHV enzymes to target KSHV-infected cells have substantially improved patient outcomes. Recently another KSHV-associated condition, the KSHV inflammatory cytokine syndrome (KICS) has been described. Its clinical manifestations resemble those of KSHV–MCD but lymphadenopathy is not prominent and the pathologic nodal changes of KSHV–MCD are absent. Patients with KICS exhibit elevated KSHV viral loads and elevation of vIL-6, homolog of human interleukin-6 and IL-10 comparable to those seen in KSHV–MCD; the cellular origin of these is a matter of investigation. KICS may contribute to the inflammatory symptoms seen in some patients with severe KS or primary effusion lymphoma. Additional research is needed to better define the clinical spectrum of KICS and its relationship to KSHV–MCD. In additional, research is needed to better understand the pathogenesis and epidemiology of both KICS and KSHV–MCD, as well as the optimal therapy for both of these disorders.

High-dose zidovudine plus valganciclovir for Kaposi sarcoma herpesvirus-associated multicentric Castleman disease: a pilot study of virus-activated cytotoxic therapy

Kaposi sarcoma herpesvirus (KSHV)-associated multicentric Castleman disease (MCD) is a lymphoproliferative disorder most commonly observed in HIV-infected patients. It is characterized by KSHV-infected plasmablasts that frequently express lytic genes. Patients manifest inflammatory symptoms attributed to overproduction of KSHV viral IL-6, human IL-6, and human IL-6. There is no standard therapy and no established response criteria. We investigated an approach targeting 2 KSHV lytic genes, ORF36 and ORF21, the protein of which, respectively, phosphorylate ganciclovir and zidovudine to toxic moieties. In a pilot study, 14 HIV-infected patients with symptomatic KSHV-MCD received high-dose zidovudine (600 mg orally every 6 hours) and the oral prodrug, valganciclovir (900 mg orally every 12 hours). Responses were evaluated using new response criteria. A total of 86% of patients attained major clinical responses and 50% attained major biochemical responses. Median progression-free survival was 6 months. With 43 months of median follow-up, overall survival was 86% at 12 months and beyond. At the time of best response, the patients showed significant improvements in C-reactive protein, albumin, platelets, human IL-6, IL-10, and KSHV viral load. The most common toxicities were hematologic. These observations provide evidence that therapy designed to target cells with lytic KSHV replication has activity in KSHV-MCD. This trial was registered at www.clinicaltrials.gov as #NCT00099073.

Control of Kaposi's sarcoma-associated herpesvirus reactivation induced by multiple signals

The ability to control cellular functions can bring about many developments in basic biological research and its applications. The presence of multiple signals, internal as well as externally imposed, introduces several challenges for controlling cellular functions. Additionally the lack of clear understanding of the cellular signaling network limits our ability to infer the responses to a number of signals. This work investigates the control of Kaposi's sarcoma-associated herpesvirus reactivation upon treatment with a combination of multiple signals. We utilize mathematical model-based as well as experiment-based approaches to achieve the desired goals of maximizing virus reactivation. The results show that appropriately selected control signals can induce virus lytic gene expression about ten folds higher than a single drug; these results were validated by comparing the results of the two approaches, and experimentally using multiple assays. Additionally, we have quantitatively analyzed potential interactions between the used combinations of drugs. Some of these interactions were consistent with existing literature, and new interactions emerged and warrant further studies. The work presents a general method that can be used to quantitatively and systematically study multi-signal induced responses. It enables optimization of combinations to achieve desired responses. It also allows identifying critical nodes mediating the multi-signal induced responses. The concept and the approach used in this work will be directly applicable to other diseases such as AIDS and cancer.

Update on KSHV epidemiology, Kaposi Sarcoma pathogenesis, and treatment of Kaposi Sarcoma

Much has been learned since the discovery of KSHV in 1994 about its epidemiology and pathology but much of what has been learned has yet to be translated into clinical practice. In this review, we survey the current state of knowledge on KSHV epidemiology and KS pathogenesis and highlight therapeutic opportunities in both the developed and developing world.

An interleukin-6-related systemic inflammatory syndrome in patients co-infected with Kaposi sarcoma-associated herpesvirus and HIV but without Multicentric Castleman disease

BACKGROUND

Kaposi sarcoma-associated herpesvirus (KSHV) is the causal agent for Kaposi sarcoma (KS) and multicentric Castleman disease (MCD) in human immunodeficiency virus (HIV)-infected patients. Patients with KSHV-MCD develop fevers, wasting, hypoalbuminemia, cytopenias, and hyponatremia that are related to overproduction of KSHV-encoded viral interleukin (IL)-6 (vIL-6) and human IL-6 (hIL-6).

METHODS

We identified 6 HIV-infected patients with KS or serological evidence of KSHV infection who had severe inflammatory MCD-like symptoms but in whom we could not diagnose MCD, and we hypothesized that these symptoms resulted from vIL-6 overproduction. Serum vIL-6 levels were assessed in these 6 patients and compared with levels in 8 control patients with symptomatic KSHV-MCD and 32 control patients with KS. KSHV viral load, serum hIL-6 level, and human IL-10 level were also evaluated.

RESULTS

Patients with inflammatory MCD-like symptoms but without MCD had elevated vIL-6 levels, comparable with levels in patients with symptomatic KSHV-MCD, and had levels that were significantly greater than those in control patients with KS (P = .003). Elevated hIL-6, IL-10, and KSHV viral loads were also comparable to patients with symptomatic KSHV-MCD and significantly greater than those with KS.

CONCLUSIONS

A subset of patients with HIV and KSHV co-infection, but without MCD, can develop severe systemic inflammatory symptoms associated with elevated levels of KSHV vIL-6, IL-6, and KSHV viral loads. Excess lytic activation of KSHV, production of the lytic gene product vIL6, and associated immunologic dysregulation may underlie the pathophysiology of these symptoms. This IL-6-related inflammatory syndrome is important to consider in critically ill patients with HIV and KSHV co-infection.

Molecular biology of Kaposi's sarcoma-associated herpesvirus and related oncogenesis

Kaposi's Sarcoma-associated Herpesvirus (KSHV), also known as human herpesvirus 8 (HHV-8), is the most recently identified human tumor virus,and is associated with the pathogenesis of Kaposi's sarcoma and two lymphoproliferative disorders known to occur frequently in AIDS patients-primary effusion lymphoma and multicentric Castleman disease. In the 15 years since its discovery, intense studies have demonstrated an etiologic role for KSHV in the development of these malignancies. Here, we review the recent advances linked to understanding KSHV latent and lytic life cycle and the molecular mechanisms of KSHV-mediated oncogenesis in terms of transformation, cell signaling, cell growth and survival, angiogenesis, immune invasion and response to microenvironmental stress, and highlight the potential therapeutic targets for blocking KSHV tumorigenesis.

Conserved herpesviral kinase promotes viral persistence by inhibiting the IRF-3-mediated type I interferon response

A conserved herpesviral kinase, designated ORF36 in murine gamma-herpesvirus 68 (MHV-68), plays multiple vital roles in the viral life cycle. Here, we show by screening mutant viruses that ORF36 counteracts the antiviral type I interferon (IFN) response. ORF36 specifically binds to the activated form of interferon regulatory factor 3 (IRF-3) in the nucleus, inhibiting IRF-3 interaction with the cotranscriptional activator CBP and thereby suppressing the recruitment of RNA polymerase II to the interferon beta promoter. The anti-IFN function of ORF36 is conserved among herpesvirus subfamilies, although the conserved kinase activity is not absolutely required for this function. MHV-68 lacking ORF36 induces a greater interferon response and is attenuated in vitro and in vivo, where acute viral infection in the lung and latency in the spleen are compromised. Our data suggest that herpesviruses have evolved within their conserved kinase an anti-IFN activity critical for evasion of host immunity and for persistence.