The heat shock protein 90 inhibitor BIIB021 suppresses the growth of T and natural killer cell lymphomas

A small molecule that selectively inhibits the growth of Epstein-Barr virus-latently infected cancer cells

Epstein-Barr virus (EBV), an oncogenic herpesvirus, is predominantly found in the latent infection form and is highly associated with many human malignancies, which mainly have poor prognoses and no effective treatments. Here, we obtained thirteen compounds from small-molecule libraries for specific inhibition of EBV-latently infected cell growth in vitro by high-throughput screening. Among them, cetrimonium bromide (CetB) was identified to selectively inhibit the growth of different EBV-infected B lymphoma cell lines. Importantly, CetB reduced EBNA1 protein stability, activated G1 arrest and early apoptosis of EBV-latently infected cells without viral lytic reactivation, which leads to dramatically inhibit colony formation and tumor growth of EBV-infected cells in vitro and in vivo, and significantly prolong the survival of tumor-bearing mice. Overall, these findings demonstrate that CetB acts as a highly selective inhibitor of the growth of EBV-infected cells and has the potential for further development of effective therapeutic strategies specific against EBV-associated cancers.

Computational Modeling to Identify Drugs Targeting Metastatic Castration-Resistant Prostate Cancer Characterized by Heightened Glycolysis

Metastatic castration-resistant prostate cancer (mCRPC) remains a deadly disease due to a lack of efficacious treatments. The reprogramming of cancer metabolism toward elevated glycolysis is a hallmark of mCRPC. Our goal is to identify therapeutics specifically associated with high glycolysis. Here, we established a computational framework to identify new pharmacological agents for mCRPC with heightened glycolysis activity under a tumor microenvironment, followed by in vitro validation. First, using our established computational tool, OncoPredict, we imputed the likelihood of drug responses to approximately 1900 agents in each mCRPC tumor from two large clinical patient cohorts. We selected drugs with predicted sensitivity highly correlated with glycolysis scores. In total, 77 drugs predicted to be more sensitive in high glycolysis mCRPC tumors were identified. These drugs represent diverse mechanisms of action. Three of the candidates, ivermectin, CNF2024, and P276-00, were selected for subsequent vitro validation based on the highest measured drug responses associated with glycolysis/OXPHOS in pan-cancer cell lines. By decreasing the input glucose level in culture media to mimic the mCRPC tumor microenvironments, we induced a high-glycolysis condition in PC3 cells and validated the projected higher sensitivity of all three drugs under this condition (p < 0.0001 for all drugs). For biomarker discovery, ivermectin and P276-00 were predicted to be more sensitive to mCRPC tumors with low androgen receptor activities and high glycolysis activities (AR(low)Gly(high)). In addition, we integrated a protein-protein interaction network and topological methods to identify biomarkers for these drug candidates. EEF1B2 and CCNA2 were identified as key biomarkers for ivermectin and CNF2024, respectively, through multiple independent biomarker nomination pipelines. In conclusion, this study offers new efficacious therapeutics beyond traditional androgen-deprivation therapies by precisely targeting mCRPC with high glycolysis.

Molecular Basis of Epstein-Barr Virus Latency Establishment and Lytic Reactivation

Epstein–Barr virus (EBV) is a causative agent of infectious mononucleosis and several types of cancer. Like other herpesviruses, it establishes an asymptomatic, life-long latent infection, with occasional reactivation and shedding of progeny viruses. During latency, EBV expresses a small number of viral genes, and exists as an episome in the host–cell nucleus. Expression patterns of latency genes are dependent on the cell type, time after infection, and milieu of the cell (e.g., germinal center or peripheral blood). Upon lytic induction, expression of the viral immediate-early genes, BZLF1 and BRLF1, are induced, followed by early gene expression, viral DNA replication, late gene expression, and maturation and egress of progeny virions. Furthermore, EBV reactivation involves more than just progeny production. The EBV life cycle is regulated by signal transduction, transcription factors, promoter sequences, epigenetics, and the 3D structure of the genome. In this article, the molecular basis of EBV latency establishment and reactivation is summarized.

HSP90 inhibition downregulates DNA replication and repair genes via E2F1 repression

Mantle cell lymphoma (MCL) is an especially aggressive and highly heterogeneous mature B-cell lymphoma. Heat shock protein 90 (HSP90) is considered an attractive therapeutic target in a variety of cancers, including MCL, but no HSP90 inhibitors have succeeded in the clinical trials to date. Exploring fine mechanisms of HSP90 inhibition in cancer cells may shed light on novel therapeutic strategies. Here, we found that HSP90 knockdown and continuous inhibition with ganetespib inhibited growth of MCL cells in vitro and in vivo. To our surprise, transient exposure over 12 h was almost as efficient as continuous exposure, and treatment with ganetespib for 12 h efficiently inhibited growth and induced G1 cell cycle arrest and apoptosis of MCL cells. Transcriptome analysis complemented by functional studies was performed to define critical MCL signaling pathways that are exceptionally sensitive to HSP90 inhibition and vital to cell fate. Six genes (cell division cycle 6, cell division cycle 45, minichromosome maintenance 4, minichromosome maintenance 7, RecQ-mediated genome instability 2, and DNA primase polypeptide 1) involved in DNA replication and repair were identified as consistently downregulated in three MCL cell lines after transient ganetespib treatment. E2F1, an important transcription factor essential for cell cycle progression, was identified as a ganetespib target mediating transcriptional downregulation of these six genes, and its stability was also demonstrated to be maintained by HSP90. This study identifies E2F1 as a novel client protein of HSP90 that is very sensitive and worthy of targeting and also finds that HSP90 inhibitors may be useful in combination therapies for MCL.

BGLF2 Increases Infectivity of Epstein-Barr Virus by Activating AP-1 upon De Novo Infection

Epstein-Barr virus (EBV) is a human gammaherpesvirus that causes infectious mononucleosis and several malignancies, such as endemic Burkitt lymphoma and nasopharyngeal carcinoma. Herpesviruses carry genes that can modify cell functions, including transcription and ubiquitination, thereby facilitating viral growth and survival in infected cells. Using a reporter screening system, we revealed the involvement of several EBV gene products in such processes. Of these, BGLF2 activated the AP-1 signaling pathway through phosphorylation of p38 and c-Jun N-terminal kinase (JNK). Knockout of the BGLF2 gene did not affect viral gene expression and viral genome DNA replication, but resulted in marked reduction of progeny titer. We also found that the BGLF2 disruption resulted in significant loss of infectivity upon de novo infection. Interestingly, expression of a binding partner, BKRF4, repressed the activation of AP-1 by BGLF2. These results shed light on the physiological role of the tegument protein BGLF2.IMPORTANCE Epstein-Barr virus (EBV), an oncogenic gammaherpesvirus, carries ~80 genes. While several genes have been investigated extensively, most lytic genes remain largely unexplored. Therefore, we cloned 71 EBV lytic genes into an expression vector and used reporter assays to screen for factors that activate signal transduction pathways, viral and cellular promoters. BGLF2 activated the AP-1 signaling pathway, likely by interacting with p38 and c-Jun N-terminal kinase (JNK), and increased infectivity of the virus. We also revealed that BKRF4 can negatively regulate AP-1 activity. Therefore, it is suggested that EBV exploits and modifies the AP-1 signaling pathway for its replication and survival.

Tofacitinib induces G1 cell-cycle arrest and inhibits tumor growth in Epstein-Barr virus-associated T and natural killer cell lymphoma cells

Epstein-Barr virus (EBV) infects not only B cells, but also T cells and natural killer (NK) cells, and is associated with T or NK cell lymphoma. These lymphoid malignancies are refractory to conventional chemotherapy. We examined the activation of the JAK3/STAT5 pathway in EBV-positive and -negative B, T and NK cell lines and in cell samples from patients with EBV-associated T cell lymphoma. We then evaluated the antitumor effects of the selective JAK3 inhibitor, tofacitinib, against these cell lines in vitro and in a murine xenograft model. We found that all EBV-positive T and NK cell lines and patient samples tested displayed activation of the JAK3/STAT5 pathway. Treatment of these cell lines with tofacitinib reduced the levels of phospho-STAT5, suppressed proliferation, induced G1 cell-cycle arrest and decreased EBV LMP1 and EBNA1 expression. An EBV-negative NK cell line was also sensitive to tofacitinib, whereas an EBV-infected NK cell line was more sensitive to tofacitinib than its parental line. Tofacitinib significantly inhibited the growth of established tumors in NOG mice. These findings suggest that tofacitinib may represent a useful therapeutic agent for patients with EBV-associated T and NK cell lymphoma.

Epstein-Barr Virus BKRF4 Gene Product Is Required for Efficient Progeny Production

Epstein-Barr virus (EBV), a member of human gammaherpesvirus, infects mainly B cells. EBV has two alternative life cycles, latent and lytic, and is reactivated occasionally from the latent stage to the lytic cycle. To combat EBV-associated disorders, understanding the molecular mechanisms of the EBV lytic replication cycle is also important. Here, we focused on an EBV lytic gene, BKRF4. Using our anti-BKRF4 antibody, we revealed that the BKRF4 gene product is expressed during the lytic cycle with late kinetics. To characterize the role of BKRF4, we constructed BKRF4-knockout mutants using the bacterial artificial chromosome (BAC) and CRISPR/Cas9 systems. Although disruption of the BKRF4 gene had almost no effect on viral protein expression and DNA synthesis, it significantly decreased progeny virion levels in HEK293 and Akata cells. Furthermore, we show that BKRF4 is involved not only in production of progeny virions but also in increasing the infectivity of the virus particles. Immunoprecipitation assays revealed that BKRF4 interacted with a virion protein, BGLF2. We showed that the C-terminal region of BKRF4 was critical for this interaction and for efficient progeny production. Immunofluorescence analysis revealed that BKRF4 partially colocalized with BGLF2 in the nucleus and perinuclear region. Finally, we showed that BKRF4 is a phosphorylated, possible tegument protein and that the EBV protein kinase BGLF4 may be important for this phosphorylation. Taken together, our data suggest that BKRF4 is involved in the production of infectious virions.IMPORTANCE Although the latent genes of EBV have been studied extensively, the lytic genes are less well characterized. This study focused on one such lytic gene, BKRF4, which is conserved only among gammaherpesviruses (ORF45 of Kaposi's sarcoma-associated herpesvirus or murine herpesvirus 68). After preparing the BKRF4 knockout virus using B95-8 EBV-BAC, we demonstrated that the BKRF4 gene was involved in infectious progeny particle production. Importantly, we successfully generated a BKRF4 knockout virus of Akata using CRISPR/Cas9 technology, confirming the phenotype in this separate strain. We further showed that BKRF4 interacted with another virion protein, BGLF2, and demonstrated the importance of this interaction in infectious virion production. These results shed light on the elusive process of EBV progeny maturation in the lytic cycle. Notably, this study describes a successful example of the generation and characterization of an EBV construct with a disrupted lytic gene using CRISPR/Cas9 technology.

A neutralized human LMP1-IgG inhibits ENKTL growth by suppressing the JAK3/STAT3 signaling pathway

Latent membrane protein 1 (LMP1), which is associated with the development of different types of Epstein-Barr virus (EBV) related lymphoma, has been suggested to be an important oncoprotein. In this study, a human anti-LMP1 IgG antibody (LMP1-IgG) was constructed and characterized by ELISA, western blotting (WB), affinity and immunohistochemistry (IHC) analyses. CCK-8, MTT, apoptosis assays, antibody-dependent cell-mediated cytotoxicity (ADCC) and CDC (complement-dependent cytotoxicity) assays were performed to evaluate the inhibitory effects of LMP1-IgG on extranodal nasal-type natural killer (NK)/T-cell lymphoma (ENKTL). Then, the influence of LMP1-IgG on the JAK/STAT signaling pathway was investigated. The results showed that the successfully constructed LMP1-IgG inhibited proliferation, induced apoptosis, and activated ADCC and CDC of ENKTL in a concentration- and time- dependent manner. Moreover, phosphorylation of JAK3 and STAT3 was inhibited by LMP1-IgG. Our data indicate that LMP1-IgG may provide a novel and promising therapeutic strategy for the treatment of LMP1-positive ENKTL.

Targeting cancer cell mitochondria as a therapeutic approach: recent updates

Mitochondria play a key role in ATP generation, redox homeostasis and regulation of apoptosis. Due to the essential role of mitochondria in metabolism and cell survival, targeting mitochondria in cancer cells is considered as an attractive therapeutic strategy. However, metabolic flexibility in cancer cells may enable the upregulation of compensatory pathways, such as glycolysis to support cancer cell survival when mitochondrial metabolism is inhibited. Thus, compounds capable of both targeting mitochondria and inhibiting glycolysis may be particularly useful to overcome such drug-resistant mechanism. This review provides an update on recent development in the field of targeting mitochondria and novel compounds that impact mitochondria, glycolysis or both. Key challenges in this research area and potential solutions are also discussed.

BIIB021: A novel inhibitor to heat shock protein 90–addicted oncology

Heat shock protein 90 is induced in response to the cell stress. Its overexpression has been reported in many cancers with poor prognosis. It acts as a chaperone to the client proteins, especially the activated oncoproteins in malignancies to protect them from degradation. Heat shock protein 90 inhibition represented anti-cancer effects in many studies. Previous natural product–based compounds are limited by their association with target toxicities. BIIB021 is an orally available, fully synthetic novel small-molecule heat shock protein 90 inhibitor that has shown strong antitumor activities in a large number of preclinical models and is now under clinical investigation. This review will summarize its therapeutic effects and highlight the prospect of targeting heat shock protein 90 in the cancer therapy.

Serum Proteomics Analysis in Rats of Immunosuppression Induced by Chronic Stress

The immune system can be damaged by chronic stress. However, for this process, the involved molecular alterations and their regulatory roles played in immunosuppression still remain unclear. This study was aimed to identify the differences in serum protein expressions that are closely associated with the effect of chronic stress on immune function. Serum protein levels of rats in control group and chronic stress group were measured by iTRAQ analysis. Subsequently, among the 121 differentially expressed proteins screened between the two groups, 46 proteins were upregulated (>1.5-fold, P < 0.05), while 75 proteins were downregulated (<0.67-fold, P < 0.05). Bioinformatics analysis revealed that most of the differentially expressed proteins were in relation with the metabolic, cellular, response stimulus and immune system processes. The significantly differential expression of ceruloplasmin, haptoglobin, catalase and peroxiredoxin-1 were picked out for reconfirmation by ELISA analysis. The results were consistent with those obtained by iTRAQ. What is more, the roles of above-mentioned four proteins, apolipoprotein B-100 and heat-shock protein 90 in immunosuppression induced by chronic stress were discussed. Taken together, these findings may provide a new insight into better understanding the molecular mechanisms of immunosuppression induced by chronic stress.

Ganetespib, an HSP90 inhibitor, kills Epstein-Barr virus (EBV)-infected B and T cells and reduces the percentage of EBV-infected cells in the blood

HSP90 inhibitors have been shown to kill Epstein-Barr virus (EBV)-infected cells by reducing the level of EBV EBNA-1 and/or LMP1. We treated virus-infected cells with ganetespib, an HSP90 inhibitor currently being evaluated in multiple clinical trials for cancer and found that the drug killed EBV-positive B and T cells and reduced the level of both EBV EBNA-1 and LMP1. Treatment of cells with ganetespib also reduced the level of pAkt. Ganetespib delayed the onset of EBV-positive lymphomas and prolonged survival in SCID mice inoculated with one EBV-transformed B-cell line, but not another B-cell line. The former cell line showed lower levels of EBNA-1 after treatment with ganetespib in vitro. Treatment of a patient with T-cell chronic active EBV with ganetespib reduced the percentage of EBV-positive cells in the peripheral blood. These data indicate that HSP90 inhibitors may have a role in the therapy of certain EBV-associated diseases.

The Role of Heat Shock Protein 90B1 in Patients with Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogenetic disorder in women that is characterized by arrested follicular growth and anovulatory infertility. The altered protein expression levels in the ovarian tissues reflect the molecular defects in folliculogenesis. To identify aberrant protein expression in PCOS, we analyzed protein expression profiles in the ovarian tissues of patients with PCOS. We identified a total of 18 protein spots that were differentially expressed in PCOS compared with healthy ovarian samples. A total of 13 proteins were upregulated and 5 proteins were downregulated. The expression levels of heat shock protein 90B1 (HSP90B1) and calcium signaling activator calmodulin 1 (CALM1) were increased by at least two-fold. The expression levels of HSP90B1 and CALM1 were positively associated with ovarian cell survival and negatively associated with caspase-3 activation and apoptosis. Knock-down of HSP90B1 with siRNA attenuated ovarian cell survival and increased apoptosis. In contrast, ovarian cell survival was improved and cell apoptosis was decreased in cells over-expressing HSP90B1. These results demonstrated the pivotal role of HSP90B1 in the proliferation and survival of ovarian cells, suggesting a critical role for HSP90B1 in the pathogenesis of PCOS. We also observed a downregulation of anti-inflammatory activity-related annexin A6 (ANXA6) and tropomyosin 2 (TPM2) compared with the normal controls, which could affect cell division and folliculogenesis in PCOS. This is the first study to identify novel altered gene expression in the ovarian tissues of patients with PCOS. These findings may have significant implications for future diagnostic and treatment strategies for PCOS using molecular interventions.

Hsp90 inhibitor, BIIB021, induces apoptosis and autophagy by regulating mTOR-Ulk1 pathway in imatinib-sensitive and -resistant chronic myeloid leukemia cells

Development of drug resistance due to BCR-ABL point mutations and the persistence of leukemia initiating cells has become a major obstacle for tyrosine kinase inhibitors (TKIs) in the treatment of chronic myeloid leukemia (CML). The BCR-ABL protein is an important client protein of heat shock protein 90 (Hsp90). BIIB021, an orally available Hsp90 inhibitor, has activity against various cancer cells. However, little is known about the inhibitory effect of BIIB021 on CML cells. We evaluated the inhibitory effects of BIIB021 on K562, K562/G (an imatinib-resistant cell lines), as well as 32D mouse leukemic cells expressing wild-type BCR-ABL (b3a2, 32Dp210) and T315I mutant BCR-ABL (32Dp210-T315I) cells. Our data showed that BIIB021 induced significant growth inhibition and apoptosis that was predominantly mediated by the mitochondrial pathway. BIIB021 also resulted in proteasomal degradation of BCR-ABL proteins. In addition to induction of apoptosis, we report for the first time that BIIB021 induced autophagic response as evidenced by the formation of autophagosome, increased conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II, decreased p62 (SQSTM1) protein levels. Further study suggested that Akt-mTOR-Ulk1 signaling pathway was involved in BIIB021-triggered autophagy. Moreover, blocking autophagy using pharmacological inhibitor 3-methyladenine and bafilomycin A1 significantly enhanced cell death and apoptosis induced by BIIB021, indicating the cytoprotective role of autophagy in BIIB021-treated CML cells. Collectively, these data provide possible molecular mechanisms for the antileukemic effect of BIIB021 on imatinib-sensitive and -resistant CML cells and provide new insights into the future application of BIIB021 in the clinical treatment of CML.