Ninib Baryawno

Detection of human cytomegalovirus in medulloblastomas reveals a potential therapeutic target

Medulloblastomas are the most common malignant brain tumors in children. They express high levels of COX-2 and produce PGE2, which stimulates tumor cell proliferation. Human cytomegalovirus (HCMV) is prevalent in the human population and encodes proteins that provide immune evasion strategies and promote oncogenic transformation and oncomodulation. In particular, HCMV induces COX-2 expression; STAT3 phosphorylation; production of PGE2, vascular endothelial growth factor, and IL-6; and tumor formation in vivo. Here, we show that a large proportion of primary medulloblastomas and medulloblastoma cell lines are infected with HCMV and that COX-2 expression, along with PGE2 levels, in tumors is directly modulated by the virus. Our analysis indicated that both HCMV immediate-early proteins and late proteins are expressed in the majority of primary medulloblastomas. Remarkably, all of the human medulloblastoma cell lines that we analyzed contained HCMV DNA and RNA and expressed HCMV proteins at various levels in vitro. When engrafted into immunocompromised mice, human medulloblastoma cells induced expression of HCMV proteins. HCMV and COX-2 expression correlated in primary tumors, cell lines, and medulloblastoma xenografts. The antiviral drug valganciclovir and the specific COX-2 inhibitor celecoxib prevented HCMV replication in vitro and inhibited PGE2 production and reduced medulloblastoma tumor cell growth both in vitro and in vivo. Ganciclovir did not affect the growth of HCMV-negative tumor cell lines. These findings imply an important role for HCMV in medulloblastoma and suggest HCMV as a novel therapeutic target for this tumor.

Small-Molecule Inhibitors of Phosphatidylinositol 3-Kinase/Akt Signaling Inhibit Wnt/β-Catenin Pathway Cross-Talk and Suppress Medulloblastoma Growth

Activation of the beta-catenin and receptor kinase pathways occurs often in medulloblastoma, the most common pediatric malignant brain tumor. In this study, we show that molecular cross-talk between the beta-catenin and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways is crucial to sustain medulloblastoma pathophysiology. Constitutive activation of phosphoinositide-dependent protein kinase 1 (PDK1), Akt, and phosphorylation of [corrected] glycogen synthase kinase 3beta (GSK-3beta) was detected by immunohistochemistry in all primary medulloblastomas examined (n = 41). Small-molecule inhibitors targeting the PI3K/Akt signaling pathway affected beta-catenin signaling by activation [corrected] of GSK-3beta, [corrected] resulting in cytoplasmic retention of beta-catenin and reduced expression of its target genes cyclin D1 and c-Myc. The PDK1 inhibitor OSU03012 induced mitochondrial-dependent apoptosis of medulloblastoma cells and enhanced the cytotoxic effects of chemotherapeutic drugs in a synergistic or additive manner. In vivo, OSU03012 inhibited the growth of established medulloblastoma xenograft tumors in a dose-dependent manner and augmented the antitumor effects of mammalian target of rapamycin inhibitor CCI-779. These findings demonstrate the importance of cross-talk between the PI3K/Akt and beta-catenin pathways in medulloblastoma and rationalize the PI3K/Akt signaling pathway as a therapeutic target in treatment of this disease.

Tumor-growth–promoting cyclooxygenase-2 prostaglandin E2 pathway provides medulloblastoma therapeutic targets

Prostaglandin E(2) (PGE(2)) has been shown to play important roles in several aspects of tumor development and progression. PGE(2) is synthesized from arachidonic acid by cyclooxygenases (COX) and prostaglandin E synthases (PGES) and mediates its biological activity through binding to the four prostanoid receptors EP(1) through EP(4). In this study, we show for the first time that medulloblastoma (MB), the most common malignant childhood brain tumor, expresses high levels of COX-2, microsomal prostaglandin E synthase-1, and EP(1) through EP(4) and secretes PGE(2). PGE(2) and the EP(2) receptor agonist butaprost stimulated MB cell proliferation. Treatment of MB cells with COX inhibitors suppressed PGE(2) production and induced caspase-dependent apoptosis. Similarly, specific COX-2 silencing by small interfering RNA inhibited MB cell growth. EP(1) and EP(3) receptor antagonists ONO-8713 and ONO-AE3-240, but not the EP(4) antagonists ONO-AE3-208 and AH 23848, inhibited tumor cell proliferation, indicating the significance of EP(1) and EP(3) but not EP(4) for MB growth. Administration of COX inhibitors at clinically achievable nontoxic concentrations significantly inhibited growth of established human MB xenografts. Apoptosis was increased, proliferation was reduced, and angiogenesis was inhibited in MBs treated with COX inhibitors. This study suggests that PGE(2) is important for MB growth and that therapies targeting the prostanoid metabolic pathway are potentially beneficial and should be tested in clinical settings for treatment of children with MB.

Targeting the hedgehog signal transduction pathway at the level of GLI inhibits neuroblastoma cell growth in vitro and in vivo

Hedgehog (HH) signaling is an important regulator of embryogenesis that has been associated with the development of several types of cancer. HH signaling is characterized by Smoothened (SMO)‐dependent activation of the GLI transcription factors, which regulate the expression of critical developmental genes. Neuroblastoma, an embryonal tumor of the sympathetic nervous system, was recently shown to express high levels of key molecules in this signaling cascade. Using compounds blocking SMO (cyclopamine and SANT1) or GLI1/GLI2 (GANT61) activity revealed that inhibition of HH signaling at the level of GLI was most effective in reducing neuroblastoma growth. GANT61 sensitivity positively correlated to GLI1 and negatively to MYCN expression in the neuroblastoma cell lines tested. GANT61 downregulated GLI1, c‐MYC, MYCN and Cyclin D1 expression and induced apoptosis of neuroblastoma cells. The effects produced by GANT61 were mimicked by GLI knockdown but not by SMO knockdown. Furthermore, GANT61 enhanced the effects of chemotherapeutic drugs used in the treatment of neuroblastoma in an additive or synergistic manner and reduced the growth of established neuroblastoma xenografts in nude mice. Taken together this study suggests that inhibition of HH signaling is a highly relevant therapeutic target for high‐risk neuroblastoma lacking MYCN amplification and should be considered for clinical testing.

Expression of enzymes and receptors of the leukotriene pathway in human neuroblastoma promotes tumor survival and provides a target for therapy

The metabolism of arachidonic acid by the cyclooxygenase (COX) or lipoxygenase (LO) pathways generates eicosanoids that have been implicated in the pathogenesis of a variety of human diseases, including cancer. In this study, we examined the expression and significance of components within the 5‐LO pathway in human neuroblastoma, an embryonal tumor of the sympathetic nervous system. High expression of 5‐LO, 5‐LO‐activating protein (FLAP), leukotriene A4 hydrolase, leukotriene C4 synthase, and leukotriene receptors was detected in a majority of primary neuro‐blastoma tumors and all cell lines investigated. Expression of 5‐LO and FLAP was evident in tumor cells but not in nonmalignant adrenal medulla where neuroblastomas typically arise. Moreover, neuroblastoma cells produce leukotrienes, and stimulation of neuroblastoma cells with leukotrienes increased neuroblastoma cell viability. Inhibitors of 5‐LO (AA‐861), FLAP (MK‐886), or the leukotriene receptor antagonist montelukast inhibited neuroblastoma cell growth by induction of G1‐cell cycle arrest and apoptosis. Similarly, specific 5‐LO and leukotriene receptor silencing by small interfering RNA decreased neuroblastoma cell growth. These findings provide new insights into the pathobiology of neuroblastoma, and the use of leukotriene pathway inhibitors as a novel adjuvant therapy for children with neuroblastoma warrants further consideration.—Sveinbjörnsson, B., Rasmuson, A., Baryawno, N., Wan, M., Ingvild Pettersen, I., Frida Ponthan, F., Orrego, A., Haeggström, J. Z., Johnsen, J. I., Kogner, P. Expression of enzymes and receptors of the leukotriene pathway in human neuroblastoma promotes tumor survival and provides a target for therapy. FASEB J. 22, 3525–3536 (2008)

Wnt/β-catenin pathway regulates MGMT gene expression in cancer and inhibition of Wnt signalling prevents chemoresistance

The DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is commonly overexpressed in cancers and is implicated in the development of chemoresistance. The use of drugs inhibiting MGMT has been hindered by their haematologic toxicity and inefficiency. As a different strategy to inhibit MGMT we investigated cellular regulators of MGMT expression in multiple cancers. Here we show a significant correlation between Wnt signalling and MGMT expression in cancers with different origin and confirm the findings by bioinformatic analysis and immunofluorescence. We demonstrate Wnt-dependent MGMT gene expression and cellular co-localization between active β-catenin and MGMT. Pharmacological or genetic inhibition of Wnt activity downregulates MGMT expression and restores chemosensitivity of DNA-alkylating drugs in mouse models. These findings have potential therapeutic implications for chemoresistant cancers, especially of brain tumours where the use of temozolomide is frequently used in treatment.

Effects of small molecule inhibitors of PI3K/Akt/mTOR signaling on neuroblastoma growth in vitro and in vivo.

Activation of the PI3K/Akt signaling pathway is correlated with poor prognosis in neuroblastoma, the most common and deadly extracranial tumor of childhood. In this study, we show that the small‐molecule inhibitors of phosphoinositide‐dependent protein kinase‐1 (PDK1) OSU03012 and the dual class I PI3K/mTOR inhibitor PI103 have profound effects on neuroblastoma survival in vitro and in vivo. Both OSU03012 and PI103 inhibited neuroblastoma growth in vitro. In treated cells, OSU03012 induced apoptosis and an S phase cell cycle arrest, whereas only minor apoptosis was detected in PI103 treated cells together with a G1 arrest. Both OSU03012 and PI103 downregulated phosphorylation of Akt and inhibited the downstream targets glycogen synthase kinase‐3β (GSK3β) and p70 S6 kinase‐1 (S6K1), as well as downregulated the expression of cyclin D1 and Mycn protein. Neuroblastoma cells expressing high levels of Mycn were more sensitive to OSU03012 or PI103 compared with cells expressing low Mycn levels. Both compounds significantly inhibited the growth of established, subcutaneous MYCN‐amplified neuroblastoma xenografts in nude NMRI nu/nu mice. These results suggest that inhibition of the PI3K/Akt signaling pathway represent a clinical relevant target for the treatment of patients with high‐risk MYCN‐amplified neuroblastoma.

Frequent detection of human cytomegalovirus in neuroblastoma: A novel therapeutic target?

Neuroblastoma is the most common and deadly tumor of childhood, where new therapy options for patients with high‐risk disease are highly warranted. Human cytomegalovirus (HCMV) is prevalent in the human population and has recently been implicated in different cancer forms where it may provide mechanisms for oncogenic transformation, oncomodulation and tumor cell immune evasion. Here we show that the majority of primary neuroblastomas and neuroblastoma cell lines are infected with HCMV. Our analysis show that HCMV immediate‐early protein was expressed in 100% of 36 primary neuroblastoma samples, and HCMV late protein was expressed in 92%. However, no infectious virus was detected in primary neuroblastoma tissue extracts. Remarkably, all six human neuroblastoma cell lines investigated contained CMV DNA and expressed HCMV proteins. HCMV proteins were expressed in neuroblastoma cells expressing the proposed stem cell markers CD133 and CD44. When engrafted into NMRI nu/nu mice, human neuroblastoma cells expressed HCMV DNA, RNA and proteins but did not produce infectious virus. The HCMV‐specific antiviral drug valganciclovir significantly reduced viral protein expression and cell growth both in vitro and in vivo. These findings indicate that HCMV is important for the pathogenesis of neuroblastoma and that anti‐viral therapy may be a novel adjuvant treatment option for children with neuroblastoma.

Medulloblastoma: a disease with disorganized developmental signaling cascades.

Sonic Hedgehog, Wnt and PI3K/Akt are three developmental signalling cascades that all have crucial functions during normal brain development. The activation of one or several of these cascades is also found in the majority of medulloblastoma, the most common pediatric malignant tumor of the central nervous system. The aberrant expression of key molecules in developmental signalling pathways or inhibition of the activity of proteins regulating the activity of these cascades is important for medulloblastoma proliferation and survival. These developmental signal transduction pathways transfer signals from the cell membrane to transcription factors in the nucleus, resulting in an altered gene expression. Molecular cross-talks between these developmental cascades have been described in several cancers and may have important functions in tumorigenesis. One common kinase for these three signalling cascades is GSK-3b, which seems to be the glue that links these cascades together. Medulloblastoma cells display many characteristics that are interrelated to the progenitor cells of the embryonic brain where these developmental cascades are essential for proper development. Hence, understanding the relationship between normal brain development and medulloblastoma molecular pathogenesis is essential for more efficient, less toxic tailored therapies to be developed and implemented.

Osteoblasts remotely supply lung tumors with cancer-promoting SiglecFhigh neutrophils

A bona fide portrayal of tumor growth Bone has a well-established role in advanced cancer. It provides a supportive microenvironment for the growth of metastatic cells that escape the primary tumor, which ultimately leads to loss of bone mass. Engblom et al. show that bone may also contribute to early-stage tumorigenesis through a mechanism that leads to an increase in bone mass (see the Perspective by Zhang and Lyden). In mouse models of lung adenocarcinoma, primary tumor cells remotely activated bone-resident cells called osteoblasts, which have a bone-building function. The activated osteoblasts in turn triggered production of a certain type of neutrophil that infiltrates the primary tumor and promotes its growth. Patients with early-stage lung cancer were also found to have an increase in bone density, consistent with the findings in mice. Science, this issue p. eaal5081; see also p. 1127 Systemic cross-talk between tumor and bone can boost the growth of early-stage lung cancer in mice. INTRODUCTION Myeloid cells have emerged as key regulators of cancer growth because of their abundance in the tumor stroma in a broad range of cancers, their association with clinical outcome, and their ability to modulate tumor progression. Most tumor-infiltrating myeloid cells derive from circulating precursors, which are produced in distant tissues, and some tumors amplify myeloid cell activity by skewing hematopoiesis toward the myeloid lineage or increasing myeloid cell populations in the periphery. For example, patients across diverse cancer types can present with elevated levels of myeloid progenitor cells in peripheral blood. Additionally, increased numbers of circulating myeloid cells, such as neutrophils, often correlate with poorer clinical outcome. It is therefore important to consider host changes that occur away from the tumor stroma to more fully understand the biological processes underlying tumor growth. RATIONALE The bone marrow is a tissue of particular interest as it is the main production site for hematopoietic cells corresponding to all circulating blood lineages in the adult. The marrow contains resident cell components, such as osteoblasts, which not only participate in bone maintenance but also regulate hematopoiesis and immune cell fate. However, our understanding of bone dynamics in the context of cancer (growing at sites distant from the local bone microenvironment) and related immune responses remains limited. To address this knowledge gap, we explored whether a common solid cancer—lung adenocarcinoma—remotely affects bone tissue and how this might shape tumor-associated hematopoietic responses and tumor growth. RESULTS We show in different mouse models and in cancer patients (n = 70) that lung adenocarcinomas increase bone stromal activity even in the absence of local metastasis. Animal studies further reveal that the cancer-induced bone phenotype involves bone-resident osteocalcin-expressing (Ocn+) osteoblastic cells. Ocn+ cells affect distant tumor progression because experimentally reducing the number of these cells limits lung tumor growth. Also, Ocn+ cells are required for full-fledged tumor infiltration by a distinct subset of neutrophils that are defined by their high expression of the lectin SiglecF (sialic acid–binding immunoglobulin-like lectin F). Compared to other neutrophils, SiglecFhigh cells express genes associated with cancer-promoting processes, including angiogenesis, myeloid cell differentiation and recruitment, extracellular matrix remodeling, suppression of T cell responses, and tumor cell proliferation and growth. Additionally, SiglecFhigh neutrophils have increased reactive oxygen species production, promote macrophage differentiation, and boost tumor progression in vivo. We further report that the soluble receptor for advanced glycation end products (sRAGE) is up-regulated in the circulation of tumor-bearing mice and fosters osteoblastic activity and osteoblast-dependent neutrophil maturation in vitro. CONCLUSION This study identifies systemic cross-talk between lung tumors and bones: Lung tumors can remotely activate Ocn+ osteoblastic cells in bones even in the absence of local metastasis. In turn, these Ocn+ cells supply tumors with SiglecFhigh neutrophils, which foster cancer progression. The findings bear scientific and therapeutic importance because they reveal contributions of the host systemic environment to tumor growth and they position Ocn+ cells, SiglecFhigh neutrophils, and sRAGE as candidate clinical biomarkers and possible intervention points for anticancer therapy. Systemic cross-talk between lung tumors and bones. Lung adenocarcinomas can remotely activate Ocn+ osteoblastic cells in bones even in the absence of local metastasis. In turn, these osteoblasts supply tumors with SiglecFhigh neutrophils, which exhibit cancer-promoting functions (left). By contrast, the bone marrow in steady state only produces SiglecFlow neutrophils (right). Bone marrow–derived myeloid cells can accumulate within tumors and foster cancer outgrowth. Local immune-neoplastic interactions have been intensively investigated, but the contribution of the systemic host environment to tumor growth remains poorly understood. Here, we show in mice and cancer patients (n = 70) that lung adenocarcinomas increase bone stromal activity in the absence of bone metastasis. Animal studies reveal that the cancer-induced bone phenotype involves bone-resident osteocalcin-expressing (Ocn+) osteoblastic cells. These cells promote cancer by remotely supplying a distinct subset of tumor-infiltrating SiglecFhigh neutrophils, which exhibit cancer-promoting properties. Experimentally reducing Ocn+ cell numbers suppresses the neutrophil response and lung tumor outgrowth. These observations posit osteoblasts as remote regulators of lung cancer and identify SiglecFhigh neutrophils as myeloid cell effectors of the osteoblast-driven protumoral response.