The regulation of angiogenesis in neuroblastoma

Identification of GB3 as a Novel Biomarker of Tumor-Derived Vasculature in Neuroblastoma Using a Stiffness-Based Model

Neuroblastoma (NB) is a childhood cancer in sympathetic nervous system cells. NB exhibits cellular heterogeneity, with adrenergic and mesenchymal states displaying distinct tumorigenic potentials. NB is highly vascularized, and blood vessels can form through various mechanisms, including endothelial transdifferentiation, leading to the development of tumor-derived endothelial cells (TECs) associated with chemoresistance. We lack specific biomarkers for TECs. Therefore, identifying new TEC biomarkers is vital for effective NB therapies. A stiffness-based platform simulating human arterial and venous stiffness was developed to study NB TECs in vitro. Adrenergic cells cultured on arterial-like stiffness transdifferentiated into TECs, while mesenchymal state cells did not. The TECs derived from adrenergic cells served as a model to explore new biomarkers, with a particular focus on GB3, a glycosphingolipid receptor implicated in angiogenesis, metastasis, and drug resistance. Notably, the TECs unequivocally expressed GB3, validating its novelty as a marker. To explore targeted therapeutic interventions, nanoparticles functionalized with the non-toxic subunit B of the Shiga toxin were generated, because they demonstrated a robust affinity for GB3-positive cells. Our results demonstrate the value of the stiffness-based platform as a predictive tool for assessing NB aggressiveness, the discovery of new biomarkers, and the evaluation of the effectiveness of targeted therapeutic strategies.

Microfluidic model of the alternative vasculature in neuroblastoma

Neuroblastoma (NB) is a highly vascularized pediatric tumor arising from undifferentiated neural crest cells early in life, exhibiting both traditional endothelial-cell-driven vasculature and an intriguing alternative vasculature. The alternative vasculature can arise from cancer cells undergoing transdifferentiation into tumor-derived endothelial cells (TEC), a trait associated with drug resistance and tumor relapse. The lack of effective treatments targeting NB vasculature primarily arises from the challenge of establishing predictive in vitro models that faithfully replicate the alternative vasculature phenomenon. In this study, we aim to recreate the intricate vascular system of NB in an in vitro context, encompassing both types of vascularization, by developing a novel neuroblastoma-on-a-chip model. We designed a collagen I/fibrin-based hydrogel closely mirroring NB's physiological composition and tumor stiffness. This biomaterial created a supportive environment for the viability of NB and endothelial cells. Implementing a physiological shear stress value, aligned with the observed range in arteries and capillaries, within the microfluidic chip facilitated the successful development of vessel-like structures and triggered transdifferentiation of NB cells into TECs. The vascularized neuroblastoma-on-a-chip model introduced here presents a promising and complementary strategy to animal-based research with a significant capacity for delving into NB tumor biology and vascular targeting therapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-023-00064-x.

MYCN Impact on High-Risk Neuroblastoma: From Diagnosis and Prognosis to Targeted Treatment

Among childhood cancers, neuroblastoma is the most diffuse solid tumor and the deadliest in children. While to date, the pathology has become progressively manageable with a significant increase in 5-year survival for its less aggressive form, high-risk neuroblastoma (HR-NB) remains a major issue with poor outcome and little survivability of patients. The staging system has also been improved to better fit patient needs and to administer therapies in a more focused manner in consideration of pathology features. New and improved therapies have been developed; nevertheless, low efficacy and high toxicity remain a staple feature of current high-risk neuroblastoma treatment. For this reason, more specific procedures are required, and new therapeutic targets are also needed for a precise medicine approach. In this scenario, MYCN is certainly one of the most interesting targets. Indeed, MYCN is one of the most relevant hallmarks of HR-NB, and many studies has been carried out in recent years to discover potent and specific inhibitors to block its activities and any related oncogenic function. N-Myc protein has been considered an undruggable target for a long time. Thus, many new indirect and direct approaches have been discovered and preclinically evaluated for the interaction with MYCN and its pathways; a few of the most promising approaches are nearing clinical application for the investigation in HR-NB.

The Tumor Microenvironment in Neuroblastoma: New Players, New Mechanisms of Interaction and New Perspectives

The contribution of the tumor microenvironment (TME) to cancer progression has been well recognized in recent decades. As cancer therapeutic strategies are increasingly precise and include immunotherapies, knowledge of the nature and function of the TME in a tumor becomes essential. Our understanding of the TME in neuroblastoma (NB), the second most common solid tumor in children, has significantly progressed from an initial focus on its Schwannian component to a better awareness of its complex nature, which includes not only immune but also non-immune cells such as cancer-associated fibroblasts (CAFs), the contribution of which to inflammation and interaction with tumor-associated macrophages (TAMs) is now recognized. Recent studies on the TME landscape of NB tumors also suggest significant differences between MYCN-amplified (MYCN-A) and non-amplified (MYCN-NA) tumors, in their content in stromal and inflammatory cells and their immunosuppressive activity. Extracellular vesicles (EVs) released by cells in the TME and microRNAs (miRs) present in their cargo could play important roles in the communication between NB cells and the TME. This review article discusses these new aspects of the TME in NB and the impact that information on the TME landscape in NB will have in the design of precise, biomarker-integrated clinical trials.

Targeting the Tumor Microenvironment in Neuroblastoma: Recent Advances and Future Directions

Neuroblastoma (NB) is the most common pediatric tumor malignancy that originates from the neural crest and accounts for more than 15% of all the childhood deaths from cancer. The neuroblastoma cancer research has long been focused on the role of MYCN oncogene amplification and the contribution of other genetic alterations in the progression of this malignancy. However, it is now widely accepted that, not only tumor cells, but the components of tumor microenvironment (TME), including extracellular matrix, stromal cells and immune cells, also contribute to tumor progression in neuroblastoma. The complexity of different components of tumor stroma and their resemblance with surrounding normal tissues pose huge challenges for therapies targeting tumor microenvironment in NB. Hence, the detailed understanding of the composition of the TME of NB is crucial to improve existing and future potential immunotherapeutic approaches against this childhood cancer. In this review article, I will discuss different components of the TME of NB and the recent advances in the strategies, which are used to target the tumor microenvironment in neuroblastoma.

Association of high microvessel αvβ3 and low PTEN with poor outcome in stage 3 neuroblastoma: rationale for using first in class dual PI3K/BRD4 inhibitor, SF1126

Neuroblastoma (NB) is the most common extracranial solid tumor in children. Our previous studies showed that the angiogenic integrin α_vβ₃ was increased in high-risk metastatic (stage 4) NB compared with localized neuroblastomas. Herein, we show that integrin α_vβ₃ was expressed on 68% of microvessels in MYCN-amplified stage 3 neuroblastomas, but only on 34% (means) in MYCN-non-amplified tumors (p < 0.001; n = 54). PTEN, a tumor suppressor involved in α_vβ₃ signaling, was expressed in neuroblastomas either diffusely, focally or not at all (immunohistochemistry). Integrin α_vβ₃ was expressed on 60% of tumor microvessels when PTEN was negative or focal, as compared to 32% of microvessels in tumors with diffuse PTEN expression (p < 0.001). In a MYCN transgenic mouse model, loss of one allele of PTEN promoted tumor growth, illustrating the potential role of PTEN in neuroblastoma pathogenesis. Interestingly, we report the novel dual PI-3K/BRD4 activity of SF1126 (originally developed as an RGD-conjugated pan PI3K inhibitor). SF1126 inhibits BRD4 bromodomain binding to acetylated lysine residues with histone H3 as well as PI3K activity in the MYCN amplified neuroblastoma cell line IMR-32. Moreover, SF1126 suppressed MYCN expression and MYCN associated transcriptional activity in IMR-32 and CHLA136, resulting in overall decrease in neuroblastoma cell viability. Finally, treatment of neuroblastoma tumors with SF1126 inhibited neuroblastoma growth in vivo. These data suggest integrin α_vβ₃, MYCN/BRD4 and PTEN/PI3K/AKT signaling as biomarkers and hence therapeutic targets in neuroblastoma and support testing of the RGD integrin α_vβ₃-targeted PI-3K/BRD4 inhibitor, SF1126 as a therapeutic strategy in this specific subgroup of high risk neuroblastoma.

PlGF and VEGF-A Regulate Growth of High-Risk MYCN-Single Copy Neuroblastoma Xenografts via Different Mechanisms

Neuroblastoma (NB) is the most common extracranial solid tumor of childhood and is a rapidly growing, highly-vascularized cancer. NBs frequently express angiogenic factors and high tumor angiogenesis has been associated with poor outcomes. Placental growth factor (PlGF) is an angiogenic protein belonging to the vascular endothelial growth factor (VEGF) family and is up-regulated mainly in pathologic conditions. Recently, PlGF was identified as a member of a gene expression signature characterizing highly malignant NB stem cells drawing attention as a potential therapeutic target in NB. In the present study, we sought to investigate the expression of PlGF in NB patients and the effect of PlGF inhibition on high-risk MYCN-non-amplified SK-N-AS NB xenografts. Human SK-N-AS cells, which are poorly differentiated and express PlGF and VEGF-A, were implanted subcutaneously in athymic nude mice. Treatment was done by intratumoral injection of replication-incompetent adenoviruses (Ad) expressing PlGF- or VEGF-specific short hairpin (sh)RNA, or soluble (s)VEGF receptor 2 (VEGFR2). The effect on tumor growth and angiogenesis was analyzed. High PlGF expression levels were observed in human advanced-stage NBs. Down-regulating PlGF significantly reduced NB growth in established NB xenografts by reducing cancer cell proliferation but did not suppress angiogenesis. In contrast, blocking VEGF by administration of Ad(sh)VEGF and Ad(s)VEGFR2 reduced tumor growth associated with decreased tumor vasculature. These findings suggest that PlGF and VEGF-A modulate MYCN-non-amplified NB tumors by different mechanisms and support a role for PlGF in NB biology.

SPARC overexpression combined with radiation retards angiogenesis by suppressing VEGF-A via miR‑410 in human neuroblastoma cells

Neuroblastoma (NB) is the most common extracranial solid tumor in children and despite aggressive therapy survival rates remain low. One of the contributing factors for low survival rates is aggressive tumor angiogenesis, which is known to increase due to radiation, one of the standard therapies for neuroblastoma. Therefore, targeting tumor angiogenesis can be a viable add-on therapy for the treatment of neuroblastomas. In the present study, we demonstrate that overexpression of secreted protein acidic and rich in cysteine (SPARC) suppresses radiation induced angiogenesis in SK-N-BE(2) and NB1691 neuroblastoma cells. We observed that overexpression of SPARC in SK-N-BE(2) and NB1691 cells reduced radiation induced angiogenesis in an in vivo mouse dorsal skin model and an ex vivo chicken CAM (chorioallantoic-membrane) model and also reduced tumor size in subcutaneous mouse tumor models of NB. We also observed that SPARC overexpression reduces VEGF-A expression, in SK-N-BE(2) and NB1691 NB cells via miR-410, a VEGF-A targeting microRNA. SPARC overexpression alone or in combination with miR-410 and radiation was shown to be effective at reducing angiogenesis. Moreover, addition of miR-410 inhibitors reversed SPARC mediated inhibition of VEGF-A in NB1691 cells but not in SK-N-BE(2) NB cells. In conclusion, the present study demonstrates that the over-expression of SPARC in combination with radiation reduced tumor angiogenesis by downregulating VEGF-A via miR-410.

More than the genes, the tumor microenvironment in neuroblastoma

Neuroblastoma is the second most common solid tumor in children. Since the seminal discovery of the role of amplification of the MYCN oncogene in the pathogenesis of neuroblastoma in the 1980s, much focus has been on the contribution of genetic alterations in the progression of this cancer. However it is now clear that not only genetic events play a role but that the tumor microenvironment (TME) substantially contributes to the biology of neuroblastoma. In this article, we present a comprehensive review of the literature on the contribution of the TME to the ten hallmarks of cancer in neuroblastoma and discuss the mechanisms of communication between neuroblastoma cells and the TME that underlie the influence of the TME on neuroblastoma progression. We end our review by discussing how the knowledge acquired over the last two decades in this field is now leading to new clinical trials targeting the TME.

Development and characterization of a human orthotopic neuroblastoma xenograft

Neuroblastoma is a pediatric cancer of the developing sympathoadrenal lineage. The tumors are known to develop from the adrenal gland or paraspinal ganglia and have molecular and cellular features of sympathetic neurons such as dense core vesicles and catecholamine production. Here we present the detailed molecular, cellular, genetic and epigenetic characterization of an orthotopic xenograft derived from a high-risk stage 4 neuroblastoma patient. Overall, the xenografted tumor retained the high risk features of the primary tumor and showed aggressive growth and metastasis in the mouse. Also, the genome was preserved with no additional copy number variations, structural variations or aneuploidy. There were 13 missense mutations identified in the xenograft that were not present in the patient's primary tumor and there were no new nonsense mutations. None of the missense mutations acquired in the xenograft were in known cancer genes. We also demonstrate the feasibility of using the orthotopic neuroblastoma xenograft to test standard of care chemotherapy and molecular targeted therapeutics. Finally, we optimized a new approach to produce primary cultures of the neuroblastoma xenografts for high-throughput drug screening which can be used to test new combinations of therapeutic agents for neuroblastoma.

The neurovascular unit and its growth factors: coordinated response in the vascular and nervous systems

The nervous and vascular systems contain many common organizational features and develop similarly in terms of anatomical patterning. During embryogenesis and in regions of the brain undergoing postnatal neurogenesis, neural stem cells and endothelial cells are found in close proximity, or within a so-called vascular niche. The similarities in patterning and proximity may reflect coordinated development based on responsiveness to similar growth factors such as vascular endothelial growth factor, semaphorin, and ephrins/Ephs: molecules involved in the development and maintenance of both the nervous and vascular systems. Despite the blatant similarities between the vascular and nervous systems, little is still known about the co-dependence and/or interactions between the two systems during development and following alterations in metabolic demand as seen during aging, exercise, and disease processes. The interactions between the two systems involving common growth factors suggest these two systems have evolved in an interconnected way.

Anti-Gb3 monoclonal antibody inhibits angiogenesis and tumor development

Inhibiting the growth of tumor vasculature represents one of the relevant strategies against tumor progression. Between all the different pro-angiogenic molecular targets, plasma membrane glycosphingolipids have been under-investigated. In this present study, we explore the anti-angiogenic therapeutic advantage of a tumor immunotherapy targeting the globotriaosylceramide Gb3. In this purpose, a monoclonal antibody against Gb3, named 3E2 was developed and characterized. We first demonstrate that Gb3 is over-expressed in proliferative endothelial cells relative to quiescent cells. Then, we demonstrate that 3E2 inhibits endothelial cell proliferation in vitro by slowing endothelial cell proliferation and by increasing mitosis duration. Antibody 3E2 is further effective in inhibiting ex vivo angiogenesis in aorta ring assays. Moreover, 3E2 treatment inhibits NXS2 neuroblastoma development and liver metastases spreading in A/J mice. Immunohistology examination of the NXS2 metastases shows that only endothelial cells, but not cancer cells express Gb3. Finally, 3E2 treatment diminishes tumor vessels density, proving a specific therapeutic action of our monoclonal antibody to tumor vasculature. Our study demonstrates that Gb3 is a viable alternative target for immunotherapy and angiogenesis inhibition.

Sorafenib inhibits neuroblastoma cell proliferation and signaling, blocks angiogenesis, and impairs tumor growth

BACKGROUND

More effective therapy for children with high-risk neuroblastoma is desperately needed. Preclinical studies have shown that neuroblastoma tumor growth can be inhibited by agents that block angiogenesis. We hypothesized that drugs which target both neuroblastoma cells and tumor angiogenesis would have potent anti-tumor activity. In this study we tested the effects of sorafenib, a multi-kinase inhibitor, on neuroblastoma cell proliferation and signaling, and in mice with subcutaneous human neuroblastoma xenografts or orthotopic adrenal tumors.

PROCEDURE

Mice with subcutaneous neuroblastoma xenografts or orthotopic adrenal tumors were treated with sorafenib, and tumor growth rates were measured. Blood vessel architecture and vascular density were evaluated histologically in treated and control neuroblastoma tumors. The in vitro effects of sorafenib on neuroblastoma proliferation, cell cycle, and signaling were also evaluated.

RESULTS

Sorafenib inhibited tumor growth in mice with subcutaneous and orthotopic adrenal tumors. Decreased numbers of cycling neuroblastoma cells and tumor blood vessels were seen in treated versus control tumors, and the blood vessels in the treated tumors had more normal architecture. Sorafenib treatment also decreased neuroblastoma cell proliferation, attenuated ERK signaling, and enhanced G(1) /G(0) cell cycle arrest in vitro.

CONCLUSIONS

Our results demonstrate that sorafenib inhibits the growth of neuroblastoma tumors by targeting both neuroblastoma cells and tumor blood vessels. Single agent sorafenib should be evaluated in future phase II neuroblastoma studies.

Cytokines in neuroblastoma: from pathogenesis to treatment

Cytokines released by cancer cells or by cells of the tumor microenvironment stimulate angiogenesis, act as autocrine or paracrine growth factors for malignant cells, promote tumor cell migration and metastasis or create an immunosuppressive microenvironment. These tumor-promoting effects of cytokines also apply to neuroblastoma (NB), a pediatric neuroectodermal malignancy with frequent metastatic presentation at diagnosis and poor prognosis. IL-6 and VEGF are the best characterized cytokines that stimulated tumor growth and metastasis, while others such as IFN-γ can exert anti-NB activity by inducing tumor cell apoptosis and inhibiting angiogenesis. On the other hand, cytokines are part of the anti-NB therapeutic armamentarium, as exemplified by IL-2 and granulocyte-macrophage colony stimulating factor that potentiate the activity of anti-NB antibodies. These recent results raise hope for more efficacious treatment of this ominous pediatric malignancy.

Identification of tumoral glial precursor cells in neuroblastoma

Neuroblastic tumors (NBT) are composed by neuroblasts and Schwannian-like stroma. The origin of these two cell subtypes remains unclear. In this study, we describe, a neuroblastic-like subpopulation in neuroblastoma (NB) coexpressing GD2 and S100A6, neuroblastic and glial lineage markers respectively. The GD2(+)/S100A6(+) neuroblastic subpopulation was found to be enriched in low risk NB, distributed around the perivascular niche. Some stromal bundles showed GD2(+)/S100A6 costaining. Metastatic bone marrow specimens also showed GD2(+)/S100A6(+) cells. During in vitro retinoic acid induced differentiation of NB cell lines, rare GD2(+)/S100A6 neuroblatic cells appeared. We conclude that GD2(+)/S100A6(+) neuroblasts may represent a tumoral glial precursor subpopulation in NBT.

How do tumors actively escape from host immunosurveillance?

The immunological background for the process of tumor growth is still obscure. However, our understanding of what happens could have important consequences, namely in the context of cancer immunotherapy. A tumor is able to grow in the host environment either because it is recognizable as normal tissue and tolerated by host immune cells, or because it can "escape" from host immunosurveillance. According to the second option the mechanisms of tumor recognition and consequent destruction are actively disturbed by such processes as: change of tumor immunogenicity, production of tumor-derived regulatory molecules, and interaction of cancer cells with tumor-infiltrating immune cells. The results of studies devoted to the problem of immunoregulation in the tumor environment seem to support the "escape" hypothesis.

Balance of pro- versus anti-angiogenic splice isoforms of vascular endothelial growth factor as a regulator of neuroblastoma growth

Neuroblastoma (NB) is the second most common extracranial tumour of childhood. Angiogenesis plays a crucial role in the growth and development of NB and vascular endothelial growth factor (VEGF), one of the most potent stimuli of angiogenesis, has been studied extensively in vitro. VEGF(165) has been shown to be the predominant angiogenic isoform expressed in NB cell lines and tumours. In this study, we investigated the anti-angiogenic isoform of VEGF-A, generated from distal splice site selection in the terminal exon of VEGF (VEGF(165)b) and shown to be down-regulated in epithelial malignancies. The expression of both the pro- (VEGF(xxx)) and the anti-angiogenic (VEGF(xxx)b) isoforms was compared in a range of NB and ganglioneuroma (GN) tumours. Whereas VEGF(xxx)b and VEGF(xxx) were both expressed in GN, specific up-regulation of the VEGF(xxx) isoforms was seen in NB at RNA and protein levels. Highly tumourigenic NB cell lines also showed up-regulation of the angiogenic isoforms relative to VEGF(xxx)b compared to less tumourigenic cell lines, and the isoforms were differentially secreted. These results indicate that VEGF(165) is up-regulated in NB and that there is a difference in the balance of isoform expression from anti-angiogenic VEGF(165)b to angiogenic VEGF(165). Treatment with recombinant human VEGF(165)b significantly reduced the growth rate of established xenografts of SK-N-BE(2)-C cells (4.24 +/- 1.01 fold increase in volume) compared with those treated with saline (9.76 +/- 3.58, p < 0.01). Microvascular density (MVD) was significantly decreased in rhVEGF(165)b-treated tumours (19.4 +/- 1.9 vessels/mm(3)) in contrast to the saline-treated tumours (45.5 +/- 8.6 vessels/mm(3)). VEGF(165)b had no significant effect on the proliferative or apoptotic activity, viability or cytotoxicity of SK-N-BE(2)-C cells after 48 h. In conclusion, VEGF(165)b is an effective inhibitor of NB growth. These findings provide the rationale for further investigation of VEGF(165)b in NB and other paediatric malignancies.

Neuroblastoma progression correlates with downregulation of the lymphangiogenesis inhibitor sVEGFR-2

PURPOSE

Tumor progression correlates with the induction of a dense supply of blood vessels and the formation of peritumoral lymphatics. Hemangiogenesis and lymphangiogenesis are potently regulated by members of the vascular endothelial growth factor (VEGF) family. Previous studies have indicated the upregulation of VEGF-A and -C in progressed neuroblastoma, however, quantification was performed using semiquantitative methods, or patients who had received radiotherapy or chemotherapy were studied.

EXPERIMENTAL DESIGN

We have analyzed primary neuroblastoma from 49 patients using real-time reverse transcription-PCR and quantified VEGF-A, -C, and -D and VEGF receptors (VEGFR)-1, 2, 3, as well as the soluble form of VEGFR2 (sVEGFR-2), which has recently been characterized as an endogenous inhibitor of lymphangiogenesis. None of the patients had received radiotherapy or chemotherapy before tumor resection.

RESULTS

We did not observe upregulation of VEGF-A, -C, and -D in metastatic neuroblastoma, but found significant downregulation of the lymphangiogenesis inhibitor sVEGFR-2 in metastatic stages III, IV, and IVs. In stage IV neuroblastoma, there were tendencies for the upregulation of VEGF-A and -D and the downregulation of the hemangiogenesis/lymphangiogenesis inhibitors VEGFR-1 and sVEGFR-2 in MYCN-amplified tumors. Similarly, MYCN transfection of the neuroblastoma cell line SH-EP induced the upregulation of VEGF-A and -D and the switching-off of sVEGFR-2.

CONCLUSION

We provide evidence for the downregulation of the lymphangiogenesis inhibitor sVEGFR-2 in metastatic neuroblastoma stages, which may promote lymphogenic metastases. Downregulation of hemangiogenesis and lymphangiogenesis inhibitors VEGFR-1 and sVEGFR-2, and upregulation of angiogenic activators VEGF-A and VEGF-D in MYCN-amplified stage IV neuroblastoma supports the crucial effect of this oncogene on neuroblastoma progression.

[Potential role of antiangiogenic treatment in neuroblastoma]

Focus on new drug development over the last few years has yielded new agents that differ from unspecific classical chemotherapeutics and ionizing radiation, while still targeting the cancer cell itself. Antiangiogenesis is a totally distinct approach targeting the tumor's blood vessels. This concept has now found its eligibility for the treatment of several adult solid tumors: the human antivascular endothelial growth factor (VEGF) antibody bevacizumab, as well as the VEGF receptor tyrosine kinase inhibitors, sunitinib and sorafinib, have recently been licensed by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) for the treatment of colorectal, renal, and lung cancer. Other antiangiogenic drugs are under preclinical and early clinical evaluation. However, what do we know of the use of these drugs in pediatric solid tumors, such as sarcomas and embryonal and neuronal tumors? For some time now, neuroblastoma has been shown to be dependent on angiogenesis. However, the first preclinical data on antiangiogenic drugs in neuroblastoma have not been published until recently, and clinical trials with antiangiogenic agents in neuroblastoma treatment protocols are scarce. This review adresses current knowledge on the important role and mechanisms of angiogenesis in neuroblastoma and summarizes available preclinical and clinical results of antiangiogenic agents used to treat neuroblastoma. Our review clearly demonstrates that clinical trials are urgently needed to bring forward promising antiangiogenesis concepts in neuroblastoma therapy.

Association of MYCN Amplification and 1p Deletion in Neuroblastomas with High Tumor Vascularity

The biologic behavior of neuroblastoma (NB) is extremely variable; therefore, the clinical behavior may be reliably predicted based on the analysis of a panel of prognostic parameters. High vascular density has been correlated with aggressive tumor progression in many types of cancers. The goal of this study was to correlate the tumor vascularity in NB with status of MYCN and the short arm of chromosome 1 (1p) to address the association between angiogenesis and genetic markers of prognostic significance. The study population consisted of 33 patients with histologically proven diagnosis of primary NB and no history of previous chemotherapy. Histologic quantitation of tumor angiogenesis was performed using 3 different methods: microvessel density, vascular grading, and Chalkley counting. MYCN amplification and 1p deletion were determined by using fluorescence in situ hybridization technique. The differentiation and mitosis-karyorrhexis index of tumor cells were also assessed using the Shimada System. MYCN amplification was present in 12 cases (36.3%), and 1p deletion in 16 (48.5%). Both genetic changes significantly correlated with increased tumor vascularity. In addition, tumor vascularity was significantly increased in tumors with high mitosis-karyorrhexis index or of undifferentiated histology. We conclude that angiogenesis shows close association with histologic and genetic prognosticators in NB. Our data support the validity of recent applications of antiangiogenic agents which interfere or block NB progression.

Neuropeptide Y (NPY) in neuroblastoma: effect on growth and vascularization

Neuroblastomas are pediatric tumors of sympathetic origin, expressing neuronal markers, such as NPY and its receptors. Due to this, neuroblastomas are often associated with elevated plasma levels of NPY, which correlates with poor clinical outcome of the disease. This clinical data corroborates the recent discovery of growth-promoting actions of NPY in neuroblastomas. The peptide has been shown to stimulate proliferation of neuroblastoma cells in an autocrine manner and induce tumor vascularization. Since both processes are mediated by the same Y2 and Y5 receptors, targeting this pathway may be a potential bidirectional therapy for these children's tumors.

Lymphangiogenesis and its regulation in human neuroblastoma

For the first time, we could detect lymph vessels in neuroblastoma (NB) by immunohistochemistry with the antibody D2_40. Furthermore, we demonstrate expression of the lymphangiogenic factors VEGF-C and VEGF-D and their receptors VEGFR-2 and VEGFR-3 in NB in vitro and in vivo by RT-PCR. However, addition of recombinant human VEGF-C or -D results in the absence of autocrine growth stimulus in NB cells. Treatment of NB cells with retinoic acid did not lead to a change in VEGF-C or VEGF-D mRNA expression. Incubation of the NB cells Lan-5 with 5-Aza-2'-deoxycytidine led to the up-regulation of VEGF-C mRNA expression, suggesting that the promotor of VEGF-C is methylated. Finally, VEGF-C mRNA expression could be effectively down-regulated by transfection with a specific siRNA in the NB cells Kelly. We conclude that lymphangiogenesis is involved in NB biology and that siRNA directed against VEGF-C may have a future role in anti-lymphangiogenic strategies in NB.

Neuropeptide Y in neural crest-derived tumors: effect on growth and vascularization

Neuropeptide Y (NPY) is a sympathetic neurotransmitter recently found to be a potent growth and angiogenic factor. The peptide and its receptors are abundant in neural crest-derived tumors, such as sympathetic neuroblastomas and pheochromocytomas, as well as parasympathetic Ewing's sarcoma family of tumors. NPY regulates their growth directly, by an autocrine activation of tumor cell proliferation or apoptosis, and indirectly, by its angiogenic activity. The overall effect of the peptide on tumor growth depends on a balance between these processes and the type of receptors expressed in the tumor cells. Thus, NPY and its receptors may become targets for the treatment of neural tumors, directed against both tumor cell proliferation and angiogenesis.

Differential effects of neuropeptide Y on the growth and vascularization of neural crest-derived tumors

Neuropeptide Y (NPY) is a sympathetic neurotransmitter recently found to be potently angiogenic and growth promoting for endothelial, vascular smooth muscle and neuronal cells. NPY and its cognate receptors, Y1, Y2 and Y5, are expressed in neural crest-derived tumors; however, their role in regulation of growth is unknown. The effect of NPY on the growth and vascularization of neuroendocrine tumors was tested using three types of cells: neuroblastoma, pheochromocytoma, and Ewing's sarcoma family of tumors (ESFT). The tumors varied in expression of NPY receptors, which was linked to differential functions of the peptide. NPY stimulated proliferation of neuroblastoma cells via Y2/Y5Rs and inhibited ESFT cell growth by Y1/Y5-mediated apoptosis. In both tumor types, NPY receptor antagonists altered basal growth levels, indicating a regulatory role of autocrine NPY. In addition, the peptide released from the tumor cells stimulated endothelial cell proliferation, which suggests its paracrine angiogenic effects. In nude mice xenografts, exogenous NPY stimulated growth of neuroblastoma tumors, whereas it increased apoptosis and reduced growth of ESFT. However, in both tumors, NPY treatment led to an increase in tumor vascularization. Taken together, this is the first report of NPY being a growth-regulatory factor for neuroendocrine tumors, acting both by autocrine activation of tumor cell proliferation or apoptosis and by angiogenesis. NPY and its receptors may become targets for novel approaches in the treatment of these diseases, directed against both tumor cell proliferation and angiogenesis.

Proadrenomedullin NH2-terminal 20 peptide is a potent angiogenic factor, and its inhibition results in reduction of tumor growth

We have found through ex vivo and in vivo angiogenesis models that the adrenomedullin gene-related peptide, proadrenomedullin NH2-terminal 20 peptide (PAMP), exhibits a potent angiogenic potential at femtomolar concentrations, whereas classic angiogenic factors such as vascular endothelial growth factor and adrenomedullin mediate a comparable effect at nanomolar concentrations. We found that human microvascular endothelial cells express PAMP receptors and respond to exogenous addition of PAMP by increasing migration and cord formation. Exposure of endothelial cells to PAMP increases gene expression of other angiogenic factors such as adrenomedullin, vascular endothelial growth factor, basic fibroblast growth factor, and platelet-derived growth factor C. In addition, the peptide fragment PAMP(12-20) inhibits tumor cell-induced angiogenesis in vivo and reduces tumor growth in xenograft models. Together, our data demonstrate PAMP to be an extremely potent angiogenic factor and implicate this peptide as an attractive molecular target for angiogenesis-based antitumor therapy.