‘Cross-talk’ between Schwannian stroma and neuroblasts promotes neuroblastoma tumor differentiation and inhibits angiogenesis

Hyperbaric oxygen suppressed tumor progression through the improvement of tumor hypoxia and induction of tumor apoptosis in A549-cell-transferred lung cancer

Tumor cells have long been recognized as a relative contraindication to hyperbaric oxygen treatment (HBOT) since HBOT might enhance progressive cancer growth. However, in an oxygen deficit condition, tumor cells are more progressive and can be metastatic. HBOT increasing in oxygen partial pressure may benefit tumor suppression. In this study, we investigated the effects of HBOT on solid tumors, such as lung cancer. Non-small cell human lung carcinoma A549-cell-transferred severe combined immunodeficiency mice (SCID) mice were selected as an in vivo model to detect the potential mechanism of HBOT in lung tumors. HBOT not only improved tumor hypoxia but also suppressed tumor growth in murine xenograft tumor models. Platelet endothelial cell adhesion molecule (PECAM-1/CD31) was significantly increased after HBOT. Immunostaining of cleaved caspase-3 was demonstrated and apoptotic tumor cells with nuclear debris were aggregated starting on the 14th-day after HBOT. In vitro, HBOT suppressed the growth of A549 cells in a time-dependent manner and immediately downregulated the expression of p53 protein after HBOT in A549 cells. Furthermore, HBOT-reduced p53 protein could be rescued by a proteasome degradation inhibitor, but not an autophagy inhibitor in A549 cells. Our results demonstrated that HBOT improved tissue angiogenesis, tumor hypoxia and increased tumor apoptosis to lung cancer cells in murine xenograft tumor models, through modifying the tumor hypoxic microenvironment. HBOT will merit further cancer therapy as an adjuvant treatment for solid tumors, such as lung cancer.

Digital Image Analysis Applied to Tumor Cell Proliferation, Aggressiveness, and Migration-Related Protein Synthesis in Neuroblastoma 3D Models

Patient-derived cancer 3D models are a promising tool that will revolutionize personalized cancer therapy but that require previous knowledge of optimal cell growth conditions and the most advantageous parameters to evaluate biomimetic relevance and monitor therapy efficacy. This study aims to establish general guidelines on 3D model characterization phenomena, focusing on neuroblastoma. We generated gelatin-based scaffolds with different stiffness and performed SK-N-BE(2) and SH-SY5Y aggressive neuroblastoma cell cultures, also performing co-cultures with mouse stromal Schwann cell line (SW10). Model characterization by digital image analysis at different time points revealed that cell proliferation, vitronectin production, and migration-related gene expression depend on growing conditions and are specific to the tumor cell line. Morphometric data show that 3D in vitro models can help generate optimal patient-derived cancer models, by creating, identifying, and choosing patterns of clinically relevant artificial microenvironments to predict patient tumor cell behavior and therapeutic responses.

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.

Murine neuroblastoma cell lines developed by conditional reprogramming preserve heterogeneous phenotypes observed in vivo

Neuroblastoma (NB) is a pediatric tumor of the peripheral nervous system. Treatment of the disease represents an unsolved clinical problem, as survival of patients with aggressive form of NB remains below 50%. Despite recent identification of numerous potential therapeutic targets, clinical trials validating them are challenging due to the rarity of the disease and its high patient-to-patient heterogeneity. Hence, there is a need for the accurate preclinical models that would allow testing novel therapeutic approaches and prioritizing the clinical studies, preferentially in personalized way. Here, we propose using conditional reprogramming (CR) technology for rapid development of primary NB cell cultures that could become a new model for such tests. This newly established method allowed for indefinite propagation of normal and tumor cells of epithelial origin in an undifferentiated state by their culture in the presence of Rho-associated kinase (ROCK) inhibitor, Y-27632, and irradiated mouse feeder cells. Using a modification of this approach, we isolated cell lines from tumors arising in the TH-MYCN murine transgenic model of NB (CR-NB). The cells were positive for neuronal markers, including Phox2B and peripherin and consisted of two distinct populations: mesenchymal and adrenergic expressing corresponding markers of their specific lineage. This heterogeneity of the CR-NB cells mimicked the different tumor cell phenotypes in TH-MYCN tumor tissues. The CR-NB cells preserved anchorage-independent growth capability and were successfully passaged, frozen and biobanked. Further studies are required to determine the utility of this method for isolation of human NB cultures, which can become a novel model for basic, translational, and clinical research, including individualized drug testing.

Decorin gene upregulation mediated by an adeno-associated virus vector increases intratumoral uptake of nab-paclitaxel in neuroblastoma via inhibition of stabilin-1

The availability of effective medication for the treatment of refractory or recurrent neuroblastoma remains limited. This study sought to investigate the effects of increased decorin (DCN) expression on the intratumoral uptake of nab-paclitaxel as a potential novel approach to NB. Correlation between the clinical characteristics of neuroblastoma and the expression of DCN, secreted protein acidic and rich in cysteine (SPARC) and stabilin-1 was evaluated. The anticancer effect of recombinant adeno-associated virus-DCN (rAAV-DCN) was assessed in vivo and in vitro. And the effect of rAAV-DCN on the intratumoral uptake of paclitaxel was also studied in neuroblastoma-grafted nude mice. Overall, 12.5%, 17.7%, and 71.9% of the tumors stained positive for DCN, SPARC and stabilin-1 respectively and correlated to age, stage and N-MYC status in 96 children and adolescents with neuroblastoma. Transfected neuroblastoma cells stably expressed DCN, with in vivo and in vitro studies demonstrating rAAV-DCN sensitized the anticancer effect of nab-paclitaxel. Systemic rAAV-DCN in neuroblastoma-grafted nude mice inhibited stabilin-1, up-regulated SPARC, and increased the intratumoral uptake of paclitaxel. Macrophage depletion or anti-stabilin-1 monoclonal antibody increased the intratumoral uptake of nab-paclitaxel and its anticancer effects to a degree comparable to that achieved by systemic rAAV-DCN. The systemic administration of rAAV-DCN up-regulates DCN in neuroblastoma and accelerates the intratumoral uptake of nab-paclitaxel by inhibiting stabilin-1 mediated SPARC degradation.

Heparin-binding epidermal growth factor-like growth factor promotes neuroblastoma differentiation

High-risk neuroblastoma is characterized by undifferentiated neuroblasts and low schwannian stroma content. The tumor stroma contributes to the suppression of tumor growth by releasing soluble factors that promote neuroblast differentiation. Here we identify heparin-binding epidermal growth factor-like growth factor (HBEGF) as a potent prodifferentiating factor in neuroblastoma. HBEGF mRNA expression is decreased in human neuroblastoma tumors compared with benign tumors, with loss correlating with decreased survival. HBEGF protein is expressed only in stromal compartments of human neuroblastoma specimens, with tissue from high-stage disease containing very little stroma or HBEGF expression. In 3 human neuroblastoma cell lines (SK-N-AS, SK-N-BE2, and SH-SY5Y), soluble HBEGF is sufficient to promote neuroblast differentiation and decrease proliferation. Heparan sulfate proteoglycans and heparin derivatives further enhance HBEGF-induced differentiation by forming a complex with the epidermal growth factor receptor, leading to activation of the ERK1/2 and STAT3 pathways and up-regulation of the inhibitor of DNA binding transcription factor. These data support a role for loss of HBEGF in the neuroblastoma tumor microenvironment in neuroblastoma pathogenesis.-Gaviglio, A. L., Knelson, E. H., Blobe, G. C. Heparin-binding epidermal growth factor-like growth factor promotes neuroblastoma differentiation.

Extracellular matrix composition defines an ultra-high-risk group of neuroblastoma within the high-risk patient cohort

Background:

Although survival for neuroblastoma patients has dramatically improved in recent years, a substantial number of children in the high-risk subgroup still die.

Methods:

We aimed to define a subgroup of ultra-high-risk patients from within the high-risk cohort. We used advanced morphometric approaches to quantify and characterise blood vessels, reticulin fibre networks, collagen type I bundles, elastic fibres and glycosaminoglycans in 102 high-risk neuroblastomas specimens. The Kaplan–Meier method was used to correlate the analysed elements with survival.

Results:

The organisation of blood vessels and reticulin fibres in neuroblastic tumours defined an ultra-high-risk patient subgroup with 5-year survival rate <15%. Specifically, tumours with irregularly shaped blood vessels, large sinusoid-like vessels, smaller and tortuous venules and arterioles and with large areas of reticulin fibres forming large, crosslinking, branching and haphazardly arranged networks were linked to the ultra-high-risk phenotype.

Conclusions:

We demonstrate that quantification of tumour stroma components by morphometric techniques has the potential to improve risk stratification of neuroblastoma patients.

A Promyelocytic Leukemia Protein-Thrombospondin-2 Axis and the Risk of Relapse in Neuroblastoma

PURPOSE

Neuroblastoma is a childhood malignancy originating from the sympathetic nervous system with a complex biology, prone to metastasize and relapse. High-risk, metastatic cases are explained in part by amplification or mutation of oncogenes, such as MYCN and ALK, and loss of tumor suppressor genes in chromosome band 1p. However, it is fundamental to identify other pathways responsible for the large portion of neuroblastomas with no obvious molecular alterations.

EXPERIMENTAL DESIGN

Neuroblastoma cell lines were used for the assessment of tumor growth in vivo and in vitro Protein expression in tissues and cells was assessed using immunofluorescence and IHC. The association of promyelocytic leukemia (PML) expression with neuroblastoma outcome and relapse was calculated using log-rank and Mann-Whitney tests, respectively. Gene expression was assessed using chip microarrays.

RESULTS

PML is detected in the developing and adult sympathetic nervous system, whereas it is not expressed or is low in metastatic neuroblastoma tumors. Reduced PML expression in patients with low-risk cancers, that is, localized and negative for the MYCN proto-oncogene, is strongly associated with tumor recurrence. PML-I, but not PML-IV, isoform suppresses angiogenesis via upregulation of thrombospondin-2 (TSP2), a key inhibitor of angiogenesis. Finally, PML-I and TSP2 expression inversely correlates with tumor angiogenesis and recurrence in localized neuroblastomas.

CONCLUSIONS

Our work reveals a novel PML-I-TSP2 axis for the regulation of angiogenesis and cancer relapse, which could be used to identify patients with low-risk, localized tumors that might benefit from chemotherapy. Clin Cancer Res; 22(13); 3398-409. ©2016 AACR.

Inhibition of hypoxia inducible factors combined with all-trans retinoic acid treatment enhances glial transdifferentiation of neuroblastoma cells

Neuroblastoma (NBL) is a heterogeneous tumor characterized by a wide range of clinical manifestations. A high tumor cell differentiation grade correlates to a favorable stage and positive outcome. Expression of the hypoxia inducible factors HIF1-α (HIF1A gene) and HIF2-α (EPAS1 gene) and/or hypoxia-regulated pathways has been shown to promote the undifferentiated phenotype of NBL cells. Our hypothesis is that HIF1A and EPAS1 expression represent one of the mechanisms responsible for the lack of responsiveness of NBL to differentiation therapy. Clinically, high levels of HIF1A and EPAS1 expression were associated with inferior survival in two NBL microarray datasets, and patient subgroups with lower expression of HIF1A and EPAS1 showed significant enrichment of pathways related to neuronal differentiation. In NBL cell lines, the combination of all-trans retinoic acid (ATRA) with HIF1A or EPAS1 silencing led to an acquired glial-cell phenotype and enhanced expression of glial-cell differentiation markers. Furthermore, HIF1A or EPAS1 silencing might promote cell senescence independent of ATRA treatment. Taken together, our data suggest that HIF inhibition coupled with ATRA treatment promotes differentiation into a more benign phenotype and cell senescence in vitro. These findings open the way for additional lines of attack in the treatment of NBL minimal residue disease.

Stromal heparan sulfate differentiates neuroblasts to suppress neuroblastoma growth

Neuroblastoma prognosis is dependent on both the differentiation state and stromal content of the tumor. Neuroblastoma tumor stroma is thought to suppress neuroblast growth via release of soluble differentiating factors. Here, we identified critical growth-limiting components of the differentiating stroma secretome and designed a potential therapeutic strategy based on their central mechanism of action. We demonstrated that expression of heparan sulfate proteoglycans (HSPGs), including TβRIII, GPC1, GPC3, SDC3, and SDC4, is low in neuroblasts and high in the Schwannian stroma. Evaluation of neuroblastoma patient microarray data revealed an association between TGFBR3, GPC1, and SDC3 expression and improved prognosis. Treatment of neuroblastoma cell lines with soluble HSPGs promoted neuroblast differentiation via FGFR1 and ERK phosphorylation, leading to upregulation of the transcription factor inhibitor of DNA binding 1 (ID1). HSPGs also enhanced FGF2-dependent differentiation, and the anticoagulant heparin had a similar effect, leading to decreased neuroblast proliferation. Dissection of individual sulfation sites identified 2-O, 3-O-desulfated heparin (ODSH) as a differentiating agent, and treatment of orthotopic xenograft models with ODSH suppressed tumor growth and metastasis without anticoagulation. These studies support heparan sulfate signaling intermediates as prognostic and therapeutic neuroblastoma biomarkers and demonstrate that tumor stroma biology can inform the design of targeted molecular therapeutics.

Inflammation: what role in pediatric cancer?

There is growing evidence for the importance of chronic inflammation in the pathogenesis of adult cancers and for an ongoing role of the inflammatory response in tumor growth and metastasis. Here, we examine how these processes relate to pediatric malignancies. While it is unlikely that chronic inflammation plays a significant role in driving malignant progression in childhood tumors that typically have developmental origins, the inflammatory response does appear to play an important role in the development and progression of many types of childhood cancer. An enhanced understanding of these processes will be of critical importance in developing novel therapeutic strategies.

Cooperative Cross-Talk between Neuroblastoma Subtypes Confers Resistance to Anaplastic Lymphoma Kinase Inhibition

Neuroblastoma is a pediatric solid tumor that can be stratified into stroma-rich and stroma-poor histological subgroups. The stromal compartment of neuroblastoma is composed mostly of Schwann cells, and they play critical roles in the differentiation, survival, and angiogenic responses of tumor cells. In certain neuroblastoma cell lines, the coexistence of neuroblastic N-type and substrate-adherent S-type is frequently observed. One such cell line, SK-N-SH, harbors a F1174L oncogenic mutation in the anaplastic lymphoma kinase (ALK) gene. Treatment of SK-N-SH with an ALK chemical inhibitor, TAE684, resulted in the outgrowth of S-type cells that expressed the Schwann cell marker, S100α6. Nucleotide sequencing analysis of these TAE684-resistant (TR) sublines revealed the presence of the ALK F1174L mutation, suggesting their tumor origin, although ALK protein was not detected. Consistent with these findings, TR cells displayed approximately 9-fold higher IC(50) values than N-type cells. Also, unlike N-type cells, TR cells have readily detectable phosphorylated STAT3 but weaker phosphorylated AKT. Under coculture conditions, TR cells conferred survival to N-type cells against the apoptotic effect of TAE684. Cocultivation also greatly enhanced the overall phosphorylation of STAT3 and its transcriptional activity in N-type cells. Finally, conditioned medium from TR clones enhanced cell viability of N-type cells, and this effect was phosphatidylinositol 3-kinase dependent. Taken together, these results demonstrate the ability of tumor-derived S-type cells in protecting N-type cells against the apoptotic effect of an ALK kinase inhibitor through upregulating prosurvival signaling.

Brain lipid-binding protein: a marker of differentiation in neuroblastic tumors

PURPOSE

Neuroblastoma (NB), ganglioneuroblastoma (GNB), and ganglioneuroma (GN) are neuroblastic tumours (NT) of sympathetic nervous system origin. Brain lipid-binding protein (BLBP) has potential morphogenic activity during nervous system development but has not been studied in these tumours. We analyzed the expression of BLBP in NT according to histological subtypes and extent of differentiation.

METHODS

Thirty cases of NT (10 each of NB, intermixed GNB, and GN) were identified from the histopathology archive of a single center. Tissue sections were obtained from representative paraffin blocks and immunohistochemistry for BLBP performed.

RESULTS

Brain lipid-binding protein was not expressed in any NB case. In all cases of GN, BLBP was strongly expressed in the cytoplasm of mature ganglion cells but negative in Schwannian stroma. In the intermixed GNB, there was similar strong BLBP immunoreactivity in the cytoplasm of fully differentiated and differentiating ganglion cells but no BLBP expression in immature neuroblasts.

CONCLUSION

Brain lipid-binding protein is strongly expressed in mature and maturing ganglion cells in NT (GN and GNB), whereas it is absent in poorly differentiated neuroblasts of GNB and NB. Cytoplasmic expression of BLBP in NT increases as the cells undergo neural differentiation and is therefore associated with the extent of tumour differentiation and favorable histology.

Differentiation in neuroblastoma: diffusion-limited hypoxia induces neuro-endocrine secretory protein 55 and other markers of a chromaffin phenotype

Background

Neuroblastoma is a childhood malignancy of sympathetic embryonal origin. A high potential for differentiation is a hallmark of neuroblastoma cells. We have previously presented data to suggest that in situ differentiation in tumors frequently proceeds along the chromaffin lineage and that decreased oxygen (hypoxia) plays a role in this. Here we explore the utility of Neuro-Endocrine Secretory Protein 55 (NESP55), a novel member of the chromogranin family, as a marker for this process.

Methodology/Principal Findings

Immunohistochemical analyses and in situ hybridizations were performed on human fetal tissues, mouse xenografts of human neuroblastoma cell lines, and on specimens of human neuroblastoma/ganglioneuroma. Effects of anaerobic exposure on gene expression by cultured neuroblastoma cells was analyzed with quantitative real-time PCR. Fetal sympathetic nervous system expression of NESP55 was shown to be specific for chromaffin cell types. In experimental and clinical neuroblastoma NESP55 immunoreactivity was specific for regions of chronic hypoxia. NESP55 expression also correlated strikingly with morphological evidence of differentiation and with other chromaffin-specific patterns of gene expression, including IGF2 and HIF2α. Anaerobic culture of five neuroblastoma cell lines resulted in an 18.9-fold mean up-regulation of NESP55.

Conclusions/Significance

The data confirms that chronic tumor hypoxia is a key microenvironmental factor for neuroblastoma cell differentiation, causing induction of chromaffin features and NESP55 provides a reliable marker for this neuronal to neuroendocrine transition. The hypoxia-induced phenotype is the predominant form of differentiation in stroma-poor tumors, while in stroma-rich tumors the chromaffin phenotype coexists with ganglion cell-like differentiation. The findings provide new insights into the biological diversity which is a striking feature of this group of tumors.

Metronomic administration of the drug GMX1777, a cellular NAD synthesis inhibitor, results in neuroblastoma regression and vessel maturation without inducing drug resistance

High-risk neuroblastoma is a rapidly growing tumor with a survival rate below 50%. A new treatment strategy is to administer chemotherapeutic drugs metronomically, i.e., at lower doses and frequent intervals. The aim of the study was to investigate the effects of GMX1777, a chemotherapeutic drug affecting cellular energy metabolism, in a mouse model for high-risk neuroblastoma. Female SCID mice were injected s.c. with MYCN-amplified human neuroblastoma cells and randomized to either treatment with GMX1777 or vehicle. In some animals, treatment was discontinued allowing tumor relapse. Treatment response was evaluated using the pediatric preclinical testing program (PPTP). Immunohistochemistry and qRT-PCR was performed on tumor cryosections to investigate the microscopic and molecular changes in tumors in response to GMX1777. Despite an increase in vessel density, tumor regression and a high group response score according to PPTP criteria was induced by GMX1777 without inducing drug resistance. Treatment resulted in inhibition of tumor cell proliferation, vessel maturation, reduced hypoxia, increased infiltration of MHC class II negative macrophages and expansion of the nonvascular stromal compartment. Decreased stromal VEGF-A and PDGF-B mRNA in response to treatment together with the structural data suggest a "deactivation" or "silencing" of the tumor stroma as a paracrine entity. In conclusion, GMX1777 was highly efficient against high-risk neuroblastoma xenografts through modulation of both the tumor cell and stromal compartment.

Enteric neural crest differentiation in ganglioneuromas implicates Hedgehog signaling in peripheral neuroblastic tumor pathogenesis

Peripheral neuroblastic tumors (PNTs) share a common origin in the sympathetic nervous system, but manifest variable differentiation and growth potential. Malignant neuroblastoma (NB) and benign ganglioneuroma (GN) stand at opposite ends of the clinical spectrum. We hypothesize that a common PNT progenitor is driven to variable differentiation by specific developmental signaling pathways. To elucidate developmental pathways that direct PNTs along the differentiation spectrum, we compared the expression of genes related to neural crest development in GN and NB. In GNs, we found relatively low expression of sympathetic markers including adrenergic biosynthesis enzymes, indicating divergence from sympathetic fate. In contrast, GNs expressed relatively high levels of enteric neuropeptides and key constituents of the Hedgehog (HH) signaling pathway, including Dhh, Gli1 and Gli3. Predicted HH targets were also differentially expressed in GN, consistent with transcriptional response to HH signaling. These findings indicate that HH signaling is specifically active in GN. Together with the known role of HH activity in enteric neural development, these findings further suggested a role for HH activity in directing PNTs away from the sympathetic lineage toward a benign GN phenotype resembling enteric ganglia. We tested the potential for HH signaling to advance differentiation in PNTs by transducing NB cell lines with Gli1 and determining phenotypic and transcriptional response. Gli1 inhibited proliferation of NB cells, and induced a pattern of gene expression that resembled the differential pattern of gene expression of GN, compared to NB (p<0.00001). Moreover, the transcriptional response of SY5Y cells to Gli1 transduction closely resembled the transcriptional response to the differentiation agent retinoic acid (p<0.00001). Notably, Gli1 did not induce N-MYC expression in neuroblastoma cells, but strongly induced RET, a known mediator of RA effect. The decrease in NB cell proliferation induced by Gli1, and the similarity in the patterns of gene expression induced by Gli1 and by RA, corroborated by closely matched gene sets in GN tumors, all support a model in which HH signaling suppresses PNT growth by promoting differentiation along alternative neural crest pathways.

All-trans retinoic acid arrests neuroblastoma cells in a dormant state. Subsequent nerve growth factor/brain-derived neurotrophic factor treatment adds modest benefit

BACKGROUND

Therapies aiming at inducing differentiation or apoptosis of neuroblastoma (NB) are an important research topic. Although retinoic acid showed promising antitumoral results, its effects against refractory disease are limited. Putative candidates for combination therapies are nerve growth factor (NGF; Tebu-Bio/Peprotech, Offenbach, Germany) and brain-derived neurotrophic factor (BDNF; Tebu-Bio/Peprotech, Offenbach, Germany) because their receptors are of prognostic clinical value in clinical neuroblastoma. Another clinical prognostic factor is the number of Schwann cells. Substances secreted by Schwann cells proved antitumoral capacities in vitro. The aim of the study was to analyze whether retinoic acid may offer an additional line of attack acting independent from Schwann cells and whether additive treatment with the neurotrophin-receptor ligands NGF/BDNF confers additional benefit.

METHODS

Human SHSY-5Y NB cells were cultured in vitro. After a 7-day all-trans retinoic acid (ATRA; Sigma-Aldrich Chemie, Taufkirchen, Germany) treatment (15 mumol/L of ATRA), NB proliferation was proportional to extinction in dimethyl-thiazol-diphenyltetrazoliumbromide (MTT) tests. Fluorescence-activated cell sorter (FACS) analysis for annexin and propidium iodide determined the degree of apoptosis and necrosis as well as the expression of the Schwann type cell marker S100. The S100 messenger RNA was assessed by reverse transcriptase polymerase chain reaction. In addition, the effect on NB proliferation was investigated when ATRA was combined with a 7-day treatment with NGF or BDNF (10, 50, 100 ng/mL) either before or after the 7-day ATRA treatment.

RESULTS

All-trans retinoic acid reduced proliferation (0.116 +/- 0.006 SEM vs 0.359 +/- 0.010 SEM in the untreated control group; P < .001). After ATRA treatment, 95% +/- 1.82% SEM were still viable, with only 2.61% +/- 1.17% SEM apoptotic and 2.38% +/- 0.69% SEM necrotic cells. All-trans retinoic acid induced a remarkable decrease in S100 expression in FACS (16.91% +/- 1.72% SEM vs 32.33% +/- 2.54% SEM in controls; P = .009). The S100 messenger RNA levels were not increased by ATRA (DeltaDeltaT values: 1.73, 2.77, and 1.43; n = 3). Both NGF and BDNF had only a modest synergistic effect when given after ATRA treatment. No effect was seen when they were administered before ATRA treatment.

CONCLUSIONS

All-trans retinoic proved to be a vigorous inhibitor of NB proliferation in vitro. However, because most NB cells remained viable combination therapies are required. Treatment with NGF and BDNF showed only a modest benefit and did not reflect the strong prognostic impact of tyrosine kinase receptors in clinical NB. The ATRA-induced proliferation arrest is not related to Schwann type subdifferentiation. This suggests that substances secreted by Schwann cells could be possible independent combination partners. We suggest studies using combinations of ATRA and substances secreted by Schwann cells.

CEACAM1/VEGF cross‐talk during neuroblastic tumour differentiation

The role of angiogenesis in tumour progression is a major subject in modern oncology and a correlation between angiogenesis and poor outcome has been demonstrated for human neuroblastomas. However, the role of angiogenesis in the maturation phase of neuroblastic tumours has never been considered. Human carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), a potent pro-angiogenic factor and mediator of vascular endothelial growth factor (VEGF)-induced angiogenesis, plays a crucial role during the activation phase of angiogenesis and it has been shown to be expressed in the microvessels of the developing central nervous system as well as in newly formed immature blood vessels in many different tumours and under physiological conditions. The present study has investigated the role of CEACAM1/VEGF-mediated angiogenesis across the whole spectrum of neuroblastic tumours, from undifferentiated to fully differentiated mature ganglioneuromas. CEACAM1 is peculiarly expressed in the microvessels of areas of active tumour maturation among differentiating neuroblastic/ganglion cells, whereas it is completely absent in the vessels of poorly differentiated/undifferentiated as well as in entirely mature Schwannian-rich areas. Interestingly, VEGF expression has been found in differentiating neuroblastic/ganglion cells adjacent to CEACAM1-positive microvessels. In keeping with these observations, VEGF expression was found in human neuroblastoma SH-SY5Y cells during differentiation after retinoic acid treatment. Moreover, conditioned medium from SH-SY5Y cells collected at different stages of differentiation induced progressive in vitro up-regulation of CEACAM1 expression in human umbilical vein endothelial cells (HUVECs) that was abrogated by the specific VEGF receptor-2/KDR inhibitor SU5416. Taken together, these data point to a role for CEACAM1/VEGF cross-talk during the maturation phase of neuroblastic tumours. This may mimic physiological events leading to maturation of the vasculature in the developing normal central nervous system. On the other hand, in poorly differentiated/undifferentiated lesions, VEGF-sustained angiogenesis does not reproduce physiological steps, but rather is associated with tumour aggressiveness and may involve other molecular pathways.