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Patient-derived xenografts (PDX) and the Avatar, a single PDX mirroring an individual patient, are emerging tools in preclinical cancer research. However, the consequences of intratumor heterogeneity for PDX modeling of biomarkers, target identification, and treatment decisions remain under-explored. In this study, we undertook serial passaging and comprehensive molecular analysis of neuroblastoma orthotopic PDXs, which revealed strong intrinsic genetic, transcriptional, and phenotypic stability for more than 2 years. The PDXs showed preserved neuroblastoma-associated gene signatures that correlated with poor clinical outcome in a large cohort of patients with neuroblastoma. Furthermore, we captured spatial intratumor heterogeneity using ten PDXs from a single high-risk patient tumor. We observed diverse growth rates, transcriptional, proteomic, and phosphoproteomic profiles. PDX-derived transcriptional profiles were associated with diverse clinical characteristics in patients with high-risk neuroblastoma. These data suggest that high-risk neuroblastoma contains elements of both temporal stability and spatial intratumor heterogeneity, the latter of which complicates clinical translation of personalized PDX-Avatar studies into preclinical cancer research. Significance: These findings underpin the complexity of PDX modeling as a means to advance translational applications against neuroblastoma. (C) 2018 AACR.

Purpose: Hypoxia is considered to be a major driving force behind tumor angiogenesis. The stabilization and activation at hypoxia of the hypoxia-inducible factors HIF-1α and HIF-2α and the concomitant induction of expression of vascular endothelial growth factor (VEGF) and other proangiogenic factors provide a molecular frame for hypoxia-driven tumor angiogenesis. This study has investigated how HIF and VEGF protein levels relate to each other with regard to vascularization, tumor stage, and overall survival in neuroblastoma. Experimental Design: Tissue cores taken from tumor specimens representing 93 children with neuroblastoma were arranged on a microarray and stained for HIF-1α, HIF-2α, VEGF, and CD31 proteins. Both fraction of positive cells and staining intensity were evaluated and protein levels were correlated with each other and with clinical variables. Results: Although high levels of both HIF-1α (P < 0.001) and HIF-2α (P < 0.001) correlated positively to VEGF expression, they did not fully correlate with each other. Moreover, HIF-1α (P = 0.002) and VEGF (P < 0.001), but not HIF-2α, correlated negatively to vascularization as determined by CD31 staining abundance. VEGF expression or degree of vascularization did not correlate with tumor stage or overall survival. High HIF-1α levels correlated with low tumor stage (P < 0.001) and were associated with a favorable patient prognosis (P = 0.08). Conclusions: The discordant results on expression of HIF-1α and HIF-2α suggest that these two proteins are differentially regulated in vivo, thus reflecting distinctive protein expression/stabilization mechanisms. The association between HIF-1α and favorable outcome stresses the importance of discriminating HIF-2α from HIF-1α expression and has implications for using HIFs as treatment targets. (Clin Cancer Res 2009;15(23):7130–6)

Treatment of high-risk childhood neuroblastoma is a clinical challenge which has been hampered by a lack of reliable neuroblastoma mouse models for preclinical drug testing. We have previously established invasive and metastasising patient-derived orthotopic xenografts (PDXs) from high-risk neuroblastomas that retained the genotypes and phenotypes of patient tumours. Given the important role of the tumour microenvironment in tumour progression, metastasis, and treatment responses, here we analysed the tumour microenvironment of five neuroblastoma PDXs in detail. The PDXs resembled their parent tumours and retained important stromal hallmarks of aggressive lesions including rich blood and lymphatic vascularisation, pericyte coverage, high numbers of cancer-associated fibroblasts, tumour-associated macrophages, and extracellular matrix components. Patient-derived tumour endothelial cells occasionally formed blood vessels in PDXs; however, tumour stroma was, overall, of murine origin. Lymphoid cells and lymphatic endothelial cells were found in athymic nude mice but not in NSG mice; thus, the choice of mouse strain dictates tumour microenvironmental components. The murine tumour microenvironment of orthotopic neuroblastoma PDXs reflects important hallmarks of aggressive and metastatic clinical neuroblastomas. Neuroblastoma PDXs are clinically relevant models for preclinical drug testing.

Background: Cancer cell lines have traditionally been established in serum-containing medium though it has been questioned whether serum-grown cell lines faithfully represent the tumors they are derived from. Potential serum-induced differentiation of in vitro cultured cells could partly explain why xenografted cell lines often lack invasive growth and robust metastasis. Direct implantation of patient tumor material into mice, i.e. patient derived xenografts (PDXs), has shown to more closely mimic the original tumor growth pattern. By isolating cells from neuroblastoma PDXs and culturing the PDX cells under serum-free conditions, we expect to preserve a less differentiated phenotype, enabling us to use PDX cells as a source for identifying potential neuroblastoma stem-like cells. Moreover, to facilitate future drug screening, we investigated conditions that would allow us to grow neuroblastoma PDX cells adherently, without compromising their tumorigenic or metastatic capacity. Materials & Methods: PDX cells were cultured in stem cell medium or serum-containing medium for up to 7 days. IHC, RT-qPCR and WB were used to investigate the expression of sympathetic neuronal differentiation markers. For monolayer culture, cells were grown on laminin. Results: PDX cells can routinely be established as neurospheres in serum-free medium with retained tumorigenic and metastatic capacity. Addition of serum induces loss of sphere formation, adherent growth and a robust increase in sympathetic differentiation markers, both at mRNA and protein level. Serum-cultured cells also show a decreased cell proliferation (without increased apoptotic rate, as determined by sub-G0/G1 analyses). The serum-induced differentiation was not irreversible since transferring serum-grown cells back to serum-free medium resulted in a phenotypic switch, with recovered proliferation and decreased expression of differentiation markers. Growing cells on laminin achieved adherent culture of PDX cells. This resulted only in slight morphological differentiation but did not affect growth rate or the cells tumorigenic and metastatic capacity. Conclusion: Culturing neuroblastoma PDX cells in serum-containing medium results in a more differentiated phenotype. Thus, avoiding serum appears to be a key strategy in order to preserve the phenotypic origin of these cells. The phenotypic effects of serum on tumor cells have largely been overlooked and might be a general effect on tumor cells explaining why serum-established cell lines do not metastasize and grow invasively. Citation Format: Camilla U. Persson, Kristoffer von Stedingk, Daniel Bexell, My Merselius, David Gisselsson, Siv Beckman, Sofie Mohlin, Sven Påhlman, Caroline Wigerup. Serum induces differentiation in aggressive MYCN-amplified neuroblastoma patient-derived xenograft cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5834. doi:10.1158/1538-7445.AM2017-5834

Neuroblastoma is a childhood tumour with heterogeneous characteristics and children with metastatic disease often have a poor outcome. Here we describe the establishment of neuroblastoma patient-derived xenografts (PDXs) by orthotopic implantation of viably cryopreserved or fresh tumour explants of patients with high risk neuroblastoma into immunodeficient mice. In vivo tumour growth was monitored by magnetic resonance imaging and fluorodeoxyglucose–positron emission tomography. Neuroblastoma PDXs retained the undifferentiated histology and proliferative capacity of their corresponding patient tumours. The PDXs expressed neuroblastoma markers neural cell adhesion molecule, chromogranin A, synaptophysin and tyrosine hydroxylase. Whole genome genotyping array analyses demonstrated that PDXs retained patient-specific chromosomal aberrations such as MYCN amplification, deletion of 1p and gain of chromosome 17q. Thus, neuroblastoma PDXs recapitulate the hallmarks of high-risk neuroblastoma in patients. PDX-derived cells were cultured in serum-free medium where they formed free-floating neurospheres, expressed neuroblastoma gene markers MYCN, CHGA, TH, SYP and NPY, and retained tumour-initiating and metastatic capacity in vivo. PDXs showed much higher degree of infiltrative growth and distant metastasis as compared to neuroblastoma SK-N-BE(2)c cell line-derived orthotopic tumours. Importantly, the PDXs presented with bone marrow involvement, a clinical feature of aggressive neuroblastoma. Thus, neuroblastoma PDXs serve as clinically relevant models for studying and targeting high-risk metastatic neuroblastoma. What's new? Neuroblastoma is a childhood tumour with heterogeneous characteristics and children with metastatic disease have a poor outcome. Here, the authors established neuroblastoma patient-derived xenografts (PDXs) by orthotopic implantation of viably cryopreserved or fresh tumour explants of patients with high-risk neuroblastoma into immunodeficient mice. The PDXs retained the genotype and phenotype of patient tumours and exhibited substantial infiltrative growth and metastasis to distant organs including bone marrow. PDX-derived neuroblastoma cells were expanded in vitro and retained tumourigenic and metastatic capacity in vivo. The PDXs may thus represent an important tool for investigating neuroblastoma growth and metastasis as well as drug targeting.

Widespread metastasis is a major problem for the treatment of high-risk neuroblastoma. Relevant neuroblastoma animal models are hence needed to study and target high-risk metastatic neuroblastoma. We developed neuroblastoma patient-derived orthotopic xenografts (PDXs) using viably cryopreserved or fresh patient neuroblastoma fragments which were implanted orthotopically into immunodeficient NSG mice. Immunohistochemistry showed that PDXs retain neuroblastoma markers and a highly infiltrative growth pattern. Importantly, we found distant metastasis to lungs, liver and bone marrow. Single nucleotide polymorphism array analysis confirmed that PDXs maintain patient-specific chromosomal aberrations 1p del, MYCN amp and 17q gain. In vitro cultures established from the PDXs express neuroblastoma markers and retain their tumorigenic and metastatic ability in vivo after orthotopic injection. PDXs were highly vascularized with mouse endothelial cells and one PDX model formed tumor vasculature through co-engrafted human tumor endothelial cells. Tumors also contained pericytes, cancer-associated fibroblasts, macrophages and extracellular components resembling the patient disease. PDXs established in athymic nude mice additionally developed intratumoral lymphatic vessels and contained mouse-derived CD45+ lymphoid cells. Thus, PDXs maintain important tumor microenvironment hallmarks for high stage neuroblastoma. Furthermore, we demonstrate the feasibility of using short-term in vitro cultured PDX-derived cells as a drug-testing model, and show that the HIF2A oncogene is transcriptionally regulated at hypoxia via the PI3K/mTORC2 pathway in these cells. The results establish the PI3K and mTORC2 pathways as potential therapeutic targets of aggressive neuroblastoma. In conclusion, neuroblastoma orthotopic PDXs resemble many clinical aspects of the patient disease, e.g., distant metastases, and PDXs are valuable models for preclinical drug testing. Citation Format: Noémie Braekeveldt, Caroline Wigerup, David Gisselsson, Sofie Mohlin, My Merselius, Siv Beckman, Irene Tadeo, Anna P. Berbegall, Ingrid Öra, Samuel Navarro, Rosa Noguera, Sven Påhlman, Daniel Bexell. Neuroblastoma patient-derived orthotopic xenografts: Clinically relevant models for drug testing. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Pediatric Cancer Research: From Mechanisms and Models to Treatment and Survivorship; 2015 Nov 9-12; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(5 Suppl):Abstract nr A02.

INTRODUCTION: Solid tumors are less oxygenated than their tissue of origin. Low intra-tumor oxygen levels are associated with worse outcome, increased metastatic potential and immature phenotype in breast cancer. We have reported that tumor hypoxia correlates to low differentiation status in breast cancer. Less is known about effects of hypoxia on non-malignant cells. Here we address whether hypoxia influences the differentiation stage of non-malignant breast epithelial cells and potentially have bearing on early stages of tumorigenesis. METHODS: Normal human primary breast epithelial cells and immortalized non-malignant mammary epithelial MCF-10A cells were grown in a three-dimensional overlay culture on laminin-rich extracellular matrix for up to 21 days at normoxic or hypoxic conditions. Acinar morphogenesis and expression of markers of epithelial differentiation and cell polarization were analyzed by immunofluorescence, immunohistochemistry, qPCR and immunoblot. RESULTS: In large ductal carcinoma in situ patient-specimens, we find that epithelial cells with high HIF-1α levels and multiple cell layers away from the vasculature are immature compared to well-oxygenated cells. We show that hypoxic conditions impaired acinar morphogenesis of primary and immortalized breast epithelial cells grown ex vivo on laminin-rich matrix. Normoxic cultures formed polarized acini-like spheres with the anticipated distribution of marker proteins associated with mammary epithelial polarization e.g. α6-integrin, laminin 5 and Human Milk Fat Globule/MUC1. At hypoxia, cells were not polarized and the sub-cellular distribution pattern of the marker proteins rather resembled that reported in vivo in breast cancer. The hypoxic cells remained in a mitotic state, whereas proliferation ceased with acinar morphogenesis at normoxia. We found induced expression of the differentiation repressor ID1 in the undifferentiated hypoxic MCF-10A cell structures. Acinar morphogenesis was associated with global histone deacetylation whereas the hypoxic breast epithelial cells showed sustained global histone acetylation, which is generally associated with active transcription and an undifferentiated proliferative state.

Neuroblastoma is a childhood tumor located in the sympathetic nervous system and most often found in the adrenal gland. Half of the patients have metastases already at diagnosis. There is a need for improved preclinical in vivo models of human high-stage neuroblastoma. Aims: 1) To establish relevant xenograft in vivo models for studying neuroblastoma orthotopic growth and metastatic growth in bone marrow, 2) to detect tumor growth by the two imaging modalities utilized in the clinic, i.e. magnetic resonance imaging (MRI) and I-123-metaiodobenzylguanidine (MIBG)-Single photon emission computed tomography (SPECT), and 3) to characterize orthotopic and bone marrow tumor growth at a pathohistological level. Methods: SK-N-Be2c and KCN-69 neuroblastoma cells were injected into adrenal gland of immunodeficient NSG mice to establish orthotopic tumors. SK-N-Be2c cells were injected directly into femur bone marrow of NSG mice to model bone marrow metastatic growth in a reproducible way. Tumor growth was monitored by MRI or by MIBG-SPECT. Histopathological assessment was performed on formalin-fixed paraffin-embedded tissue sections. Conclusion: We have established a model for orthotopic neuroblastoma growth and characterized the model by MRI and MIBG-SPECT. Orthotopic tumors grow infiltratively into surrounding tissues and resemble the histopathological hallmarks of patient neuroblastoma. We also describe a reproducible in vivo model for neuroblastoma bone marrow metastatic growth. The in vivo models will be important tools for studying mechanisms of neuroblastoma growth and for preclinical drug testing. Citation Format: Daniel Bexell, Noémie Braekeveldt, Siv Beckman, Sofie Mohlin, David Gisselsson, Sven Påhlman. Modeling human metastatic neuroblastoma in immunodeficient mice. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr B57.

Small cell lung carcinoma (SCLC) is an extremely aggressive tumor that is widely metastasized in early stages of the disease and the 5-year survival rate for these patients is only approximately 9-15%. Here we study the adaptive response of SCLC cells to lower oxygen levels, since tumor hypoxia (∼1% oxygen) is related to aggressive tumor behaviour and poor outcome in several tumor forms. Areas of hypoxia are a common characteristic in solid tumors and in response to hypoxia tumor cells induce expression of several genes involved in a variety of processes. This adaptive response is primarily regulated by the transcription factors hypoxia inducible factor (HIF)-1α and HIF-2α, which become stable at low oxygen levels. Studies using among others lung adenocarcinoma, neuroblastoma and breast carcinoma cells have demonstrated that HIF-1α primarily mediates the acute hypoxic response, whereas HIF-2α dominates during the more chronic phase of hypoxia. We investigated the viability of SCLC cells cultured at hypoxia and characterized the expression levels of HIF transcription factors in SCLC cells and specimens using quantitative real-time PCR, western blot and immunohistochemistry. Expression levels of well known hypoxia-driven genes were studied and to further characterize the hypoxic adaptive response, a gene expression profile of hypoxic SCLC cells was performed using microarray analyses. In all experiments a panel of non-SCLC cells and neuroblastoma cells were included for comparison. Our results show that SCLC cells have a high adaptive capacity to hypoxia, even though a modest induction of well known hypoxia-driven genes is observed. Interestingly, the HIF-1α and HIF-2α are differentially regulated in SCLC cells as compared to non-SCLC. In SCLC cells, no HIF-2α protein is detectable whereas HIF-1α protein levels are sustained and increased up to 96 hours. In addition, knock-down of HIF-1α at 0.1% oxygen are not affecting the viability of the SCLC cells and our gene expression profile of hypoxic SCLC cells has identified genes important for SCLC cells survival at hypoxia. Our data suggest that SCLC cells have an adaptive response to hypoxia that is partially HIF-independent. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2058. doi:10.1158/1538-7445.AM2011-2058

We study the effect of hypoxia on mammary epithelial cell differentiation at a non-malignant stage as a putative step in early malignant progression. Due to inadequate vasculature solid tumors often contain regions with low oxygen levels (hypoxia). Hypoxia is associated with increased metastatic potential and worse patient outcome. The hypoxic response is in large driven by the two transcription factors hypoxia inducible factor (HIF) 1 and HIF 2. We have reported that hypoxia leads to a less differentiated phenotype in breast cancer and in neuroblastoma, and in the clinic low tumor cell differentiation is related to poor prognosis in these diseases. To investigate the effect of hypoxia on mammary epithelial cell differentiation we employed the model of acinar morphogenesis. In this model immortalized mammary epithelial cells in three-dimensional (3D) culture on a laminin-rich matrix differentiate and form acini-like structures with evacuated lumen surrounded by polarized cells. We have previously seen that hypoxia (1% oxygen) impairs the process of acinar morphogenesis. The hypoxic cells failed to obtain polarity and markers of differentiation were affected at expression level as well as cellular localization. Addressing the mechanism behind the hypoxia-impaired differentiation, we find that hypoxia impairs the global histone deacetylation that is associated with changes in cell morphology and differentiation of the mammary epithelial cells. Three days post-seeding, during the proliferation stage, both normoxic and hypoxic cells stained positive for acetylated histone 4 (AcH4). When the normoxic cells go through morphological changes and acinar formation the acetylation of histone 4 is reduced whereas it is maintained in the hypoxic cell-clusters 10 days after seeding. Transfer of acini from normoxia to hypoxia at this time-point leads to an increase in AcH4. Thus, the hypoxic condition prevents global deacetylation, which is generally associated with high level of transcription and an undifferentiated proliferative cell state, rendering the cells an open chromatin state and hindering acinar formation. These data indicate that hypoxia promotes loss of differentiation also at a non-malignant stage. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 463.