Phosphoproteomics of primary AML patient samples reveals rationale for AKT combination therapy and p53 context to overcome selinexor resistance

Acute myeloid leukemia (AML) is a heterogeneous disease with variable patient responses to therapy. Selinexor, an inhibitor of nuclear export, has shown promising clinical activity for AML. To identify the molecular context for monotherapy sensitivity as well as rational drug combinations, we profile selinexor signaling responses using phosphoproteomics in primary AML patient samples and cell lines. Functional phosphosite scoring reveals that p53 function is required for selinexor sensitivity consistent with enhanced efficacy of selinexor in combination with the MDM2 inhibitor nutlin-3a. Moreover, combining selinexor with the AKT inhibitor MK-2206 overcomes dysregulated AKT-FOXO3 signaling in resistant cells, resulting in synergistic anti-proliferative effects. Using high-throughput spatial proteomics to profile subcellular compartments, we measure global proteome and phospho-proteome dynamics, providing direct evidence of nuclear translocation of FOXO3 upon combination treatment. Our data demonstrate the potential of phosphoproteomics and functional phosphorylation site scoring to successfully pinpoint key targetable signaling hubs for rational drug combinations.

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Phosphoproteomics with functional scoring uncovers context for selinexor sensitivity

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Functional p53 correlates with selinexor sensitivity, which is enhanced by nutlin-3a

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Dysregulated AKT-FOXO3 drives selinexor resistance, which is overcome with MK-2206

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Spatial proteomics reveals selinexor-induced nucleocytoplasmic protein shuttling

ARNT-dependent HIF-2 transcriptional activity is not sufficient to regulate downstream target genes in neuroblastoma

BACKGROUND

Hypoxia-inducible factor (HIF)-2α associates with poor outcome in neuroblastoma and glioblastoma, and gain-of-function mutations in the EPAS1 gene (encoding HIF-2α) have been reported in paragangliomas and pheochromocytomas. Specific targeting of a druggable hydrophobic pocket in the HIF-2α PAS-B domain with PT2385 have demonstrated promising clinical results for clear cell renal cell carcinoma (ccRCC). Here, we investigated the effect of PT2385-mediated inhibition of ARNT dependent HIF-2 activity.

METHODS

Neuroblastoma patient-derived xenograft (PDX) cells were treated with PT2385 and analyzed for HIF-2-dependent gene expression, HIF activity, HIF-2α protein localization, response to chemotherapy and orthotopic tumor growth in vivo. Two-sided student t-test was used.

RESULTS

We detected high levels of HIF-2α protein in perivascular niches in neuroblastoma PDXs in vivo and at oxygenated conditions in PDX-derived cell cultures in vitro, particularly in the cytoplasmic fraction. Nuclear HIF-2α expression was reduced following PT2385 treatment, but surprisingly, virtually no effects on tumor growth in vivo or expression of canonical HIF downstream target genes in vitro were observed. In coherence, RNA sequencing of PT2385-treated PDX cells revealed a virtually unaffected transcriptome. Treatment with PT2385 did not affect cellular response to chemotherapy. In contrast, HIF-2α protein knockdown resulted in profound downregulation of target genes.

CONCLUSIONS

The lack of effect from PT2385 treatment in combination with high cytoplasmic HIF-2α expression at normoxia suggest that HIF-2α have additional roles than acting as an ARNT dependent transcription factor. It is important to further unravel the conditions at which HIF-2α has transcriptional and non-transcriptional roles in neuroblastoma.

HIF2α contributes to antiestrogen resistance via positive bilateral crosstalk with EGFR in breast cancer cells

The majority of breast cancers express estrogen receptor α (ERα), and most patients with ERα-positive breast cancer benefit from antiestrogen therapy. The ERα-modulator tamoxifen and ERα-downregulator fulvestrant are commonly employed antiestrogens. Antiestrogen resistance remains a clinical challenge, with few effective treatments available for patients with antiestrogen-resistant breast cancer. Hypoxia, which is intrinsic to most tumors, promotes aggressive disease, with the hypoxia-inducible transcription factors HIF1 and HIF2 regulating cellular responses to hypoxia. Here, we show that the ERα-expressing breast cancer cells MCF-7, CAMA-1, and T47D are less sensitive to antiestrogens when hypoxic. Furthermore, protein and mRNA levels of HIF2α/HIF2A were increased in a panel of antiestrogen-resistant cells, and antiestrogen-exposure further increased HIF2α expression. Ectopic expression of HIF2α in MCF-7 cells significantly decreased sensitivity to antiestrogens, further implicating HIF2α in antiestrogen resistance. EGFR is known to contribute to antiestrogen resistance: we further show that HIF2α drives hypoxic induction of EGFR and that EGFR induces HIF2α expression. Downregulation or inhibition of EGFR led to decreased HIF2α levels. This positive and bilateral HIF2-EGFR regulatory crosstalk promotes antiestrogen resistance and, where intrinsic hypoxic resistance exists, therapy itself may exacerbate the problem. Finally, inhibition of HIFs by FM19G11 restores antiestrogen sensitivity in resistant cells. Targeting HIF2 may be useful for counteracting antiestrogen resistance in the clinic.

Neuroblastoma patient-derived xenograft cells cultured in stem-cell promoting medium retain tumorigenic and metastatic capacities but differentiate in serum

Cultured cancer cells serve as important models for preclinical testing of anti-cancer compounds. However, the optimal conditions for retaining original tumor features during in vitro culturing of cancer cells have not been investigated in detail. Here we show that serum-free conditions are critical for maintaining an immature phenotype of neuroblastoma cells isolated from orthotopic patient-derived xenografts (PDXs). PDX cells could be grown either as spheres or adherent on laminin in serum-free conditions with retained patient-specific genomic aberrations as well as tumorigenic and metastatic capabilities. However, addition of serum led to morphological changes, neuronal differentiation and reduced cell proliferation. The epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) were central for PDX cell proliferation and MYCN expression, and also hindered the serum-induced differentiation. Although serum induced a robust expression of neurotrophin receptors, stimulation with their cognate ligands did not induce further sympathetic differentiation, which likely reflects a block in PDX cell differentiation capacity coupled to their tumor genotype. Finally, PDX cells cultured as spheres or adherent on laminin responded similarly to various cytotoxic drugs, suggesting that both conditions are suitable in vitro screening models for neuroblastoma-targeting compounds.

Abstract 3880: Assessment of ALDH activity in neuroblastoma patient-derived xenograft cells as a potential marker of neuroblastoma stem cells

Neuroblastoma is a tumor derived from immature neuroblasts predestined to form the sympathetic nervous system. Children with aggressive neuroblastoma are at high-risk of disease relapse despite their initial response to treatment. The molecular mechanisms underlying these relapses are poorly understood, although clonal expansion and de novo mutations have been suggested as potential mechanisms. An alternative hypothesis is that neuroblastoma initiating capacity and resistance to chemotherapy reside in a subpopulation of tumor initiating cells or cancer stem cells, which are not genetically different from most tumor bulk cells but through unknown mechanisms differ phenotypically and functionally. Here we examine aldehyde dehydrogenase (ALDH) expression and activity in neuroblastoma patient-derived xenograft (PDX) cells, cultured under stem cell-promoting conditions, as a potential marker for neuroblastoma stem cells. We found that neuroblastoma PDX cells in general expressed higher levels of various ALDH isoforms as compared to an aggressive classical serum-grown neuroblastoma cell line. Also, a distinct subgroup with high ALDH activity was observed in PDX cells but not in the serum-grown cell line. Growing the PDX cells in serum induced neuronal differentiation accompanied with lower expression of ALDH1 isoforms and reduced ALDH activity. The change in ALDH expression and activity was reversible, implying phenotypic plasticity. Re-analyzing cells initially sorted on ALDH activity also confirmed an inter-conversion of cells with low and high ALDH activity. Furthermore, in vitro clonogenic capacity was significantly higher in cells with high ALDH activity. Serial in vivo passaging of PDXs allowed us to compare PDX cells isolated from different in vivo generations. Interestingly, cells derived from later in vivo generations contained a higher frequency of cells with high ALDH activity. Finally, orthotopic injection of cells with either low or high ALDH activity showed that both subgroups led to tumor formation, however a higher tumor take was observed when injecting cells with high ALDH activity. In conclusion, our results suggest that ALDH activity is associated with an immature phenotype, which is of clinical importance since less differentiated tumors are more aggressive and associated with poor prognosis. Also, cells with high ALDH activity showed higher in vivo tumor initiating capacity. We are currently pursuing a more extensive characterization of neuroblastoma cells with high ALDH activity.

Citation Format: Camilla Persson, Kristoffer von Stedingk, Daniel Bexell, My Merselius, Noémie Braekeveldt, Sven Påhlman, Caroline Wigerup. Assessment of ALDH activity in neuroblastoma patient-derived xenograft cells as a potential marker of neuroblastoma stem 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 3880. doi:10.1158/1538-7445.AM2017-3880

Abstract 5834: Serum induces differentiation in aggressive MYCN-amplified neuroblastoma patient-derived xenograft cells

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

Hypoxia, pseudohypoxia and cellular differentiation

Tumor hypoxia correlates to aggressive disease, and while this is explained by a variety of factors, one clue to understand this phenomena was the finding that hypoxia induces a de-differentiated, stem cell-like phenotype in neuroblastoma and breast tumor cells. The hypoxia inducible transcription factors (HIFs) are regulated at the translational level by fluctuating oxygen concentrations, but emerging data reveal that both HIF-1α and HIF-2α expression can be induced by aberrantly activated growth factor signaling independently of oxygen levels. Furthermore, HIF-2α is regulated by hypoxia also at the transcriptional level in neuroblastoma and glioma cells. In cultured tumor cells, HIF-2α is stabilized at physiological oxygen concentrations followed by induced expression of classical hypoxia-driven genes, resulting in a pseudohypoxic phenotype. In addition, in neuroblastoma and glioma specimens, a small subset of HIF-2α positive, HIF-1α negative, tumor cells is found adjacent to blood vessels, i.e. in areas with presumably adequate oxygenation. These tumor niches are thus pseudohypoxic, and the HIF-2α expressing cells present immature features. We have postulated that this niche in neuroblastomas encompass the tumor stem cells. Oncogenes or tumor suppressor genes associated with pseudohypoxia are frequently mutated or deleted in the germline, implicating that the pseudohypoxic phenotype indeed is tumorigenic. In summary, the hypoxic and pseudohypoxic phenotypes of solid tumors are attractive therapeutic targets.

Abstract B23: Neuroblastoma patient-derived orthotopic xenografts: Clinically relevant models for drug testing

Background: We previously established neuroblastoma patient-derived orthotopic xenografts (PDXs) by implanting patient neuroblastoma fragments into immunodeficient NSG mice. SNP array analysis confirmed that PDXs maintain patient-specific chromosomal aberrations 1p del, MYCN amp and 17q gain. Immunohistochemistry showed that PDXs retain neuroblastoma markers and a highly infiltrative growth pattern. Importantly, we found spontaneous distant metastasis to lungs, liver and bone marrow. In vitro cultures established from the PDXs express neuroblastoma markers and retain their tumorigenic and metastatic ability in vivo after orthotopic injection.

Methods and Results: Given the important role of the tumor stroma for tumor progression and treatment response, we examined PDX stroma by immunohistochemistry. PDXs were highly vascularized with mouse endothelial cells and two PDX models also formed tumor vasculature by co-engrafted human tumor endothelial cells. Tumors 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 reflect 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.

Conclusion: Neuroblastoma orthotopic PDXs reflect clinical aspects of high-risk disease including spontaneous metastasis, copy number changes and microenvironmental hallmarks. Neuroblastoma PDXs are relevant models for in vitro and in vivo preclinical drug testing.

Citation Format: Daniel Bexell, Noémie Braekeveldt, Sofie Mohlin, Caroline Wigerup, David Gisselsson, Irene Tadeo, Ana P. Berbegall, Sam Navarro, Rosa Noguera, Sven Påhlman. Neuroblastoma patient-derived orthotopic xenografts: Clinically relevant models for drug testing. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B23.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Abstract A02: Neuroblastoma patient-derived orthotopic xenografts: Clinically relevant models for drug testing

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.

Neuroblastoma patient-derived orthotopic xenografts retain metastatic patterns and geno- and phenotypes of patient tumours

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.

Abstract 3464: The effect of EPO-receptor in estrogen receptor positive breast cancer

The main function of Erythropoietin (EPO) and its receptor (EPOR) is the stimulation of erythropoiesis. Recombinant human EPO (rhEPO) is therefore used to treat anemia in cancer patients. However, recent clinical trials have indicated that rhEPO treatment might promote tumor progression and have a negative effect on patient survival. In addition, EPOR expression has been detected in several cancer forms. Using a newly produced anti-EPOR antibody that reliably detects the full-length isoform of the EPOR we show that breast cancer tissue and cells express the EPOR protein. rhEPO stimulation of cultured EPOR expressing breast cancer cells did not result in increased proliferation, overt activation of EPOR (receptor phosphorylation) or a consistent activation of canonical EPOR signaling pathway mediators such as JAK2, STAT3, STAT5, or AKT. However, EPOR knockdown experiments suggested functional EPO receptors in estrogen receptor positive (ERα+) breast cancer cells, as reduced EPOR expression resulted in decreased proliferation. This effect on proliferation was not seen in ERα negative cells. EPOR knockdown decreased ERα activity in ERα+ breast cancer cells and diminished ERα+ phosphorylation on Ser118, results that further support a mechanism by which EPOR affects proliferation via ERα+ mediated mechanisms. In conclusion, we show that EPOR protein is expressed in breast cancer cells, where it appears to promote proliferation in ERα+ expressing breast cancer cells, in part via its capacity to positively modulate ERα activity.

Citation Format: Marica C. Vaapil, Susann Reinbothe, Anna-Maria Larsson, Caroline Wigerup, Jianmin Sun, Annika Jögi, Drorit Neumann, Lars Rönnstrand, Sven Påhlman. The effect of EPO-receptor in estrogen receptor positive breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3464. doi:10.1158/1538-7445.AM2014-3464

P3-01-11: Increased Gene Copy Number of c-KIT and VEGFR2 at 4q12 in Primary Breast Cancer Is Related to an Aggressive Phenotype and Impaired Prognosis

Introduction: Triple-negative breast cancer (TNBC) accounts for approximately 15% of all female breast cancer and is associated with aggressive clinical behaviour. No targeted treatments are available for TNBC. Drugs inhibiting tyrosine kinases, such as vascular endothelial growth factor receptor 2 (VEGFR2) and c-KIT, have however shown some promising results for patients with TNBC. The aim of the present study was to investigate whether gains and/or amplifications of VEGFR2 and c-KIT occur in TNBC. These genes may constitute novel candidate biomarkers for selecting TNBC patients for treatment with tyrosine kinase inhibitors.

Material & Methods: Fluorescence in situ hybridization (FISH) was used to quantify gene copy numbers of VEGFR2 and c-KIT in 83 primary human breast cancers, of which 31 were classified as TNBC. Gains were defined as ≥4 gene copies in more than 40% of the cancer cells, while amplification was defined as gene copy/CEP ratio >2 in more than 10% of the cancer cells. A tumour was considered FISH positive for c-KIT and/or VEGFR2 if it displayed copy number gain and/or amplification. Immunohistochemical (IHC) staining was performed for assessment of c-KIT protein expression.

Results: Ten (32%) of the TNBCs were VEGFR2 FISH positive and nine (29%) were c-KIT FISH positive, whereas non-TNBCs were FISH positive for VEGFR2 and c-KIT in nine (18%) cases for both genes. No significant difference in frequency between TNBCs and non-TNBCs was found. There was a correlation between FISH positivity for VEGFR2 and c-KIT (c2 test, P<0.001), and VEGFR2 and c-KIT FISH positivity correlated to ER/PgR negativity and high Nottingham histological grade (NHG). A significantly worse breast cancer specific survival (BCSS) was seen for FISH positive cases in the whole cohort as well as among untreated patients and non-TNBCs, but not among TNBC cases.

Discussion: The high correlation between VEGFR2 and c-KIT FISH positivity suggests that the genes are co-amplified. Increased copy number of both genes was related to aggressive disease and a worse prognosis, and thus has the potential of functioning as a novel predictive biomarker for selected targeted therapy particularly in the difficult-to-treat TNBC patient category.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-01-11.

Neuroblastoma aggressiveness in relation to sympathetic neuronal differentiation stage

Neuroblastoma is a childhood malignancy of the sympathetic neuronal lineage. It is a rare disease, but since it is frequently diagnosed during infancy, neuroblastoma causes life-long medical follow up of those children that survive the disease. It was early recognized that a high tumor cell differentiation stage correlates to favorable clinical stage and positive clinical outcome. Today, highly differentiated tumors are surgically removed and not further treated. Cells of many established human neuroblastoma cell lines have the capacity to differentiate when stimulated properly, and these cell lines have been used as models for studying and understanding central concepts of tumor cell differentiation. One recent aspect of this issue is the observation that tumor cells can dedifferentiate and gain a stem cell-like phenotype during hypoxic conditions, which was first shown in neuroblastoma. Aberrant or blocked differentiation is a central aspect of neuroblastoma genesis. In this review we summarize known genetic and non-genetic events in neuroblastoma that might be coupled to an aberrant sympathetic neuronal differentiation and thereby indirectly influencing tumorigenesis and/or aggressive neuroblastoma behavior.

p27Kip1 is a predictive factor for tamoxifen treatment response but not a prognostic marker in premenopausal breast cancer patients

The cell-cycle regulating protein p27(Kip1) (p27) has dual roles by acting as both a cdk inhibitor and as an assembly factor for different cdk complexes. Loss of p27 has been linked to malignant features in tumours; however, the exact role of p27 deregulation in breast cancer regarding prognostic and treatment predictive information has not been fully clarified. We have evaluated p27 expression in 328 primary, Stage II breast cancers from premenopausal patients who had been randomised to either tamoxifen treatment or no adjuvant treatment after surgery. p27 was associated with the oestrogen receptor and cyclin D1, and p27 downregulation was associated with high proliferation. There was no association between recurrence-free survival (RFS) and p27 (HR = 0.800, 95% CI 0.523-1.222, p = 0.300), indicating that p27 is not a prognostic marker. The predictive value of p27 was analysed by comparing RFS in tamoxifen-treated and untreated patients in subgroups of low and high p27 expression (HR = 0.747, 95% CI 0.335-1.664, p = 0.474 and HR = 0.401, 95% CI 0.240-0.670, p < 0.001, respectively). Only patients with p27-high tumours benefited from tamoxifen (multivariate interaction analysis p = 0.034). Our study suggests that p27 downregulation is associated with tamoxifen resistance in premenopausal breast cancer but is not linked to impaired prognosis.

Abstract LB-366: Patient-derived EBV-immortalized B-lymphocytes are a dominant contaminant of in vitro cultured human neuroblastoma tumor-initiating cells isolated from bone marrow

Neuroblastoma is one of the most common solid tumors of infancy and is believed to originate from immature sympathetic nervous system progenitor cells. Tumor stem cells from different cancer forms have during the last decade been isolated and propagated in vitro in stem cell-promoting medium. These cells have given the opportunity to study the population within the tumor that is believed to be responsible for relapse and metastatic disease. Three years ago, putative neuroblastoma tumor-initiating cells (TICs) were isolated from bone marrow of patients with high stage disease. Several findings concerning these cells have been difficult to explain in a neuroblastoma context, i.e. that initially only cells from MYCN non-amplified tumors could be established as proliferating cultures in vitro, that they have a B-cell phenotype with VDJ rearrangement as presented at the 2010 Advances in Neuroblastoma Research (ANR) meeting, and as presented here, that they lack genomic imbalances and fail to recapitulate neuroblastoma morphology when xenografted. We show that these widely studied patient-derived TIC cultures (NB12, NB88 and NB122R), also at low passages, are highly contaminated by proliferating cells of a B-lymphocyte phenotype, with the absolute majority of cells expressing multiple B-cell antigens while lacking expression of neuroblastoma-associated markers. We further show that these lymphoblastoid cells are Epstein-Barr virus (EBV)-infected with robust expression of the two EBV nuclear antigens EBNA2 and EBNA3A. In addition, orthotopic and subcutaneous TIC-derived xenograft tumors all have EBNA2 and B-cell marker CD19 positive cells at a high frequency. Published and unpublished results based on the use of the proposed TIC lines as a model for neuroblastoma development should be considered with caution, as these lines, at least with time in culture, mainly consist of EBV-transformed B-lymphoblastoid cells.

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 LB-366. doi:10.1158/1538-7445.AM2011-LB-366

Laser capture microdissection (LCM) and whole genome amplification (WGA) of DNA from normal breast tissue --- optimization for genome wide array analyses

Background

Laser capture microdissection (LCM) can be applied to tissues where cells of interest are distinguishable from surrounding cell populations. Here, we have optimized LCM for fresh frozen normal breast tissue where large amounts of fat can cause problems during microdissection. Since the amount of DNA needed for genome wide analyses, such as single nucleotide polymorphism (SNP) arrays, is often greater than what can be obtained from the dissected tissue, we have compared three different whole genome amplification (WGA) kits for amplification of DNA from LCM material. In addition, the genome wide profiling methods commonly used today require extremely high DNA quality compared to PCR based techniques and DNA quality is thus critical for successful downstream analyses.

Findings

We found that by using FrameSlides without glass backing for LCM and treating the slides with acetone after staining, the problems caused by excessive fat could be significantly decreased. The amount of DNA obtained after extraction from LCM tissue was not sufficient for direct SNP array analysis in our material. However, the two WGA kits based on Phi29 polymerase technology (Repli-g^® (Qiagen) and GenomiPhi (GE Healthcare)) gave relatively long amplification products, and amplified DNA from Repli-g^® gave call rates in the subsequent SNP analysis close to those from non-amplified DNA. Furthermore, the quality of the input DNA for WGA was found to be essential for successful SNP array results and initial DNA fragmentation problems could be reduced by switching from a regular halogen lamp to a VIS-LED lamp during LCM.

Conclusions

LCM must be optimized to work satisfactorily in difficult tissues. We describe a work flow for fresh frozen normal breast tissue where fat is inclined to cause problems if sample treatment is not adapted to this tissue. We also show that the Phi29-based Repli-g^® WGA kit (Qiagen) is a feasible approach to amplify DNA of high quality prior to genome wide analyses such as SNP profiling.

Acetylation-dependent oncogenic activity of metastasis-associated protein 1 co-regulator

High expression of metastasis-associated protein 1 co-regulator (MTA1), a component of the nuclear remodelling and histone deacetylase complex, has been associated with human tumours. However, the precise role of MTA1 in tumorigenesis remains unknown. In this study, we show that induced levels of MTA1 are sufficient to transform Rat1 fibroblasts and that the transforming potential of MTA1 is dependent on its acetylation at Lys626. Underlying mechanisms of MTA1-mediated transformation include activation of the Ras-Raf pathway by MTA1 but not by acetylation-inactive MTA1; this was due to the repression of Galphai2 transcription, which negatively influences Ras activation. We observed that acetylated MTA1-histone deacetylase (HDAC) interaction was required for the recruitment of the MTA1-HDAC complex to the Galphai2 regulatory element and consequently for the repression of Galphai2 transcription and expression leading to activation of the Ras-Raf pathway. The findings presented in this study provide for the first time--to the best of our knowledge--evidence of acetylation-dependent oncogenic activity of a cancer-relevant gene product.