Loen M. Hansford

Neuroblastoma Cells Isolated from Bone Marrow Metastases Contain a Naturally Enriched Tumor-Initiating Cell

Neuroblastoma is a heterogeneous pediatric tumor thought to arise from the embryonic neural crest. Identification of the cell responsible for propagating neuroblastomas is essential to understanding this often recurrent, rapidly progressing disease. We have isolated and characterized putative tumor-initiating cells from 16 tumors and bone marrow metastases from patients in all neuroblastoma risk groups. Dissociated cells from tumors or bone marrow grew as spheres in conditions used to culture neural crest stem cells, were capable of self-renewal, and exhibited chromosomal aberrations typical of neuroblastoma. Primary spheres from all tumor risk groups differentiated under neurogenic conditions to form neurons. Tumor spheres from low-risk tumors frequently formed large neuronal networks, whereas those from high-risk tumors rarely did. As few as 10 passaged tumor sphere cells from aggressive neuroblastoma injected orthotopically into severe combined immunodeficient/Beige mice formed large neuroblastoma tumors that metastasized to liver, spleen, contralateral adrenal and kidney, and lung. Furthermore, highly tumorigenic tumor spheres were isolated from the bone marrow of patients in clinical remission, suggesting that this population of cells may predict clinical behavior and serve as a biomarker for minimal residual disease in high-risk patients. Our data indicate that high-risk neuroblastoma contains a cell with cancer stem cell properties that is enriched in tumor-initiating capacity. These cells may serve as a model system to identify the molecular determinants of neuroblastoma and to develop new therapeutic strategies for this tumor.

HIF-2 alpha maintains an undifferentiated state in neural crest-like human neuroblastoma tumor-initiating cells

High hypoxia-inducible factor-2α (HIF-2α) protein levels predict poor outcome in neuroblastoma, and hypoxia dedifferentiates cultured neuroblastoma cells toward a neural crest-like phenotype. Here, we identify HIF-2α as a marker of normoxic neural crest-like neuroblastoma tumor-initiating/stem cells (TICs) isolated from patient bone marrows. Knockdown of HIF-2α reduced VEGF expression and induced partial sympathetic neuronal differentiation when these TICs were grown in vitro under stem cell-promoting conditions. Xenograft tumors of HIF-2α-silenced cells were widely necrotic, poorly vascularized, and resembled the bulk of tumor cells in clinical neuroblastomas by expressing additional sympathetic neuronal markers, whereas control tumors were immature, well-vascularized, and stroma-rich. Thus, HIF-2α maintains an undifferentiated state of neuroblastoma TICs. Because low differentiation is associated with poor outcome and angiogenesis is crucial for tumor growth, HIF-2α is an attractive target for neuroblastoma therapy.

Selective targeting of neuroblastoma tumour‐initiating cells by compounds identified in stem cell‐based small molecule screens

Neuroblastoma (NB) is the most deadly extra‐cranial solid tumour in children necessitating an urgent need for effective and less toxic treatments. One reason for the lack of efficacious treatments may be the inability of existing drugs to target the tumour‐initiating or cancer stem cell population responsible for sustaining tumour growth, metastases and relapse. Here, we describe a strategy to identify compounds that selectively target patient‐derived cancer stem cell‐like tumour‐initiating cells (TICs) while sparing normal paediatric stem cells (skin‐derived precursors, SKPs) and characterize two therapeutic candidates. DECA‐14 and rapamycin were identified as NB TIC‐selective agents. Both compounds induced TIC death at nanomolar concentrations in vitro, significantly reduced NB xenograft tumour weight in vivo, and dramatically decreased self‐renewal or tumour‐initiation capacity in treated tumours. These results demonstrate that differential drug sensitivities between TICs and normal paediatric stem cells can be exploited to identify novel, patient‐specific and potentially less toxic therapies.

CCM2 Mediates Death Signaling by the TrkA Receptor Tyrosine Kinase

The TrkA receptor tyrosine kinase is crucial for differentiation and survival of nerve-growth-factor-dependent neurons. Paradoxically, TrkA also induces cell death in pediatric tumor cells of neural origin, via an unknown mechanism. Here, we show that CCM2, a gene product associated with cerebral cavernous malformations, interacts with the juxtamembrane region of TrkA via its phosphotyrosine binding (PTB) domain and mediates TrkA-induced death in diverse cell types. Both the PTB and Karet domains of CCM2 are required for TrkA-dependent cell death, such that the PTB domain determines the specificity of the interaction, and the Karet domain links to death pathways. Downregulation of CCM2 in medulloblastoma or neuroblastoma cells attenuates TrkA-dependent death. Combined high expression levels of CCM2 and TrkA are correlated with long-term survival in a large cohort of human neuroblastoma patients. Thus, CCM2 is a key mediator of TrkA-dependent cell death in pediatric neuroblastic tumors.

System-Level Analysis of Neuroblastoma Tumor–Initiating Cells Implicates AURKB as a Novel Drug Target for Neuroblastoma

Purpose: Neuroblastoma (NB) is an aggressive tumor of the developing peripheral nervous system that remains difficult to cure in the advanced stages. The poor prognosis for high-risk NB patients is associated with common disease recurrences that fail to respond to available therapies. NB tumor-initiating cells (TICs), isolated from metastases and primary tumors, may escape treatment and contribute to tumor relapse. New therapies that target the TICs may therefore prevent or treat tumor recurrences. Experimental Design: We undertook a system-level characterization of NB TICs to identify potential drug targets against recurrent NB. We used next-generation RNA sequencing and/or human exon arrays to profile the transcriptomes of 11 NB TIC lines from six NB patients, revealing genes that are highly expressed in the TICs compared with normal neural crest-like cells and unrelated cancer tissues. We used gel-free two-dimensional liquid chromatography coupled to shotgun tandem mass spectrometry to confirm the presence of proteins corresponding to the most abundant TIC-enriched transcripts, thereby providing validation to the gene expression result. Results: Our study revealed that genes in the BRCA1 signaling pathway are frequently misexpressed in NB TICs and implicated Aurora B kinase as a potential drug target for NB therapy. Treatment with a selective AURKB inhibitor was cytotoxic to NB TICs but not to the normal neural crest-like cells. Conclusion: This work provides the first high-resolution system-level analysis of the transcriptomes of 11 primary human NB TICs and identifies a set of candidate NB TIC-enriched transcripts for further development as therapeutic targets. Clin Cancer Res; 16(18); 4572–82. ©2010 AACR.

N-myc transcription molecule and oncoprotein

N-myc has emerged as a member of a transcriptional regulatory network which impinges directly on the machinery of cell growth and proliferation. Critical during neural crest embryogenesis, N-myc is rapidly down-regulated as tissues become terminally differentiated and growth-arrested. The involvement of N-myc in these fundamental cellular processes necessitates an intricate strategy for its regulation, which is still being elucidated. Deregulated N-myc over-expression has clear transforming ability in vitro and in vivo. The transcriptional target genes responsible for this activity are beginning to be unravelled.

Glial cell line-derived neurotrophic factor (GDNF) family ligands reduce the sensitivity of neuroblastoma cells to pharmacologically induced cell death, growth arrest and differentiation.

The glial cell line-derived neurotrophic factor (GDNF) family of ligands play essential roles in promoting normal neural crest differentiation during embryogenesis, and, may have a therapeutic role in malignancies of neural crest origin, such as neuroblastoma. However, we report here that GDNF and neurturin blocked the growth inhibitory and neuritogenic effects of all-trans-retinoic acid in neuroblastoma cells in vitro. GDNF caused neuroblastoma cells to proliferate in the presence of a range of cytotoxic chemotherapeutic agents at low concentrations. Thus, our findings suggest a role for GDNF signaling in promoting resistance to differentiation or cytotoxic therapy of neuroblastoma, and, preclude their use in this neural crest tumor.

Cloning and characterization of the human neural cell adhesion molecule, CNTN4 (alias BIG-2)

We report the isolation and characterization of human contactin 4 (CNTN4), a brain-derived, immunoglobulin superfamily molecule-2 (alias BIG-2) as a candidate gene responsible for the differentiation potential of human neuroblastoma cells. Northern blot analysis showed highest CNTN4 expression in testes, thyroid, small intestine, uterus and brain. Induction of CNTN4 mRNA expression in human neuroblastoma tumor cells treated with retinoic acid correlated with a block in retinoid-induced neuritogenesis. Our findings suggest a role for human contactin 4 protein in the response of neuroblastoma cells to differentiating agents.

TLX activates MMP-2, promotes self-renewal of tumor spheres in neuroblastoma and correlates with poor patient survival

Nuclear orphan receptor TLX (Drosophila tailless homolog) is essential for the maintenance of neural stem/progenitor cell self-renewal, but its role in neuroblastoma (NB) is not well understood. Here, we show that TLX is essential for the formation of tumor spheres in three different NB cell lines, when grown in neural stem cell media. We demonstrate that the knock down of TLX in IMR-32 cells diminishes its tumor sphere-forming capacity. In tumor spheres, TLX is coexpressed with the neural progenitor markers Nestin, CD133 and Oct-4. In addition, TLX is coexpressed with the migratory neural progenitor markers CD15 and matrix metalloproteinase-2 (MMP-2) in xenografts of primary NB cells from patients. Subsequently, we show the effect of TLX on the proliferative, invasive and migratory properties of IMR-32 cells. We attribute this to the recruitment of TLX to both MMP-2 and Oct-4 gene promoters, which resulted in the respective gene activation. In support of our findings, we found that TLX expression was high in NB patient tissues when compared with normal peripheral nervous system tissues. Further, the Kaplan–Meier estimator indicated a negative correlation between TLX expression and survival in 88 NB patients. Therefore, our results point at TLX being a crucial player in progression of NB, by promoting self-renewal of NB tumor-initiating cells and altering their migratory and invasive properties.

A Phosphoproteomics Approach to Identify Candidate Kinase Inhibitor Pathway Targets in Lymphoma-Like Primary Cell Lines

Mass spectrometry-based technologies are increasingly utilized in drug discovery. Phosphoproteomics in particular has allowed for the efficient surveying of phosphotyrosine signaling pathways involved in various diseases states, most prominently in cancer. We describe a phosphotyrosine-based proteomics screening approach to identify signaling pathways and tyrosine kinase inhibitor targets in highly tumorigenic human lymphoma-like primary cells. We identified several receptor tyrosine kinase pathways and validated SRC family kinases (SFKs) as potential drug targets for targeted selection of small molecule inhibitors. BMS-354825 (dasatinib) and SKI-606 (bosutinib), second and third generation clinical SFK/ABL inhibitors, were found to be potent cytotoxic agents against tumorigenic cells with low toxicity to normal pediatric stem cells. Both SFK inhibitors reduced ERK1/2 and AKT phosphorylation and induced apoptosis. This study supports the adaptation of high-end mass spectrometry techniques for the efficient identification of candidate tyrosine kinases as novel therapeutic targets in primary cancer cell lines.