An in vivo avian model of human melanoma to perform rapid and robust preclinical studies.

Metastatic melanoma patients carrying a BRAFV600 mutation can be treated with a combination of BRAF and MEK inhibitors (BRAFi/MEKi), but innate and acquired resistance invariably occurs. Predicting patient response to targeted therapies is crucial to guide clinical decision. We describe here the development of a highly efficient patient-derived xenograft model adapted to patient melanoma biopsies, using the avian embryo as a host (AVI-PDXTM ). In this in vivo paradigm, we depict a fast and reproducible tumor engraftment of patient samples within the embryonic skin, preserving key molecular and phenotypic features. We show that sensitivity and resistance to BRAFi/MEKi can be reliably modeled in these AVI-PDXTM , as well as synergies with other drugs. We further provide proof-of-concept that the AVI-PDXTM models the diversity of responses of melanoma patients to BRAFi/MEKi, within days, hence positioning it as a valuable tool for the design of personalized medicine assays and for the evaluation of novel combination strategies.

GPC3-Unc5 receptor complex structure and role in cell migration.

Neural migration is a critical step during brain development that requires the interactions of cell-surface guidance receptors. Cancer cells often hijack these mechanisms to disseminate. Here, we reveal crystal structures of Uncoordinated-5 receptor D (Unc5D) in complex with morphogen receptor glypican-3 (GPC3), forming an octameric glycoprotein complex. In the complex, four Unc5D molecules pack into an antiparallel bundle, flanked by four GPC3 molecules. Central glycan-glycan interactions are formed by N-linked glycans emanating from GPC3 (N241 in human) and C-mannosylated tryptophans of the Unc5D thrombospondin-like domains. MD simulations, mass spectrometry and structure-based mutants validate the crystallographic data. Anti-GPC3 nanobodies enhance or weaken Unc5-GPC3 binding and, together with mutant proteins, show that Unc5/GPC3 guide migrating pyramidal neurons in the mouse cortex, and cancer cells in an embryonic xenograft neuroblastoma model. The results demonstrate a conserved structural mechanism of cell guidance, where finely balanced Unc5-GPC3 interactions regulate cell migration.

Environmental cues from neural crest derivatives act as metastatic triggers in an embryonic neuroblastoma model.

Embryonic malignant transformation is concomitant to organogenesis, often affecting multipotent and migratory progenitors. While lineage relationships between malignant cells and their physiological counterparts are extensively investigated, the contribution of exogenous embryonic signals is not fully known. Neuroblastoma (NB) is a childhood malignancy of the peripheral nervous system arising from the embryonic trunk neural crest (NC) and characterized by heterogeneous and interconvertible tumor cell identities. Here, using experimental models mimicking the embryonic context coupled to proteomic and transcriptomic analyses, we show that signals released by embryonic sympathetic ganglia, including Olfactomedin-1, induce NB cells to shift from a noradrenergic to mesenchymal identity, and to activate a gene program promoting NB metastatic onset and dissemination. From this gene program, we extract a core signature specifically shared by metastatic cancers with NC origin. This reveals non-cell autonomous embryonic contributions regulating the plasticity of NB identities and setting pro-dissemination gene programs common to NC-derived cancers.

An avian embryo patient-derived xenograft model for preclinical studies of human breast cancers.

Lack of preclinical patient-derived xenograft cancer models in which to conduct large-scale molecular studies seriously impairs the development of effective personalized therapies. We report here an in vivo concept consisting of implanting human tumor cells in targeted tissues of an avian embryo, delivering therapeutics, evaluating their efficacy by measuring tumors using light sheet confocal microscopy, and conducting large-scale RNA-seq analysis to characterize therapeutic-induced changes in gene expression. The model was established to recapitulate triple-negative breast cancer (TNBC) and validated using TNBC standards of care and an investigational therapeutic agent.

Hijacking of Embryonic Programs by Neural Crest-Derived Neuroblastoma: From Physiological Migration to Metastatic Dissemination.

In the developing organism, complex molecular programs orchestrate the generation of cells in adequate numbers, drive them to migrate along the correct pathways towards appropriate territories, eliminate superfluous cells, and induce terminal differentiation of survivors into the appropriate cell-types. Despite strict controls constraining developmental processes, malignancies can emerge in still immature organisms. This is the case of neuroblastoma (NB), a highly heterogeneous disease, predominantly affecting children before the age of 5 years. Highly metastatic forms represent half of the cases and are diagnosed when disseminated foci are detectable. NB arise from a transient population of embryonic cells, the neural crest (NC), and especially NC committed to the establishment of the sympatho-adrenal tissues. The NC is generated at the dorsal edge of the neural tube (NT) of the vertebrate embryo, under the action of NC specifier gene programs. NC cells (NCCs) undergo an epithelial to mesenchymal transition, and engage on a remarkable journey in the developing embryo, contributing to a plethora of cell-types and tissues. Various NCC sub-populations and derived lineages adopt specific migratory behaviors, moving individually as well as collectively, exploiting the different embryonic substrates they encounter along their path. Here we discuss how the specific features of NCC in development are re-iterated during NB metastatic behaviors.

Microenvironment-Driven Shift of Cohesion/Detachment Balance within Tumors Induces a Switch toward Metastasis in Neuroblastoma.

Neuroblastoma (NB) is a childhood cancer arising from sympatho-adrenal neural crest cells. Disseminated forms have high frequency of multiple tumoral foci whose etiology remains unknown; NB embryonic origin limits investigations in patients and current models. We developed an avian embryonic model driving human NB tumorigenesis in tissues homologous to patients. We found that aggressive NBs display a metastatic mode, secondary dissemination via peripheral nerves and aorta. Through tumor transcriptional profiling, we found that NB dissemination is induced by the shutdown of a pro-cohesion autocrine signal, SEMA3C, which constrains the tumoral mass. Lowering SEMA3C levels shifts the balance toward detachment, triggering NB cells to collectively evade the tumor. Together with patient cohort analysis, this identifies a microenvironment-driven pro-metastatic switch for NB.

Regulation by miR181 family of the dependence receptor CDON tumor suppressive activity in neuroblastoma.

BACKGROUND: The Sonic Hedgehog (SHH) signaling pathway plays an important role in neural crest cell fate during embryonic development and has been implicated in the progression of multiple cancers that include neuroblastoma, a neural crest cell-derived disease. While most of the SHH signaling is mediated by the well-described canonical pathway leading to the activation of Smoothened and Gli, it has recently been shown that cell-adhesion molecule-related/downregulated by oncogenes (CDON) serves as a receptor for SHH and contributes to SHH-induced signaling. CDON has also been recently described as a dependence receptor, triggering apoptosis in the absence of SHH. This CDON proapoptotic activity has been suggested to constrain tumor progression. METHODS: CDON expression was analyzed by quantitative-reverse transcription-polymerase chain reaction in a panel of 226 neuroblastoma patients and associated with stages, overall survival, and expression of miR181 family members using Kaplan Meier and Pearson correlation methods. Cell death assays were performed in neuroblastoma cell lines and tumor growth was investigated in the chick chorioallantoic model. All statistical tests were two-sided. RESULTS: CDON expression was inversely associated with neuroblastoma aggressiveness (P < .001). Moreover, re-expression of CDON in neuroblastoma cell lines was associated with apoptosis in vitro and tumor growth inhibition in vivo. We show that CDON expression is regulated by the miR181 miRNA family, whose expression is directly associated with neuroblastoma aggressiveness (survival: high miR181-b 73.2% vs low miR181-b 54.6%; P = .03). CONCLUSIONS: Together, these data support the view that CDON acts as a tumor suppressor in neuroblastomas, and that CDON is tightly regulated by miRNAs.

Sonic Hedgehog promotes the survival of neural crest cells by limiting apoptosis induced by the dependence receptor CDON during branchial arch development.

Cell-adhesion molecule-related/Downregulated by Oncogenes (CDO or CDON) was identified as a receptor for the classic morphogen Sonic Hedgehog (SHH). It has been shown that, in cell culture, CDO also behaves as a SHH dependence receptor: CDO actively triggers apoptosis in absence of SHH via a proteolytic cleavage in CDO intracellular domain. We present evidence that CDO is also pro-apoptotic in the developing neural tube where SHH is known to act as a survival factor. SHH, produced by the ventral foregut endoderm, was shown to promote survival of facial neural crest cells (NCCs) that colonize the first branchial arch (BA1). We show here that the survival activity of SHH on neural crest cells is due to SHH-mediated inhibition of CDO pro-apoptotic activity. Silencing of CDO rescued NCCs from apoptosis observed upon SHH inhibition in the ventral foregut endoderm. Thus, the pair SHH/dependence receptor CDO may play an important role in neural crest cell survival during the formation of the first branchial arch.

Netrin-1 expression is an independent prognostic factor for poor patient survival in brain metastases.

The multifunctional molecule netrin-1 is upregulated in various malignancies and has recently been presented as a major general player in tumorigenesis leading to tumor progression and maintenance in various animal models. However, there is still a lack of clinico-epidemiological data related to netrin-1 expression. Therefore, the aim of our study was to elucidate the association of netrin-1 expression and patient survival in brain metastases since those constitute one of the most limiting factors for patient prognosis. We investigated 104 brain metastases cases for netrin-1 expression using in-situ hybridization and immunohistochemistry with regard to clinical parameters such as patient survival and MRI data. Our data show that netrin-1 is strongly upregulated in most cancer subtypes. Univariate analyses revealed netrin-1 expression as a significant factor associated with poor patient survival in the total cohort of brain metastasis patients and in sub-entities such as non-small cell lung carcinomas. Interestingly, many cancer samples showed a strong nuclear netrin-1 signal which was recently linked to a truncated netrin-1 variant that enhances tumor growth. Nuclear netrin-1 expression was associated with poor patient survival in univariate as well as in multivariate analyses. Our data indicate both total and nuclear netrin-1 expression as prognostic factors in brain metastases patients in contrast to other prognostic markers in oncology such as patient age, number of brain metastases or Ki67 proliferation index. Therefore, nuclear netrin-1 expression constitutes one of the first reported molecular biomarkers for patient survival in brain metastases. Furthermore, netrin-1 may constitute a promising target for future anti-cancer treatment approaches in brain metastases.

Sonic Hedgehog promotes tumor cell survival by inhibiting CDON pro-apoptotic activity.

The Hedgehog signaling is a determinant pathway for tumor progression. However, while inhibition of the Hedgehog canonical pathway-Patched-Smoothened-Gli-has proved efficient in human tumors with activating mutations in this pathway, recent clinical data have failed to show any benefit in other cancers, even though Sonic Hedgehog (SHH) expression is detected in these cancers. Cell-adhesion molecule-related/down-regulated by Oncogenes (CDON), a positive regulator of skeletal muscle development, was recently identified as a receptor for SHH. We show here that CDON behaves as a SHH dependence receptor: it actively triggers apoptosis in the absence of SHH. The pro-apoptotic activity of unbound CDON requires a proteolytic cleavage in its intracellular domain, allowing the recruitment and activation of caspase-9. We show that by inducing apoptosis in settings of SHH limitation, CDON expression constrains tumor progression, and as such, decreased CDON expression observed in a large fraction of human colorectal cancer is associated in mice with intestinal tumor progression. Reciprocally, we propose that the SHH expression, detected in human cancers and previously considered as a mechanism for activation of the canonical pathway in an autocrine or paracrine manner, actually provides a selective tumor growth advantage by blocking CDON-induced apoptosis. In support of this notion, we present the preclinical demonstration that interference with the SHH-CDON interaction triggers a CDON-dependent apoptosis in vitro and tumor growth inhibition in vivo. The latter observation qualifies CDON as a relevant alternative target for anticancer therapy in SHH-expressing tumors.

Nucleolar localization of a netrin-1 isoform enhances tumor cell proliferation.

Netrin-1 displays proto-oncogenic activity in several cancers, which is thought to be due to the ability of this secreted cue to stimulate survival when bound to its receptors. We showed that in contrast to full-length, secreted netrin-1, some cancer cells produced a truncated intranuclear form of netrin-1 (ΔN-netrin-1) through an alternative internal promoter. Because of a nucleolar localization signal located in its carboxyl terminus, ΔN-netrin-1 was targeted to the nucleolus, where it interacted with nucleolar proteins, affected nucleolar ultrastructure, and interacted with the promoters of ribosomal genes. Moreover, ΔN-netrin-1 stimulated cell proliferation in vitro and tumor growth in vivo. Thus, some cancer cells produce not only a full-length, secreted form of netrin-1 that promotes cell survival but also a truncated netrin-1 that stimulates cell proliferation, potentially by enhancing ribosome biogenesis.

Novel roles for Slits and netrins: axon guidance cues as anticancer targets?

Over the past few years, several genes, proteins and signalling pathways that are required for embryogenesis have been shown to regulate tumour development and progression by playing a major part in overriding antitumour safeguard mechanisms. These include axon guidance cues, such as Netrins and Slits. Netrin 1 and members of the Slit family are secreted extracellular matrix proteins that bind to deleted in colorectal cancer (DCC) and UNC5 receptors, and roundabout receptors (Robos), respectively. Their expression is deregulated in a large proportion of human cancers, suggesting that they could be tumour suppressor genes or oncogenes. Moreover, recent data suggest that these ligand-receptor pairs could be promising targets for personalized anticancer therapies.

The dependence receptor UNC5H2/B triggers apoptosis via PP2A-mediated dephosphorylation of DAP kinase.

The UNC5H dependence receptors promote apoptosis in the absence of their ligand, netrin-1, and this is important for neuronal and vascular development and for limitation of cancer progression. UNC5H2 (also called UNC5B) triggers cell death through the activation of the serine-threonine protein kinase DAPk. While performing a siRNA screen to identify genes implicated in UNC5H-induced apoptosis, we identified the structural subunit PR65ß of the holoenzyme protein phosphatase 2A (PP2A). We show that UNC5H2/B recruits a protein complex that includes PR65ß and DAPk and retains PP2A activity. PP2A activity is required for UNC5H2/B-induced apoptosis, since it activates DAPk by triggering its dephosphorylation. Moreover, netrin-1 binding to UNC5H2/B prevents this effect through interaction of the PP2A inhibitor CIP2A to UNC5H2/B. Thus we show here that, in the absence of netrin-1, recruitment of PP2A to UNC5H2/B allows the activation of DAPk via a PP2A-mediated dephosphorylation and that this mechanism is involved in angiogenesis regulation.

Neurotrophin-3 production promotes human neuroblastoma cell survival by inhibiting TrkC-induced apoptosis.

Tropomyosin-related kinase receptor C (TrkC) is a neurotrophin receptor with tyrosine kinase activity that was expected to be oncogenic. However, it has several characteristics of a tumor suppressor: its expression in tumors has often been associated with good prognosis; and it was recently demonstrated to be a dependence receptor, transducing different positive signals in the presence of ligand but inducing apoptosis in the absence of ligand. Here we show that the TrkC ligand neurotrophin-3 (NT-3) is upregulated in a large fraction of aggressive human neuroblastomas (NBs) and that it blocks TrkC-induced apoptosis of human NB cell lines, consistent with the idea that TrkC is a dependence receptor. Functionally, both siRNA knockdown of NT-3 expression and incubation with a TrkC-specific blocking antibody triggered apoptosis in human NB cell lines. Importantly, disruption of the NT-3 autocrine loop in malignant human neuroblasts triggered in vitro NB cell death and inhibited tumor growth and metastasis in both a chick and a mouse xenograft model. Thus, we believe that our data suggest that NT-3/TrkC disruption is a putative alternative targeted therapeutic strategy for the treatment of NB.

Upstream ORF affects MYCN translation depending on exon 1b alternative splicing.

BACKGROUND: The MYCN gene is transcribed into two major mRNAs: one full-length (MYCN) and one exon 1b-spliced (MYCNDelta1b) mRNA. But nothing is known about their respective ability to translate the MYCN protein. METHODS: Plasmids were prepared to enable translation from the upstream (uORF) and major ORF of the two MYCN transcripts. Translation was studied after transfection in neuroblastoma SH-EP cell line. Impact of the upstream AUG on translation was evaluated after directed mutagenesis. Functional study with the two MYCN mRNAs was conducted by a cell viability assay. Existence of a new protein encoded by the MYCNDelta1b uORF was explored by designing a rabbit polyclonal antibody against a specific epitope of this protein. RESULTS: Both are translated, but higher levels of protein were seen with MYCNDelta1b mRNA. An upstream ORF was shown to have positive cis-regulatory activity on translation from MYCN but not from MYCNDelta1b mRNA. In transfected SH-EP neuroblastoma cells, high MYCN dosage obtained with MYCNDelta1b mRNA translation induces an antiapoptotic effect after serum deprivation that was not observed with low MYCN expression obtained with MYCN mRNA. Here, we showed that MYCNOT: MYCN Overlap Transcript, a new protein of unknown function is translated from the upstream AUG of MYCNDelta1b mRNA. CONCLUSIONS: Existence of upstream ORF in MYCN transcripts leads to a new level of MYCN regulation. The resulting MYCN dosage has a weak but significant anti-apoptotic activity after intrinsic apoptosis induction.

Netrin-1 up-regulation in inflammatory bowel diseases is required for colorectal cancer progression.

Chronic inflammation and cancer are intimately associated. This is particularly true for inflammatory bowel diseases (IBD), such as ulcerative colitis and Crohn's disease, which show a major increased risk for colorectal cancer. While the understanding of the molecular pathogenesis of IBD has recently improved, the mechanisms that link these chronic inflammatory states to colorectal cancer development are in large part unknown. One of these mechanisms is NF-kappaB pathway activation which in turn may contribute to tumor formation by providing anti-apoptotic survival signals to the epithelial cells. Based on the observation that netrin-1, the anti-apoptotic ligand for the dependence receptors DCC and UNC5H is up-regulated in colonic crypts in response to NF-kappaB, we show here that colorectal cancers from inflammatory bowel diseases patients have selected up-regulation of netrin-1. Moreover, we demonstrate that this inflammation-driven netrin-1 up-regulation is causal for colorectal cancer development as interference with netrin-1 autocrine loop in a mouse model for ulcerative colitis-associated colorectal cancer, while showing no effect on inflammation, inhibits colorectal cancer progression.

Inhibition of endothelial cell apoptosis by netrin-1 during angiogenesis.

Netrin-1 was recently proposed to play an important role in embryonic and pathological angiogenesis. However, data reported led to the apparently contradictory conclusions that netrin-1 is either a pro- or an antiangiogenic factor. Here, we reconcile these opposing observations by demonstrating that netrin-1 acts as a survival factor for endothelial cells, blocking the proapoptotic effect of the dependence receptor UNC5B and its downstream death signaling effector, the serine/threonine kinase DAPK. The netrin-1 effect on blood vessel development is mimicked by caspase inhibitors in ex vivo assays, and the inhibition of caspase activity, the silencing of the UNC5B receptor, and the silencing of DAPK are each sufficient to rescue the vascular sprouting defects induced by netrin-1 silencing in zebrafish. Thus, the proapoptotic effect of unbound UNC5B and the survival effect of netrin-1 on endothelial cells finely tune the angiogenic process.

Netrin-1 acts as a survival factor for aggressive neuroblastoma.

Neuroblastoma (NB), the most frequent solid tumor of early childhood, is diagnosed as a disseminated disease in >60% of cases, and several lines of evidence support the resistance to apoptosis as a prerequisite for NB progression. We show that autocrine production of netrin-1, a multifunctional laminin-related molecule, conveys a selective advantage in tumor growth and dissemination in aggressive NB, as it blocks the proapoptotic activity of the UNC5H netrin-1 dependence receptors. We show that such netrin-1 up-regulation is a potential marker for poor prognosis in stage 4S and, more generally, in NB stage 4 diagnosed infants. Moreover, we propose that interference with the netrin-1 autocrine loop in malignant neuroblasts could represent an alternative therapeutic strategy, as disruption of this loop triggers in vitro NB cell death and inhibits NB metastasis in avian and mouse models.

Interference with netrin-1 and tumor cell death in non-small cell lung cancer.

BACKGROUND: Netrin-1 may promote colorectal and breast tumorigenesis, by inhibiting apoptosis induced by its dependence receptors, deleted in colorectal cancer (DCC) and uncoordinated-5-homolog (UNC5H). The status of netrin-1 and its receptors in non-small cell lung cancer (NSCLC) was unknown. METHODS: The levels of netrin-1 and its receptors were analyzed in a panel of 92 NSCLC and 25 human lung cancer cell lines by quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. In lung cancer cell lines that express netrin-1, the expression of netrin-1 was inhibited by using small interfering RNA (siRNA), or interference with netrin-1 was performed by treatment with a decoy recombinant DCC ectodomain protein (DCC-5Fbn). Cell death was monitored with a trypan blue exclusion assay or by measuring caspase-3 activity. The effect of netrin-1 interference on tumor growth was analyzed by DCC-5Fbn intratumoral or netrin-1 siRNA intraperitoneal injection in mice engrafted with lung cancer cell lines. All statistical tests were two-sided. RESULTS: High levels of netrin-1 were found in 43 of the 92 NSCLC tumor samples (47%). Interference with netrin-1 in human lung cancer cell lines was associated with UNC5H-mediated cell death in vitro (percentage of cell death in untreated and in DCC-5Fbn-treated cells = 8% and 26%, respectively, difference = 18%, 95% confidence interval [CI] = 10% to 26%; P = .049) and with lung tumor growth inhibition and/or regression in xenografted nude mice (12 mice in DCC-5Fbn-treated group and 13 mice in control group). Mean volume of control and DCC-5Fbn-treated tumors on day 46 was 489 and 84 mm(3), respectively (difference = 404 mm(3), 95% CI = 145 to 664 mm(3); P < .001). CONCLUSIONS: Almost half of the NSCLC tissue samples examined expressed high levels of netrin-1. Extracellular targeting of the interaction between netrin-1 and UNC5H may be a promising therapeutic approach for NSCLCs that express netrin-1.