The DMT1 isoform lacking the iron-response element regulates normal and malignant hematopoiesis via NOTCH pathway activation

Natural resistance-associated macrophage protein 2 (NRAMP 2; also known as DMT1 and encoded by SLC11A2) is mainly known for its iron transport activity. Recently, the DMT1 isoform lacking the iron-response element (nonIRE) was associated with aberrant NOTCH pathway activity. In this report, we investigated the function of DMT1 nonIRE in normal and malignant hematopoiesis. Knockdown of Dmt1 nonIRE in mice showed that it has non-canonical functions in hematopoietic stem cell differentiation: its knockdown suppressed development along the myeloid and lymphoid lineages, while promoting the production of platelets. These phenotypic effects on the hematopoietic system induced by Dmt1 nonIRE knockdown were linked to suppression of Notch/Myc pathway activity. Conversely, our data indicate a non-canonical function for DMT1 nonIRE overexpression in boosting NOTCH pathway activity in T-cell leukemia homeobox protein 1 (TLX1)-defective leukemia. This work sets the stage for future investigation using a multiple-hit T-cell acute lymphoblastic leukemia (T-ALL) model to further investigate the function of DMT1 nonIRE in T-ALL disease development and progression.

Targeting serine/glycine metabolism improves radiotherapy response in non-small cell lung cancer

BACKGROUND

Lung cancer is the most lethal cancer, and 85% of cases are classified as non-small cell lung cancer (NSCLC). Metabolic rewiring is a cancer hallmark that causes treatment resistance, and lacks insights into serine/glycine pathway adaptations upon radiotherapy.

METHODS

We analyzed radiotherapy responses using mass-spectrometry-based metabolomics in NSCLC patient's plasma and cell lines. Efficacy of serine/glycine conversion inhibitor sertraline with radiotherapy was investigated by proliferation, clonogenic and spheroid assays, and in vivo using a serine/glycine dependent NSCLC mouse model by assessment of tumor growth, metabolite and cytokine levels, and immune signatures.

RESULTS

Serine/glycine pathway metabolites were significantly consumed in response to radiotherapy in NSCLC patients and cell models. Combining sertraline with radiotherapy impaired NSCLC proliferation, clonogenicity and stem cell self-renewal capacity. In vivo, NSCLC tumor growth was reduced solely in the sertraline plus radiotherapy combination treatment group. Tumor weights linked to systemic serine/glycine pathway metabolite levels, and were inhibited in the combination therapy group. Interestingly, combination therapy reshaped the tumor microenvironment via cytokines associated with natural killer cells, supported by eradication of immune checkpoint galectin-1 and elevated granzyme B levels.

CONCLUSION

Our findings highlight that targeting serine/glycine metabolism using sertraline restricts cancer cell recovery from radiotherapy and provides tumor control through immunomodulation in NSCLC.

Iron-responsive element of Divalent metal transporter 1 (Dmt1) controls Notch-mediated cell fates

Notch receptor activation is regulated by the intramembrane protease γ-secretase, which cleaves and liberates the Notch intracellular domain (Nicd) that regulates gene transcription. While γ-secretase cleavage is necessary, we demonstrate it is insufficient for Notch activation and requires vesicular trafficking. Here, we report Divalent metal transporter 1 (Dmt1, Slc11A2) as a novel and essential regulator of Notch signalling. Dmt1-deficient cells are defective in Notch signalling and have perturbed endolysosomal trafficking and function. Dmt1 encodes for two isoforms, with and without an iron response element (ire). We show that isoform-specific silencing of Dmt1-ire and Dmt1+ire has opposite consequences on Notch-dependent cell fates in cell lines and intestinal organoids. Loss of Dmt1-ire suppresses Notch activation and promotes differentiation, whereas loss of Dmt1+ire causes Notch activation and maintains stem-progenitor cell fates. Dmt1 isoform expression correlates with Notch and Wnt signalling in Apc-deficient intestinal organoids and human colorectal cancers. Consistently, Dmt1-ire silencing induces Notch-dependent differentiation in colorectal cancer cells. These data identify Dmt1 isoforms as binary switches controlling Notch cell fate decisions in normal and tumour cells.

Patient-derived glioblastoma organoids reflect tumor heterogeneity and treatment sensitivity

Background

Treatment resistance and tumor relapse are the primary causes of mortality in glioblastoma (GBM), with intratumoral heterogeneity playing a significant role. Patient-derived cancer organoids have emerged as a promising model capable of recapitulating tumor heterogeneity. Our objective was to develop patient-derived GBM organoids (PGO) to investigate treatment response and resistance.

Methods

GBM samples were used to generate PGOs and analyzed using whole-exome sequencing (WES) and single-cell karyotype sequencing. PGOs were subjected to temozolomide (TMZ) to assess viability. Bulk RNA sequencing was performed before and after TMZ.

Results

WES analysis on individual PGOs cultured for 3 time points (1-3 months) showed a high inter-organoid correlation and retention of genetic variants (range 92.3%-97.7%). Most variants were retained in the PGO compared to the tumor (range 58%-90%) and exhibited similar copy number variations. Single-cell karyotype sequencing demonstrated preservation of genetic heterogeneity. Single-cell multiplex immunofluorescence showed maintenance of cellular states. TMZ treatment of PGOs showed a differential response, which largely corresponded with MGMT promoter methylation. Differentially expressed genes before and after TMZ revealed an upregulation of the JNK kinase pathway. Notably, the combination treatment of a JNK kinase inhibitor and TMZ demonstrated a synergistic effect.

Conclusions

Overall, these findings demonstrate the robustness of PGOs in retaining the genetic and phenotypic heterogeneity in culture and the application of measuring clinically relevant drug responses. These data show that PGOs have the potential to be further developed into avatars for personalized adaptive treatment selection and actionable drug target discovery and as a platform to study GBM biology.

The ins and outs of serine and glycine metabolism in cancer

Cancer cells reprogramme their metabolism to support unrestrained proliferation and survival in nutrient-poor conditions. Whereas non-transformed cells often have lower demands for serine and glycine, several cancer subtypes hyperactivate intracellular serine and glycine synthesis and become addicted to de novo production. Copy-number amplifications of serine- and glycine-synthesis genes and genetic alterations in common oncogenes and tumour-suppressor genes enhance serine and glycine synthesis, resulting in high production and secretion of these oncogenesis-supportive metabolites. In this Review, we discuss the contribution of serine and glycine synthesis to cancer progression. By relying on de novo synthesis pathways, cancer cells are able to enhance macromolecule synthesis, neutralize high levels of oxidative stress and regulate methylation and tRNA formylation. Furthermore, we discuss the immunosuppressive potential of serine and glycine, and the essentiality of both amino acids to promoting survival of non-transformed neighbouring cells. Finally, we point to the emerging data proposing moonlighting functions of serine- and glycine-synthesis enzymes and examine promising small molecules targeting serine and glycine synthesis.

Hallmarks of ribosomopathies

Ribosomopathies are diseases caused by defects in ribosomal constituents or in factors with a role in ribosome assembly. Intriguingly, congenital ribosomopathies display a paradoxical transition from early symptoms due to cellular hypo-proliferation to an elevated cancer risk later in life. Another association between ribosome defects and cancer came into view after the recent discovery of somatic mutations in ribosomal proteins and rDNA copy number changes in a variety of tumor types, giving rise to somatic ribosomopathies. Despite these clear connections between ribosome defects and cancer, the molecular mechanisms by which defects in this essential cellular machinery are oncogenic only start to emerge. In this review, the impact of ribosomal defects on the cellular function and their mechanisms of promoting oncogenesis are described. In particular, we discuss the emerging hallmarks of ribosomopathies such as the appearance of ‘onco-ribosomes’ that are specialized in translating oncoproteins, dysregulation of translation-independent extra-ribosomal functions of ribosomal proteins, rewired cellular protein and energy metabolism, and extensive oxidative stress leading to DNA damage. We end by integrating these findings in a model that can provide an explanation how ribosomopathies could lead to the transition from hypo- to hyper-proliferation in bone marrow failure syndromes with elevated cancer risk.

Cancer Biogenesis in Ribosomopathies

Ribosomopathies are congenital diseases with defects in ribosome assembly and are characterized by elevated cancer risks. Additionally, somatic mutations in ribosomal proteins have recently been linked to a variety of cancers. Despite a clear correlation between ribosome defects and cancer, the molecular mechanisms by which these defects promote tumorigenesis are unclear. In this review, we focus on the emerging mechanisms that link ribosomal defects in ribosomopathies to cancer progression. This includes functional "onco-specialization" of mutant ribosomes, extra-ribosomal consequences of mutations in ribosomal proteins and ribosome assembly factors, and effects of ribosomal mutations on cellular stress and metabolism. We integrate some of these recent findings in a single model that can partially explain the paradoxical transition from hypo- to hyperproliferation phenotypes, as observed in ribosomopathies. Finally, we discuss the current and potential strategies, and the associated challenges for therapeutic intervention in ribosome-mutant diseases.

The ribosomal RPL10 R98S mutation drives IRES-dependent BCL-2 translation in T-ALL

The R98S mutation in ribosomal protein L10 (RPL10 R98S) affects 8% of pediatric T-cell acute lymphoblastic leukemia (T-ALL) cases, and was previously described to impair cellular proliferation. The current study reveals that RPL10 R98S cells accumulate reactive oxygen species which promotes mitochondrial dysfunction and reduced ATP levels, causing the proliferation defect. RPL10 R98S mutant leukemia cells can survive high oxidative stress levels via a specific increase of IRES-mediated translation of the anti-apoptotic factor B-cell lymphoma 2 (BCL-2), mediating BCL-2 protein overexpression. RPL10 R98S selective sensitivity to the clinically available Bcl-2 inhibitor Venetoclax (ABT-199) was supported by suppression of splenomegaly and the absence of human leukemia cells in the blood of T-ALL xenografted mice. These results shed new light on the oncogenic function of ribosomal mutations in cancer, provide a novel mechanism for BCL-2 upregulation in leukemia, and highlight BCL-2 inhibition as a novel therapeutic opportunity in RPL10 R98S defective T-ALL.

Ribosomal Lesions Promote Oncogenic Mutagenesis

Ribosomopathies are congenital disorders caused by mutations in ribosomal proteins (RP) or assembly factors and are characterized by cellular hypoproliferation at an early stage. Paradoxically, many of these disorders have an elevated risk to progress to hyperproliferative cancer at a later stage. In addition, somatic RP mutations have recently been identified in various cancer types, for example, the recurrent RPL10-R98S mutation in T-cell acute lymphoblastic leukemia (T-ALL) and RPS15 mutations in chronic lymphocytic leukemia (CLL). We previously showed that RPL10-R98S promotes expression of oncogenes, but also induces a proliferative defect due to elevated oxidative stress. In this study, we demonstrate that this proliferation defect is eventually rescued by RPL10-R98S mouse lymphoid cells that acquire 5-fold more secondary mutations than RPL10-WT cells. The presence of RPL10-R98S and other RP mutations also correlated with a higher mutational load in patients with T-ALL, with an enrichment in NOTCH1-activating lesions. RPL10-R98S-associated cellular oxidative stress promoted DNA damage and impaired cell growth. Expression of NOTCH1 eliminated these phenotypes in RPL10-R98S cells, in part via downregulation of PKC-θ, with no effect on RPL10-WT cells. Patients with RP-mutant CLL also demonstrated a higher mutational burden, enriched for mutations that may diminish oxidative stress. We propose that oxidative stress due to ribosome dysfunction causes hypoproliferation and cellular insufficiency in ribosomopathies and RP-mutant cancer. This drives surviving cells, potentiated by genomic instability, to acquire rescuing mutations, which ultimately promote transition to hyperproliferation. SIGNIFICANCE: Ribosomal lesions cause oxidative stress and increase mutagenesis, promoting acquisition of rescuing mutations that stimulate proliferation.

VEGFC Antibody Therapy Drives Differentiation of AML

High expression of VEGFC predicts adverse prognosis in acute myeloid leukemia (AML). We therefore explored VEGFC-targeting efficacy as an AML therapy using a VEGFC mAb. VEGFC antibody therapy enforced myelocytic differentiation of clonal CD34⁺ AML blasts. Treatment of CD34⁺ AML blasts with the antibody reduced expansion potential by 30% to 50% and enhanced differentiation via FOXO3A suppression and inhibition of MAPK/ERK proliferative signals. VEGFC antibody therapy also accelerated leukemia cell differentiation in a systemic humanized AML mouse model. Collectively, these results define a regulatory function of VEGFC in CD34⁺ AML cell fate decisions via FOXO3A and serve as a new potential differentiation therapy for patients with AML.Significance: These findings reveal VEGFC targeting as a promising new differentiation therapy in AML. Cancer Res; 78(20); 5940-8. ©2018 AACR.

The ribosomal protein gene RPL5 is a haploinsufficient tumor suppressor in multiple cancer types

For many years, defects in the ribosome have been associated to cancer. Recently, somatic mutations and deletions affecting ribosomal protein genes were identified in a few leukemias and solid tumor types. However, systematic analysis of all 81 known ribosomal protein genes across cancer types is lacking. We screened mutation and copy number data of respectively 4926 and 7322 samples from 16 cancer types and identified six altered genes (RPL5, RPL11, RPL23A, RPS5, RPS20 and RPSA). RPL5 was located at a significant peak of heterozygous deletion or mutated in 11% of glioblastoma, 28% of melanoma and 34% of breast cancer samples. Moreover, patients with low RPL5 expression displayed worse overall survival in glioblastoma and in one breast cancer cohort. RPL5 knockdown in breast cancer cell lines enhanced G2/M cell cycle progression and accelerated tumor progression in a xenograft mouse model. Interestingly, our data suggest that the tumor suppressor role of RPL5 is not only mediated by its known function as TP53 or c-MYC regulator. In conclusion, RPL5 heterozygous inactivation occurs at high incidence (11-34%) in multiple tumor types, currently representing the most common somatic ribosomal protein defect in cancer, and we demonstrate a tumor suppressor role for RPL5 in breast cancer.

Abstract 1546: Contribution of heterozygous loss of ribosomal protein L5 as general tumor suppressor in cancer

The association between ribosome defects and cancer became clear with the recent discovery of somatic mutations in ribosomal protein genes in several cancers, such as lymphoid leukemia’s and glioblastoma (Nat Genet. 2013 Feb;45(2):186-90 & Blood. 2016 Feb 25;127(8):1007-16 & Nature. 2014 Jan 23;505(7484):495-501). To further delineate the role of ribosomal proteins in human cancer, we systematically screened the TCGA database for genetic lesions in ribosomal protein genes, confirmed the contributing capacity of the most common somatic ribosomal protein defect in cancer pathogenesis by molecular interference, and explored the mode of action of this ribosomal protein defect. Systematic analysis of TCGA mutation and copy number data of respectively 4926 and 7322 patients representing 16 cancer types for defects in all 81 ribosomal protein genes. After stringent filtering, six ribosomal protein encoding genes (RPL5, RPL11, RPL23A, RPS5, RPS20 and RPSA) were significantly altered and identified as candidate cancer driver genes. RPL5 was located at a significant peak of heterozygous deletion on chromosome 1p22 and showed significant mutations and deletions in 11% of glioblastoma (GBM), 28% of melanoma, 34% of breast cancer (BRCA), and in 20% of multiple myeloma cases, thereby supporting heterozygous RPL5 inactivation to be the most common somatic ribosomal protein defect in human cancer. Human specific RPL5 doxycycline inducible knockdown (sh-hRPL5) in TP53 WT and TP53 mutant human breast cancer cell lines (MCF7 and MDA-MB-231) and in a TP53 mutant human glioblastoma cell line (U-118 MG) proved that RPL5 knockdown accelerated in vivo tumor progression in NSG mice. This acceleration was associated with reduced phosphorylation of CDK1tyr15, which is required for cell cycle progression from G2 to mitosis. Whereas RPL5 has been implicated in TP53 and MYC regulation, no consistent effects of RPL5 downregulation on these proteins could be detected in TP53 WT and TP53 homozygous R280K mutant breast cancer models (sh-hRPL5). Interestingly, partial RPL5 inactivation was found to be associated with PTEN protein suppression in these tumors. This observation was confirmed in various cell models; in normal mouse neural stem/progenitor cells and mouse bone marrow cells (RPL5+/lox by INFβ and poly I:C), and also in GBM cancer pre-disposition mouse neural stem/progenitor cell model (sh-mRPL5 TP53 -/-). RPL5 downregulation also accelerated tumor formation in the PTEN deficient GBM cell line U-118 MG, underscoring undefined PTEN-independent mechanisms of RPL5. Overall, we identified RPL5 as a new tumor suppressor that shows heterozygous inactivation in 11-34% of multiple human cancer types. Partial molecular inactivation of RPL5 supported a tumor suppressor function for RPL5 in accelerating breast cancer and glioblastoma progression in vivo, which may be, in part, due to a new function of RPL5 in regulating PTEN.

Citation Format: Kim R. Kampen, Laura Fancello, Jelle Verbeeck, Kim De Keersmaecker. Contribution of heterozygous loss of ribosomal protein L5 as general tumor suppressor in cancer [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 1546. doi:10.1158/1538-7445.AM2017-1546

Essential role for cyclic-AMP responsive element binding protein 1 (CREB) in the survival of acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) relapse remains a leading cause of cancer related death in children, therefore, new therapeutic options are needed. Recently, we showed that a peptide derived from Cyclic-AMP Responsive Element Binding Protein (CREB) was highly phosphorylated in pediatric leukemias.

In this study, we determined CREB phosphorylation and mRNA levels showing that CREB expression was significantly higher in ALL compared to normal bone marrow (phosphorylation: P < 0.0001, mRNA: P = 0.004). High CREB and phospho-CREB expression was correlated with a lower median overall survival in a cohort of 140 adult ALL patients. ShRNA mediated knockdown of CREB in ALL cell lines blocked leukemic cell growth by inducing cell cycle arrest and apoptosis. Gene expression array analysis showed downregulation of CREB target genes regulating cell proliferation and glucose metabolism and upregulation of apoptosis inducing genes. Similar to CREB knockdown, the CREB inhibitor KG-501 decreased leukemic cell viability and induced apoptosis in ALL cell lines, as well as primary T-ALL samples, with cases showing high phospho-CREB levels being more sensitive than those with lower phospho-CREB levels.

Together, these in vitro findings support an important role for CREB in the survival of ALL cells and identify this transcription factor as a potential target for treatment.

Signaling and molecular basis of bone marrow niche angiogenesis in leukemia

Angiogenesis, the process of blood vessel formation, is necessary for tissue survival in normal and pathologic conditions. Increased angiogenesis in BM niche is correlated with leukemia progression and resistance to treatment. Angiogenesis can interfere with disease progression and several angiogenic (such as vascular growth factors) as well as anti-angiogenic factors (i.e. angiostatin) can affect angiogenesis. Furthermore, miRs can affect the angiogenic process by inhibiting angiogenesis or increasing the expression of growth factors. Given the importance of angiogenesis in BM for maintenance of leukemic clones, recognition of angiogenic and anti-angiogenic factors and miRs as well as drug resistance mechanisms of leukemic blasts can improve the therapeutic strategies. We highlight the changes in angiogenic balance within the BM niche in different leukemia types. Moreover, we explored the pathways leading to drug resistance in relation to angiogenesis and attempted to assign interesting candidates for future research.

Can kinomics and proteomics bridge the gap between pediatric cancers and newly designed kinase inhibitors?

The introduction of kinase inhibitors in cancer medicine has transformed chronic myeloid leukemia from a fatal disease into a leukemia subtype with a favorable prognosis by interfering with the constitutively active kinase BCR-ABL. This success story has resulted in the development of multiple kinase inhibitors. We are currently facing significant limitations in implementing these kinase inhibitors into the clinic for the treatment of pediatric malignancies. As many hallmarks of cancer are known to be regulated by intracellular protein signaling networks, we suggest focusing on these networks to improve the implementation of kinase inhibitors. This viewpoint will provide a short overview of currently used strategies for the implementation of kinase inhibitors as well as reasons why kinase inhibitors have unfortunately not yet been widely used for the treatment of pediatric cancers. We argue that by using a future personalized medicine strategy combining kinomics, proteomics, and drug screen approaches, the gap between pediatric cancers and the use of kinase inhibitors may be bridged.

EphB1 Suppression in Acute Myelogenous Leukemia: Regulating the DNA Damage Control System

Loss of ephrin receptor (EphB1) expression may associate with aggressive cancer phenotypes; however, the mechanism of action remains unclear. To gain detailed insight into EphB1 function in acute myelogenous leukemia (AML), comprehensive analysis of EphB1 transcriptional regulation was conducted. In AML cells, EphB1 transcript was inversely correlated with EphB1 promoter methylation. The presence of EphB1 allowed EfnB1 ligand-mediated p53 DNA binding, leading to restoration of the DNA damage response (DDR) cascade by the activation of ATR, Chk1, p53, p21, p38, CDK1(tyr15), and Bax, and downregulation of HSP27 and Bcl2. Comparatively, reintroduction of EphB1 expression in EphB1-methylated AML cells enhanced the same cascade of ATR, Chk1, p21, and CDK1(tyr15), which consequently enforced programmed cell death. Interestingly, in pediatric AML samples, EphB1 peptide phosphorylation and mRNA expression were actively suppressed as compared with normal bone marrow, and a significant percentage of the primary AML specimens had EphB1 promoter hypermethylation. Finally, EphB1 repression associated with a poor overall survival in pediatric AML. Combined, the contribution of EphB1 to the DDR system reveals a tumor-suppressor function for EphB1 in pediatric AML.

IMPLICATIONS

The tumor-suppressor function of EphB1 is clinically relevant across many malignancies, suggesting that EphB1 is an important regulator of common cancer cell transforming pathways.

Growth-factor-driven rescue to receptor tyrosine kinase (RTK) inhibitors through Akt and Erk phosphorylation in pediatric low grade astrocytoma and ependymoma

Up to now, several clinical studies have been started investigating the relevance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, single targeted kinase inhibition failed, possibly due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth factor receptor (VEGFR)-2, platelet derived growth factor receptor (PDGFR)β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potentially drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue. This was investigated in pediatric low grade astrocytoma and ependymoma cell lines treated with receptor tyrosine kinase (RTK) inhibitors e.g. sorafenib, dasatinib, canertinib and crizotinib. Flow cytometry analyses showed high percentage of cells expressing VEGFR-1, fibroblast growth factor receptor (FGFR)-1, ErbB1/EGFR, HGFR and recepteur d’origine nantais (RON) (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%). Their respective inhibitors induced decrease of cell viability, measured with WST-1 cell viability assays. At least this was partially due to increased apoptotic levels measured by Annexin V/Propidium Iodide apoptosis assays. EGF, HGF and FGF, which are normally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue). Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by significantly activating downstream Akt and/or Erk phosphorylation and increased tumor cell migration. Combination treatment showed to be able to overcome the growth-factor-driven rescue. In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing tumor escape towards RTK inhibitors in pediatric low grade astrocytoma and ependymoma. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in these pediatric brain tumors.

Abstract B4: Growth-factor-driven rescue to receptor tyrosine kinase inhibitors in pediatric low-grade astrocytoma and ependymoma

Introduction: Brain tumors are still the leading cause of cancer morbidity and mortality among children, despite different therapeutic options including neurosurgery, chemotherapy and radiation. Up to now, several clinical studies have been started investigating the importance of receptor tyrosine kinase (RTK) inhibitors upon progression free survival in various pediatric brain tumors. However, it has been shown that single targeted kinase inhibition failed due to tumor resistance mechanisms. The present study will extend our previous observations that vascular endothelial growth receptor (VEGFR) 2, platelet derived growth factor receptor (PDGFR) β, Src, the epidermal growth factor receptor (ErbB) family, and hepatocyte growth factor receptor (HGFR/cMet) are potential drugable targets in pediatric low grade astrocytoma and ependymoma with investigations concerning growth-factor-driven rescue.

Material and methods: Expression of various RTKs in pediatric low grade astrocytoma (Res-186, Res-259, UW-467) and ependymoma (Res-196) cell lines were determined using flow cytometry analyses. Growth-factor-driven rescue during RTK inhibition with agents including sorafenib, dasatinib, canertinib and crizotinib were analyzed on cell viability level measured with WST-1 cell viability assays and on phosphorylation level of the crucial downstream PI3K/Akt and MAPK/Erk survival signaling pathways using western blot analyses.

Results: VEGFR-1, fibroblast growth factor receptor (FGFR) 1, ErbB-1, HGFR and recepteur d'origine nantais (RON) were highly expressed (respectively 52-77%, 34-51%, 63-90%, 83-98%, 65-95%) and their respective inhibitors showed induced decrease of tumor cell viability. EGF, HGF and FGF, which are normally environmentally expressed in brain (tumor) tissue, showed to be effective rescue inducing growth factors resulting in increased cell survival especially during treatment with dasatinib (complete rescue) or sorafenib (partial rescue) in both low grade astrocytoma and ependymoma. Growth-factor-driven rescue was less prominent when canertinib or crizotinib were used. Rescue was underscored by activating downstream Akt and/or Erk phosphorylation. Combination treatment showed to be able to overcome the growth-factor-driven resistance.

Conclusions: In conclusion, our study highlights the extensive importance of environmentally present growth factors in developing resistance towards RTK inhibitors. It is of great interest to anticipate upon these results for the design of new therapeutic trials with RTK inhibitors in pediatric low grade astrocytoma and ependymoma.

Citation Format: Mariska Sie, Wilfred F.A. den Dunnen, Harm Jan Lourens, Tiny G.J. Meeuwsen-de Boer, Frank J.G. Scherpen, Kim R. Kampen, Eelco W. Hoving, Eveline S.J.M. de Bont. Growth-factor-driven rescue to receptor tyrosine kinase inhibitors in pediatric low-grade astrocytoma and ependymoma. [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 B4.

Abstract 2772: Inhibition of EGFR activity reduces AML cell survival via inhibition of downstream Akt and Erk signaling pathways

Epidermal growth factor receptor (EGFR) inhibitor erlotinib, has been shown to induce complete remission of acute myeloid leukemia (AML) in two patients with concurrent lung cancer, suggesting a prominent role for EGFR in AML. However, EGFR expression analysis in AML is poorly defined and the role of EGFR in AML is still unclear.

In this study, we determined the EGFR protein expression in different human AML cell lines and studied the impact of EGFR inhibition by canertinib on the AML cell survival, proliferation, apoptosis and their downstream signaling routes. Using flowcytometry, we have shown that total EGFR as well as the phosphorylated residue Tyr1068 is expressed in five out of the eight AML cell lines (range of 4.9-46.6% for total and phosphorylated EGFR). EGFR phosphorylation was found to be induced by EGF stimulation, which could be prevented by canertinib treatment, showing functional activity and specificity of the EGFR phosphorylation site. Canertinib was shown to decrease the AML cell survival sufficiently (at a median IC50 of 6.2 μM, range: 0.9 - 15.2 μM canertinib in n=8 AML cell lines) as measured by WST-1 assays. The lower cell survival was the net result of lower numbers of mitotic phospho-histone H3 positive cells and an increase in the number of Annexin V positive cells. Immunoblot analysis revealed that canertinib treatment (5uM) reduced the phosphorylation of Akt and Erk intracellular proteins downstream of the EGFR signaling pathway in AML cells. Long-term canertinib treatment (5uM) showed that downstream targets were re-activated after 24 hours, which suggest kinomic reprogramming by alternative escape mechanisms compensating for the loss of EGFR activity. These findings suggest encouraging possibilities for targeting EGFR as a therapeutic strategy in AML. Future studies are necessary to determine the exact mechanism through which EGFR activity might contribute to AML progression, relapses as well as to interact with possible escape mechanisms of AML cells.

Citation Format: Ellen R. Scheepers, Kim R. Kampen, Eveline SJM de Bont. Inhibition of EGFR activity reduces AML cell survival via inhibition of downstream Akt and Erk signaling pathways. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2772. doi:10.1158/1538-7445.AM2013-2772

EphB2 activity plays a pivotal role in pediatric medulloblastoma cell adhesion and invasion

Eph/ephrin signaling has been implicated in various types of key cancer-enhancing processes, like migration, proliferation, and angiogenesis. In medulloblastoma, invading tumor cells characteristically lead to early recurrence and a decreased prognosis. Based on kinase-activity profiling data published recently, we hypothesized a key role for the Eph/ephrin signaling system in medulloblastoma invasion. In primary medulloblastoma samples, a significantly higher expression of EphB2 and the ligand ephrin-B1 was observed compared with normal cerebellum. Furthermore, medulloblastoma cell lines showed high expression of EphA2, EphB2, and EphB4. Stimulation of medulloblastoma cells with ephrin-B1 resulted in a marked decrease in in vitro cell adhesion and an increase in the invasion capacity of cells expressing high levels of EphB2. The cell lines that showed an ephrin-B1-induced phenotype possessed increased levels of phosphorylated EphB2 and, to a lesser extent, EphB4 after stimulation. Knockdown of EphB2 expression by short hairpin RNA completely abolished ephrin ligand-induced effects on adhesion and migration. Analysis of signal transduction identified p38, Erk, and mTOR as downstream signaling mediators potentially inducing the ephrin-B1 phenotype. In conclusion, the observed deregulation of Eph/ephrin expression in medulloblastoma enhances the invasive phenotype, suggesting a potential role in local tumor cell invasion and the formation of metastases.

Vascular endothelial growth factor signaling in acute myeloid leukemia

This review is designed to provide an overview of the current literature concerning vascular endothelial growth factor signaling (VEGF) in acute myeloid leukemia (AML). Aberrant VEGF signaling operates in the bone marrow of AML patients and is related to a poor prognosis. The altered signaling pathway demonstrated to interfere in several autocrine and paracrine signaling pathways. VEGF signaling promotes autocrine AML blast cell proliferation, survival, and chemotherapy resistance. In addition, VEGF signaling can mediate paracrine vascular endothelial cell-controlled angiogenesis in AML. Both effects presumably explain the association of high VEGF levels and poor therapeutic outcome. More recently, researches focusing on bone marrow stem cell niches demonstrate a role for VEGF signaling in the preservation of several cell types within these niches. The bone marrow niches are proposed to be a protective microenvironment for AML cells that could be responsible for relapses in AML patients. This implies the need of sophisticated VEGF-targeted therapeutics in AML therapy strategies. This review highlights our current understanding of aberrant VEGF signaling in AML, appoints the interference of VEGF signaling in the AML-associated microenvironment, and reflects the novelty of current VEGF-targeted therapeutics used in clinical trails for the treatment of AML.

Abstract 1974: EphB2 signaling activity plays a vital role in medulloblastoma cell adhesion and invasion

Eph/ephrin signaling has been implicated in various types of cancer, enhancing key processes like migration, proliferation and angiogenesis. In medulloblastoma, invading tumor cells characteristically lead to early recurrence and a decreased prognosis. Based on kinase activity profiling data published recently we hypothesized on a key function of the Eph/ephrin signaling system in medulloblastoma invasion.

In a panel of medulloblastoma cell lines a limited subset of Eph receptors was found to be expressed of which EphB2 was the most predominant. Furthermore, a significantly higher expression of EphB2 and its ligands ephrin-B1 and ephrin-B3 was observed in medulloblastoma patient tissue compared to normal cerebellum. To determine the relative importance of the EphB and EphA receptor families, 3 medulloblastoma cell lines (Daoy, Uw-402, Res-256) were stimulated with either ephrin-A1 or ephrin-B1 followed by assessment of the migration and adhesion capacity of the cells. Upon stimulation with ephrin-A1 no phenotype could be observed. However, stimulation with ephrin-B1 resulted in a marked increase in migration capacity of Daoy and, to a lesser extent, Uw-402 in concentrations as low as 0.2 ug/mL. The adhesion capacity of these cell lines upon stimulation with ephrin-B1 was determined employing collagen and laminin coated culture dishes. Again, no effects could be observed on Res-256 whereas the adhesive capacity of Daoy and Uw-402 decreased significantly. In addition, stable transfection of Daoy medulloblastoma cells with shRNA against EphB2 significantly reduced the ephrin-B1 induced effects on tumor cell adhesion.

The observed differences in the effects of EphB receptor stimulation correspond with the expression levels of EphB2 in the cell lines. Furthermore, a substantial increase of EphB2 and EphB4 phosphorylation could be observed for Daoy and to a lesser extent Uw-402. Res-256 had a low mRNA expression of EphB2 and B4 and also showed no increase in phosphorylation of these receptors upon stimulation. Interestingly, the increase in phosphorylated EphB2 and EphB4 is accompanied by a sharp decrease in EGFR phosphorylation. Possibly this plays a role in the ephrin-B1 induced effects, as has been reported recently for ephrin-A5 in glioblastoma.

Recent studies report an epigenetic regulation by hypermethylation of Eph/ephrin family gene expression in acute lymphoblastic leukemia. To assess the presence of epigenetic regulation of EphB receptor expression in medulloblastoma we treated the medulloblastoma cell lines with the demethylating agent 5-aza-2′-deoxycytidine. This resulted in a substantial increase in expression of all EphB type receptors in Daoy.

In conclusion, our results indicate a selective Eph expression profile in favor of medulloblastoma invasion. Furthermore, the expression of Eph receptors is regulated, at least in part, through DNA methylation.

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 1974. doi:10.1158/1538-7445.AM2011-1974

Vascular Endothelial Growth Factor A isoform mRNA expression in pediatric acute myeloid leukemia

In AML high VEGFA protein expression correlates with poor overall and relapse-free survival (OS/RFS). To date, the relevance of the various VEGFA isoforms is unclear. We determined VEGF121, VEGF145, VEGF148, VEGF165, VEGF183, and VEGF189 mRNA expression in pediatric AML samples and investigated the relation between VEGFA isoform expression and clinicopatholologic characteristics and outcome. A significant co-expression of VEGF121, VEGF165, VEGF183, and VEGF189 isoforms was apparent (mean rho = 0.716, P < 0.0001). This co-expression justifies measuring a single VEGFA isoform (e.g., 121, 165, 183, and 189) as representative expression of all VEGFA isoforms in future studies designed to determine the prognostic importance of VEGFA isoforms.

Identification of new possible targets for leukemia treatment by kinase activity profiling

To date, the biology of acute leukemia has been unclear, and defining new therapeutic targets without prior knowledge remains complicated. The use of high-throughput techniques would enable us to learn more about the biology of the disease, and make it possible to directly assess a broader range of therapeutic targets. In this study we have identified comprehensive tyrosine kinase activity profiles in leukemia samples using the PamChip® kinase activity profiling system. Strikingly, 31% (44/120) of the detected peptides were active in all three groups of leukemia samples. The recently reported activity of platelet-derived growth factor receptor (PDGFR) and neurotrophic tyrosine kinase receptors (NTRK1 and NTRK2) in leukemia could be appreciated in our array results. In addition, high levels of peptide phosphorylation were demonstrated for peptides related to macrophage stimulating 1 receptor (MST1R). A provisional signal transduction scheme of the common active peptides was constructed and used to specifically select an inhibitor for leukemic blast cell survival assays. As expected, a dose-dependent decrease in leukemic blast cell survival was achieved for all leukemia samples. Our data demonstrate that kinase activity profiling in leukemic samples is feasible and provides novel insights into the pathogenesis of leukemia. This approach can be used for the rapid discovery of potential drug targets.