Group-specific cellular metabolism in Medulloblastoma.

BACKGROUND: Cancer metabolism influences multiple aspects of tumorigenesis and causes diversity across malignancies. Although comprehensive research has extended our knowledge of molecular subgroups in medulloblastoma (MB), discrete analysis of metabolic heterogeneity is currently lacking. This study seeks to improve our understanding of metabolic phenotypes in MB and their impact on patients' outcomes. METHODS: Data from four independent MB cohorts encompassing 1,288 patients were analysed. We explored metabolic characteristics of 902 patients (ICGC and MAGIC cohorts) on bulk RNA level. Moreover, data from 491 patients (ICGC cohort) were searched for DNA alterations in genes regulating cell metabolism. To determine the role of intratumoral metabolic differences, we examined single-cell RNA-sequencing (scRNA-seq) data from 34 additional patients. Findings on metabolic heterogeneity were correlated to clinical data. RESULTS: Established MB groups exhibit substantial differences in metabolic gene expression. By employing unsupervised analyses, we identified three clusters of group 3 and 4 samples with distinct metabolic features in ICGC and MAGIC cohorts. Analysis of scRNA-seq data confirmed our results of intertumoral heterogeneity underlying the according differences in metabolic gene expression. On DNA level, we discovered clear associations between altered regulatory genes involved in MB development and lipid metabolism. Additionally, we determined the prognostic value of metabolic gene expression in MB and showed that expression of genes involved in metabolism of inositol phosphates and nucleotides correlates with patient survival. CONCLUSION: Our research underlines the biological and clinical relevance of metabolic alterations in MB. Thus, distinct metabolic signatures presented here might be the first step towards future metabolism-targeted therapeutic options.

A Carboxy-terminal Smarcb1 Point Mutation Induces Hydrocephalus Formation and Affects AP-1 and Neuronal Signalling Pathways in Mice.

The BAF (BRG1/BRM-associated factor) chromatin remodelling complex is essential for the regulation of DNA accessibility and gene expression during neuronal differentiation. Mutations of its core subunit SMARCB1 result in a broad spectrum of pathologies, including aggressive rhabdoid tumours or neurodevelopmental disorders. Other mouse models have addressed the influence of a homo- or heterozygous loss of Smarcb1, yet the impact of specific non-truncating mutations remains poorly understood. Here, we have established a new mouse model for the carboxy-terminal Smarcb1 c.1148del point mutation, which leads to the synthesis of elongated SMARCB1 proteins. We have investigated its impact on brain development in mice using magnetic resonance imaging, histology, and single-cell RNA sequencing. During adolescence, Smarcb11148del/1148del mice demonstrated rather slow weight gain and frequently developed hydrocephalus including enlarged lateral ventricles. In embryonic and neonatal stages, mutant brains did not differ anatomically and histologically from wild-type controls. Single-cell RNA sequencing of brains from newborn mutant mice revealed that a complete brain including all cell types of a physiologic mouse brain is formed despite the SMARCB1 mutation. However, neuronal signalling appeared disturbed in newborn mice, since genes of the AP-1 transcription factor family and neurite outgrowth-related transcripts were downregulated. These findings support the important role of SMARCB1 in neurodevelopment and extend the knowledge of different Smarcb1 mutations and their associated phenotypes.

Smarcb1 Loss Results in a Deregulation of esBAF Binding and Impacts the Expression of Neurodevelopmental Genes.

The murine esBAF complex plays a major role in the regulation of gene expression during stem cell development and differentiation. As one of its core subunits, Smarcb1 is indispensable for its function and its loss is connected to neurodevelopmental disorders and participates in the carcinogenesis of entities such as rhabdoid tumours. We explored how Smarcb1 regulates gene programs in murine embryonic stem cells (mESC) and in this way orchestrates differentiation. Our data underline the importance of Smarcb1 expression and function for the development of the nervous system along with basic cellular functions, such as cell adhesion and cell organisation. Using ChIP-seq, we were able to portray the consequences of Smarcb1 knockdown (kd) for the binding of esBAF and PRC2 as well as its influence on histone marks H3K27me3, H3K4me3 and H3K27ac. Their signals are changed in gene and enhancer regions of genes connected to nervous system development and offers a plausible explanation for changes in gene expression. Further, we describe a group of genes that are, despite increased BAF binding, suppressed after Smarcb1 kd by mechanisms independent of PRC2 function.

Splice variants denote differences between a cancer stem cell side population of EWSR1­ERG­based Ewing sarcoma cells, its main population and EWSR1­FLI­based cells.

Ewing sarcoma is a challenging cancer entity, which, besides the characteristic presence of a fusion gene, is driven by multiple alternative splicing events. So far, splice variants in Ewing sarcoma cells were mainly analyzed for EWSR1­FLI1. The present study provided a comprehensive alternative splicing study on CADO­ES1, an Ewing model cell line for an EWSR1­ERG fusion gene. Based on a well­-characterized RNA­sequencing dataset with extensive control mechanisms across all levels of analysis, the differential spliced genes in Ewing cancer stem cells were ATP13A3 and EPB41, while the main population was defined by ACADVL, NOP58 and TSPAN3. All alternatively spliced genes were further characterized by their Gene Ontology (GO) terms and by their membership in known protein complexes. These results confirm and extend previous studies towards a systematic whole­transcriptome analysis. A highlight is the striking segregation of GO terms associated with five basic splice events. This mechanistic insight, together with a coherent integration of all observations with prior knowledge, indicates that EWSR1­ERG is truly a close twin to EWSR1­FLI1, but still exhibits certain individuality. Thus, the present study provided a measure of variability in Ewing sarcoma, whose understanding is essential both for clinical procedures and basic mechanistic insight.

The Receptor Tyrosine Kinase RON and Its Isoforms as Therapeutic Targets in Ewing Sarcoma.

The receptor tyrosine kinase (RTK) RON is linked to an aggressive metastatic phenotype of carcinomas. While gaining interest as a therapeutic target, RON remains unstudied in sarcomas. In Ewing sarcoma, we identified RON among RTKs conferring resistance to insulin-like growth factor-1 receptor (IGF1R) targeting. Therefore, we explored RON in pediatric sarcoma cell lines and an embryonic Tg(kdrl:mCherry) zebrafish model, using an shRNA-based approach. To examine RON-IGF1R crosstalk, we employed the clinical-grade monoclonal antibody IMC-RON8, alone and together with the IGF1R-antibody IMC-A12. RON silencing demonstrated functions in vitro and in vivo, particularly within micrometastatic cellular capacities. Signaling studies revealed a unidirectional IGF1-mediated cross-activation of RON. Yet, IMC-A12 failed to sensitize cells to IMC-RON8, suggesting additional mechanisms of RON activation. Here, RT-PCR revealed that childhood sarcomas express short-form RON, an isoform resistant to antibody-mediated targeting. Interestingly, in contrast to carcinomas, treatment with DNA methyltransferase inhibitor did not diminish but increased short-form RON expression. Thus, this first report supports a role for RON in the metastatic progression of Ewing sarcoma. While principal molecular functions appear transferrable between carcinomas, Ewing sarcoma and possibly more common sarcoma subtypes, RON highlights that specific regulations of cellular networks and isoforms require better understanding to successfully transfer targeting strategies.

Defining a Characteristic Gene Expression Set Responsible for Cancer Stem Cell-Like Features in a Sub-Population of Ewing Sarcoma Cells CADO-ES1.

One of the still open questions in Ewing sarcoma, a rare bone tumor with weak therapeutic options, is to identify the tumor-driving cell (sub) population and to understand the specifics in the biological network of these cells. This basic scientific insight might foster the development of more specific therapeutic target patterns. The experimental approach is based on a side population (SP) of Ewing cells, based on the model cell line CADO-ES1. The SP is established by flow cytometry and defined by the idea that tumor stem-like cells can be identified by the time-course in clearing a given artificial dye. The SP was characterized by a higher colony forming activity, by a higher differentiation potential, by higher resistance to cytotoxic drugs, and by morphology. Several SP and non-SP cell fractions and bone marrow-derived mesenchymal stem cell reference were analyzed by short read sequencing of the full transcriptome. The double-differential analysis leads to an altered expression structure of SP cells centered around the AP-1 and APC/c complex. The SP cells share only a limited proportion of the full mesenchymal stem cell stemness set of genes. This is in line with the expectation that tumor stem-like cells share only a limited subset of stemness features which are relevant for tumor survival.

Suberanilohydroxamic acid (vorinostat) synergistically enhances the cytotoxicity of doxorubicin and cisplatin in osteosarcoma cell lines.

Osteosarcoma is the most common primary bone cancer in children and is a highly malignant disease, in which 25% of patients present with metastasis at diagnosis. Considerable advances in the treatment of localized disease have been achieved since the introduction of combined modality treatment, increasing the prognosis of overall survival to 70%. Yet, established therapies have only limited success in treating both metastatic disease and nonresponders to primary chemotherapy. Therefore, new therapeutic approaches are required, particularly for the control of osteosarcoma in these patient groups. Epigenetically modifying substances are a class of emerging drugs that have shown therapeutic potential in various hematological and solid cancers. We examined the cytotoxic effects of 5-azacitidine, 3-deazaneplanocin A, and suberanilohydroxamic acid (SAHA) on osteosarcoma cell lines HOS, MG-63, MNNG, and ZK-58. SAHA was the only chemical agent that exerted a strong, growth-limiting effect in all cell lines tested. The growth-limiting effect of SAHA was accompanied by features characteristic of apoptotic death. We found that cotreatment with SAHA and cisplatin showed strong synergism in all cell lines. The effect of cotreatment with SAHA and doxorubicin was cell line dependent. In the cell lines HOS, MG-63, and MNNG, the combined effect was synergistic, whereas in the cell line ZK-58, SAHA antagonized doxorubicin. The strong synergism of SAHA indicated that in combination with cisplatin, it might enable a promising add-on to current therapy regimens. However, considering the cell line-dependent effect that was found when SAHA was combined with doxorubicin, further experimentation is needed.

Suberoylanilide hydroxamic acid synergistically enhances the antitumor activity of etoposide in Ewing sarcoma cell lines.

Ewing sarcomas (ES) are highly malignant tumors arising in bone and soft tissues. Given the poor outcome of affected patients with primary disseminated disease or at relapse, there is a clear need for new targeted therapies. The HDAC inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA, Vorinostat) inhibits ES tumor growth and induces apoptosis in vitro and in vivo. Thus, SAHA may be considered a novel treatment. However, it is most likely that not a single agent but a combination of agents with synergistic mechanisms will help improve the prognosis in high-risk ES patients. Therefore, the aim of the present study was to assess a putative synergistic effect of SAHA in combination with conventional chemotherapeutic agents. The antitumor activity of SAHA in combination with conventional chemotherapeutics (doxorubicin, etoposide, rapamycin, topotecan) was assessed using an MTT cell proliferation assay on five well-characterized ES cell lines (CADO-ES-1, RD-ES, TC-71, SK-ES-1, SK-N-MC) and a newly established ES cell line (DC-ES-15). SAHA antagonistically affected the antiproliferative effect of doxorubicin and topotecan in the majority of the ES cell lines, but synergistically enhanced the antiproliferative activity of etoposide. In functional analyses, pretreatment with SAHA significantly increased the effects of etoposide on apoptosis and clonogenicity. The in-vitro analyses presented in this work show that SAHA synergistically enhances the antitumor activity of etoposide in ES cells. Sequential treatment with etoposide combined with SAHA may represent a new therapeutic approach in ES.

Kinetics of porphyrin fluorescence accumulation in pediatric brain tumor cells incubated in 5-aminolevulinic acid.

BACKGROUND: Fluorescence-guided surgery with 5-aminolevulinic acid (5-ALA) enables more complete resections of tumors in adults. 5-ALA elicits accumulation of fluorescent porphyrins in various cancerous tissues, which can be visualized using a modified neurosurgical microscope with blue light. Although this technique is well established in adults, it has not been investigated systematically in pediatric brain tumors. Specifically, it is unknown how quickly, how long, and to what extent various pediatric tumors accumulate fluorescence. The purpose of this study was to determine utility and time course of 5-ALA-induced fluorescence in typical pediatric brain tumors in vitro. METHODS: Cell cultures of medulloblastoma [DAOY and UW228], cPNET [PFSK] atypical teratoid rhabdoid tumor [BT16] and ependymoma [RES196] were incubated with 5-ALA for either 60 minutes or continuously. Porphyrin fluorescence intensities were determined using a fluorescence-activated cell sorter (FACS) after 1, 3, 6, 9, 12 and 24 hours. C6 and U87 cells served as controls. RESULTS: All pediatric brain tumor cell lines displayed fluorescence compared to their respective controls without 5-ALA (p < 0.05). Sixty minutes of incubation resulted in peaks between 3 and 6 hours, whereas continuous incubation resulted in peaks at 12 hours or beyond. 60 minute incubation peak levels were between 52 and 91 % of maxima achieved with continuous incubation. Accumulation and clearance varied between cell types. CONCLUSIONS: We demonstrate that 5-ALA exposure of cell lines derived from typical pediatric central nervous system (CNS) tumors induces accumulation of fluorescent porphyrins. Differences in uptake and clearance indicate that different application modes may be necessary for fluorescence-guided resection, depending on tumor type.

Arsenic trioxide inhibits tumor cell growth in malignant rhabdoid tumors in vitro and in vivo by targeting overexpressed Gli1.

Rhabdoid tumors are highly aggressive tumors occurring in infants and very young children. Despite multimodal and intensive therapy prognosis remains poor. Molecular analyses have uncovered several deregulated pathways, among them the CDK4/6-Rb-, the WNT- and the Sonic hedgehog (SHH) pathways. The SHH pathway is activated in rhabdoid tumors by GLI1 overexpression. Here, we demonstrate that arsenic trioxide (ATO) inhibits tumor cell growth of malignant rhabdoid tumors in vitro and in a mouse xenograft model by suppressing Gli1. Our data uncover ATO as a promising therapeutic approach to improve prognosis for rhabdoid tumor patients.

A Novel Role of IGF1 in Apo2L/TRAIL-Mediated Apoptosis of Ewing Tumor Cells.

Insulin-like growth factor 1 (IGF1) reputedly opposes chemotoxicity in Ewing sarcoma family of tumor (ESFT) cells. However, the effect of IGF1 on apoptosis induced by apoptosis ligand 2 (Apo2L)/tumor necrosis factor (TNF-) related apoptosis-inducing ligand (TRAIL) remains to be established. We find that opposite to the partial survival effect of short-term IGF1 treatment, long-term IGF1 treatment amplified Apo2L/TRAIL-induced apoptosis in Apo2L/TRAIL-sensitive but not resistant ESFT cell lines. Remarkably, the specific IGF1 receptor (IGF1R) antibody α-IR3 was functionally equivalent to IGF1. Short-term IGF1 incubation of cells stimulated survival kinase AKT and increased X-linked inhibitor of apoptosis (XIAP) protein which was associated with Apo2L/TRAIL resistance. In contrast, long-term IGF1 incubation resulted in repression of XIAP protein through ceramide (Cer) formation derived from de novo synthesis which was associated with Apo2L/TRAIL sensitization. Addition of ceramide synthase (CerS) inhibitor fumonisin B1 during long-term IGF1 treatment reduced XIAP repression and Apo2L/TRAIL-induced apoptosis. Noteworthy, the resistance to conventional chemotherapeutic agents was maintained in cells following chronic IGF1 treatment. Overall, the results suggest that chronic IGF1 treatment renders ESFT cells susceptible to Apo2L/TRAIL-induced apoptosis and may have important implications for the biology as well as the clinical management of refractory ESFT.

EZH2 is a mediator of EWS/FLI1 driven tumor growth and metastasis blocking endothelial and neuro-ectodermal differentiation.

Ewing tumors (ET) are highly malignant, localized in bone or soft tissue, and are molecularly defined by ews/ets translocations. DNA microarray analysis revealed a relationship of ET to both endothelium and fetal neural crest. We identified expression of histone methyltransferase enhancer of Zeste, Drosophila, Homolog 2 (EZH2) to be increased in ET. Suppressive activity of EZH2 maintains stemness in normal and malignant cells. Here, we found EWS/FLI1 bound to the EZH2 promoter in vivo, and induced EZH2 expression in ET and mesenchymal stem cells. Down-regulation of EZH2 by RNA interference in ET suppressed oncogenic transformation by inhibiting clonogenicity in vitro. Similarly, tumor development and metastasis was suppressed in immunodeficient Rag2(-/-)gamma(C)(-/-) mice. EZH2-mediated gene silencing was shown to be dependent on histone deacetylase (HDAC) activity. Subsequent microarray analysis of EZH2 knock down, HDAC-inhibitor treatment and confirmation in independent assays revealed an undifferentiated phenotype maintained by EZH2 in ET. EZH2 regulated stemness genes such as nerve growth factor receptor (NGFR), as well as genes involved in neuroectodermal and endothelial differentiation (EMP1, EPHB2, GFAP, and GAP43). These data suggest that EZH2 might have a central role in ET pathology by shaping the oncogenicity and stem cell phenotype of this tumor.

S100A2 induces metastasis in non-small cell lung cancer.

PURPOSE: S100 proteins are implicated in metastasis development in several cancers. In this study, we analyzed the prognostic role of mRNA levels of all S100 proteins in early stage non-small cell lung cancer (NSCLC) patients as well as the pathogenetic of S100A2 in the development of metastasis in NSCLC. EXPERIMENTAL DESIGN: Microarray data from a large NSCLC patient cohort was analyzed for the prognostic role of S100 proteins for survival in surgically resected NSCLC. Metastatic potential of the S100A2 gene was analyzed in vitro and in a lung cancer mouse model in vivo. Overexpression and RNAi approaches were used for analysis of the biological functions of S100A2. RESULTS: High mRNA expression levels of several S100 proteins and especially S100A2 were associated with poor survival in surgically resected NSCLC patients. Upon stable transfection into NSCLC cell lines, S100A2 did not alter proliferation. However, S100A2 enhanced transwell migration as well as transendothelial migration in vitro. NOD/SCID mice injected s.c. with NSCLC cells overexpressing S100A2 developed significantly more distant metastasis (64%) than mice with control vector transfected tumor cells (17%; P < 0.05). When mice with S100A2 expressing tumors were treated i.v. with shRNA against S100A2, these mice developed significantly fewer lung metastasis than mice treated with control shRNA (P = 0.021). CONCLUSIONS: These findings identify S100A2 as a strong metastasis inducer in vivo. S100A2 might be a potential biomarker as well as a novel therapeutic target in NSCLC metastasis.

In childhood acute lymphoblastic leukemia, blasts at different stages of immunophenotypic maturation have stem cell properties.

We examined the leukemic stem cell potential of blasts at different stages of maturation in childhood acute lymphoblastic leukemia (ALL). Human leukemic bone marrow was transplanted intrafemorally into NOD/scid mice. Cells sorted using the B precursor differentiation markers CD19, CD20, and CD34 were isolated from patient samples and engrafted mice before serial transplantation into primary or subsequent (up to quaternary) recipients. Surprisingly, blasts representative of all of the different maturational stages were able to reconstitute and reestablish the complete leukemic phenotype in vivo. Sorted blast populations mirrored normal B precursor cells with transcription of a number of stage-appropriate genes. These observations inform a model for leukemia-propagating stem cells in childhood ALL.

Adjuvant therapy with small hairpin RNA interference prevents non-small cell lung cancer metastasis development in mice.

Development of distant metastasis is the major reason for cancer-related deaths worldwide. Adjuvant therapy approaches after local therapies are most effective when specific targets are inhibited. Recently, we identified S100P overexpression as a strong predictor for metastasis development in early-stage non-small cell lung cancer (NSCLC) patients. Here, we show that S100P overexpression increased angiogenesis in and metastasis formation from s.c. xenotransplants of NSCLC cells. Plasmid-derived short hairpin RNAs (shRNA) were developed as specific adjuvant therapy. I.v. injected shRNA against S100P significantly decreased S100P protein expression in xenograft tumors and inhibited tumor angiogenesis in vivo. Metastasis formation 8 weeks after primary tumor resection was significantly reduced. Lung metastases developed in 31% of mice treated with S100P-targeting shRNAs compared with 64% in control shRNA-treated mice (P < 0.05). These findings suggest that RNA interference-based therapy approaches can be highly effective in the adjuvant setting.

Successful high-resolution animal positron emission tomography of human Ewing tumours and their metastases in a murine xenograft model.

PURPOSE: As primary osseous metastasis is the main adverse prognostic factor in patients with Ewing tumours, a NOD/scid mouse model for human Ewing tumour metastases has been established to examine the mechanisms of metastasis. The aim of this study was to evaluate the feasibility of diagnostic molecular imaging by small animal PET in this mouse model. METHODS: Human Ewing tumour cells were transplanted into immune-deficient NOD/scid mice via s.c injection (n=17) or i.v. injection (n=17). The animals (mean weight 23.2 g) were studied 2-7 weeks after transplantation using a submillimetre resolution animal PET scanner. To assess glucose utilisation and bone metabolism, mice were scanned after intravenous injection of 9.6 MBq (mean) 2-[(18)F]fluoro-2-deoxy-D: -glucose (FDG) or 9.4 MBq (mean) [(18)F]fluoride. Whole-body PET images were analysed visually and semi-quantitatively [%ID/g, tumour to non-tumour ratio (T/NT)]. Foci of pathological uptake were identified with respect to the physiological organ uptake in corresponding regions. RESULTS: Subcutaneously transplanted Ewing tumours demonstrated a moderately increased glucose uptake (median %ID/g 2.5; median T/NT 2.2). After i.v. transplantation, the pattern of metastasis was similar to that in patients with metastases in lung, bone and soft tissue. These metastases showed an increased FDG uptake (median %ID/g 3.6; median T/NT 2.7). Osseous metastases were additionally visible on [(18)F]fluoride PET by virtue of decreased [(18)F]fluoride uptake (osteolysis; median %ID/g 8.4; median T/NT 0.59). Metastases were confirmed immunohistologically. CONCLUSION: Diagnostic molecular imaging of Ewing tumours and their small metastases in an in vivo NOD/scid mouse model is feasible using a submillimetre resolution PET scanner.

Synthesis and DNA binding properties of novel benzo[b]isoquino[2,3-h]-naphthyridines.

Several benzo[b]isoquino[2,3-h]-naphthyridines have been prepared via formal hetero-Diels Alder reaction of N-aryl imines as a key step. These compounds have different side chains at C-11, and a cis or trans configuration at the C-8a,C-14a ring junction. Binding constants for the interaction with oligonucleotides and polynucleotides were determined by UV absorption and melting experiments. NMR experiments (NOE) revealed that the cis isomers, showing a slightly folded structure, preferentially bind to the minor groove of AT-rich oligomers. In contrast, the trans isomers prefer the CG-rich sequences, leading to cap-complexes with the isoquinoline moiety stacked at the top of the double helix, in agreement with the flatter shape, and with a preference for the 3'-terminals, as found for camptothecins. Models of the complexes were built up by molecular dynamics (MD) calculations, by using the inter-proton distances derived from the NOE values. Cytotoxicity assays against human Ewing sarcoma cell lines RD-ES and CAD-ES1 were performed.

Leukemic stem cells in childhood high-risk ALL/t(9;22) and t(4;11) are present in primitive lymphoid-restricted CD34+CD19- cells.

Open questions in the pathogenesis of childhood acute lymphoblastic leukemia (ALL) are which hematopoietic cell is target of the malignant transformation and whether primitive stem cells contribute to the leukemic clone. Although good-prognosis ALL is thought to originate in a lymphoid progenitor, it is unclear if this applies to high-risk ALL. Therefore, immature CD34(+)CD19(-) bone marrow cells from 8 children with ALL/t(9;22) and 12 with ALL/t(4;11) were purified and analyzed by fluorescence in situ hybridization, reverse transcription-PCR (RT-PCR), and colony assays. Fifty-six percent (n = 8, SD 31%) and 68% (n = 12, SD 26%) of CD34(+)CD19(-) cells in ALL/t(9;22) and ALL/t(4;11), respectively, carried the translocation. In addition, 5 of 168 (3%) and 22 of 228 (10%) myeloerythroid colonies expressed BCR/ABL and MLL/AF4. RT-PCR results were confirmed by sequence analysis. Interestingly, in some patients with ALL/t(4;11), alternative splicing was seen in myeloid progenitors compared with the bulk leukemic population, suggesting that these myeloid colonies might be part of the leukemic cell clone. Fluorescence in situ hybridization analysis, however, shows that none of these myeloid colonies (0 of 41 RT-PCR-positive colonies) originated from a progenitor cell that carries the leukemia-specific translocation. Thus, leukemic, translocation-positive CD34(+)CD19(-) progenitor/stem cells that were copurified by cell sorting were able to survive in these colony assays for up to 28 days allowing amplification of the respective fusion transcripts by sensitive RT-PCR. In conclusion, we show that childhood high-risk ALL/t(9;22) and t(4;11) originate in a primitive CD34(+)CD19(-) progenitor/stem cell without a myeloerythroid developmental potential.

Selective and nonselective toxicity of TRAIL/Apo2L combined with chemotherapy in human bone tumour cells vs. normal human cells.

Although TRAIL/Apo2L preferably induces apoptosis in tumour cells without toxicity in normal cells, many tumour cell types display TRAIL/Apo2L resistance. Whether TRAIL/Apo2L in combination with chemotherapy may overcome TRAIL/Apo2L resistance while maintaining tumour selectivity remains to be determined. Here, we report that while ActD, DOX and CDDP sensitised both OS and Ewing's tumour cell lines and normal cells (hOBs, synovial cells, fibroblasts) to TRAIL/Apo2L-induced apoptosis, the combination of etoposide (VP16) and TRAIL/Apo2L was selectively active on tumour cells without affecting normal cells. Sensitisation of OS cells and hOBs to TRAIL/Apo2L did not correlate with a compatible change in the gene expression profile of the receptors for TRAIL/Apo2L determined by quantitative real-time RT-PCR. Also, sensitisation of the TRAIL/Apo2L death pathway did not rely entirely on the chemotherapy-induced, caspase-dependent cytotoxicity. Further, chemotherapy did not cause a compatible change in expression levels of proteins such as Bcl-2, Bcl-x(L), Bax, cIAP2, XIAP and survivin. However, ActD, DOX and CDDP downregulated expression of cFLIP in OS cells as well as expression of p21 in normal hOBs. Interestingly, while VP16 also extinguished cFLIP in OS cells, which were sensitised for TRAIL/Apo2L by VP16, VP16 induced cFLIP and enhanced p21 levels in normal hOBs, which remained refractory to VP16 plus TRAIL/Apo2L. Together, our data reveal that TRAIL/Apo2L combined with certain chemotherapeutic drugs is toxic to bone tumour and normal human cells and suggest that cotreatment with TRAIL/Apo2L and VP16 provides an attractive approach for selective killing of tumour cells while leaving unaffected normal cells.

c-KIT-expressing Ewing tumour cells are insensitive to imatinib mesylate (STI571).

PURPOSE: In order to determine whether Ewing tumour patients may be potential candidates for imatinib mesylate therapy, we analysed the expression of the currently known imatinib mesylate-sensitive tyrosine kinases and tested sensitivity to imatinib mesylate in a panel of eight Ewing tumour cell lines in vitro. METHODS: Expression of the different tyrosine kinases was assessed by flow cytometry and RT-PCR. Sensitivity to imatinib mesylate was analysed using a standard MTT proliferation assay. RESULTS: Flow cytometric and RT-PCR analyses in a panel of eight Ewing tumour cell lines demonstrated expression of several imatinib mesylate-sensitive tyrosine kinases, including c-KIT, platelet-derived growth factor receptor, c-ABL and c-ARG. However, in the MTT proliferation assay, all eight Ewing tumour cell lines were found to be resistant to imatinib mesylate at concentrations ranging from 0.1 to 10 micro M. CONCLUSIONS: Despite the expression of imatinib mesylate-sensitive tyrosine kinases, Ewing tumour cells proved resistant to imatinib mesylate in vitro. This observation has implications for the selection of patients for experimental therapy with imatinib mesylate.