Malignant Peripheral Nerve Sheath Tumors Cell Research Articles

Ras-Driven Transcriptome Analysis Identifies Aurora Kinase A as a Potential Malignant Peripheral Nerve Sheath Tumor Therapeutic Target

Patients with neurofibromatosis type 1 (NF1) develop malignant peripheral nerve sheath tumors (MPNST), which are often inoperable and do not respond well to current chemotherapies or radiation. The goal of this study was to use comprehensive gene expression analysis to identify novel therapeutic targets. Nerve Schwann cells and/or their precursors are the tumorigenic cell types in MPNST because of the loss of the NF1 gene, which encodes the RasGAP protein neurofibromin. Therefore, we created a transgenic mouse model, CNP-HRas12V, expressing constitutively active HRas in Schwann cells and defined a Ras-induced gene expression signature to drive a Bayesian factor regression model analysis of differentially expressed genes in mouse and human neurofibromas and MPNSTs. We tested functional significance of Aurora kinase overexpression in MPNST in vitro and in vivo using Aurora kinase short hairpin RNAs (shRNA) and compounds that inhibit Aurora kinase. We identified 2,000 genes with probability of linkage to nerve Ras signaling of which 339 were significantly differentially expressed in mouse and human NF1-related tumor samples relative to normal nerves, including Aurora kinase A (AURKA). AURKA was dramatically overexpressed and genomically amplified in MPNSTs but not neurofibromas. Aurora kinase shRNAs and Aurora kinase inhibitors blocked MPNST cell growth in vitro. Furthermore, an AURKA selective inhibitor, MLN8237, stabilized tumor volume and significantly increased survival of mice with MPNST xenografts. Integrative cross-species transcriptome analyses combined with preclinical testing has provided an effective method for identifying candidates for molecular-targeted therapeutics. Blocking Aurora kinases may be a viable treatment platform for MPNST.

Targeting the PI3K/mTOR Axis, Alone and in Combination with Autophagy Blockade, for the Treatment of Malignant Peripheral Nerve Sheath Tumors

There is a critical need for efficacious therapeutic strategies to improve the outcome of patients afflicted by malignant peripheral nerve sheath tumors (MPNST). Multiple lines of evidence suggest a role for deregulated phosphoinositide 3-kinase (PI3K)/mTOR signaling in MPNST, making this axis an attractive target for therapeutic manipulation. On the basis of previous observations obtained from in vitro experimentation, here we aimed to assess the effects of PI3K/mTOR blockade on MPNST growth in vivo. The anti-MPNST impact of XL765, a dual PI3K/mTOR inhibitor currently being evaluated in human cancer clinical trials, was tested in two human MPNST xenograft models (STS26T and MPNST724) and an experimental model of pulmonary metastasis (STS26T). XL765 abrogated human MPNST local and metastatic growth in severe combined immunodeficient mice. Notably, this therapeutic approach failed to induce apoptosis in MPNST cells but rather resulted in marked productive autophagy. Importantly, genetic and pharmacologic autophagy blockade reversed apoptotic resistance and resulted in significant PI3K/mTOR inhibition-induced MPNST cell death. The addition of the autophagy inhibitor, chloroquine, to the therapeutic regimen of MPNST xenografts after pretreatment with XL765 resulted in superior antitumor effects as compared with either agent alone. Together, preclinical studies described here expand our previous findings and suggest that PI3K/mTOR inhibition alone and (most importantly) in combination with autophagy blockade may comprise a novel and efficacious therapy for patients harboring MPNST.

MicroRNA-204 critically regulates carcinogenesis in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas accounting for 3%-10% of all soft tissue sarcomas. Neurofibromatosis type 1 (NF1) is the most important known risk factor. MPNSTs are often diagnosed at an advanced stage when distant metastases have developed. Although surgical resection remains the main treatment for MPNSTs, complete surgical resection is rarely possible. The prognosis for patients with MPNSTs is poor. There is an urgent need for improved therapies. To this end, we investigated whether microRNA (miR), specifically miR-204, might be implicated in MPNSTs because it is located at a cancer-associated genomic region exhibiting high frequency of loss of heterozygosity in tumors. We show that miR-204 expression is downregulated in NF1 and non-NF1 MPNST tumor tissues and in tumor cell lines. Restoring miR-204 expression in MPNST cell lines STS26T (non-NF1), ST88-14 (NF1), and T265p21 (NF1) significantly reduces cellular proliferation, migration, and invasion in vitro. Restoring miR-204 expression in STS26T decreases tumor growth and malignant progression in vivo. We also report that miR-204 inhibits Ras signaling and expression of high mobility group gene A2. These findings support the hypothesis that miR-204 plays critical roles in MPNST development and tumor progression. miR-204 may represent a novel biomarker for diagnosis and a candidate target with which to develop effective therapies for MPNSTs.

Inhibition of Bcl-xL by ABT-737 enhances chemotherapy sensitivity in neurofibromatosis type 1-associated malignant peripheral nerve sheath tumor cells

Neurofibromatosis type 1 (NF1) is one of the most commonly inherited autosomal dominant disorders. The malignant peripheral nerve sheath tumor (MPNST) is a major cause of mortality in patients with NF1. In this study, we found that overexpression of Bcl-xL in the established NF1-associated MPNST cell line and primary tissue cultured MPNST cells derived from an NF1 patient was closely associated with anticancer drug resistance of the NF1-associated MPNST cells. We demonstrated that high expression of Bcl-xL in the MPNST cells was caused by a decreased transcriptional expression of the NF1 gene. Downregulation of the NF1 gene by RNA interference (RNAi) induced an increase in Bcl-xL expression and a decrease in its sensitivity to apoptosis in the benign neurofibroma cell line and primary normal cells. These results suggest that an alteration of Bcl-xL expression levels by somatic expression changes in the NF1 locus may contribute to the malignant development of benign tumor tissues or normal tissues to MPNSTs. We further demonstrated that either depletion of Bcl-xL expression by RNAi or inactivation of Bcl-xL by ABT-737, a mimetic of the BH3-only protein BAD, was very effective in sensitizing the MPNST cells to apoptotic cell death by combined treatment with the tested anticancer drug doxorubicin. Notably, a low concentration of ABT-737 and doxorubicin could effectively induce synergistic cytotoxicity in the MPNST cells. These results suggest that pharmacological inhibition of Bcl-xL by ABT-737 in combination with doxorubicin can be a potential therapeutic strategy for the treatment of NF1-associated MPNSTs.

Survivin Is a Viable Target for the Treatment of Malignant Peripheral Nerve Sheath Tumors

To examine the role of survivin as a therapeutic target in preclinical models of human malignant peripheral nerve sheath tumors (MPNST) EXPERIMENTAL DESIGN: Survivin protein expression levels and subcellular localization were examined immunohistochemically in an MPNST tissue microarray. Human MPNST cells were studied in vitro and in vivo; real-time PCR, Western blotting, and immunocytochemical analyses were used to evaluate survivin expression and localization activation. Cell culture assays were used to evaluate the impact of anti-survivin-specific siRNA inhibition on cell growth and cell-cycle progression and survival. The effect of the small-molecule survivin inhibitor YM155 on local and metastatic MPNST growth was examined in vivo. Survivin was found to be highly expressed in human MPNSTs; enhanced cytoplasmic subcellular localization differentiated MPNSTs from their plexiform neurofibroma premalignant counterparts. Human MPNST cell lines exhibited survivin mRNA and protein overexpression; expression in both nuclear and cytoplasmic compartments was noted. Survivin knockdown abrogated MPNST cell growth, inducing G(2) cell-cycle arrest and marked apoptosis. YM155 inhibited human MPNST xenograft growth and metastasis in severe combined immunodeficient (SCID) mice. Antitumor effects were more pronounced in fast-growing xenografts. Our studies show an important role for survivin in human MPNST biology. Patients with MPNSTs should be considered for ongoing or future clinical trials that evaluate anti-survivin therapeutic strategies. Most importantly, future investigations should evaluate additional pathways that can be targeted in combination with survivin for maximal synergistic anti-MPNST effects.

MicroRNA-21 correlates with tumorigenesis in malignant peripheral nerve sheath tumor (MPNST) via programmed cell death protein 4 (PDCD4)

We investigated the miRNA profile in peripheral nerve tumors and clarified the involvement of miRNA in the development and progression of MPNST in comparison with neurofibroma (NF). In addition, we attempted to seek associations between the miRNA and their potential targets in MPNST. Global miRNA expression profiling was investigated for clinical samples of 6 MPNSTs and 6 NFs. As detected by profiling analysis, the expressions of miR-21 in clinical samples of 12 MPNSTs, 11 NFs, and 5 normal nerves, and 3 MPNST cell lines were compared using quantitative real-time reverse transcription PCR. MPNST cell line (YST-1) was transfected with miR-21 inhibitor to study its effects on cell proliferation, caspase activity, and the expression of miR-21 targets. Analysis of miRNA expression profiles in MPNST and NF revealed significantly altered expression levels of nine miRNAs, one of those, miR-21, and its putative target, programmed cell death protein 4 (PDCD4), were selected for further studies. miR-21 expression level in MPNST was significantly higher than that in NF (P<0.05). In MPNST cells, transfection of miR-21 inhibitor significantly increased caspase activity (P<0.01), significantly suppressed cell growth (P<0.05), and upregulated protein level of PDCD4, indicating that miR-21 inhibitor could induce cell apoptosis of MPNST cells. These results suggest that miR-21 plays an important role in MPNST tumorigenesis and progression through its target, PDCD4. MiR-21 and PDCD4 may be candidate novel therapeutic targets against the development or progression of MPNSTs.

Abstract 4577: Targeting N-glycosylation of tyrosine kinase receptors for preventing tumorigenesis and malignant transformation of neurofibromatosis type I

Abstract Neurofibromatosis type I (NF1) is a dominantly inherited disease affecting 1 in every 2,500 to 3,000 individuals, representing the most common familial cancer predisposition syndrome. The hallmark of clinical manifestation of NF1 is the development of multiple neurofibromas, which are highly heterotypic benign tumors of peripheral nerve sheath mainly composed of immature Schwann cells, fibroblasts, perineurial and inflammatory matrix. NF1 patients are also at high risk for the development of certain maligancies such as pheochromocytomas, childhood myeloid leukemias, neuroblastomas, rhabdomyosarcomas, and malignant peripheral nerve sheath tumors (MPNSTs). Because of the potential involvement of underlying nerves and blood vessels, surgical removal of tumors is not always an option. Once progressing to MPNSTs, although the resection is possible, most patients will eventually relapse locally or systemically. There is no effective treatment for NF1, nor effective approaches for predicting or preventing the occurrence of devastating complications. Thus, to develop agents for preventing or reversing the tumorigenesis and malignant transformation of NF1 are critically needed. In this report, we found HGF, c-MET, EGF and EGFR are aberrantly expressed in clinical specimens of neurofibromas and MPNSTs with NF and that autocrine and/or paracrine HGF/c-MET and EGF/EGFR loops promote MPSNT cell migration and invasion in vitro (Fig1). We also found that the loss of Nf1 in neurofibromas and MPNSTs results in hyperactive of Ras (Fig2). Compared with normal Schwann cells, MPNST cells express more N-glycoproteins and display different N-glycoprotein signatures (Fig3). In order to confirm our hypothesis, we treated cells with Tunicamycin, or 2-DG (N-glycosylation inhibitors) respectively in variable doses for different time. We found that both Tunicamycin and 2-DG inhibited the proliferation and promoted apoptosis of MPNST cell lines but had no effect on normal human Schwann cells (Fig4); inhibited the glycosylation and phosphorylation of EGFR and c-MET and impaired receptor-mediated MEK-ERK1/2 and PI3K-AKT signaling in a dose-dependent manner (Fig5). Moreover, 2-DG inhibited the maturation of c-MET as demonstrated by the intact premature chain, failing to cleave into one mature α-chain and another mature α-chain. In addition, 2-DG inhibited the translocation of the receptors from the cytoplasm onto the cell surface and retained receptors in the ER and Golgi apparatus (Fig6). To date, 2-DG inhibition of N-glycosylation and phosphorylation of tyrosine kinase receptors has not been reported. These novel findings prompted us to explore whether 2-DG disrupts Ras-directed N-glycosylation of tyrosine receptors in Schwann cell progenitors and tumor cells and to evaluate its roles in preventing the tumorigenesis and malignant transformation of NF1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4577. doi:1538-7445.AM2012-4577

Overactivation of Ras signaling pathway in CD133+ MPNST cells

Cancer stem cells (CSCs) are believed to be the regenerative pool of cells responsible for repopulating tumors. Gaining knowledge about the signaling characteristics of CSCs is important for understanding the biology of tumors and developing novel anti-cancer therapies. We have identified a subpopulation of cells positive for CD133 (a CSC marker) from human primary malignant peripheral nerve sheath tumor (MPNST) cells which were absent in non-malignant Schwann cells. CD133 was also found to be expressed in human tissue samples and mouse MPNST cells. CD133+cells were capable of forming spheres in non-adherent/serum-free conditions. The activation levels of Ras and its downstream effectors such as ERK, JNK, PI3K, p38K, and RalA were significantly increased in this population. Moreover, the CD133+cells showed enhanced invasiveness which was linked to the increased expression of β-Catenin and Snail, two important proteins involved in the epithelial to mesenchymal transition, and Paxilin, a focal adhesion protein. Among other important characteristics of the CD133+population, endoplasmic reticulum stress marker IRE1α was decreased, implying the potential sensitivity of CD133+to the accumulation of unfolded proteins. Apoptotic indicators seemed to be unchanged in CD133+cells when compared to the wild (unsorted) cells. Finally, in order to test the possibility of targeting CD133+MPNST cells with Ras pathway pharmacological inhibitors, we exposed these cells to an ERK inhibitor. The wild population was more sensitive to inhibition of proliferation by this inhibitor as compared with the CD133+cells supporting previous studies observing enhanced chemoresistance of these cells.

Involvement of PACAP/ADNP Signaling in the Resistance to Cell Death in Malignant Peripheral Nerve Sheath Tumor (MPNST) Cells

Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas able to grow under conditions of metabolic stress caused by insufficient nutrients or oxygen. Both pituitary adenylate cyclase-activating polypeptide (PACAP) and activity-dependent neuroprotective protein (ADNP) have glioprotective potential. However, whether PACAP/ADNP signaling is involved in the resistance to cell death in MPNST cells remains to be clarified. Here, we investigated the involvement of this signaling system in the survival response of MPNST cells against hydrogen peroxide (H(2)O(2))-evoked death both in the presence of normal serum (NS) and in serum-starved (SS) cells. Results showed that ADNP levels increased time-dependently (6-48 h) in SS cells. Treatment with PACAP38 (10(-9) to 10(-5) M) dose-dependently increased ADNP levels in NS but not in SS cells. PAC(1)/VPAC receptor antagonists completely suppressed PACAP-stimulated ADNP increase and partially reduced ADNP expression in SS cells. NS-cultured cells exposed to H(2)O(2) showed significantly reduced cell viability (~50 %), increased p53 and caspase-3, and DNA fragmentation, without affecting ADNP expression. Serum starvation significantly reduced H(2)O(2)-induced detrimental effects in MPNST cells, which were not further ameliorated by PACAP38. Altogether, these finding provide evidence for the involvement of an endogenous PACAP-mediated ADNP signaling system that increases MPNST cell resistance to H(2)O(2)-induced death upon serum starvation.

Microarray-based copy number analysis of neurofibromatosis type-1 (NF1)-associated malignant peripheral nerve sheath tumors reveals a role for Rho-GTPase pathway genes in NF1 tumorigenesis

Neurofibromatosis type-1 (NF1) is associated with the growth of benign and malignant tumors. Approximately 15% of NF1 patients develop malignant peripheral nerve sheath tumors (MPNSTs), underlining the need to identify specific diagnostic/prognostic biomarkers associated with MPNST development. The Affymetrix Genome-Wide Human single-nucleotide polymorphism (SNP) Array 6.0 was used to perform SNP genotyping and copy number alteration (CNA), loss-of-heterozygosity (LOH), and copy number neutral-LOH (CNN-LOH) analyses of DNA isolated from 15 MPNSTs, five benign plexiform neurofibromas (PNFs), and patient-matched lymphocyte DNAs. MPNSTs exhibited high-level CNN-LOH, with recurrent changes occurring in MPNSTs but not PNFs. CNN-LOH was evident in MPNSTs but occurred less frequently than genomic deletions. CNAs involving the ITGB8, PDGFA, Ras-related C3 botulinum toxin substrate 1 (RAC1) (7p21-p22), PDGFRL (8p22-p21.3), and matrix metallopeptidase 12 (MMP12) (11q22.3) genes were specific to MPNSTs. Pathway analysis revealed the MPNST-specific amplification of seven Rho-GTPase pathway genes and several cytoskeletal remodeling/cell adhesion genes. In knockdown experiments employing short-hairpin RAC1, ROCK2, PTK2, and LIMK1 RNAs to transfect both control and MPNST-derived cell lines, cell adhesion was significantly increased in the MPNST cell lines, whereas wound healing, cell migration, and invasiveness were reduced, consistent with a role for these Rho-GTPase pathway genes in MPNST development and metastasis. These results suggest new targets for therapeutic intervention in relation to MPNSTs.

The pan erbB inhibitor PD168393 enhances lysosomal dysfunction-induced apoptotic death in malignant peripheral nerve sheath tumor cells

Malignant peripheral nerve sheath tumors (MPNSTs) are rapidly progressive Schwann cell neoplasms. The erbB family of membrane tyrosine kinases has been implicated in MPNST mitogenesis and invasion and, thus, is a potential therapeutic target. However, tyrosine kinase inhibitors (TKIs) used alone have limited tumoricidal activity. Manipulating the autophagy lysosomal pathway in cells treated with cytostatic agents can promote apoptotic cell death in some cases. The goal of this study was to establish a mechanistic basis for formulating drug combinations to effectively trigger death in MPNST cells. We assessed the effects of the pan erbB inhibitor PD168393 on MPNST cell survival, caspase activation, and autophagy. PD168393 induced a cytostatic but not a cytotoxic response in MPNST cells that was accompanied by suppression of Akt and mTOR activation and increased autophagic activity. The effects of autophagy modulation on MPNST survival were then assessed following the induction of chloroquine (CQ)-induced lysosomal stress. In CQ-treated cells, suppression of autophagy was accompanied by increased caspase activation. In contrast, increased autophagy induction by inhibition of mTOR did not trigger cytotoxicity, possibly because of Akt activation. We thus hypothesized that dual targeting of mTOR and Akt by PD168393 would significantly increase cytotoxicity in cells exposed to lysosomal stress. We found that PD168393 and CQ in combination significantly increased cytotoxicity. We conclude that combinatorial therapies with erbB inhibitors and agents inducing lysosomal dysfunction may be an effective means of treating MPNSTs.

Oncogene Mutation Survey in MPNST Cell Lines Enhances the Dominant Role of Hyperactive Ras in NF1 Associated Pro-Survival and Malignancy

Malignant peripheral nerve sheath tumors (MPNST) are a type of soft tissue sarcoma that can be associated with germline mutations in Neurofibromatosis type 1 (NF1) or may occur sporadically. Although the etiology of MPNST is poorly understood, it is clear that a loss of function of the NF1 gene, encoding a Ras-GAP, is an important factor in the tumorigenesis of the inherited form of MPNST. Tumor latency in NF1 patients suggests that additional mutational events are probably required for malignancy. In order to define oncogene mutations associated with 5 MPNST cell lines, we assayed the 238 most frequent mutations in 19 commonly activated oncogenes using mass spectroscopy-based analysis. All 238 mutation sites in the assayed oncogenes were determined to harbor only wild-type sequences. These data suggest that hyperactive Ras resulting from the loss function of neurofibromin may be sufficient to set up the direction of malignant transformation of Schwann cells to MPNST.

Genomic and Molecular Characterization of Malignant Peripheral Nerve Sheath Tumor Identifies the IGF1R Pathway as a Primary Target for Treatment

Malignant peripheral nerve sheath tumor (MPNST) is a rare sarcoma that lacks effective therapeutic strategies. We gain insight into the most recurrent genetically altered pathways with the purpose of scanning possible therapeutic targets. We conducted a microarray-based comparative genomic hybridization profiling of two cohorts of primary MPNST tissue samples including 25 patients treated at The University of Texas MD Anderson Cancer Center and 26 patients from Tianjin Cancer Hospital. Immunohistochemistry (IHC) and cell biology detection and validation were carried out on human MPNST tissues and cell lines. Genomic characterization of 51 MPNST tissue samples identified several frequently amplified regions harboring 2,599 genes and regions of deletion including 4,901 genes. At the pathway level, we identified a significant enrichment of copy number-altering events in the insulin-like growth factor 1 receptor (IGF1R) pathway, including frequent amplifications of the IGF1R gene itself. To validate the IGF1R pathway as a potential target in MPNSTs, we first confirmed that high IGF1R protein correlated with worse tumor-free survival in an independent set of samples using IHC. Two MPNST cell lines (ST88-14 and STS26T) were used to determine the effect of attenuating IGF1R. Inhibition of IGF1R in ST88-14 cells using siRNAs or an IGF1R inhibitor, MK-0646, led to significant decreases in cell proliferation, invasion, and migration accompanied by attenuation of the PI3K/AKT and mitogen-activated protein kinase pathways. These integrated genomic and molecular studies provide evidence that the IGF1R pathway is a potential therapeutic target for patients with MPNST.

Phenotypic Reversion of Invasive Neurofibromin-Deficient Schwannoma by FTS: Ras Inhibition Reduces BMP4/Erk/Smad Signaling

Neurofibromin-deficient (Nf1(-/-)) malignant peripheral nerve sheath tumors (MPNST) are highly invasive, refractory to chemotherapy, and characterized by overactivated Ras. Ras activates mitogenic pathways and regulates morphogenic programs--such as those induced by bone morphogenetic proteins (BMP) and TGF-β. The role of such a cross-talk in determining the phenotype and transformation potential of MPNSTs is unknown. Here, we used MPNST cell lines and selective Ras inhibition with S-trans,trans-farnesylthiosalicylic-acid (FTS; salirasib) in conjunction with specific inhibitors of TGF-β and BMP signaling. FTS perturbed signaling of BMP4 and TGF-β1 to Smad-dependent and Erk-dependent pathways. Furthermore, FTS inhibited motility and spreading, reduced the gelatinase secretion, eliminated the expression and activation of regulators of cell-matrix interaction, and altered gene expression. These phenomena are indicative of a phenotypic reversion of NF1-deficient cells by FTS. Inhibition of BMP4 and TGF-β by noggin and SB-431542, respectively, mimicked the FTS-mediated effects on adhesion, spreading, and cell morphology. This strongly suggests that a cross-talk among TGF-β superfamily ligands and Ras plays a significant role in the transformation of NF1(-/-) MPNSTs. Our results support the therapeutic potential of FTS, in conjuncture with BMP and TGF-β pathway inhibitors, toward the inhibition of mitogenic and morphogenic signaling pathways and the alleviation of NF1 symptoms.

Activated MET Is a Molecular Prognosticator and Potential Therapeutic Target for Malignant Peripheral Nerve Sheath Tumors

MET signaling has been suggested a potential role in malignant peripheral nerve sheath tumors (MPNST). Here, MET function and blockade were preclinically assessed. Expression levels of MET, its ligand hepatocyte growth factor (HGF), and phosphorylated MET (pMET) were examined in a clinically annotated MPNST tissue microarray (TMA) incorporating univariable and multivariable statistical analyses. Human MPNST cells were studied in vitro and in vivo; Western blot (WB) and ELISA were used to evaluate MET and HGF expression, activation, and downstream signaling. Cell culture assays tested the impact of HGF-induced MET activation and anti-MET-specific siRNA inhibition on cell proliferation, migration, and invasion; in vivo gel-foam assays were used to evaluate angiogenesis. Cells stably transduced with anti-MET short hairpin RNA (shRNA) constructs were tested for growth and metastasis in severe combined immunodeficient (SCID) mice. The effect of the tyrosine kinase inhibitor XL184 (Exelixis) targeting MET/VEGFR2 (vascular endothelial growth factor receptor 2) on local and metastatic MPNST growth was examined in vivo. All three markers were expressed in MPNST human samples; pMET expression was an independent prognosticator of poor patient outcome. Human MPNST cell lines expressed MET, HGF, and pMET. MET activation increased MPNST cell motility, invasion, angiogenesis, and induced matrix metalloproteinase-2 (MMP2) and VEGF expression; MET knockdown had inverse effects in vitro and markedly decreased local and metastatic growth in vivo. XL184 abrogated human MPNST xenograft growth and metastasis in SCID mice. Informative prognosticators and novel therapies are crucially needed to improve MPNST management and outcomes. We show an important role for MET in MPNST, supporting continued investigation of novel anti-MET therapies in this clinical context.

Cancer Stem Cell-Like Cells Derived from Malignant Peripheral Nerve Sheath Tumors

This study aims to examine whether or not cancer stem cells exist in malignant peripheral nerve sheath tumors (MPNST). Cells of established lines, primary cultures and freshly dissected tumors were cultured in serum free conditions supplemented with epidermal and fibroblast growth factors. From one established human MPNST cell line, S462, cells meeting the criteria for cancer stem cells were isolated. Clonal spheres were obtained, which could be passaged multiple times. Enrichment of stem cell-like cells in these spheres was also supported by increased expression of stem cell markers such as CD133, Oct4, Nestin and NGFR, and decreased expression of mature cell markers such as CD90 and NCAM. Furthermore, cells of these clonal S462 spheres differentiated into Schwann cells, smooth muscle/fibroblast and neurons-like cells under specific differentiation-inducing cultural conditions. Finally, subcutaneous injection of the spheres into immunodeficient nude mice led to tumor formation at a higher rate compared to the parental adherent cells (66% versus 10% at 2.5×105). These results provide evidence for the existence of cancer stem cell-like cells in malignant peripheral nerve sheath tumors.

Orthotopic Xenografting of Human Luciferase-Tagged Malignant Peripheral Nerve Sheath Tumor Cells for &lt;em&gt;in vivo&lt;/em&gt; Testing of Candidate Therapeutic Agents

Although in vitro screens are essential for the initial identification of candidate therapeutic agents, a rigorous assessment of the drug's ability to inhibit tumor growth must be performed in a suitable animal model. The type of animal model that is best for this purpose is a topic of intense discussion. Some evidence indicates that preclinical trials examining drug effects on tumors arising in transgenic mice are more predictive of clinical outcome1and so candidate therapeutic agents are often tested in these models. Unfortunately, transgenic models are not available for many tumor types. Further, transgenic models often have other limitations such as concerns as to how well the mouse tumor models its human counterpart, incomplete penetrance of the tumor phenotype and an inability to predict when tumors will develop. Consequently, many investigators use xenograft models (human tumor cells grafted into immunodeficient mice) for preclinical trials if appropriate transgenic tumor models are not available. Even if transgenic models are available, they are often partnered with xenograft models as the latter facilitate rapid determination of therapeutic ranges. Further, this partnership allows a comparison of the effectiveness of the agent in transgenic tumors and genuine human tumor cells. Historically, xenografting has often been performed by injecting tumor cells subcutaneously (ectopic xenografts). This technique is rapid and reproducible, relatively inexpensive and allows continuous quantitation of tumor growth during the therapeutic period2. However, the subcutaneous space is not the normal microenvironment for most neoplasms and so results obtained with ectopic xenografting can be misleading due to factors such as an absence of organ-specific expression of host tissue and tumor genes. It has thus been strongly recommended that ectopic grafting studies be replaced or complemented by studies in which human tumor cells are grafted into their tissue of origin (orthotopic xenografting)2. Unfortunately, implementation of this recommendation is often thwarted by the fact that orthotopic xenografting methodologies have not yet been developed for many tumor types. Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive sarcomas that occur sporadically or in association with neurofibromatosis type 13and most commonly arise in the sciatic nerve4. Here we describe a technically straightforward method in which firefly luciferase-tagged human MPNST cells are orthopically xenografted into the sciatic nerve of immunodeficient mice. Our approach to assessing the success of the grafting procedure in individual animals and subsequent non-biased randomization into study groups is also discussed.

Orthotopic Xenografting of Human Luciferase-Tagged Malignant Peripheral Nerve Sheath Tumor Cells for &lt;em&gt;in vivo&lt;/em&gt; Testing of Candidate Therapeutic Agents

Although in vitro screens are essential for the initial identification of candidate therapeutic agents, a rigorous assessment of the drug's ability to inhibit tumor growth must be performed in a suitable animal model. The type of animal model that is best for this purpose is a topic of intense discussion. Some evidence indicates that preclinical trials examining drug effects on tumors arising in transgenic mice are more predictive of clinical outcome1and so candidate therapeutic agents are often tested in these models. Unfortunately, transgenic models are not available for many tumor types. Further, transgenic models often have other limitations such as concerns as to how well the mouse tumor models its human counterpart, incomplete penetrance of the tumor phenotype and an inability to predict when tumors will develop.Consequently, many investigators use xenograft models (human tumor cells grafted into immunodeficient mice) for preclinical trials if appropriate transgenic tumor models are not available. Even if transgenic models are available, they are often partnered with xenograft models as the latter facilitate rapid determination of therapeutic ranges. Further, this partnership allows a comparison of the effectiveness of the agent in transgenic tumors and genuine human tumor cells. Historically, xenografting has often been performed by injecting tumor cells subcutaneously (ectopic xenografts). This technique is rapid and reproducible, relatively inexpensive and allows continuous quantitation of tumor growth during the therapeutic period2. However, the subcutaneous space is not the normal microenvironment for most neoplasms and so results obtained with ectopic xenografting can be misleading due to factors such as an absence of organ-specific expression of host tissue and tumor genes. It has thus been strongly recommended that ectopic grafting studies be replaced or complemented by studies in which human tumor cells are grafted into their tissue of origin (orthotopic xenografting)2. Unfortunately, implementation of this recommendation is often thwarted by the fact that orthotopic xenografting methodologies have not yet been developed for many tumor types.Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive sarcomas that occur sporadically or in association with neurofibromatosis type 13and most commonly arise in the sciatic nerve4. Here we describe a technically straightforward method in which firefly luciferase-tagged human MPNST cells are orthopically xenografted into the sciatic nerve of immunodeficient mice. Our approach to assessing the success of the grafting procedure in individual animals and subsequent non-biased randomization into study groups is also discussed.

Comparative methylome analysis of benign and malignant peripheral nerve sheath tumors

Aberrant DNA methylation (DNAm) was first linked to cancer over 25 yr ago. Since then, many studies have associated hypermethylation of tumor suppressor genes and hypomethylation of oncogenes to the tumorigenic process. However, most of these studies have been limited to the analysis of promoters and CpG islands (CGIs). Recently, new technologies for whole-genome DNAm (methylome) analysis have been developed, enabling unbiased analysis of cancer methylomes. By using MeDIP-seq, we report a sequencing-based comparative methylome analysis of malignant peripheral nerve sheath tumors (MPNSTs), benign neurofibromas, and normal Schwann cells. Analysis of these methylomes revealed a complex landscape of DNAm alterations. In contrast to what has been reported for other tumor types, no significant global hypomethylation was observed in MPNSTs using methylome analysis by MeDIP-seq. However, a highly significant (P < 10(-100)) directional difference in DNAm was found in satellite repeats, suggesting these repeats to be the main target for hypomethylation in MPNSTs. Comparative analysis of the MPNST and Schwann cell methylomes identified 101,466 cancer-associated differentially methylated regions (cDMRs). Analysis showed these cDMRs to be significantly enriched for two satellite repeat types (SATR1 and ARLα) and suggests an association between aberrant DNAm of these sequences and transition from healthy cells to malignant disease. Significant enrichment of hypermethylated cDMRs in CGI shores (P < 10(-60)), non-CGI-associated promoters (P < 10(-4)) and hypomethylated cDMRs in SINE repeats (P < 10(-100)) was also identified. Integration of DNAm and gene expression data showed that the expression pattern of genes associated with CGI shore cDMRs was able to discriminate between disease phenotypes. This study establishes MeDIP-seq as an effective method to analyze cancer methylomes.

Autophagic Survival in Resistance to Histone Deacetylase Inhibitors: Novel Strategies to Treat Malignant Peripheral Nerve Sheath Tumors

Histone deacetylase inhibitors (HDACi) show promise as cancer therapeutics; however, the full scope of their utility remains unknown. Here we report findings that strongly rationalize clinical evaluation of HDACis in malignant peripheral nerve sheath tumors (MPNST), a class of highly aggressive, therapeutically resistant, and commonly fatal malignancies that occur sporadically or in patients with the inherited neurofibromatosis type-1 (NF1) syndrome. We evaluated the effects of the chemical HDACis PCI-24781, suberoylanilide hydroxamic acid, and MS-275 on a panel of human NF1-associated and sporadic MPNSTs in vitro and in vivo. A subset of MPNSTs was found to be highly sensitive to HDACis, especially to PCI-24781. All cell lines in this group were NF1-associated. Significant proapoptotic effects were noted in vitro and in vivo and were independent of p53 mutational status. In contrast, as a group the sporadic-MPNST cells were markedly resistant to HDACi treatment. HDACis were found to induce productive autophagy in MPNST cells. Genetic and/or pharmacologic autophagy blockade resulted in significant HDACi-induced apoptosis in cells defined as resistant or sensitive, leading to abrogated growth of primary tumors and lung metastases in tumor xenograft assays. Among autophagy-associated genes expressed in response to HDACi, the immunity-related GTPase family, M was validated as a critical target in mediating HDACi-induced autophagy and enhanced apoptosis. Taken together, our findings strongly support the evaluation of HDACi currently in clinical trials as an important new therapeutic strategy to treat MPNST, including in combination with autophagy blocking combination regimens in particular for patients with sporadic MPNST.