ABSTRACT
PURPOSE: MET signaling has been suggested a potential role in malignant peripheral nerve sheath tumors (MPNST). Here, MET function and blockade were preclinically assessed. EXPERIMENTAL DESIGN: 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. RESULTS: 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. CONCLUSIONS: 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.
Subject(s)
Nerve Sheath Neoplasms/diagnosis , Proto-Oncogene Proteins c-met/metabolism , Anilides/pharmacology , Animals , Cell Line, Tumor , Cell Movement/genetics , Cell Survival/drug effects , Gene Expression Regulation, Neoplastic , Gene Knockdown Techniques , Hepatocyte Growth Factor/metabolism , Humans , Mice , Mice, SCID , Neoplasm Invasiveness/genetics , Neovascularization, Pathologic/genetics , Nerve Sheath Neoplasms/mortality , Nerve Sheath Neoplasms/pathology , Phenotype , Prognosis , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-met/genetics , Pyridines/pharmacology , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
BACKGROUND: There is a crucial need for better therapeutic approaches for the treatment of Ewing sarcoma (EWS). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in EWS cells in vitro. However, in vivo, acquired resistance to TRAIL is a major limiting factor. Platelet-derived growth factor receptor-beta (PDGFR-beta) is highly expressed on EWS cells. Thus, the authors evaluated whether PDGFR-beta blockade could sensitize EWS cells to TRAIL-induced apoptosis in vitro and in vivo. METHODS: The effect of combined imatinib mesylate (Gleevec) and TRAIL on EWS cell growth and apoptosis was tested in vitro. Stable PDGFR-beta knockdown in EWS cells was achieved by short-hairpin RNA transduction, and TRAIL sensitivity of these cells was measured. Expression of death receptors was measured by fluorescence-activated cell-sorting (FACS) analysis, and caspase 8 activity was evaluated by Western blot analysis. An orthotopic human xenograft model of EWS growth and spontaneous metastasis in nude mice was used to assess the in vivo affect of combined imatinib mesylate and TRAIL. RESULTS: Imatinib mesylate induced a significant TRAIL proapoptotic effect in EWS cells in vitro. Specific PDGFR-beta silencing in EWS cells enhanced the effects of TRAIL, possibly through an increase in the expression of death receptors 4 and 5. The combination of imatinib mesylate and TRAIL significantly inhibited the growth of primary tumors and decreased the incidence of spontaneous EWS pulmonary metastasis compared with either drug alone. CONCLUSIONS: PDGFR-beta blockade combined with TRAIL resulted in antihuman EWS activity in vitro and in vivo, suggesting the possibility that combining these treatments will improve anti-EWS therapy.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Piperazines/administration & dosage , Protein Kinase Inhibitors/administration & dosage , Pyrimidines/administration & dosage , Receptor, Platelet-Derived Growth Factor beta/antagonists & inhibitors , Sarcoma, Ewing/drug therapy , TNF-Related Apoptosis-Inducing Ligand/administration & dosage , Animals , Benzamides , Humans , Imatinib Mesylate , Mice , Mice, Nude , Neoplasm Metastasis/prevention & control , Sarcoma, Ewing/pathology , Tumor Cells, CulturedABSTRACT
BACKGROUND: Despite aggressive therapy, Ewing's sarcoma (ES) patients have a poor five-year overall survival of only 20-40%. Pulmonary metastasis is the most common form of demise in these patients. The pathogenesis of pulmonary metastasis is poorly understood and few orthotopic models exist that allow study of spontaneous pulmonary metastasis in ES. MATERIALS AND METHODS: We have developed a novel orthotopic xenograft model in which spontaneous pulmonary metastases develop. While the underlying biology of ES is incompletely understood, in addition to the EWS-FLI-1 mutation, it is known that platelet-derived growth factor receptor beta (PDGFR-beta) is highly expressed in ES. Hypothesizing that PDGFR-beta expression is indicative of a specific role for this receptor protein in ES progression, the effect of PDGFR-beta inhibition on ES growth and metastasis was assessed in this novel orthotopic ES model. RESULTS: Silencing PDGFR-beta reduced spontaneous growth and metastasis in ES. CONCLUSION: Preclinical therapeutically relevant findings such as these may ultimately lead to new treatment initiatives in ES.
