BackgroundGlioblastoma multiforme (GBM) is characterized by extensive local invasion, which is in contrast with extremely rare systemic metastasis of GBM. Molecular mechanisms inhibiting systemic metastasis of GBM would be a novel therapeutic candidate for GBM in the brain.MethodsPatient-derived GBM cells were primarily cultured from surgical samples of GBM patients and were inoculated into the brains of immune deficient BALB/c-nude or NOD-SCID IL2Rgammanull (NSG) mice. Human NK cells were isolated from peripheral blood mononucleated cells and expanded in vitro.ResultsPatient-derived GBM cells in the brains of NSG mice unexpectedly induced spontaneous lung metastasis although no metastasis was detected in BALB/c-nude mice. Based on the difference of the innate immunity between two mouse strains, NK cell activities of orthotopic GBM xenograft models based on BALB/c-nude mice were inhibited. NK cell inactivation induced spontaneous lung metastasis of GBM cells, which indicated that NK cells inhibit the systemic metastasis. In vitro cytotoxic activities of human NK cells against GBM cells indicated that cytotoxic activity of NK cells against GBM cells prevents systemic metastasis of GBM and that NK cells could be effective cell therapeutics against GBM. Accordingly, NK cells transplanted into orthotopic GBM xenograft models intravenously or intratumorally induced apoptosis of GBM cells in the brain and showed significant therapeutic effects.ConclusionsOur results suggest that innate NK immunity is responsible for rare systemic metastasis of GBM and that sufficient supplementation of NK cells could be a promising immunotherapeutic strategy for GBM in the brain.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-015-2034-y) contains supplementary material, which is available to authorized users.
An unfortunate consequence of improvements in the treatments of advanced primary cancers is the concurrent increase of metastatic brain tumors. Despite of unfavorable clinical prognosis, radiation therapy is still the only viable treatment option for brain metastases. Expression of c-Met induces cell migration and invasion in many cancers, which are indispensable steps for metastasis. Accordingly, we examined the effects of gene silencing of c-Met on brain metastasis to evaluate the possibility of c-Met as a potential target. MDA-MB-435 cells were transfected with c-Met targeting short hairpin RNAs (shRNAs). Effects of c-Met shRNAs on the expression of epithelial mesenchymal transition (EMT) related proteins, in vitro migration, and in vivo brain metastasis were examined. Expression of mesenchymal markers and in vitro migration of MDA-MB-435 cells were significantly inhibited by introduction of c-Met shRNAs. When c-Met-silenced MDA-MB-435 cells were stereotactically implanted into the brains of immune-compromised mice or injected into the right internal carotid arteries, c-Met-silenced MDA-MB-435 cells produced significantly smaller tumor masses or survival time was significantly prolonged, respectively, compared with MDA-MB-435 cells transfected with control shRNA. The data reveal the novel function of c-Met in the process of brain metastasis and its potential as a preventive and/or therapeutic target in this disease.
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