Abstract
The malignant brain cancer medulloblastoma is characterized by mutations in Hedgehog (Hh) signaling pathway genes, which lead to constitutive activation of the G protein (heterotrimeric guanosine triphosphate-binding protein)-coupled receptor Smoothened (Smo). The Smo antagonist NVP-LDE225 inhibits Hh signaling and induces tumor regression in animal models of medulloblastoma. However, evidence of resistance was observed during the course of treatment. Molecular analysis of resistant tumors revealed several resistance mechanisms. We noted chromosomal amplification of Gli2, a downstream effector of Hh signaling, and, more rarely, point mutations in Smo that led to reactivated Hh signaling and restored tumor growth. Analysis of pathway gene expression signatures also, unexpectedly, identified up-regulation of phosphatidylinositol 3-kinase (PI3K) signaling in resistant tumors as another potential mechanism of resistance. Probing the relevance of increased PI3K signaling, we demonstrated that addition of the PI3K inhibitor NVP-BKM120 or the dual PI3K-mTOR (mammalian target of rapamycin) inhibitor NVP-BEZ235 to the initial treatment with the Smo antagonist markedly delayed the development of resistance. Our findings may be useful in informing treatment strategies for medulloblastoma.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Aminopyridines / pharmacology*
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Aminopyridines / therapeutic use
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Animals
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Cell Proliferation / drug effects
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Drug Resistance, Neoplasm / drug effects*
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Gene Amplification / drug effects
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Hedgehog Proteins / metabolism
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Insulin-Like Growth Factor I / metabolism
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Kruppel-Like Transcription Factors / metabolism
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Medulloblastoma / drug therapy
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Medulloblastoma / enzymology*
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Medulloblastoma / genetics
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Medulloblastoma / pathology
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Mice
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Morpholines / pharmacology*
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Morpholines / therapeutic use
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Mutation / genetics
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Phosphatidylinositol 3-Kinases / metabolism
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Phosphoinositide-3 Kinase Inhibitors*
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Protein Kinase Inhibitors / pharmacology*
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Protein Kinase Inhibitors / therapeutic use
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Receptors, G-Protein-Coupled / antagonists & inhibitors*
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Receptors, G-Protein-Coupled / metabolism
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Signal Transduction / drug effects*
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Smoothened Receptor
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Tumor Suppressor Protein p53 / metabolism
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Up-Regulation / drug effects
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Zinc Finger Protein Gli2
Substances
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Aminopyridines
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Gli2 protein, mouse
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Hedgehog Proteins
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Kruppel-Like Transcription Factors
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Morpholines
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NVP-BKM120
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Phosphoinositide-3 Kinase Inhibitors
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Protein Kinase Inhibitors
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Receptors, G-Protein-Coupled
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Smo protein, mouse
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Smoothened Receptor
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Tumor Suppressor Protein p53
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Zinc Finger Protein Gli2
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Insulin-Like Growth Factor I
Associated data
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GEO/GSE19657
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GEO/GSE22005
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GEO/GSE22006