ABSTRACT
Glioblastoma (GBM) is the most common malignant primary brain tumor of adults and one of the most lethal of all cancers. Epidermal growth factor receptor (EGFR) mutations (EGFRvIII) and phosphoinositide 3-kinase (PI3K) hyperactivation are common in GBM, promoting tumor growth and survival, including through sterol regulatory element-binding protein 1 (SREBP-1)-dependent lipogenesis. The role of cholesterol metabolism in GBM pathogenesis, its association with EGFR/PI3K signaling, and its potential therapeutic targetability are unknown. In our investigation, studies of GBM cell lines, xenograft models, and GBM clinical samples, including those from patients treated with the EGFR tyrosine kinase inhibitor lapatinib, uncovered an EGFRvIII-activated, PI3K/SREBP-1-dependent tumor survival pathway through the low-density lipoprotein receptor (LDLR). Targeting LDLR with the liver X receptor (LXR) agonist GW3965 caused inducible degrader of LDLR (IDOL)-mediated LDLR degradation and increased expression of the ABCA1 cholesterol efflux transporter, potently promoting tumor cell death in an in vivo GBM model. These results show that EGFRvIII can promote tumor survival through PI3K/SREBP-1-dependent upregulation of LDLR and suggest a role for LXR agonists in the treatment of GBM patients.
Subject(s)
Brain Neoplasms/drug therapy , Cell Death/drug effects , ErbB Receptors/metabolism , Glioblastoma/drug therapy , Orphan Nuclear Receptors/agonists , Proto-Oncogene Proteins c-akt/genetics , Receptors, LDL/metabolism , Signal Transduction/drug effects , Sterol Regulatory Element Binding Protein 1/metabolism , ATP Binding Cassette Transporter 1 , ATP-Binding Cassette Transporters/genetics , ATP-Binding Cassette Transporters/metabolism , Animals , Brain Neoplasms/genetics , Brain Neoplasms/metabolism , Brain Neoplasms/pathology , Cell Death/genetics , Cholesterol/genetics , Cholesterol/metabolism , ErbB Receptors/genetics , Glioblastoma/genetics , Glioblastoma/metabolism , Glioblastoma/pathology , HeLa Cells , Humans , Lapatinib , Liver X Receptors , Mice , Mice, SCID , Orphan Nuclear Receptors/genetics , Orphan Nuclear Receptors/metabolism , Phosphatidylinositol 3-Kinases/genetics , Phosphatidylinositol 3-Kinases/metabolism , Proto-Oncogene Proteins c-akt/metabolism , Quinazolines/therapeutic use , Receptors, LDL/genetics , Sterol Regulatory Element Binding Protein 1/genetics , Up-Regulation/drug effectsABSTRACT
The clinical practice of oncology is being transformed by molecular diagnostics that will enable predictive and personalized medicine. Current technologies for quantitation of the cancer proteome are either qualitative (e.g., immunohistochemistry) or require large sample sizes (e.g., flow cytometry). Here, we report a microfluidic platform-microfluidic image cytometry (MIC)-capable of quantitative, single-cell proteomic analysis of multiple signaling molecules using only 1,000 to 2,800 cells. Using cultured cell lines, we show simultaneous measurement of four critical signaling proteins (EGFR, PTEN, phospho-Akt, and phospho-S6) within the oncogenic phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway. To show the clinical application of the MIC platform to solid tumors, we analyzed a panel of 19 human brain tumor biopsies, including glioblastomas. Our MIC measurements were validated by clinical immunohistochemistry and confirmed the striking intertumoral and intratumoral heterogeneity characteristic of glioblastoma. To interpret the multiparameter, single-cell MIC measurements, we adapted bioinformatic methods including self-organizing maps that stratify patients into clusters that predict tumor progression and patient survival. Together with bioinformatic analysis, the MIC platform represents a robust, enabling in vitro molecular diagnostic technology for systems pathology analysis and personalized medicine.
