Alveolar rhabdomyosarcoma: morphoproteomics and personalized tumor graft testing further define the biology of PAX3-FKHR(FOXO1) subtype and provide targeted therapeutic options.

Alveolar rhabdomyosarcoma (ARMS) represents a block in differentiation of malignant myoblasts. Genomic events implicated in the pathogenesis of ARMS involve PAX3-FKHR (FOXO1) or PAX7-FKHR (FOXO1) translocation with corresponding fusion transcripts and fusion proteins. Commonalities in ARMS include uncontrollable proliferation and failure to differentiate. The genomic-molecular correlates contributing to the etiopathogenesis of ARMS incorporate PAX3-FKHR (FOXO1) fusion protein stimulation of the IGF-1R, c-Met and GSK3-ß pathways. With sequential morphoproteomic profiling on such a case in conjunction with personalized tumor graft testing, we provide an expanded definition of the biology of PAX3-FKHR (FOXO1) ARMS that integrates genomics, proteomics and pharmacogenomics. Moreover, therapies that target the genomic and molecular biology and lead to tumoral regression and/or tumoral growth inhibition in a xenograft model of ARMS are identified. SIGNIFICANCE: This case study could serve as a model for clinical trials using relatively low toxicity agents in both initial and maintenance therapies to induce remission and reduce the risk of recurrent disease in PAX3-FKHR (FOXO1) subtype of ARMS.

MEK inhibitors block growth of lung tumours with mutations in ataxia-telangiectasia mutated.

Lung cancer is the leading cause of cancer deaths, and effective treatments are urgently needed. Loss-of-function mutations in the DNA damage response kinase ATM are common in lung adenocarcinoma but directly targeting these with drugs remains challenging. Here we report that ATM loss-of-function is synthetic lethal with drugs inhibiting the central growth factor kinases MEK1/2, including the FDA-approved drug trametinib. Lung cancer cells resistant to MEK inhibition become highly sensitive upon loss of ATM both in vitro and in vivo. Mechanistically, ATM mediates crosstalk between the prosurvival MEK/ERK and AKT/mTOR pathways. ATM loss also enhances the sensitivity of KRAS- or BRAF-mutant lung cancer cells to MEK inhibition. Thus, ATM mutational status in lung cancer is a mechanistic biomarker for MEK inhibitor response, which may improve patient stratification and extend the applicability of these drugs beyond RAS and BRAF mutant tumours.

Osteopontin-CD44 signaling in the glioma perivascular niche enhances cancer stem cell phenotypes and promotes aggressive tumor growth.

Stem-like glioma cells reside within a perivascular niche and display hallmark radiation resistance. An understanding of the mechanisms underlying these properties will be vital for the development of effective therapies. Here, we show that the stem cell marker CD44 promotes cancer stem cell phenotypes and radiation resistance. In a mouse model of glioma, Cd44(-/-) and Cd44(+/-) animals showed improved survival compared to controls. The CD44 ligand osteopontin shared a perivascular expression pattern with CD44 and promoted glioma stem cell-like phenotypes. These effects were mediated via the γ-secretase-regulated intracellular domain of CD44, which promoted aggressive glioma growth in vivo and stem cell-like phenotypes via CBP/p300-dependent enhancement of HIF-2α activity. In human glioblastoma multiforme, expression of CD44 correlated with hypoxia-induced gene signatures and poor survival. Altogether, these data suggest that in the glioma perivascular niche, osteopontin promotes stem cell-like properties and radiation resistance in adjacent tumor cells via activation of CD44 signaling.

Astrocyte-specific expression patterns associated with the PDGF-induced glioma microenvironment.

BACKGROUND: The tumor microenvironment contains normal, non-neoplastic cells that may contribute to tumor growth and maintenance. Within PDGF-driven murine gliomas, tumor-associated astrocytes (TAAs) are a large component of the tumor microenvironment. The function of non-neoplastic astrocytes in the glioma microenvironment has not been fully elucidated; moreover, the differences between these astrocytes and normal astrocytes are unknown. We therefore sought to identify genes and pathways that are increased in TAAs relative to normal astrocytes and also to determine whether expression of these genes correlates with glioma behavior. METHODOLOGY/PRINCIPAL FINDINGS: We compared the gene expression profiles of TAAs to normal astrocytes and found the Antigen Presentation Pathway to be significantly increased in TAAs. We then identified a gene signature for glioblastoma (GBM) TAAs and validated the expression of some of those genes within the tumor. We also show that TAAs are derived from the non-tumor, stromal environment, in contrast to the Olig2+ tumor cells that constitute the neoplastic elements in our model. Finally, we validate this GBM TAA signature in patients and show that a TAA-derived gene signature predicts survival specifically in the human proneural subtype of glioma. CONCLUSIONS/SIGNIFICANCE: Our data identifies unique gene expression patterns between populations of TAAs and suggests potential roles for stromal astrocytes within the glioma microenvironment. We show that certain stromal astrocytes in the tumor microenvironment express a GBM-specific gene signature and that the majority of these stromal astrocyte genes can predict survival in the human disease.

Recruited cells can become transformed and overtake PDGF-induced murine gliomas in vivo during tumor progression.

BACKGROUND: Gliomas are thought to form by clonal expansion from a single cell-of-origin, and progression-associated mutations to occur in its progeny cells. Glioma progression is associated with elevated growth factor signaling and loss of function of tumor suppressors Ink4a, Arf and Pten. Yet, gliomas are cellularly heterogeneous; they recruit and trap normal cells during infiltration. METHODOLOGY/PRINCIPAL FINDINGS: We performed lineage tracing in a retrovirally mediated, molecularly and histologically accurate mouse model of hPDGFb-driven gliomagenesis. We were able to distinguish cells in the tumor that were derived from the cell-of-origin from those that were not. Phenotypic, tumorigenic and expression analyses were performed on both populations of these cells. Here we show that during progression of hPDGFb-induced murine gliomas, tumor suppressor loss can expand the recruited cell population not derived from the cell-of-origin within glioma microenvironment to dominate regions of the tumor, with essentially no contribution from the progeny of glioma cell-of-origin. Moreover, the recruited cells can give rise to gliomas upon transplantation and passaging, acquire polysomal expression profiles and genetic aberrations typically present in glioma cells rather than normal progenitors, aid progeny cells in glioma initiation upon transplantation, and become independent of PDGFR signaling. CONCLUSIONS/SIGNIFICANCE: These results indicate that non-cell-of-origin derived cells within glioma environment in the mouse can be corrupted to become bona fide tumor, and deviate from the generally established view of gliomagenesis.

Gli activity correlates with tumor grade in platelet-derived growth factor-induced gliomas.

Gli signaling is critical for central nervous system development and is implicated in tumorigenesis. To monitor Gli signaling in gliomas in vivo, we created platelet-derived growth factor-induced gliomas in a Gli-luciferase reporter mouse. We find that Gli activation is found in gliomas and correlates with grade. In addition, we find that sonic hedgehog (SHH) is expressed in these tumors and also correlates with grade. We identify microvascular proliferation and pseudopalisades, elements that define high-grade gliomas as SHH-producing microenvironments. We describe two populations of SHH-producing stromal cells that reside in perivascular niche (PVN), namely low-cycling astrocytes and endothelial cells. Using the Ptc-LacZ knock-in mouse as a second Gli responsive reporter, we show beta-galactosidase activity in the PVN and in some tumors diffusely throughout the tumor. Lastly, we observe that SHH is similarly expressed in human gliomas and note that an intact tumor microenvironment or neurosphere conditions in vitro are required for Gli activity.