Inhibition of SHP2-mediated dephosphorylation of Ras suppresses oncogenesis

Ras is phosphorylated on a conserved tyrosine at position 32 within the switch I region via Src kinase. This phosphorylation inhibits the binding of effector Raf while promoting the engagement of GTPase-activating protein (GAP) and GTP hydrolysis. Here we identify SHP2 as the ubiquitously expressed tyrosine phosphatase that preferentially binds to and dephosphorylates Ras to increase its association with Raf and activate downstream proliferative Ras/ERK/MAPK signalling. In comparison to normal astrocytes, SHP2 activity is elevated in astrocytes isolated from glioblastoma multiforme (GBM)-prone H-Ras(12V) knock-in mice as well as in glioma cell lines and patient-derived GBM specimens exhibiting hyperactive Ras. Pharmacologic inhibition of SHP2 activity attenuates cell proliferation, soft-agar colony formation and orthotopic GBM growth in NOD/SCID mice and decelerates the progression of low-grade astrocytoma to GBM in a spontaneous transgenic glioma mouse model. These results identify SHP2 as a direct activator of Ras and a potential therapeutic target for cancers driven by a previously 'undruggable' oncogenic or hyperactive Ras

TRANSCRIPTOME ANALYSIS IDENTIFIES THE PI3K/AKT/mTOR PATHWAY AS A TARGETABLE PATHWAY IN SCHWANNOMA

Schwannomas are common benign tumors of the vestibular nerve, or arise from nerves within the spinal canal. Although benign, both Spinal schwannoma (SS) and vestibular schwannoma (VS) cause significant morbidities. The current treatment strategies for VS and SS include surgery or radiation with each treatment option having associated complications and side effects. The transcriptional landscape of schwannoma remains largely unknown. We interrogated the transcriptome by gene-expression array analysis of 49 schwannomas and seven normal control vestibular nerves to identify tumor-specific gene expression patterns. We identified over 4000 differentially expressed genes between control and schwannoma with network analysis uncovering proliferation and anti-apoptotic pathways previously not implicated in VS. Using several distinct clustering technologies, we could not reproducibly identify VS subtypes or significant differences between sporadic and germline NF2 associated schwannomas suggesting that VS comprises of a highly similar entity. We next performed a transcript analysis comparing VS to SS. Surprisingly; we identified few differential transcripts demonstrating that schwannoma maybe a homogenous entity. Current studies are focused on DNA methylation profiling and genome wide sequencing analysis. To date our group and others have identified that inactivating mutations in NF2 is the most recurrent aberration in schwannoma. The most recurrent activated pathway in schwannoma was over-expression of PI3K/AKT/mTOR signaling pathway, which is directly druggable and we evaluated this pathway for therapeutic targeting. Testing compounds BEZ235 and PKI-587, both novel dual inhibitors of PI3K and mTOR, attenuated tumor growth in a cell line model of schwannoma. Our In vitro findings demonstrated that pharmacological inhibition of the PI3K/AKT/mTOR pathway with next generation compounds lead to decreased cell viability, and increased cell death. Future work is testing these compounds in vivo using relevant cell lines and primary cultures of schwannoma. Our findings implicate that targeting the PI3K/AKT/mTOR pathway may serve as a potential treatment strategy

The genomic landscape of schwannoma

Schwannomas are common peripheral nerve sheath tumors that can cause debilitating morbidities. We performed an integrative analysis to determine genomic aberrations common to sporadic schwannomas. Exome sequence analysis with validation by targeted DNA sequencing of 125 samples uncovered, in addition to expected NF2 disruption, recurrent mutations in ARID1A, ARID1B and DDR1. RNA sequencing identified a recurrent in-frame SH3PXD2A-HTRA1 fusion in 12/125 (10%) cases, and genomic analysis demonstrated the mechanism as resulting from a balanced 19-Mb chromosomal inversion on chromosome 10q. The fusion was associated with male gender predominance, occurring in one out of every six men with schwannoma. Methylation profiling identified distinct molecular subgroups of schwannomas that were associated with anatomical location. Expression of the SH3PXD2A-HTRA1 fusion resulted in elevated phosphorylated ERK, increased proliferation, increased invasion and in vivo tumorigenesis. Targeting of the MEK-ERK pathway was effective in fusion-positive Schwann cells, suggesting a possible therapeutic approach for this subset of tumors