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Glioblastoma multiforme (GBM) is a deadly and common brain tumor. Poor prognosis is linked to high proliferation and cell heterogeneity, including glioma stem cells (GSCs). Telomere genes are frequently mutated. The telomere binding protein TRF1 is essential for telomere protection, and for adult and pluripotent stem cells. Here, we find TRF1 upregulation in mouse and human GBM. Brain-specific Trf1 genetic deletion in GBM mouse models inhibited GBM initiation and progression, increasing survival. Trf1 deletion increased telomeric DNA damage and reduced proliferation and stemness. TRF1 chemical inhibitors mimicked these effects in human GBM cells and also blocked tumor sphere formation and tumor growth in xenografts from patient-derived primary GSCs. Thus, targeting telomeres throughout TRF1 inhibition is an effective therapeutic strategy for GBM., (Copyright © 2017 Elsevier Inc. All rights reserved.)

In this issue of Cancer Cell, Giachino and colleagues, employing various approaches, describe a tumor suppressor function for Notch signaling in forebrain tumors and suggest that decreased Notch activity could be a key molecular event in supratentorial primitive neuroectodermal tumors (sPNET)., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Clinical evidence indicates that mutation/activation of EGF receptors (EGFRs) is mutually exclusive with the presence of K-RAS oncogenes in lung and colon tumors. We have validated these observations using genetically engineered mouse models. However, development of pancreatic ductal adenocarcinomas driven by K-Ras oncogenes are totally dependent on EGFR signaling. Similar results were obtained using human pancreatic tumor cell lines. EGFRs were also essential even in the context of pancreatic injury and absence of p16Ink4a/p19Arf. Only loss of p53 made pancreatic tumors independent of EGFR signaling. Additional inhibition of PI3K and STAT3 effectively prevented proliferation of explants derived from these p53-defective pancreatic tumors. These findings may provide the bases for more rational approaches to treat pancreatic tumors in the clinic., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Pancreatic acinar cells of adult mice (≥P60) are resistant to transformation by some of the most robust oncogenic insults including expression of K-Ras oncogenes and loss of p16Ink4a/p19Arf or Trp53 tumor suppressors. Yet, these acinar cells yield pancreatic intraepithelial neoplasias (mPanIN) and ductal adenocarcinomas (mPDAC) if exposed to limited bouts of non-acute pancreatitis, providing they harbor K-Ras oncogenes. Pancreatitis contributes to tumor progression by abrogating the senescence barrier characteristic of low-grade mPanINs. Attenuation of pancreatitis-induced inflammation also accelerates tissue repair and thwarts mPanIN expansion. Patients with chronic pancreatitis display senescent PanINs, providing they have received antiinflammatory drugs. These results support the concept that antiinflammatory treatment of people diagnosed with pancreatitis may reduce their risk of developing PDAC., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Pancreatic ductal adenocarcinoma (PDA), one of the deadliest human cancers, often involves somatic activation of K-Ras oncogenes. We report that selective expression of an endogenous K-Ras(G12V) oncogene in embryonic cells of acinar/centroacinar lineage results in pancreatic intraepithelial neoplasias (PanINs) and invasive PDA, suggesting that PDA originates by differentiation of acinar/centroacinar cells or their precursors into ductal-like cells. Surprisingly, adult mice become refractory to K-Ras(G12V)-induced PanINs and PDA. However, if these mice are challenged with a mild form of chronic pancreatitis, they develop the full spectrum of PanINs and invasive PDA. These observations suggest that, during adulthood, PDA stems from a combination of genetic (e.g., somatic K-Ras mutations) and nongenetic (e.g., tissue damage) events.