Activation of the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway is a frequent occurrence in human cancers and a major promoter of chemotherapeutic resistance. Inhibition of one downstream target in this pathway, mTORC1, has shown potential to improve chemosensitivity. However, the mechanisms and genetic modifications that confer sensitivity to mTORC1 inhibitors remain unclear. Here, we demonstrate that loss of TSC2 in the E-myc murine lymphoma model leads to mTORC1 activation and accelerated oncogenesis caused by a defective apoptotic program despite compromised AKT phosphorylation. Tumors from Tsc2 ؉/؊ E-Myc mice underwent rapid apoptosis upon blockade of mTORC1 by rapamycin. We identified myeloid cell leukemia sequence 1 (Mcl-1), a bcl-2 like family member, as a translationally regulated genetic determinant of mTORC1-dependent survival. Our results indicate that the extent by which rapamycin can modulate expression of Mcl-1 is an important feature of the rapamycin response.rapamycin response ͉ Tsc2 loss ͉ apoptosis ͉ lymphoma ͉ Akt

Glioblastoma multiforme (GBM) is a highly lethal brain tumor for which little treatment is available. The epidermal growth factor receptor (EGFR) signaling pathway is thought to play a crucial role in GBM pathogenesis, initiating the early stages of tumor development, sustaining tumor growth, promoting infiltration, and mediating resistance to therapy. The importance of this pathway is highlighted in the fact that EGFR is mutationally activated in over 50% of GBM tumors. Consistent with this, we show here that concomitant activation of wild-type and/or mutant (vIII) EGFR and ablation of Ink4A/Arf and PTEN tumor suppressor gene function in the adult mouse central nervous system generates a fully penetrant, rapid-onset high-grade malignant glioma phenotype with prominent pathological and molecular resemblance to GBM in humans. Studies of the activation of signaling events in these GBM tumor cells revealed notable differences between wild-type and vIII EGFR-expressing cells. We show that wild-type EGF receptor signals through its canonical pathways, whereas tumors arising from expression of mutant EGFR vIII do not use these same pathways. Our findings provide critical insights into the role of mutant EGFR signaling function in GBM tumor biology and set the stage for testing of targeted therapeutic agents in the preclinical models described herein. glioblastoma ͉ mouse model ͉ receptor tyrosine kinase ͉ mTORC1/2 ͉ STAT3 G lioblastoma multiforme is the most common and lethal primary malignant cancer of the central nervous system (CNS). Despite multimodal therapies, the median survival of GBM patients is Ϸ1 year. The deadly nature of GBMs resides in their explosive growth characteristic, extreme invasive behavior, and intrinsic resistance to current therapies. Despite efforts to develop novel treatments, little improvement in overall survival or progression-free survival has been achieved in the past 5 decades, reflecting an unmet need in the treatment of this cancer (1). Personalized medicine based on targeting essential molecular mechanisms for GBM survival offers an alternative therapeutic strategy.Over the years, our knowledge of GBM biology has steadily improved. From a molecular standpoint, GBMs are a highly heterogeneous tumor with multiple signaling pathways differentially activated or silenced with converging and parallel complex interactions (2). It is these intricacies that are thought to confer GBM with its notorious plasticity in response to therapeutic interventions. Therefore, a major challenge in the clinic is to determine the appropriate events to target. The most common genetic abnormality in GBMs is the activation of receptor tyrosine kinases (RTKs), of which, aberrant expression of EGFR is the most frequent (2). Concomitant with EGFR gene amplification events is the occurrence of an intragenic in-frame deletion of exons 2Ϫ7 of the EGFR gene. This rearrangement product, known as EGFRvIII, codes for a ligandindependent receptor, which is constitutively activated and highly oncogenic (reviewed in ref....

Oncogenic c-ros oncogene1 (ROS1) fusion kinases have been identified in a variety of human cancers and are attractive targets for cancer therapy. The MET/ALK/ROS1 inhibitor crizotinib (Xalkori, PF-02341066) has demonstrated promising clinical activity in ROS1 fusion-positive non-small cell lung cancer. However, emerging clinical evidence has shown that patients can develop resistance by acquiring secondary point mutations in ROS1 kinase. In this study we characterized the ROS1 activity of PF-06463922, a novel, orally available, CNS-penetrant, ATP-competitive small-molecule inhibitor of ALK/ROS1. In vitro, PF-06463922 exhibited subnanomolar cellular potency against oncogenic ROS1 fusions and inhibited the crizotinib-refractory ROS1 G2032R mutation and the ROS1 G2026M gatekeeper mutation. Compared with crizotinib and the second-generation ALK/ROS1 inhibitors ceritinib and alectinib, PF-06463922 showed significantly improved inhibitory activity against ROS1 kinase. A crystal structure of the PF-06463922-ROS1 kinase complex revealed favorable interactions contributing to the high-affinity binding. Taken together, our results indicate that PF-06463922 has potential for treating ROS1 fusion-positive cancers, including those requiring agents with CNS-penetrating properties, as well as for overcoming crizotinib resistance driven by ROS1 mutation.PF-06463922 | ROS1 | kinase inhibitor R eceptor tyrosine kinases (RTKs) are vital conduits of extracellular signals that direct cell growth and survival pathways. Unregulated RTK activation through chromosomal rearrangements, point mutations, and gene amplification has been shown to be responsible for the initiation and progression of many cancers. The orphan RTK c-ros oncogene1 (ROS1) normally is expressed transiently in various tissues during development with little to no expression in adult tissues (1). Elevated full-length c-ROS1 expression levels have been observed in 20-30% of patients with nonsmall cell lung cancer (NSCLC) by gene expression profiling (2-4) and in 13% of patients with lung adenocarcinoma using immunohistochemistry (IHC) (5). However, its function, both in normal physiology and disease, remains poorly defined mainly because of its still unidentified ligand. Chromosomal rearrangements resulting in oncogenic activation of ROS1 have been observed in a subset of patients with glioblastoma (6-9), NSCLC (10-14), cholangiocarcinoma (15), ovarian cancer (16), angiosarcoma (17), inflammatory myofibroblastic tumors (18), and Spitzoid melanoma (19). To date, interchromosomal translocations or intrachromosomal deletions have resulted in the production of 20 different N-terminal ROS1 fusion genes in a variety of cancers (Table S1).ROS1 is a distinct receptor with a kinase domain that is phylogenetically related to the anaplastic lymphoma kinase/lymphocyte-specific protein tyrosine kinase (ALK/LTK) and insulin receptor (INSR) RTK families (20), suggesting that tyrosine kinase inhibitors for these receptors could have cross-activity against ROS1. A recent phase I/II cl...