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Oncogenic Kras is required for both the initiation and maintenance of pancreatic cancer in mice

Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan, USA.
The Journal of clinical investigation (Impact Factor: 13.77). 02/2012; 122(2):639-53. DOI: 10.1172/JCI59227
Source: PubMed

ABSTRACT Pancreatic cancer is almost invariably associated with mutations in the KRAS gene, most commonly KRASG12D, that result in a dominant-active form of the KRAS GTPase. However, how KRAS mutations promote pancreatic carcinogenesis is not fully understood, and whether oncogenic KRAS is required for the maintenance of pancreatic cancer has not been established. To address these questions, we generated two mouse models of pancreatic tumorigenesis: mice transgenic for inducible KrasG12D, which allows for inducible, pancreas-specific, and reversible expression of the oncogenic KrasG12D, with or without inactivation of one allele of the tumor suppressor gene p53. Here, we report that, early in tumorigenesis, induction of oncogenic KrasG12D reversibly altered normal epithelial differentiation following tissue damage, leading to precancerous lesions. Inactivation of KrasG12D in established precursor lesions and during progression to cancer led to regression of the lesions, indicating that KrasG12D was required for tumor cell survival. Strikingly, during all stages of carcinogenesis, KrasG12D upregulated Hedgehog signaling, inflammatory pathways, and several pathways known to mediate paracrine interactions between epithelial cells and their surrounding microenvironment, thus promoting formation and maintenance of the fibroinflammatory stroma that plays a pivotal role in pancreatic cancer. Our data establish that epithelial KrasG12D influences multiple cell types to drive pancreatic tumorigenesis and is essential for tumor maintenance. They also strongly support the notion that inhibiting KrasG12D, or its downstream effectors, could provide a new approach for the treatment of pancreatic cancer.

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Available from: Stefanie Galbán, Mar 25, 2014
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    • "Therefore, it is highly desirable to discover and characterize more effective therapeutic targets for pancreatic cancer treatment. The oncogene KRAS plays an essential role in the progression of pancreatic cancer [9] [10]. In our previous studies , two stable transfected cell lines (P-M and P-W) were constructed through lentivirus-mediated short hairpin RNA (shRNA) targeting of the KRAS gene in PANC-1 cells, enabling us to investigate the cellular response to KRAS knockdown [11]. "
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    ABSTRACT: Pancreatic cancer remains a major unsolved health problem lacking a potent therapeutic option. Our previous studies showed that the ribosomal protein L39 (RPL39) gene was up-regulated after long-term silencing of oncogenic KRAS in pancreatic cancer PANC-1 cells, which indicated that RPL39 may be important for pancreatic cancer development and survival. In the current study, small interfering RNA (siRNA) targeting of the RPL39 gene was performed to determine the effects of the RPL39 gene on growth of pancreatic cancer PANC-1 and BxPC-3 cells in vitro and in vivo. Results from in vitro experiments showed that knockdown of RPL39 expression with RPL39-siRNA suppressed cell proliferation and specifically enhanced cell apoptosis significantly in both PANC-1 and BxPC-3 cells. The increase of caspase-8 activities and the loss of mitochondrial membrane potential after RPL39 silencing indicated that the RPL39 gene may be involved in caspase-8-related mitochondrial apoptosis. Further, treatment with the RPL39-siRNA inhibited the growth of a human pancreatic cancer xenograft in BALB/c nude mice, accompanied by a decreased expression of RPL39. In the xenograft tumors with injection of RPL39-siRNA, the expressions of Ki-67 and CD31 were significantly down-regulated, and apoptosis was markedly induced. Our findings suggested that siRNA against the RPL39 gene may be of value for gene therapy of pancreatic cancer.
    Biotechnology Journal 05/2014; 9(5):652-663. DOI:10.1002/biot.201300321 · 3.71 Impact Factor
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    • "During all stages of pancreatic carcinogenesis , Kras upregulates inflammatory and signaling pathways that mediate paracrine interactions between epithelia and their surrounding microenvironment, and these Kras-dependent pathways drive tumorigenesis [16]. Given the predominant role of Ras oncogene in pancreatic carcinogenesis, there is an intense ongoing effort to identify inhibitors of the Ras protein [15]. "
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    ABSTRACT: Pancreatic cancer has one of the poorest prognoses among all cancers partly because of its persistent resistance to chemotherapy. The currently limited treatment options for pancreatic cancer underscore the need for more efficient agents. Because activating Kras mutations initiate and maintain pancreatic cancer, inhibition of this pathway should have a major therapeutic impact. We synthesized phospho-farnesylthiosalicylic acid (PFTS; MDC-1016) and evaluated its efficacy, safety, and metabolism in preclinical models of pancreatic cancer. PFTS inhibited the growth of human pancreatic cancer cells in culture in a concentration- and time-dependent manner. In an MIA PaCa-2 xenograft mouse model, PFTS at a dose of 50 and 100 mg/kg significantly reduced tumor growth by 62% and 65% (P < .05 vs vehicle control). Furthermore, PFTS prevented pancreatitis-accelerated acinar-to-ductal metaplasia in mice with activated Kras. PFTS appeared to be safe, with the animals showing no signs of toxicity during treatment. Following oral administration, PFTS was rapidly absorbed, metabolized to FTS and FTS glucuronide, and distributed through the blood to body organs. Mechanistically, PFTS inhibited Ras-GTP, the active form of Ras, both in vitro and in vivo, leading to the inhibition of downstream effector pathways c-RAF/mitogen-activated protein-extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK1/2 kinase and phosphatidylinositol 3-kinase/AKT. In addition, PFTS proved to be a strong combination partner with phospho-valproic acid, a novel signal transducer and activator of transcription 3 (STAT3) inhibitor, displaying synergy in the inhibition of pancreatic cancer growth. In conclusion, PFTS, a direct Ras inhibitor, is an efficacious agent for the treatment of pancreatic cancer in preclinical models, deserving further evaluation.
    Neoplasia (New York, N.Y.) 10/2013; 15(10):1184-95. DOI:10.1593/neo.131368 · 5.40 Impact Factor
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    • "Here, pancreas-specific expression of Kras G12D recapitulated the whole spectrum of human PDAC pathologies, from its precursor lesions to locally invasive and metastatic entities (Hingorani et al., 2003). Recent studies have demonstrated that the activity of Kras G12D is required for all stages of carcinogenesis including inception, progression and metastasis because inactivation of Kras G12D using genetic approaches invariably reversed the ongoing carcinogenic process (Collins et al., 2012). However, it remains largely elusive how Kras G12D exactly promotes PDAC development. "
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    ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease without clearly known disease causes. Recent epidemiological and animal studies suggest that the supplementation of dietary antioxidants (e.g., vitamins C and E) decreases cancer risk, implying that increased reactive oxygen species (ROS) may play a role in pancreatic carcinogenesis. However, oncogenic Kras mutations (e.g., Kras(G12D)), which are present in more than 90% of PDAC, have been proven to foster low intracellular ROS levels. Here, oncogenic Kras activates expression of a series of anti-oxidant genes via Nrf2 (nuclear factor, erythroid derived 2, like 2) and also mediates an unusual metabolic pathway of glutamine to generate NADPH. This can then be used as the reducing power for ROS detoxification, leading collectively to low ROS levels in pancreatic pre-neoplastic cells and in cancer cells. In adult stem cells and cancer stem cells, low ROS levels have been associated with the formation of a proliferation-permissive intracellular environment and with perseverance of self-renewal capacities. Therefore, it is conceivable that low intracellular ROS levels may contribute significantly to oncogenic Kras-mediated PDAC formation.
    Frontiers in Physiology 09/2013; 4:246. DOI:10.3389/fphys.2013.00246 · 3.50 Impact Factor
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