Georg Feldmann

University of Bonn, Bonn, North Rhine-Westphalia, Germany

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Publications (88)439.6 Total impact


  • No preview · Article · Aug 2015 · Zeitschrift für Gastroenterologie
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    ABSTRACT: Despite considerable progress in recent years, the overall prognosis of metastatic malignant melanoma remains poor, and curative therapeutic options are lacking. Therefore, better understanding of molecular mechanisms underlying melanoma progression and metastasis, as well as identification of novel therapeutic targets that allow inhibition of metastatic spread, are urgently required. The current study provides evidence for aberrant cyclin-dependent kinase 5 (CDK5) activation in primary and metastatic melanoma lesions by overexpression of its activator protein CDK5R1/p35. Moreover, using melanoma in vitro model systems, shRNA-mediated inducible knockdown of CDK5 was found to cause marked inhibition of cell motility, invasiveness, and anchorage-independent growth, while at the same time net cell growth was not affected. In vivo, CDK5 knockdown inhibited growth of orthotopic xenografts as well as formation of lung and liver colonies in xenogenic injection models mimicking systemic metastases. Inhibition of lung metastasis was further validated in a syngenic murine melanoma model. CDK5 knockdown was accompanied by dephosphorylation and overexpression of caldesmon, and concomitant caldesmon knockdown rescued cell motility and proinvasive phenotype. Finally, it was found that pharmacological inhibition of CDK5 activity by means of roscovitine as well as by a novel small molecule CDK5-inhibitor, N-(5-isopropylthiazol-2-yl)-3-phenylpropanamide, similarly caused marked inhibition of invasion/migration, colony formation, and anchorage-independent growth of melanoma cells. Thus, experimental data presented here provide strong evidence for a crucial role of aberrantly activated CDK5 in melanoma progression and metastasis and establish CDK5 as promising target for therapeutic intervention. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Preview · Article · Aug 2015 · Translational oncology
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    ABSTRACT: The evolutionarily conserved Hedgehog (Hh) signaling pathway is essential for correct embryogenesis and is misregulated in several malignancies. In cell culture, Hh-sensitive cells display a striking dependence on cell density with active Hh signaling requiring cell-to-cell contact. As the Hippo/YAP system is tightly linked to cell density control and contact inhibition, we investigated the cross-talk between the two pathways. Our data reveal that the suppression of Hh signaling in the absence of cellular contacts is independent of primary cilia and is mediated by the YAP oncogene. Overexpression of YAP blocks Hh signaling whereas RNA interference-mediated knockdown of YAP enhances Hh/GLI activity. Despite this negative regulation, Hh signaling promotes YAP activity through post-transcriptional mechanisms, resulting in a negative feedback loop. In vivo, we found strong nuclear YAP immunoreactivity restricted to compartments with low Hh pathway activity in human and mouse pancreatic cancer. Finally, we identified protease-activated receptors (PARs) as molecules being able to override the inverse Hippo/Hh regulation, potentially giving tumors a mechanism to utilize both oncogenic pathways in parallel.Oncogenesis (2014) 3, e112; doi:10.1038/oncsis.2014.27; published online 11 August 2014.
    Preview · Article · Aug 2014 · Oncogenesis
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    ABSTRACT: Recent work has identified dysfunctional Hippo signaling to be involved in maintenance and progression of various human cancers, although data on clear cell renal cell carcinoma (ccRCC) have been limited. Here, we provide evidence implicating aberrant Hippo signaling in ccRCC proliferation, invasiveness, and metastatic potential. Nuclear overexpression of the Hippo target Yes-associated protein (YAP) was found in a subset of patients with ccRCC. Immunostaining was particularly prominent at the tumor margins and highlighted neoplastic cells invading the tumor-adjacent stroma. Short hairpin RNA-mediated knockdown of YAP significantly inhibited proliferation, migration, and anchorage-independent growth of ccRCC cells in soft agar and led to significantly reduced murine xenograft growth. Microarray analysis of YAP knockdown versus mock-transduced ccRCC cells revealed down-regulation of endothelin 1, endothelin 2, cysteine-rich, angiogenic inducer, 61 (CYR61), and c-Myc in ccRCC cells as well as up-regulation of the cell adhesion molecule cadherin 6. Signaling pathway impact analysis revealed activation of the p53 signaling and cell cycle pathways as well as inhibition of mitogen-activated protein kinase signaling on YAP down-regulation. Our data suggest CYR61 and c-Myc as well as signaling through the endothelin axis as bona fide downstream effectors of YAP and establish aberrant Hippo signaling as a potential therapeutic target in ccRCC.
    Full-text · Article · Apr 2014 · Translational oncology
  • Hanno Matthaei · Georg Feldmann · Philipp Lingohr · Jörg C Kalff
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    ABSTRACT: Due to an extensive use of modern imaging, incidental pancreatic cysts are increasingly diagnosed these days. Fortunately, comprehensive research over the past years has remarkably improved our pathogenetic and clinical understanding of pancreatic cysts that, as we know, are in majority harmless. However, mucinous cysts including intraductal papillary mucinous neoplasms, mucinous cystic neoplasms, as well as solid pseudopapillary neoplasms harbor relevant potential for developing into a lethal invasive cancer and may therefore require immediate surgical resection or at least close surveillance. In order to allow an optimized clinical management, it is crucial to gather reliable information about entity as well as biologic behavior of every cyst detected. Unfortunately, in the absence of reliable biomarkers and by just applying currently available diagnostic means such as clinical and radiologic criteria or cyst fluid cytology, there is still a risk for incorrect preoperative diagnoses. This may be followed by inappropriate treatment possibly resulting in severe morbidity or even mortality. In this review article, we summarize some of the salient recent advances in molecular diagnostics of pancreatic cysts. Herein, we put particular focus on the emerging field of biomarker research in pancreatic cyst fluid based on protein, DNA, and microRNA analyses.
    No preview · Article · Sep 2013 · Langenbeck s Archives of Surgery
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    ABSTRACT: Current therapies to treat cancer, although successful for some patients, have significant side-effects and a high number of patients have disease that is either non-responsive or which develops resistance. Our goal was to design a small peptide that possesses similar functions to an antibody drug conjugate with regard to targeting and killing cancer cells, but that overcomes size restrictions. We designed a novel cancer-specific killer peptide created by fusion of the toxic peptide (KLAKLAK)2 with the cancer recognition peptide LTVSPWY. Results. This bi-functional peptide showed toxicity to breast cancer, prostate cancer, and neuroblastoma cell lines. Only low toxicity to non-cancer cells, colon cancer, lung cancer, and lymphoma cell lines was observed. In vivo injections of the bi-functional peptide caused tumor growth retardation compared to mice treated with control peptides. The bi-functional peptide caused retardation of MDA-MB-435S tumors in vivo and increased survival to 80% at day 100 after tumor implantation, whereas all control animals died at day 70. Previous reports showed that the recognition moiety LTVSPWY targets the tumor-associated antigen HER2. Here we found that our new peptide TP-Tox also excerts toxic effects on HER2-negative cell lines. Therefore, we searched for the molecular target of the bi-specific peptide using immunoprecipitation and mass spectrometry. Our data suggest a possible interaction with RAS GTPase-activating protein binding protein 1 (G3BP1). We designed a bi-functional peptide of 23 amino acids and demonstrated its ability to bind and kill several cancer cell lines in vitro and to strongly increase survival in breast cancer bearing mice in vivo. This novel toxin could be used in future cancer therapies and warrants further pre-clinical and clinical exploration.
    No preview · Article · Jul 2013 · In vivo (Athens, Greece)
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    ABSTRACT: Management of patients suffering from metastatic malignant melanoma and brain metastasis remains challenging in routine clinical practice. The inhibitory anti-CTLA-4 antibody ipilimumab has recently been approved as second-line therapeutic option for melanoma patients. Increasing evidence suggests distinct therapeutic activity on central nervous system metastases, although this continues to be actively debated. Here, we present the case of a patient suffering from metastatic melanoma, including symptomatic brain metastasis, who showed a partial response to ipilimumab in extracranial tumor manifestations, while the disease was progressing intracranially. Subsequently, intracranial disease progression could be managed by local irradiation. An overview of currently available literature on the efficacy of ipilimumab in melanoma patients with central nervous system metastases is provided.
    Preview · Article · Apr 2013 · Case Reports in Oncology
  • Savita Bisht · Georg Feldmann · Peter Brossart
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    ABSTRACT: Introduction: Despite being the second most common malignancy of the pancreas, pancreatic neuroendocrine tumors (PNET) have long been understudied due to their low incidence and heterogeneous clinical presentation. Emerging data from a Phase III trial demonstrates improved progression-free survival of patients with advanced PNET on treatment with sunitinib . Areas covered: This article reviews the role of sunitinib, a multitargeted tyrosine kinase inhibitor with potent antiangiogenic and antitumor effects, in the clinical management of PNET. Furthermore, the authors also discuss the pharmacokinetics and pharmacodynamics as well as other clinically relevant aspects regarding sunitinib. Expert opinion: A recent Phase III clinical trial of sunitinib demonstrated significant improvement of progression-free survival in patients with advanced or metastatic well-differentiated PNET that led to its approval in several countries, including Europe and United States. This marks a significant step forward in the clinical management of this disease and spurs hopes to further improve overall survival in this once difficult-to-treat set of patients in the coming years. Fields of future interest will include evaluation of combinatorial regimens, including conventional cytotoxic agents as well as additional targeted drugs in order to overcome resistance to sunitinib.
    No preview · Article · Apr 2013 · Expert Opinion on Drug Metabolism & Toxicology

  • No preview · Article · Apr 2013 · Annals of Hematology
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    ABSTRACT: Purpose: High-throughput chemosensitivity testing of low-passage cancer cell lines can be used to prioritize agents for personalized chemotherapy. However, generating cell lines from primary cancers is difficult because contaminating stromal cells overgrow the malignant cells. Experimental design: We produced a series of hypoxanthine phosphoribosyl transferase (hprt)-null immunodeficient mice. During growth of human cancers in these mice, hprt-null murine stromal cells replace their human counterparts. Results: Pancreatic and ovarian cancers explanted from these mice were grown in selection media to produce pure human cancer cell lines. We screened one cell line with a 3,131-drug panel and identified 77 U.S. Food and Drug Administration (FDA)-approved drugs with activity, and two novel drugs to which the cell line was uniquely sensitive. Xenografts of this carcinoma were selectively responsive to both drugs. Conclusion: Chemotherapy can be personalized using patient-specific cell lines derived in biochemically selectable mice.
    Full-text · Article · Jan 2013 · Clinical Cancer Research
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    ABSTRACT: Cytokine secretion by cancer cells contributes to cancer-induced symptoms and angiogenesis. Studies show that the sirtuin SIRT6 promotes inflammation by enhancing TNF expression. Here, we aimed to determine whether SIRT6 is involved in conferring an inflammatory phenotype to cancer cells and to define the mechanisms linking SIRT6 to inflammation. We show that SIRT6 enhances the expression of pro-inflammatory cyto/chemokines, such as IL8 and TNF, and promotes cell migration in pancreatic cancer cells by enhancing Ca2+ responses. Via its enzymatic activity, SIRT6 increases the intracellular levels of ADP-ribose, an activator of the Ca2+-channel TRPM2. In turn, TRPM2 and Ca2+ are shown to be involved in SIRT6-induced TNF and IL8 expression. SIRT6 increases the nuclear levels of the Ca2+-dependent transcription factor NFAT and cyclosporin A, a calcineurin inhibitor that reduces NFAT activity, reduces TNF and IL8 expression in SIRT6 overexpressing cells. These results implicate a role for SIRT6 in the synthesis of Ca2+-mobilizing second messengers, in the regulation of Ca2+-dependent transcription factors, and in the expression of pro-inflammatory, pro-angiogenic and chemotactic cytokines. SIRT6 inhibition may help combat cancer-induced inflammation, angiogenesis and metastasis.
    Full-text · Article · Oct 2012 · Journal of Biological Chemistry
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    ABSTRACT: Introduction: Pancreatic neuroendocrine tumors (PNET) represent the second most common primary malignancy of the pancreas. Until recently, therapeutic options for advanced PNET have been limited. Areas covered: A recently published Phase III clinical trial demonstrated striking therapeutic activity of the mTOR inhibitor everolimus in advanced PNET and led to its approval for this indication by the FDA. This review discusses this landmark discovery in the context of currently available therapeutic options, pathophysiology and molecular genetics of PNET. Expert opinion: The approval of everolimus for the treatment of PNET marks a major step forward in the clinical management of this disease and represents a notable example of the successful translation of a targeted therapy that was initially developed based on findings at the lab bench, into everyday clinical practice. These results encourage hopes that the overall therapeutic efficacy of such approaches can be further enhanced by the introduction of combinatorial regimens, simultaneously targeting more than one oncogenic signaling pathway, as well as by stratification of patients based on the individual genetic setup of their tumors.
    No preview · Article · Aug 2012 · Expert Opinion on Pharmacotherapy
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    ABSTRACT: It is a challenging task to distinguish between benign and malignant lesions in patients with biliary strictures. Here we analyze whether determination of target gene mRNA levels in intraductal brush cytology specimens may be used to improve the diagnosis of bile duct carcinoma. Brush cytology specimens from 119 patients with biliary strictures (malignant: n = 72; benign: n = 47) were analyzed in a retrospective cohort study. mRNA of IGF-II mRNA-binding protein 3 (IGF2BP3), homeobox B7 (HOXB7), Forkhead box M1 (FOXM1), kinesin family member 2C (KIF2C) and serine/threonine kinase NEK2 was determined by semi-quantitative RT-PCR using the ΔCt method. IGF2BP3 (p<0.0001), HOXB7 (p<0.0001), and NEK2 (p<0.0001) mRNA expression levels were significantly increased in patients with cholangiocarcinoma or pancreatic cancer. Median ΔCt values differed by 3.5 cycles (IGF2BP3), 2.8 cycles (HOXB7) and 1.3 cycles (NEK2) corresponding to 11-fold, 7-fold and 2.5-fold increased mRNA levels in malignant versus benign samples. Sensitivity to detect biliary cancer was 76.4% for IGF2BP3 (80.9% specificity); 72.2% for HOXB7 (78.7% specificity) and 65.3% for NEK2 (72.3% specificity), whereas routine cytology reached only 43.1% sensitivity (85.4% specificity). Diagnostic precision was further improved, when all three molecular markers were assessed in combination (77.8% sensitivity, 87.2% specificity) and achieved 87.5% sensitivity and 87.2% specificity when molecular markers were combined with routine cytology. Our data suggest that measuring IGF2BP3, HOXB7 and NEK2 mRNA levels by RT-PCR in addition to cytology has the potential to improve detection of malignant biliary disorders from brush cytology specimens.
    Full-text · Article · Aug 2012 · PLoS ONE
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    ABSTRACT: Pancreatic cancer is one of the most lethal of human malignancies, and potent therapeutic options are lacking. Inhibition of cell cycle progression through pharmacological blockade of cyclin-dependent kinases (CDK) has been suggested as a potential treatment option for human cancers with deregulated cell cycle control. Dinaciclib (SCH727965) is a novel small molecule multi-CDK inhibitor with low nanomolar potency against CDK1, CDK2, CDK5 and CDK9 that has shown favorable toxicity and efficacy in preliminary mouse experiments, and has been well tolerated in Phase I clinical trials. In the current study, the therapeutic efficacy of SCH727965 on human pancreatic cancer cells was tested using in vitro and in vivo model systems. Treatment with SCH727965 significantly reduced in vitro cell growth, motility and colony formation in soft agar of MIAPaCa-2 and Pa20C cells. These phenotypic changes were accompanied by marked reduction of phosphorylation of Retinoblastoma (Rb) and reduced activation of RalA. Single agent therapy with SCH727965 (40 mg/kg i.p. twice weekly) for 4 weeks significantly reduced subcutaneous tumor growth in 10/10 (100%) of tested low-passage human pancreatic cancer xenografts. Treatment of low passage pancreatic cancer xenografts with a combination of SCH727965 and gemcitabine was significantly more effective than either agent alone. Gene Set Enrichment Analysis identified overrepresentation of the Notch and Transforming Growth Factor-β (TGF-β) signaling pathways in the xenografts least responsive to SCH727965 treatment. Treatment with the cyclin-dependent kinase inhibitor SCH727965 alone or in combination is a highly promising novel experimental therapeutic strategy against pancreatic cancer.
    Full-text · Article · Oct 2011 · Cancer biology & therapy
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    ABSTRACT: Ligand-dependent activation of the Hedgehog (Hh) signaling pathway has been implicated in both tumor initiation and metastasis of pancreatic ductal adenocarcinoma (PDAC). Prior studies in genetically engineered mouse models (GEMMs) have assessed the role of Hh signaling by cell autonomous expression of a constitutively active Gli2 within epithelial cells. On the contrary, aberrant pathway reactivation in the human exocrine pancreas occurs principally as a consequence of Sonic Hh ligand (Shh) overexpression from epithelial cells. To recapitulate the cognate pathophysiology of Hh signaling observed in the human pancreas, we examined GEMM where Hh ligand is conditionally overexpressed within the mature exocrine pancreas using a tamoxifen-inducible Elastase-Cre promoter (Ela-CreERT2;LSL-mShh). We also facilitated potential cell autonomous epithelial responsiveness to secreted Hh ligand by generating compound transgenic mice with concomitant expression of the Hh receptor Smoothened (Ela-CreERT2;LSL-mShh;LSL-mSmo). Of interest, none of these mice developed intraductal precursor lesions or PDAC during the follow-up period of up to 12 months after tamoxifen induction. Instead, all animals demonstrated marked expansion of stromal cells, consistent with the previously described epithelial-to-stromal paracrine Hh signaling. Hh responsiveness was mirrored by the expression of primary cilia within the expanded mesenchymal compartment and the absence within mature acinar cells. In the absence of cooperating mutations, Hh ligand overexpression in the mature exocrine pancreas is insufficient to induce neoplasia, even when epithelial cells coexpress the Smo receptor. This autochthonous model serves as a platform for studying epithelial stromal interactions in pancreatic carcinogenesis.
    Full-text · Article · Oct 2011 · Neoplasia (New York, N.Y.)
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    ABSTRACT: An inactivating germline mutation in BRCA2 is the most common known genetic basis for familial pancreatic cancer (FPC), accounting for 5-10% of inherited cases. A genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDAC) arising on the backdrop of Brca2 deficiency is likely to elucidate valuable diagnostic and therapeutic insights for FPC. Both Brca2 alleles were conditionally deleted during development within the pancreatic epithelium by generating Pdx1-Cre; Brca2(f/f) (CB) mice; in addition, triple transgenic Pdx1-Cre; Brca2(f/f); LSL-Trp53(R172H) (CBP) mice were generated, in order to determine the impact of p53 deregulation on Brca2-deficient carcinogenesis. Both CB and CBP mice developed non-invasive ductal precursor lesions (murine pancreatic intraepithelial neoplasia or mPanIN), although these were observed at an earlier time point (5 versus 8 months) and with higher prevalence in CBP mice. A minority of CB mice (15%) developed invasive and metastatic PDAC at a latency of 15 months or greater; in contrast, CBP mice of comparable age uniformly developed PDAC with variable histological features. Mortality in the absence of neoplasia in CB and CBP mice was associated with profound loss of pancreatic parenchyma, consistent with progressive elimination of Brca2-deficient cells. Widespread DNA damage, as evidenced by overexpression of the phosphorylated histone H(2)AX(Ser139), was observed in the non-neoplastic exocrine pancreas, as well as in the mPanIN and PDAC lesions of Brca2-deficient mice, independent of p53 status. Loss of Brca2 function predisposes the exocrine pancreas to profound DNA damage, and the frequency of invasive neoplasia is accentuated by the concomitant deregulation of p53.
    Full-text · Article · Jun 2011 · Cancer biology & therapy
  • Ute Schütte · Savita Bisht · Peter Brossart · Georg Feldmann
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    ABSTRACT: Pancreatic cancer is a devastating disease associated with near uniform mortality. Usually diagnosed at advanced, metastatic stages when surgical resection with curative intention is not possible any more, most patients succumb to progressive disease after a few months. Despite recent advances in understanding pancreatic carcinogenesis and continuous efforts in translational research, so far these results failed to translate into clinically relevant improvements of patient survival. Preclinical evaluation of drug candidates and novel therapeutic strategies rely on in vitro and in vivo model systems to predict response in patients. This article reviews mouse models of pancreatic cancer, their respective applications in translational research and discusses their potential to predict clinical responses in patients. This article provides a profound overview of individual strength as well as of shortcomings of mouse models of pancreatic cancer currently available for translational research. Considerable progress in designing mouse models of pancreatic cancer has been made over the last decade and several xenograft as well as genetically engineered mouse models faithfully recapitulating human disease development has been developed. Taken together, these newly developed in vivo model systems provide powerful tools likely to boost preclinical evaluation and bench-to-bedside transition of novel therapeutic approaches directed against this dire malady.
    No preview · Article · Jan 2011 · Expert Opinion on Drug Discovery
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    ABSTRACT: Although activating mutations in RAS oncogenes are known to result in aberrant signaling through multiple pathways, the role of microRNAs (miRNAs) in the Ras oncogenic program remains poorly characterized. Here we demonstrate that Ras activation leads to repression of the miR-143/145 cluster in cells of human, murine, and zebrafish origin. Loss of miR-143/145 expression is observed frequently in KRAS mutant pancreatic cancers, and restoration of these miRNAs abrogates tumorigenesis. miR-143/145 down-regulation requires the Ras-responsive element-binding protein (RREB1), which represses the miR-143/145 promoter. Additionally, KRAS and RREB1 are targets of miR-143/miR-145, revealing a feed-forward mechanism that potentiates Ras signaling.
    Preview · Article · Dec 2010 · Genes & development
  • Savita Bisht · Peter Brossart · Anirban Maitra · Georg Feldmann
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    ABSTRACT: Recent evidence has demonstrated that aberrant reactivation of the Hedgehog signaling pathway contributes to tumor initiation and progression in various human malignancies, including pancreatic cancer; therefore, the Hedgehog pathway has emerged as a promising novel therapeutic target. Initial translational studies conducted using cyclopamine, a small-molecule inhibitor of the Smoothened (SMO) component of the Hedgehog pathway, demonstrated that pharmacological blockade of aberrant Hedgehog signaling has the potential to inhibit tumor initiation, progression and metastatic spread. This concept has been corroborated using different compounds in various preclinical models of pancreatic cancer and other malignancies; several of these studies suggest possible therapeutic synergisms of Hedgehog inhibitors with established antineoplastic agents. This review provides a concise overview of translational studies assessing the use of Hedgehog inhibitors as novel therapeutic strategy for cancer, particularly pancreatic cancer.
    No preview · Article · Dec 2010 · Current opinion in investigational drugs (London, England: 2000)
  • Georg Feldmann · Anirban Maitra
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    ABSTRACT: Pancreatic cancer has both genetic and epigenetic underlying causes. The importance of epigenetic alterations in the formation and maintenance of malignant tumors has become apparent in the last decade, with accumulating evidence suggesting this is probably the most common clonal aberration in human neoplasia. Identifying epigenetic alterations in pancreatic cancer has not only enhanced our understanding of pancreatic cancer biology, but has also opened up avenues for the development of early detection and novel therapeutic strategies. In this chapter, an overview of the current literature on epigenetic alterations found in pancreatic cancer is presented and discussed in the light of potential therapeutic applicability as well as pointing out possible future directions of studies combining global genetic and epigenetic analyses.
    No preview · Chapter · Nov 2010

Publication Stats

6k Citations
439.60 Total Impact Points

Institutions

  • 2004-2015
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 2013-2014
    • University of Bonn - Medical Center
      Bonn, North Rhine-Westphalia, Germany
  • 2006-2013
    • Johns Hopkins University
      • • Department of Pathology
      • • Department of Medicine
      Baltimore, Maryland, United States
  • 2006-2011
    • Philipps University of Marburg
      Marburg, Hesse, Germany