Steven D Leach

Memorial Sloan-Kettering Cancer Center, New York, New York, United States

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Publications (156)1217.61 Total impact

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    ABSTRACT: Unlabelled: Patient-specific induced pluripotent stem cells (iPSCs) represent a potential source for developing novel drug and cell therapies. Although increasing numbers of disease-specific iPSCs have been generated, there has been limited progress in iPSC-based drug screening/discovery for liver diseases, and the low gene-targeting efficiency in human iPSCs warrants further improvement. Using iPSC lines from patients with alpha-1 antitrypsin (AAT) deficiency, for which there is currently no drug or gene therapy available, we established a platform to discover new drug candidates and correct disease-causing mutation with a high efficiency. A high-throughput format screening assay, based on our hepatic differentiation protocol, was implemented to facilitate automated quantification of cellular AAT accumulation using a 96-well immunofluorescence reader. To expedite the eventual application of lead compounds to patients, we conducted drug screening utilizing our established library of clinical compounds (the Johns Hopkins Drug Library) with extensive safety profiles. Through a blind large-scale drug screening, five clinical drugs were identified to reduce AAT accumulation in diverse patient iPSC-derived hepatocyte-like cells. In addition, using the recently developed transcription activator-like effector nuclease technology, we achieved high gene-targeting efficiency in AAT-deficiency patient iPSCs with 25%-33% of the clones demonstrating simultaneous targeting at both diseased alleles. The hepatocyte-like cells derived from the gene-corrected iPSCs were functional without the mutant AAT accumulation. This highly efficient and cost-effective targeting technology will broadly benefit both basic and translational applications. Conclusions: Our results demonstrated the feasibility of effective large-scale drug screening using an iPSC-based disease model and highly robust gene targeting in human iPSCs, both of which are critical for translating the iPSC technology into novel therapies for untreatable diseases.
    Hepatology 06/2013; 57(6). DOI:10.1002/hep.26237 · 11.06 Impact Factor
  • Elayne Provost · Christopher A Weier · Steven D Leach ·
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    ABSTRACT: Abstract Ribosomal protein L (rpl) genes are essential for assembly of the 60S subunit of the eukaryotic ribosome and may also carry out additional extra-ribosomal functions. We have identified a common expression pattern for rpl genes in developing zebrafish larvae. After initially widespread expression in early embryos, the expression of multiple rpl genes becomes increasingly restricted to the endoderm. With respect to the pancreas, rpl genes are highly expressed in ptf1a-expressing pancreatic progenitors at 48 hpf, suggesting possible functional roles in pancreatic morphogenesis and/or differentiation. Utilizing two available mutant lines, rpl23a(hi2582) and rpl6(hi3655b), we found that ptf1a-expressing pancreatic progenitors fail to properly expand in embryos homozygous for either of these genes. In addition to these durable homozygous phenotypes, we also demonstrated recoverable delays in ptf1a-expressing pancreatic progenitor expansion in rpl23a(hi2582) and rpl6(hi3655b) heterozygotes. Disruptions in ribosome assembly are generally understood to initiate a p53-dependent cellular stress response. However, concomitant p53 knockdown was unable to rescue normal pancreatic progenitor expansion in either rpl23a(hi2582) or rpl6(hi3655b) mutant embryos, suggesting required and p53-independent roles for rpl23a and rpl6 in pancreas development.
    Zebrafish 05/2013; 10(2). DOI:10.1089/zeb.2013.0884 · 1.95 Impact Factor
  • Yue J Wang · Jennifer M Bailey · Meritxell Rovira · Steven D Leach ·
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    ABSTRACT: Sphere-forming assays are an in vitro technique to assay both normal and neoplastic cells for clonogenic growth potential. Currently, the identification of adult progenitors in the pancreas remains an area of intense investigation. The use of sphere-forming assays provides a critical step to identify new cell types in the pancreas that are capable of clonogenic growth and differentiation. In the field of cancer biology, cancer stem cells have been defined functionally by two major criteria: their ability to undergo self-renewal and their ability to produce differentiated progeny, two conditions which satisfy the criteria of stem cells. Here we briefly review both the capabilities of pancreatosphere and pancreatic tumorsphere assays, discuss important caveats regarding their use, and provide detailed protocols for the assay of both normal and neoplastic cells.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 980:281-90. DOI:10.1007/978-1-62703-287-2_15 · 1.29 Impact Factor
  • Anirban Maitra · Steven D Leach ·
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    ABSTRACT: In this issue of Cancer Cell, Kopp and colleagues report that pancreatic ductal cells are largely refractory to the induction of pancreatic neoplasia. Whereas a rare ductal subpopulation may still prove capable of neoplastic transformation, these findings refocus attention on acinar and other non-ductal cell types as initiators of this deadly neoplasm.
    Cancer cell 12/2012; 22(6):701-3. DOI:10.1016/j.ccr.2012.11.015 · 23.52 Impact Factor
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    ABSTRACT: Mutations in the human Shwachman-Bodian-Diamond syndrome (SBDS) gene cause defective ribosome assembly and are associated with exocrine pancreatic insufficiency, chronic neutropenia and skeletal defects. However, the mechanism underlying these phenotypes remains unclear. Here we show that knockdown of the zebrafish sbds ortholog fully recapitulates the spectrum of developmental abnormalities observed in the human syndrome, and further implicate impaired proliferation of ptf1a-expressing pancreatic progenitor cells as the basis for the observed pancreatic phenotype. It is thought that diseases of ribosome assembly share a p53-dependent mechanism. However, loss of p53 did not rescue the developmental defects associated with loss of zebrafish sbds. To clarify the molecular mechanisms underlying the observed organogenesis defects, we performed transcriptional profiling to identify candidate downstream mediators of the sbds phenotype. Among transcripts displaying differential expression, functional group analysis revealed marked enrichment of genes related to ribosome biogenesis, rRNA processing and translational initiation. Among these, ribosomal protein L3 (rpl3) and pescadillo (pes) were selected for additional analysis. Similar to knockdown of sbds, knockdown or mutation of either rpl3 or pes resulted in impaired expansion of pancreatic progenitor cells. The pancreatic phenotypes observed in rpl3- and pes-deficient embryos were also independent of p53. Together, these data suggest novel p53-independent roles for ribosomal biogenesis genes in zebrafish pancreas development.
    Development 09/2012; 139(17):3232-41. DOI:10.1242/dev.077107 · 6.46 Impact Factor
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    ABSTRACT: Feeling a bit cagey: morpholino-based antisense reagents have been caged through oligonucleotide cyclization, enabling photocontrol of gene expression in zebrafish embryos and larvae. Using these reagents, the timing of exocrine cell fate commitment in the developing pancreas has been examined.
    Angewandte Chemie International Edition 07/2012; 51(28):6908-11. DOI:10.1002/anie.201201690 · 11.26 Impact Factor
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    ABSTRACT: This review summarizes our current understanding of exocrine pancreas development, including the formation of acinar, ductal and centroacinar cells. We discuss the transcription factors associated with various stages of exocrine differentiation, from multipotent progenitor cells to fully differentiated acinar and ductal cells. Within the branching epithelial tree of the embryonic pancreas, this involves the progressive restriction of multipotent pancreatic progenitor cells to either a central "trunk" domain giving rise to the islet and ductal lineages, or a peripheral "tip" domain giving rise to acinar cells. This review also discusses the soluble morphogens and other signaling pathways that influence these events. Finally, we examine centroacinar cells as an enigmatic pancreatic cell type whose lineage remains uncertain, and whose possible progenitor capacities continue to be explored.
    Seminars in Cell and Developmental Biology 06/2012; 23(6):711-9. DOI:10.1016/j.semcdb.2012.06.008 · 6.27 Impact Factor

  • Cancer Research 04/2012; 72(8 Supplement):2968-2968. DOI:10.1158/1538-7445.AM2012-2968 · 9.33 Impact Factor
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    ABSTRACT: Dicer is a ribonuclease whose major role is to generate mature microRNAs, although additional functions have been proposed. Deletion of Dicer leads to embryonic lethality in mice. To study the role of Dicer in adults, we generated mice in which administration of tamoxifen induces deletion of Dicer. Surprisingly, disruption of Dicer in adult mice induced lipid accumulation in the small intestine. To dissect the underlying mechanisms, we carried out miRNA, mRNA, and proteomic profiling of the small intestine. The proteomic analysis was done using mice metabolically labeled with heavy lysine (SILAC mice) for an in vivo readout. We identified 646 proteins, of which 80 were up-regulated >2-fold and 75 were down-regulated. Consistent with the accumulation of lipids, Dicer disruption caused a marked decrease of microsomal triglyceride transfer protein, long-chain fatty acyl-CoA ligase 5, fatty acid binding protein, and very-long-chain fatty acyl-CoA dehydrogenase, among others. We validated these results using multiple reaction monitoring (MRM) experiments by targeting proteotypic peptides. Our data reveal a previously unappreciated role of Dicer in lipid metabolism. These studies demonstrate that a systems biology approach by integrating mouse models, metabolic labeling, gene expression profiling, and quantitative proteomics can be a powerful tool for understanding complex biological systems.
    Journal of Proteome Research 02/2012; 11(4):2193-205. DOI:10.1021/pr2009884 · 4.25 Impact Factor
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    ABSTRACT: Metastasis is the leading cause of cancer-associated death but has been difficult to study because it involves a series of rare, stochastic events. To capture these events, we developed a sensitive method to tag and track pancreatic epithelial cells in a mouse model of pancreatic cancer. Tagged cells invaded and entered the bloodstream unexpectedly early, before frank malignancy could be detected by rigorous histologic analysis; this behavior was widely associated with epithelial-to-mesenchymal transition (EMT). Circulating pancreatic cells maintained a mesenchymal phenotype, exhibited stem cell properties, and seeded the liver. EMT and invasiveness were most abundant at inflammatory foci, and induction of pancreatitis increased the number of circulating pancreatic cells. Conversely, treatment with the immunosuppressive agent dexamethasone abolished dissemination. These results provide insight into the earliest events of cellular invasion in situ and suggest that inflammation enhances cancer progression in part by facilitating EMT and entry into the circulation.
    Cell 01/2012; 148(1-2):349-61. DOI:10.1016/j.cell.2011.11.025 · 32.24 Impact Factor
  • Jennifer M. Bailey · Steven D. Leach ·
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    ABSTRACT: Pancreatic cancer is an extremely aggressive disease characterized by a complex stromal or desmoplastic response. This dense desmoplastic response is in part the result of pancreatic stellate cell activation in response to paracrine signals from pre- neoplastic and neoplastic pancreatic epithelium. Activated stellate cells secrete a large array of soluble factors that directly influence malignant epithelial, vascular and inflammatory cells, and also alter the composition of the extracellular matrix. Thus, the signaling interactions between tumor and stellate cells represent a large, diverse spectrum of bidirectional and reciprocal influences necessary for the initiation and promotion of pancreatic cancer. A number of pathways including Hedgehog, Notch and Transforming growth factor-beta are involved in mediating cross-talk between the malignant pancreatic epithelium and its associated stroma, making them unique pathways to target for the treatment of pancreatic cancer.
    Pancreatic Cancer and Tumor Microenvironment, Edited by Paul J. Grippo, Hidayatullah G. Munshi, 01/2012: chapter Chapter 7; Transworld Research Network., ISBN: 9788178955483
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    ABSTRACT: The intracellular protein p120ctn controls cell–cell adhesion by regulation of E-cadherin stability. p120ctn binds to the juxtamembrane region of E-cadherin and regulates its retention at the cell–cell surface. Mice null for p120ctn are not viable. Using Pdx1:Cre and a conditional allele of p120ctn, we deleted p120ctn in all epithelial lineages of the developing mouse pancreas: islet, acinar, and ductal. Loss of p120ctn in the developing pancreas results in expansion of ductal epithelia and loss of acinar cells. Defects in branching morphogenesis are evident at E12.5. During development the phenotype becomes more severe, ultimately resulting in a pancreas comprised primarily of abnormal ductal tissue. Pdx1:Cre; p120ctn fl/fl animals are born dead. Loss of p120ctn results in mislocalization of E-cadherin and loss of b-catenin. Additionally, at E17.5 we observed broad expression of Sox9 and Pdx in Pdx1:Cre; p120ctn fl/fl animals. This suggests inappropriate persistence of progenitor cells at late developmental timepoints. Taken together, our data demonstrates an essential role for p120ctn in pancreatic acinar cell development and differentiation.
    Developmental Biology - DEVELOP BIOL, Chicago, Illinois; 08/2011
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    Elayne Provost · Foram Ashar · Michael Parsons · Steven Leach ·

    Developmental Biology 08/2011; 356(1):224-224. DOI:10.1016/j.ydbio.2011.05.368 · 3.55 Impact Factor
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    Bidyut Ghosh · Steven D Leach ·
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    ABSTRACT: Comment on: Andreia V. Pinho, et al. Cell Cycle 2011; 10: In press.
    Cell cycle (Georgetown, Tex.) 06/2011; 10(11):1717. DOI:10.4161/cc.10.11.15686 · 4.57 Impact Factor

  • Cancer Research 04/2011; 71(8 Supplement):2449-2449. DOI:10.1158/1538-7445.AM2011-2449 · 9.33 Impact Factor
  • Shu Liu · Steven D Leach ·
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    ABSTRACT: First established as a valuable vertebrate model system for studying development, zebrafish have emerged as an attractive animal system for modeling human cancers. Major technical advances have been essential for the generation of zebrafish cancer models relevant to human diseases. These models develop tumors in various organ sites that bear striking resemblance to human malignances, both histologically and genetically. Thus, the focus of cancer research in zebrafish has transcended the need to validate zebrafish as a viable model organism to study cancer biology. With the significant advantages of in vivo imaging, the power of forward genetics, well-established high efficiency for transgenesis, and ease of transplantation, further exploration of the zebrafish cancer models not only will generate unique insights into underlying mechanisms of cancer but will also provide platforms useful for drug discovery.
    Annual Review of Pathology Mechanisms of Disease 02/2011; 6(1):71-93. DOI:10.1146/annurev-pathol-011110-130330 · 18.75 Impact Factor
  • Shu Liu · Michael J. Parsons · Jon M. Davison · Steven D. Leach ·

    Cancer Research 01/2011; 70(8 Supplement):4162-4162. DOI:10.1158/1538-7445.AM10-4162 · 9.33 Impact Factor
  • Shu Liu · Steven D Leach ·
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    ABSTRACT: Pancreatic cancer is a genetic disease in which somatic mutations in the KRAS proto-oncogene are detected in a majority of tumors. KRAS mutations represent an early event during pancreatic tumorigenesis, crucial for cancer initiation and progression. Recent studies, including comprehensive sequencing of the pancreatic cancer exome, have implicated the involvement of a number of additional core signaling pathways during pancreatic tumorigenesis. Improving our understanding of genetic interactions between KRAS and these additional pathways represents a critical challenge, as these interactions may provide novel opportunities for diagnosis and treatment. However, studying these interactions requires the expression of multiple transgenes in relevant cell types, an effort that has proven very difficult to achieve using gene targeted mice and is also technically challenging in zebrafish. Based on the ability of the Gal4 transcriptional activator to drive the expression of multiple transgenes under regulation of UAS (upstream activator sequence) regulatory elements, the Gal4/UAS system represents an attractive strategy for the study of genetic interactions. In this chapter, we review our experience using the Gal4/UAS system to model KRAS-initiated pancreatic cancer in zebrafish, as well as our early efforts using this system to study the influence of other cooperating oncogenes. We also describe techniques used to identify and characterize pancreatic tumors in adult transgenic fish.
    Methods in cell biology 01/2011; 105:367-81. DOI:10.1016/B978-0-12-381320-6.00015-1 · 1.42 Impact Factor
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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.
    Genes & development 12/2010; 24(24):2754-9. DOI:10.1101/gad.1950610 · 10.80 Impact Factor
  • Oscar K Serrano · Muhammad A Chaudhry · Steven D Leach ·
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    ABSTRACT: The strength of functional imaging lies in its ability to detect malignant disease irrespective of lesion morphology. In this setting, 18FDG-PET can complement management by providing a more accurate diagnosis. When combined as an adjunct to CT, 18FDG-PET can increase the sensitivity, specificity, and accuracy for detecting a pancreatic malignancy, especially in patients in whom CT alone fails to identify a discrete mass or in whom biopsy results are indeterminate. This capability is accentuated with small lesions of the pancreas. 18FDG-PET is significantly more sensitive in detecting metastatic disease than conventional CT imaging. Moreover, 18FDG-PET is able to differentiate tumor response to therapy in the postoperative setting, and could potentially serve to monitor recurrence patterns in the setting of neoadjuvant or adjuvant chemoradiotherapy. Finally, as 18FDG-PET/CT fusion modalities become more widespread and technical advances in image acquisition progress, 18FDG-PET will continue to have an increasing role in the diagnosis, staging, and surveillance of pancreatic cancer, integrating anatomic information with functional imaging.
    Advances in Surgery 09/2010; 44(1):313-25. DOI:10.1016/j.yasu.2010.05.007

Publication Stats

9k Citations
1,217.61 Total Impact Points


  • 2014-2015
    • Memorial Sloan-Kettering Cancer Center
      • Department of Pathology
      New York, New York, United States
  • 2001-2014
    • Johns Hopkins University
      • • Department of Surgery
      • • McKusick-Nathans Institute of Genetic Medicine
      • • Department of Cell Biology
      Baltimore, Maryland, United States
  • 2001-2013
    • Johns Hopkins Medicine
      • • McKusick-Nathans Institute of Genetic Medicine
      • • Department of Surgery
      • • Department of Cell Biology
      • • Division of General Surgery and Surgical Oncology
      • • Department of Pathology
      Baltimore, MD, United States
  • 2009
    • University of Pennsylvania
      • Division of Gastroenterology
      Philadelphia, PA, United States
  • 2008
    • Philipps University of Marburg
      Marburg, Hesse, Germany
    • Bryn Mawr College
      • Department of Biology
      Bryn Mawr, Pennsylvania, United States
  • 1998-2005
    • Vanderbilt University
      • • Department of Surgery
      • • Department of Radiology and Radiological Sciences
      • • Division of Surgical Oncology
      Nashville, MI, United States
  • 2004
    • University Pompeu Fabra
      Barcino, Catalonia, Spain
  • 1997-2001
    • Gateway-Vanderbilt Cancer Treatment Center
      Clarksville, Tennessee, United States
  • 1995-1996
    • University of Texas MD Anderson Cancer Center
      • Department of Surgical Oncology
      Houston, TX, United States