Youngkyu Park

Organoid Models of Human and Mouse Ductal Pancreatic Cancer

Pancreatic cancer is one of the most lethal malignancies due to its late diagnosis and limited response to treatment. Tractable methods to identify and interrogate pathways involved in pancreatic tumorigenesis are urgently needed. We established organoid models from normal and neoplastic murine and human pancreas tissues. Pancreatic organoids can be rapidly generated from resected tumors and biopsies, survive cryopreservation, and exhibit ductal- and disease-stage-specific characteristics. Orthotopically transplanted neoplastic organoids recapitulate the full spectrum of tumor development by forming early-grade neoplasms that progress to locally invasive and metastatic carcinomas. Due to their ability to be genetically manipulated, organoids are a platform to probe genetic cooperation. Comprehensive transcriptional and proteomic analyses of murine pancreatic organoids revealed genes and pathways altered during disease progression. The confirmation of many of these protein changes in human tissues demonstrates that organoids are a facile model system to discover characteristics of this deadly malignancy.

The Utilization of Extracellular Proteins as Nutrients Is Suppressed by mTORC1

Despite being surrounded by diverse nutrients, mammalian cells preferentially metabolize glucose and free amino acids. Recently, Ras-induced macropinocytosis of extracellular proteins was shown to reduce a transformed cells dependence on extracellular glutamine. Here, we demonstrate that protein macropinocytosis can also serve as an essential amino acid source. Lysosomal degradation of extracellular proteins can sustain cell survival and induce activation of mTORC1 but fails to elicit significant cell accumulation. Unlike its growth-promoting activity under amino-acid-replete conditions, we discovered that mTORC1 activation suppresses proliferation when cells rely on extracellular proteins as an amino acid source. Inhibiting mTORC1 results in increased catabolism of endocytosed proteins and enhances cell proliferation during nutrient-depleted conditions in vitro and within vascularly compromised tumors in vivo. Thus, by preventing nutritional consumption of extracellular proteins, mTORC1 couples growth to availability of free amino acids. These results may have important implications for the use of mTOR inhibitors as therapeutics.

Distinct populations of inflammatory fibroblasts and myofibroblasts in pancreatic cancer

Pancreatic stellate cells (PSCs) differentiate into cancer-associated fibroblasts (CAFs) that produce desmoplastic stroma, thereby modulating disease progression and therapeutic response in pancreatic ductal adenocarcinoma (PDA). However, it is unknown whether CAFs uniformly carry out these tasks or if subtypes of CAFs with distinct phenotypes in PDA exist. We identified a CAF subpopulation with elevated expression of &agr;-smooth muscle actin (&agr;SMA) located immediately adjacent to neoplastic cells in mouse and human PDA tissue. We recapitulated this finding in co-cultures of murine PSCs and PDA organoids, and demonstrated that organoid-activated CAFs produced desmoplastic stroma. The co-cultures showed cooperative interactions and revealed another distinct subpopulation of CAFs, located more distantly from neoplastic cells, which lacked elevated &agr;SMA expression and instead secreted IL6 and additional inflammatory mediators. These findings were corroborated in mouse and human PDA tissue, providing direct evidence for CAF heterogeneity in PDA tumor biology with implications for disease etiology and therapeutic development.

A pipeline for the generation of shRNA transgenic mice

RNA interference (RNAi) is an extremely effective tool for studying gene function in almost all metazoan and eukaryotic model systems. RNAi in mice, through the expression of short hairpin RNAs (shRNAs), offers something not easily achieved with traditional genetic approaches—inducible and reversible gene silencing. However, technical variability associated with the production of shRNA transgenic strains has so far limited their widespread use. Here we describe a pipeline for the generation of miR30-based shRNA transgenic mice that enables efficient and consistent targeting of doxycycline-regulated, fluorescence-linked shRNAs to the Col1a1 locus. Notably, the protocol details crucial steps in the design and testing of miR30-based shRNAs to maximize the potential for developing effective transgenic strains. In all, this 14-week procedure provides a fast and cost-effective way for any laboratory to investigate gene function in vivo in the mouse.

Acquired Dependence Of Acute Myeloid Leukemia On The DEAD-BOX RNA Helicase DDX5

Acute myeloid leukemia (AML) therapy involves compounds that are cytotoxic to both normal and cancer cells, and relapsed AML is resistant to subsequent chemotherapy. Thus, agents are needed that selectively kill AML cells with minimal toxicity. Here, we report that AML is dependent on DDX5 and that inhibiting DDX5 expression slows AML cell proliferation in vitro and AML progression in vivo but is not toxic to cells from normal bone marrow. Inhibition of DDX5 expression in AML cells induces apoptosis via induction of reactive oxygen species (ROS). This apoptotic response can be blocked either by BCL2 overexpression or treatment with the ROS scavenger N-acetyl-L-cysteine. Combining DDX5 knockdown with a BCL2 family inhibitor cooperates to induce cell death in AML cells. By inhibiting DDX5 expression in vivo, we show that DDX5 is dispensable for normal hematopoiesis and tissue homeostasis. These results validate DDX5 as a potential target for blocking AML.

Creating Transgenic shRNA Mice by Recombinase-Mediated Cassette Exchange

RNA interference (RNAi) enables sequence-specific, experimentally induced silencing of virtually any gene by tapping into innate regulatory mechanisms that are conserved among most eukaryotes. The principles that enable transgenic RNAi in cell lines can also be used to create transgenic animals, which express short-hairpin RNAs (shRNAs) in a regulated or tissue-specific fashion. However, RNAi in transgenic animals is somewhat more challenging than RNAi in cultured cells. The activities of promoters that are commonly used for shRNA expression in cell culture can vary enormously in different tissues, and founder lines also typically vary in transgene expression due to the effects of their single integration sites. There are many ways to produce mice carrying shRNA transgenes and the method described here uses recombinase-mediated cassette exchange (RMCE). RMCE permits insertion of the shRNA transgene into a well-characterized locus that gives reproducible and predictable expression in each founder and enhances the probability of potent expression in many cell types. This procedure is more involved and complex than simple pronuclear injection, but if even a few shRNA mice are envisioned, for example, to probe the functions of several genes, the effort of setting up the processes outlined below are well worthwhile. Note that when creating a transgenic mouse, one should take care to use the most potent shRNA possible. As a rule of thumb, the sequence chosen should provide >90% knockdown when introduced into cultured cells at single copy (e.g., on retroviral infection at a multiplicity of ≤0.3).

PanIN neuroendocrine cells promote tumorigenesis via neuronal crosstalk

Nerves are a notable feature of the tumor microenvironment in some epithelial tumors, but their role in the malignant progression of pancreatic ductal adenocarcinoma (PDAC) is uncertain. Here we identify dense innervation in the microenvironment of precancerous pancreatic lesions, known as pancreatic intraepithelial neoplasms (PanIN), and describe a unique subpopulation of neuroendocrine PanIN cells that express the neuropeptide substance P (SP) receptor Neurokinin 1-R (NK1-R). Using organoid culture, we demonstrated that sensory neurons promoted the proliferation of PanIN organoids via SP-NK1-R signaling and Stat3 activation. Nerve-responsive neuroendocrine cells exerted trophic influences and potentiated global PanIN organoid growth. Sensory denervation of a genetically engineered mouse model of PDAC led to loss of Stat3 activation, a decrease in the neoplastic neuroendocrine cell population, and impaired PanIN progression to tumor. Overall, our data provide evidence that nerves of the PanIN microenvironment promote oncogenesis, likely via direct signaling to neoplastic neuroendocrine cells capable of trophic influences. These findings identify neuroepithelial crosstalk as a potential novel target in PDAC treatment.

Abstract A27: Exploring the role of glycosylation in pancreatic disease

Pancreatic ductal adenocarcinoma (PDA) is almost uniformly lethal and surgical intervention is the only cure. Unfortunately, most patients are ineligible for resection because of the advanced stage of disease by the time of diagnosis. This is due in part to the lack of diagnostic tools, especially for families with elevated risk. The PDA biomarker, CA19-9, is measured in the blood to follow tumor burden longitudinally, but is neither sensitive nor specific enough to be used for diagnosis. The use of CA19-9 in PDA diagnosis is problematic given the elevation of CA19-9 in benign pancreatic disease, such as pancreatitis. While CA19-9 has been traditionally used as a diagnostic, retrospective studies reported that PDA patients who maintain a CA19-9 negative/low status have a significantly longer survival relative to those with higher CA19-9 levels in multivariate analyses. The functional significance of CA19-9 to PDA initiation, maintenance, and progression remains unclear due in part to the absence of this carbohydrate modification in mice. We found that expression of CA19-9 in the mouse pancreas is sufficient to induce pancreatitis, a benign proliferative condition that often confounds the diagnosis of PDA. Specifically, CA19-9 elevation resulted in rapid elevation of pancreatic enzymes in the blood, pancreatic infiltration of immune cells, acinar-to-ductal metaplasia and atrophy, as well as increased proliferation. Furthermore, we explored the utility of CA19-9 as a therapeutic target for both acute and chronic pancreatitis. This avenue of treatment strategy exhibits potential given that a pilot study demonstrated that turning off CA19-9 expression results in the normalization of pancreatic enzyme levels within four days following an acute episode of pancreatitis. Future work will focus on how elevation of this glycosylation modification mediates the development of pancreatitis by identifying the signaling pathways that are altered upon CA19-9 expression. In addition, we will explore the efficacy of therapeutically targeting CA19-9 in both pancreatitis and PDA with a larger goal of delineating the role of CA19-9 in pancreatic disease

Abstract B43: The utilization of extracellular proteins as nutrients is suppressed by mTORC1

To engage in growth and proliferation, cells require a continuous supply of precursors for macromolecular synthesis. Despite being surrounded by diverse nutrients, mammalian cells preferentially metabolize glucose and free amino acids. However, it was recently shown that Ras-induced macropinocytosis of extracellular proteins could reduce a transformed cell9s dependence on extracellular amino acids. Here, we show that macropinocytosis and lysosomal catabolism of extracellular proteins can serve as a source of essential amino acids. Lysosomal degradation of internalized proteins can sustain cell survival and induce lysosomal recruitment and activation of mammalian target of rapamycin complex 1 (mTORC1), but fails to elicit significant cell accumulation. Surprisingly, we discovered that unlike its growth-promoting activity under amino acid-replete conditions, mTORC1 activation suppresses proliferation when cells rely on extracellular proteins as an amino acid source. Inhibiting mTORC1 results in increased catabolism of endocytosed proteins and enhances cell proliferation during nutrient-depleted conditions in vitro and within vascularly compromised tumors in vivo. Thus, by preventing consumption of extracellular proteins as nutrients, mTORC1 couples growth to availability of free amino acids. These results may have important implications for the use of mTOR inhibitors as therapeutics. Citation Format: Wilhelm Palm, Youngkyu Park, Kevin Wright, Natalya N. Pavlova, David A. Tuveson, Craig B. Thompson. The utilization of extracellular proteins as nutrients is suppressed by mTORC1. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B43.

Abstract B16: Using human patient-derived organoids to identify genetic dependencies in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignancies due to its late diagnosis and limited response to treatment. Tractable model systems to interrogate pathways involved in pancreatic tumorigenesis and to probe individual responses to novel therapies are urgently needed. To that end, we established methods to culture normal and neoplastic pancreatic duct cells as three-dimensional organoid cultures. Pancreatic organoids can be rapidly generated from resected tumors or fine needle biopsies, survive cryopreservation, and exhibit ductal- and disease-stage-specific characteristics. Following orthotopic transplant, neoplastic organoids recapitulated the full spectrum of tumor development by forming early-grade neoplasms that progressed to locally invasive and metastatic carcinomas, demonstrating the utility of organoids to model the stages of PDA tumorigenesis. Monolayer cell lines were generated from organoid cultures with high efficiency, creating a diverse collection of new PDA cell lines. To better understand pathways involved in PDA progression, we performed transcriptomic and proteomic analyses of murine organoids derived from normal pancreatic ducts, pancreatic intraepithelial neoplasias (PanINs), and PDAs. These datasets revealed expression changes associated with early and late pancreatic tumorigenesis. To identify genes dysregulated during pancreatic tumorigenesis whose depletion impaired human PDA cells, a CRISPR-Cas competition assay was employed. Taken together, pancreatic organoids offer a novel model system for studying pancreatic cancer biology and can be used to screen for genetic dependencies in PDA. Citation Format: Lindsey A. Baker, Herve Tiriac, Vincenzo Corbo, Sylvia F. Boj, Chang-il Hwang, Iok In Christine Chio, Danielle D. Engle, Myrthe Jager, Mariano Ponz-Sarvise, Mona S. Spector, Ana Gracanin, Tobiloba Oni, Kenneth H. Yu, Ruben van Boxtel, Meritxell Huch, Keith D. Rivera, John P. Wilson, Michael E. Feigin, Daniel Ohlund, Abram Handly-Santana, Christine M. Ardito-Abraham, Michael Ludwig, Ela Elyada, Brinda Alagesan, Giulia Biffi, Georgi N. Yordanov, Bethany Delcuze, Brianna Creighton, Kevin Wright, Youngkyu Park, Folkert H.M. Morsink, I. Quintus Molenaar, Inne H. Borel Rinkes, Edwin Cuppen, Yuan Hao, Ying Jin, Isaac J. Nijman, Christine Iacobuzio-Donahue, Steven D. Leach, Darryl J. Pappin, Molly Hammell, David S. Klimstra, Olca Basturk, Ralph H. Hruban, George Johan Offerhaus, Robert G.J. Vries, Hans Clevers, David A. Tuveson. Using human patient-derived organoids to identify genetic dependencies in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B16.