Identification of Mechanisms of Gemcitabine Resistance Using a Whole Genome Shrna Screen in a Novel in Vitro Coculture Model of Pancreatic Cancer
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Identification of mechanisms of gemcitabine resistance using a whole genome shRNA screen in a novel in vitro coculture model of pancreatic cancer. Graham David Mills Wolfson College Cancer Research UK Cambridge Institute University of Cambridge This dissertation is submitted for the degree of Doctor of Philosophy August 2018 Declaration This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration except as declared in the Preface and specified in the text. It is not substantially the same as any that I have submitted, or, is being concurrently submitted for a degree or diploma or other qualification at the University of Cambridge or any other University or similar institution except as declared in the Preface and specified in the text. I further state that no substantial part of my dissertation has already been submitted, or, is being concurrently submitted for any such degree, diploma or other qualification at the University of Cambridge or any other University or similar institution except as declared in the Preface and specified in the text. It does not exceed the prescribed word limit for the relevant Degree Committee. 1 Abstract Identification of mechanisms of gemcitabine resistance using a whole genome shRNA screen in a novel in vitro coculture model of pancreatic cancer. Graham David Mills Pancreatic ductal adenocarcinoma (PDAC) remains one of the most difficult to treat major cancers, with a 5-year survival of less than 5%, and little to no improvement in prognosis over the previous fifty years. The complexity and heterogeneity of the pancreatic tumour and its highly desmoplastic stromal microenvironment present major physical and biochemical barriers to the delivery and efficacy of therapeutics. Improving the success rate of therapeutic interventions for this cancer requires both a detailed understanding of stromal dynamics and drug resistance within the tumour, as well validated in vitro and in vivo models through which novel therapeutic targets can be identified and investigated. Within this project I focused initially on further developing, validating, and evaluating mechanistically a coculture model of gemcitabine resistance, established previously. I demonstrated that the gemcitabine resistance observed in coculture was a product of cell- cell contact, transient in nature, and related to cell density-mediated signalling processes. I discovered that the mesenchymal-like cell lines thought to drive the resistance effect within the model were epithelial cancer cells in origin, rather than a cancer associated fibroblast (CAF) line, verified through genotype and protein signature experiments. This finding was expanded through demonstration that true pancreatic CAFs did not induce gemcitabine resistance in the coculture model and hence demonstrated the real challenge in isolating true pancreatic CAFs from genetically engineered mouse PDAC tumour tissue using canonical techniques. Nevertheless, the in vitro coculture model data was congruent with in vivo and clinical gemcitabine efficacy data, suggesting it may have utility as a lower cost model for evaluating efficacy of novel drug combinations with the aim of subsequent translation into the clinic. The coculture model was used as the foundation of a genome-wide shRNA depletion screen to identify sensitizers of gemcitabine resistance in PDAC in vitro culture. The primary screen and subsequent validation screen identified 19 high confidence genes with potential 2 translational value, of which knockdown sensitised to gemcitabine within this model. This is alongside an expanded list of 444 genes significantly contributing to the resistance phenotype, representing pathways such as MTORC signalling and DNA damage response. This dataset serves as the first shRNA-mediated coculture screen for gemcitabine resistance in PDAC. My findings lay credence to the value of this model of gemcitabine resistance for preclinical use and provides a robust and voluminous shRNA dataset supporting target identification for the ablation of gemcitabine chemoresistance in PDAC. 3 Acknowledgements I would like to express sincere gratitude towards my supervisor Professor Duncan Jodrell for his support, guidance, and encouragement throughout my doctoral studies. Further, I would like to extend this gratitude to Dr Frances Richards, who has provided unwavering and truly invaluable scientific and pastoral support during my time in the laboratory. I would further like to thank Professor Greg Hannon, my secondary supervisor, for scientific guidance throughout my project as well as Dr Nicolas Erard, a fellow doctoral candidate of the Hannon laboratory, with whom I collaborated with extensively through my degree. I also would like to express thanks to the numerous members of the Jodrell laboratory who provided collaboration and support throughout my time, including Ms Jo Bramhall, Dr Séverine Mollard, Dr Siang Boon Koh, Dr Aarthi Gopinathan, and Dr Sandra Bernaldo de Quirós Fernández. The value of pastoral support and guidance provided by Dr Ann Kaminski will forever be appreciated, as will the funding by Cancer Research UK, and the scientific support of the CRUK CI core facilities, most notably from Chandra Sekhar Reddy Chilamakuri in Bioinformatics. Finally, I would like to acknowledge the unconditional support and encouragement from my parents, John and Felicity Mills, my sister Laura Mills, as well as from friendships old and new. A sympathetic friend can be quite as dear as a brother. 4 List of Abbreviations CAF Cancer-associated fibroblast CDA Cytidine deaminase CRISPR Clustered regularly interspaced short palindromic repeats ECM Extracellular matrix EMT Epithelial-mesenchymal transition FLC Fibroblast-like cell GEDA Genetically engineered mouse-derived allograft GEMM Genetically engineered mouse model GSEA Gene set enrichment analysis IF Immunofluorescence LSL Lox-stop-lox PDAC Pancreatic ductal adenocarcinoma PK/PD Pharmacokinetic/pharmacodynamic PSC Pancreatic stellate cell shRNA short hairpin RNA TCGA The cancer genome atlas 5 Table of Contents 1. Introduction ............................................................................................................... 11 1.1 Introduction to PDAC ................................................................................................ 11 1.1.1 Biology of the pancreas ..................................................................................... 11 1.1.2 Pathology of disease .......................................................................................... 12 1.1.3 Molecular and genetic characterisation ............................................................ 14 1.2 Clinical management of PDAC ................................................................................... 16 1.2.1 Current clinical paradigms ................................................................................. 16 1.2.2 Novel targeted strategies .................................................................................. 17 1.2.3 Challenges in treatment resistance ................................................................... 19 1.2.4 Molecular basis of resistance ............................................................................ 19 1.2.5 Approaches to combat resistance ..................................................................... 21 1.3 Role of stroma and tumour micro-environment in PDAC ......................................... 21 1.3.1 Cell type composition and introduction ............................................................ 21 1.3.2 Pro- and anti-tumourigenic components .......................................................... 23 1.3.3 Targeting stroma for clinical benefit .................................................................. 24 1.4 Use of models to identify and develop new treatment strategies ........................... 26 1.4.1 Overview ............................................................................................................ 26 1.4.2 In silico approaches for drug target identification ............................................ 26 1.4.3 In vivo model development ............................................................................... 26 1.4.4 The role of in vitro models in the drug development process .......................... 28 1.4.5 Development of novel in vitro models .............................................................. 29 1.4.6 Screening techniques for drug development in vitro ........................................ 31 1.4.7 Incorporating stromal analysis into in vitro models in PDAC ............................ 31 1.5 Project aims ............................................................................................................... 33 6 2. Materials and methods .............................................................................................. 34 2.1 Materials ........................................................................................................................ 34 2.1.1 Reagents .................................................................................................................. 34 2.1.2 Cell lines ................................................................................................................... 34 2.1.3 Cell culture reagents ................................................................................................ 35 2.1.4 Buffers.....................................................................................................................