DESIGNING TUNABLE VISCOELASTIC HYDROGELS FOR STUDYING PANCREATIC CANCER CELL FATE

Pancreatic ductal adenocarcinoma (PDAC) is the most common and lethal pancreatic cancer subtype. The silent tumor progression and aggressive development of chemo-resistance are the primary factors behind the dismal 13% 5-year survival rate. The tumor microenvironment (TME) has been the focus of many pancreatic cancer research since the TME actively interacts with cancer cells to promote tumor growth, drug resistance, and invasion. A thorough comprehension of PDAC cell and TME interaction is crucial to uncover the mechanism and key regulators behind PDAC’s rapid progression, high propensity for metastasis, and exceptional resistance to cancer therapeutics. Hydrogels have emerged as invaluable tools for investigating cell-matrix communication in three-dimensional (3D) environments, as their chemical and mechanical properties can be easily tuned to mimic the dynamic nature of native tissue. However, current biomimetic hydrogels used in PDAC models are elastic and often lack tissue-relevant viscoelastic properties, such as hysteresis and stress-relaxation. Stress-relaxation influences various cellular processes, including differentiation, proliferation, and cancer progression. This dissertation aims to address this gap by introducing viscoelasticity and fast stress relaxation into existing hydrogel platforms to more accurately replicate PDAC tissue mechanics. Specifically, we employ two chemistries: thiol-norbornene photopolymerization and boronic ester dynamic bonding to fabricate gelatin-based hydrogels. Gels formed solely via irreversible thiol-norbornene chemistry exhibit elasticity and slow stress-relaxation, while gels formed with both thiol-norbornene and reversible boronic ester bonds display viscoelastic properties and fast stress-relaxation. Cell-laden hydrogels with varying mechanical properties (low vs high stiffness, slow vs fast relaxation) were used as tools to explore the effects of matrix stiffening and viscoelasticity in promoting cancer aggressiveness. It was revealed that matrix stiffening, coupled with the inclusion of cancer-associated fibroblast induced the epithelial-mesenchymal transition phenotype (EMT) in pancreatic cancer cells. In addition, fast-relaxing hydrogels promoted cancer cell survival, growth, and EMT via engaging integrin β-1 (ITGB1). Blocking of ITGB1 receptors diminished cell growth, however, cells in fast-relaxing gels upregulated SNAIL1, a biomarker of poor cancer prognosis. Collectively, results from these studies describe our recent progress in understanding the mechanism by which stiff and viscoelastic substrates facilitate cancer development and how cellular functions can be controlled via modulating cell receptor-matrix binding.