Challenges and Opportunities in Modeling Pancreatic Cancer

The Crosstalk Analysis between mPSCs and Panc1 Cells Identifies CCN1 as a Positive Regulator of Gemcitabine Sensitivity in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is a deadly disease that is almost entirely resistant to conventional chemotherapy and radiation therapy. A significant factor in this resistance appears to be the dense desmoplastic stroma, which contains various cancer-associated fibroblast (CAF) populations. However, our understanding of the communication between tumor cells and CAFs that contributes to this aggressive malignancy is still developing. Recently, we used an advanced three-dimensional heterospecies, heterospheroid co-culture model to investigate the signaling between human pancreatic tumor Panc1 cells and mouse pancreatic stellate cells (mPSCs) through global expression profiling. Upon discovering that CCN1 was significantly upregulated in Panc1 cells during co-culture, we decided to explore the role of CCN1 using CRISPR-Cas9 knockout technology. Panc1 cells lacking CCN1 showed reduced differentiation and decreased sensitivity to gemcitabine, primarily due to lower expression of genes involved in gemcitabine transport and metabolism. Additionally, we observed that stimulation with TGF-β1 and lysophosphatidic acid increased CCN1 expression in Panc1 cells and induced a shift in mPSCs towards a more myofibroblastic CAF-like phenotype.

Theranostic nanoparticles for detection and treatment of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most recalcitrant cancers due to its late diagnosis, poor therapeutic response, and highly heterogeneous microenvironment. Nanotechnology has the potential to overcome some of the challenges to improve diagnostics and tumor-specific drug delivery but they have not been plausibly viable in clinical settings. The review focuses on active targeting strategies to enhance pancreatic tumor-specific uptake for nanoparticles. Additionally, this review highlights using actively targeted liposomes, micelles, gold nanoparticles, silica nanoparticles, and iron oxide nanoparticles to improve pancreatic tumor targeting. Active targeting of nanoparticles toward either differentially expressed receptors or PDAC tumor microenvironment (TME) using peptides, antibodies, small molecules, polysaccharides, and hormones has been presented. We focus on microenvironment-based hallmarks of PDAC and the potential for actively targeted nanoparticles to overcome the challenges presented in PDAC. It describes the use of nanoparticles as contrast agents for improved diagnosis and the delivery of chemotherapeutic agents that target various aspects within the TME of PDAC. Additionally, we review emerging nano-contrast agents detected using imaging-based technologies and the role of nanoparticles in energy-based treatments of PDAC. This article is categorized under: Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Targeting ROCK2 improves macromolecular permeability in a 3D fibrotic pancreatic cancer microenvironment model

Pancreatic cancer is characterized by a densely fibrotic stroma. The fibrotic stroma hinders the intratumoral penetration of nanomedicine and diminishes therapeutic efficacy. Fibrosis is characterized by an abnormal organization of extracellular matrix (ECM) components, namely the abnormal deposition and/or orientation of collagen and fibronectin. Abnormal ECM organization is chiefly driven by pathological signaling in pancreatic stellate cells (PSCs), the main cell type involved in fibrogenesis. However, whether targeting signaling pathways involved in abnormal ECM organization improves the intratumoral penetration of nanomedicines is unknown. Here, we show that targeting transforming growth factor-β (TGFβ)/Rho-associated kinase (ROCK) 1/2 signaling in PSCs normalizes ECM organization and concomitantly improves macromolecular permeability of the fibrotic stroma. Using a 3-dimensional cell culture model of the fibrotic pancreatic cancer microenvironment, we found that pharmacological inhibition of TGFβ or ROCK1/2 improves the permeation of various macromolecules. By using an isoform-specific pharmacological inhibitor and siRNAs, we show that targeting ROCK2, but not ROCK1, alone is sufficient to normalize ECM organization and improve macromolecular permeability. Moreover, we found that ROCK2 inhibition/knockdown attenuates Yes-associated protein (YAP) nuclear localization in fibroblasts co-cultured with pancreatic cancer cells in 3D. Finally, pharmacological inhibition or siRNA-mediated knockdown of YAP normalized ECM organization and improved macromolecular permeability. Our results together suggest that the TGFβ/ROCK2/YAP signaling axis may be therapeutically targeted to normalize ECM organization and improve macromolecular permeability to augment therapeutic efficacy of nanomedicines in pancreatic cancer.

Therapeutic Strategies to Overcome Fibrotic Barriers to Nanomedicine in the Pancreatic Tumor Microenvironment

Pancreatic cancer is notorious for its dismal prognosis. The enhanced permeability and retention (EPR) effect theory posits that nanomedicines (therapeutics in the size range of approximately 10-200 nm) selectively accumulate in tumors. Nanomedicine has thus been suggested to be the "magic bullet"-both effective and safe-to treat pancreatic cancer. However, the densely fibrotic tumor microenvironment of pancreatic cancer impedes nanomedicine delivery. The EPR effect is thus insufficient to achieve a significant therapeutic effect. Intratumoral fibrosis is chiefly driven by aberrantly activated fibroblasts and the extracellular matrix (ECM) components secreted. Fibroblast and ECM abnormalities offer various potential targets for therapeutic intervention. In this review, we detail the diverse strategies being tested to overcome the fibrotic barriers to nanomedicine in pancreatic cancer. Strategies that target the fibrotic tissue/process are discussed first, which are followed by strategies to optimize nanomedicine design. We provide an overview of how a deeper understanding, increasingly at single-cell resolution, of fibroblast biology is revealing the complex role of the fibrotic stroma in pancreatic cancer pathogenesis and consider the therapeutic implications. Finally, we discuss critical gaps in our understanding and how we might better formulate strategies to successfully overcome the fibrotic barriers in pancreatic cancer.

3D In Vivo Models for Translational Research on Pancreatic Cancer: The Chorioallantoic Membrane (CAM) Model

Simple Summary

The 5-year overall survival rate for all stages of pancreatic cancer is relatively low at about only 6%. As a result of this exceedingly poor prognosis, new research models are necessary to investigate this highly malignant cancer. One model that has been used extensively for a vast variety of different cancers is the chorioallantoic membrane (CAM) model. It is based on an exceptionally vascularized membrane that develops within fertilized chicken eggs and can be used for the grafting and analysis of tumor tissue. The aim of the study was to summarize already existing works on pancreatic ductal adenocarcinoma (PDAC) and the CAM model. The results were subdivided into different categories that include drug testing, angiogenesis, personalized medicine, modifications of the model, and further developments to help improve the unfavorable prognosis of this disease.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with adverse outcomes that have barely improved over the last decade. About half of all patients present with metastasis at the time of diagnosis, and the 5-year overall survival rate across all stages is only 6%. Innovative in vivo research models are necessary to combat this cancer and to discover novel treatment strategies. The chorioallantoic membrane (CAM) model represents one 3D in vivo methodology that has been used in a large number of studies on different cancer types for over a century. This model is based on a membrane formed within fertilized chicken eggs that contain a dense network of blood vessels. Because of its high cost-efficiency, simplicity, and versatility, the CAM model appears to be a highly valuable research tool in the pursuit of gaining more in-depth insights into PDAC. A summary of the current literature on the usage of the CAM model for the investigation of PDAC was conducted and subdivided into angiogenesis, drug testing, modifications, personalized medicine, and further developments. On this comprehensive basis, further research should be conducted on PDAC in order to improve the abysmal prognosis of this malignant disease.

Modeling human pancreatic ductal adenocarcinoma for translational research: current options, challenges, and prospective directions

Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy with one of the lowest survival rates. Early detection, an improved understanding of tumor biology, and novel therapeutic discoveries are needed in order to improve overall patient survival. Scientific progress towards meeting these goals relies upon accurate modeling of the human disease. From two-dimensional (2D) cell lines to the advanced modeling available today, we aim to characterize the critical tools in efforts to further understand PDAC biology. The National Center for Biotechnology Information's PubMed and the Elsevier's SCOPUS were used to perform a comprehensive literature review evaluating preclinical human-derived PDAC models. Keywords included pancreatic cancer, PDAC, preclinical models, KRAS mutations, xenograft, co-culturing fibroblasts, co-culturing lymphocytes and PDAC immunotherapy Initial search was limited to articles about PDAC and was then expanded to include other gastrointestinal malignancies where information may complement our effort. A supervised review of the key literature's references was utilized to augment the capture of relevant data. The discovery and refinement of techniques enabling immortalized 2D cell culture provided the cornerstone for modern cancer biology research. Cell lines have been widely used to represent PDAC in vitro but are limited in capacity to model three-dimensional (3D) tumor attributes and interactions within the tumor microenvironment. Xenografts are an alternative method to model PDAC with improved capacity to understand certain aspects of 3D tumor biology in vivo while limited by the use of immunodeficient mice. Advances of in vitro modeling techniques have led to 3D organoid models for PDAC biology. Co-culturing models in the 3D environment have been proposed as an efficient modeling system for improving upon the limitations encountered in the standard 2D and xenograft tumor models. The integrated network of cells and stroma that comprise PDAC in vivo need to be accurately depicted ex vivo to continue to make progress in this disease. Recapitulating the complex tumor microenvironment in a preclinical model of human disease is an outstanding and urgent need in PDAC. Definitive characterization of available human models for PDAC serves to further the core mission of pancreatic cancer translational research.

Microenvironmental Determinants of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) belongs to the most lethal solid tumors in humans. A histological hallmark feature of PDAC is the pronounced tumor microenvironment (TME) that dynamically evolves during tumor progression. The TME consists of different non-neoplastic cells such as cancer-associated fibroblasts, immune cells, endothelial cells, and neurons. Furthermore, abundant extracellular matrix components such as collagen and hyaluronic acid as well as matricellular proteins create a highly dynamic and hypovascular TME with multiple biochemical and physical interactions among the various cellular and acellular components that promote tumor progression and therapeutic resistance. In recent years, intensive research efforts have resulted in a significantly improved understanding of the biology and pathophysiology of the TME in PDAC, and novel stroma-targeted approaches are emerging that may help to improve the devastating prognosis of PDAC patients. However, none of anti-stromal therapies has been approved in patients so far, and there is still a large discrepancy between multiple successful preclinical results and subsequent failure in clinical trials. Furthermore, recent findings suggest that parts of the TME may also possess tumor-restraining properties rendering tailored therapies even more challenging.

Synergistic cytotoxicity and co-autophagy inhibition in pancreatic tumor cells and cancer-associated fibroblasts by dual functional peptide-modified liposomes

Pancreatic ductal adenocarcinoma (PDA) is a highly fatal disease with 5-year survival of ∼8.5%. Nanoplatforms such as nab-paclitaxel and nanoliposomal irinotecan demonstrate superiority and utility in treating different progressions of PDA by prolonging the median overall survival by only a few months. Due to the dense surrounding stroma and the high autophagy in pancreatic cancer, integrin ɑ_vβ₃ targeting, acid environmental sensitive, TR peptide-modified liposomal platforms loaded with combined autophagy inhibiting hydroxychloroquine (HCQ), and cytotoxic paclitaxel (PTX) were designed (TR-PTX/HCQ-Lip) to accomplish the aim of synergistically killing tumor cells while inhibiting stroma fibrosis. The results showed that TR peptide-modified liposomes (TR-Lip) have superior targeting and penetrating effects both in vitro and in vivo. TR-PTX/HCQ-Lip efficiently inhibited autophagy in pancreatic cells and surrounding cancer-associated fibroblasts. The synergistic anti-fibrosis roles were also confirmed both in vitro and in vivo, all of which contributes to the enhanced curative effects of TR-PTX/HCQ-Lip in both heterogenetic and orthotopic pancreatic cancer models. STATEMENT OF SIGNIFICANCE: Autophagy plays a significant role in pancreatic ductal adenocarcinoma, especially in activating cancer associated fibroblasts which is also related to collagen generation that promotes the formation of dense stroma, which hinder the cytotoxic drugs to target and kill cancer cells. In this study, we designed integrin ɑvβ3 targeting, acid environmental sensitive liposomal platforms to co-loaded paclitaxel and the autophagy inhibitor hydroxychloroquine. The results showed that the muti-functional liposomes can target to the pancreatic tumor and efficiently kill tumor cells and inhibit stroma fibrosis, thus improve the therapeutic effect in orthotopic pancreatic cancer models.

Pancreatic Ductal Adenocarcinoma: Recent Updates

This Guest Editorial introduces this month's special Pancreatic Cancer Theme Issue, a series of reviews intended to highlight the pathologic to molecular profiles and diagnoses of benign and neoplastic pancreatic lesions.

Simultaneous Inhibition of MEK and Hh Signaling Reduces Pancreatic Cancer Metastasis

Pancreatic cancer, mostly pancreatic ductal adenocarcinoma (PDAC), is one of the most lethal cancer types, with an estimated 44,330 death in 2018 in the US alone. While targeted therapies and immune checkpoint inhibitors have significantly improved treatment options for patients with lung cancer and renal cell carcinomas, little progress has been made in pancreatic cancer, with a dismal 5-year survival rate currently at ~8%. Upon diagnosis, the majority of pancreatic cancer cases (~80%) are already metastatic. Thus, identifying ways to reduce pancreatic cancer metastasis is an unmet medical need. Furthermore, pancreatic cancer is notorious resistant to chemotherapy. While Kirsten RAt Sarcoma virus oncogene (K-RAS) mutation is the major driver for pancreatic cancer, specific inhibition of RAS signaling has been very challenging, and combination therapy is thought to be promising. In this study, we report that combination of hedgehog (Hh) and Mitogen-activated Protein/Extracellular Signal-regulated Kinase Kinase (MEK) signaling inhibitors reduces pancreatic cancer metastasis in mouse models. In mouse models of pancreatic cancer metastasis using human pancreatic cancer cells, we found that Hh target gene Gli1 is up-regulated during pancreatic cancer metastasis. Specific inhibition of smoothened signaling significantly altered the gene expression profile of the tumor microenvironment but had no significant effects on cancer metastasis. By combining Hh signaling inhibitor BMS833923 with RAS downstream MEK signaling inhibitor AZD6244, we observed reduced number of metastatic nodules in several mouse models for pancreatic cancer metastasis. These two inhibitors also decreased cell proliferation significantly and reduced CD45⁺ cells (particularly Ly6G⁺CD11b⁺ cells). We demonstrated that depleting Ly6G⁺ CD11b⁺ cells is sufficient to reduce cancer cell proliferation and the number of metastatic nodules. In vitro, Ly6G⁺ CD11b⁺ cells can stimulate cancer cell proliferation, and this effect is sensitive to MEK and Hh inhibition. Our studies may help design novel therapeutic strategies to mitigate pancreatic cancer metastasis.

Stromal barriers to nanomedicine penetration in the pancreatic tumor microenvironment

Pancreatic cancer is known for its dismal prognosis despite efforts to improve therapeutic outcome. Recently, cancer nanomedicine, application of nanotechnology to cancer diagnosis and treatment, has gained interest for treatment of pancreatic cancer. The enhanced permeability and retention (EPR) effect that promotes selective accumulation of nanometer‐sized molecules within tumors is the theoretical rationale of treatment. However, it is clear that EPR may be insufficient in pancreatic cancer as a result of stromal barriers within the tumor microenvironment (TME). These limit intratumoral accumulation of macromolecules. The TME and stromal barriers inside it consist of various stromal cell types which interact both with each other and with tumor cells. We are only beginning to understand the complexities of the stromal barriers within the TME and its functional consequences for nanomedicine. Understanding the complex crosstalk between barrier stromal cells is challenging because of the difficulty of modeling pancreatic cancer TME. Here we provide an overview of stromal barriers within the TME. We also describe the preclinical models, both in vivo and in vitro, developed to study them. We furthermore discuss the critical gaps in our understanding, and how we might formulate a better strategy for using nanomedicine against pancreatic cancer.