Determination of the ligand-binding specificities of the alpha2beta1 and alpha1beta1 integrins in a novel 3-dimensional in vitro model of pancreatic cancer

Natural Killer Cell Mechanosensing in Solid Tumors

Natural killer (NK) cells, which are an exciting alternative cell source for cancer immunotherapies, must sense and respond to their physical environment to traffic to and eliminate cancer cells. Herein, we review the mechanisms by which NK cells receive mechanical signals and explore recent key findings regarding the impact of the physical characteristics of solid tumors on NK cell functions. Data suggest that different mechanical stresses present in solid tumors facilitate NK cell functions, especially infiltration and degranulation. Moreover, we review recent engineering advances that can be used to systemically study the role of mechanical forces on NK cell activity. Understanding the mechanisms by which NK cells interpret their environment presents potential targets to enhance NK cell immunotherapies for the treatment of solid tumors.

Comparison of Engineered Liver 3D Models and the Role of Oxygenation for Patient-Derived Tumor Cells and Immortalized Cell Lines Cocultured with Tumor Stroma in the Detection of Hepatotoxins

In metabolically active tumors, responses of cells to drugs are heavily influenced by oxygen availability via the surrounding vasculature alongside the extracellular matrix signaling. The objective of this study is to investigate hepatotoxicity by replicating critical features of hepatocellular carcinoma (HCC). This includes replicating 3D structures, metabolic activities, and tumor-specific markers. The internal environment of spheroids comprised of cancerous human patient-derived hepatocytes using microparticles is modulated to enhance the oxygenation state and recreate cell-extracellular matrix interactions. Furthermore, the role of hepatic stellate cells in maintaining hepatocyte survival and function is explored and hepatocytes from two cellular sources (immortalized and patient-derived) to create four formulations with and without microparticles are utilized. To investigate drug-induced changes in metabolism and apoptosis in liver cells, coculture spheroids with and without microparticles are exposed to three hepatotoxic drugs. The use of microparticles increases levels of apoptotic markers in both liver models under drug treatments. This coincides with reduced levels of anti-apoptotic proteins and increased levels of pro-apoptotic proteins. Moreover, cells from different origins undergo apoptosis through distinct apoptotic pathways in response to identical drugs. This 3D microphysiological system offers a viable tool for liver cancer research to investigate mechanisms of apoptosis under different microenvironmental conditions.

Integrins in cancer: Emerging mechanisms and therapeutic opportunities

Integrins are vital surface adhesion receptors that mediate the interactions between the extracellular matrix (ECM) and cells and are essential for cell migration and the maintenance of tissue homeostasis. Aberrant integrin activation promotes initial tumor formation, growth, and metastasis. Recently, many lines of evidence have indicated that integrins are highly expressed in numerous cancer types and have documented many functions of integrins in tumorigenesis. Thus, integrins have emerged as attractive targets for the development of cancer therapeutics. In this review, we discuss the underlying molecular mechanisms by which integrins contribute to most of the hallmarks of cancer. We focus on recent progress on integrin regulators, binding proteins, and downstream effectors. We highlight the role of integrins in the regulation of tumor metastasis, immune evasion, metabolic reprogramming, and other hallmarks of cancer. In addition, integrin-targeted immunotherapy and other integrin inhibitors that have been used in preclinical and clinical studies are summarized.

Predictive Value of MUC5AC Signature in Pancreatic Ductal Adenocarcinoma: A Hypothesis Based on Preclinical Evidence

Mucin 5AC (MUC5AC) glycoprotein plays a crucial role in carcinogenesis and drug sensitivity in pancreatic ductal adenocarcinoma (PDAC), both individually and in combination with other mucins. Its function and localization are glycoform-specific. The immature isoform (detected by the CLH2 monoclonal antibody, or mab) is usually in the perinuclear (cytoplasmic) region, while the mature (45 M1, 2-11, Nd2) variants are in apical and extracellular regions. There is preclinical evidence suggesting that mature MUC5AC has prognostic and predictive (response to treatment) value. However, these findings were not validated in clinical studies. We propose a MUC5AC signature with three components of MUC5AC-localization, variant composition, and intensity-suggesting a reliable marker in combination of variants than with individual MUC5AC variants alone. We also postulate a theory to explain the occurrence of different MUC5AC variants in abnormal pancreatic lesions (benign, precancerous, and cancerous). We also analyzed the effect of mature MUC5AC on sensitivity to drugs often used in PDAC management, such as gemcitabine, 5-fluorouracil, oxaliplatin, irinotecan, cisplatin, and paclitaxel. We found preliminary evidence of its predictive value, but there is a need for large-scale studies to validate them.

The Extracellular Matrix: A Key Accomplice of Cancer Stem Cell Migration, Metastasis Formation, and Drug Resistance in PDAC

Pancreatic ductal adenocarcinoma (PDAC) is rich in dense fibrotic stroma that are composed of extracellular matrix (ECM) proteins. A disruption of the balance between ECM synthesis and secretion and the altered expression of matrix remodeling enzymes lead to abnormal ECM dynamics in PDAC. This pathological ECM promotes cancer growth, survival, invasion, and alters the behavior of fibroblasts and immune cells leading to metastasis formation and chemotherapy resistance, which contribute to the high lethality of PDAC. Additionally, recent evidence highlights that ECM, as a major structural component of the tumor microenvironment, is a highly dynamic structure in which ECM proteins establish a physical and biochemical niche for cancer stem cells (CSCs). CSCs are characterized by self-renewal, tumor initiation, and resistance to chemotherapeutics. In this review, we will discuss the effects of the ECM on tumor biological behavior and its molecular impact on the fundamental signaling pathways in PDAC. We will also provide an overview of how the different ECM components are able to modulate CSCs properties and finally discuss the current and ongoing therapeutic strategies targeting the ECM. Given the many challenges facing current targeted therapies for PDAC, a better understanding of molecular events involving the interplay of ECM and CSC will be key in identifying more effective therapeutic strategies to eliminate CSCs and ultimately to improve survival in patients that are suffering from this deadly disease.

Modelling liver cancer microenvironment using a novel 3D culture system

The tumor microenvironment and its contribution to tumorigenesis has been a focal highlight in recent years. A two-way communication between the tumor and the surrounding microenvironment sustains and contributes to the growth and metastasis of tumors. Progression and metastasis of hepatocellular carcinoma (HCC) have been reported to be exceedingly influenced by diverse microenvironmental cues. In this study, we present a 3D-culture model of liver cancer to better mimic in vivo tumor settings. By creating novel 3D co-culture model that combines free-floating and scaffold-based 3D-culture techniques of liver cancer cells and fibroblasts, we aimed to establish a simple albeit reproducible ex vivo cancer microenvironment model that captures tumor-stroma interactions. The model presented herein exhibited unique gene expression and protein expression profiles when compared to 2D and 3D mono-cultures of liver cancer cells. Our results showed that in vivo like conditions cannot be mimicked by simply growing cancer cells as spheroids, but by co-culturing them with 3D fibroblast with which they were able to crosstalk. This was evident by the upregulation of several pathways involved in HCC, and the increase in secreted factors by co-cultured cancer cells, many of which are also involved in tumor-stroma interactions. Compared to the conventional 2D culture, the proposed model exhibits an increase in the expression of genes associated with development, progression, and poor prognosis of HCC. Our results correlated with an aggressive outcome that better mirrors in vivo HCC, and therefore, a more reliable platform for molecular understanding of HCC.

The PDAC Extracellular Matrix: A Review of the ECM Protein Composition, Tumor Cell Interaction, and Therapeutic Strategies

Pancreatic ductal adenocarcinoma (PDAC) is notorious for a dense fibrotic stroma that is interlaced with a collagen-based extracellular matrix (ECM) that plays an important role in tumor biology. Traditionally thought to only provide a physical barrier from host responses and systemic chemotherapy, new studies have demonstrated that the ECM maintains biomechanical and biochemical properties of the tumor microenvironment (TME) and restrains tumor growth. Recent studies have shown that the ECM augments tumor stiffness, interstitial fluid pressure, cell-to-cell junctions, and microvascularity using a mix of biomechanical and biochemical signals to influence tumor fate for better or worse. In addition, PDAC tumors have been shown to use ECM-derived peptide fragments as a nutrient source in nutrient-poor conditions. While collagens are the most abundant proteins found in the ECM, several studies have identified growth factors, integrins, glycoproteins, and proteoglycans in the ECM. This review focuses on the dichotomous nature of the PDAC ECM, the types of collagens and other proteins found in the ECM, and therapeutic strategies targeting the PDAC ECM.

Morphological Heterogeneity in Pancreatic Cancer Reflects Structural and Functional Divergence

Simple Summary

Pancreatic cancer has a poor prognosis, which is largely due to resistance to treatment. Tumor heterogeneity is a known cause for treatment failure and has been studied at the molecular level. Morphological heterogeneity is common but has not been investigated, despite the fact that pathology examination is an integral part of clinical diagnostics. This study assessed whether morphological heterogeneity reflects structural and functional diversity in key cancer biological processes. Using archival tissues from resected pancreatic cancer, we selected four common and distinct morphological phenotypes and demonstrated that these differed significantly for a panel of 26 structural and functional features of the cancer-cell and stromal compartments. The strong link between these features and morphological phenotypes allowed prediction of the latter based on the results for the panel of features. The findings of this study indicate that morphological heterogeneity reflects biological diversity and that its assessment may potentially provide clinically relevant information.

Abstract

Inter- and intratumor heterogeneity is an important cause of treatment failure. In human pancreatic cancer (PC), heterogeneity has been investigated almost exclusively at the genomic and transcriptional level. Morphological heterogeneity, though prominent and potentially easily assessable in clinical practice, remains unexplored. This proof-of-concept study aims at demonstrating that morphological heterogeneity reflects structural and functional divergence. From the wide morphological spectrum of conventional PC, four common and distinctive patterns were investigated in 233 foci from 39 surgical specimens. Twenty-six features involved in key biological processes in PC were analyzed (immuno-)histochemically and morphometrically: cancer cell proliferation (Ki67) and migration (collagen fiber alignment, MMP14), cancer stem cells (CD44, CD133, ALDH1), amount, composition and spatial arrangement of extracellular matrix (epithelial proximity, total collagen, collagen I and III, fibronectin, hyaluronan), cancer-associated fibroblasts (density, αSMA), and cancer-stroma interactions (integrins α2, α5, α1; caveolin-1). All features differed significantly between at least two of the patterns. Stromal and cancer-cell-related features co-varied with morphology and allowed prediction of the morphological pattern. In conclusion, morphological heterogeneity in the cancer-cell and stromal compartments of PC correlates with structural and functional diversity. As such, histopathology has the potential to inform on the operationality of key biological processes in individual tumors.

Cancer Stem Cell Microenvironment Models with Biomaterial Scaffolds In Vitro

Defined by its potential for self-renewal, differentiation and tumorigenicity, cancer stem cells (CSCs) are considered responsible for drug resistance and relapse. To understand the behavior of CSC, the effects of the microenvironment in each tissue are a matter of great concerns for scientists in cancer biology. However, there are many complicated obstacles in the mimicking the microenvironment of CSCs even with current advanced technology. In this context, novel biomaterials have widely been assessed as in vitro platforms for their ability to mimic cancer microenvironment. These efforts should be successful to identify and characterize various CSCs specific in each type of cancer. Therefore, extracellular matrix scaffolds made of biomaterial will modulate the interactions and facilitate the investigation of CSC associated with biological phenomena simplifying the complexity of the microenvironment. In this review, we summarize latest advances in biomaterial scaffolds, which are exploited to mimic CSC microenvironment, and their chemical and biological requirements with discussion. The discussion includes the possible effects on both cells in tumors and microenvironment to propose what the critical factors are in controlling the CSC microenvironment focusing the future investigation. Our insights on their availability in drug screening will also follow the discussion.

Three-Dimensional Cell Culture Systems in Radiopharmaceutical Cancer Research

In preclinical cancer research, three-dimensional (3D) cell culture systems such as multicellular spheroids and organoids are becoming increasingly important. They provide valuable information before studies on animal models begin and, in some cases, are even suitable for reducing or replacing animal experiments. Furthermore, they recapitulate microtumors, metastases, and the tumor microenvironment much better than monolayer culture systems could. Three-dimensional models show higher structural complexity and diverse cell interactions while reflecting (patho)physiological phenomena such as oxygen and nutrient gradients in the course of their growth or development. These interactions and properties are of great importance for understanding the pathophysiological importance of stromal cells and the extracellular matrix for tumor progression, treatment response, or resistance mechanisms of solid tumors. Special emphasis is placed on co-cultivation with tumor-associated cells, which further increases the predictive value of 3D models, e.g., for drug development. The aim of this overview is to shed light on selected 3D models and their advantages and disadvantages, especially from the radiopharmacist's point of view with focus on the suitability of 3D models for the radiopharmacological characterization of novel radiotracers and radiotherapeutics. Special attention is paid to pancreatic ductal adenocarcinoma (PDAC) as a predestined target for the development of new radionuclide-based theranostics.

Mechanically stressed cancer microenvironment: Role in pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal solid malignancies in the world due to its insensitivity to current therapies and its propensity to metastases from the primary tumor mass. This is largely attributed to its complex microenvironment composed of unique stromal cell populations and extracellular matrix (ECM). The recruitment and activation of these cell populations cause an increase in deposition of ECM components, which highly influences the behavior of malignant cells through disrupted forms of signaling. As PDAC progresses from premalignant lesion to invasive carcinoma, this dynamic landscape shields the mass from immune defenses and cytotoxic intervention. This microenvironment influences an invasive cell phenotype through altered forms of mechanical signaling, capable of enacting biochemical changes within cells through activated mechanotransduction pathways. The effects of altered mechanical cues on malignant cell mechanotransduction have long remained enigmatic, particularly in PDAC, whose microenvironment significantly changes over time. A more complete and thorough understanding of PDAC's physical surroundings (microenvironment), mechanosensing proteins, and mechanical properties may help in identifying novel mechanisms that influence disease progression, and thus, provide new potential therapeutic targets.

Characteristics of multicellular tumor spheroids formed by pancreatic cells expressing different adhesion molecules

AIMS

Multicellular tumor spheroids (MCTS) produced by different methods vary in forms, sizes, and properties. The aim of this work was to characterize MCTS formed by six pancreatic cell lines on a non-adherent surface.

MATERIALS AND METHODS

Human pancreatic cells were grown in 2D and 3D conditions and compared for the expression of E- and desmosomal cadherins (PCR, confocal microscopy), growth, cell cycling, apoptosis (flow cytometry), and a response to antitumor drugs doxorubicin and gemcitabine (MTT-assay).

KEY FINDINGS

Three types of MCTS were identified: BxPC-3, T₃M₄ formed small number of large and dense spheroids representing type I MCTS; COLO-357 and AsPC-1 generated type II multiple and loose MCTS of different sizes while MiaPaCa-2 and PANC-1 represented type III cultures which grew almost as floating monolayer films. Formation of type I MCTS depended on the simultaneous expression of DSG3 and several DSC proteins; II MCTS expressed solely DSG2-DSC2 but not DSG3, while type III cells either did not express E-cadherin or a pair of DSG and DSC proteins. Cells in type I MCTS but not in types II and III ones quickly became quiescent which correlated with a decrease in the proliferation, increased apoptosis, and a higher resistance to antitumor drugs doxorubicin and gemcitabine.

SIGNIFICANCE

Taken collectively, pancreatic cells significantly vary in the expression of desmosomal cadherins, resulting in the formation of MCTS with different characteristics. The sensitivity of MCTS to various drugs depends on the type of cells and the method of spheroid preparation used.

Novel prognostic markers within the CD44-stromal ligand network in pancreatic cancer

The dense stroma in pancreatic cancer tumours is rich in secreted extracellular matrix proteins and proteoglycans. Secreted hyaluronan, osteopontin and type IV collagen sustain oncogenic signalling by interactions with CD44s and its variant isoform CD44v6 on cancer cell membranes. Although well established in animal and in vitro models, this oncogenic CD44-stromal ligand network is less explored in human cancer. Here, we use a pancreatic cancer tissue microarray from 69 primary tumours and 37 metastatic lymph nodes and demonstrate that high tumour cell expression of CD44s and, surprisingly, low stromal deposition of osteopontin correlate with poor survival independent of established prognostic factors for pancreatic cancer. High stromal expression of hyaluronan was a universal trait of both primary tumours and metastatic lymph nodes. However, hyaluronan species of different molecular mass are known to function differently in pancreatic cancer biology and immunohistochemistry cannot distinguish between them. Using gas-phase electrophoretic molecular mobility analysis, we uncover a shift towards high molecular mass hyaluronan in pancreatic cancer tissue compared to normal pancreas and at a transcriptional level, we find that hyaluronan synthesising HAS2 correlates positively with CD44. The resulting prediction that high molecular mass hyaluronan would then correlate with poor survival in pancreatic cancer was confirmed in serum samples, where we demonstrate that hyaluronan >27 kDa measured before surgery is an independent predictor of postoperative survival. Our findings confirm the prognostic value of CD44 tissue expression and highlight osteopontin tissue expression and serum high molecular mass hyaluronan as novel prognostic markers in pancreatic cancer.

The Extracellular Matrix and Pancreatic Cancer: A Complex Relationship

Pancreatic ductal adenocarcinoma (PDAC) has an extraordinarily dense fibrotic stroma that impedes tumor perfusion and delivery of anticancer drugs. Since the extracellular matrix (ECM) comprises the bulk of the stroma, it is primarily responsible for the increased interstitial tissue pressure and stiff mechanical properties of the stroma. Besides its mechanical influence, the ECM provides important biochemical and physical cues that promote survival, proliferation, and metastasis. By serving as a nutritional source, the ECM also enables PDAC cells to survive under the nutrient-poor conditions. While therapeutic strategies using stroma-depleting drugs have yielded disappointing results, an increasing body of research indicates the ECM may offer a variety of potential therapeutic targets. As preclinical studies of ECM-targeted drugs have shown promising effects, a number of clinical trials are currently investigating agents with the potential to advance the future treatment of PDAC. Thus, the present review seeks to give an overview of the complex relationship between the ECM and PDAC.

Modeling pancreatic cancer with organoids

Pancreatic ductal adenocarcinoma (PDA) is a highly lethal malignancy for which new treatment and diagnostic approaches are urgently needed. In order for such breakthroughs to be discovered, researchers require systems that accurately model the development and biology of PDA. While cell lines, genetically engineered murine models, and xenografts have all led to valuable clinical insights, organotypic culture models have emerged as tractable systems to recapitulate the complex three-dimensional organization of PDA. Recently, multiple methods for modeling PDA using organoids have been reported. This review aims to summarize these organoid methods in the context of other PDA models. While each model system has unique benefits and drawbacks, ultimately, organoids hold special promise for the development of personalized medicine approaches.

Modelling of pancreatic ductal adenocarcinoma in vitro with three-dimensional microstructured hydrogels

Development of a novelin vitro3D model of pancreas cancer based on microstructured polyelectrolyte complex (mPEC) hydrogel.

Induction of integrin α2 in a highly bone metastatic human prostate cancer cell line: roles of RANKL and AR under three-dimensional suspension culture

Background

Prostate cancer (PCa) bone metastasis can be markedly enhanced by increased receptor activator of NF kappa-B ligand (RANKL) expression in PCa cells. Molecular mechanisms that account for the increased predilection of PCa for bone include increased bone turnover, promotion of PCa cell growth and survival in the bone environment, and recruitment of bystander dormant cells to participate in bone metastasis. The current study tests the hypothesis that PCa cells acquire high adhesion to bone matrix proteins, which controls PCa bone colonization, under the RANKL/RANK and AR axes.

Methods

We used a highly bone metastatic RANKL-overexpressing LNCaP PCa cell line, LNCaP^RANKL, as a model to pursue the molecular mechanisms underlying the increased adhesion of PCa cells to collagens. A three-dimensional (3-D) suspension PCa organoid model was developed. The functions of integrin α₂ in cell adhesion and survival were evaluated by flow cytometry and western blot. AR expression and functionality were compared in 2-D monolayer versus 3-D suspension cultures using AR promoter- and PSA promoter-luciferase activity. AR role in cell adhesion was assessed using an adhesion assay.

Results

LNCaP^RANKL cells were shown to adhere tightly to ColI matrix through increased α₂ integrin expression. This increased adhesion, concomitant with activation of the FAK and Akt pathways, was further enhanced by culturing LNCaP^RANKL cells in 3-D suspension. Under the influence of 3-D suspension culture, AR was restored in LNCaP^RANKL cells via downregulation of AP-4 transcription factor, and supported increased α₂ integrin expression and adhesion to ColI.

Conclusion

3-D suspension culture and in vivo PCa tumor growth restore AR through downregulation of AP-4, enhancing integrin α₂ expression and adhesion to ColI which is rich in bone matrices. The interactions of PCa with ColI, mediated by integrin α₂ and AR expression, could be a key molecular event accounting for PCa bone metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-208) contains supplementary material, which is available to authorized users.

Pancreatic cancer organotypics: High throughput, preclinical models for pharmacological agent evaluation

Pancreatic cancer carries a terrible prognosis, as the fourth most common cause of cancer death in the Western world. There is clearly a need for new therapies to treat this disease. One of the reasons no effective treatment has been developed in the past decade may in part, be explained by the diverse influences exerted by the tumour microenvironment. The tumour stroma cross-talk in pancreatic cancer can influence chemotherapy delivery and response rate. Thus, appropriate preclinical in vitro models which can bridge simple 2D in vitro cell based assays and complex in vivo models are required to understand the biology of pancreatic cancer. Here we discuss the evolution of 3D organotypic models, which recapitulare the morphological and functional features of pancreatic ductal adenocarcinoma (PDAC). Organotypic cultures are a valid high throughput preclinical in vitro model that maybe a useful tool to help establish new therapies for PDAC. A huge advantage of the organotypic model system is that any component of the model can be easily modulated in a short time-frame. This allows new therapies that can target the cancer, the stromal compartment or both to be tested in a model that mirrors the in vivo situation. A major challenge for the future is to expand the cellular composition of the organotypic model to further develop a system that mimics the PDAC environment more precisely. We discuss how this challenge is being met to increase our understanding of this terrible disease and develop novel therapies that can improve the prognosis for patients.

Interaction of tumour cells with their microenvironment: ion channels and cell adhesion molecules. A focus on pancreatic cancer

Cancer must be viewed as a 'tissue', constituted of both transformed cells and a heterogeneous microenvironment, the 'tumour microenvironment' (TME). The TME undergoes a complex remodelling during the course of multistep tumourigenesis, hence strongly contributing to tumour progression. Ion channels and transporters (ICTs), being expressed on both tumour cells and in the different cellular components of the TME, are in a strategic position to sense and mediate signals arising from the TME. Often, this transmission is mediated by integrin adhesion receptors, which are the main cellular receptors capable of mediating cell-to-cell and cell-to-matrix bidirectional signalling. Integrins can often operate in conjunction with ICT because they can behave as functional partners of ICT proteins. The role of integrin receptors in the crosstalk between tumour cells and the TME is particularly relevant in the context of pancreatic cancer (PC), characterized by an overwhelming TME which actively contributes to therapy resistance. We discuss the possibility that this occurs through integrins and ICTs, which could be exploited as targets to overcome chemoresistance in PC.

Type IV collagen stimulates pancreatic cancer cell proliferation, migration, and inhibits apoptosis through an autocrine loop

Background

Pancreatic cancer shows a highly aggressive and infiltrative growth pattern and is characterized by an abundant tumor stroma known to interact with the cancer cells, and to influence tumor growth and drug resistance. Cancer cells actively take part in the production of extracellular matrix proteins, which then become deposited into the tumor stroma. Type IV collagen, an important component of the basement membrane, is highly expressed by pancreatic cancer cells both in vivo and in vitro. In this study, the cellular effects of type IV collagen produced by the cancer cells were characterized.

Methods

The expression of type IV collagen and its integrin receptors were examined in vivo in human pancreatic cancer tissue. The cellular effects of type IV collagen were studied in pancreatic cancer cell lines by reducing type IV collagen expression through RNA interference and by functional receptor blocking of integrins and their binding-sites on the type IV collagen molecule.

Results

We show that type IV collagen is expressed close to the cancer cells in vivo, forming basement membrane like structures on the cancer cell surface that colocalize with the integrin receptors. Furthermore, the interaction between type IV collagen produced by the cancer cell, and integrins on the surface of the cancer cells, are important for continuous cancer cell growth, maintenance of a migratory phenotype, and for avoiding apoptosis.

Conclusion

We show that type IV collagen provides essential cell survival signals to the pancreatic cancer cells through an autocrine loop.

Knockdown of the β(1) integrin subunit reduces primary tumor growth and inhibits pancreatic cancer metastasis

To address the role of β(1) integrins in pancreatic cancer progression, we stably knocked down β(1) integrin subunit expression in human FG-RFP pancreatic cancer cells using lentiviral-based RNA interference. We then examined the effects of β(1) integrin subunit knockdown on pancreatic cancer cell adhesion, migration and proliferation on tumor microenvironment-specific extracellular matrix proteins in vitro and on tumor progression in vivo using a clinically relevant fluorescent orthotopic mouse model of pancreatic cancer. Knockdown of the β(1) integrin subunit inhibited cell adhesion, migration and proliferation on types I and IV collagen, fibronectin and laminin in vitro. In vivo, knockdown of the β(1) integrin subunit reduced primary tumor growth by 50% and completely inhibited spontaneously occurring metastasis. These observations indicate a critical role for the β(1) integrin subunit in pancreatic cancer progression and metastasis in particular. Our results suggest the β(1) integrin subunit as a therapeutic target for the treatment of pancreatic cancer, especially in the adjuvant setting to prevent metastasis of this highly aggressive cancer.

An optical method to quantify the density of ligands for cell adhesion receptors in three-dimensional matrices

The three-dimensional matrix that surrounds cells is an important insoluble regulator of cell phenotypes. Examples of such insoluble surfaces are the extracellular matrix (ECM), ECM analogues and synthetic polymeric biomaterials. Cell-matrix interactions are mediated by cell adhesion receptors that bind to chemical entities (adhesion ligands) on the surface of the matrix. There are currently no established methods to obtain quantitative estimates of the density of adhesion ligands recognized by specific cell adhesion receptors. This article presents a new optical-based methodology for measuring ligands of adhesion receptors on three-dimensional matrices. The study also provides preliminary quantitative results for the density of adhesion ligands of integrins alpha(1)beta(1) and alpha(2)beta(1) on the surface of collagen-based scaffolds, similar to biomaterials that are used clinically to induce regeneration in injured skin and peripheral nerves. Preliminary estimates of the surface density of the ligands of these two major collagen-binding receptors are 5775 +/- 2064 ligands microm(-2) for ligands of alpha(1)beta(1) and 17 084 +/- 5353 ligands microm(-2) for ligands of alpha(2)beta(1). The proposed methodology can be used to quantify the surface chemistry of insoluble surfaces that possess biological activity, such as native tissue ECM and biomaterials, and therefore can be used in cell biology, biomaterials science and regenerative medical studies for quantitative description of a matrix and its effects on cells.

Divalent cations modulate alpha2beta1 integrin-mediated malignancy in a novel 3-dimensional in vitro model of pancreatic cancer

OBJECTIVES

We previously showed that divalent cations regulate alpha2beta1 integrin-mediated pancreatic cancer cell interactions with type I collagen in 2 dimensions (2D), including cell adhesion, migration, and proliferation. Presently, we examined divalent cation-dependent alpha2beta1 integrin-mediated pancreatic cancer cell adhesion and proliferation on type I collagen in a novel 3D in vitro model.

METHODS

Cell attachment, proliferation, and antibody inhibition assays on type I collagen in both 2D and 3D, and microscopy and immunoblotting were used for these studies.

RESULTS

As in 2D, cell attachment on type I collagen in 3D is Mg-dependent and inhibited by Ca. Proliferation in 3D is also Mg-dependent, but maximal when Mg is present at concentrations that promote maximal cell adhesion and Ca is present at concentrations less than Mg. Immunoblotting studies demonstrate that the divalent cation-dependent changes in cell-cell adhesion observed on type I collagen in both 2D and 3D are associated with the changes in E-cadherin and beta-catenin expression. Antibody inhibition assays indicate further that the alpha2beta1 integrin specifically mediates proliferation on type I collagen in 3D under altered divalent cation conditions.

CONCLUSIONS

Divalent cation shifts could activate alpha2beta1 integrin-mediated malignancy in the type I collagen-rich 3D tumor microenvironment of pancreatic cancer.

Biologically active collagen-based scaffolds: advances in processing and characterization

A small number of type I collagen-glycosaminoglycan scaffolds (collagen-GAG scaffolds; CGSs) have unusual biological activity consisting primarily in inducing partial regeneration of organs in the adult mammal. Two of these are currently in use in a variety of clinical settings. CGSs appear to induce regeneration by blocking the adult healing response, following trauma, consisting of wound contraction and scar formation. Several structural determinants of biological activity have been identified, including ligands for binding of fibroblasts to the collagen surface, the mean pore size (which affects ligand density) and the degradation rate (which affects the duration of the wound contraction-blocking activity by the scaffold). Processing variables that affect these determinants include the kinetics of swelling of collagen fibres in acetic acid, freezing of the collagen-GAG suspension and cross-linking of the freeze-dried scaffold. Recent developments in the processing of CGSs include fabrication of scaffolds that are paucidisperse in pore size, scaffolds with gradients in physicochemical properties (and therefore biological activity) and scaffolds that incorporate a mineral component. Advances in the characterization of the pore structure of CGSs have been made using confocal and nonlinear optical microscopy (NLOM). The mechanical behaviour of CGSs, as well as the resistance to degradative enzymes, have been studied. Following seeding with cells (typically fibroblasts), contractile forces in the range 26-450 nN per cell are generated by the cells, leading to buckling of scaffold struts. Ongoing studies of cell-seeded CGSs with NLOM have shown an advantage over the use of confocal microscopy due to the ability of the former method to image the CGS surfaces without staining (which alters its surface ligands), reduced cell photodamage, reduced fluorophore photobleaching and the ability to image deeper inside the scaffold.

Pancreatic cancer organotypic cultures

Pancreatic cancer, the fourth most common cause of cancer-related death, is a devastating disease with poor prognosis. Over the last four decades, no effective new treatments have been developed for this cancer. As a result, its prognosis has remained unchanged. Appropriate cancer models, representing all aspects of pancreatic cancer, will enhance our understanding of its biology. In this review we discuss the evolution and merit of organotypic culture models. These co-culture in vitro systems of cancer and stromal cells grown within, or on top of, reconstituted extracellular matrix gels model pancreatic cancer more realistically than 2D systems. Different methodologies are discussed which enable interrogation of various hypotheses examining the tumour-stroma cross-talk. Thus this validated organotypic culture model provides a system, which can be easily manipulated and used to test (novel) treatment options targeting the cancer, the stromal compartment or both, in a physiologically relevant environment. The big challenge for future research is to expand this model further so that its mimicry of the human tumour is more robust. This will increase our understanding of the biology of this aggressive tumour; ultimately resulting in improved therapies and, therefore, a better prognosis.

Organotypic culture model of pancreatic cancer demonstrates that stromal cells modulate E-cadherin, beta-catenin, and Ezrin expression in tumor cells

Pancreatic cancer is characterized by an intense stromal reaction. Reproducible three-dimensional in vitro systems for exploring interactions of the stroma with pancreatic cancer cells have not previously been available, prompting us to develop such a model. Cancer cells were grown on collagen/Matrigel and embedded with or without stromal cells (hTERT-immortalized human PS-1 stellate cells or MRC-5 fibroblasts) for 7 days. Proliferation and apoptosis, as well as important cell-cell adhesion and cytoskeleton-regulating proteins, were studied. PS-1 cells were confirmed as stellate based on the expression of key cytoskeletal proteins and lipid vesicles. Capan-1, and to a lesser extent PaCa-3, cells differentiated into luminal structures, exhibiting a central apoptotic core with a proliferating peripheral rim and an apico-basal polarity. Presence of either stromal cell type translocated Ezrin from apical (when stromal cells were absent) to basal aspects of cancer cells, where it was associated with invasive activity. Interestingly, the presence of 'normal' (not tumor-derived) stromal cells induced total tumor cell number reduction (P < 0.005) associated with a significant decrease in E-cadherin expression (P < 0.005). Conversely, beta-catenin expression was up-regulated (P < 0.01) in the presence of stromal cells with predominant cytoplasmic expression. Moreover, patient samples confirmed that these data recapitulated the clinical situation. In conclusion, pancreatic organotypic culture offers a reproducible, bio-mimetic, three-dimensional in vitro model that allows examination of the interactions between stromal elements and pancreatic cancer cells.

Type IV collagen is a tumour stroma-derived biomarker for pancreas cancer

BACKGROUND

Pancreas cancer is a dreaded disease with high mortality, despite progress in surgical and oncological treatments in recent years. The field is hampered by a lack of good prognostic and predictive tumour biomarkers to be used during follow-up of patients.

METHODS

The circulating level of type IV collagen was measured by ELISA in pancreas cancer patients and controls. The expression pattern of type IV collagen in normal pancreas, pancreas cancer tissue and in pancreas cancer cell lines was studied by immunofluorescence and Western blot techniques.

RESULTS

Patients with pancreas cancer have significantly increased circulating levels of type IV collagen. In pancreas cancer tissue high levels of type IV collagen expression was found in close proximity to cancer cells in the tumour stroma. Furthermore, pancreas cancer cells were found to produce and secrete type IV collagen in vitro, which in part can explain the high type IV collagen expression observed in pancreas cancer tissue, and the increased circulating levels in pancreas cancer patients. Of clinical importance, our results show that the circulating level of type IV collagen after surgery is strongly related to prognosis in patients treated for pancreas cancer by pancreatico-duodenectomy with curative intent. Persisting high levels of circulating type IV collagen after surgery indicates a quick relapse in disease and poor survival.

CONCLUSION

Our results most importantly show that stroma related substances can be evaluated as potential cancer biomarkers, and thereby underline the importance of the tumour microenvironment also in this context.

Divalent cations modulate the integrin-mediated malignant phenotype in pancreatic cancer cells

We have previously demonstrated that pathophysiological shifts in the concentrations of extracellular Mg(2+) and Ca(2+) activate the alpha(2)beta(1) integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells, as evidenced by increased adhesion, migration and proliferation. In the present study, we examined the integrin and divalent cation specificity of pancreatic cancer cell interactions with other physiologically relevant extracellular matrix proteins, including fibronectin, type IV collagen, laminin and vitronectin. Our results indicate that, like alpha(2)beta(1) integrin-mediated interactions with type I collagen, beta(1) integrin-mediated adhesion to fibronectin, type IV collagen and laminin are promoted by Mg(2+) but not by Ca(2+). On vitronectin, cells attach via alpha(v)beta(5) and beta(1) integrins, and in the presence of either divalent cation. We also demonstrate that, like type I collagen, pancreatic cancer cell migration and proliferation on fibronectin, laminin and type IV collagen is maximal when Mg(2+) is present at concentrations that promote optimal adhesion and Ca(2+) is present at concentrations less than Mg(2+). On vitronectin, Panc-1 cell migration is maximal with decreased Mg(2+) and increased Ca(2+), but the reverse is true for BxPC-3 cells. Both cell lines exhibited maximal proliferation with increased Mg(2+) and decreased Ca(2+), however. Together with evidence indicating that the in vivo local tumor microenvironment contains increased Mg(2+) and decreased Ca(2+), our studies demonstrate that such divalent cation shifts could activate the integrin-mediated malignant phenotype in pancreatic cancer.

Activation of the alpha2beta1 integrin-mediated malignant phenotype on type I collagen in pancreatic cancer cells by shifts in the concentrations of extracellular Mg2+ and Ca2+

The authors have previously demonstrated that alpha(2)beta(1) integrin-mediated pancreatic cancer cell adhesion to Type I collagen is Mg(2+)-dependent, inhibited by Ca(2+), and that this integrin, purified from cell lysates using Type I-collagen-sepharose in Mg(2+), can be eluted with Ca(2+). In the present study, the authors examined the divalent cation-dependency of alpha(2)beta(1) integrin-mediated pancreatic cancer cell adhesion, migration and proliferation on Type I collagen, an extracellular matrix protein shown to be highly up-regulated, and to promote the malignant phenotype in vitro and in vivo. The results indicate that cells attach to Type I collagen maximally when Mg(2+) is greater than 1 mM, and that addition of increasing concentrations of Ca(2+) reduces this adhesion. These effects are reversible, in that previous cell attachment in Mg(2+) can be reversed by adding Ca(2+), and vice versa. They also demonstrate that pancreatic cancer cells migrate and proliferate on Type I collagen in Mg(2+) alone, but maximally when Mg(2+) is present at concentrations that promote maximal cell adhesion and Ca(2+) is present at concentrations less than Mg(2+). Cell adhesion and proliferation assays, as well as affinity chromatography on Type I collagen using anti-integrin function-blocking monoclonal antibodies indicate that the effects of these divalent cation shifts are mediated specifically by the alpha(2)beta(1) integrin. As pancreatic juice contains over 1,200-fold more Mg(2+) than Ca(2+) and solid tumors are characterized by increased magnesium load, these data indicate that such pathophysiological divalent cation shifts could be involved in the activation of the alpha(2)beta(1) integrin-mediated malignant phenotype on Type I collagen in the pancreatic cancer.

The integrin-extracellular matrix axis in pancreatic cancer

Pancreatic cancer is the fifth leading cause of adult cancer death in the United States, with 5-year survival rates of only 1% to 4%. Current therapeutic strategies generally result in only a few months of extended life. Recent evidence from several independent laboratories in vitro and in vivo indicate that integrin-mediated cell attachment to the extracellular matrix (ECM), components of which are highly up-regulated in pancreatic cancer, evokes phenotypes and signaling pathways that regulate tumor cell growth and migration. In this review, we will discuss our current understanding of the role of the ECM in directing pancreatic cancer growth, progression, and metastasis. Topics covered include a survey of the existing literature regarding the in vivo and in vitro expression of the ECM and its cell surface receptors, the integrins, in pancreatic cancer; mechanisms involved in the integrin-ECM-mediated malignant phenotype; and future directions for the study of the integrin-ECM axis and its role in pancreatic cancer progression, including potential therapeutic strategies.

Integrin-mediated laminin-1 adhesion upregulates CXCR4 and IL-8 expression in pancreatic cancer cells

BACKGROUND

We have shown recently that alpha(2)beta(1) integrin-mediated type I collagen adhesion promotes a more malignant phenotype in pancreatic cancer cell lines than other extracellular matrix (ECM) proteins. MiaPaCa-2 cells, by contrast, do not express collagen-binding integrins, but are metastatic in our orthotopic mouse model and migrate maximally on laminin-1 (Ln-1). It has also been shown that CXCR4 and IL-8 expression correlates directly with metastasis in pancreatic cancer in vivo. We therefore examined the potential of the ECM to regulate CXCR4 and IL-8 expression in pancreatic cancer cells.

METHODS

We cultured 8 pancreatic cancer cell lines on fibronectin (Fn), types I and IV collagen, Ln-1 and vitronectin (Vn), and examined cell lysates for CXCR4 by immunoblotting and media for IL-8 by ELISA. We also conducted cell migration assays with stromal-derived factor-1 (SDF-1) as the chemoattractant to examine integrin-binding specificity and CXCR4 function.

RESULTS

All cell lines expressed CXCR4 protein. MiaPaCa-2 cell growth on Ln-1 increased significantly CXCR4 and IL-8 expression relative to other ECM proteins. Migration inhibition studies showed that both the alpha(6)beta(1) and alpha(3)beta(1) integrins mediate MiaPaCa-2 migration on Ln-1. Growth studies showed further that CXCR4 expression on Ln-1 was mediated by the alpha(6)beta(1) integrin whereas IL-8 expression was mediated by both the alpha(6)beta(1) and alpha(3)beta(1) integrins. The expression of functional CXCR4 was also shown in migration assays, where SDF-1 significantly increased pancreatic cancer cell chemotaxis on Ln-1.

CONCLUSIONS

These data indicate that integrin-mediated Ln-1 adhesion upregulates CXCR4 and IL-8 expression and may play a mechanistic role in pancreatic cancer metastases.