Electron microscopic analysis of different cell types in human pancreatic cancer spheres

Artificial intelligence-based analysis of time-lapse images of sphere formation and process of plate adhesion and spread of pancreatic cancer cells

Background: Most pancreatic cancers are pancreatic ductal adenocarcinomas (PDAC). Spherical morphology formed in three-dimensional (3D) cultures and the effects of anticancer drugs differ between epithelial and mesenchymal PDAC cell lines. In the human pancreas, cancer cells form 3D tumors, migrate to adjacent tissues, and metastasize to other organs. However, no effective methods exist to examine the ability of the tumor mass to migrate to surrounding tissues in vitro. We used spheres formed in 3D culture to investigate whether the migratory ability of tumors of PDAC cell lines, including epithelial and mesenchymal cell lines, varies. Methods: Sphere formation and adhesion and spread on culture plates were examined by artificial intelligence-based analysis of time-lapse imaging using five epithelial and three mesenchymal PDAC cell lines. Fused and non-fused areas of the sphere surface during sphere formation on low-attachment plates, the adhesion area to normal culture plates, and the sphere area maintaining its original form during adhesion to plates were measured. Results: Immunocytochemical staining confirmed that E-cadherin was highly expressed in epithelial PDAC spheres, as was vimentin in mesenchymal PDAC spheres, in 2D culture. When forming spheres using low-attachment plates, most epithelial PDAC cell lines initially showed decreased sphere area, and then the covering cells fused to form a smooth surface on the sphere. Mesenchymal PANC-1 and MIA PaCa-2 cells showed little reduction in sphere area and few areas of sphere surface fusion. When formed PDAC spheres were seeded onto normal culture plates, spheres of epithelial PK-8 cells-which have the highest E-cadherin expression, form numerous cysts, and have smooth sphere surfaces-did not adhere to normal plates even after 60 h, and epithelial PK45-P and T3M-4 spheres hardly adhered. Conversely, the area of adhesion and spread of mesenchymal PANC-1 and KP4 cell spheres on normal plates markedly increased from early on, forming large areas of attachment to plates. Conclusion: Seeding spheres formed in 3D culture onto culture plates can clarify differences in tumor migration potential to surrounding areas. The masses formed by each PDAC cell line varied in migratory ability, with mesenchymal PDAC masses being more migratory than epithelial PDAC masses.

Epithelial and Mesenchymal Features of Pancreatic Ductal Adenocarcinoma Cell Lines in Two- and Three-Dimensional Cultures

Pancreatic ductal adenocarcinoma (PDAC) is an intractable cancer that is difficult to diagnose early, and there is no cure other than surgery. PDAC is classified as an adenocarcinoma that has limited effective anticancer drug and molecular-targeted therapies compared to adenocarcinoma found in other organs. A large number of cancer cell lines have been established from patients with PDAC that have different genetic abnormalities, including four driver genes; however, little is known about the differences in biological behaviors among these cell lines. Recent studies have shown that PDAC cell lines can be divided into epithelial and mesenchymal cell lines. In 3D cultures, morphological and functional differences between epithelial and mesenchymal PDAC cell lines were observed as well as the drug effects of different anticancer drugs. These effects included gemcitabine causing an increased growth inhibition of epithelial PDAC cells, while nab-paclitaxel caused greater mesenchymal PDAC cell inhibition. Thus, examining the characteristics of epithelial or mesenchymal PDAC cells with stromal cells using a 3D co-culture may lead to the development of new anticancer drugs.

Gp130-Mediated STAT3 Activation Contributes to the Aggressiveness of Pancreatic Cancer through H19 Long Non-Coding RNA Expression

Simple Summary

The signal transducer and activator of transcription 3 (STAT3) activation correlate with the aggressiveness of pancreatic ductal adenocarcinoma (PDAC). We demonstrated that the autocrine/paracrine interleukin-6 (IL-6) or leukemia inhibitory factor (LIF)/glycoprotein 130 (gp130)/STAT3 pathway contributes to the maintenance of stemness features and membrane-type 1 matrix metalloproteinase (MT1-MMP) expression, and modulates transforming growth factor (TGF)-β1/Smad signaling-mediated epithelial-mesenchymal transition (EMT) and invasion through regulation of TGFβ-RII expression in PDAC cancer stem cell (CSC)-like cells. Furthermore, we demonstrated that p-STAT3 acts through the IL-6 or LIF/gp130/STAT3 pathway to access the active promoter region of metastasis-related long non-coding RNA H19 and contribute to its transcription in CSC-like cells. Therefore, the autocrine/paracrine IL-6 or LIF/gp130/STAT3 pathway in PDAC CSC-like cells exhibiting H19 expression is considered to be involved in the aggressiveness of PDAC, and inhibition of the gp130/STAT3 pathway is a promising strategy to target CSCs for the elimination of PDAC (146/150).

Abstract

Signaling pathways involving signal transducer and activator of transcription 3 (STAT3) play key roles in the aggressiveness of pancreatic ductal adenocarcinoma (PDAC), including their tumorigenesis, invasion, and metastasis. Cancer stem cells (CSCs) have been correlated with PDAC aggressiveness, and activation of STAT3 is involved in the regulation of CSC properties. Here, we investigated the involvement of interleukin-6 (IL-6) or the leukemia inhibitory factor (LIF)/glycoprotein 130 (gp130)/STAT3 pathway and their role in pancreatic CSCs. In PDAC CSC-like cells formed by culturing on a low attachment plate, autocrine/paracrine IL-6 or LIF contributes to gp130/STAT3 pathway activation. Using a gp130 inhibitor, we determined that the gp130/STAT3 pathway contributes to the maintenance of stemness features, the expression of membrane-type 1 matrix metalloproteinase (MT1-MMP), and the invasion of PDAC CSC-like cells. The gp130/STAT3 pathway also modulates the transforming growth factor (TGF)-β1/Smad pathway required for epithelial-mesenchymal transition induction through regulation of TGFβ-RII expression in PDAC CSC-like cells. Furthermore, chromatin immunoprecipitation assays revealed that p-STAT3 can access the active promoter region of H19 to influence this metastasis-related long non-coding RNA and contribute to its transcription in PDAC CSC-like cells. Therefore, the autocrine/paracrine IL-6 or LIF/gp130/STAT3 pathway in PDAC CSC-like cells may eventually facilitate invasion and metastasis, two hallmarks of malignancy. We propose that inhibition of the gp130/STAT3 pathway provides a promising strategy for targeting CSCs for the treatment of PDAC.

Fzd7/Wnt7b signaling contributes to stemness and chemoresistance in pancreatic cancer

Mining databases and data obtained from assays on human specimens had shown that Fzd7 is closely associated with Wnt7b, that Fzd7/Wnt7b expression is upregulated in pancreatic cancer tissues compared with normal tissues, and its expression is negatively correlated with survival. Fzd7/Wnt7b knockdown in Capan‐2 and Panc‐1 cells reduced the proliferative capacity of pancreatic cancer stem cells (PCSCs), reduced drug resistance, decreased the percentage of CD24⁺CD44⁺ subset of cells and the levels of ABCG2, inhibited cell‐sphere formation, and reduced gemcitabine (GEM) resistance. In contrast, Fzd7/Wnt7b overexpression increased the percentage of the CD24⁺CD44⁺ subset of cells, and increased the levels of ABCG2 detected in cell spheroids. The gem‐resistant cells exhibited higher levels of Fzd7/Wnt7b expression, an increased percentage of CD24⁺CD44⁺ cells, and higher levels of ABCG2 compared with the parental cells. Taken together, Fzd7/Wnt7b knockdown can reduce PDAC cell stemness and chemoresistance by reducing the percentage of CSCs. Mechanistically, Fzd7 binds with Wnt7b and modulates the levels of β‐catenin, and they may exert their role via modulation of the canonical Wnt pathway.

Morphofunctional analysis of human pancreatic cancer cell lines in 2- and 3-dimensional cultures

Genetic, transcriptional, and morphological differences have been reported in pancreatic ductal adenocarcinoma (PDAC) cases. We recently found that epithelial or mesenchymal features were enhanced in three-dimensional (3D) cultures compared to two-dimensional (2D) cultures. In this study, we examined the differences in the morphological and functional characteristics of eight PDAC cell lines in 2D and 3D cultures. Most PDAC cells showed similar pleomorphic morphologies in 2D culture. Under 3D culture, PDAC cells with high E-cadherin and low vimentin expression levels (epithelial) formed small round spheres encircled with flat lining cells, whereas those with high vimentin and low E-cadherin expression levels (mesenchymal) formed large grape-like spheres without lining cells and were highly proliferative. In 3D culture, gemcitabine was more effective for the spheres formed by PDAC cells with epithelial features, while abraxane was more effective on those with mesenchymal features. The expression levels of drug transporters were highest PDAC cells with high vimentin expression levels. These findings indicate that PDAC cells possess various levels of epithelial and mesenchymal characteristics. The 3D-culture method is useful for investigating the diversity of PDAC cell lines and may play important roles in the development of personalized early diagnostic methods and anticancer drugs for PDAC.

Standardization of esophageal adenocarcinoma in vitro model and its applicability for model drug testing

FLO-1 cell line represents an important tool in esophageal adenocarcinoma (EAC) research as a verified and authentic cell line to study the disease pathophysiology and antitumor drug screenings. Since in vitro characteristics of cells depend on the microenvironment and culturing conditions, we performed a thorough characterization of the FLO-1 cell line under different culturing conditions with the aim of (1) examining the effect of serum-free growth medium and air–liquid interface (A–L) culturing, which better reflect physiological conditions in vivo and (2) investigating the differentiation potential of FLO-1 cells to mimic the properties of the in vivo esophageal epithelium. Our study shows that the composition of the media influenced the morphological, ultrastructural and molecular characteristics of FLO-1 cells, such as the expression of junctional proteins. Importantly, FLO-1 cells formed spheres at the A–L interface, recapitulating key elements of tumors in the esophageal tube, i.e., direct contact with the gas phase and three-dimensional architecture. On the other hand, FLO-1 models exhibited high permeability to model drugs and zero permeability markers, and low transepithelial resistance, and therefore poorly mimicked normal esophageal epithelium. In conclusion, the identified effect of culture conditions on the characteristics of FLO-1 cells should be considered for standardization, data reproducibility and validity of the in vitro EAC model. Moreover, the sphere-forming ability of FLO-1 cells at the A–L interface should be considered in EAC tumor biology and anticancer drug studies as a reliable and straightforward model with the potential to increase the predictive efficiency of the current in vitro approaches.

Polyvinyl alcohol increased growth, migration, invasion, and sphere size in the PK-8 pancreatic ductal adenocarcinoma cell line

Polyvinyl alcohol (PVA) is a water-soluble synthetic polymer used in eye drops, embolization particles, and artificial cartilage. It has also been shown to cause expansion of functional multipotent self-renewing hematopoietic stem cells under serum-free conditions. In this study, we examined the effects of PVA on human pancreatic ductal adenocarcinoma (PDAC) cell lines using 2-dimensional (2D) and 3D-cultures with serum-free medium. In the 2D-culture, PVA-treatment induced an aggregated colony-like appearance in PDAC cells. It increased the growth of PK-8 cells in a dose-dependent manner as well as significantly increasing migration and invasion abilities. qRT-PCR showed an increase in α2 integrin and a decrease in matrix metalloprotease levels in PVA-treated PK-8 cells. Through qRT-PCR analysis, β1 integrin expression at the mRNA level was found to be decreased; however, it was unaltered at the protein level when assessed using FACS analysis.

PVA further induced mesenchymal to epithelial transition-like alterations, including increased E-cadherin and decreased Vimentin and N-cadherin expression. Four cancer stem cell (CSC) markers were higher in PVA-treated PK-8 cells compared to controls. In 3D-culture, PVA-treated PK-8 cells showed a rod-like appearance with larger sphere size and higher growth ability. qRT-PCR showed that CSC markers did not increase and 2 of 4 drug transporters had decreased in PVA-treated PK-8 cells. These findings suggest that PVA increases the growth, migration, invasion, and sphere size of PK-8 cells, but does not increase the proportion of pancreatic CSCs under 3D-culture conditions with serum-free medium.

FGFR4 Inhibitor BLU9931 Attenuates Pancreatic Cancer Cell Proliferation and Invasion While Inducing Senescence: Evidence for Senolytic Therapy Potential in Pancreatic Cancer

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that is projected to become the leading cause of cancer death by 2050. Fibroblast growth factor receptor 4 (FGFR4) is a transmembrane receptor that is overexpressed in half of PDACs. We determined that its expression in PDAC positively correlated with larger tumor size and more advanced tumor stage, and that BLU9931, a selective FGFR4 inhibitor, reduced PDAC cell proliferation and invasion while promoting their senescence. Quercetin, a senolytic drug, induced cell death in BLU9931-treated cells. We propose that targeting FGFR4 in combination with senolysis could provide a novel therapeutic strategy in patients whose PDAC expresses high FGFR4 levels.

Abstract

Fibroblast growth factor receptor 4 (FGFR4), one of four tyrosine kinase receptors for FGFs, is involved in diverse cellular processes. Activation of FGF19/FGFR4 signaling is closely associated with cancer development and progression. In this study, we examined the expression and roles of FGF19/FGFR4 signaling in human pancreatic ductal adenocarcinoma (PDAC). In human PDAC cases, FGFR4 expression positively correlated with larger primary tumors and more advanced stages. Among eight PDAC cell lines, FGFR4 was expressed at the highest levels in PK-1 cells, in which single-nucleotide polymorphism G388R in FGFR4 was detected. For inhibition of autocrine/paracrine FGF19/FGFR4 signaling, we used BLU9931, a highly selective FGFR4 inhibitor. Inhibition of signal transduction through ERK, AKT, and STAT3 pathways by BLU9931 reduced proliferation in FGF19/FGFR4 signaling-activated PDAC cells. By contrast, BLU9931 did not alter stemness features, including stemness marker expression, anticancer drug resistance, and sphere-forming ability. However, BLU9931 inhibited cell invasion, in part, by downregulating membrane-type matrix metalloproteinase-1 in FGF19/FGFR4 signaling-activated PDAC cells. Furthermore, downregulation of SIRT1 and SIRT6 by BLU9931 contributed to senescence induction, priming these cells for quercetin-induced death, a process termed senolysis. Thus, we propose that BLU9931 is a promising therapeutic agent in FGFR4-positive PDAC, especially when combined with senolysis (195/200).

Novel [l,2,4]triazolo[3,4-a]isoquinoline chalcones as new chemotherapeutic agents: Block IAP tyrosine kinase domain and induce both intrinsic and extrinsic pathways of apoptosis

Two novel chemotherapeutic chalcones were synthesized and their structures were confirmed by different spectral tools. Theoretical studies such as molecular modeling were done to detect the mechanism of action of these compounds. In vitro cytotoxicity showed a strong effect against all tested cell lines (MCF7, A459, HepG2, and HCT116), and low toxic effect against normal human melanocytes (HFB4). The lung carcinoma cell line was chosen for further molecular studies. Real-time PCR demonstrated that the two compounds upregulated gene expression of (BAX, p53, casp-3, casp-8, casp-9) genes and decreased the expression of anti-apoptotic genes bcl2, CDK4, and MMP1. Flow-cytometry indicated that cell cycle arrest of A459 was induced at the G2/M phase and the apoptotic percentage increased significantly compared to the control sample. Cytochrome c oxidase and VEGF enzyme activity were detected by ELISA assay. SEM tool was used to follow the morphological changes that occurred on the cell surface, cell granulation, and average roughness of the cell surface. The change in the number and morphology of mitochondria, cell shrinkage, increase in the number of cytoplasmic organelles, membrane blebbing, chromatin condensation, and apoptotic bodies were observed using TEM. The obtained data suggested that new chalcones exerted their pathways on lung carcinoma through induction of two pathways of apoptosis. Graphical abstract Novel chalcones were prepared and confirmed by different spectral tools. Docking simulations were done to detect the mechanism of action. In vitro cytotoxicity indicated a strong effect against different cancer cell lines and low toxic effects against normal human melanocytes (HFB4). The lung carcinoma cell line was chosen for further molecular studies that include Real-time PCR, Flow-cytometry, Cytochrome c oxidase, and ELISA assay. SEM and TEM tool were used to follow the morphological changes occurred on the cell surface.

Ganglioside GM2, highly expressed in the MIA PaCa-2 pancreatic ductal adenocarcinoma cell line, is correlated with growth, invasion, and advanced stage

Gangliosides, a group of glycosphingolipids, are known to be cell surface markers and functional factors in several cancers. However, the association between gangliosides and pancreatic ductal adenocarcinoma (PDAC) has not been well elucidated. In this study, we examined the expression and roles of ganglioside GM2 in PDAC. GM2+ cells showed a higher growth rate than GM2− cells in the adherent condition. When GM2– and GM2+ cells were cultured three-dimensionally, almost all cells in the spheres expressed GM2, including cancer stem cell (CSC)-like cells. A glycolipid synthesis inhibitor reduced GM2 expression and TGF-β1 signaling in these CSC-like cells, presumably by inhibiting the interaction between GM2 and TGFβ RII and suppressing invasion. Furthermore, suppression of GM2 expression by MAPK inhibition also reduced TGF-β1 signaling and suppressed invasion. GM2+ cells formed larger subcutaneous tumors at a high incidence in nude mice than did GM2– cells. In PDAC cases, GM2 expression was significantly associated with younger age, larger tumor size, advanced stage and higher histological grade. These findings suggest that GM2 could be used as a novel diagnostic and therapeutic target for PDAC.

Biphenotypic Differentiation of Pancreatic Cancer in 3-Dimensional Culture

OBJECTIVE

Pancreatic ductal adenocarcinoma (PDAC) is the third most common cause of cancer death in the United States. Improved characterized models of PDAC are needed for drug screening.

METHODS

We grew 4 established pancreatic cancer cell lines in hanging drop cultures to produce spheroids. We also grew organoids from explanted xenografted PDAC and surgically resected primary PDAC. We performed transmission and scanning electron microscopy and compared findings with those of the normal pancreatic duct. We also performed single-cell cloning to determine the potential options for differentiation.

RESULTS

Spheroids contained tight junctions and desmosomes but lacked zymogen granules, as expected. The former features were present in normal pancreatic duct but absent from PDAC cell lines grown in standard 2-dimensional culture. Spheroids functionally excluded macromolecules in whole mounts. Cells on the surface of PDAC spheroids were carpeted by microvilli except for rare cells with prominent stereocilia. Carpets of microvilli were also seen in low passage organoids produced from xenografts and surgically resected human PDAC, in addition to normal human pancreatic duct. We performed single-cell cloning and resulting spheroids produced both cell phenotypes at the same approximate ratios as those from bulk cultures.

CONCLUSIONS

Pancreatic cancer spheroids/organoids are capable of biphenotypic differentiation.

Enhanced morphological and functional differences of pancreatic cancer with epithelial or mesenchymal characteristics in 3D culture

Pancreatic cancer, composed of heterogeneous cancer cells, alters epithelial to mesenchymal features during growth and metastasis. In this study, we aimed to characterize pancreatic ductal adenocarcinoma (PDAC) cells showing epithelial or mesenchymal features in 3D culture. In 3D culture, PK-1 cells had high E-cadherin and low vimentin expression and exhibited a round-like appearance encircled by flat cells. PANC-1 cells had high vimentin and low E-cadherin expression and formed grape-like spheres. PK-1 cells had secretary granules and many microvilli, desmosomes, and adherens junctions, while PANC-1 cells had few microvilli, adherens junction, and no desmosomes. Cytokeratin 7, trypsin, CA19-9, and E-cadherin were highly expressed in PK-1 cells but not in PANC-1 cells. Ki-67 was diffusely expressed in PANC-1 spheres but was restricted to the peripheral flat cells of PK-1 spheres. PANC-1 and PK-1 cells were positive for transforming growth factor (TGF) β receptor II and phosphorylated smad2/3, but PK-1 cells were smad4 negative. Taken together, 3D culture enhanced morphofunctional differences of PDAC cells showing epithelial or mesenchymal characteristics, and epithelial phenotype maintenance may be due to the ineffectiveness of the TGF- β pathway. Clarification of heterogeneity using 3D culture may be useful for development of individualized diagnostic and therapeutic methods in patients with PDAC.

Pancreatic cancer stem cells: features and detection methods

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a high incidence of distant metastasis and recurrence. Cancer stem cells (CSCs), which are pluripotent, self-renewable, and capable of forming tumors, contribute to PDAC initiation and metastasis and are responsible for resistance to chemotherapy and radiation. Three types of experimental methods are commonly used to identify CSCs: CSC-specific marker detection, a sphere-formation assay that reveals cell proliferation under non-adherent conditions, and detection of side-population (SP) cells that possess high intracellular-to-extracellular pump functions. Several CSC-specific markers have been reported in PDACs, including CD133, CD24, CD44, CXCR4, EpCAM, ABCG2, c-Met, ALDH-1, and nestin. There remains controversy regarding which markers are specific to PDAC CSCs and which are expressed alone or in combination in CSCs. Examining characteristics of isolated CSCs and discovering CSC-specific treatment options are important to improve the prognosis of PDAC cases. This review summarizes CSC-detection methods for PDAC, including CSC-marker detection, the sphere-formation assay, and detection of SP cells.

Stemness and anti-cancer drug resistance in ATP-binding cassette subfamily G member 2 highly expressed pancreatic cancer is induced in 3D culture conditions

The expression of ATP-binding cassette subfamily G member 2 (ABCG2) is related to tumorigenic cancer stem cells (CSC) in several cancers. However, the effects of ABCG2 on CSC-related malignant characteristics in pancreatic ductal adenocarcinoma (PDAC) are not well elucidated. In this study, we compared the characteristics of low (ABCG2-) and high (ABCG2+)-ABCG2-expressing PDAC cells after cell sorting. In adherent culture condition, human PDAC cells, PANC-1, contained approximately 10% ABCG2+ cell populations, and ABCG2+ cells displayed more and longer microvilli compared with ABCG2- cells. Unexpectedly, ABCG2+ cells did not show significant drug resistance against fluorouracil, gemcitabine and vincristine, and ABCG2- cells exhibited higher sphere formation ability and stemness marker expression than those of ABCG2+ cells. Cell growth and motility was greater in ABCG2- cells compared with ABCG2+ cells. In contrast, epithelial-mesenchymal transition ability between ABCG2- and ABCG2+ cells was comparable. In 3D culture conditions, spheres derived from ABCG2- cells generated a large number of ABCG2+ cells, and the expression levels of stemness markers in these spheres were higher than spheres from ABCG2+ cells. Furthermore, spheres containing large populations of ABCG2+ cells exhibited high resistance against anti-cancer drugs presumably depending on ABCG2. ABCG2+ cells in PDAC in adherent culture are not correlated with stemness and malignant behaviors, but ABCG2+ cells derived from ABCG2- cells after sphere formation have stemness characteristics and anti-cancer drug resistance. These findings suggest that ABCG2- cells generate ABCG2+ cells and the malignant potential of ABCG2+ cells in PDAC varies depending on their environments.