Multiple cystic sphere formation from PK-8 cells in three-dimensional culture

Transmission electron microscopic analysis of pancreatic ductal adenocarcinoma cell spheres formed in 3D cultures

Pancreatic ductal adenocarcinoma (PDAC) cell lines are classified into two types: epithelial and mesenchymal protein-expressing. Using scanning electron microscopy, we reported that these two groups differ in terms of morphology when they formed tumor spheres under three-dimensional (3D) culturing. In this study, we used transmission electron microscopy (TEM) to examine the intracellular microstructures of five epithelial and three mesenchymal PDAC cell lines in 3D culture, and compared them to the morphologies of the same cell types in two-dimensional (2D) cultures. Microvilli were present in all PDAC cells cultured in 2D and 3D, and were well developed in epithelial PDAC cells. Desmosome-like structures were only observed in epithelial PDAC cells, and were more common in 3D cultures. Secretory granules were observed in epithelial PDAC and mesenchymal PANC-1 cells, and were more common in 3D cultures. Intracytoplasmic lumina were only observed in epithelial PK-59 and T3M-4 cells cultured in 3D. Abundant filamentous aggregates were observed in 2D-cultured T3M-4 and MIA PaCa-2 cells. By contrast, entosis was observed in 3D-cultured PK-59, PK-1, and KP4 cells. Microstructural differences enhanced by 3D culturing revealed significant phenotypic diversity among PDAC cells, and may provide key insights into curing intractable pancreatic cancer.

Morphological and functional analysis of colorectal cancer cell lines in 2D and 3D culture models

The epithelial and mesenchymal features of colorectal adenocarcinoma (CRAC) cell lines were compared in two-dimensional (2D) and three-dimensional (3D) cultures. In 2D cultures, the three CRAC cell lines exhibited epithelial characteristics with high E-cadherin and low vimentin levels, whereas two exhibited mesenchymal traits with opposite expression patterns. In 3D cultures using low-attachment plates, mesenchymal cells from 2D cultures showed reduced vimentin mRNA levels. Morphologically, the five CRAC cell lines appeared similarly shaped in 2D culture but formed different structures in 3D culture. Epithelial DLD-1 and mesenchymal COLO-320 cells produced large granular spheres, whereas epithelial HCT-15 cells formed small solid spheres. Tubular structures were observed in epithelial CACO-2 and mesenchymal SW480 spheres. Desmosome-like structures developed in epithelial CRAC cells, whereas entosis was observed in CACO-2, HCT-15, and SW480 cells. The Ki-67-positive proliferating cell count varied in 2D and 3D cultures of epithelial cells but remained high and unchanged in mesenchymal cells. These findings suggest that while CRAC cells display distinct epithelial and mesenchymal properties in 2D cultures, they form diverse 3D structures, irrespective of these traits.

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.