Artificial tumor: a novel heterotypic, polymorphic, three-dimensional in vitro model of individual human solid tumors

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

Hollow-spheres: a new model for analyses of differentiation of pancreatic duct epithelial cells

We discovered a unique feature of a subclone of the pancreatic carcinoma cell line A818. A818-1-derived hollow-spheres developed under three-dimensional growth conditions. Hollow-spheres consist of a single layer of 50-200 epithelial cells surrounding an inner lumen. In contrast to A818-1, the subclone A818-4 and all other pancreatic tumor cell lines tested (n = 5), formed spheroids as the only three-dimensional phenotype. A dramatically reduced proliferation rate compared to the corresponding monolayer was observed in hollow-spheres when bromodeoxyuridine (BrdU) incorporation was measured. This finding was confirmed by immunostaining using the MIB-1 antibody. Mechanically disrupted hollow-spheres not only attached but also grew as monolayer with the same doubling time as the founder cells. Hollow-spheres developed in fetal calf serum (FCS) containing RPMI 1640 medium without additionally added cytokines. A818-1 hollow-sphere formation and integrity was influenced by interferon-gamma. Tumor necrosis factor-alpha (TNF-alpha) led to cell death. Exogenously added hepatocyte growth factor (HGF) showed no effect neither on hollow-sphere formation nor on the integrity of completely developed hollow-spheres. Moreover, no changes were observed when cells were treated with a neutralizing antibody for HGF. Interestingly, hollow-spheres showed intensive immunoreactivity for the HGF-receptor (c-met) and its ligand (HGF). Immunostaining for the biliary glycoprotein (BGP), the non-specific cross-reacting antigen 95 (NCA95) and beta-catenin revealed a polar organization of hollow-spheres. Immunhistochemically, hollow-spheres were negative for the carcinoembryonic antigen (CEA). When hollow-spheres were embedded into matrigel, duct-like tubes grew out. Taken together, A818-1 hollow-spheres resemble normally differentiated duct-like structures and will serve as an excellent model to study differentiation of human pancreatic epithelial cells.

Isolated extracellular matrix-based three-dimensional in vitro models to study orthotopically cancer cell infiltration and invasion

An initial event in colon cancer progression is the migration of epithelial cells through the basement membrane (BM) and the invasion of the colon submucosa, where tumour cells enter blood and lymph vessels to spread throughout the body. To interrupt this process would mean the prevention of metastasis. In order to investigate tumour cell invasion orthotopically in the human system, we established novel in vitro models which mimic normal human colon tissue (colon reproductions, CoRes) and primary colon carcinomas (artificial tumours, ArTs). These models are based on the isolated extracellular matrix (iECM) of the respective human tissues. Two isolation methods were established, the Digestion Method and the Lysis Method neither of which destroyed the characteristic architecture of the ECM found in the original tissues. BM components, i.e. laminin, fibronectin and collagen IV, were detectable in the iECM isolated with the Lysis Method but not those isolated with the Digestion Method. Scanning electron microscopic analysis of the normal colon iECM demonstrated that even if the BM was missing, the luminal surface consisted of densely packed ECM filaments which do not allow cell infiltration without degradation of the iECM. Furthermore, we demonstrated that iECM can be separately supplemented with different cell types, i.e. colorectal carcinoma cells, normal fibroblasts and immune cells at any desired concentration, combination and localisation. Therefore, these models could be used to determine the role of the BM and of the tumour cell/normal cell crosstalk in the infiltration process of human colorectal carcinoma cells.

Three-dimensional cell cultures: from molecular mechanisms to clinical applications

This article reviews actual advances in the development and application of three-dimensional (3-D) cell culture systems. Recent therapeutically oriented studies include characterization of multicellular-mediated drug resistance, novel ways of quantifying hypoxia, and new approaches to more efficient immunotherapy. Recent progress toward understanding the development of necrosis in tumor spheroids has been made using novel spheroid models. 3-D cultures have been used for studies on molecular mechanisms involved in invasion and metastasis, with a major focus on the role of E-cadherin. Similarly, tumor angiogenesis and the significance of vascular endothelial growth factor have been investigated in a variety of 3-D culture systems. There are many ongoing developments in tissue modeling or remodeling that promise significant progress toward the development of bioartificial liver support and artificial blood. Perhaps one of the most interesting areas of basic research with 3-D cultures is the characterization of embryoid bodies obtained from stable embryonic stem cells. These models have greatly increased the understanding of embryonic development, in particular through the notable exceptional advances in cardiogenesis.

The influence of the local environment on tissue architecture of colorectal carcinoma (CRC) cell aggregates and its consequence for tumour attack by lymphocytes in vitro and in vivo

We analysed colorectal carcinoma (CRC) specimens, tumour cell spheroids and artificial tumours (ArTs) for tissue architecture, carcinoembryonic antigen (CEA) expression and lymphocyte infiltration. Two distinct organisation forms of well-differentiated CRC cells were found in vivo and in vitro. Tumour cells having contact with the tumour stroma in primary tumours, and tumour cells growing within a stroma-like structure in vitro (ArTs) were arranged as pseudoglands. In contrast, tumour cells grown as spheroids or tumour cells having lost contact with the tumour stroma in primary tumours, and most probably in the circulation, showed an inversion of the architecture of these pseudoglands, presenting their apical cell membrane to the environment. These different tumour cell formations affect lymphocytes attacking the tumour, which need contact with specific cellular membranes of polarised tumour cells, depending on the tumour architecture. Recently, we demonstrated that the CEA expression of CRC cells correlated with their resistance against LAK-cell lysis. Since CEA is mainly expressed on the apical membrane of the tumour cells, independent of the tissue architecture, the change from the pseudoglandular to the spheroid-like formation may represent an escape mechanism for malignant cells.