Multicellular 3D Models to Study Tumour-Stroma Interactions

Abstract

Two-dimensional (2D) cell cultures have been the standard for many different applications, ranging from basic research to stem cell and cancer research to regenerative medicine, for most of the past century. Hence, almost all of our knowledge about fundamental biological processes has been provided by primary and established cell lines cultured in 2D monolayer. However, cells in tissues and organs do not exist as single entities, and life in multicellular organisms relies on the coordination of several cellular activities, which depend on cell–cell communication across different cell types and tissues. In addition, cells are embedded within a complex non-cellular structure known as the extracellular matrix (ECM), which anchors them in a three-dimensional (3D) formation. Likewise, tumour cells interact with their surrounding matrix and tissue, and the physical and biochemical properties of this microenvironment regulate cancer differentiation, proliferation, invasion, and metastasis. 2D models are unable to mimic the complex and dynamic interactions of the tumour microenvironment (TME) and ignore spatial cell–ECM and cell–cell interactions. Thus, multicellular 3D models are excellent tools to recapitulate in vitro the spatial dimension, cellular heterogeneity, and molecular networks of the TME. This review summarizes the biological significance of the cell–ECM and cell–cell interactions in the onset and progression of tumours and focuses on the requirement for these interactions to build up representative in vitro models for the study of the pathophysiology of cancer and for the design of more clinically relevant treatments.

3D Bioprinting of Model Tissues That Mimic the Tumor Microenvironment

“…Conventional cancer models, such as 2D cultures of cancer cells and stromal cells, cannot mimic the TME, especially in what concerns oxygen and nutrient availability, thereby being limited as biomimetic models for anti-cancer drug testing or fundamental research in cancer biology [ 8 ]. The lack of tumor-stroma interaction is also a weak point in patient-derived tumor organoid models otherwise highly valued for their ability to replicate intra- and intertumor heterogeneity in high-throughput cultures of 3D constructs [ 9 ].…”

Three-Dimensional Culture Models to Study Innate Anti-Tumor Immune Response: Advantages and Disadvantages

“…The addition of appropriate scaffolds and flow-based systems could mimic the architecture of the tumor tissue and the dynamic conditions faced by immune cells approaching and invading the tumor [ 15 , 16 ]. It is evident that the molecular events detected in conventional culture systems, consisting of a mixture of different cell types, cannot be compared to what happens in a 3D-growing tumor mass.…”

“…It is evident that the molecular events detected in conventional culture systems, consisting of a mixture of different cell types, cannot be compared to what happens in a 3D-growing tumor mass. On the other side, human tumor cells injected in mice do not find the micro (cell and matrix component) and macro environment (vascular, lymphatic and nervous systems) in which the original tumor mass developed [ 15 , 16 ].…”

“…In this case, using appropriate tools such as humanized monoclonal antibodies (hmAb) to programmed cell death receptor 1 (PD1), programmed cell death receptor ligand 1 (PDL1) or cytotoxic activated T lymphocyte 4 receptor (CTLA4), it is possible to reactivate the adaptive anti-tumor-specific immune response [ 7 , 8 , 9 , 10 , 11 ]. This strategy is effective when IC-inhibited tumor-specific T cells are already present in the host, thus targeted hmAb can relieve the tumor microenvironment (TME)-mediated immunosuppression [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…The study of the molecular mechanisms underlying IC-immunosuppression and patient-specific immune response is difficult in animal models [ 15 , 16 ]. Humanized murine models and patient-derived tumor xenografts (PDX) have been extensively used, with some success.…”