Strategies for developing complex multi-component in vitro tumor models: Highlights in glioblastoma

Abstract

In recent years, many research groups have begun to utilize bioengineered in vitro models of cancer to study mechanisms of disease progression, test drug candidates, and develop platforms to advance personalized drug treatment options. Due to advances in cell and tissue engineering over the last few decades, there are now a myriad of tools that can be used to create such in vitro systems. In this review, we describe the considerations one must take when developing model systems that accurately mimic the in vivo tumor microenvironment (TME) and can be used to answer specific scientific questions. We will summarize the importance of cell sourcing in models with one or multiple cell types and outline the importance of choosing biomaterials that accurately mimic the native extracellular matrix (ECM) of the tumor or tissue that is being modeled. We then provide examples of how these two components can be used in concert in a variety of model form factors and conclude by discussing how biofabrication techniques such as bioprinting and organ-on-a-chip fabrication can be used to create highly reproducible complex in vitro models. Since this topic has a broad range of applications, we use the final section of the review to dive deeper into one type of cancer, glioblastoma, to illustrate how these components come together to further our knowledge of cancer biology and move us closer to developing novel drugs and systems that improve patient outcomes.

Keywords: Biofabrication; Biomaterials; Bioprinting; In vitro; Organ-on-a-chip; Organoids; Tumor models; Tumor-on-a-chip.

Figure 1.

A visual representation of the workflow and considerations in building in vitro cancer model systems.

Figure 2:. Overview of various form factors used in in vitro cancer modeling.

In vitro cancer models occupy a wide variety of forms. These range from relatively simple a) spheroids that can be homogeneous or heterogeneous to more complex b) organoids that spontaneously form in materials such as Matrigel. c) Other forms of organoids, or 3D tumor constructs, can be formed by encapsulating tumor cells, including those derived from a patient’s tumor, in an ECM hydrogel, which can then be subsequently deposited or bioprinted in small volumes to form organoids. d) Transwell inserts or permeable support wells have been widely used to assess tumor cell migration towards cytokines, chemokines, or other cell types. e-g) Microfluidic device technologies have rapidly advanced in cancer research, resulting in a wide variety of tumor-on-a-chip systems. These include e) directed 3D tumor cell invasion models, f) microvascular tissue chips containing self-organizing blood vessels and tumor foci, and g) metastasis-on-achip systems allowing tracking of tumor cells through microfluidic circulation to other tissue sites.

Figure 3.. Overview of the components necessary to design complex multi-component models of glioblastoma.

a) Like many other cancers, the GBM TME consists of many unique cell types including tumor cells, glial cells, immune cells, and vascular cells. GBM tumors cells are also composed of multiple distinct subpopulations. b) These subpopulations can be labeled and combined in a spheroid or organoid culture and their growth and proliferation studied in response to treatment. c) The blood brain barrier plays a key role in regulating tumor growth and in the delivery of therapeutics to the tumor site. d) Microfluidic models have been created to model the BBB in vitro. e) The extracellular matrix in and around the tumor in GBM is different from that of the healthy brain. There is an increase in stiffness and deposition of certain ECM molecules such as hyaluronan and vitronectin. The stiffness (f) and the relative concentration of various ECM components (g) can be controlled via chemical modification of the hydrogel biomaterials used.