Engineering approaches to studying cancer cell migration in three-dimensional environments

Abstract

Cancer is one of the most devastating diseases of our time, with 17 million new cancer cases and 9.5 million cancer deaths in 2018 worldwide. The mortality associated with cancer results primarily from metastasis, i.e. the spreading of cancer cells from the primary tumour to other organs. The invasion and migration of cells through basement membranes, tight interstitial spaces and endothelial cell layers are key steps in the metastatic cascade. Recent studies demonstrated that cell migration through three-dimensional environments that mimic the in vivo conditions significantly differs from their migration on two-dimensional surfaces. Here, we review recent technological advances made in the field of cancer research that provide more 'true to the source' experimental platforms and measurements for the study of cancer cell invasion and migration in three-dimensional environments. These include microfabrication, three-dimensional bioprinting and intravital imaging tools, along with force and stiffness measurements of cells and their environments. These techniques will enable new studies that better reflect the physiological environment found in vivo, thereby producing more robust results. The knowledge achieved through these studies will aid in the development of new treatment options with the potential to ultimately lighten the devastating cost cancer inflicts on patients and their families. This article is part of a discussion meeting issue 'Forces in cancer: interdisciplinary approaches in tumour mechanobiology'.

Keywords: decellularized tissue; force generation; intravital imaging; microfluidics; nuclear mechanics; three-dimensional bioprinting.

Figure 1.

The metastatic process. Cancer cells detach from the primary tumour, translocate into a distant organ and colonize it to form metastases. Some cancer cells within the primary tumour acquire an invasion phenotype (i), then detach from the primary tumour (ii) to invade the surrounding extracellular matrix, likely aided by cancer-associated cells such as fibroblasts and macrophages (ii′). Tumour cells intravasate lymphatic and blood vessels (iii) and are carried by the circulation to distant organs (iv), where they extravasate from the blood vessels (v) and invade the microenvironment of the distant tissue (vi′). There, tumour cells must survive and proliferate to create micro-metastases (vi), which further grow to generate macro-metastases (vii).

Figure 2.

Methods of studying cancer cell invasion. (a). Traction force measurements in three-dimensional environments. Fluorescent beads (red) are embedded in collagen matrices or engineered hydrogels (pale green) containing tumour cells (grey). The traction forces cells generated are calculated by analysing the displacement of the fluorescent beads between the strained and unstrained states of the gels. (b) Schematic depiction of a brain organotypic slice and tumour co-culture. Medium is added to the bottom of a culture dish; the brain slice is placed on the top of a semi-porous membrane. Fluorescently labelled tumour spheroids (green) are implanted into the slice, so that tumour cell invasion can be imaged and tracked. (c) A schematic representation of a cell migrating through a microfluidic device mimicking the confined spaces in tissues [33]. Media reservoirs (i) allow cells to be maintained for multiple days and can be used to establish chemotactic gradients. Cells are loaded through seeding ports (ii). Large bypass channels (iii) connect the media reservoirs to allow for rapid equilibration of media levels. The central part of the device contains 5 µm tall constriction channels (iv) with constrictions of 1–20 µm in width. Arrow represents the direction of cell migration. (d) Conceptual representation of three-dimensional bioprinting. The printing nozzle dispenses bio-ink to fabricate complex in vitro three-dimensional structures using computer guidance. This technique allows control over the cellular composition of the bio-inks, as well as the mechanical properties of the resulting structures. (e) Intravital imaging of tumour cell invasion in vivo. Imaging chambers/windows can be inserted into the skin in several locations, such as the cranium (i), abdomen (ii), skin (iii) and nipple area (iv). Note that actual experiments typically use only a single imaging window.