Engineering Tools for Regulating Hypoxia in Tumour Models

Abstract

Major advances in the field of genomic technologies have led to an improvement in cancer diagnosis, classification and prognostication. However, many cancers remain incurable due to the development of drug resistance, minimal residual disease (MRD) and disease relapse, highlighting an incomplete understanding of the mechanisms underlying these processes. In recent years, the impact of non-genetic factors on neoplastic transformations has increasingly been acknowledged, and growing evidence suggests that low oxygen (O₂ ) levels (ie hypoxia) in the tumour microenvironment play a critical role in the development and treatment of cancer. As a result, there is a growing need to develop research tools capable of reproducing physiologically relevant O₂ conditions encountered by cancer cells in their natural environments in order to gain in-depth insight into tumour cell metabolism and function. In this review, the authors highlight the importance of hypoxia in the pathogenesis of malignant diseases and provide an overview of novel engineering tools that have the potential to further drive this evolving, yet technically challenging, field of cancer research.

FIGURE 1

Tissue oxygenation and HIF regulation. (A) O₂ concentrations as measured in selected mammalian tissues. (B) Regulation of HIF stability by O₂

FIGURE 2

Microfluidic‐based engineering tools for controlling O₂ content. (A) Image of a gradient‐generating microfluidic device. (B) Schematic of step O₂ concentrations formed in each outlet of the gradient‐generating microfluidic device. O₂ diffusion in the chamber is controlled by diffusion through 3‐sided glass coating. (C) Schematic of the microfluidic device capable of performing collective cell migration assays with O₂ gradients. (D) Photographs of the fabricated microfluidic devices. O₂ scavenging chemical reaction between pyrogallol and NaOH was performed in the reaction channel in order to generate O₂ gradient. (E) Schematic illustration of O₂ consumption and gradient‐generating mechanism in a microfluidic chamber. Reprint with permission

FIGURE 3

O₂‐consuming enzymes for controlling O₂ content. (A) The principle of the glucose oxidase/catalase (GOX/CAT) system for independent control of hypoxia and H₂O₂ level. (B) Reaction scheme of GOX immobilized PEGDA hydrogel. (C) Conceptual illustration and digital images of the 3D‐printed insert with immobilized biomaterial for on demand generation of various O₂ tensions for in vitro cell cultures. The biomaterial consisting of glucose oxidase and catalase enzymes consumes O₂ in the cell culture media without interfering with the testing environment. Reprint with permission

FIGURE 4

Laccase‐based hypoxia‐inducible hydrogels for controlling O₂ content in 3D. (A) Schematic representation of HI hydrogel formation. HI hydrogels are formed via laccase‐mediated dimerization of FA molecules with O₂ consumption. (B) Hydrogel height controls O₂ gradients. (C) Model predictions of O₂ levels and gradients after 30 min of hydrogel formation in the layer model (airgel and air–media‐gel). Reprint with permission