Development of Cancer‐on‐a‐chip Technology for the Study of Tumor Microenvironment and Metabolism

Abstract

Cancer metabolism has become an area of intense interest. In the 1920s, Otto Warburg showed that cancer cells metabolize glucose to produce lactate and ATP in the presence of oxygen, i.e. aerobic glycolysis, also known as the Warburg Effect. It is now appreciated that cancer cells display a complex metabolic phenotype. Metabolic reprogramming by oncogenes and tumor suppressor genes has been linked to the altered metabolic function of cancer cells. However, the tumor microenvironment (TME), which has different nutrient gradients for glucose, oxygen, and amino acids, has a dramatic effect on cancer cell growth and proliferation. In vivo studies have demonstrated a heterogeneous metabolic phenotype that is difficult to characterize. In addition, the exchange of nutrients and metabolites between the TME, vasculature, and tumor cells has been difficult to fully recapitulate. As a tumor grows, nutrients diffuse from the blood vessels to the cancer cells, in a process partially described by A. Krogh in 1919 through a reaction‐diffusion differential equation. Krogh’s work showed that for typical tissues the oxygen decay radius is around 150μm and we find approximately the same ‘Krogh radius’ for high glucose consumption cancer cells (e.g. MDA‐MB‐231). Thus, around 150μm from a blood vessel exists an oxygen deprived environment that imposes tremendous competitive stresses on the cancer cells for survival. There is rising evidence that this selection pressure favors the transformation to metastasis and causes invasive tumor cell lines to exhibit high glycolytic rates and overall metabolic reprogramming. However, most studies focused on defining the metabolic function of tumor cells have been conducted in vitro, under conditions that do not represent the physiological conditions accurately.Here, we present a cancer‐on‐a‐chip technology that produces a well‐defined 3D TME that can be exposed to precise nutrient stresses such as varying oxygen or other nutrient gradients. In addition, we can determine the metabolic phenotype of cancer cells with varying oncogenic changes and degrees of aggressiveness. Our technology should be able to address the question of the role of the TME on metabolic reprogramming and in particular glycolysis. Our design is based on growing tumor microenvironments inside 360µm ID capillary tubing that can be accessed by 360µm PEEK tubing. To allow/control perfusion through the microenvironment we embed a 70µm nylon fiber into a photocross‐linkable gelatin gel in which the cells are dispersed (MDA‐MB‐231/GFP). After exposing the gel to UV‐light for a few seconds, the nylon fiber is pulled, leaving a perfusable microchannel. Using this technique, we have successfully perfused cell‐laden hydrogels over weeks while observing cell‐growth in a fluorescence microscope.