Glucose, a small six-carbon molecule, is elemental to life. Upon consuming it, cells metabolize it, releasing the energy needed for all biological processes. Normal physiological function, including functioning of neurons in the human brain, depends on effective utilization of glucose as a main source of energy. Usually, cells take up glucose and it is metabolized (broken down) through biosynthetic reactions releasing energy for cellular processes.
Aberrant glucose metabolism is usually involved in many different types of cancers leading to increased proliferation and cell growth and ultimately tumor formation. Glucose is also abnormally metabolized in various other diseases including metabolic diseases such as diabetes and obesity as well as neurodegenerative disease. The importance of this metabolite for our survival and in disease and the limitations of current glucose metabolism imaging methods have sparked a search for a more sensitive and effective way to measure and image how cells use glucose. Today, many researchers are using tissue culture and animal models of disease to study glucose metabolism with the ultimate goal of developing useful treatments for cancer and many other devastating diseases.
Recently, Dr. Elena Goun and her research team at the École Polytechnique Fédérale de Lausanne quantified glucose metabolism in cells grown in dishes as well as cancer tumors in tumor xenograft cancer models —a challenging task since bioluminescence in living and deep tissue is not easily detected and quantifiable—by elegantly and non-invasively using the bioluminescence generated by the Luciferase enzyme.
This group developed a “bioluminescent glucose-uptake probe” or BiGluc that is based on bioluminescent imaging (BLI) where luciferase oxidizes a molecular substrate resulting in production of visible and detectable light in live animals that can be measured and monitored without having to sacrifice the animal.
In this method, luciferin and glucose are both modified by adding small chemical groups. These modified molecules are taken up by cells just as the unmodified molecules would be. However, the modification of these molecules allows for a click reaction to occur where these modified molecules react specifically with one another.
In this biological process, the “caged” luciferin (CLP) and modified glucose molecule (glucose azide 4, GAz4, glucose reagent) are taken up by a luciferase-expressing cell, and upon reacting, luciferin is freed to interact with available luciferase, resulting in bioluminescence that can be captured with a camera in real-time. Thus, the more “glucose reagent” GAz4 is taken up by the cells in the tumors, the more bioluminescence is produced.
In this study, they confirmed that glucose uptake can be imaged and quantified in vitro. But more importantly, they injected mice bearing luciferase-expressing tumors with CLP, which entered tumor cells. Then, 24 hours later the mice were injected with GAz4, which is also taken up by cells in the mouse. The mice were then anesthetized and bioluminescence was monitored for 1 hour. Inside these cells, released luciferin interacted with luciferase, and light was produced showing how the tumor cells metabolize available glucose in real-time.
While this is certainly not the first imaging tool used to detect glucose metabolism in cancerous cells, this new method does present multiple advantages. Mainly, Dr. Goun’s BiGluc method is very sensitive and results in a strong signal that can be detected not only in cells grown in a dish, but also in the deep tissue of cancerous tumors in animal mouse models. In addition, it does not require radioactive reagents, is easy to use and does not require expensive reagents or instruments.
In the past, in vitro cancer models have yielded useful results allowing us to learn more about cancer cell metabolism and how these cells utilize glucose. However, the in vivo study of cancer cell metabolism would yield invaluable data, and is the type of study that is currently posing a bigger challenge. Thus, Dr. Goun’s findings using bioluminescence to observe metabolism in cancerous tumors presents not only as novel but also as very promising. Perhaps in the near future this same approach can be taken in pre-clinical and clinical studies to shed light into metabolism mechanisms in many different types of cancer and hopefully develop effective treatments.
Many studies have shown that in addition to glucose, many other metabolites are linked to devastating diseases such as Alzheimer’s disease and cardiovascular disease. This bioluminescent imaging tool could be applied to study and image glucose AND other metabolites to expand our understanding of the metabolite-disease mechanism and perhaps gives us insight into new metabolite-disease associations.
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Fernanda Ruiz is a science content writer at Gold Biotechnology. She holds a bachelor's of science in biology from St. Mary's University and a PhD in molecular biology from Baylor College of Medicine.