Metabolism is defined as the chemical processes that enable a living organism to maintain life.
An indispensable metabolic process is energy production that must occur to provide "fuel" for cells to carry out necessary activities and maintain life.
Glucose is converted to ATP (adenosine triphosphate), in which cellular fuel is stored to enable and sustain cellular activities. A single glucose molecule can generate 32 ATP molecules via a three-stage process: (1) glycolysis, (2) citric acid cycle, and (3) oxidative phosphorylation.
In normal healthy cells, glycolysis yields 2 molecules of ATP, citric acid cycle adds another 2 ATP molecules, and oxidative phosphorylation adds the remaining 28 molecules of ATP. Clearly, glycolysis alone is not an efficient means for ATP production. Normal cells rely on all three stages for efficient ATP production.
Cancer cells are constantly undergoing proliferation, hence they need constant ATP supplies. Despite this high demand of ATP, cancer cells are observed to rely on glycolysis, which, as we just discussed, is not at all efficient, yielding only 2 molecules of ATP per one molecule of glucose.
So, how do cancer cells ensure a constant and sufficient cellular fuel supply? There are two mechanisms. The first mechanism is for the cancer cells to accelerate the rate of glycolysis. This rate is estimated to be several folds faster compared to the rate of glycolysis by normal cells. The second mechanism utilized by cancer cells for adequate ATP supply is to increase the expression of glucose transporter (GLUT) proteins to increase glucose transport intracellularly.
GLUT1 and GLUT3 are reported to play essential roles in promoting glucose transport and ATP production by glioblastoma multiforme (GBM) cells. More details on GBM are provided in later topics of this course.
