PART II
Modern Technologies in Radiotherapy (Cont'd)
2. Improvement of radiotherapy by
using radiosensitizers
A radiosensitizer (also referred to as a radiosensitizing agent) is a pharmaceutical agent that makes tumor cells more sensitive to radiation, thus, increasing the efficiency of radiotherapy. For example, oxygen is known to increase tumor sensitivity to radiation by forming free radicals that can damage DNA.
As a solid tumor continues to grow, some cancer cells outgrow their blood supply and become sufficiently removed from their capillaries to become hypoxic (lack of oxygen). As a result, cancer cells survive by another mechanism called glycolysis. Glycolysis is a process in which glucose is converted into pyruvate by an oxygen-independent metabolic pathway; the process produces energy which is then stored in the form of ATP (adenosine triphosphate) for anaerobic cancer cells. In the presence of oxygen, ATP is formed through oxidative phosphorylation.
The process of glycolysis further results in excess lactic acid, which makes solid tumor more acidic (pH can be as low as 6.2). In general, cancer cells under acidic condition (mainly due to hypoxia) are more resistant to killing by radiotherapy and some cancer drugs.
Currently, there are a number of agents being investigated as potential radiosensitizers. Some examples of radiosensitizers are shown in Part III.
