In this blog post, we will explore the principles and possibilities of photodynamic therapy, which selectively destroys cancer cells.
As of 2025, cancer is the leading cause of death in South Korea. Despite ongoing attempts to overcome cancer through various methods, such as anticancer drugs and radiation therapy, cancer has not yet been completely conquered and remains a major concern for humanity. Curing cancer means removing cancer cells. While it is important to completely eradicate cancer cells, it is equally important to treat the disease without destroying normal cells. Even if all cancer cells in the body are removed, the treatment is meaningless if other organs are damaged during the process, preventing the patient from living a normal life. Therefore, most of the cancer treatments developed in recent years are targeted therapies that attack and destroy only cancer cells. Among these targeted therapies is photodynamic therapy, which uses light to destroy cancer cells.
Photodynamic therapy, also known as photochemotherapy, consists of three main steps. These three steps, which involve the administration of a photosensitizing agent, the projection of light, and the generation of oxygen, work together organically. Photosensitizers react to light of a specific wavelength. The photosensitizers used in photodynamic therapy are harmless to the human body and generate active oxygen when exposed to light. Active oxygen has different properties from the oxygen commonly found in the air. Oxygen in the air exists in the form of molecules consisting of two oxygen atoms, which are not very reactive and do not easily react with surrounding substances. However, active oxygen is highly reactive because it exists as a single oxygen atom that is not bonded to other oxygen atoms, and therefore easily reacts with surrounding substances. Therefore, when active oxygen is generated in the body, the surrounding cells cannot function properly and are destroyed.
Therefore, when performing photodynamic therapy, it is important to accurately attach the photosensitizer to the tissue composed of cancer cells in the body. If treatment is performed while the photosensitizer is attached to normal tissue, the active oxygen generated by the photosensitizer will destroy the normal tissue, and the treatment will fail. This problem is solved by using a substance called an antibody. Cells and the substances that make up cells have unique structures that allow them to be distinguished from one another. When a substance that is not normally found in the body is detected, our body produces antibodies that bind to the characteristic structure of that substance. The original function of these antibodies is to help white blood cells recognize foreign substances and remove them from the body, but in photodynamic therapy, antibodies help photosensitizers bind to cancer cells. When photosensitizers are attached to antibodies specific to cancer cells, the antibodies bind to the cancer cells, causing the photosensitizers to accumulate in the vicinity of the cancer cells. When light of a specific wavelength that causes the photosensitizer to react is shone on the cells, active oxygen is generated around the cancer cells, destroying them.
Photodynamic therapy, which functions as a targeted therapy, has recently been attracting attention as a treatment with few side effects and low toxicity. This is because it has fewer aftereffects than conventional radiation and drug therapies, and the photosensitizer is excreted from the body over time after treatment. However, the limitations of photodynamic therapy are that patients cannot undergo treatment until the photosensitizer has settled in the cancer cells and all of the remaining photosensitizer has been removed, and that cancer cells located deep within the body cannot be removed with current technology due to the limited depth of light penetration.
However, photodynamic therapy is advancing day by day. On September 5, 2022, the second-generation photosensitizer used in photodynamic therapy was designated as an orphan drug by the Ministry of Food and Drug Safety. Compared to the first-generation photosensitizer, the waiting time for treatment has been reduced from 48 hours to 3 hours, and the treatment depth has been rapidly increased from about 4 mm to 12-15 mm. In addition, recent studies have confirmed that petahertz pulse lasers can effectively treat intractable cancers such as ocular melanoma. This technology has succeeded in destroying cancer cells while minimizing damage to surrounding normal tissue by irradiating high-energy light for a fraction of a second.
In addition, new porphyrin dimers are attracting attention as potential drugs for photodynamic therapy. Dimer shows higher photoreactivity than existing monomers, which can greatly improve the efficiency and safety of treatment. The steady advancement of photodynamic therapy is opening up new possibilities for cancer treatment and is establishing itself as an innovative method for treating various types of cancer.
When the day comes that we can maintain the advantages of photodynamic therapy while overcoming its disadvantages, that day will be the day that humanity conquers cancer.
