What is photodynamic therapy (PDT)?

Quick Answer
Treatment of local precancerous and cancerous lesions of epithelial origin using a class of drugs called photosensitizers that become active when exposed to specific light wavelengths.
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Cancers treated: Esophageal cancer, lung cancer, bladder carcinoma, nonmelanoma skin cancer

Subclasses of this group: Currently, most of the clinically approved photosensitizers are porphyrins, but other drugs under clinical investigation belong to the chlorin or purpurin family. According to the American Cancer Society as of 2013, the photosensitizing agents porfimer sodium, aminolevulinic acid (ALA), and methyl ester of ALA have been approved by the US Food and Drug Administration.

Delivery routes: Intravenous or topical, depending on the drug’s chemical structure and the type of cancer and its location

How these drugs work: The first clinical application of PDT was reported in 1903 by two German researchers, who used a topical coal tar dye called eosin in combination with visible light to treat skin cancer. The isolation of safer and more effective photosensitive dyes, called porphyrins, has propelled the field forward. Photosensitizers preferentially accumulate in abnormal tissues and cause little damage to surrounding healthy cells.

PDT is a two-part process. First, a nontoxic photosensitizer is administered to the patient. The lesion site is then exposed to light that is of a suitable wavelength to excite the photosensitive drug. Activated drug molecules initiate cytotoxic reactions that destroy tumor cells. They transfer energy to molecular oxygen, which, in turn, generates reactive oxygen species (ROS), such as singlet oxygen. These active molecular species damage deoxyribonucleic acid (DNA) and cause the oxidation of proteins and lipids. As a result, cancer cells undergo necrosis or apoptosis, the natural process of cell death. Because light needed to activate most photosensitizers cannot penetrate deeply into tissue, the therapeutic potential of PDT is limited to the treatment of local superficial tumors rather than large tumors or metastases.

Side effects: One side effect of PDT is increased sensitivity to light (sunburn-like reactions), which may last for several weeks after administration. Other side effects include constipation, irritation at the injection site, back pain, chest pain, fever, flu-like syndrome, and general weakness.

Bibliography

Abdel-Kader, Mahmoud H., ed. Photodynamic Therapy: From Theory to Application. New York: Springer, 2014. Print.

Agostinis, Patrizia, et al. “Photodynamic Therapy of Cancer: An Update.” CA: A Cancer Journal for Clinicians 61.4 (2011): 250–81. Print.

Gold, Michael H., ed. Photodynamic Therapy in Dermatology. New York: Springer, 2011. Print.

Majumdar, Poulomi, Raju Nomula, and Jianzhang Zhao. “Activatable Triplet Photosensitizers: Magic Bullets for Targeted Photodynamic Therapy.” Journal of Materials Chemistry C 30 (2014): 5982–97. Print.

Simone, Charles B., et al. “Photodynamic Therapy for the Treatment of Non-Small Cell Lung Cancer.” Journal of Thoracic Disease 4.1 (2012): n. pag. Web. 30 Sept. 2014.

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