Abstract
According to the World Health Organization (WHO), cancer is one of main causes of death worldwide, with 8.2 million people dying from this disease in 2012. Because of this, new forms of treatments or improvement of current treatments are crucial. In this regard, Photodynamic therapy (PDT) has been used to successfully treat cancers that can be easily accessed externally or by fibre-optic endoscopes, such as skin, bladder and esophagus cancers. In addition, this therapy can used alongside radiotherapy and chemotherapy in order to kill cancer cells. The main problem in implementing PDT is penetration of visible light deeper than 10 mm in tissues, due to scattering and absorption by tissue chromophores. Unfortunately, this excludes several internal organs affected by cancer. Another issue in this regard is the use of a selective cancer cell-photosensitizing compound. Nevertheless, several groups have recently developed scintillation nanoparticles, which can be stimulated by X-rays, thereby making this a possible solution for light production in deeper tissues. Alternative approaches have also been developed, such as photosensitizer structure modifications and cell membrane permeabilizing agents. In this context, certain channels lead to transitory plasma membrane permeability changes, such as pannexin, connexin hemmichannels, TRPV1-4 and P2×7, which allow for the non-selective passage of molecules up to 1,000 Da. Herein, we discuss the particular case of the P2×7 receptor-associated pore as a drug delivery system for hydrophilic substances to be applied in PDT, which could also be carried out with other channels. Methylene blue (MB) is a low cost dye used as a prototype photosensitizer, approved for clinical use in several other clinical conditions, as well as photodynamic therapy for fungi infections.
Highlights
In the western World, the term photodynamic action, a literal translation of the German word “Wirkung der photodynamischen”, was coined by von Tappeiner and collaborators to differentiate photodynamic action from the sensitization that occurs in photography films [1, 2]
The use of Photodynamic Therapy (PDT) to treat in vivo tumors was little explored until 1972, when Diamond and co-workers demonstrated a small decrease in tumors derived from a glioma cell line implanted in rats exposed to light and treated with haematoporphyrin [9]
In 1975, a breakthrough study was published on eleven human bladder carcinomas xenografted to artificially immunosuppressed mice treated with PDT, that demonstrated remarkable damage to the tumors [10]
Summary
Photodynamic action: a brief history of cancer treatmentIn the western World, the term photodynamic action, a literal translation of the German word “Wirkung der photodynamischen”, was coined by von Tappeiner and collaborators to differentiate photodynamic action from the sensitization that occurs in photography films [1, 2]. Based on that study, and on their own data, Von Tappeiner, H., and Jesionek, A. treated three patients presenting skin cancer and other pathologies with Photodynamic Therapy (PDT) [7].
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