Porphyrins are chemical compounds that are key in the development of a large number of photosensitizers assigned for use in photodynamic therapy (PDT). Porphyrin plays a very important role in photodynamic therapy (PDT). These roles include the transmission of oxygen and photosynthesis. Porphyrins are applied in many areas, such as light imaging. In medicine, it is used to cure cancer through photoimmunotherapy, which leads to the treatment of the diseased tissue. Photodynamic therapy is used in the treatment of acne.
Porphyrins come into effect when a photosensitizer of relatively small dark toxicity is administered into the body and accumulates in slowly separating the cells (Yasunaka; K. Aizawa p.34). When the drug reaches a particular ratio of accumulation in the tumor tissue together with the healthy tissue, a careful amount of light is administered to the diseased tissue, and the reactive oxygen destroys the diseased tissue. The quantity of light needed is relatively large enough to kill the tumor cells, but it should also be small enough to avoid destroying the closest healthy tissue. After being treated, the damaged cells become healthy.
Photodynamic therapy solely depends on the presence of molecular oxygen. Initiation of very big atoms into photosensitizers facilitates a radiation process that causes the conversion of two electronic amongst them (intersystem crossing) and leads to improvement of quantum yield of singlet oxygen through photosensitization of molecular triplet oxygen, which is a key component in photodynamic therapy (PDT) (Luger, T.; Schwartz p.45). However, there is little information that supports the physiological importance of the heavy-atom effect.
Photodynamic therapy is a method of selective toxicity because the drug shows an absence of biological activity until light is administered. The importance of photodynamic therapy agents is the optimization of tumor or tissue ratio. However, photodynamic therapy agents do not target specific receptors, i.e., are site non-specific drugs. A study by Boyle and Dolphin concludes that with only one available exception to note, there is no particular location bounded by the sensitizer.
An ideal photodynamic drug should have a solid absorption in the near-infrared part of the spectrum, relatively very large quantum production of triplet formation, richly singlet oxygen quantum production, and negligible dark toxicity (Luger, T.; Schwartz, p.13). Should tumorous tissues exhibit selectivity versus healthy tissue, the drug should be easily and simply formulated. It should be highly soluble, it should gradually clear from the body, and finally, it should have a strong proprietary position.
It should have very small photobleaching to prevent the photosensitizer from fading away so that it continues producing more oxygen. A photodynamic drug should also have a natural fluorescence (light) that has a longer wavelength with lower energy than the absorbed radiation.
In conclusion, porphyrin has proved to be an area to explore all over the world since it’s the first drug for photodynamic therapy (PDT) and linked areas. Most of the photosensitizers that are in existence today from various clinical tests and experiments are porphyrin based and we can predict a remained study and area of more concern to be researched on.
References
Luger, T.; Schwartz, T. In Photoimmunology, Krutman, J.; Elmets, C., Eds. Blackwell Scientific Ltd.: Oxford, 1995 s
P.C. Wilson, In Photosensitizing Compounds: Their Chemistry, Jan 1989
Johan E. Van Lier, Photosensitisation: Reaction Pathways, Jan 1991
Y. Yasunaka; K. Aizawa; T. Asahara; H. Kato; I. Ishikura; In vivo accumulation of photosensitizers in atherosclerotic lesions and blood in atherosclerotic rabbit, Jan 1991
Van Lier, J. E. In Photobiological Techniques; D. P. Valenzo, R. H. Pottier, P. Mathis and R. H. Douglas, Ed.; Plenum Press: New York, London, 1991; Vol. 216
