الفهرس 
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Abstract
Porphyrins are well-recognized photosensitizing drugs for the treatment of cancer. Many efforts have been made to find novel porphyrin derivatives that have good physiologic properties and a reduced side-effect for photo Dynamic Therapy (PDT). A number of porphyrin analogs, including hematoporphyrins and photofrin II, the former have been used for tumor treatment and the latter has currently been approved by the U.S. Food and Drug Administration (FDA) for general use as a PDT agent in the treatment of solid tumors and cancers. Moreover, porphyrins as photosensitizers have the advantages of lack of toxicity in the dark, stable composition, selective photosensitization of tumor tissue, and high synthesis of Reactive Oxygen Species (ROS). However, the structures of porphyrins, which are based on a macrocyclic structure and possess a lipophilic property, are often modified with various polar functional groups to overcome solubility problems. Porphyrins that are modified with ether, ester, amino, and phenyl for easy substitution are well known to show phototoxicity and selective accumulation in tumor cells. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are very attractive techniques to investigate living substances by using appropriated radionuclide-labeled molecules.
It has been demonstrated that hydrophobic porphyrin-based sensitizers are mainly carried in blood by lipoproteins (which also do not ‘like’ water), particularly LDLs. LDLs are of particular interest because they are recognized by a specific receptor called the apo B/E receptor, which results in rapid internalization and delivery of the LDL particle to the lysosomal compartment. The number of LDL receptors is generally higher in tumor cells compared to their normal counterparts. This is because the hyperproliferating cells require an extra supply of cholesterol and phospholipids.