A Review on Future Prospects of Photosensitizers in Photodynamic Therapy

Abstract

Photodynamic therapy (PDT) was discovered more than 100 years ago, and has since become a well studied therapy for cancer and various non-malignant diseases including infections. PDT uses photosensitizers (PSs, non-toxic dyes) that are activated by absorption of visible light to initially form the excited singlet state, followed by transition to the long-lived excited triplet state. This triplet state can undergo photochemical reactions in the presence of oxygen to form reactive oxygen species (including singlet oxygen) that can destroy cancer cells, pathogenic microbes and unwanted tissue. The dual specificity of PDT relies on accumulation of the PS in diseased tissue and on localized light delivery. Photosensitization can be defined as a process in which a reaction to normally harmless radiation is induced by the introduction of a specific radiation-absorbing substance (photosensitizer) that causes another component (substrate) to be changed by the radiation. Photosensitivity is characterized by phototoxic and photoallergic effects. Drugs and chemicals may interact with UV to induce photosensitivity. Photosensitive disorders may be classified as those entirely caused by solar exposure and the photo aggravated disorders. Those in the former category include polymorphic light eruption, hydroa vacciniforme, actinic prurigo, solar urticaria and chronic actinic dermatitis. Photosensitivity can be diagnosed by photo test, photo patch test and photo drug test. Recently the photodynamic therapy (PDT) is used for the treatment of cancers. There are various photosensitizers such as photofrin, foscan, 5-Aminolevulinic acid (5-ALA) etc which used in photodynamic therapy. Photosensitizers are also used to treat vitiligo, microbial infections and acne.