Photodynamic therapy

Abstract

Photodynamic therapy (PDT) has been developed over the past decade into a useful treatment for several types of solid cancers in man. This unique therapy requires a photosensitiser accumulated in tumours and local activation by visible light generally delivered from lasers and delivered to the patient through various types of fibers and endoscopes. PDT appears to be most effective in treating certain superficial, difficult to treat cancers such as carcinoma in situ of the urinary bladder (here complete control is the intent), but also is effectively used in bulkier tumours obstructing bronchi or the oesophagus where palliation can be achieved. The primary mechanism of action is the in situ generation of an active form of molecular oxygen (singlet oxygen) which causes the rapid, local onset of vascular stasis and eventual vascular haemorrhage and tumour wall destruction. This process appears to be mediated through various cytokines such as prostaglandin, lymphokines and thromboxanes. The ultimate clinical value of PDT will be seen over the next few years following health agency approval worldwide.

Photodynamic Therapy-induced Apoptosis in Epidermoid Carcinoma Cells

“…In photodynamic therapy (PDT) 1 , visible light activates a photosensitizing drug accumulated in tumor or other abnormal tissue (1)(2)(3). The interaction between the excited photosensitizer and molecular oxygen produces singlet oxygen ( 1 O 2 ) as well as other reactive oxygen species (ROS) to induce cell death (4 -8).…”

Accumulation of Porphyrins in Plasma and Tissues of Dogs after δ-Aminolevulinic Acid Administration: Implications for Photodynamic Therapy

“…Photodynamic therapy is being developed for many neoplasms, including those occur ring in skin, oropharynx, lung, gastrointesti nal tract, urogenital tissues, and central ner vous system [1,2], Tumor destruction is achieved by administration of a photosensi tizer followed by application of light of an appropriate wavelength, usually generated by laser, to achieve tumor destruction [2][3][4], Many agents under investigation for this pur pose are porphyrins and related compounds. Hcmatoporphyrin derivative has been most widely studied; it is an approved drug in some countries, but commonly causes prolonged photosensitivity [5], Administration of large doses of S-aminolevulinic acid, the first intermediate of the heme biosynthetic pathway committed to porphyrin and heme formation, results in the production and accumulation of protopor phyrin in many tissues of laboratory animals [6], Protoporphyrin generated from adminis tered 8-aminolevulinic acid has been shown to be an effective photosensitizer for photody namic therapy in animals and humans [7][8][9][10][11][12][13], A major advantage of this agent is the rela tively rapid clearance of protoporphyrin from tissues, such that prolonged photosensitivity is avoided.…”

The Activation of the c-Jun N-terminal Kinase and p38 Mitogen-activated Protein Kinase Signaling Pathways Protects HeLa Cells from Apoptosis Following Photodynamic Therapy with Hypericin

“…25). Upon irradiation with tissue-penetrating light, the photosensitizer is activated and generates reactive oxygen species, which then cause cell death.…”