Photodynamic therapy treatment

The development of so-called photodynamic therapy uses lasers for treatment of cancer. The patient is injected with a substance called hematoporphyrin derivative [68335-15-9] which is preferentially localized in cancerous tissues. The patient is later irradiated with laser light, often with a dye laser at a wavelength around 630 nm. The light energy catalyticaHy photooxidizes the hematoporphyrin derivative, releasing materials which kill the nearby cancerous tissue. Normal tissue which did not retain the chemical is not harmed. Photodynamic therapy offers promise as a new form of cancer treatment. 

Photodynamic therapy uses non-thermal red light to activate verteporfin, which produces reactive oxygen species that locally damage the neovascular endothelium.24 Verteporfin treatment reduces the risk of loss of visual acuity and legal blindness over 1 to 2 years. Long-term results are not yet available. Severe photosensitivity for 3 to 5 days after the procedure is common and some patients experience a severe loss of vision. Eventually, most patients have some visual recovery. This procedure requires multiple treatments over time.22... 

The most important application for singlet oxygen generators (SOGs), namely the anti-cancer treatment known as photodynamic therapy (PDT), is described elsewhere in this series (see Chapter 9.22). However, SOGs are also being evaluated in other areas, such as hard surface disinfectants, soaps and washing powders,73 and insecticides.74,75... 

Singlet Oxygen and Photodynamic Therapy for Cancer Treatment... 

Photodynamic therapy for the treatment of tumours involves the selective uptake and retention of a highly-coloured porphyrin sensitiser (Figure 6.17) in the tumour. Irradiation by a laser with a wavelength corresponding to the absorption maximum of the porphyrin (D) causes excitation of the porphyrin to the excited singlet state. 

Kubler AC, de Carpentier J, Hopper C, Leonard AG, Putnam G (2001) Treatment of squamous cell carcinoma of the lip using Foscan-mediated photodynamic therapy. International Journal of Oral and Maxillofacial Surgery 30 504-509. 

Li Lb, Luo Re, Liao Wj, Zhang Mj, Luo Yl, Miao Jx (2006) Clinical study of Photofrin photodynamic therapy for the treatment of relapse nasopharyngeal carcinoma. Photodiagnosis and Photodynamic Therapy 3 266-271. 

Phototherapy is the generic term covering therapies which use light either with or without a sensitiser. Those that do not require a sensitiser use the natural chromophores within the tissue to perform this function e.g. treatment of vitamin D deficiency in rickets, and neonatal jaundice). Those that do use an added sensitiser include photochemotherapy (largely psoriasis and skin disorders) and photodynamic therapy (currently mainly cancer). Photodynamic therapy is differentiated from photochemotherapy by its additional requirement for the presence of oxygen at molecular or ambient levels.In this text we will deal only with photodynamic therapy since, at the present time, this is the main driving force in phototherapy. ° ... 

Work during the last ten years on photodynamic therapy (PDT) has established the methodology as effective in the early treatment of cancers, and in the treattnent of certain skin disorders and viral infections. Approval by the regulatory authorities for sensitisers in this process began in 1993 when Canada allowed the use of Photofrin (QLT Therapeutics), an action followed later by most countries around the world. Now many other companies have sensitisers at late stage clinical dials (2001), see below in Table 4.5. An excellent introduction to the chemistry of this topic is provided in the book written by Bonnett. ... 

Figure 4.21 Outline of photodynamic therapy (PDT) treatment of tumours.

Photodiagnosis is a method based on selective excitation of luminescence emitted by a compound (e.g. Zn(PPIX)) accumulated in blood (e.g. in a treatment of iron-deficiency anemia) or cells (e.g. in a treatment of malignant neoplasms, when the photodiagnosis can precede photodynamic therapy). 

The use of photochemical treatment to stimulate translocation of endocytosed macromolecules into the cytosol is a novel technology to improve therapeutic efficacy. The technology as described in this review is derived from photodynamic therapy (PDT) and is named PCI. In both cases a photosensitizer is used in combination with light to exert the treatment effects. The basic mechanisms of the photosensitizers and their tissue interaction in combination with light will be described with emphasis on the properties of the photosensitizers used in PCI before describing the use of PCI for cytosolic delivery of macromolecules. 

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