Photodynamic treatment oxygen

A principal appHcation for photomedicine is the photodynamic treatment of cancer. Photochemical and clinical aspects of this topic have been reviewed (10,11). Direct irradiation of tumors coupled with adininistration of a sensitizer is used to effect necrosis of the malignancy. In this process, an excited state sensitizer interacts with dissolved in vivo to effect conversion of the oxygen from its triplet ground state to an excited singlet state, which is highly cytotoxic. In principle, excited sensitizers in either the singlet or the triplet state can effect this conversion of molecular oxygen (8). In... 

Units and methods are developed to study the effect of active forms of oxygen on fullerene-based photosensitizers. The kinetics of the inactivation of influenza vims in saline and allantoic fluid during the course of photodynamic treatment using fullerene preparations is studied. Optimization of conditions has been conducted for viral inactivation (irradiation, doses, concentration of fullerene, and intensity of oxygen flow). Experiments are performed for inactivation of vims in blood semm. 

B.W. Henderson, V.H. Fingar (1989). Oxygen limitation of direct tumor cell kill during photodynamic treatment of a murine tumor model. Photochem. PhotobioL, 49, 299-304. 

HpD has been used to treat a variety of tumours and bladder cancers, breast cancers, and certain ocular cancers. Just as bilirubin photosensitises the production of singlet oxygen to bring about its own destruction in the photodynamic treatment of neonatal hyperbilirubinaemia (see Chapter 6), so components of HpD also produce singlet oxygen. And because the HpD tends to localise in tumour cells, so photosensitisation leads to then-destruction. 

Henderson, B.W. and Miller, A.C., Effects of scavengers of reactive oxygen and radical species on cell survival following photodynamic treatment in vitro comparison to ionizing radiation, Radiat. Res., 108, 196, 1986. 

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... 

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. ° ... 

Aminolevulinic acid (ALA HCl, Levulan Kerastick) is indicated for the treatment of nonhyperkeratotic actinic keratosis of the face and scalp. It has two components, an alcohol solution vehicle and ALA HCl as a dry solid. The two are mixed prior to application to the skin. When applied to human skin, ALA is metabolized to protoporphyrin, which accumulates and on exposure to visible light produces a photodynamic reaction that generates reactive oxygen species (ROS).The ROS produce cytotoxic effects that may explain therapeutic efficacy. Local burning and stinging of treated areas of skin due to photosensitization can occur. 

Photodynamic therapy (PDT) is a developing approach to the treatment of cancer and certain other diseases, such as age-related macular degeneration, which uses a combination of a photosensitizing dye and laser light to obtain a therapeutic effect [75], There is also an absolute requirement for oxygen. If any of the... 

Singlet oxygen is used in the treatment of cancer by photosensitization (photodynamic therapy). This involves treatment with certain porphyrin derivatives which localize preferentially in the tumour, fol-... 

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