Art and Science of Photodynamic Therapy

Abstract

4. Light sources have moved from the use of white light with specific filters in the old days to the more recent use of monochromatic light sources, such as lasers, to more sophisticated light-emitting diodes. However, dosimetry remains a big issue mainly because of difficulties in establishing the optimum treatment conditions for an approach that requires the finetuning of several variables, such as sensitizer and light doses and drug-to-light interval, as well as the issues of skin photosensitivity and low selectivity. A newer development to circumvent these and provide a broader application for this concept has been the phenomenon of photo-activation, whereby photo-exposure of chromophores to generate novel, small biologically active compounds has been demonstrated successfully.5. The aim of the present review was to provide a general overview of the art and science of photodynamic therapy and to highlight some of the issues and recent developments in further advancing this modality of treatment.

Ophthalmic light sensitive nanocarrier systems

“…Damaged neovascular endothelial cells are known to release procoagulant and vasoactive factors through the lipo-oxygenase and cyclo-oxygenase pathways, resulting in platelet aggregation, fibrin clot formation and vasoconstriction [3]. Effective PDT is dependent upon an abundant supply of molecular O 2, which ensures its usefulness in living tissue [1]. When treating corneal angiogenesis associated with transplant rejections, destruction of neovascular vessels is often needed [4].…”

“…Since repeated injections by these routes are inconvenient, steps are still being taken to optimize the efficiency of intravenous photodynamic therapy. Attention is focused on enhancing aspects of the delivery mechanism, such as the particle size, sensitizer type and concentration, administration route, cellular uptake, appropriate light dose and appropriate drug-to-light interval in addition to issues of skin photosensitivity [1]. The nanoparticles previously discussed include liposomes, polymeric micelles, vectosomes, and hydrogels.…”

“…Raab hypothesized that upon irradiation, acrydine dye converted light energy into chemical energy. The chemical reaction initiated phototoxic effects in the presence of molecular oxygen to kill the paramecia; hence, the term "photodynamic reaction" was coined for the reactions [1]. Such photodynamic reactions are of potential value in reducing undesirable cell proliferation in various disorders, especially endothelial cell or other cell proliferation associated with neovascular or angiogenic disorders including cancers.…”

“…Throughout ancient Egypt, India and China, light alone, or light in combination with chemical compounds, was used extensively to induce therapeutic effects in various conditions including depigmented skin lesions (vitiligo), psoriasis and neurodermite [1]. Around the turn of the last century, a medical student named Oscar Raab observed that low concentrations of acrydine dye in the presence of light could be lethal to the protozoan paramecium [1]. Raab hypothesized that upon irradiation, acrydine dye converted light energy into chemical energy.…”

Biodistribution of PVP-hypericin and hexaminolevulinate-induced PpIX in normal and orthotopic tumor-bearing rat urinary bladder

“…PDT for cancer involves the local or systemic administration of a photosensitizer followed by local irradiation of 4 the tumor tissue with non-thermal visible light of a specific wavelength. The local generation of ROS (reactive oxygen species) by the irradiated photosensitizer results in tumor destruction [7,24].…”