Photopharmica discovering and developing photosensitisers and light sources for medical use.

Advantages of Photodynamic Therapy

1. Selectivity

Photodynamic therapy can provide distinct advantages over traditional methods for treating disease, and many of these stem from the unique selectivity or targeting ability of the technique. Thus it is possible to kill target cells (e.g. bacteria or cancer cells) whilst sparing normal body cells. This can be achieved because of the following:

The activating light source can be precisely targeted to the treatment area.

Singlet oxygen, the prime cytotoxic agent, has only a very short lifetime in a cellular environment, and consequently it can only harm the cell in which it is generated. This also means that once the light source is removed there is no further toxic effect.

The rate at which a photosensitiser is taken up will be different for different cells and tissues. Thus it is possible to select a time interval between administering the photosensitiser and applying the light source that will optimise the preferential uptake of the photosensitiser by the target cells.

2. Broad spectrum activity

Singlet oxygen can kill any living cell providing (a) it is generated in sufficiently close proximity to vital cell components, and (b) it is generated in sufficiently high concentration. As the first requirement is determined by the correct choice of photosensitiser, and the second by the intensity and duration of the light, in principle any microrganism (virus, bacterium, yeast, spore, parasite) can be destroyed by the photodynamic effect. This has particular implications for the treatment of infections involving antibiotic-resistant strains of bacteria, such as MRSA, VRSA and C.difficile, as these can be killed with equal facility as normal bacteria using a suitable photosensitiser.

3. Low risk of acquired resistance by infective microorganisms

Unlike antibiotics and other conventional anti-infective agents, the photodynamic effect is multi-targeted as singlet oxygen attacks many cell sites and disrupts many cell processes. Thus the likelihood of a microorganism mutating to protect itself against all such types of event is small.

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