Selectivity of photodynamic treatment

Efficient biological responses to PDT require three components and this renders PDT a complicated treatment modality. There is, however, some opportunity for an 

ANNE C.E. MOOR, BERNHARD ORTEL AND TAYYABA HASAN 

Selectivity of PDT effects may also be enhanced by appropriate manipulation of the illumination process. The spatial control of the illumination is an obvious advantage of PDT, but it is also an important source of the complexity of this modality [48,49]. Since most photosensitizers are non-toxic in the dark at the clinically used doses, only illuminated areas will be damaged by the treatment. The introduction of fiber-optic coupling to lasers has opened a range of opportunities to treat not only superficial lesions, but also more complex body sites, such as the abdominal cavity. An additional way to achieve specificity is the timing of the illumination. Since photosensitizer distribution is dependent on the time after delivery (initially more vascular, later more in tumor cells) [50,51], the time of illumination is an important tool in tailoring PDT for specific applications. 

Finally, there appears to be a threshold for PDT effects at low doses of light and/or photosensitizer tissue damage seems reparable [52]. Since this threshold value can be different for tumor and normal tissue it provides an opportunity for added selectivity. 

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As a result of our experiments, it was shown that the growth properties of the serum do not change after photodynamic treatment. Nevertheless, the infectious titer of influenza virus both in blood serum and allantoic fluid decreased from 6 to 0 log10 EID50 after the treatment. This fact suggests a selectivity of photodynamic treatment regarding the virions. In our opinion, this can be explained by the following. 

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