Comparative study of photodegradation of three hematoporphyrin derivative:: Photofrin®, Photogem® and Photosan

We report the photodegradation of the three different photosensitizers derived from hematoporphyrin. In this paper we use the term phototransformation for describing the photodegradation or photobleaching process. This photodegradation alters the fluorescence during illumination. The rate of fluorescence variation was normalized to the solution absorption and the photon energy, resulting in the determination of the necessary number of photons to be absorbed to induce photosensitizer phototransformation. The parameter for rate of the molecules decay, the photon fluence rate and optical properties of the solution, allow us to determine the photosensitizer stability in solution during illumination. The results show that the order of susceptibility for phototransformation rate is: Photofrin (R) congruent to Photogem (R) < Photosan (R) This difference in the phototransformation rate for Photosan(D can be explained by the high proportion of aggregates in solution that inhibit the photo-oxidative process that impede the singlet oxygen formation. We hypothesize that there is a con-elation between phototransformation rate and photodynamic efficacy witch is governed by singlet oxygen formation responsible by most relevant reaction for the photodynamic induction of cell death.