Fluorescence analysis of a tumor model in the chorioallantoic membrane used for the evaluation of different photosensitizers for photodynamic therapy

The development of a tumor in the chicken chorioallantoic membrane (CAM) enables a more individualized understanding of the dynamics of the photosensitizer (PS) interaction with the tumor blood vessels and cells. Photogem® and 5-aminolevulinic acid (ALA), a protoporphyrin IX (PpIX) precursor, were used as PS and their red fluorescence enabled the monitoring of PS dynamic distribution in the vessels and in the tumor. With a tumor model in CAM and fluorescence assessment, the aim of this study was to evaluate the PDT parameters comparing different photosensitezers. In this model, the topical application was chosen as the best way of drug delivery and widefield fluorescence images were at every 30 min. The images were processed in a MATLAB® routine for a semi-quantitative analysis of the red fluorescence. PpIX formation in the blood vessels and in the tumor region was observed after 3 h and 1.5 h, respectively, whereas Photogem® was accumulated in the tumor region after 2 h. The illumination was performed by a diode laser with emission centered at 635 nm and irradiance of 80 mW/cm2 for 10 min. After PDT irradiation, the photobleaching for both compounds was observed. Photogem® showed a reduced photobleaching, however, both PS induced a destruction of the tumor mass and vascular network in the treated area.