LASER-INDUCED FLUORESCENCE STUDIES OF MESO-TETRA(HYDROXYPHENYL)CHLORIN IN MALIGNANT AND NORMAL-TISSUES IN RATS

meso-Tetra(hydroxyphenyl)chlorin (mTHPC) is an attractive second-gener ation dihydroporphyrin photosensitiser for use in photodynamic therapy . In this study, 1.3mgkg(-1) body weight mTHPC was administered intrav enously, and laser-induced fluorescence was used to characterise and c ompare its localisation and retention in different rat tissues, includ ing an induced experimental adenocarcinoma, 24 h and 48 h post injecti on. These studies were performed in an attempt to predict the anatomic al locations where mTHPC PDT might be most effective and suggest suita ble injection-irradiation intervals in each case. Of particular intere st were the intra-abdominal and intrathoracic tissues. The fluorescenc e was induced at 405 nm and the fluorescence spectrum in the region 45 0-750 nm was analysed. All collected spectra were dominated by the flu orescence signature of mTHPC with its peak at 652 nm, and all values i n this study are in terms of background-free drug-specific fluorescenc e intensity at that wavelength. The photosensitiser accumulated in hig h concentrations in the tumour and the reticuloendothelial system. Mus cular organs, such as the heart and the abdominal wall, were character ised by a low drug fluorescence signature.