ENZYME-ASSISTED CELL PHOTOSENSITIZATION - A PROPOSAL FOR AN EFFICIENTAPPROACH TO TUMOR-THERAPY AND DIAGNOSIS - THE ROSE-BENGAL FLUOROGENICSUBSTRATE

Rose bengal, a xanthene derivative among the most efficient producer o f singlet oxygen, was submitted to a chemical modification consisting in the introduction of an acetate group into the aromatic ring fluorop hore structure, The acetate group acts as a quencher, thus inactivatin g both fluorescence and photosensitization properties of the molecule, In the modified structure, rose bengal acts as a fluorogenic substrat e giving rise to the cellular reaction termed fluorochromasia. The ace tate group is recognized by a carboxylic esterase activity that splits it, Removal of the quencher group results in restoring the native str ucture of photosensitizer inside the cells, The intracellular turnover of rose bengal acetate was studied in rat glioma-derived cultured cel ls, in terms of the balance of the precesses of influx and enzyme hydr olysis of the fluorogenic substrate, and of the efflux of the fluoresc ent product, A large intracellular accumulation of photosensitizer is obtained when treatments are performed with the fluorogenic substrate, even at the drug concentration at which rose bengal does not enter th e cells, The intracellular localization allows rose bengal to exert a more effective photosensitization effect, Provided that the quencher g roup is selected according to the metabolic properties of the tumor ce lls, the use of fluorogenic substrates as photosensitizer precursors c ould improve fluorescence diagnosis and the photodynamic therapy of tu mors, exploiting the biological properties that distinguish pathologic al from normal conditions.