The paper, published on Histochemistry and Cell Biology - the official organ of the International Society for Histochemistry - refers to a research activity carried out since years at the IGM-CNR of Pavia in cooperation with the Department of Animal Biology of the University of Pavia, which focuses on the development of Photodynamic-Diagnosis/Therapy (PDD/T). This consists in a procedure of diagnosis and therapy of pathologies, in particular tumors, based on the activation of phototoxic processes by means of the combined use of light and photosensitizers. To respond to the need of the PDT selectivity, research interest was moved from porphyrin derivatives (traditionally and still the most used in clinics, despite they are not chemically well defined) to photosensitizers with a well defined chemical structure, suitable to be changed by addition of chemical groups, for example acetate. As a result, the photodynamic properties are altered, and the increase in hydrophobicity favors the uptake in the cells (enzyme-assisted PDT/D). Thus, the photosensitizer behaves as a "fluorogenic substrate": specific enzymes recognize and split the chemical group, restoring the native molecule with its original photodynamic properties in sensitive sites, in dependence on the biological properties of the cells. In the case of Rose bengal, a great increase in the accumulation of active photosensitizer was obtained treating the cells with fluorogenic acetate substrate rather than directly with the native molecule. The exact knowledge of the accumulation, retention and intracellular distribution of the photosensitizer, along with the control of the times and conditions of administration of the fluorogenic substrate, provides a suitable model for a selective study of the roles played by the subcellular organelles in the mechanisms leading to cell death, as a basis for optimization of PDT efficacy. In the present study, we found that Rose bengal acetate induces apoptosis; moreover, we demonstrated that both the caspase-dependent and caspase-independent apoptotic pathways are activated by this fluorogenic substrate. The ability of Rose bengal acetate to induce the simultaneous release of apoptogenic signals from different photodamaged organelles makes it an especially powerful cytotoxic agent.
Supported by MIUR (PRIN n. 2002055584 001; PRIN n. 2005058254), University of Pavia (FAR 2007) and Regione Lombardia (Metadistretti di Eccellenza n. 4238).
Bottone MG, Soldani C, Fraschini A, Croce AC, Bottiroli G, Camboni T, Scovassi AI, Pellicciari C.Enzyme-assisted photosensitization activates different apoptotic pathways in Rose Bengal acetate treated HeLa cells. Histochem Cell Biol. 2009, 131: 391-399.
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