EPR Monitoring of Oxygenation Levels in Tumors After Chlorophyllide-Based Photodynamic Therapy May Allow for Early Prediction of Treatment Outcome.

PURPOSE: Molecular oxygen, besides a photosensitizer and light of appropriate wavelength, is one of the three factors necessary for photodynamic therapy (PDT). In tumor tissue, PDT leads to the killing of tumor cells, destruction of endothelial cells and vasculature collapse, and the induction of strong immune responses. All these effects may influence the oxygenation levels, but it is the vasculature changes that have the main impact on pO2. The purpose of our study was to monitor changes in tumor oxygenation after PDT and explore its significance for predicting long-term treatment response. PROCEDURES: Electron paramagnetic resonance (EPR) spectroscopy enables direct, quantitative, and sequential measurements of partial pressure of oxygen (pO2) in the same animal. The levels of chlorophyll derived photosensitizers in tumor tissue were determined by transdermal emission measurements. RESULTS: The noninvasive monitoring of pO2 in the tumor tissue after PDT showed that the higher ΔpO2 (pO2 after PDT minus pO2 before PDT), the greater the inhibition of tumor growth. ΔpO2 also correlated with higher levels of the photosensitizers in the tumor and with the occurrence of a severe edema/erythema after PDT. CONCLUSION: Monitoring of PDT-induced changes in tumor oxygenation is a valuable prognostic factor and could be also used to identify potentially resistant tumors, which is important in predicting long-term treatment response.

Calcitriol and Calcidiol Can Sensitize Melanoma Cells to Low⁻LET Proton Beam Irradiation.

Proton beam irradiation promises therapeutic utility in the management of uveal melanoma. Calcitriol (1,25(OH)2D3)-the biologically active metabolite of vitamin D3-and its precursor, calcidiol (25(OH)D3), exert pleiotropic effects on melanoma cells. The aim of the study was to evaluate the effect of both calcitriol and calcidiol on melanoma cell proliferation and their response to proton beam irradiation. Three melanoma cell lines (human SKMEL-188 and hamster BHM Ma and BHM Ab), pre-treated with 1,25(OH)2D3 or 25(OH)D3 at graded concentrations (0, 10, 100 nM), were irradiated with 0⁻5 Gy and then cultured in vitro. Growth curves were determined by counting the cell number every 24 h up to 120 h, which was used to calculate surviving fractions. The obtained survival curves were analysed using two standard models: linear-quadratic and multi-target single hit. Calcitriol inhibited human melanoma proliferation at 10 nM, while only calcidiol inhibited proliferation of hamster lines at 10 and 100 nM doses. Treatment with either 1,25(OH)2D3 or 25(OH)D3 radio sensitized melanoma cells to low doses of proton beam radiation. The strength of the effect increased with the concentration of vitamin D3. Our data suggest that vitamin D3 may be an adjuvant that modifies proton beam efficiency during melanoma therapy.

NO-dependent phototoxicity of Roussin's black salt against cancer cells.

A metal-nitrosyl complex, Roussin's black salt (RBS), releases nitric oxide after illumination. Approximately 3.7 NO molecules were released from one RBS molecule. Both short- and long-term effects of photogenerated NO on the two neoplastic cell lines: human (SK-MEL188) and mouse (S91) have been investigated. Exogenous NO from RBS was toxic to cells in a dose-dependent manner. Apoptotic damage predominates in the response to the injury, as shown by TUNEL assay. NO and its short-lived metabolites, but not other RBS photoproducts, are responsible for cellular death. RBS in dark was toxic to cells at concentrations above 1 microM. This relatively high cytotoxicity of RBS in the dark prevents its application as a systemic anticancer agent in vivo, unless it is applied locally.

Indocyanine green as a prospective sensitizer for photodynamic therapy of melanomas.

Spectroscopic, photochemical and biological properties of indocyanine green (ICG) are presented. Light over 800 nm is effectively absorbed by ICG. This property as well as photochemical behaviour of ICG make it a very suitable dye for photodynamic treatment of melanoma cells. Cytotoxicity of ICG itself and the effect of photodynamic therapy (PDT) were evaluated by following the growth of human (SKMEL 188) and mouse (S91) melanoma cells. The surviving fraction of the cells irradiated (lambda(ex) = 830 nm) vs non-irradiated, treated with the same dose of ICG, is significantly decreased (5- to 10-fold). These results show that ICG is a very promising dye for photodynamic therapy of melanomas.