Halogen-containing BODIPY derivatives for photodynamic therapy

Two iodinated (1 and 2) and two brominated (3 and 4) BODIPY-based photosensitizers are prepared and characterized using slightly modified synthetic procedures previously described. 1-4 present intense absorption bands in the 510-540 nm interval and very weak emissions due to the presence of halogen atoms in their structure. Irradiation of aqueous solutions of 1-4 with visible light (wavelength > 475 nm) induce the generation of singlet oxygen with quantum yields of ca. 0.62-0.66 for the photosensitizers containing iodine atoms (1 and 2) and of ca. 0.16-0.21 for the brominated counterparts (3 and 4). In vitro studies carried out with HeLa, SCC-13 and HaCaT cell lines and the four photosensitizers show marked reductions in cell viability with lower IC50 values for the iodinated derivatives (in the 0.82-2.51 range) than those found for the brominated compounds (in the 0.91-8.26 range) suggesting that these compounds could be used in photodynamic therapy protocols. Subcellular localization studies carried out using confocal microscopy show that photosensitizers accumulated in the endoplasmic reticulum.