In vitro photobiological evaluation of Rhodac, a new rhodacyanine photosensitizer

We have previously shown that the rhodacyanine dye, Rhodac, exhibits a pote nt photocytotoxic activity in HeLa cells. In this study several aspects of the photobiological activity of Rhodac were further examined. Rhodac displa yed no selective cytotoxicity toward several malignant cell lines after pho tosensitization (3.6 J/cm(2)), although HeLa cells were found to be the mos t sensitive. Interestingly, MCF-7/Adr cells, a multidrug-resistant subline, were less sensitive to the anti proliferative effect of photoactivated Rho dac. The subcellular localization, as revealed by confocal laser microscopy , demonstrated that the dye was mainly concentrated in the cytosolic membra nes of the perinuclear region. The Rhodac-induced inhibition of HeLa cell p roliferation after light exposure was found to be strictly oxygen dependent . In addition, photoactivated Rhodac induced poly(adenosine 5' diphosphate- ribose)polymerase cleavage, caspase-3 activation and apoptosis in HeLa cell s. In the current work it was further demonstrated that Rhodac binds specif ically to high-density lipoproteins and low-density lipoproteins, while no binding was observed to very low-density and heavy proteins. To sum up, our results show that Rhodac is an interesting and potent photosensitizer. Fur ther in vivo experiments are required to elucidate whether the lipoprotein binding leads to a selective uptake of Rhodac in tumor cells and to address its efficacy in photodynamic therapy.