Phototoxicity, distribution and kinetics of association of UVA-activated chlorpromazine, 8-methoxypsoralen, and 4,6,4′-trimethylangelicin in Jurkat cells

Extracorporeal phototherapy (ECP) is a therapeutic approach based on photobiological effects of 8-methoxypsoralen (8-MOP) on white blood cells isolated from the blood, exposed to UVA and then reinfused into the patient. 8-MOP is presently the only drug approved for clinical application of ECP; therefore, identification of other photosensitizers with better photochemical and pharmacokinetic properties might enhance the efficacy of this treatment modality. Among such alternative drugs are 4,6,4′-trimethylangelicin (TMA) and chlorpromazine (CPZ), which have previously been studied in an animal model for ECP. In this current study, cellular bioavailability of 8-MOP, TMA and CPZ was investigated in vitro, using low doses of UVA relevant for the clinical setting of ECP. Our fluorescence microscopy study revealed that 8-MOP and CPZ penetrated readily into the cells, where they accumulated with similar kinetics. No distinct fluorescence was observed in cells incubated with TMA. We found that the phototoxic efficiency of 8-MOP was an order of magnitude greater than that of CPZ, i.e., to obtain a similar reduction in survival of cells subjected to photosensitization by the drugs, the concentration of CPZ needed to be 10 times higher than that of 8-MOP. The photoactivated TMA exhibited the highest pro-apoptotic efficiency. A clear indication of photoinduced formation of reactive oxygen species and peroxidation of lipids was observed only in CPZ-sensitized cells, suggesting different mechanisms for phototoxicity mediated by CPZ and by the two furocoumarins.