Dose-dependent photodynamic effects of 9-acetoxy-2,7,12,17-tetrakis-(beta-methoxyethyl)porphycene in vitro

Porphycenes are chemically pure photosensitizers for topical and systemic photodynamic therapy (PDT). Fast cellular uptake of 9-acetoxy-2,7,12,17-tetrakis-(beta-methoxyethyl)-porphycene (ATMPn) has been shown previously. HaCaT human keratinocytes were incubated with ATMPn (1nmol 1(-1) to 1 mu mol 1(-1) in DMSO or DOPC liposomes). After 1 h, cells were irradiated with different light doses (0, 24, 48J cm(-2)) using an incoherent light source (580-740nm, 40mW cm(-2)). Cytotoxic effects were determined by assessing the mitochondrial activity using the MTT assay 24 h following irradiation. Cytotoxic effects were dependent on ATMPn concentration and light dose. Using 20nmol 1(-1), a 50% decrease of mitochondrial activity (EC50) after irradiation with 24J cm(-2) was achieved. Lowering the ATMPn concentration (10nmol 1(-1)) and increasing the light dose (48J cm(-2)) yielded the same effect (EC50). Maximal decrease of mitochondrial activity (> 90%) was achieved using ATMPn concentrations of 50-100nmol 1(-1) and a light dose of 24J cm(-2) or 25nmol 1(-1) ATMPn and 48J cm(-2) There was no difference regarding the dose-dependent cytotoxic effects using either ATMPn in DMSO or DOPC liposomes. In the control group (incubation with 1nmol 1(-1) to 1 mu mol 1(-1) ATMPn, no irradiation), dark toxicity was not observed. Cell photosensitization with ATMPn was very efficient in vitro yielding the maximal cytotoxic effect very low ATMPn concentrations as compared to other photosensitizers. Since ATMPn in DMSO and DOPC liposomes revealed the same cytotoxic effects without dark toxicity, the DMSO formulation, which is much easier to prepare, will be preferred in future studies.