Photophysical properties and in vitro photocytotoxicity of disodium salt 2.4-di(alpha-methoxyethyl)-deuteroporphyrin-IX (Dimegine)

Abstract Photophysical and in vitro photocytotoxicity studies were performed for the photosensitizer Dimegine, a disodium salt 2.4-di(alpha-methoxyethyl)-deuteroporphyrin-IX with very low systemic toxicity. The singlet oxygen and luminescence quantum yield were Φ Δ  = 0,65 ± 0,06, and Φ ƒ = 0,11 ± 0,01 respectively, and were independent of the excitation wavelength. The photobleaching coefficients for Dimegine dissolved in phosphate buffer (pH 7.4), and DMEM medium at concentration 2 μM/l and in phosphate buffer (pH 7.0) at concentration 10 μM/l were 16·10 -5 , 9·10 -5 and 2·10 -5 respectively. In vitro cellular distribution and photocytotoxicity was studied in two human ( U87 – primary glioblastoma and HT1376 – bladder cancer) and two rat cell lines ( RG2 – glioma, and AY27 – bladder carcinoma). Fluorescence microscopy analysis shows primary Dimegine accumulation as small fluorescent inclusion bodies around the nuclei, suggesting an apoptotic over a necrotic cell death mechanism. The PDT efficacy was slightly higher for the rat cell lines over the human-derived cell lines, with LD 50 values of 2,5 μM/l, 2.8 μM/l, 4.5 μM/l, 2.8 μM/l using 530 nm excitation wavelength for AY27 , RG2 , HT1376 and U87 respectively, and 1.8 μM/l, 2 μM/l, 5 μM/l, 2.4 μM/l using 625 nm excitation wavelength for AY27 , RG2 , HT1376 and U87 respectively. Comparison to literature data showed that Dimegine demonstrated improved phototherapeutic characteristics comparing to PpIX-mediated PDT.