Several forms of Chlorin e6 and its derivatives are reported as efficient photosensitizers (PS) studied in Photodynamic Therapy (PDT) for oncologic applications. Fotolon® is a pure form of Chlorin e6 trisodium salt developed by Apocare Pharma.
OBJECTIVES: In this study the effectiveness of Fotolon®-PDT in the treatment of glioblastoma multiforme (GBM) - represented by the human cell line U87 - was evaluated. Furthermore, the sensitivity of glioma cells over-expressing cancer stem-like multidrug resistance transporter (ABCG2) towards Fotolon®-PDT was examined using an ABCG2 transfected U251 cell line.
METHODS: flow cytometry was applied to measure Fotolon® cellular accumulation while varying the incubation periods (15 min-4 h) and Fotolon® concentrations (1-100 µM). For PDT, 665 nm diode laser was used and 4 h after irradiation, the cell viability was measured by performing Cell Titer Blue assay in case of U87 cells and MTT assay for ABCG2 over-expressing ones.
RESULTS: Fotolon® was detected in the cells after 15 min of incubation. The tested concentrations did not show dark toxicity. Lethal dose 50 (LD50) for U87 cells after treatment using 10 µM Fotolon® was 2.5 and 0.8 J/cm2 when the incubation periods were 15 min and 4 hr, respectively. The PDT action was confirmed by a 12 times increase in ROS level in comparison to the control and the mechanism of cell death was found to be apoptotic. ABCG2 over-expressing cells showed 6 times lower Fotolon® cellular accumulation in comparison to the control cells. This decrease was restored by the co-incubation with the selective ABCG2 inhibitor KO143. Regardless of this, they were sensitive towards Fotolon®-PDT as their LD50 was 1 J/cm2.
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