ErPC increases cytotoxicity of ionizing radiation in A172 cells. A172 cells were irradiated with a single dose of 0, 2.5, 5 or 10 Gy and subsequently treated with 0, 12.5, 25 or 50 μM ErPC as indicated. Induction of apoptosis and necrosis was quantified 24 h, 48 h and 72 h after treatment by fluorescence microscopy counting the cells with apoptotic and necrotic morphology upon combined staining with Hoechst33342 and PI. The percentage of viable cells was calculated as indicated in Fig.1. Data show (A) one representative of three independent experiments (B, C, D) or means ± s.d. ; n = 3. (A) Morphologic appearance of A172 cells upon treatment with medium (control), 10 Gy, 50 μM ErPC or 10 Gy and 50 μM ErPC. (B) Increased efficacy of ErPC in combination with ionizing radiation depends on the radiation dose and the ErPC-concentration. (C and D) Increased efficacy of ErPC in combination with 10 or 5 Gy depends on the treatment time.