ErPC3 exerts potent cytotoxic effects on T98G cells alone and in combination with ionizing radiation. T98G were treated with 0–50 μM ErPC3 alone or in combination with 0, 2.5, 5 or 10 Gy for 48 h as indicated. Induction of apoptosis and necrosis was determined by fluorescence microscopy upon staining with Hoechst33342 and PI. The percentage of apoptotic and necrotic cells was then quantified by counting of the cells with apoptotic and necrotic morphology, respectively. The percentage of viable cells was calculated as indicated in Fig.1. Data show (C) means ± s.d., n = 3 or (A, B, D) one representative of three independent experiments. (A) ErPC3 induces growth arrest and apoptosis in a dose-dependent manner in T98G cells as indicated by a decrease in cell density and increase in cells with apoptotic morphology. (B) Combined treatment with ErPC3 sensitizes T98G cells to radiation-induced growth arrest and apoptosis. (C) Increased efficacy of ErPC3 in combination with ionizing radiation depends on the radiation dose and drug concentration, respectively. (D) Isobolgram analysis of combined treatment with 10 Gy and 25 μM ErPC3 after 48 h reveals synergistic effects.