Apoptosis induction in response to ErPC3 and ionizing radiation. PC3 and LNCaP cells were treated with 1-50 µM ErPC3 or irradiated with a single dose of 2 or 10 Gy. 48 h later, cells were stained with propidium iodide in a hypotonic citrate buffer containing Triton X-100 and subjected to flow cytometric analysis to estimate DNA fragmentation which occurs upon induction of apoptosis. 5 µM ErPC3 were sufficient to induce DNA fragmentation in PC3 cells (A), whereas 25 µM ErPC3 were required to trigger apoptotic DNA-fragmentation in LNCaP cells (B). Ionizing radiation up to 10 Gy did not induce DNA-fragmentation above a background level in PC3 (C) and LNCaP cells (D).