Combined effects of ErPC3 and ionizing radiation on apoptosis induction in prostate cancer cell lines. PC3 and LNCaP cells were irradiated with 10 Gy, treated with 12.5 µM ErPC3 or both treatments were combined. DNA fragmentation (A, B) and caspase activation (C, D) were analyzed 48 h later. (A) Approximately 30% of PC3 cells showed DNA fragmentation after a single treatment with ErPC3, whereas radiation-induced apoptosis was below 10%. The amount of apoptotic cells significantly increased when cells were subjected to combined treatment (data show means ± SD; n = 3; ***: p < 0,001). (B) Although a single therapy with ionizing radiation or ErPC3 did not induce apoptotic DNA fragmentation in LNCaP cells, the combination of both treatments resulted in apoptosis levels comparable to that in PC3 cells. The results were confirmed by Western blotting analyzing caspase-3 and PARP cleavage (C, D). Cleavage of caspase-3 (PC3 and LNCaP cells) and PARP (LNCaP cells) was more effective when ErPC3 and ionizing radiation were combined (C, D).