Anti-neoplastic effect of combined treatment with ErPC3 and ionizing radiation. PC3 cells (A), DU145 cells (B), and LNCaP cells (C) were treated with increasing concentrations of ErPC3 (1-100 µM) and ionizing radiation (2, 5, 10 Gy) alone or in combination as indicated. Cell viability was analyzed 48 h after treatment by using the WST-1 assay. PC3 and DU145 cell did not respond to irradiation alone but responded to single treatment with ErPC3 (A, B). The anti-neoplastic effects of the combination were mainly attributed to the effects of ErPC3 (A, B). In contrast, LNCaP cells were highly sensitive to treatment with radiation alone, as well as to ≥ 50 µM ErPC3 (C). When LNCaP cells were treated with subtoxic ErPC3-concentrations in combination with irradiation, the reduction in the number of viable cells was mainly due to ionizing radiation (C). However, the cell viability was further reduced when LNCaP cells were treated with toxic ErPC3-concentrations (≥ 50µM) in combination with irradiation.