The effect of SG-1721 in combination with radiation on STAT3 signaling cascade (A) MDA–MB-468 cells treated with irradiation (1, 5, or 10 Gy) after 4 h of pretreatment with SG-1721 (0.5, 1, or 1.5 μM) incubated for 20 h. The cytotoxicity was determined by MTT assays (left panel). SG-1721 synergistically enhances radiation-induced cell death in MDA–MB-468 cells (right panel). The average of the CI values was obtained at nine different combinations. (B) MDA–MB-468 cells were treated with 0.5 μM of SG-1721 or 10 Gy of irradiation alone or in combination for 4 h. Thereafter, Western blot analysis was performed. (C) MDA–MB-468 cells were treated with irradiation (10 Gy) after 4 h of pretreatment with SG-1721 (0.5 μM) and incubated for 20 h followed by Western blot analysis. (D) MDA–MB-468 cells were treated as described above in panel C, and Western blot was performed using various antibodies.