In vivo antileukemic activity of combined treatment with sorafenib and obatoclax. Nude mice were subcutaneously injected with U937 cells and subjected to treatment with sorafenib (80 mg/kg) and obatoclax (3.5 mg/kg) alone or together. Tumor volumes were measured at the indicated intervals (A), and pictures of 2 representative tumors for each group were obtained after 8 days of treatment (B). Xenograft-bearing mice were treated with sorafenib and/or obatoclax by IM administration twice over a 24-hour interval, after which tumors were excised, and either subjected to TUNEL analysis assays (C), or lysed, and subjected to Western blot analysis (D). (E) Kaplan-Meier survival plot for mice treated with sorafenib and obatoclax alone or in combination. The data shown are representative of 3 separate experiments each involving 5 mice/condition. The survival curves differed significantly between sorafenib/obatoclax and various other treatments (P = .001 to .04; log-rank test).