Resistance to ABT-737 is reversed on suppression of Mcl-1 in the Eμ-myc model. (A) Schematic diagram illustrating derivation of the ABT-737–responsive Arf^−/−Eμ-myc/Bcl-2 tumor model. (B) Immunoblot analysis of selective Bcl-2–related family members in extracts from Arf^−/−Eμ-myc/Bcl-2 lymphomas transduced with MLS expressing shMcl1.1334 and/or the Bcl-2 cDNA. (C) Knockdown of Mcl-1 is synthetic lethal with ABT-737 in Arf^−/−Eμ-myc/Bcl-2 lymphomas ex vivo. Flow cytometry analysis of Arf^−/−Eμ-myc/Bcl-2 lymphomas infected with MLS/shMcl-1.1334 and cultured in the presence of vehicle or 600 nM ABT-737 for the indicated time periods. (D) Western blot analysis indicating that inhibition of protein synthesis results in rapid depletion of MCL-1. Arf^−/−Eμ-myc/Bcl-2 lymphomas were exposed to the indicated CHX (concentration) for 12 hours, at which point cell extracts were prepared and probed by western blot for the indicated proteins. (E) Loss of MCL-1 protein levels by blocking protein synthesis is synthetic lethal with ABT-737 in Arf^−/−Eμ-myc/Bcl-2 lymphomas. Cells were treated with 600 nM ABT-737 and 25 μM CHX for 16 hours, and cell death was quantitated by PI staining. Cell death was determined by PI staining. n = 3; errors bars represent ± standard error of the mean. (F) Schematic representation of experimental procedure used to assess ABT-737 sensitivity in vivo in Arf^−/−Eμ-myc/Bcl-2 lymphomas. (G) Suppression of Mcl-1 is synthetic lethal with ABT-737 in Arf^−/−Eμ-myc/Bcl-2 lymphomas in vivo. Following infection of Arf^−/−Eμ-myc/Bcl-2 (RFP⁺) with FLuc.1309 or Mcl-1.1334 (GFP⁺), cells were injected into syngeneic C57BL/6 mice. ABT-737 treatment was initiated 2 days following delivery of cells and continued for 7 days, at which point lymphomas were harvested and analyzed by flow cytometry.