HuMcl-1;Eµ-Myc lymphoma cells are more sensitive to S63845 compared with control Eu-Myc lymphoma cells expressing mouse MCL-1. (A) Eµ-Myc–transgenic mice that were Mcl-1^wt/wt, Mcl-1^wt/hu, or Mcl-1^hu/hu were aged and monitored for tumor-free survival. Kaplan-Meier survival curve shown with median latency for each genotype. (B) Primary wild-type or huMcl-1 Eµ-Myc lymphoma cells were isolated and immunostained for surface Ig (sIg) expression (IgD and/or IgM) and analyzed by flow cytometry. p53 and p19 expression were detected by western blotting. Proportions of p53 wild-type (p53 low-negative, p19 low-negative), p53 knockout (p53 negative, p19 high), and p53 mutant (p53 high, p19 high) are shown. (C) Viability of Eµ-Myc lymphoma cells that are wild-type for Mcl-1 (n = 3, red bars) or homozygous for the huMcl-1 allele (n = 7, blue bars) after treatment with increasing concentrations of S63845. Cell viability was determined by Annexin V/PI staining and FACS analysis. Data points are IC₅₀ values calculated from a range of concentrations (1.6 nM to 1 µM) analyzed in triplicate. (D) Cell viability data generated and shown in panel C were pooled to compare the overall IC₅₀ values of control Eµ-Myc and huMcl-1;Eµ-Myc lymphoma cell lines. Combined IC₅₀ curves for cell lines of each genotype are shown, with IC₅₀ values depicted in the legend. (E-G) Survival curves of huMcl-1;Ly5.1 mice transplanted with huMcl-1;Eµ-Myc lymphomas and treated with vehicle, S63845 alone for 5 consecutive days (E), or S63845 in combination with CP (F-G) (doses as indicated). n indicates the number of recipient mice with number of cell lines tested indicated in parentheses. Significance relative to vehicle shown in graph; significance relative to combination treatment shown on the right. Calculated by Mantel-Cox test. ***P < .001, ****P < .0001. ko, knockout; mut, mutant; ns, not significant; wt, wild-type.