MALT1/PI3Kδ simultaneous inhibition synergistically kills ABC-DLBCL in vitro and in vivo. Apoptosis for CAL-101 combinations with structurally unrelated MALT1 inhibitors MI-2 (A) and C3 (B) was studied using annexin V/DAPI staining in the indicated cell lines. Cells were treated for 4 days, and the following drug concentrations were used: 1 μM CAL-101, 250 nM MI-2 (100 nM for HBL-1), and 1 μM C3. Results are the percentage of cells ± standard error of the mean (SEM) of ≥2 independent experiments in triplicate. CFSE dilution assay results for CAL-101 combinations with MI-2 (C) or C3 (D) in the indicated cell lines, treated as above. The y-axis shows CFSE mean fluorescence intensity (MFI) fold to vehicle ± SEM of ≥2 independent experiments in triplicate. (E) Dosing schedule of MI-2/CAL-101 combinations in vivo. TTD, time to death. (F) Tumor growth curve for TMD8 xenografts (n = 6 per group). Mice were treated with 25 mg/kg per day of MI-2, 30 mg/kg per day of CAL-101, their combination, or the same volume of vehicle for 21 days, following the schedule in (E). (G) Representative western blot results for the indicated targets in TMD8 xenografted tumors treated long-term (21 days) with vehicle, MI-2, CAL-101, or their combination (n = 3 per group). (H) Quantification of western blots in (G) for all mice (n = 6 per group). Protein levels were normalized to actin and are relative to the average of vehicle-treated mice. (I) Short-term treatment schedule of TMD8 xenografted mice. Dosing as in (F). (J) Western blot results for the indicated targets in TMD8 xenografted tumors treated short-term (28 hours) with vehicle, MI-2, CAL-101, or their combination (n = 3 per group). (K) Quantification of results in (J). Protein levels were normalized to actin and are relative to the average of vehicle-treated mice. *P < .05, **P < .01, ***P < .001, 1-way analysis of variance corrected for multiple comparisons 5% FDR. FC, fold change; ns, not significant (P > .05).