Figure 5.
BCL6 degradation impairs BL growth and potentiates MYC inhibition. (A) Western blot analyses for BCL6 expression on the indicated BL cell lines. Cells were treated for 60 minutes with BI-3802 (1 or 5 μM), BI-3812 (1 μM), or vehicle (-) before collection. Data are representative of 2 experiments. β-actin was used as loading control. (B) Western blot analysis for BCL6 on immortalized lymphoma cell lines obtained from FBXO11-WT (Eμ-myc) or -KO (Eμ-myc/FBXO11fl/fl;CD19-Cretg/+) mice. Cells were treated for 1 hour with BI-3802 (1 or 5 μM), BI-3812 (1 μM), or vehicle (-) before collection. Data are representative of 2 experiments with similar results. β-actin was used as loading control. (C) Effects of BCL6 degradation on WT and FBXO11-KO RAJI (clones #1 and #2) cell growth. Cells were kept at constant concentrations of the degrader BI-3802 as indicated (1 μM or 5 μM) and split to 100 000 cells per milliliter every 3 days. Split rates were multiplied to derive growth curves. Data are mean ± standard error of the mean (SEM) and are representative of ≥3 independent experiments. *P < .05, **P < .01, unpaired 2-tailed Student t test. (D) Growth of tumor xenografts in NSG mice of WT and FBXO11-KO RAJI (clones #1 and #2) cells treated with BI-3802 (5 μM) for 24 hours before injection. Data (n = 5 mice per group) are shown as mean ± SEM. **P < .01, paired 2-tailed Student t test. (E) Growth curves of WT and FBXO11-KO RAJI (clones #1 and #2) cells treated with Omomyc mini-protein (2 or 5 μM), alone or in combination with BI-3802 (5 μM). Total cell number was quantified at the indicated time points. Data are mean ± SEM of triplicates from a single experiment representative of 2 repeats. **P < .01, ***P < .001, unpaired 2-tailed Student t test. (F) Growth curves of WT and FBXO11-KO RAJI (clones #1 and #2) cells infected with a doxycycline-inducible lentiviral vector expressing Omomyc. Cells were treated only with doxycycline to induce Omomyc expression (Omomyc), or BI-3802 (5 μM) or a combination of doxycycline and BI-3802 (Omomyc + BI-3802). Total cell number was quantified at the indicated time points. Data are mean ± SEM of triplicates from a single experiment representative of two repeats. **P < .01, ***P < .001, unpaired 2-tailed Student t test.