Figure 6. BCL6 knock-out in a DLBCL xenograft induces tumor stasis.
Tumor xenografts were established in C.B-17 SCID mice by subcutaneous injection of inducible SU-DHL-4 Cas9 BCL6 and control sgRNA cells. Mice were randomized to receive drinking water with DOX (2 mg/kg) plus 5% sucrose (DOX on) or 5% sucrose only (DOX off). (A) After 5 days DOX treatment tumors from four mice were harvested and analyzed for Cas9 GFP induction using flow cytometry. Cas9-GFP-induced cells are indicated in green, non-induced cells in red. (B–E) Tumor-bearing mice were treated with DOX for 8 days after which tumors from control and BCL6 knock-out tumors were harvested 17/20 days after start of DOX treatment, respectively. Tumor volumes from (B) BCL6 sgRNA tumors (n = 10 DOX off, n = 7 DOX on) and (C) control (n = 10 DOX off, n = 8 DOX on) were measured. * p < 0.05; *** p ≤ 0.001. (D) Tumor BCL6 protein levels were determined using IHC analysis. Representative images of BCL6 IHC staining in SU-DHL-4 tumors are shown. Scale bars 100 μm. (E) Quantification of BCL6 positive cells in SU-DHL-4 BCL6 sgRNA tumor sections after vehicle (DOX off) and DOX treatment (5 days and 20 days after start of DOX treatment). Data are shown as means ± SD relative to DOX off (n = 4 – 10).