CBD, an Id1 inhibitor, blocks leukemogenesis and induces the apoptosis of leukemia cells. (A) CBD treatment downregulates Id1 expression in AE9a cells (left panel) and Kasumi-1 cells (right panel). (B) AE9a leukemia cells were treated with CBD at 15 μM or vehicle control for 12 hours, and 1 × 105 living cells were injected into individual sublethally irradiated recipient mice. The frequency of GFP+C-Kit+ AE9a cells in the peripheral blood was examined 3 weeks after transplantation. (C) Leukemia blast cells are found in the peripheral blood of AE9a mice in the control group but not the CBD treatment group on day 21. (D) The WBC counts of the mice that received CBD-treated AE9a cells were lower than the mice that received control vehicle-treated cells, whereas the red blood cell (RBC) and platelet (PLT) counts of the CBD-treated group were significantly higher (± SD; n = 5). (E) Twelve hours of CBD ex vivo treatment, at 15 μM, prolongs the survival time of the recipient mice transplanted with AE9a cells. (F) Forty-eight hours of CBD, at 10 μM, inhibited the growth of primary t(8;21)+ leukemia cells and Kasumi-1 cells (± SD; n = 3) but not normal human CD34+ HSPCs. (G) Twenty-four-hour treatment with CBD, at 15 μM, caused G0/G1-phase cell cycle arrest in Kasumi-1 cells (upper panel) and AE9a cells (lower panel). (H) CBD treatment induces the apoptosis of Kasumi-1 (upper panel) and AE9a (lower panel) cells, based on 5-bromo-2′-deoxyuridine (BrdU) incorporation assays.
