Targeting S1pr1/Stat3 signaling inhibited murine B-cell lymphoma tumor growth in a syngeneic mouse model. (A) Inhibition of S1pr1 induced apoptosis and growth inhibition of the murine B-cell lymphoma A20 cell line in vitro. A20 B-cell lymphoma cells were treated with FTY720 at indicated concentrations. Tumor cell proliferation and apoptosis were examined 24 or 48 hours after treatment. The results represent 3 independent experiments. (B) S1pr1 and phospho-Stat3 levels in A20 tumor cells were determined by Western blot analysis after treating with FTY720 for 6 hours. (C) A20 tumor growth and Stat3 activity were decreased by FTY720 treatment in vivo. Left panel: tumor growth curve showing that FTY720 inhibited A20 tumor growth in vivo; N = 5. **P < .01. Data are representative of 2 independent experiments. Right panel: Western blotting analysis of S1pr1 and phospho-Stat3 protein levels in A20 tumors after FTY720 treatment in vivo. Five tumors were pooled to make protein lysates. Data are representative of 2 independent experiments.