SK1-I suppresses U937 xenograft tumor growth. CB17 SCID/beige mice (5 mice per group) with palpable U937 cell tumors (4 tumors per mouse) were injected intraperitoneally with saline or SK1-I (20 mg/kg) for 7 days. (A) Tumor volumes were measured daily. Data are expressed as mean volumes (± SD). (B) After 7 days, animals were killed and tumors excised and weighed. Average and representative results are shown. *P ≤ .01. (C) Tumor histology. Paraffin-embedded tumor sections were stained with either H&E or immunostained with Ki67. Apoptotic cells were visualized by TUNEL staining and counterstained with DAPI. Slides were examined with an Olympus BX-40 microscope (Olympus, Melville, NY) equipped with a UPlan F1 20×/0.5 NA objective and WH10x eyepiece, and analyzed with RS Image version 1.7.3 (Alpha Innotech). Representative sections from n = 4 individual treated tumors. Scale bar represents 30 μm.