6S markedly inhibits tumor growth and induces apoptosis in the xenograft animal model. Five- to six-week-old NOD/SCID nude mice were injected subcutaneously with 2.5 × 106 U937 cells into the right flank. From the fifth day, mice were randomized into a control group (7 mice per group) and treated group (7 mice per group, 6S of 50 mg/kg/day). Intraperitoneal administration of 6S and tumor volume assessment were conducted as described in the method of murine model. The 6S significantly inhibits tumor growth (a), which is further confirmed by the tumor volume size (b). Data are means ± SD. Values of tumor volume for 6S treatment groups were significantly decreased compared with those for the control group by Student’s t-test; *p < 0.05, **p < 0.01. The change of body weight is shown in (c). Compared with the control group, TUNEL (× 400) assay shows increased numbers of apoptotic cells in the 6S treatment group (d). Tumors were obtained from animals 20 days after drug exposure. Tumors were fixed and stained with hemtoxylin and eosin (H&E) stain to examine tumor cell morphology, using TUNEL assay to determine apoptosis.