Antitumor activity of BBL22 in PC3 xenografts. Palpable tumors were established by inoculating nude athymic mice s.c. with 5 × 106 PC3 cells. At day 17 after tumor cell inoculation, animals were injected s.c. with vehicle alone (filled diamonds), BBL22 50 mg/kg per day (open squares), or BBL22 250 mg/kg per day (filled circles) for 4 consecutive days (days 17–20, indicated by arrows). Tumor volumes were determined on days 14, 18, 20, 24, and 32. Horizontal lines indicate mean values for each treatment group.