In vivo efficacy of silvestrol. (A) B-cell selectivity of silvestrol in vivo: Eμ-TCL1 mice with leukemia were injected intraperitoneally either with vehicle or 1.5 mg/kg silvestrol (n = 4 each) daily for 5 days for 2 weeks. Percentages of B and T cells were assessed by CD3/CD19 flow cytometry and total lymphocytes by blood smear. Each shape represents 1 animal; circles represent B cells, and triangles represent T cells. Horizontal bars are the average for the group. B-cell reduction in silvestrol-treated mice relative to that in vehicle-treated control mice at week 2 was significant (P = .009). No significant changes in T cells were detected. (B) In vivo efficacy of silvestrol in a xenograft model of ALL: SCID mice that received a transplant of 697 ALL cells were injected intraperitoneally with vehicle only (n = 13) or silvestrol (n = 14) at 1.5 mg/kg every other day, starting 1 week after engraftment. Survival difference between the treated and untreated groups was significant (P = .002). * indicates 3 silvestrol-treated mice survived to 6 weeks after engraftment without symptoms of disease or toxicity. These mice were then followed without treatment for an additional 6 weeks and killed for examination. No evidence of disease or toxicity was found.