GSI treatment induces apoptosis of leukemic cells in vivo.(A) Leukemic mice were treated with a 150-mg/kg dose of MRK-003 or with vehicle for 3 days. Tumor sections were fixed in 10% buffered formalin and number of apoptotic cells was quantified using TUNEL assay (ApoTag Plus peroxidase from Chemicon, Temecula, CA). (B) Bar graph representing the fold change in TUNEL-positive cells compared with vehicle. Ten independent fields/section were counted to obtain the representative value.