Nude Balb/c mice were bred at the animal facility of Guangzhou Medical College. The mice were housed in barrier facilities with a 12-hour light/dark cycle, with food and water available ad libitum. A total of 3 × 107 of KBM5 or KBM5-T315I cells were inoculated subcutaneously on the flanks of 5-week-old male nude mice. After 72 hours of inoculation, mice were treated with vehicle (10% DMSO, 30% cremophor and 60% NaCl), gambogic acid (3 mg/kg/2 days, i.p.), imatinib (50 mg/kg/d, i.g.) and the combination of gambogic acid and imatinib for a total of 17 days. Tumors were measured and tumor volumes were calculated by the following formula: a2 × b × 0.4, where a is the smallest diameter and b is the diameter perpendicular to a. Tumor xenografts were removed, weighed, stored, and fixed. All animal studies were conducted with the approval of the Institutional Animal Care and Use Committee of Guangzhou Medical College.