Targeting Survivin Using ICG-001 May Overcome Drug Resistance in Primary B-Cell Acute Lymphoblastic Leukemia.

Abstract 3072

Poster Board III-9

Despite advances in chemotherapeutic treatment of acute lymphoblastic leukemia (ALL), 20% of children relapse with high death rates, highlighting the need for new treatment modalities. Recent population studies have demonstrated that Survivin, a member of the inhibitor of apoptosis (IAP) family proteins, is expressed in most cancerous cells but has also been implicated in normal erythropoiesis. It is upregulated in ALL of relapsed patients but not in drug-sensitive ALL. The expression of Survivin depends on the formation of a complex between β-catenin and its co-activator CBP. Selective suppression of CBP/β-catenin signaling using the novel small-molecule inhibitor ICG-001 offers a novel mechanism to target Survivin in the sensitization of leukemia cells to conventional drug treatment. We hypothesize that inhibition of CBP/β-catenin signaling by ICG-001 in combination with conventional therapy represents a promising therapeutic principle to eradicate drug resistant ALL while sparing normal hematopoiesis. An in vivo study utilized our bioluminescent model to non-invasively monitor leukemogenesis of a primary ALL, transduced with a lentiviral construct encoding firefly luciferase prior to xenotransplantation. NOD/SCIDIL2R gamma-/- mice were sublethally irradiated prior intravenous injection of 50,000 cells per animal. Leukemic animals were treated with a combination of intraperitoneally administered VDL and ICG-001 (100mg/kg/d) (n=3), which was delivered via subcutaneous osmotic pumps to ensure stable plasma levels, with VDL only (n=4), or PBS only (n=2) as a control for 4 weeks. Bioluminescent imaging on Day 42 post-injection showed a contrast in the containment of leukemia of ICG-001+VDL mice as compared to those of the VDL control group. The animals in the PBS control group and the VDL+PBS Pump control groups had Median Survival Times (MST) of 35 days and 66.5 days post-treatment, respectively. In marked contrast, the animals treated with a combination of VDL+ICG-001 had a significant 14% extension in MST of 76 days post-treatment (p=0.016 compared to VDL group). Survivin mRNA expression was found to be downregulated after VDL+ICG treatment compared to treatment with VDL only. Analysis of peripheral blood showed no effect of ICG-001 on leukocyte or red blood cells compared to control groups. Next, we determined in vitro the ability of ICG-001 to increase sensitivity of patient-derived ALL cells and ALL celllines including BEL-1, REH, 697 and SUPB15 to chemotherapy including VDL or Imatinib. After 4 days we observed significantly increased toxicity assessed by MTT assay and AnnexinV staining as well as downregulation of Survivin confirmed by real-time PCR and Western Blot. To determine if ICG-001 is non-toxic to normal hematopoiesis, we treated normalC57BL/6 mice for 3 weeks with ICG-001 only. At end of treatment, normal blood counts including red blood cell, white blood cells and platelets, normal histology and normal weight gain indicated that ICG-001 is not detrimental to the recipient. In vitro apoptotic studies using normal white blood cells isolated from peripheral blood and co-cultured with a stromal layer confirmed further the non-toxicity of ICG-001 to normal cells. In summary, the sustained survival of the mice treated with combination of standard chemotherapy and ICG-001 is compatible with our hypothesis that ICG-001 can sensitize drug resistant leukemia cells to treatment with standard chemotherapy while sparing normal hematopoiesis and may lead to novel therapeutic options to overcome drug resistance.