Abstract B218: CBP/catenin antagonism inhibits self-renewal of acute lymphoblastic leukemia.

Abstract

Abstract Background: Despite advances in chemotherapeutic treatment of acute lymphoblastic leukemia (ALL), drug resistance in ALL remains a major problem warranting new treatment strategies. Recent studies have demonstrated that survivin, a member of the inhibitor of apoptosis (IAP) family proteins, 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 catenin (beta or gamma) and its co-activator CBP. T-cell factor (TCF)/catenin/CBP mediated transcription is involved in self-renewal of progenitor cells. However, a switch to TCF/catenin/p300 mediated transcription, which can be induced pharmacologically with ICG-001, a novel specific inhibitor of binding to the N-terminus of CBP, is described as critical to inhibit CBP-mediated self-renewal. We hypothesized that selective suppression of CBP/catenin signaling using ICG-001 offers a promising therapeutic principle to eradicate drug resistant ALL and showed previously that ICG-001 can sensitize patient-derived (primary) pre-B ALL cells to chemotherapy in vitro and in vivo. However, the underlying mechanism has not been described. Results: For this purpose, we initially determined expression of nuclear and cytosolic β- and γ-catenin expression in 13 primary ALL cases encompassing various cytogenetic aberrations by Western blot. Primary pre-B ALL cells were treated with and without ICG-001 and co-cultured with a murine stromal layer (OP9 cells) for 48 hours. Co-Immunoprecipitation showed that the binding of β- and γ-catenin with CBP, but not with p300, was inhibited by ICG-001 indicating that ICG-001 binds CBP and selectively disrupts β- and γ-catenin/CBP interaction. To determine the effect of ICG-001 on self-renewal in ALL, we performed a colony forming (CFU) assay with two primary ALL cells (LAX7R, SFO2) treated with single agent ICG-001 (10 m and 25 m). LAX7R showed a significant reduction with ICG-001 treatment (10 m and 25 m) compared with media only group (331.3× 42.8 and 57×13.5 vs 698.3× 68.4; p<0.05) in primary platings, and there were no colonies found in secondary platings of cells treated with ICG-001 (25 m), indicating that ICG-001 abrogates self-renewal of ALL cells. Similarly SFO2 cells showed no secondary colony counts with ICG-001 treatment (25 m) whereas control cells were replatable. These experiments were repeated three times in triplicate. Preclinical in vitro evaluation of five primary ALL cells treated continuously with ICG-001 (10μM- or, 25μM) or DMSO as vehicle control with and without chemotherapy consisting of Nilotinib for Philadelphia chromosome (Ph) positive ALL and Vincristine, Dexamethasone and L-Asparaginase for Ph negative ALL, that chemotherapy alone cannot eradicate primary ALL cells. However, in combination with ICG-001, chemotherapy led to the eradication of all five primary ALL cases, indicating that CBP/catenin antagonism can overcome drug resistance in ALL. Conclusion: Taken together, our data shows that targeting CBP/β- and γ-catenin by the small molecule inhibitor ICG-001 can abrogate primary ALL by inhibition of self-renewal of ALL cells. These findings provide the basis for a new treatment approach against drug resistant ALL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B218.