Combined effects of novel tyrosine kinase inhibitor AMN107 and histone deacetylase inhibitor LBH589 against unmutated or mutant Bcr-Abl-expressing human leukemia cells

Abstract

6592 Background: AMN107 has potent in vitro and in vivo activity against the un-mutated and most mutant forms of Bcr-Abl tyrosine kinase (TK). We have previously demonstrated that in CML cells the pan-histone deacetylase inhibitor LBH589 depletes both unmutated and mutated Bcr-Abl, as well as attenuates p-AKT and Raf-1 levels. In the present studies we determined the effects of AMN107 and/or LBH589 in unmutated or mutated Bcr-Abl-expressing mouse BaF3 cells, or human CML K562 and LAMA-84 cells, as well as in primary CML cells procured from patients with imatinib mesylate (IM)-refractory CML. Methods: Cultured and primary CML cells were exposed to 20 to 100 nM AMN107 and/or LBH589 for 24 to 48 hours. Following this, the % of apoptotic cells was determined, as well as immunoblot analyses were performed to determine Bcr-Abl, p-STAT5, p-AKT, p-CrkL, Bim, Bcl-xL and p27 levels. Synergy between the apoptotic effects was determined by the median dose-effect isobologram analysis. Results: AMN107 was 20-fold more potent than IM, and was more potent in inhibiting Bcr-Abl TK activity and attenuating p-STAT5, p-AKT, Bcl-xL, and c-Myc levels in K562 and LAMA-84 cells. Co-treatment with LBH589 and AMN107 exerted synergistic apoptotic effects against human CML (but not the normal bone marrow progenitor cells), with more attenuation of p-STAT5, p-ERK1/2, c-Myc and Bcl-xL and increased p27 and Bim levels. LBH589 attenuated Bcr-Abl levels and induced apoptosis of mouse pro-B BaF3 cells containing ectopic expression of unmutated Bcr-Abl or the IM-resistant Bcr-AblT315I and Bcr-AblE255K. Treatment with LBH589 also depleted Bcr-Abl levels and induced apoptosis in IM-resistant primary human CML cells, including those with expression of Bcr-AblT315I. As compared to either agent alone, co-treatment with AMN107 and LBH589 induced more loss of cell viability of primary IM-resistant CML cells. Conclusions: These findings support in vivo testing of the combination of LBH589 and AMN107 against IM naïve or resistant CML, with the goal to eradicate IM sensitive or resistant CML. [Table: see text]