A combination of histone deacetylase inhibitor LBH589 and the hsp90 inhibitor 17-AAG is highly active against human CML-BC and AML cells with constitutively active mutant FLT-3 tyrosine kinase

Abstract

6541 Background: We have reported that treatment with histone deacetylase inhibitors, LAQ824 and LBH589 (Novartis Pharma AG), and hsp90 inhibitor 17-AAG attenuates the levels of Bcr-Abl and FLT-3, as well induces apoptosis of human CML-BC and AML cells. In these studies we determined the antileukemia activity of the combination of LBH589 and 17-AAG. Methods: K562 (CML-BC), MV4–11 (AML cells with the activating length mutation of FLT-3) and primary AML (with FLT-3 mutation) were exposed to 0.1 to 2.0 uM 17-AAG and/or 5 to 100 nM LBH589 for 24 to 48 hours. Following this, the cell cycle status and apoptosis (by flow cytometry), as well as the expressions of p21, hsp70, p-FLT-3, FLT-3, p-AKT, p-ERK1/2 and p-STAT5 (by Western analyses) were determined. Results: LBH589 treatment induced p21 levels and mediated cell cycle G1 phase accumulation as well as apoptosis of MV4–11 and K562 cells. In MV4–11 cells, this was associated with marked attenuation of the protein levels of p-FLT-3, FLT-3, p-AKT, p-ERK1/2 and p-STAT5, as well as the DNA binding activity of STAT5. Furthermore, co-treatment with LBH589 and the FLT-3 kinase inhibitor PKC412 (Novartis Pharma AG) exerted synergistic cytotoxic effect against MV4–11 cells. In K562 cells, exposure to LBH589 attenuated Bcr-Abl, p-AKT, p-ERK1/2 and p-STAT5. Treatment with 17-AAG or LBH589 inhibited the chaperone association of hsp90 with FLT-3 and Bcr-Abl in MV4–11 and K562 cells, respectively, resulting in polyubiquitylation and proteasomal degradation of FLT-3 and Bcr-Abl. Significantly, co-treatment with LBH589 and 17-AAG induced more apoptosis of MV4–11 and K562 cells that either agent alone. The combination also attenuated the levels of mutant T315I Bcr-Abl and induced apoptosis of Gleevec-refractory primary CML-BC,as well as induced more apoptosis of primary AML cells with FLT-3 mutations. Conclusions: These studies demonstrate that the combination of LBH589 and 17-AAG may be highly effective in attenuating p-FLT-3 and Bcr-Abl, as well as inducing apoptosis of CML-BC and AML cells with FLT-3 mutations. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis Corp. Novartis Corp.