Abstract 5412: Synergistic interactions between histone deacetylase inhibitors and aurora kinase inhibitor KW2449 Ph+ cells

Abstract

Abstract Resistance to tyrosine kinase inhibitors (imatinib, nilotinib, dasatinib) remains a major therapeutic challenge in Bcr/abl+ leukemia. Consequently, novel and more effective therapeutic strategies are urgently needed in this setting. KW-2449 is a multi-kinase inhibitor which inhibits Bcr/abl, aurora kinase, and FLT3, among other targets, and which has shown activity against T315I “gatekeeper” mutant Bcr/abl cells. Previous studies have shown that histone deacetylase inhibitors (HDACIs) such as vorinostat sharply promote the antileukemic effects of Bcr/abl and aurora kinase inhibitors such as MK-0457 in CML cells (Dai et al., Blood 112:793-804, 2008). However, MK-0457 is not currently under clinical development. The purpose of this study was to assess the effects of HDACIs (e.g., SBHA, MS-275) on responses to the dual aurora kinase-Bcr/abl inhibitor (KW-2449) in various Bcr/Abl + cells. Coadministration of HDACIs synergistically increased KW-2449 lethality in CML (K562, LAMA84) and Ph+ ALL cells (TOM-1, SD-1, SUP-B15, BV173). Notably, HDACI/KW-2449 regimens were also highly active against multiple imatinib resistant cells including BV-173/E255K, BaF3/Bcr-Abl/T315I, as well as Bcr/Abl -overexpressing and Bcr/abl-independent K562 cells. Combined treatment with HDACIs and KW-2449 was associated with inactivation and down-regulation of Bcr/Abl and its downstream target CrkL in CML and ALL cell lines including BaF3/T315I. Moreover treatment with KW-2449/HDACi resulted in a pronounced increase in DNA damage (γH2A.X) documented by Western blot and confocal microscopy. In addition, coadministration of HDACIs and KW-2449 strikingly blocked phosphorylation of histone H3, a marker of aurora kinase inhibition, and diminished HDACI-induced p21CIP1 expression. Notably, down-regulation of Bim by siRNA significantly diminished the lethality of the HDACI/KW-2449 regimen. Treatment of K562 cells with HDACIs alone resulted in G1S arrest, an effect abrogated by KW-2449, and which resulted in pronounced cellular endoreduplication. Furthermore, knockdown of either Aurora A or Aurora B in K562 cells dramatically increased the HDACI-mediated cell death. Finally, cotreatment with KW-2449 and HDACIs significantly increased cell death in seven CML primary samples (including both naïve and imatinib-resistant specimens, one carrying the I242T, Y257C mutations) compared to treatment with either agent alone, while exhibiting minimal toxicity to normal CD34+ progenitors. Together, these findings indicate that HDACIs strikingly increase KW-2449 activity against IM-sensitive and -resistant Bcr/Abl+ cells, and suggest that this strategy warrants further attention in Bcr/abl+ leukemias. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5412.