Abstract 2572: The histone deacetylase inhibitors (HDACIs) vorinostat and entinostat interact synergistically with the Bcr/Abl, FLT3, and aurora kinase inhibitor KW-2449 to induce apoptosis in imatininb mesylate (IM)-sensitive and -resistant CML and ALL cells in vitro and in vivo
Authors: Nguyen Tri K. , Attkisson Elisa , Dai Yun , Kramer Lora , Muschen Markus , Grant Steven 
Published: June 2012

Abstract
Introduction: The purpose of the present study was to determine whether HDACIs such as vorinostat or SNDX-275 could enhance the antileukemic effects of the multi-kinase inhibitor KW-2449, which inhibits Bcr/Abl, FLT3, and aurora kinases, in IM-sensitive and -resistant Bcr/Abl+ CML and ALL cells.
Experimental Procedures: KW-2449, vorinostat, and SNDX-275 were from Kyowa-Kirin, Merck, and Syndax Pharmaceuticals respectively. Human ALL subclones bearing E255K or T315I mutations were selected by culturing cells in IM. Patient samples were acquired with informed consent. CBySmn.CB17-Prkds scid/J (BALB/C) mice were used for in vivo studies.
Results: Co-administration of HDACIs synergistically increased KW-2449-mediated lethality in CML (K562, LAMA84) and Ph+ ALL cells (TOM-1, SD-1, SUP-B15, BV173). Notably, HDACI/KW-2449 regimens were highly active against multiple resistant cells, including recently developed IM-resistant BV-173/E255K and patient-derived Adult/T315I. Combined treatment induced inactivation of Bcr/Abl and its downstream targets STAT5 and CRKL in Ph+ CML and ALL cell lines sensitive and resistant to IM. KW-2449/HDACI exposure resulted in a marked increase in mitochondrial damage and caspase activation in association with induction of reactive oxygen species (ROS), DNA damage (γH2A.X), and G2/M arrest. The MnSOD2 mimetic TBAP reduced apoptosis and caspase activation but not Bcr/Abl inactivation in KW-2449/HDACI-treated cells; DNA damage was partially attenuated. HDACIs potentiated KW-2449 lethality in multiple primary CD34+ Bcr/Abl+ leukemia specimens but not in normal bone marrow cells. Finally, sub-effective vorinostat or SNDX275 doses markedly increased KW2449 anti-tumor effects and significantly prolonged the survival of murine xenografts bearing IM-resistant ALL cells (BV173/E255K). HDACI/KW-2449 regimens also decreased the percentage of leukemia cells (CD19+, CD45+) in murine bone marrow compared to the effects of single agent treatment.
Conclusions: These findings indicate that the HDACIs vorinostat and SNDX-275 strikingly increase KW-2449 activity against IM-sensitive and -resistant Bcr/Abl+ CML and ALL cells. These events are associated with the marked inactivation of Bcr/Abl, induction of ROS, DNA damage, and G2/M arrest, and occur in primary Bcr/Abl+ CD34+ cells. Finally, HDACI/KW-2449 regimens displayed marked activity in a highly IM-resistant BV173/E255K mutant Ph+ ALL in vivo model. Collectively, these findings suggest that a strategy combining vorinostat or SNDX-275 with KW-2449 warrants further consideration in IM-resistant Bcr/Abl+ CML and ALL.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2572. doi:10.1158/1538-7445.AM2011-2572