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Research Articles: Therapeutics, Targets, and Development

Role of histone deacetylase inhibitor-induced reactive oxygen species and DNA damage in LAQ-824/fludarabine antileukemic interactions

Departments of ¹ Medicine and ² Biochemistry, Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia and ³ Department of Oncology, Novartis Institutes for Biomedical Research, East Hanover, New Jersey

Requests for reprints: Steven Grant, Division of Hematology/Oncology, Massey Cancer Center, Virginia Commonwealth University, MCV Station Box 230, Richmond, VA 23298. Phone: 804-828-5211; Fax: 804-828-8079. E-mail: stgrant{at}vcu.edu

Abstract

The role of reactive oxygen species (ROS) production on DNA damage and potentiation of fludarabine lethality by the histone deacetylase inhibitor (HDACI) LAQ-824 was investigated in human leukemia cells. Preexposure (24 h) of U937, HL-60, Jurkat, or K562 cells to LAQ-824 (40 nmol/L) followed by fludarabine (0.4 µmol/L) dramatically potentiated apoptosis (75%). LAQ-824 triggered an early ROS peak (30 min-3 h), which declined by 6 h, following LAQ-824-induced manganese superoxide dismutase 2 (Mn-SOD2) upregulation. LAQ-824/fludarabine lethality was significantly diminished by either ROS scavengers N-acetylcysteine or manganese (III) tetrakis (4-benzoic acid) porphyrin or ectopic Mn-SOD2 expression and conversely increased by Mn-SOD2 antisense knockdown. During this interval, LAQ-824 induced early (4-8 h) increases in -H2AX, which persisted (48 h) secondary to LAQ-824-mediated inhibition of DNA repair (e.g., down-regulation of Ku86 and Rad50, increased Ku70 acetylation, diminished Ku70 and Ku86 DNA-binding activity, and down-regulated DNA repair genes BRCA1, CHEK1, and RAD51). Addition of fludarabine further potentiated DNA damage, which was incompatible with cell survival, and triggered multiple proapoptotic signals including activation of nuclear caspase-2 and release of histone H1.2 into the cytoplasm. The latter event induced activation of Bak and culminated in pronounced mitochondrial injury and apoptosis. These findings provide a mechanistic basis for understanding the role of early HDACI-induced ROS generation and modulation of DNA repair processes in potentiation of nucleoside analogue-mediated DNA damage and lethality in leukemia. Moreover, they show for the first time the link between HDACI-mediated ROS generation and the recently reported DNA damage observed in cells exposed to these agents. [Mol Cancer Ther 2008;7(9):3285–97]

Grant support: National Cancer Institute grants CA63753, CA93738, and CA100866 and a V Foundation award.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

⁴ Supplementary material for this article is available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/).

Received 4/22/08; revised 6/10/08; accepted 7/13/08.