Chlorambucil cytotoxicity in malignant B lymphocytes is synergistically increased by 2-(morpholin-4-yl)-benzo[h]chomen-4-one (NU7026)-mediated inhibition of DNA double-strand break repair via inhibition of DNA-dependent protein kinase.

Abstract

Chlorambucil (CLB) treatment is used in chronic lymphocytic leukemia (CLL) but resistance to CLB develops in association with accelerated repair of CLB-induced DNA damage. Phosphorylated histone H2AX (gammaH2AX) is located at DNA double-strand break (DSB) sites; furthermore, it recruits and retains damage-responsive proteins. This damage can be repaired by nonhomologous DNA end-joining (NHEJ) and/or homologous recombinational repair (HR) pathways. A key component of NHEJ is the DNA-dependent protein kinase (DNA-PK) complex. Increased DNA-PK activity is associated with resistance to CLB in CLL. We used the specific DNA-PK inhibitor 2-(morpholin-4-yl)-benzo[h]chomen-4-one (NU7026) to sensitize CLL cells to chlorambucil. Our results indicate that in a CLL cell line (I83) and in primary CLL-lymphocytes, chlorambucil plus NU7026 has synergistic cytotoxic activity at nontoxic doses of NU7026. CLB treatment results in G(2)/M phase arrest, and NU7026 increases this CLB-induced G(2)/M arrest. Moreover, a kinetic time course demonstrates that CLB-induced DNA-PK activity was inhibited by NU7026, providing direct evidence of the ability of NU7026 to inhibit DNA-PK function. DSBs, visualized as gammaH2AX, were enhanced 24 to 48 h after CLB and further increased by CLB plus NU7026, suggesting that the synergy of the combination is mediated by NU7026 inhibition of DNA-PK with subsequent inhibition of DSB repair.

• Authors: Lilian Amrein, Martin Loignon, Anne-Christine Goulet, Michael Dunn, Bertrand Jean-Claude, Raquel Aloyz, Lawrence Panasci
• Journal: The Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 321 Issue 3 Pg. 848-55 (Jun 2007) ISSN: 0022-3565 [Print] United States
• PMID: 17351105 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• 2-(morpholin-4-yl)benzo(h)chromen-4-one
• Chromones
• Enzyme Inhibitors
• H2AX protein, human
• Histones
• Morpholines
• Chlorambucil
• DNA-Activated Protein Kinase

Topics

• Apoptosis (drug effects)
• B-Lymphocytes (drug effects, metabolism, pathology)
• Cell Cycle (drug effects)
• Cell Line, Tumor
• Cell Proliferation (drug effects)
• Cell Survival (drug effects)
• Chlorambucil (pharmacology)
• Chromones (pharmacology)
• DNA Repair (drug effects)
• DNA-Activated Protein Kinase (antagonists & inhibitors, metabolism)
• Drug Resistance, Neoplasm
• Drug Synergism
• Enzyme Inhibitors (pharmacology)
• Histones (metabolism)
• Humans
• Inhibitory Concentration 50
• Morpholines (pharmacology)
• Phosphorylation (drug effects)