HDAC inhibitor PCI-24781 decreases RAD51 expression and inhibits homologous recombination

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 49; pp. 19482 - 19487
• Main Authors: Adimoolam, Shanthi, Sirisawad, Mint, Chen, Jun, Thiemann, Patti, Ford, James M, Buggy, Joseph J
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 04.12.2007; National Acad Sciences
• Subjects: Animals; Apoptosis; Benzofurans - pharmacology; Biological Sciences; Cell Line, Tumor; Cell lines; CHO cells; DNA repair; DNA Repair - drug effects; DNA Repair - genetics; Dosage; Drug Synergism; Enzyme Inhibitors - pharmacology; Enzymes; Gene expression; Gene Expression Regulation - drug effects; HCT116 cells; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids - pharmacology; Inhibitor drugs; Irradiation; Phenanthrenes - pharmacology; Poly(ADP-ribose) Polymerase Inhibitors; Rad51 Recombinase - genetics; Rad51 Recombinase - metabolism; Radiation Tolerance - drug effects; Radiation-Sensitizing Agents - pharmacology; Radiotherapy; Recombination, Genetic - drug effects; Transcription, Genetic - drug effects; Tumors; Up-Regulation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0707828104

Histone deacetylase (HDAC) inhibitors such as the phenyl hydroxamic acid PCI-24781 have emerged recently as a class of therapeutic agents for the treatment of cancer. Recent data showing synergy of HDAC inhibitors with ionizing radiation and other DNA-damaging agents have suggested that HDAC inhibitors may act, in part, by inhibiting DNA repair. Here we present evidence that HDAC enzymes are important for homologous recombinational repair of DNA double-strand breaks. Combination studies of PCI-24781 with the poly(ADP-ribose) polymerase inhibitor PJ34, an agent thought to produce lesions repaired by homologous recombination (HR), resulted in a synergistic effect on apoptosis. Immunofluorescence analysis demonstrated that HDAC inhibition caused a complete inhibition of subnuclear repair foci in response to ionizing radiation. Mechanistic investigations revealed that inhibition of HDAC enzymes by PCI-24781 led to a significant reduction in the transcription of genes specifically associated with HR, including RAD51. RAD51 protein levels were significantly decreased after 24 h of drug exposure both in vitro and in vivo. Consistent with inhibition of HR, treatment with PCI-24781 resulted in a decreased ability to perform homology directed repair of I-SceI-induced chromosome breaks in transfected CHO cells. In addition, an enhancement of cell killing was observed in Ku mutant cells lacking functional nonhomologous end joining compared with WT cells. Together these results demonstrate that HDAC enzymes are critically important to enable functional HR by controlling the expression of HR-related genes and promoting the proper assembly of HR-directed subnuclear foci.