Histone deacetylase inhibitors selectively target homology dependent DNA repair defective cells and elevate non-homologous endjoining activity.
BACKGROUND
We have previously used the ATAD5-luciferase high-throughput screening assay to identify genotoxic compounds with potential chemotherapeutic capabilities. The successful identification of known genotoxic agents, including the histone deacetylase inhibitor (HDACi) trichostatin A (TSA), confirmed the specificity of the screen since TSA has been widely studied for its ability to cause apoptosis in cancer cells. Because many cancers have acquired mutations in DNA damage checkpoints or repair pathways, we hypothesized that these cancers may be susceptible to treatments that target compensatory pathways. Here, we used a panel of isogenic chicken DT40 B lymphocyte mutant and human cell lines to investigate the ability of TSA to define selective pathways that promote HDACi toxicity.


RESULTS
HDACi induced a DNA damage response and reduced viability in all repair deficient DT40 mutants although ATM-nulls were least affected. The most dramatic sensitivity was observed in mutants lacking the homology dependent repair (HDR) factor BLM or the non-homologous end-joining (NHEJ) and HDR factors, KU/RAD54, suggesting an involvement of either HDR or NHEJ in HDACi-induced cell death. To extend these findings, we measured the frequencies of HDR and NHEJ after HDACi treatment and monitored viability in human cell lines comparably deficient in HDR or NHEJ. Although no difference in HDR frequency was observed between HDACi treated and untreated cells, HDR-defective human cell lines were clearly more sensitive than wild type. Unexpectedly, cells treated with HDACis showed a significantly elevated NHEJ frequency.


CONCLUSIONS
HDACi targeting drugs induced significant increases in NHEJ activity in human cell lines but did not alter HDR frequency. Moreover, HDR is required for cellular resistance to HDACi therapy; therefore, NHEJ does not appear to be a critical axis for HDACi resistance. Rather, HDACi compounds induced DNA damage, most likely double strand breaks (DSBs), and HDR proficiency is correlated with cell survival.
Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Stephanie
S
Smith
Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Jennifer
J
Fox
Department of Molecular Biology and Microbiology, College of Medicine, University of Central Florida, Orlando, Florida, United States of America.
Marco
M
Mejia
Department of Molecular Biology and Microbiology, College of Medicine, University of Central Florida, Orlando, Florida, United States of America.
Wanvipa
W
Ruangpradit
Department of Radiation Genetics Kyoto University, Medical School, Kyoto, 606-8501 Japan.
Alihossein
A
Saberi
Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America ; Department of Radiation Genetics Kyoto University, Medical School, Kyoto, 606-8501 Japan ; Department of Environmental Health School of Public Hearth, Seoul National University, Seoul, Korea.
Sunmi
S
Kim
Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Yongjun
Y
Choi
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Medical School, Minneapolis, Minnesota, United States of America.
Sehyun
S
Oh
Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America ; The University of Texas Graduate School of Biomedical Sciences at Houston, Houston Texas, United States of America.
Yucai
Y
Wang
Department of Environmental Health School of Public Hearth, Seoul National University, Seoul, Korea.
Kyungho
K
Choi
Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America ; Department of Genetics, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America.
Lei
L
Li
Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Medical School, Minneapolis, Minnesota, United States of America.
Eric A
EA
Hendrickson
Department of Radiation Genetics Kyoto University, Medical School, Kyoto, 606-8501 Japan.
Shunichi
S
Takeda
Department of Molecular Biology and Microbiology, College of Medicine, University of Central Florida, Orlando, Florida, United States of America.
Mark
M
Muller
Genome Instability Section, Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
Kyungjae
K
Myung
D000818:Animals; D034961:Antigens, Nuclear / Q000235:genetics / Q000378:metabolism; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015153:Blotting, Western; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002645:Chickens; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics; D059766:DNA End-Joining Repair / Q000187:drug effects / Q000235:genetics*; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D016521:Electrophoresis, Gel, Pulsed-Field; D005455:Fluorescent Antibody Technique; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D000072200:Ku Autoantigen; D008156:Luciferases / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D034741:RNA, Small Interfering / Q000235:genetics; D051135:Rad51 Recombinase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism; D000077337:Vorinostat
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D034741:RNA, Small Interfering; C012589:trichostatin A; D000077337:Vorinostat; D008156:Luciferases; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; C097151:Bloom syndrome protein; D053484:RecQ Helicases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen