251
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Saunthararajah Y, Triozzi P, Rini B, Singh A, Radivoyevitch T, Sekeres M, Advani A, Tiu R, Reu F, Kalaycio M, Copelan E, Hsi E, Lichtin A, Bolwell B. p53-Independent, normal stem cell sparing epigenetic differentiation therapy for myeloid and other malignancies. Semin Oncol 2012; 39:97-108. [PMID: 22289496 PMCID: PMC3655437 DOI: 10.1053/j.seminoncol.2011.11.011] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cytotoxic chemotherapy for acute myeloid leukemia (AML) usually produces only temporary remissions, at the cost of significant toxicity and risk for death. One fundamental reason for treatment failure is that it is designed to activate apoptosis genes (eg, TP53) that may be unavailable because of mutation or deletion. Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors. Mutations in these transcription factors (eg, CEBPA) or their cofactors (eg., RUNX1) affect transactivation function and produce epigenetic repression of late-differentiation genes that antagonize MYC. Importantly, this aberrant epigenetic repression can be redressed clinically by depleting DNA methyltransferase 1 (DNMT1, a central component of the epigenetic network that mediates transcription repression) using the deoxycytidine analogue decitabine at non-cytotoxic concentrations. The DNMT1 depletion is sufficient to trigger upregulation of late-differentiation genes and irreversible cell cycle exit by p53-independent differentiation mechanisms. Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors. The biological rationale for this approach to therapy appears to apply to cancers other than MDS/AML also. Decitabine or 5-azacytidine dose and schedule can be rationalized to emphasize this mechanism of action, as an alternative or complement to conventional apoptosis-based oncotherapy.
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Affiliation(s)
- Yogen Saunthararajah
- Department of Translational Hematology and Oncology Research, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
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252
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Synthesis and solution behaviour of stable mono-, di- and trinuclear Pd(II) complexes of 2,5-pyridinedihydroxamic acid: X-ray crystal structure of a novel Pd(II) hydroxamato complex. Inorganica Chim Acta 2012. [DOI: 10.1016/j.ica.2011.09.050] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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253
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Lee YJ, Won AJ, Lee J, Jung JH, Yoon S, Lee BM, Kim HS. Molecular mechanism of SAHA on regulation of autophagic cell death in tamoxifen-resistant MCF-7 breast cancer cells. Int J Med Sci 2012; 9:881-93. [PMID: 23155362 PMCID: PMC3498753 DOI: 10.7150/ijms.5011] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 10/30/2012] [Indexed: 11/30/2022] Open
Abstract
OBJECTIVE Tamoxifen is currently used for the treatment of estrogen receptor-positive breast cancer patients, but acquired resistance to tamoxifen is a critical problem in breast cancer therapy. Suberoylanilide hydroxamic acid (SAHA) is a prototype of the newly developed HDAC inhibitor. The aim of this study is to investigate the anticancer effects of SAHA in tamoxifen-resistant MCF-7 (TAMR/MCF-7) cells. METHODS Cytotoxicity, apoptosis and autophagic cell death induced by SAHA were studied. A TAMR/MCF-7 cells xenograft model was established to investigate the inhibitory effect of SAHA on tumor growth in vivo. RESULTS SAHA inhibited the proliferation of TAMR/MCF-7 cells in a dose-dependent manner. SAHA significantly reduced the expression of HDAC1, 2, 3, 4 and 7 and increased acetylated histone H3 and H4. Although SAHA induced G2/M phase arrest of cell cycle, apoptotic cell death was very low, which is correlated with the slight change in the activation of caspases and PARP cleavage. Interestingly, expression of the autophagic cell death markers, LC3-II and beclin-1, was significantly increased in TAMR/MCF-7 cells treated with SAHA. Autophagic cell death induced by SAHA was confirmed by acridine orange staining and transmission electron microscopy (TEM) in TAMR/MCF-7 cells. In mice bearing the TAMR/MCF-7 cell xenografts, SAHA significantly reduced the tumor growth and weight, without apparent side effects. CONCLUSION These results suggest that SAHA can induce caspase-independent autophagic cell death rather than apoptotic cell death in TAMR/MCF-7 cells. SAHA-mediated autophagic cell death is a promising new strategy to treatment of tamoxifen-resistant human breast cancer.
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Affiliation(s)
- Young Ju Lee
- Laboratory of Molecular Toxicology, College of Pharmacy, Pusan National University, Jangjeon-dong, Geumjeung-gu, Busan, Republic of Korea
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Abstract
Histone deacetylase (HDAC) inhibitors are a new class of anticancer agents. HDAC inhibitors induce acetylation of histones and nonhistone proteins which are involved in regulation of gene expression and in various cellular pathways including cell growth arrest, differentiation, DNA damage and repair, redox signaling, and apoptosis (Marks, 2010). The U.S. Food and Drug Administration has approved two HDAC inhibitors, vorinostat and romidepsin, for the treatment of cutaneous T-cell lymphoma (Duvic & Vu, 2007; Grant et al., 2010; Marks & Breslow, 2007). Over 20 chemically different HDAC inhibitors are in clinical trials for hematological malignancies and solid tumors. This review considers the mechanisms of resistance to HDAC inhibitors that have been identified which account for the selective effects of these agents in inducing cancer but not normal cell death. These mechanisms, such as functioning Chk1, high levels of thioredoxin, or the prosurvival BCL-2, may also contribute to resistance of cancer cells to HDAC inhibitors.
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255
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Ververis K, Rodd AL, Tang MM, El-Osta A, Karagiannis TC. Histone deacetylase inhibitors augment doxorubicin-induced DNA damage in cardiomyocytes. Cell Mol Life Sci 2011; 68:4101-14. [PMID: 21584806 PMCID: PMC11115072 DOI: 10.1007/s00018-011-0727-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2010] [Revised: 04/19/2011] [Accepted: 05/03/2011] [Indexed: 01/11/2023]
Abstract
Histone deacetylase inhibitors have emerged as a new class of anticancer therapeutics with suberoylanilide hydroxamic acid (Vorinostat) and depsipeptide (Romidepsin) already being approved for clinical use. Numerous studies have identified that histone deacetylase inhibitors will be most effective in the clinic when used in combination with conventional cancer therapies such as ionizing radiation and chemotherapeutic agents. One promising combination, particularly for hematologic malignancies, involves the use of histone deacetylase inhibitors with the anthracycline, doxorubicin. However, we previously identified that trichostatin A can potentiate doxorubicin-induced hypertrophy, the dose-limiting side-effect of the anthracycline, in cardiac myocytes. Here we have the extended the earlier studies and evaluated the effects of combinations of the histone deacetylase inhibitors, trichostatin A, valproic acid and sodium butyrate on doxorubicin-induced DNA double-strand breaks in cardiomyocytes. Using γH2AX as a molecular marker for the DNA lesions, we identified that all of the broad-spectrum histone deacetylase inhibitors tested augment doxorubicin-induced DNA damage. Furthermore, it is evident from the fluorescence photomicrographs of stained nuclei that the histone deacetylase inhibitors also augment doxorubicin-induced hypertrophy. These observations highlight the importance of investigating potential side-effects, in relevant model systems, which may be associated with emerging combination therapies for cancer.
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Affiliation(s)
- Katherine Ververis
- Epigenomic Medicine, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, 75 Commercial Road, Melbourne, VIC Australia
- Department of Anatomy and Cell Biology, The University of Melbourne, Parkville, VIC Australia
| | - Annabelle L. Rodd
- Epigenomic Medicine, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, 75 Commercial Road, Melbourne, VIC Australia
- Department of Pathology, The University of Melbourne, Parkville, VIC Australia
| | - Michelle M. Tang
- Epigenomic Medicine, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, 75 Commercial Road, Melbourne, VIC Australia
- Epigenetics in Human Health and Disease, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, Melbourne, VIC Australia
| | - Assam El-Osta
- Department of Pathology, The University of Melbourne, Parkville, VIC Australia
- Epigenetics in Human Health and Disease, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, Melbourne, VIC Australia
- Epigenomics Profiling Facility, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, Melbourne, VIC Australia
- Faculty of Medicine, Monash University, Melbourne, VIC Australia
| | - Tom C. Karagiannis
- Epigenomic Medicine, Baker IDI Heart and Diabetes Institute, The Alfred Medical Research and Education Precinct, 75 Commercial Road, Melbourne, VIC Australia
- Department of Pathology, The University of Melbourne, Parkville, VIC Australia
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256
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Perego P, Zuco V, Gatti L, Zunino F. Sensitization of tumor cells by targeting histone deacetylases. Biochem Pharmacol 2011; 83:987-94. [PMID: 22120677 DOI: 10.1016/j.bcp.2011.11.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 11/10/2011] [Accepted: 11/14/2011] [Indexed: 01/05/2023]
Abstract
Epigenetic mechanisms may contribute to drug resistance by interfering with tumor growth regulatory pathways and pro-apoptotic programs. Since gene expression is regulated by acetylation status of histones, a large variety of histone deacetylase (HDAC) inhibitors have been studied as antitumor agents. On the basis of their pro-apoptotic activity, HDAC inhibitors have been combined with conventional antitumor agents or novel target-specific agents to increase susceptibility to apoptosis and drug sensitivity of cancer cells. Several combination strategies including HDAC inhibitors have been explored in preclinical studies. Promising therapeutic effects have been reported in combination with DNA damaging agents, taxanes, targeted agents, death receptor agonists and hormonal therapies. Some histone deacetylases, such as HDAC6, can also modulate the function of non-histone proteins involved in critical regulatory processes which may be relevant as therapeutic targets. Given the pleiotropic effects of most of the available inhibitors, the mechanisms of the sensitization are not completely elucidated. A better understanding of the involved mechanisms will provide a rational basis to improve the therapeutic outcome of the available antitumor agents.
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Affiliation(s)
- Paola Perego
- Fondazione IRCCS Istituto Nazionale Tumori, Milan, Italy.
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257
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Role of checkpoint kinase 1 (Chk1) in the mechanisms of resistance to histone deacetylase inhibitors. Proc Natl Acad Sci U S A 2011; 108:19629-34. [PMID: 22106282 DOI: 10.1073/pnas.1117544108] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Histone deacetylase inhibitors (HDACi) are a new group of anticancer drugs with tumor selective toxicity. Normal cells are relatively resistant to HDACi-induced cell death compared with cancer cells. Previously, we found that vorinostat induces DNA breaks in normal and transformed cells, which normal but not cancer cells can repair. In this study, we found that checkpoint kinase 1 (Chk1), a component of the G2 DNA damage checkpoint, is important in the resistance of normal cells to HDACi in vitro and in vivo. Inhibition of Chk1 activity with Chk1 inhibitor (UCN-01, AZD7762, or CHIR-124) in normal cells increases their sensitivity to HDACi (vorinostat, romidepsin, or entinostat) induced cell death, associated with extensive mitotic disruption. Mitotic abnormalities included loss of sister chromatid cohesion and chromosomal disruption. Inhibition of Chk1 did increase HDACi-induced cell death of transformed cells. Thus, Chk1 is an important factor in the resistance of normal cells, and some transformed cells, to HDACi-induced cell death. Use of Chk1 inhibitors in combination with anticancer agents to treat cancers may be associated with substantial toxicity.
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258
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LBH-589 (panobinostat) potentiates fludarabine anti-leukemic activity through a JNK- and XIAP-dependent mechanism. Leuk Res 2011; 36:491-8. [PMID: 22074700 DOI: 10.1016/j.leukres.2011.10.020] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Revised: 09/15/2011] [Accepted: 10/18/2011] [Indexed: 02/05/2023]
Abstract
Effects of the HDAC inhibitor LBH-589 (panobinostat) on fludarabine lethality toward acute myeloid leukemia (AML) cells were examined in vitro and in vivo. LBH-589 pretreatment sensitized U937, HL-60, and primary leukemia cells to fludarabine while blocking NF-κB activation accompanied by XIAP down-regulation and JNK activation. Pharmacologic or genetic JNK inhibition significantly attenuated LBH-589/fludarabine lethality, whereas XIAP over-expression diminished JNK activation and apoptosis. Combined in vivo treatment abrogated leukemia growth in a U937 xenograft murine model and substantially increased animal survival. These studies highlight the interplay between NF-κB activation, XIAP down-regulation, and JNK activation in anti-leukemic synergism between fludarabine and LBH-589.
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259
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Rajendran P, Ho E, Williams DE, Dashwood RH. Dietary phytochemicals, HDAC inhibition, and DNA damage/repair defects in cancer cells. Clin Epigenetics 2011; 3:4. [PMID: 22247744 PMCID: PMC3255482 DOI: 10.1186/1868-7083-3-4] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Accepted: 10/26/2011] [Indexed: 12/21/2022] Open
Abstract
Genomic instability is a common feature of cancer etiology. This provides an avenue for therapeutic intervention, since cancer cells are more susceptible than normal cells to DNA damaging agents. However, there is growing evidence that the epigenetic mechanisms that impact DNA methylation and histone status also contribute to genomic instability. The DNA damage response, for example, is modulated by the acetylation status of histone and non-histone proteins, and by the opposing activities of histone acetyltransferase and histone deacetylase (HDAC) enzymes. Many HDACs overexpressed in cancer cells have been implicated in protecting such cells from genotoxic insults. Thus, HDAC inhibitors, in addition to unsilencing tumor suppressor genes, also can silence DNA repair pathways, inactivate non-histone proteins that are required for DNA stability, and induce reactive oxygen species and DNA double-strand breaks. This review summarizes how dietary phytochemicals that affect the epigenome also can trigger DNA damage and repair mechanisms. Where such data is available, examples are cited from studies in vitro and in vivo of polyphenols, organosulfur/organoselenium compounds, indoles, sesquiterpene lactones, and miscellaneous agents such as anacardic acid. Finally, by virtue of their genetic and epigenetic mechanisms, cancer chemopreventive agents are being redefined as chemo- or radio-sensitizers. A sustained DNA damage response coupled with insufficient repair may be a pivotal mechanism for apoptosis induction in cancer cells exposed to dietary phytochemicals. Future research, including appropriate clinical investigation, should clarify these emerging concepts in the context of both genetic and epigenetic mechanisms dysregulated in cancer, and the pros and cons of specific dietary intervention strategies.
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Affiliation(s)
- Praveen Rajendran
- Cancer Chemoprotection Program, Linus Pauling Institute, 307 Linus Pauling Science Center, Oregon State University, Corvallis OR 97331, USA
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260
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Robey RW, Chakraborty AR, Basseville A, Luchenko V, Bahr J, Zhan Z, Bates SE. Histone deacetylase inhibitors: emerging mechanisms of resistance. Mol Pharm 2011; 8:2021-31. [PMID: 21899343 DOI: 10.1021/mp200329f] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The histone deacetylase inhibitors (HDIs) have shown promise in the treatment of a number of hematologic malignancies, leading to the approval of vorinostat and romidepsin for the treatment of cutaneous T-cell lymphoma and romidepsin for the treatment of peripheral T-cell lymphoma by the U.S. Food and Drug Administration. Despite these promising results, clinical trials with the HDIs in solid tumors have not met with success. Examining mechanisms of resistance to HDIs may lead to strategies that increase their therapeutic potential in solid tumors. However, relatively few examples of drug-selected cell lines exist, and mechanisms of resistance have not been studied in depth. Very few clinical translational studies have evaluated resistance mechanisms. In the current review, we summarize many of the purported mechanisms of action of the HDIs in clinical trials and examine some of the emerging resistance mechanisms.
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Affiliation(s)
- Robert W Robey
- Medical Oncology Branch, National Cancer Institute, National Institutes of Health, 9000 Rockville Pike, Bethesda, Maryland 20892, United States.
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261
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Cleaver JE. γH2Ax: biomarker of damage or functional participant in DNA repair "all that glitters is not gold!". Photochem Photobiol 2011; 87:1230-9. [PMID: 21883247 DOI: 10.1111/j.1751-1097.2011.00995.x] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The phosphorylation of H2Ax on its S139 site, γH2Ax, is important for the assembly of repair complexes at DNA double strand breaks (DSBs). The formation and functional role of γH2Ax after other kinds of DNA damage, especially UV light, where DSBs are rare, is less clear. Following UV light in the UVB and UVC ranges, complex distributions of γH2Ax can be identified, quite unlike the discrete enumerable foci seen after ionizing radiation. Several distinct distributions of γH2Ax occur: a low level nuclear-wide distribution of γH2Ax occurs during nucleotide excision repair; irregular focal distributions occur at arrested replication forks; high intensity nuclear-wide γH2Ax occurs in association with S-phase apoptosis. The intensity and distributions of γH2Ax vary according to the activity of excision repair, bypass polymerase and apoptotic caspases. The frequency of DSBs at arrested replication forks is low but highly variable in different cell types, and probably caused by enzymatic action. Despite the prominence of S139 phosphorylation following UV damage, mutation of this site has no influence on the UV damage response indicating that γH2Ax is a biomarker but not a participant in the UV-DNA damage response.
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Affiliation(s)
- James E Cleaver
- Department of Dermatology, University of California, San Francisco, CA, USA.
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262
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Generation of reactive oxygen species during apoptosis induced by DNA-damaging agents and/or histone deacetylase inhibitors. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2011; 2011:253529. [PMID: 21949898 PMCID: PMC3178180 DOI: 10.1155/2011/253529] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Revised: 07/15/2011] [Accepted: 07/26/2011] [Indexed: 01/08/2023]
Abstract
Reactive oxygen species play an important role in the process of apoptosis in many cell types. In this paper, we analyzed the role of ROS in DNA-damaging agents (actinomycin D or decitabine), which induced apoptosis of leukemia cell line CML-T1 and normal peripheral blood lymphocytes (PBL). The possibility of synergism with histone deacetylase inhibitors butyrate or SAHA is also reported. We found that in cancer cell line, ROS production significantly contributed to apoptosis triggering, while in normal lymphocytes treated by cytostatic or cytotoxic drugs, necrosis as well as apoptosis occurred and large heterogeneity of ROS production was measured. Combined treatment with histone deacetylase inhibitor did not potentiate actinomycin D action, whereas combination of decitabine and SAHA brought synergistic ROS generation and apoptotic features in CML cell line. Appropriate decrease of cell viability indicated promising therapeutic potential of this combination in CML, but side effects on normal PBL should be taken into attention.
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263
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Wilson AJ, Holson E, Wagner F, Zhang YL, Fass DM, Haggarty SJ, Bhaskara S, Hiebert SW, Schreiber SL, Khabele D. The DNA damage mark pH2AX differentiates the cytotoxic effects of small molecule HDAC inhibitors in ovarian cancer cells. Cancer Biol Ther 2011; 12:484-93. [PMID: 21738006 DOI: 10.4161/cbt.12.6.15956] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
High grade epithelial ovarian cancers are relatively sensitive to DNA damaging platinum-based chemotherapy, suggesting that the dependencies of ovarian tumors on DNA damage response pathways can be harnessed for therapeutic purposes. Our goal was to determine if the DNA damage mark gamma-H2AX phosphorylation (pH2AX) could be used to identify suitable cytotoxic histone deacetylase inhibitors (HDACi) for ovarian cancer treatment. Nineteen chemically diverse HDACi compounds were tested in 7 ovarian cancer cell lines. Fluorescent, biochemical and cell-based assays were performed to assess DNA damage by induction of pH2AX and to measure cell viability and apoptosis. The relationships between pH2AX and the cellular effects of cell viability and apoptosis were calculated. Selected HDACi were tested in combination with cisplatin and other DNA damaging agents to determine if the HDACi improved upon the effects of the DNA damaging agents. The HDACi compounds induced differing levels of pH2AX expression. High levels of pH2AX in HDACi-treated ovarian cancer cells were tightly associated with decreased cell viability and increased apoptosis. Consequently, a ketone-based HDACi was chosen and found to enhance the effects of cisplatin, even in ovarian cancer cells with extreme resistance to DNA damaging drugs. In conclusion, a fluorescent-based assay for pH2AX can be used to determine cellular responses to HDACi in vitro and may be a useful tool to identify potentially more effective HDACi for the treatment of ovarian cancer. In addition, these results lend support to the inclusion of ketone-derived HDACi compounds for future development.
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Affiliation(s)
- Andrew J Wilson
- Vanderbilt University School of Medicine, Nashville, TN, USA
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264
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Spiegel S, Milstien S, Grant S. Endogenous modulators and pharmacological inhibitors of histone deacetylases in cancer therapy. Oncogene 2011; 31:537-51. [PMID: 21725353 DOI: 10.1038/onc.2011.267] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The class-I histone deacetylases (HDACs) HDAC1 and HDAC2 belong to a family of 11 zinc-dependent human HDACs and are overexpressed in many cancers. Inhibitors of these HDACs now in clinical trials show activity against several types of cancers. This review is focused on recent advances in both clinical and preclinical efforts to understand the basis for the actions of HDACis, with emphasis on implications for rational combinations with conventional or other targeted agents. We will address new perspectives on the molecular mechanisms by which HDACs act and how these actions relate to cancer. We will also review new evidence showing that HDACs are direct intracellular targets of the potent sphingolipid mediator S1P, the first identified endogenous nuclear regulator of these enzymes, linking sphingolipid metabolism in the nucleus to remodeling of chromatin and epigenetic regulation of gene expression. Understanding how endogenous molecules regulate HDAC activity in vivo may facilitate the search for safer and more effective anticancer drugs capable of interfering with HDAC functions in a highly specific manner.
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Affiliation(s)
- S Spiegel
- Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine Richmond, Richmond, VA 23298, USA.
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265
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Ouyang DY, Ji YH, Saltis M, Xu LH, Zhang YT, Zha QB, Cai JY, He XH. Valproic acid synergistically enhances the cytotoxicity of gossypol in DU145 prostate cancer cells: an iTRTAQ-based quantitative proteomic analysis. J Proteomics 2011; 74:2180-93. [PMID: 21726675 DOI: 10.1016/j.jprot.2011.06.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Revised: 05/31/2011] [Accepted: 06/15/2011] [Indexed: 12/01/2022]
Abstract
Gossypol (GOS), a BH3 mimetic, has been investigated as a sensitizing co-therapy to radiation and chemotherapy in treatment of metastatic prostate cancer. In this study, we found that valproic acid (VPA), a histone deacetylase inhibitor (HDACI), counteracted the suppressive effect of GOS on histone H3 acetylation and enhanced the cytotoxicity of GOS to DU145 prostate cancer cells. Significant synergistic effects were observed in combined GOS and VPA treatment, culminating in more DNA damage and cell death. The iTRAQ-based quantitative proteomic analysis revealed differential proteomic profiles in cells treated with VPA, GOS or their combination. In GOS-treated cells, oxidative phosphorylation-related proteins were depressed and endoplasmic reticulum stress markers were upregulated. In the presence of VPA, the GOS-induced mitochondrial stress was further enhanced since glycolysis- and hypoxia-associated proteins were upregulated, suggesting a disruption of energy metabolism in these cells. Furthermore, the DNA damage repair ability of cells co-treated with GOS and VPA was also decreased, as evidenced by the downregulation of DNA damage repair proteins and the enhancement of DNA fragmentation and cell death. These findings suggest that GOS in combination with an HDACI has the potential to increase its clinical efficacy in the treatment of prostate cancer.
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Affiliation(s)
- Dong-yun Ouyang
- Institute of Tissue Transplantation and Immunology, Jinan University, Guangzhou 510632, China
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266
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Functional relevance of the histone gammaH2Ax in the response to DNA damaging agents. Proc Natl Acad Sci U S A 2011; 108:8663-7. [PMID: 21555580 DOI: 10.1073/pnas.1105866108] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The phosphorylation of H2Ax on its S139 site, γH2Ax, is important during DNA double-strand repair and is considered necessary for assembly of repair complexes, but its functional role after other kinds of DNA damage is less clear. We have measured the survival of isogenic mouse cell lines with the H2Ax gene knocked out, and replaced with wild-type or mutant (S139A) H2Ax genes, exposed to a range of agents with varied mechanisms of DNA damage. Knockout and mutant cells were sensitive to γ-rays, etoposide, temozolamide, and endogenously generated reactive oxygen species, each of which can include double-strand breaks among their spectra of DNA lesions. The absence or mutation of H2Ax had no influence on sensitivity to cisplatin or mitomycin C. Although UV light induced the highest levels of γH2Ax, mutation of S139 had no influence on UV sensitivity or the UV DNA damage response. Complete loss of H2Ax reduced the survival of cells exposed to UV light and reduced pChk1 induction, suggesting that sites other than S139 may impact the ATR-pChk1 pathway. The relative intensity of γH2Ax measured in Western blots in wild-type cells did not correlate with the functional importance of γH2Ax. The use of γH2Ax as a general biomarker of DNA damage is therefore potentially misleading because it is not an unambiguous indicator of double-strand breaks, and a significant fraction of DNA repair, especially involving nucleotide excision or crosslink repair, can occur without functional involvement of γH2Ax.
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267
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Abstract
Histone deacetylase inhibitors represent a new class of anticancer therapeutics and the expectation is that they will be most effective when used in combination with conventional cancer therapies, such as the anthracycline, doxorubicin. The dose-limiting side effect of doxorubicin is severe cardiotoxicity and evaluation of the effects of combinations of the anthracycline with histone deacetylase inhibitors in relevant models is important. We used a well-established in vitro model of doxorubicin-induced hypertrophy to examine the effects of the prototypical histone deacetylase inhibitor, Trichostatin A. Our findings indicate that doxorubicin modulates the expression of the hypertrophy-associated genes, ventricular myosin light chain-2, the alpha isoform of myosin heavy chain and atrial natriuretic peptide, an effect which is augmented by Trichostatin A. Furthermore, we show that Trichostatin A amplifies doxorubicin-induced DNA double strand breaks, as assessed by γH2AX formation. More generally, our findings highlight the importance of investigating potential side effects that may be associated with emerging combination therapies for cancer.
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268
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Mueller S, Yang X, Sottero TL, Gragg A, Prasad G, Polley MY, Weiss WA, Matthay KK, Davidoff AM, DuBois SG, Haas-Kogan DA. Cooperation of the HDAC inhibitor vorinostat and radiation in metastatic neuroblastoma: efficacy and underlying mechanisms. Cancer Lett 2011; 306:223-9. [PMID: 21497989 DOI: 10.1016/j.canlet.2011.03.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 03/06/2011] [Accepted: 03/16/2011] [Indexed: 11/16/2022]
Abstract
Histone deacetylase (HDAC) inhibitors can radiosensitize cancer cells. Radiation is critical in high-risk neuroblastoma treatment, and combinations of HDAC inhibitor vorinostat and radiation are proposed for neuroblastoma trials. Therefore, we investigated radiosensitizing effects of vorinostat in neuroblastoma. Treatment of neuroblastoma cell lines decreased cell viability and resulted in additive effects with radiation. In a murine metastatic neuroblastoma in vivo model vorinostat and radiation combinations decreased tumor volumes compared to single modality. DNA repair enzyme Ku-86 was reduced in several neuroblastoma cells treated with vorinostat. Thus, vorinostat potentiates anti-neoplastic effects of radiation in neuroblastoma possibly due to down-regulation of DNA repair enzyme Ku-86.
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Affiliation(s)
- Sabine Mueller
- Department of Neurology, University of California, San Francisco, 505 Parnassus Avenue, San Francisco, CA 94143-0106, USA.
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269
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Nguyen T, Dai Y, Attkisson E, Kramer L, Jordan N, Nguyen N, Kolluri N, Muschen M, Grant S. HDAC inhibitors potentiate the activity of the BCR/ABL kinase inhibitor KW-2449 in imatinib-sensitive or -resistant BCR/ABL+ leukemia cells in vitro and in vivo. Clin Cancer Res 2011; 17:3219-32. [PMID: 21474579 DOI: 10.1158/1078-0432.ccr-11-0234] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
PURPOSE The purpose of this study was to determine whether histone deacetylase (HDAC) inhibitors (HDACI) such as vorinostat or entinostat (SNDX-275) could increase the lethality of the dual Bcr/Abl-Aurora kinase inhibitor KW-2449 in various Bcr/Abl(+) human leukemia cells, including those resistant to imatinib mesylate (IM). EXPERIMENTAL DESIGN Bcr/Abl(+) chronic myelogenous leukemia (CML) and acute lymphoblastic leukemia (ALL) cells, including those resistant to IM (T315I, E255K), were exposed to KW-2449 in the presence or absence of vorinostat or SNDX-275, after which apoptosis and effects on signaling pathways were examined. In vivo studies combining HDACIs and KW2449 were carried out by using a systemic IM-resistant ALL xenograft model. RESULTS Coadministration of HDACIs synergistically increased KW-2449 lethality in vitro in multiple CML and Ph(+) ALL cell types including human IM resistant cells (e.g., BV-173/E255K and Adult/T315I). Combined treatment resulted in inactivation of Bcr/Abl and downstream targets (e.g., STAT5 and CRKL), as well as increased reactive oxygen species (ROS) generation and DNA damage (γH2A.X). The latter events and cell death were significantly attenuated by free radical scavengers (TBAP). Increased lethality was also observed in primary CD34(+) cells from patients with CML, but not in normal CD34(+) cells. Finally, minimally active vorinostat or SNDX275 doses markedly increased KW2449 antitumor effects and significantly prolonged the survival of murine xenografts bearing IM-resistant ALL cells (BV173/E255K). CONCLUSIONS HDACIs increase KW-2449 lethality in Bcr/Abl(+) cells in association with inhibition of Bcr/Abl, generation of ROS, and induction of DNA damage. This strategy preferentially targets primary Bcr/Abl(+) hematopoietic cells and exhibits enhanced in vivo activity. Combining KW-2449 with HDACIs warrants attention in IM-resistant Bcr/Abl(+) leukemias.
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Affiliation(s)
- Tri Nguyen
- Division of Hematology/Oncology, Department of Biochemistry, and Massey Cancer Center, Virginia Commonwealth University Health Sciences Center, Richmond, Virginia 23298, USA
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270
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Chen Q, Ouyang DY, Geng M, Xu LH, Zhang YT, Wang FP, He XH. Valproic acid exhibits biphasic effects on apoptotic cell death of activated lymphocytes through differential modulation of multiple signaling pathways. J Immunotoxicol 2011; 8:210-8. [PMID: 21457087 DOI: 10.3109/1547691x.2011.568979] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, possesses potent anti-tumor activity against a variety of malignant cells. However, its action on lymphocytes and the underlying mechanism are not completely understood. In this study, we aimed to analyze the effects of VPA on the proliferation, activation, and apoptosis of murine lymphocytes activated with concanavalin A (ConA). Our results showed that VPA inhibited the proliferation of ConA-activated lymphocytes in a dose-dependent manner. Low-dose VPA (≤ 1.1 mM) enhanced CD69 expression on the activated lymphocytes, whereas at high doses (≥ 3.3 mM) it decreased CD69 expression. Furthermore, VPA reduced activation-induced apoptotic cell death at low doses, but at high doses it promoted apoptotic cell death of activated lymphocytes dramatically. It was found that the Bax/Bcl-2 ratio and phosphorylation of histone H2A.X was decreased at low doses of VPA but was increased at high doses. The phosphorylation of STAT3 was also differentially regulated by different doses of VPA. VPA, at 5 mM induced the phosphorylation of p38 but not JNK and extracellular signal-regulated kinase (ERK)1/2. In addition, VPA induced a dose-dependent increase in the acetylation of histone H3. These results demonstrate that VPA exhibits dose-dependent biphasic effect on apoptosis of activated lymphocytes probably through differential modulation of several apoptosis-related signaling pathways.
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Affiliation(s)
- Qing Chen
- Institute of Tissue Transplantation and Immunology, Jinan University, Guangzhou, P.R. China
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271
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Histone deacetylase 6 and heat shock protein 90 control the functions of Foxp3(+) T-regulatory cells. Mol Cell Biol 2011; 31:2066-78. [PMID: 21444725 DOI: 10.1128/mcb.05155-11] [Citation(s) in RCA: 203] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Foxp3(+) T-regulatory cells (Tregs) are key to immune homeostasis such that their diminished numbers or function can cause autoimmunity and allograft rejection. Foxp3(+) Tregs express multiple histone/protein deacetylases (HDACs) that regulate chromatin remodeling, gene expression, and protein function. Pan-HDAC inhibitors developed for oncologic applications enhance Treg production and Treg suppression function but have limited nononcologic utility given their broad actions and various side effects. We show, using HDAC6-deficient mice and wild-type (WT) mice treated with HDAC6-specific inhibitors, that HDAC6 inhibition promotes Treg suppressive activity in models of inflammation and autoimmunity, including multiple forms of experimental colitis and fully major histocompatibility complex (MHC)-incompatible cardiac allograft rejection. Many of the beneficial effects of HDAC6 targeting are also achieved by inhibition of the HDAC6-regulated protein heat shock protein 90 (HSP90). Hence, selective targeting of a single HDAC isoform, HDAC6, or its downstream target, HSP90, can promote Treg-dependent suppression of autoimmunity and transplant rejection.
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272
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Dai Y, Chen S, Wang L, Pei XY, Kramer LB, Dent P, Grant S. Bortezomib interacts synergistically with belinostat in human acute myeloid leukaemia and acute lymphoblastic leukaemia cells in association with perturbations in NF-κB and Bim. Br J Haematol 2011; 153:222-35. [PMID: 21375523 DOI: 10.1111/j.1365-2141.2011.08591.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Interactions between the histone deacetylase inhibitor belinostat and the proteasome inhibitor bortezomib were investigated in acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL) cells. Co-administration of sub-micromolar concentrations of belinostat with low nanomolar concentrations of bortezomib sharply increased apoptosis in both AML and ALL cell lines and primary blasts. Synergistic interactions were associated with interruption of both canonical and non-canonical nuclear factor (NF)-κB signalling pathways, e.g. accumulation of the phosphorylated (S32/S36) form of IκBα, diminished belinostat-mediated RelA/p65 hyperacetylation (K310), and reduced processing of p100 into p52. These events were accompanied by down-regulation of NF-κB-dependent pro-survival proteins (e.g. XIAP, Bcl-xL). Moreover, belinostat/bortezomib co-exposure induced up-regulation of the BH3-only pro-death protein Bim. Significantly, shRNA knock-down of Bim substantially reduced the lethality of belinostat/bortezomib regimens. Administration of belinostat ± bortezomib also induced hyperacetylation (K40) of α-tubulin, indicating histone deacetylase inhibitor 6 inhibition. Finally, in contrast to the pronounced lethality of belinostat/bortezomib toward primary leukaemia blasts, equivalent treatment was relatively non-toxic to normal CD34(+) cells. Together, these findings indicate that belinostat and bortezomib interact synergistically in both cultured and primary AML and ALL cells, and raise the possibilities that up-regulation of Bim and interference with NF-κB pathways contribute to this phenomenon. They also suggest that combined belinostat/bortezomib regimens warrant further attention in acute leukaemias.
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Affiliation(s)
- Yun Dai
- Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University and the Massey Cancer Center, VCU Health Sciences Center, 401 College Street, Richmond, VA 23298, USA
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273
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Iwamoto FM, Lamborn KR, Kuhn JG, Wen PY, Yung WKA, Gilbert MR, Chang SM, Lieberman FS, Prados MD, Fine HA. A phase I/II trial of the histone deacetylase inhibitor romidepsin for adults with recurrent malignant glioma: North American Brain Tumor Consortium Study 03-03. Neuro Oncol 2011; 13:509-16. [PMID: 21377994 DOI: 10.1093/neuonc/nor017] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Romidepsin, a potent histone deacetylase inhibitor, has shown activity in preclinical glioma models. The primary objectives of this trial were to determine the pharmacokinetics of romidepsin in patients with recurrent glioma on enzyme-inducing antiepileptic drugs (EIAEDs) and to evaluate the antitumor efficacy of romidepsin in patients with recurrent glioblastoma who were not receiving EIAEDs. Two dose cohorts were studied in the phase I component of the trial (13.3 and 17.7 mg/m(2)/d). Patients in the phase II component were treated with intravenous romidepsin at a dosage of 13.3 mg/m(2)/day on days 1, 8, and 15 of each 28-day cycle. Eight patients were treated on the phase I component. A similar romidepsin pharmacokinetic profile was demonstrated between patients receiving EIAEDs to those not receving EIAEDs. Thirty-five patients with glioblastoma were accrued to the phase II component. There was no objective radiographic response. The median progression-free survival (PFS) was 8 weeks and only 1 patient had a PFS time ≥6 months (PFS6 = 3%). To date, 34 patients (97%) have died, with a median survival duration of 34 weeks. Despite in vitro studies showing that romidepsin is primarily metabolized by CYP3A4, no decrease in exposure to romidepsin was seen in patients receiving potent CYP3A4 inducers. Romidepsin, at its standard dose and schedule, was ineffective for patients with recurrent glioblastomas. ClinicalTrials.gov identifier: NCT00085540.
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Affiliation(s)
- Fabio M Iwamoto
- Neuro-Oncology Branch, National Cancer Institute, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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274
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Zhou X, Hua X, Ding X, Bian Y, Wang X. Trichostatin Differentially Regulates Th1 and Th2 Responses and Alleviates Rheumatoid Arthritis in Mice. J Clin Immunol 2011; 31:395-405. [DOI: 10.1007/s10875-011-9508-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2010] [Accepted: 01/19/2011] [Indexed: 12/21/2022]
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275
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Thurn KT, Thomas S, Moore A, Munster PN. Rational therapeutic combinations with histone deacetylase inhibitors for the treatment of cancer. Future Oncol 2011; 7:263-83. [PMID: 21345145 PMCID: PMC3127396 DOI: 10.2217/fon.11.2] [Citation(s) in RCA: 188] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Histone deacetylases (HDACs) regulate the acetylation of a variety of histone and nonhistone proteins, controlling the transcription and regulation of genes involved in cell cycle control, proliferation, survival, DNA repair and differentiation. Unsurprisingly, HDAC expression is frequently altered in hematologic and solid tumor malignancies. Two HDAC inhibitors (vorinostat and romidepsin) have been approved by the US FDA for the treatment of cutaneous T-cell lymphoma. As single agents, treatment with HDAC inhibitors has demonstrated limited clinical benefit for patients with solid tumors, prompting the investigation of novel treatment combinations with other cancer therapeutics. In this article, the rationales and clinical progress of several combinations with HDAC inhibitors are presented, including DNA-damaging chemotherapeutic agents, radiotherapy, hormonal therapies, DNA methyltransferase inhibitors and various small-molecule inhibitors. The future application of HDAC inhibitors as a treatment for cancer is discussed, examining current hurdles to overcome before realizing the potential of this new approach.
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Affiliation(s)
- K Ted Thurn
- Department of Medicine, Hematology/Oncology Division. University of California, San Francisco, CA, USA
| | - Scott Thomas
- Department of Medicine, Hematology/Oncology Division. University of California, San Francisco, CA, USA
| | - Amy Moore
- Department of Medicine, Hematology/Oncology Division. University of California, San Francisco, CA, USA
| | - Pamela N Munster
- Department of Medicine, Hematology/Oncology Division. University of California, San Francisco, CA, USA
- Author for correspondence: 1600 Divisadero St, Room A722, Box 1770, San Francisco, CA 94115, USA Tel.: +1 415 885 7810 Fax: +1 415 353 7779
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276
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Bountra C, Oppermann U, Heightman TD. Animal models of epigenetic regulation in neuropsychiatric disorders. Curr Top Behav Neurosci 2011; 7:281-322. [PMID: 21225415 DOI: 10.1007/7854_2010_104] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Epigenetics describes the phenomenon of heritable changes in gene regulation that are governed by non-Mendelian processes, primarily through biochemical modifications to chromatin structure that occur during cell development and differentiation. Numerous lines of evidence link abnormal levels of chromatin modifications (either to DNA, histones, or both) in patients with a wide variety of diseases including cancer, psychiatry, neurodegeneration, metabolic and inflammatory disorders. Drugs that target the proteins controlling chromatin modifications can modulate the expression of clusters of genes, potentially offering higher therapeutic efficacy than classical agents with single target pharmacologies that are susceptible to biochemical pathway degeneracy. Here, we summarize recent research linking epigenetic dysregulation with diseases in neurosciences, the application of relevant animal models, and the potential for small molecule modulator development to facilitate target discovery, validation and translation into clinical treatments.
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Affiliation(s)
- Chas Bountra
- Structural Genomics Consortium, University of Oxford, Oxford, OX3 7DQ, UK,
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277
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Lopez G, Torres K, Liu J, Hernandez B, Young E, Belousov R, Bolshakov S, Lazar AJ, Slopis JM, McCutcheon IE, McConkey D, Lev D. Autophagic survival in resistance to histone deacetylase inhibitors: novel strategies to treat malignant peripheral nerve sheath tumors. Cancer Res 2010; 71:185-96. [PMID: 21084276 DOI: 10.1158/0008-5472.can-10-2799] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Histone deacetylase inhibitors (HDACi) show promise as cancer therapeutics; however, the full scope of their utility remains unknown. Here we report findings that strongly rationalize clinical evaluation of HDACis in malignant peripheral nerve sheath tumors (MPNST), a class of highly aggressive, therapeutically resistant, and commonly fatal malignancies that occur sporadically or in patients with the inherited neurofibromatosis type-1 (NF1) syndrome. We evaluated the effects of the chemical HDACis PCI-24781, suberoylanilide hydroxamic acid, and MS-275 on a panel of human NF1-associated and sporadic MPNSTs in vitro and in vivo. A subset of MPNSTs was found to be highly sensitive to HDACis, especially to PCI-24781. All cell lines in this group were NF1-associated. Significant proapoptotic effects were noted in vitro and in vivo and were independent of p53 mutational status. In contrast, as a group the sporadic-MPNST cells were markedly resistant to HDACi treatment. HDACis were found to induce productive autophagy in MPNST cells. Genetic and/or pharmacologic autophagy blockade resulted in significant HDACi-induced apoptosis in cells defined as resistant or sensitive, leading to abrogated growth of primary tumors and lung metastases in tumor xenograft assays. Among autophagy-associated genes expressed in response to HDACi, the immunity-related GTPase family, M was validated as a critical target in mediating HDACi-induced autophagy and enhanced apoptosis. Taken together, our findings strongly support the evaluation of HDACi currently in clinical trials as an important new therapeutic strategy to treat MPNST, including in combination with autophagy blocking combination regimens in particular for patients with sporadic MPNST.
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Affiliation(s)
- Gonzalo Lopez
- Department of Cancer Biology, University of Texas, MD Anderson Cancer Center, Houston, Texas 77030, USA
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