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Ruiz FM, Gil-Redondo R, Morreale A, Ortiz ÁR, Fábrega C, Bravo J. Structure-Based Discovery of Novel Non-nucleosidic DNA Alkyltransferase Inhibitors: Virtual Screening and in Vitro and in Vivo Activities. J Chem Inf Model 2008; 48:844-54. [DOI: 10.1021/ci700447r] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Federico M. Ruiz
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
| | - Rubén Gil-Redondo
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
| | - Antonio Morreale
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
| | - Ángel R. Ortiz
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
| | - Carmen Fábrega
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
| | - Jerónimo Bravo
- Signal Transduction Group, Structural Biology and Biocomputing Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Melchor Fernández Almagro 3, E-28029 Madrid, Spain, and Bioinformatics Unit, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónma de Madrid, Nicolás Cabrera, 1. Cantoblanco, 28049 Madrid, Spain
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102
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Akbari M, Krokan HE. Cytotoxicity and mutagenicity of endogenous DNA base lesions as potential cause of human aging. Mech Ageing Dev 2008; 129:353-65. [PMID: 18355895 DOI: 10.1016/j.mad.2008.01.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 01/25/2008] [Accepted: 01/28/2008] [Indexed: 11/26/2022]
Abstract
Endogenous factors constitute a substantial source of damage to the genomic DNA. The type of damage includes a number of different base lesions and single- and double-strand breaks. Unrepaired DNA damage can give rise to mutations and may cause cell death. A number of studies have demonstrated an association between aging and the accumulation of DNA damage. This may be attributed to reduced DNA repair with age, although this is apparently not a general feature for all types of damage and repair mechanisms. Therefore, detailed studies that improve our knowledge of DNA repair systems as well as mutagenic and toxic effects of DNA lesions will help us to gain a better insight into the mechanisms of aging. The aim of this review is to provide a brief description of cytotoxic and mutagenic endogenous DNA lesions that are mainly repaired by base excision repair and single-strand break repair pathways and to discuss the potential role of DNA lesions and DNA repair dysfunction in the onset of human aging.
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Affiliation(s)
- Mansour Akbari
- Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
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103
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Coulter R, Blandino M, Tomlinson JM, Pauly GT, Krajewska M, Moschel RC, Peterson LA, Pegg AE, Spratt TE. Differences in the rate of repair of O6-alkylguanines in different sequence contexts by O6-alkylguanine-DNA alkyltransferase. Chem Res Toxicol 2007; 20:1966-71. [PMID: 17975884 DOI: 10.1021/tx700271j] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
O6-alkylguanine-DNA alkyltransferase (AGT) repairs O6-alkylguanine residues at different rates depending on the identity of the alkyl group as well as the sequence context. To elucidate the mechanism(s) underlying the differences in rates, we examined the repair of five alkyl groups in three different sequence contexts. The kinact and Km values were determined by measuring the rates of repair of oligodeoxynucleotide duplexes containing the O6-alkylguanine residues with various concentrations of AGT in excess. The time course of the reactions all followed pseudo-first-order kinetics except for one of the O6-ethylguanine substrates, which could be analyzed in a two-phase exponential equation. The differences in rates of repair between the different alkyl groups and the different sequence contexts are dependent on rates of alkyl transfer and not substrate recognition. The relative rates of reaction are in general benzyl>methyl>ethyl>2-hydroxyethyl>4-(3-pyridyl)-4-oxobutyl, but the absolute rates are dependent on sequence. The kinact values between benzyl and 4-(3-pyridyl)-4-oxobutyl range from 2300 to 350000 depending on sequence. The sequence-dependent variation in kinact varied the most for O6-[4-(3-pyridyl)-4-oxobutyl]guanine, which ranged from 0.022 to 0.000016 s(-1). The results are consistent with a mechanism in which the O6-alkylguanine can bind to AGT in either a reactive or an unreactive orientation, the proportion of which depends on the sequence context.
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Affiliation(s)
- Richard Coulter
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
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104
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Bugni JM, Han J, Tsai MS, Hunter DJ, Samson LD. Genetic association and functional studies of major polymorphic variants of MGMT. DNA Repair (Amst) 2007; 6:1116-26. [PMID: 17569599 DOI: 10.1016/j.dnarep.2007.03.023] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The DNA repair protein, O(6)-methylguanine DNA-methyltransferase (MGMT) prevents mutations and cell death that result from aberrant alkylation of DNA. The polymorphic variants Leu84Phe, Ile143Val, and Lys178Arg are frequent in the human population. We review here studies of these and other MGMT polymorphisms and their association with risk for lung, breast, colorectal and endometrial cancer with a consideration of gene-environment interactions. In addition, we review studies of the effects of polymorphic variation on alkyltransferase activity and expression. It is formally possible that polymorphic variation could modify functions of MGMT other than its alkyltransferase activity. While it was previously reported that an alkylated form of MGMT modifies Estrogen Receptor alpha activity, from our studies we conclude that this regulation is not a major function of MGMT. Overall, the effects of polymorphic variation on protein function are subtle, and further investigation is required to provide a comprehensive mechanism that explains the observed associations of these variants with risk for cancer.
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Affiliation(s)
- James M Bugni
- Biological Engineering Division, Biology Department, and Center for Environmental Health Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
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105
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Abstract
This article summarizes the current understanding of known variant forms of the MGMT gene that encode an altered protein. Epidemiological studies have been carried out to test whether these alterations are associated with altered cancer risk. Laboratory studies using recombinant proteins and cells expressing the known variants have investigated the possible effects of these sequence alterations on the ability of the encoded O(6)-alkylguanine-DNA alkyltransferase protein to protect cells from alkylation damage and to respond to therapeutic inactivators currently undergoing trials for cancer chemotherapy.
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Affiliation(s)
- Anthony E Pegg
- Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
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106
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Tubbs JL, Pegg AE, Tainer JA. DNA binding, nucleotide flipping, and the helix-turn-helix motif in base repair by O6-alkylguanine-DNA alkyltransferase and its implications for cancer chemotherapy. DNA Repair (Amst) 2007; 6:1100-15. [PMID: 17485252 PMCID: PMC1993358 DOI: 10.1016/j.dnarep.2007.03.011] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
O(6)-Alkylguanine-DNA alkyltransferase (AGT) is a crucial target both for the prevention of cancer and for chemotherapy, since it repairs mutagenic lesions in DNA, and it limits the effectiveness of alkylating chemotherapies. AGT catalyzes the unique, single-step, direct damage reversal repair of O(6)-alkylguanines by selectively transferring the O(6)-alkyl adduct to an internal cysteine residue. Recent crystal structures of human AGT alone and in complex with substrate DNA reveal a two-domain alpha/beta fold and a bound zinc ion. AGT uses its helix-turn-helix motif to bind substrate DNA via the minor groove. The alkylated guanine is then flipped out from the base stack into the AGT active site for repair by covalent transfer of the alkyl adduct to Cys145. An asparagine hinge (Asn137) couples the helix-turn-helix DNA binding and active site motifs. An arginine finger (Arg128) stabilizes the extrahelical DNA conformation. With this newly improved structural understanding of AGT and its interactions with biologically relevant substrates, we can now begin to unravel the role it plays in preserving genetic integrity and discover how it promotes resistance to anticancer therapies.
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Affiliation(s)
- Julie L. Tubbs
- The Scripps Research Institute, The Skaggs Institute for Chemical Biology and Department of Molecular Biology, 10550 North Torrey Pines Road, MB4, La Jolla, CA 92037
| | - Anthony E. Pegg
- Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - John A. Tainer
- The Scripps Research Institute, The Skaggs Institute for Chemical Biology and Department of Molecular Biology, 10550 North Torrey Pines Road, MB4, La Jolla, CA 92037
- Life Sciences Division, Department of Molecular Biology, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- *To whom correspondence should be addressed: Tel: +1-858-784-8119; fax: +1-858-784-2289;
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107
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Kaina B, Christmann M, Naumann S, Roos WP. MGMT: key node in the battle against genotoxicity, carcinogenicity and apoptosis induced by alkylating agents. DNA Repair (Amst) 2007; 6:1079-99. [PMID: 17485253 DOI: 10.1016/j.dnarep.2007.03.008] [Citation(s) in RCA: 443] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
O(6)-methylguanine-DNA methyltransferase (MGMT) plays a crucial role in the defense against alkylating agents that generate, among other lesions, O(6)-alkylguanine in DNA (collectively termed O(6)-alkylating agents [O(6)AA]). The defense is highly important, since O(6)AA are common environmental carcinogens, are formed endogenously during normal cellular metabolism and possibly inflammation, and are being used in cancer therapy. O(6)AA induced DNA damage is subject to repair, which is executed by MGMT, AlkB homologous proteins (ABH) and base excision repair (BER). Although this review focuses on MGMT, the mechanism of repair by ABH and BER will also be discussed. Experimental systems, in which MGMT has been modulated, revealed that O(6)-methylguanine (O(6)MeG) and O(6)-chloroethylguanine are major mutagenic, carcinogenic, recombinogenic, clastogenic and killing lesions. O(6)MeG-induced clastogenicity and cell death require MutS alpha-dependent mismatch repair (MMR), whereas O(6)-chloroethylguanine-induced killing occurs independently of MMR. Extensive DNA replication is required for O(6)MeG to provoke cytotoxicity. In MGMT depleted cells, O(6)MeG induces apoptosis almost exclusively, barely any necrosis, which is presumably due to the remarkable ability of secondarily formed DNA double-strand breaks (DSBs) to trigger apoptosis via ATM/ATR, Chk1, Chk2, p53 and p73. Depending on the cellular background, O(6)MeG activates both the death receptor and the mitochondrial apoptotic pathway. The inter-individual expression of MGMT in human lymphocytes is highly variable. Given the key role of MGMT in cellular defense, determination of MGMT activity could be useful for assessing a patient's drug sensitivity. MGMT is expressed at highly variable amounts in human tumors. In gliomas, a correlation was found between MGMT activity, MGMT promoter methylation and response to O(6)AA. Although the human MGMT gene is inducible by glucocorticoids and genotoxins such as radiation and alkylating agents, the role of this induction in the protection against carcinogens and the development of chemotherapeutic alkylating drug resistance are still unclear. Modulation of MGMT expression in tumors and normal tissue is currently being investigated as a possible strategy for improving cancer therapy.
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Affiliation(s)
- Bernd Kaina
- Department of Toxicology, University of Mainz, Obere Zahlbacher Str. 67, D-55131 Mainz, Germany.
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108
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Johnson SP, Kamen BA, Bigner DD, Friedman HS. O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines. Cancer Chemother Pharmacol 2007; 60:883-9. [PMID: 17333191 DOI: 10.1007/s00280-007-0435-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Accepted: 02/02/2007] [Indexed: 11/25/2022]
Abstract
PURPOSE The DNA repair protein, O (6)-alkylguanine-DNA alkyltransferase (AGT), is a primary source of tumor resistance to agents such as temozolomide and chloroethylnitrosoureas that form DNA lesions at the O (6)-position of guanines. To increase the efficacy of these drugs, pseudosubstrate inactivators of AGT such as O (6)-benzylguanine have been developed. A novel inactivator of AGT, O (4)-benzylfolic acid (O(4)-BFA), has been reported which is more potent and water soluble than O (6)-benzylguanine. Previous studies have suggested that uptake of O(4)-BFA is mediated by the folate receptor (FR), and, thus, its use may be limited to cells expressing FR. METHODS We measured AGT activity in cell extracts from a panel of brain tumor cells exposed to O(4)-BFA. Inactivation of AGT by O(4)-BFA was measured in cells grown without folic acid as well as in cells grown in folic acid-containing media. Competitive binding studies were performed using purified FR to determine its affinity for O(4)-BFA. RESULTS The observed IC(50) for O(4)-BFA in brain tumor cell lines ranged from 0.2 to 1.3 microM for cells grown in media containing 2.3 microM folic acid. At this concentration, folic acid would saturate the FR and the FR would be unable to take up O(4)-BFA. When cells were grown in folic acid free media, there was at most a 50% decrease in the observed IC(50)s, indicating that the FR was not essential for O(4)-BFA uptake. Competitive binding studies using purified FR confirmed that the IC(50) for O(4)-BFA is approximately 180 times greater than folic acid, i.e., it has a very weak affinity for FR. CONCLUSION These results indicate that O(4)-BFA has potentially broad use as an inactivator of AGT as its use is not limited to tumors expressing high levels of FR.
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Affiliation(s)
- Stewart P Johnson
- Department of Surgery, Duke University Medical Center, Box 2616, Durham, NC 27710, USA.
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109
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Rasimas JJ, Kar SR, Pegg AE, Fried MG. Interactions of human O6-alkylguanine-DNA alkyltransferase (AGT) with short single-stranded DNAs. J Biol Chem 2007; 282:3357-66. [PMID: 17138560 PMCID: PMC1941669 DOI: 10.1074/jbc.m608876200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The O6-alkylguanine-DNA alkyltransferase (AGT) repairs O6-alkylguanine and O4-alkylthymine adducts in single-stranded and duplex DNAs. Here we characterize the binding of AGT to single-stranded DNAs ranging in length from 5 to 78 nucleotides (nt). Binding is moderately cooperative (37.9 +/- 3.0
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Affiliation(s)
- Joseph J. Rasimas
- Department of Molecular Physiology, Penn State University
College of Medicine, Hershey, PA 17033 and
| | - Sambit R. Kar
- Department of Molecular Physiology, Penn State University
College of Medicine, Hershey, PA 17033 and
- Department of Molecular and Cellular Biochemistry and Center
for Structural Biology, University of Kentucky, Lexington, KY 40536
| | - Anthony E. Pegg
- Department of Molecular Physiology, Penn State University
College of Medicine, Hershey, PA 17033 and
| | - Michael G. Fried
- Department of Molecular and Cellular Biochemistry and Center
for Structural Biology, University of Kentucky, Lexington, KY 40536
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110
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Mijal RS, Kanugula S, Vu CC, Fang Q, Pegg AE, Peterson LA. DNA sequence context affects repair of the tobacco-specific adduct O(6)-[4-Oxo-4-(3-pyridyl)butyl]guanine by human O(6)-alkylguanine-DNA alkyltransferases. Cancer Res 2006; 66:4968-74. [PMID: 16651455 DOI: 10.1158/0008-5472.can-05-3803] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT) protects cells from the mutagenic and carcinogenic effects of alkylating agents by removing O(6)-alkylguanine adducts from DNA. Recently, we established that AGT protects against the mutagenic effects of pyridyloxobutylation resulting from the metabolic activation of the tobacco-specific nitrosamines (TSNA) 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and N-nitrosonornicotine by repairing O(6)-[4-oxo-4-(3-pyridyl)butyl]guanine (O(6)-pobG). There have been several epidemiologic studies examining the association between the I143V/K178R AGT genotype and lung cancer risk. Two studies have found positive associations, suggesting that AGT proteins differ in their repair of DNA damage caused by TSNA. However, it is not known how this genotype alters the biochemical activity of AGT. We proposed that AGT proteins may differ in their ability to remove large O(6)-alkylguanine adducts, such as O(6)-pobG, from DNA. Therefore, we examined the repair of O(6)-pobG by wild-type (WT) human, I143V/K178R, and L84F AGT proteins when contained in multiple sequence contexts, including the twelfth codon of H-ras, a mutational hotspot within this oncogene. The AGT-mediated repair of O(6)-pobG was more profoundly influenced by sequence context than that of O(6)-methylguanine. These differences are not the result of secondary structure (hairpin) formation in DNA. In addition, the I143V/K178R variant seems less sensitive to the effects of sequence context than the WT or L84F proteins. These studies indicate that the sequence dependence of O(6)-pobG repair by human AGT (hAGT) varies with subtle changes in protein structure. These data establish a novel functional difference between the I143V/K178R protein and other hAGTs in the repair of a toxicologically relevant substrate, O(6)-pobG.
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Affiliation(s)
- Renée S Mijal
- Division of Environmental Health Sciences and The Cancer Center, University of Minnesota, Minneapolis, Minnesota 55455, USA
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111
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Tentori L, Leonetti C, Scarsella M, Muzi A, Mazzon E, Vergati M, Forini O, Lapidus R, Xu W, Dorio AS, Zhang J, Cuzzocrea S, Graziani G. Inhibition of poly(ADP-ribose) polymerase prevents irinotecan-induced intestinal damage and enhances irinotecan/temozolomide efficacy against colon carcinoma. FASEB J 2006; 20:1709-11. [PMID: 16809434 DOI: 10.1096/fj.06-5916fje] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Poly(ADP-ribose) polymerase (PARP) inhibitors enhance the antitumor activity of the topoisomerase I inhibitor irinotecan (CPT-11), which is used to treat advanced colorectal carcinoma. Since PARP inhibitors sensitize tumor cells also to the methylating agent temozolomide (TMZ) and clinical trials are evaluating CPT-11 in combination with TMZ, we tested whether the PARP inhibitor GPI 15427 (10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one) increases the efficacy of CPT-11 + TMZ against colon cancer. Moreover, due to the ability of PARP inhibitors to avoid cell death consequent to PARP-1 overactivation, we evaluated whether oral administration of GPI 15427 provides protection from the dose-limiting intestinal toxicity of CPT-11. The results of colony formation assay indicated that GPI 15427 increased the antiproliferative effects (combination index <1) of TMZ + SN-38 (the active metabolite of CPT-11) against colon cancer cells. Accordingly, GPI 15427 (40 mg/kg/dayx5 days per os) in combination with TMZ (10 mg/kg/dayx5 days) + CPT-11 (4 mg/kg/dayx5 days) significantly reduced the growth of tumor xenografts. Oral administration of GPI 15427 (40 mg/kg/q2x3 days) prevented intestinal injury and diarrhea induced by CPT-11 (30 mg/kg/day x 3 days) reducing inflammation and PARP-1 overactivation, as evidenced by immunohistochemical staining of intestinal tissue with antipoly(ADP-ribose) antibody (Ab). In conclusion, the PARP inhibitor represents a novel strategy to enhance the antitumor efficacy and reduce toxicity of chemotherapy in colon cancer.
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Affiliation(s)
- Lucio Tentori
- Department of Neuroscience, University of Rome Tor Vergata, Via Montpellier 1, Rome 00133, Italy
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112
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Affiliation(s)
- Yukiko Mishina
- Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637
| | - Erica M. Duguid
- Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637
| | - Chuan He
- Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637
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113
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Rasimas JJ, Dalessio PA, Ropson IJ, Pegg AE, Fried MG. Active-site alkylation destabilizes human O6-alkylguanine DNA alkyltransferase. Protein Sci 2004; 13:301-5. [PMID: 14691244 PMCID: PMC2286524 DOI: 10.1110/ps.03319404] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
O(6)-alkylguanine-DNA alkyltransferase (AGT) repairs pro-mutagenic O(6)-alkylguanine and O(4)-alkylthymine lesions in DNA. The alkylated form of the protein is not reactivated; instead, it is rapidly ubiquitinated and degraded. Here, we show that alkylation destabilizes the native fold of the protein by 0.5-1.2 kcal/mole and the DNA-binding function by 0.8-1.4 kcal/mole. On this basis, we propose that destabilization of the native conformational ensemble acts as a signal for ubiquitination.
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Affiliation(s)
- Joseph J Rasimas
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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114
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Keppler A, Pick H, Arrivoli C, Vogel H, Johnsson K. Labeling of fusion proteins with synthetic fluorophores in live cells. Proc Natl Acad Sci U S A 2004; 101:9955-9. [PMID: 15226507 PMCID: PMC454197 DOI: 10.1073/pnas.0401923101] [Citation(s) in RCA: 330] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2004] [Indexed: 11/18/2022] Open
Abstract
A general approach for the sequential labeling of fusion proteins of O(6)-alkylguanine-DNA alkyltransferase (AGT) with different fluorophores in mammalian cells is presented. AGT fusion proteins with different localizations in the cell can be labeled specifically with different fluorophores, and the fluorescence labeling can be used for applications such as multicolor analysis of dynamic processes and fluorescence resonance energy transfer measurements. The facile access to a variety of different AGT substrates as well as the specificity of the labeling reaction should make the approach an important tool to study protein function in live cells.
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Affiliation(s)
- Antje Keppler
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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115
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Hernandez-Pigeon H, Laurent G, Humbert O, Salles B, Lautier D. Degadration of mismatch repair hMutSalpha heterodimer by the ubiquitin-proteasome pathway. FEBS Lett 2004; 562:40-4. [PMID: 15043999 DOI: 10.1016/s0014-5793(04)00181-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2003] [Revised: 01/30/2004] [Accepted: 02/16/2004] [Indexed: 11/24/2022]
Abstract
Mismatch repair plays a critical role in genome stability. This process requires several proteins including hMSH2/hMSH6 (hMutSalpha) heterodimer involved in the first stage of the process, the mispair recognition. We previously reported that in U937 and HL-60 cell lines, hMSH2 and hMSH6 protein expression was much lower than that in HeLa and KG1a cells. Here, we showed that the decreased expression of hMutSalpha results from differences in the degradation rate of both proteins by the ubiquitin-proteasome pathway. Our data suggest that in human cell lines, ubiquitin-proteasome could play an important role in the regulation of hMutSalpha protein expression, thereby regulating mismatch repair activity.
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Affiliation(s)
- Hélène Hernandez-Pigeon
- INSERM U563, Centre de Physiopathologie Toulouse Purpan, Institut Claudius Regaud, 20 rue du Pont Saint-Pierre, 31052 Toulouse, France
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116
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Liu L, Pegg AE, Williams KM, Guengerich FP. Paradoxical enhancement of the toxicity of 1,2-dibromoethane by O6-alkylguanine-DNA alkyltransferase. J Biol Chem 2002; 277:37920-8. [PMID: 12151404 DOI: 10.1074/jbc.m205548200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The presence of the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT) paradoxically increases the mutagenicity and cytotoxicity of 1,2-dibromoethane (DBE) in Escherichia coli. This enhancement of genotoxicity did not occur when the inactive C145A mutant of human AGT (hAGT) was used. Also, hAGT did not enhance the genotoxicity of S-(2-haloethyl)glutathiones that mimic the reactive product of the reaction of DBE with glutathione, which is catalyzed by glutathione S-transferase. These experiments support a mechanism by which hAGT activates DBE. Studies in vitro showed a direct reaction between purified recombinant hAGT and DBE resulting in a loss of AGT repair activity and a formation of an hAGT-DBE conjugate at Cys(145). A 2-hydroxyethyl adduct was found by mass spectrometry to be present in the Gly(136)-Arg(147) peptide from tryptic digests of AGT reacted with DBE. Incubation of AGT with DBE and oligodeoxyribonucleotides led to the formation of covalent AGT-oligonucleotide complexes. These results indicate that DBE reacts at the active site of AGT to generate an S-(2-bromoethyl) intermediate, which forms a highly reactive half-mustard at Cys(145). In the presence of DNA, the DNA-binding function of AGT facilitates formation of DNA adducts. In the absence of DNA, the intermediate undergoes hydrolytic decomposition to form AGT-Cys(145)-SCH(2)CH(2)OH.
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Affiliation(s)
- Liping Liu
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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