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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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52
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Hattermann K, Mehdorn HM, Mentlein R, Schultka S, Held-Feindt J. A methylation-specific and SYBR-green-based quantitative polymerase chain reaction technique for O6-methylguanine DNA methyltransferase promoter methylation analysis. Anal Biochem 2008; 377:62-71. [PMID: 18384736 DOI: 10.1016/j.ab.2008.03.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Revised: 03/05/2008] [Accepted: 03/07/2008] [Indexed: 01/28/2023]
Abstract
The O(6)-methylguanine DNA methyltransferase (MGMT) gene encodes a DNA repair enzyme whose activity is a major mechanism of resistance to alkylating drugs in glioblastoma treatment. Hypermethylation of the MGMT promoter is associated with chemosensitivity because it reduces MGMT activity. Here we present a method combining methylation-specific and SYBR-green-based quantitative PCR (MSQP) for MGMT promoter methylation analysis. This highly specific, sensitive, and reproducible method allows the quantification of fully methylated and fully unmethylated MGMT DNA species in terms of percentage. Values are related to standard curves, corrected for DNA input by an internal standard, and calculated in relation to methylated and unmethylated control DNAs as a percentage share. Finally, values are defined relative to the sum of fully methylated and unmethylated MGMT DNA sample amount to obtain percentage of methylated reference and percentage of unmethylated reference results. We have used this technique to investigate MGMT promoter methylation in relation to MGMT mRNA expression in nine tumor cell lines and 15 primary glioblastoma patients. Presented data confirm that this assay is suitable for detection of low amounts of methylated and unmethylated MGMT promoter DNA. Carefully validated quantitative MSQP assays will be useful in both research and clinical molecular diagnosis.
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Affiliation(s)
- Kirsten Hattermann
- Department of Anatomy, University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany
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53
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Abstract
DNA repair pathways can enable tumour cells to survive DNA damage that is induced by chemotherapeutic treatments; therefore, inhibitors of specific DNA repair pathways might prove efficacious when used in combination with DNA-damaging chemotherapeutic drugs. In addition, alterations in DNA repair pathways that arise during tumour development can make some cancer cells reliant on a reduced set of DNA repair pathways for survival. There is evidence that drugs that inhibit one of these pathways in such tumours could prove useful as single-agent therapies, with the potential advantage that this approach could be selective for tumour cells and have fewer side effects.
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Affiliation(s)
- Thomas Helleday
- Radiation Oncology & Biology, University of Oxford, Old Road Campus Research Building, off Roosevelt Drive, Headington, Oxford, OX3 7DQ, UK.
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54
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Tagne JB, Kakumanu S, Ortiz D, Shea T, Nicolosi RJ. A nanoemulsion formulation of tamoxifen increases its efficacy in a breast cancer cell line. Mol Pharm 2008; 5:280-6. [PMID: 18171014 DOI: 10.1021/mp700091j] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This paper reports on the preparation of a water-soluble nanoemulsion of the highly lipid-soluble drug tamoxifen (TAM). In addition, relative to a suspension of TAM, the nanoemulsion preparation demonstrated a greater zeta potential (increased negative charge) which has previously been associated with increasing drug/membrane permeability. This study also reports that relative to suspensions of TAM with particle sizes greater than 6000 nm, nanoemulsions of TAM, having mean particle sizes of 47 nm, inhibited cell proliferation 20-fold greater and increased cell apoptosis 4-fold greater in the HTB-20 breast cancer cell line. Thus, this work suggests that a nanoemulsion compared to a suspension preparation of TAM increases its anticancer properties relative to breast cancer.
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Affiliation(s)
- Jean-Bosco Tagne
- Center for Health and Disease Research, University of Massachusetts-Lowell, Lowell, Massachusetts 01854, USA
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55
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Khan O, Middleton MR. The therapeutic potential ofO6-alkylguanine DNA alkyltransferase inhibitors. Expert Opin Investig Drugs 2007; 16:1573-84. [DOI: 10.1517/13543784.16.10.1573] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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56
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Fang Q, Loktionova NA, Moschel RC, Javanmard S, Pauly GT, Pegg AE. Differential inactivation of polymorphic variants of human O6-alkylguanine-DNA alkyltransferase. Biochem Pharmacol 2007; 75:618-26. [PMID: 17996846 DOI: 10.1016/j.bcp.2007.09.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Revised: 09/25/2007] [Accepted: 09/26/2007] [Indexed: 11/25/2022]
Abstract
The human DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (hAGT) is an important source of resistance to some therapeutic alkylating agents and attempts to circumvent this resistance by the use of hAGT inhibitors have reached clinical trials. Several human polymorphisms in the MGMT gene that encodes hAGT have been described including L84F and the linked double alteration I143V/K178R. We have investigated the inactivation of these variants and the much rarer variant W65C by O(6)-benzylguanine, which is currently in clinical trials, and a number of other second generation hAGT inhibitors that contain folate derivatives (O(4)-benzylfolic acid, the 3' and 5' folate esters of O(6)-benzyl-2'-deoxyguanosine and the folic acid gamma ester of O(6)-(p-hydroxymethyl)benzylguanine). The I143V/K178R variant was resistant to all of these compounds. The resistance was due solely to the I143V change. These results suggest that the frequency of the I143V/K178R variant among patients in the clinical trials with hAGT inhibitors and the correlation with response should be considered.
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Affiliation(s)
- Qingming Fang
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
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57
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Javanmard S, Loktionova NA, Fang Q, Pauly GT, Pegg AE, Moschel RC. Inactivation of O(6)-alkylguanine-DNA alkyltransferase by folate esters of O(6)-benzyl-2'-deoxyguanosine and of O(6)-[4-(hydroxymethyl)benzyl]guanine. J Med Chem 2007; 50:5193-201. [PMID: 17880193 PMCID: PMC2597536 DOI: 10.1021/jm0705859] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
O6-Alkylguanine-DNA alkyltransferase (alkyltransferase) provides an important source of resistance to some cancer chemotherapeutic alkylating agents. Folate ester derivatives of O6-benzyl-2'-deoxyguanosine and of O6-[4-(hydroxymethyl)benzyl]guanine were synthesized and tested for their ability to inactivate human alkyltransferase. Inactivation of alkyltransferase by the gamma-folate ester of O6-[4-(hydroxymethyl)benzyl]guanine was similar to that of the parent base. The gamma-folate esters of O6-benzyl-2'-deoxyguanosine were more potent alkyltransferase inactivators than the parent nucleoside. The 3'-ester was considerably more potent than the 5'-ester and was more than an order of magnitude more active than O6-benzylguanine, which is currently in clinical trials to enhance therapy with alkylating agents. They were also able to sensitize human tumor cells to killing by 1,3-bis(2-chloroethyl)-1-nitrosourea, with O6-benzyl-3'-O-(gamma-folyl)-2'-deoxyguanosine being most active. These compounds provide a new class of highly water-soluble alkyltransferase inactivators and form the basis to construct more tumor-specific and potent compounds targeting this DNA repair protein.
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Affiliation(s)
- Sahar Javanmard
- Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, PO Box B, Bldg. 538, Frederick, MD 21702
| | - Natalia A. Loktionova
- Departments of Cellular and Molecular Physiology and Pharmacology, The Pennsylvania State University College of Medicine, PO Box 850, Hershey, PA 17033
| | - Qingming Fang
- Departments of Cellular and Molecular Physiology and Pharmacology, The Pennsylvania State University College of Medicine, PO Box 850, Hershey, PA 17033
| | - Gary T. Pauly
- Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, PO Box B, Bldg. 538, Frederick, MD 21702
| | - Anthony E. Pegg
- Departments of Cellular and Molecular Physiology and Pharmacology, The Pennsylvania State University College of Medicine, PO Box 850, Hershey, PA 17033
- Author to whom correspondence should be addressed. Phone: 717-531-8152. Fax: 717-531-5157. E-mail:
| | - Robert C. Moschel
- Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, PO Box B, Bldg. 538, Frederick, MD 21702
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58
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Damia G, D'Incalci M. Targeting DNA repair as a promising approach in cancer therapy. Eur J Cancer 2007; 43:1791-801. [PMID: 17588740 DOI: 10.1016/j.ejca.2007.05.003] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Accepted: 05/01/2007] [Indexed: 12/22/2022]
Abstract
An increased DNA-repair activity in tumour cells has been associated with resistance to treatment to DNA-directed drugs, while defects in DNA repair pathways result in hypersensitivity to these agents. In the past years the unravelling of the molecular basis of these DNA pathways, with a better understanding of the DNA damage caused by different anticancer agents, has provided the rationale for the use of some DNA repair inhibitors to optimise the therapeutic use of DNA-damaging agents currently used in the treatment of tumours. In addition, the possibility to specifically target the differences in DNA repair capacity between normal and tumour cells has recently emerged as an exciting possibility. The present review will mainly cover those approaches that are currently under clinical investigation.
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Affiliation(s)
- Giovanna Damia
- Department of Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Via Eritrea 62, 20157 Milan, Italy
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59
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Ranson M, Hersey P, Thompson D, Beith J, McArthur GA, Haydon A, Davis ID, Kefford RF, Mortimer P, Harris PA, Baka S, Seebaran A, Sabharwal A, Watson AJ, Margison GP, Middleton MR. Randomized trial of the combination of lomeguatrib and temozolomide compared with temozolomide alone in chemotherapy naive patients with metastatic cutaneous melanoma. J Clin Oncol 2007; 25:2540-5. [PMID: 17577032 DOI: 10.1200/jco.2007.10.8217] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PURPOSE To evaluate tumor response, pharmacodynamic effects, and safety of a combination of lomeguatrib (LM), an O6-methylguanine DNA-methyltransferase (MGMT) inactivator, and temozolomide (TMZ), TMZ alone, and LM/TMZ after disease progression on TMZ alone in patients with advanced melanoma. PATIENTS AND METHODS Patients with unresectable stage III or IV cutaneous melanoma who had no prior systemic chemotherapy were randomly assigned to receive either 40 to 80 mg LM and 125 mg/m2 TMZ or 200 mg/m2 TMZ on days 1 through 5 of each 28-day treatment cycle. Drugs were administered orally for up to six cycles of treatment. Patients on TMZ alone were offered LM/TMZ at progression, if fit enough to receive treatment. RESULTS One hundred four patients were enrolled, with 52 in each trial arm. Twenty-seven TMZ-treated patients received LM/TMZ after progression on TMZ. Unexpectedly, analysis of tumor biopsies showed rapid recovery of MGMT after LM/TMZ with 40 mg/d LM. Therefore, doses of LM were escalated to 60 then 80 mg/d. Tumor response rates were 13.5% with LM/TMZ and 17.3% with TMZ alone. No patient responded to LM/TMZ having progressed through TMZ. Median time to disease progression was 65.5 days for LM/TMZ and 68 days for TMZ. All treatments were well tolerated, although hematologic and gastrointestinal adverse events were common. A higher incidence of hematological adverse events was observed in the LM/TMZ combination arm. CONCLUSION The efficacy of LM and TMZ in the current dosing schedule is similar to that of TMZ alone. To maintain MGMT depletion in tumor dosing of LM needs to be continued beyond that of TMZ.
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Affiliation(s)
- Malcolm Ranson
- Department of Medical Oncology, University of Manchester, United Kingdom
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60
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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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61
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Rabik CA, Njoku MC, Dolan ME. Inactivation of O6-alkylguanine DNA alkyltransferase as a means to enhance chemotherapy. Cancer Treat Rev 2006; 32:261-76. [PMID: 16698182 DOI: 10.1016/j.ctrv.2006.03.004] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Revised: 03/14/2006] [Accepted: 03/15/2006] [Indexed: 10/24/2022]
Abstract
DNA adducts at the O6-position of guanine are a result of the carcinogenic, mutagenic and cytotoxic actions of methylating and chloroethylating agents. The presence of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) renders cells resistant to the biological effects induced by agents that attack at this position. O6-Benzylguanine (O6-BG) is a low molecular weight substrate of AGT and therefore, results in sensitizing cells and tumors to alkylating agent-induced cytotoxicity and antitumor activity. Presently, chemotherapy regimens of O6-BG in combination with BCNU, temozolomide and Gliadel are in clinical development. Other ongoing clinical trials include expression of mutant AGT proteins that confer resistance to O6-BG in bone marrow stem cells, in an effort to reduce the potential enhanced toxicity and mutagenicity of alkylating agents in the bone marrow. O6-BG has also been found to enhance the cytotoxicity of agents that do not form adducts at the O6-position of DNA, including platinating agents. O6-BG's mechanism of action with these agents is not fully understood; however, it is independent of AGT activity or AGT inactivation. A better understanding of the effects of this agent will contribute to its clinical usefulness and the design of better analogs to further improve cancer chemotherapy.
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Affiliation(s)
- Cara A Rabik
- Department of Medicine, Committee on Cancer Biology, Committee on Clinical Pharmacology and Pharmacogenomics, University of Chicago, Chicago, IL 60637, USA
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62
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Ranson M, Middleton MR, Bridgewater J, Lee SM, Dawson M, Jowle D, Halbert G, Waller S, McGrath H, Gumbrell L, McElhinney RS, Donnelly D, McMurry TBH, Margison GP. Lomeguatrib, a potent inhibitor of O6-alkylguanine-DNA-alkyltransferase: phase I safety, pharmacodynamic, and pharmacokinetic trial and evaluation in combination with temozolomide in patients with advanced solid tumors. Clin Cancer Res 2006; 12:1577-84. [PMID: 16533784 DOI: 10.1158/1078-0432.ccr-05-2198] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE A major mechanism of resistance to temozolomide involves the DNA repair protein O6-alkylguanine-DNA-alkyltransferase (ATase). The main aims of this phase I trial were to determine an ATase-depleting dose (ADD) of lomeguatrib, a potent pseudosubstrate inhibitor, and to define a suitable dose of temozolomide to be used in combination with lomeguatrib in patients with advanced cancer. EXPERIMENTAL DESIGN Lomeguatrib was administered at dose levels of 10 to 40 mg/m2 days 1 to 5, as a single agent, and also in combination with temozolomide. Once the ADD of lomeguatrib was identified, the dose of temozolomide in combination was increased, in successive patient cohorts, from 50 to 175 mg/m2 on days 1 to 5 of a 28-day cycle to define the maximal tolerated dose and dose-limiting toxicity of the combination. RESULTS Thirty-eight patients with advanced solid tumors were enrolled. More than 95% ATase depletion within 4 hours of the first dose was achieved in peripheral blood mononuclear cells at lomeguatrib doses of > or =10 mg/m2/d i.v. or > or =20 mg/m2/d orally, and tumor biopsies showed > or =92% ATase depletion. At the ADD of lomeguatrib i.v., the maximal tolerated dose of temozolomide in combination was 150 mg/m2 days 1 to 5. The dose limiting toxicity of the combination of lomeguatrib and temozolomide was myelosuppression. The toxicity of lomeguatrib alone was minimal. In 23 patients with measurable disease, one complete response was seen and 12 patients had stable disease for at least 3 months. CONCLUSION This first administration of lomeguatrib to man successfully established an oral ADD of lomeguatrib and identified a combination regimen with temozolomide suitable for future clinical evaluation.
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Affiliation(s)
- Malcolm Ranson
- Department of Medical Oncology, University of Manchester, UK
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63
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Shankar S, Zalutsky MR, Friedman H, Vaidyanathan G. Molecular imaging of alkylguanine-DNA alkyltransferase: further evaluation of radioiodinated derivatives of O6-benzylguanine. Nucl Med Biol 2006; 33:399-407. [PMID: 16631089 DOI: 10.1016/j.nucmedbio.2005.12.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 12/19/2005] [Accepted: 12/26/2005] [Indexed: 11/17/2022]
Abstract
PURPOSE An inverse correlation has been established between tumor levels of the DNA repair protein alkylguanine-DNA alkyltransferase (AGT) and a positive outcome after alkylator chemotherapy. Quantitative imaging of AGT could provide important information for patient-specific cancer treatment. Several radiolabeled analogues of O6-benzylguanine (BG), a potent AGT inactivator, have been developed and shown to be capable of labeling pure AGT protein. Herein, two of these analogues--O6-3-[*I]iodobenzylguanine ([*I]IBG) and O6-3-[*I]iodobenzyl-2'-deoxyguanosine ([*I]IBdG)--were further evaluated in two murine xenograft models. (AcO)2-[131I]IBdG, a peracetylated derivative of IBdG, also was investigated as an alternative agent. METHODS Several biodistribution studies of radioiodinated IBG and IBdG were performed in TE-671 human rhabdomyosarcoma and DAOY human medulloblastoma murine xenograft models. Mice were treated with BG or its nucleoside analogue dBG to deplete the tumor AGT content. The effect of unlabeled IBG and that of 7,8-benzoflavone (BF), an inhibitor of the cytochrome P-450 isozyme CYP1A2, on the tumor uptake of the tracers was determined. The uptake of (AcO)2-[131I]IBdG along with that of [125I]IBdG in DAOY cells in vitro was determined in the presence and absence of a nucleoside transporter inhibitor, dipyridamole. RESULTS Pretreatment of mice either with BG or dBG failed to reduce tumor levels of [*I]IBG or [*I]IBdG even though such treatments completely depleted tumor AGT content. Treatment of mice with BF increased tumor uptake of [125I]IBG by 56%; however, differentiation of tumors with and without AGT still was not possible. (AcO)2-[131I]IBdG, a peracetylated derivative of IBdG, had a higher uptake in vitro in DAOY tumor cells. However, its uptake, like that of [125I]IBdG, was blocked by dipyridamole. CONCLUSIONS Taken together, these results suggest that labeled agents that are more specific for cellular AGT and that are more metabolically stable are needed.
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Affiliation(s)
- Sriram Shankar
- Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA
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Paik J, Duncan T, Lindahl T, Sedgwick B. Sensitization of human carcinoma cells to alkylating agents by small interfering RNA suppression of 3-alkyladenine-DNA glycosylase. Cancer Res 2006; 65:10472-7. [PMID: 16288039 DOI: 10.1158/0008-5472.can-05-1495] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
One of the major cytotoxic lesions generated by alkylating agents is DNA 3-alkyladenine, which can be excised by 3-alkyladenine DNA glycosylase (AAG). Inhibition of AAG may therefore result in increased cellular sensitivity to chemotherapeutic alkylating agents. To investigate this possibility, we have examined the role of AAG in protecting human tumor cells against such agents. Plasmids that express small interfering RNAs targeted to two different regions of AAG mRNA were transfected into HeLa cervical carcinoma cells and A2780-SCA ovarian carcinoma cells. Stable derivatives of both cell types with low AAG protein levels were sensitized to alkylating agents. Two HeLa cell lines with AAG protein levels reduced by at least 80% to 90% displayed a 5- to 10-fold increase in sensitivity to methyl methanesulfonate, N-methyl-N-nitrosourea, and the chemotherapeutic drugs temozolomide and 1,3-bis(2-chloroethyl)-1-nitrosourea. These cells showed no increase in sensitivity to UV light or ionizing radiation. After treatment with methyl methanesulfonate, AAG knockdown HeLa cells were delayed in S phase but accumulated in G2-M. Our data support the hypothesis that ablation of AAG activity in human tumor cells may provide a useful strategy to enhance the efficacy of current chemotherapeutic regimens that include alkylating agents.
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Affiliation(s)
- Johanna Paik
- Clare Hall Laboratories, Cancer Research UK London Research Institute, South Mimms, Hertfordshire, United Kingdom
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65
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Clemons M, Kelly J, Watson AJ, Howell A, McElhinney RS, McMurry TBH, Margison GP. O6-(4-bromothenyl)guanine reverses temozolomide resistance in human breast tumour MCF-7 cells and xenografts. Br J Cancer 2005; 93:1152-6. [PMID: 16278661 PMCID: PMC2361498 DOI: 10.1038/sj.bjc.6602833] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Tumour resistance to chemotherapy involving methylating agents such as DTIC (dacarbazine) and temozolomide is linked to expression of the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (MGMT). There is considerable interest in improving the efficacy of such O(6)-alkylating chemotherapy by the prior inactivation of MGMT. We have examined the effect of the modified guanine base, O(6)-(4-bromothenyl)guanine (PaTrin-2, Patrin, Lomeguatrib) on MGMT activity and cell or xenograft tumour growth inhibition by temozolomide in the human breast carcinosarcoma cell line, MCF-7. PaTrin-2 effectively inactivated MGMT in MCF-7 cells (IC(50) approximately 6 nM) and in xenografts there was complete inactivation of MGMT within 2 h of dosing (20 mg kg(-1) i.p.) and only slight recovery by 24 h. MGMT inactivation in a range of murine host tissues varied between complete and approximately 60%, with extensive recovery by 24 h. PaTrin-2 (10 microM) substantially increased the growth inhibitory effects of temozolomide in MCF-7 cells (D(60)=10 microM with PaTrin-2 vs 400 microM without). In MCF-7 xenografts, neither temozolomide (100 mg kg(-1) day(-1) for 5 days) nor PaTrin-2 (20 mg kg(-1) day(-1) for 5 days) had any significant effect on tumour growth. In contrast, the PaTrin-2-temozolomide combination produced a substantial tumour growth delay: median tumour quintupling time was increase by 22 days (P<0.005) without any significant increase in toxicity as assessed from animal weight. A PaTrin-2-temozolomide combination may therefore be beneficial in the treatment of human breast cancers.
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Affiliation(s)
- M Clemons
- Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 9BX, UK
- Cancer Research UK Department of Medical Oncology, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK
| | - J Kelly
- Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 9BX, UK
| | - A J Watson
- Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 9BX, UK
| | - A Howell
- Cancer Research UK Department of Medical Oncology, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK
| | - R S McElhinney
- University Chemical Laboratory, Trinity College, University of Dublin, Dublin 2, Ireland
| | - T B H McMurry
- University Chemical Laboratory, Trinity College, University of Dublin, Dublin 2, Ireland
| | - G P Margison
- Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 9BX, UK
- Cancer Research UK Carcinogenesis Group, Paterson Institute for Cancer Research, Wilmslow Road, Manchester M20 9BX, UK. E-mail:
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66
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Rasmussen AK, Rasmussen LJ. Targeting of O6-MeG DNA methyltransferase (MGMT) to mitochondria protects against alkylation induced cell death. Mitochondrion 2005; 5:411-7. [PMID: 16233991 DOI: 10.1016/j.mito.2005.08.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2005] [Revised: 08/23/2005] [Accepted: 08/29/2005] [Indexed: 11/24/2022]
Abstract
Mitochondrial DNA (mtDNA) mutations are implicated in pathogenesis of human diseases including cancer. To prevent mutations cells have developed repair systems to counteract harmful genetic changes caused by DNA damaging agents. One such DNA repair protein is the O(6)-Methylguanine-DNA methyltransferase (MGMT) that prevents certain types of alkylation damage. Yet, the role of MGMT in preventing alkylation induced DNA damage in mtDNA is unclear. We explored the idea of increasing cell survival after alkylation damage by overexpressing MGMT in mitochondria. We show that overexpression of this repair protein in mitochondria increases cell survival after treatment with the DNA damaging agent MNNG.
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Affiliation(s)
- Anne Karin Rasmussen
- Department of Life Sciences and Chemistry, Roskilde University, 4000 Roskilde, Denmark
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67
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Madhusudan S, Middleton MR. The emerging role of DNA repair proteins as predictive, prognostic and therapeutic targets in cancer. Cancer Treat Rev 2005; 31:603-17. [PMID: 16298073 DOI: 10.1016/j.ctrv.2005.09.006] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Advanced cancer is the second leading cause of death in the western world. Chemotherapy and radiation are the two main treatment modalities currently available to improve patient outcomes, but treatment related toxicity and the emergence of resistance limit their effectiveness. Hence there is an urgent need to develop novel treatment strategies. Rapid advances in cancer biology have identified key pathways involved in the repair of DNA damage induced by chemotherapeutic agents and irradiation. Efficient DNA repair in the cancer cell is an important mechanism for therapeutic resistance. Up to 130 genes have been identified that are associated with human DNA repair. Several of these proteins are emerging as important predictive and prognostic factors in solid tumours. Inhibition of DNA repair has the potential to enhance the efficacy of currently available DNA damaging agents. In recent years, several promising drug targets have been identified and novel drugs synthesised that target specific DNA repair proteins. These agents have shown impressive anti-cancer effects in preclinical studies in combination with chemotherapy or irradiation. Their role in human cancer is now being investigated in early phase clinical trials in combination with chemotherapy. MGMT inhibitors, PARP inhibitors and methoxyamine are currently in early stages of clinical development. Innovative clinical trial designs are essential to evaluate the potential of DNA repair inhibitor in cancer therapy.
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Affiliation(s)
- Srinivasan Madhusudan
- Cancer Research UK, Medical Oncology Unit, University of Oxford, The Churchill, Oxford Radcliffe Hospitals, Oxford OX3 7LJ, United Kingdom
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68
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Abstract
The same doses of medication cause considerable heterogeneity in efficacy and toxicity across human populations. Genetic factors are thought to represent important determinants of drug efficacy and toxicity. Pharmacogenetics focuses on the prediction of the response of tumor and normal tissue to standard therapy by genetic profiling and, thereby, to select the most appropriate medication at optimal doses for each individual patient. In the present review, we discuss the relevance of single nucleotide polymorphisms (SNP) in genes, whose gene products act upstream of the actual drug target sites, that is, drug transporters and drug metabolizing phase I and II enzymes, or downstream of them, that is, apoptosis-regulating genes and chemokines. SNPs in relevant genes, which encode for proteins that interact with anticancer drugs, were also considered, that is, enzymes of DNA biosynthesis and metabolism, DNA repair enzymes, and proteins of the mitotic spindle. A significant body of evidence supports the concept of predicting drug efficacy and toxicity by SNP genotyping. As the efficacy of cancer chemotherapy, as well as the drug-related toxicity in normal tissues is multifactorial in nature, sophisticated approaches such as genome-wide linkage analyses and integrate drug pathway profiling may improve the predictive power compared with genotyping of single genes. The implementation of pharmacogenetics into clinical routine diagnostics including genotype-based recommendations for treatment decisions and risk assessment for practitioners represents a challenge for the future.
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Affiliation(s)
- Thomas Efferth
- German Cancer Research Center, M070, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.
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69
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Madhusudan S, Hickson ID. DNA repair inhibition: a selective tumour targeting strategy. Trends Mol Med 2005; 11:503-11. [PMID: 16214418 DOI: 10.1016/j.molmed.2005.09.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2005] [Revised: 09/07/2005] [Accepted: 09/19/2005] [Indexed: 10/25/2022]
Abstract
Advanced cancer is a leading cause of death in the developed world. Chemotherapy and radiation are the two main treatment modalities currently available. The cytotoxicity of many of these agents is directly related to their propensity to induce DNA damage. However, the ability of cancer cells to recognize this damage and initiate DNA repair is an important mechanism for therapeutic resistance and has a negative impact upon therapeutic efficacy. Pharmacological inhibition of DNA repair, therefore, has the potential to enhance the cytotoxicity of a diverse range of anticancer agents. Moreover, the use of inhibitors of DNA repair or DNA damage signalling pathways appears to provide an exciting opportunity to target the genetic differences that exist between normal and tumour tissue.
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Affiliation(s)
- Srinivasan Madhusudan
- Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
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70
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Abstract
Carcinogenesis and cancer therapy are two sides of the same coin, such that the same cytotoxic agent can cause cancer and be used to treat cancer. This review links carcinogenesis, chemoprevention and cancer therapy in one process driven by cytotoxic agents (carcinoagents) that select either for or against cells with oncogenic alterations. By unifying therapy and cancer promotion and by distinguishing nononcogenic and oncogenic mechanisms of resistance, I discuss anticancer- and chemopreventive agent-induced carcinogenesis and tumor progression and, vice versa, carcinogens as anticancer drugs, anticancer drugs as chemopreventive agents and exploiting oncogene-addiction and drug resistance for chemoprevention and cancer therapy.
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Affiliation(s)
- M V Blagosklonny
- Brander Cancer Research Institute, New York Medical College, 19 Bradhurst Ave., Hawthorne, NY 10532, USA.
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71
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Bobola MS, Silber JR, Ellenbogen RG, Geyer JR, Blank A, Goff RD. O6-methylguanine-DNA methyltransferase, O6-benzylguanine, and resistance to clinical alkylators in pediatric primary brain tumor cell lines. Clin Cancer Res 2005; 11:2747-55. [PMID: 15814657 DOI: 10.1158/1078-0432.ccr-04-2045] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Primary brain tumors are the leading cause of cancer death in children. Our purpose is (a) to assess the contribution of the DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) to the resistance of pediatric brain tumor cell lines to clinical alkylating agents and (b) to evaluate variables for maximal potentiation of cell killing by the MGMT inhibitor O6-benzylguanine, currently in clinical trials. Few such data for pediatric glioma lines, particularly those from low-grade tumors, are currently available. EXPERIMENTAL DESIGN We used clonogenic assays of proliferative survival to quantitate cytoxicity of the chloroethylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and the methylating agent temozolomide in 11 glioma and five medulloblastoma lines. Twelve lines are newly established and characterized here, nine of them from low-grade gliomas including pilocytic astrocytomas. RESULTS (a) MGMT is a major determinant of BCNU resistance and the predominant determinant of temozolomide resistance in both our glioma and medulloblastoma lines. On average, O(6)-benzylguanine reduced LD10 for BCNU and temozolomide, 2.6- and 26-fold, respectively, in 15 MGMT-expressing lines. (b) O6-Benzylguanine reduced DT (the threshold dose for killing) for BCNU and temozolomide, 3.3- and 138-fold, respectively. DT was decreased from levels higher than, to levels below, clinically achievable plasma doses for both alkylators. (c) Maximal potentiation by O6-benzylguanine required complete and prolonged suppression of MGMT. CONCLUSIONS Our results support the use of O6-benzylguanine to achieve full benefit of alkylating agents, particularly temozolomide, in the chemotherapy of pediatric brain tumors.
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Affiliation(s)
- Michael S Bobola
- Division of Neurosurgery, Department of Surgery and Hematology/Oncology, Children's Hospital and Regional Medical Center, Seattle, Washington 98105, USA.
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72
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Margison GP, Heighway J, Pearson S, McGown G, Thorncroft MR, Watson AJ, Harrison KL, Lewis SJ, Rohde K, Barber PV, O'Donnell P, Povey AC, Santibáñez-Koref MF. Quantitative trait locus analysis reveals two intragenic sites that influence O6-alkylguanine-DNA alkyltransferase activity in peripheral blood mononuclear cells. Carcinogenesis 2005; 26:1473-80. [PMID: 15831531 DOI: 10.1093/carcin/bgi087] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The repair of specific types of DNA alkylation damage by O6-alkylguanine-DNA alkyltransferase (MGMT) is a major mechanism of resistance to the carcinogenic and chemotherapeutic effects of certain alkylating agents. MGMT expression levels vary widely between individuals but the underlying causes of this variability are not known. To address this, we used an expressed single nucleotide polymorphism (SNP) and demonstrated that the MGMT alleles are frequently expressed at different levels in peripheral blood mononuclear cells (PBMC). This suggests that there is a genetic component of inter-allelic variation of MGMT levels that maps close to or within the MGMT locus. We then used quantitative trait locus (QTL) analysis using intragenic SNPs and found that there are at least two sites influencing inter-individual variation in PBMC MGMT activity. One is characterized by an SNP at the 3' end of the first intron and the second by two SNPs in the last exon. The latter are in perfect disequilibrium and both result in amino acid substitutions-one of them, Ile143Val, affecting an amino acid close to the Cys145 residue at the active site of MGMT. Using in vitro assays, we further showed that while the Val143 variant did not affect the activity of the protein on methylated DNA substrate, it was more resistant to inactivation by the MGMT pseudosubstrate, O6-(4-bromothenyl)guanine. These findings suggest that further investigations of the potential epidemiological and clinical significance of inherited differences in MGMT expression and activity are warranted.
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Affiliation(s)
- Geoffrey P Margison
- Cancer Research-UK Carcinogenesis Group, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, UK.
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73
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Drabløs F, Feyzi E, Aas PA, Vaagbø CB, Kavli B, Bratlie MS, Peña-Diaz J, Otterlei M, Slupphaug G, Krokan HE. Alkylation damage in DNA and RNA--repair mechanisms and medical significance. DNA Repair (Amst) 2005; 3:1389-407. [PMID: 15380096 DOI: 10.1016/j.dnarep.2004.05.004] [Citation(s) in RCA: 443] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2004] [Indexed: 12/13/2022]
Abstract
Alkylation lesions in DNA and RNA result from endogenous compounds, environmental agents and alkylating drugs. Simple methylating agents, e.g. methylnitrosourea, tobacco-specific nitrosamines and drugs like temozolomide or streptozotocin, form adducts at N- and O-atoms in DNA bases. These lesions are mainly repaired by direct base repair, base excision repair, and to some extent by nucleotide excision repair (NER). The identified carcinogenicity of O(6)-methylguanine (O(6)-meG) is largely caused by its miscoding properties. Mutations from this lesion are prevented by O(6)-alkylG-DNA alkyltransferase (MGMT or AGT) that repairs the base in one step. However, the genotoxicity and cytotoxicity of O(6)-meG is mainly due to recognition of O(6)-meG/T (or C) mispairs by the mismatch repair system (MMR) and induction of futile repair cycles, eventually resulting in cytotoxic double-strand breaks. Therefore, inactivation of the MMR system in an AGT-defective background causes resistance to the killing effects of O(6)-alkylating agents, but not to the mutagenic effect. Bifunctional alkylating agents, such as chlorambucil or carmustine (BCNU), are commonly used anti-cancer drugs. DNA lesions caused by these agents are complex and require complex repair mechanisms. Thus, primary chloroethyl adducts at O(6)-G are repaired by AGT, while the secondary highly cytotoxic interstrand cross-links (ICLs) require nucleotide excision repair factors (e.g. XPF-ERCC1) for incision and homologous recombination to complete repair. Recently, Escherichia coli protein AlkB and human homologues were shown to be oxidative demethylases that repair cytotoxic 1-methyladenine (1-meA) and 3-methylcytosine (3-meC) residues. Numerous AlkB homologues are found in viruses, bacteria and eukaryotes, including eight human homologues (hABH1-8). These have distinct locations in subcellular compartments and their functions are only starting to become understood. Surprisingly, AlkB and hABH3 also repair RNA. An evaluation of the biological effects of environmental mutagens, as well as understanding the mechanism of action and resistance to alkylating drugs require a detailed understanding of DNA repair processes.
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Affiliation(s)
- Finn Drabløs
- Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, N-7489 Trondheim, Norway
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74
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Paz MF, Yaya-Tur R, Rojas-Marcos I, Reynes G, Pollan M, Aguirre-Cruz L, García-Lopez JL, Piquer J, Safont MJ, Balaña C, Sanchez-Cespedes M, García-Villanueva M, Arribas L, Esteller M. CpG island hypermethylation of the DNA repair enzyme methyltransferase predicts response to temozolomide in primary gliomas. Clin Cancer Res 2005; 10:4933-8. [PMID: 15297393 DOI: 10.1158/1078-0432.ccr-04-0392] [Citation(s) in RCA: 204] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE The DNA repair enzyme O(6)-methylguanine DNA methyltransferase (MGMT) inhibits the killing of tumor cells by alkylating agents, and its loss in cancer cells is associated with hypermethylation of the MGMT CpG island. Thus, methylation of MGMT has been correlated with the clinical response to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in primary gliomas. Here, we investigate whether the presence of MGMT methylation in gliomas is also a good predictor of response to another emergent alkylating agent, temozolomide. EXPERIMENTAL DESIGN Using a methylation-specific PCR approach, we assessed the methylation status of the CpG island of MGMT in 92 glioma patients who received temozolomide as first-line chemotherapy or as treatment for relapses. RESULTS Methylation of the MGMT promoter positively correlated with the clinical response in the glioma patients receiving temozolomide as first-line chemotherapy (n = 40). Eight of 12 patients with MGMT-methylated tumors (66.7%) had a partial or complete response, compared with 7 of 28 patients with unmethylated tumors (25.0%; P = 0.030). We also found a positive association between MGMT methylation and clinical response in those patients receiving BCNU (n = 35, P = 0.041) or procarbazine/1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (n = 17, P = 0.043) as first-line chemotherapy. Overall, if we analyze the clinical response of all of the first-line chemotherapy treatments with temozolomide, BCNU, and procarbazine/1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea as a group in relation to the MGMT methylation status, MGMT hypermethylation was strongly associated with the presence of partial or complete clinical response (P < 0.001). Finally, the MGMT methylation status determined in the initial glioma tumor did not correlate with the clinical response to temozolomide when this drug was administered as treatment for relapses (P = 0.729). CONCLUSIONS MGMT methylation predicts the clinical response of primary gliomas to first-line chemotherapy with the alkylating agent temozolomide. These results may open up possibilities for more customized treatments of human brain tumors.
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Affiliation(s)
- Maria F Paz
- Cancer Epigenetics Laboratory, Spanish National Cancer Centre, Madrid, Spain
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75
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Barvaux VA, Lorigan P, Ranson M, Gillum AM, McElhinney RS, McMurry TBH, Margison GP. Sensitization of a human ovarian cancer cell line to temozolomide by simultaneous attenuation of the Bcl-2 antiapoptotic protein and DNA repair by O6-alkylguanine-DNA alkyltransferase. Mol Cancer Ther 2004. [DOI: 10.1158/1535-7163.1215.3.10] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Temozolomide is an alkylating agent that mediates its cytotoxic effects via O6-methylguanine (O6-meG) adducts in DNA. O6-alkylguanine-DNA-alkyltransferase (MGMT) can repair such adducts and therefore constitutes a major resistance mechanism to the drug. MGMT activity can be attenuated in vitro and in vivo by the pseudosubstrate O6-(4-bromothenyl)guanine (PaTrin-2, Patrin, Lomeguatrib), which in clinical trials is in combination with temozolomide. Resistance to cytotoxic agents can also be mediated by the Bcl-2 protein, which inhibits apoptosis and is frequently up-regulated in tumor cells. Attenuation of Bcl-2 expression can be affected by treatment of cells with the antisense oligonucleotide, oblimersen sodium (Genasense), currently in phase III clinical trials in combination with the methylating agent dacarbazine. Using a human ovarian cancer cell line (A2780) that expresses both Bcl-2 and MGMT, we show that cells treated with active dose levels of either oblimersen (but not control reverse sequence or mismatch oligonucleotides) or PaTrin-2 are substantially sensitized to temozolomide. Furthermore, the exposure of oblimersen-pretreated cells to PaTrin-2 leads to an even greater sensitization of these cells to temozolomide. Thus, growth of cells treated only with temozolomide (5 μg/mL) was 91% of control growth, whereas additional exposure to PaTrin-2 alone (10 μmol/L) or oblimersen alone (33 nmol/L) reduced this to 81% and 66%, respectively, and the combination of PaTrin-2 (10 μmol/L) and oblimersen (33 nmol/L) reduced growth to 25% of control. These results suggest that targeting both Bcl-2 with oblimersen and MGMT with PaTrin-2 would markedly enhance the antitumor activity of temozolomide and merits testing in clinical trials.
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Affiliation(s)
| | - Paul Lorigan
- 2Department of Medical Oncology, Christie Hospital, Manchester, United Kingdom
| | - Malcolm Ranson
- 2Department of Medical Oncology, Christie Hospital, Manchester, United Kingdom
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76
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Nelson ME, Loktionova NA, Pegg AE, Moschel RC. 2-Amino-O4-benzylpteridine Derivatives: Potent Inactivators ofO6-Alkylguanine-DNA Alkyltransferase. J Med Chem 2004; 47:3887-91. [PMID: 15239666 DOI: 10.1021/jm049758+] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
2-amino-O4-benzylpteridine (1), 2-amino-O4-benzyl-6,7-dimethylpteridine (2), 2-amino-O4-benzyl-6-hydroxymethylpteridine (4), 2-amino-O4-benzylpteridine-6-carboxylic acid (5), 2-amino-O4-benzyl-6-formylpteridine (6), and O4-benzylfolic acid (7) are shown to be as potent or more potent inactivators of the human DNA repair protein O6-alkylguanine-DNA alkyltransferase (alkyltransferase) in vitro than O6-benzylguanine, the prototype alkyltransferase inactivator currently in clinical trials. Additionally, the negatively charged (at physiological pH) inactivators 2-amino-O4-benzylpteridine-6-carboxylic acid (5) and O4-benzylfolate (7) are far more water soluble than O6-benzylguanine. The activity of O4-benzylfolic acid (7) is particularly noteworthy because it is roughly 30 times more active than O6-benzylguanine against the wild-type alkyltransferase and is even capable of inactivating the P140K mutant alkyltransferase that is resistant to inactivation by O6-benzylguanine. All the pteridine derivatives except 2-amino-O4-benzylpteridine-6-carboxylic acid are effective in enhancing cell killing by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). However, the effectiveness of O4-benzylfolate as an adjuvant for cell killing by BCNU appears to be a function of a cell's alpha-folate receptor expression. Thus, O4-benzylfolate is least effective as an adjuvant in A549 cells (which express little if any receptor), is moderately effective in HT29 cells (which express low levels of the receptor), but is very effective in KB cells (which are known to express high levels of the alpha-folate receptor). Therefore, O4-benzylfolic acid shows promise as an agent for possible tumor-selective alkyltransferase inactivation, which suggests it may prove to be superior to O6-benzylguanine as a chemotherapy adjuvant.
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Affiliation(s)
- Michael E Nelson
- Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, P.O. Box B, Building 538, Frederick, MD 21702, USA
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77
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West CML, Jones T, Price P. The potential of positron-emission tomography to study anticancer-drug resistance. Nat Rev Cancer 2004; 4:457-69. [PMID: 15170448 DOI: 10.1038/nrc1368] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Catharine M L West
- Academic Department of Radiation Oncology and Manchester Molecular Imaging Centre, University of Manchester, Christie NHS Trust Hospital, Wilmslow Road, Manchester, M20 4BX, United Kingdom.
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78
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Breivik J, Gaudernack G. Resolving the evolutionary paradox of genetic instability: a cost-benefit analysis of DNA repair in changing environments. FEBS Lett 2004; 563:7-12. [PMID: 15063714 DOI: 10.1016/s0014-5793(04)00282-0] [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: 01/07/2004] [Revised: 02/18/2004] [Accepted: 02/24/2004] [Indexed: 12/15/2022]
Abstract
Loss of genetic stability is a critical phenomenon in cancer and antibiotic resistance, and the prevailing dogma is that unstable cells survive because instability provides adaptive mutations. Challenging this view, we have argued that genetic instability arises because DNA repair may be a counterproductive strategy in mutagenic environments. This paradoxical relationship has also been confirmed by explicit experiments, but the underlying evolutionary principles remain controversial. This paper aims to clarify the issue, and presents a model that explains genetic instability from the basic perspective of molecular evolution and information processing.
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Affiliation(s)
- Jarle Breivik
- Section for Immunotherapy, University of Oslo at the Norwegian Radium Hospital, 0310 Oslo, Norway.
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79
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Abstract
Methylating agents modify DNA at many different sites, thereby producing lethal and mutagenic lesions. To remove all the main harmful base lesions, at least three types of DNA-repair activities can be used, each of which involves a different reaction mechanism. These activities include DNA-glycosylases, DNA-methyltransferases and the recently characterized DNA-dioxygenases. The Escherichia coli AlkB dioxygenase and the two human homologues, ABH2 and ABH3, represent a novel mechanism of DNA repair. They use iron-oxo intermediates to oxidize stable methylated bases in DNA and directly revert them to the unmodified form.
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Affiliation(s)
- Barbara Sedgwick
- Cancer Research UK London Research Institute, Clare Hall Laboratories, Blanche Lane, South Mimms, Hertfordshire EN6 3LD, UK.
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80
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Esteller M, Herman JG. Generating mutations but providing chemosensitivity: the role of O6-methylguanine DNA methyltransferase in human cancer. Oncogene 2004; 23:1-8. [PMID: 14712205 DOI: 10.1038/sj.onc.1207316] [Citation(s) in RCA: 222] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
O(6)-methylguanine DNA methyltransferase (MGMT) is a key enzyme in the DNA repair network. MGMT removes mutagenic and cytotoxic adducts from O(6)-guanine in DNA, the preferred point of attack of many carcinogens (i.e. methylnitrosourea) and alkylating chemotherapeutic agents (i.e. BCNU, temozolamide, etc.). Hypermethylation of the CpG island located in the promoter region of MGMT is primarily responsible for the loss of MGMT function in many tumor types. The methylation-mediated silencing of MGMT has two consequences for cancer. First, tumors with MGMT methylation have a new mutator phenotype characterized by the generation of transition point mutations in genes involved in cancer etiology, such as the tumor suppressor p53 and the oncogene K-ras. Second, MGMT hypermethylation demonstrates the possibility of pharmacoepigenomics: methylated tumors are more sensitive to the killing effects of alkylating drugs used in chemotherapy. These recent results underscore the importance of MGMT in basic and translational cancer research.
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Affiliation(s)
- Manel Esteller
- Cancer Epigenetics Laboratory, Molecular Pathology Program, Spanish National Cancer Center (CNIO), Melchor Fernandez Almagro 3, Madrid 28029, Spain.
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81
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Lage C, de Pádula M, de Alencar TAM, da Fonseca Gonçalves SR, da Silva Vidal L, Cabral-Neto J, Leitão AC. New insights on how nucleotide excision repair could remove DNA adducts induced by chemotherapeutic agents and psoralens plus UV-A (PUVA) in Escherichia coli cells. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2003; 544:143-57. [PMID: 14644316 DOI: 10.1016/j.mrrev.2003.06.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Chemotherapeutic agents such as mitomycin C or nitrogen mustards induce DNA inter-strand cross-links (ICL) and are highly toxic, thus constituting an useful tool to treat some human degenerative diseases, such as cancer. Additionally, psoralens plus UV-A (PUVA), which also induce ICL, find use in treatment of patients afflicted with psoriasis and vitiligo. The repair of DNA ICL generated by different molecules involves a number of multi-step DNA repair pathways. In bacteria, as in eukaryotic cells, if DNA ICL are not tolerated or repaired via nucleotide excision repair (NER), homologous recombination or translesion synthesis pathways, these DNA lesions may lead to mutations and cell death. Herein, we bring new insights to the role of Escherichia coli nucleotide excision repair genes uvrA, uvrB and uvrC in the repair of DNA damage induced by some chemotherapeutic agents and psoralen derivatives plus UV-A. These new observations point to a novel role for the UvrB protein, independent of its previously described role in the Uvr(A)BC complex, which could be specific for repair of monoadducts, intra-strand biadducts and/or ICL.
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Affiliation(s)
- Claudia Lage
- Laboratório de Radiobiologia Molecular, Instituto de Biofísica Carlos Chagas Filho, Bloco G, Centro de Ciencias da Saude, Universidade de Federal do Rio de Janeiro, 21949-900 Rio de Janeiro, RJ, Brazil
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82
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Abstract
Most metastatic cancers are fatal. More than 80% of patients with metastatic testicular germ-cell tumours (TGCTs), however, can be cured using cisplatin-based combination chemotherapy. Why are TGCTs more sensitive to chemotherapeutics than most other tumour types? Answers to this question could lead to new treatments for metastatic cancers.
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Affiliation(s)
- John R W Masters
- The Prostate Cancer Research Centre, Institute of Urology, University College London, 3rd Floor, 67 Riding House Street, London W1W 7EJ, UK.
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