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Ye M, Fang Y, Chen L, Song Z, Bao Q, Wang F, Huang H, Xu J, Wang Z, Xiao R, Han M, Gao S, Liu H, Jiang B, Qing G. Therapeutic targeting nudix hydrolase 1 creates a MYC-driven metabolic vulnerability. Nat Commun 2024; 15:2377. [PMID: 38493213 PMCID: PMC10944511 DOI: 10.1038/s41467-024-46572-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Accepted: 02/28/2024] [Indexed: 03/18/2024] Open
Abstract
Tumor cells must rewire nucleotide synthesis to satisfy the demands of unbridled proliferation. Meanwhile, they exhibit augmented reactive oxygen species (ROS) production which paradoxically damages DNA and free deoxy-ribonucleoside triphosphates (dNTPs). How these metabolic processes are integrated to fuel tumorigenesis remains to be investigated. MYC family oncoproteins coordinate nucleotide synthesis and ROS generation to drive the development of numerous cancers. We herein perform a Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based functional screen targeting metabolic genes and identified nudix hydrolase 1 (NUDT1) as a MYC-driven dependency. Mechanistically, MYC orchestrates the balance of two metabolic pathways that act in parallel, the NADPH oxidase 4 (NOX4)-ROS pathway and the Polo like kinase 1 (PLK1)-NUDT1 nucleotide-sanitizing pathway. We describe LC-1-40 as a potent, on-target degrader that depletes NUDT1 in vivo. Administration of LC-1-40 elicits excessive nucleotide oxidation, cytotoxicity and therapeutic responses in patient-derived xenografts. Thus, pharmacological targeting of NUDT1 represents an actionable MYC-driven metabolic liability.
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Affiliation(s)
- Minhui Ye
- Department of Urology, Medical Research Institute, Zhongnan Hospital of Wuhan University, Wuhan University, Wuhan, 430071, China
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Yingzhe Fang
- Department of Urology, Medical Research Institute, Zhongnan Hospital of Wuhan University, Wuhan University, Wuhan, 430071, China
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Lu Chen
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Zemin Song
- TaiKang Center for Life and Medical Sciences, School of Basic Medical Sciences, Wuhan University, Wuhan, 430071, China
| | - Qing Bao
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Fei Wang
- School of Life Science and Technology, ShanghaiTech University, Shanghai, 201210, China
| | - Hao Huang
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Jin Xu
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Ziwen Wang
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, 510060, China
| | - Ruijing Xiao
- TaiKang Center for Life and Medical Sciences, School of Basic Medical Sciences, Wuhan University, Wuhan, 430071, China
| | - Meng Han
- Protein Chemistry and Proteomics Facility, Tsinghua University Technology Center for Protein Research, Beijing, 10084, China
| | - Song Gao
- State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, 510060, China
| | - Hudan Liu
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China
| | - Baishan Jiang
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China.
| | - Guoliang Qing
- Department of Urology, Medical Research Institute, Zhongnan Hospital of Wuhan University, Wuhan University, Wuhan, 430071, China.
- Frontier Science Center for Immunology and Metabolism, Wuhan University, Wuhan, 430071, China.
- TaiKang Center for Life and Medical Sciences, School of Basic Medical Sciences, Wuhan University, Wuhan, 430071, China.
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Carter R, Cheraghchi-Bashi A, Westhorpe A, Yu S, Shanneik Y, Seraia E, Ouaret D, Inoue Y, Koch C, Wilding J, Ebner D, Ryan AJ, Buffa FM, Sharma RA. Identification of anticancer drugs to radiosensitise BRAF-wild-type and mutant colorectal cancer. Cancer Biol Med 2019; 16:234-246. [PMID: 31516745 PMCID: PMC6713640 DOI: 10.20892/j.issn.2095-3941.2018.0284] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Accepted: 12/21/2018] [Indexed: 12/12/2022] Open
Abstract
OBJECTIVE Patients with BRAF-mutant colorectal cancer (CRC) have a poor prognosis. Molecular status is not currently used to select which drug to use in combination with radiotherapy. Our aim was to identify drugs that radiosensitise CRC cells with known BRAF status. METHODS We screened 298 oncological drugs with and without ionising radiation in colorectal cancer cells isogenic for BRAF. Hits from rank product analysis were validated in a 16-cell line panel of human CRC cell lines, using clonogenic survival assays and xenograft models in vivo. RESULTS Most consistently identified hits were drugs targeting cell growth/proliferation or DNA damage repair. The most effective class of drugs that radiosensitised wild-type and mutant cell lines was PARP inhibitors. In clonogenic survival assays, talazoparib produced a radiation enhancement ratio of 1.9 in DLD1 (BRAF-wildtype) cells and 1.8 in RKO (BRAF V600E) cells. In DLD1 xenografts, talazoparib significantly increased the inhibitory effect of radiation on tumour growth (P ≤ 0.01). CONCLUSIONS Our method for screening large drug libraries for radiosensitisation has identified PARP inhibitors as promising radiosensitisers of colorectal cancer cells with wild-type and mutant BRAF backgrounds.
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Affiliation(s)
- Rebecca Carter
- NIHR University College London Hospitals Biomedical Research Centre, UCL Cancer Institute, University College London, London WC1E 6DD, UK
- NIHR Oxford Biomedical Research Centre, Department of Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Azadeh Cheraghchi-Bashi
- NIHR Oxford Biomedical Research Centre, Department of Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Adam Westhorpe
- NIHR University College London Hospitals Biomedical Research Centre, UCL Cancer Institute, University College London, London WC1E 6DD, UK
- NIHR Oxford Biomedical Research Centre, Department of Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Sheng Yu
- Computational Biology and Integrative Genomics, University of Oxford, Oxford OX1 2JD, UK
| | - Yasmin Shanneik
- NIHR Oxford Biomedical Research Centre, Department of Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Elena Seraia
- NDM Research Building, Nuffield Department of Medicine, University of Oxford, Oxford OX1 2JD, UK
| | - Djamila Ouaret
- Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX1 2JD, UK
| | - Yasuhiro Inoue
- Mie University, Graduate School of Medicine, Department of Gastrointestinal and Pediatric Surgery, Division of Reparative Medicine, Institute of Life Sciences, Edobashi 2-174, Tsu, Japan
| | - Catherine Koch
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
| | - Jenny Wilding
- Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX1 2JD, UK
| | - Daniel Ebner
- Target Discovery Institute, National Phenotypic Screening Centre, Nuffield Department of Medicine, University of Oxford, Oxford OX1 2JD, UK
| | - Anderson J. Ryan
- CRUK & MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Francesca M. Buffa
- CRUK & MRC Oxford Institute for Radiation Oncology, University of Oxford, Oxford OX1 2JD, UK
| | - Ricky A. Sharma
- NIHR University College London Hospitals Biomedical Research Centre, UCL Cancer Institute, University College London, London WC1E 6DD, UK
- NIHR Oxford Biomedical Research Centre, Department of Oncology, University of Oxford, Oxford OX1 2JD, UK
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Huff SE, Mohammed FA, Yang M, Agrawal P, Pink J, Harris ME, Dealwis CG, Viswanathan R. Structure-Guided Synthesis and Mechanistic Studies Reveal Sweetspots on Naphthyl Salicyl Hydrazone Scaffold as Non-Nucleosidic Competitive, Reversible Inhibitors of Human Ribonucleotide Reductase. J Med Chem 2018; 61:666-680. [PMID: 29253340 PMCID: PMC5808567 DOI: 10.1021/acs.jmedchem.7b00530] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ribonucleotide reductase (RR), an established cancer target, is usually inhibited by antimetabolites, which display multiple cross-reactive effects. Recently, we discovered a naphthyl salicyl acyl hydrazone-based inhibitor (NSAH or E-3a) of human RR (hRR) binding at the catalytic site (C-site) and inhibiting hRR reversibly. We herein report the synthesis and biochemical characterization of 25 distinct analogs. We designed each analog through docking to the C-site of hRR based on our 2.7 Å X-ray crystal structure (PDB ID: 5TUS). Broad tolerance to minor structural variations preserving inhibitory potency is observed. E-3f (82% yield) displayed an in vitro IC50 of 5.3 ± 1.8 μM against hRR, making it the most potent in this series. Kinetic assays reveal that E-3a, E-3c, E-3t, and E-3w bind and inhibit hRR through a reversible and competitive mode. Target selectivity toward the R1 subunit of hRR is established, providing a novel way of inhibition of this crucial enzyme.
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Affiliation(s)
- Sarah E. Huff
- Department of Chemistry, Case Western Reserve University, College of Arts and Sciences, Millis Science Center: Rm 216, 2074, Adelbert Road, Cleveland, OH 44106-7078
| | - Faiz Ahmad Mohammed
- Department of Pharmacology, Case Western Reserve University, School of Medicine, 10900 Euclid Ave, Cleveland, OH 44106
| | - Mu Yang
- Department of Chemistry, Case Western Reserve University, College of Arts and Sciences, Millis Science Center: Rm 216, 2074, Adelbert Road, Cleveland, OH 44106-7078
| | - Prashansa Agrawal
- Department of Chemistry, Case Western Reserve University, College of Arts and Sciences, Millis Science Center: Rm 216, 2074, Adelbert Road, Cleveland, OH 44106-7078
| | - John Pink
- Case Comprehensive Cancer Center, Case Western Reserve University, School of Medicine, 10900 Euclid Ave, Cleveland, OH 44106
| | - Michael E. Harris
- Department of Chemistry, University of Florida, PO Box 117200, Gainseville, FL 32611
| | - Chris G. Dealwis
- Department of Pharmacology, Case Western Reserve University, School of Medicine, 10900 Euclid Ave, Cleveland, OH 44106
- Center for Proteomics and the Department of Chemistry, Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106
| | - Rajesh Viswanathan
- Frank Hovorka Assistant Professor of Chemistry and Scientific Oversight Board Member – Small Molecule Drug Discovery Core, CWRU, 10900 Euclid Ave, Cleveland, OH 44106
- Department of Chemistry, Case Western Reserve University, College of Arts and Sciences, Millis Science Center: Rm 216, 2074, Adelbert Road, Cleveland, OH 44106-7078
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4
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Potent competitive inhibition of human ribonucleotide reductase by a nonnucleoside small molecule. Proc Natl Acad Sci U S A 2017; 114:8241-8246. [PMID: 28716944 DOI: 10.1073/pnas.1620220114] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human ribonucleotide reductase (hRR) is crucial for DNA replication and maintenance of a balanced dNTP pool, and is an established cancer target. Nucleoside analogs such as gemcitabine diphosphate and clofarabine nucleotides target the large subunit (hRRM1) of hRR. These drugs have a poor therapeutic index due to toxicity caused by additional effects, including DNA chain termination. The discovery of nonnucleoside, reversible, small-molecule inhibitors with greater specificity against hRRM1 is a key step in the development of more effective treatments for cancer. Here, we report the identification and characterization of a unique nonnucleoside small-molecule hRR inhibitor, naphthyl salicylic acyl hydrazone (NSAH), using virtual screening, binding affinity, inhibition, and cell toxicity assays. NSAH binds to hRRM1 with an apparent dissociation constant of 37 µM, and steady-state kinetics reveal a competitive mode of inhibition. A 2.66-Å resolution crystal structure of NSAH in complex with hRRM1 demonstrates that NSAH functions by binding at the catalytic site (C-site) where it makes both common and unique contacts with the enzyme compared with NDP substrates. Importantly, the IC50 for NSAH is within twofold of gemcitabine for growth inhibition of multiple cancer cell lines, while demonstrating little cytotoxicity against normal mobilized peripheral blood progenitor cells. NSAH depresses dGTP and dATP levels in the dNTP pool causing S-phase arrest, providing evidence for RR inhibition in cells. This report of a nonnucleoside reversible inhibitor binding at the catalytic site of hRRM1 provides a starting point for the design of a unique class of hRR inhibitors.
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5
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Im MM, Flanagan SA, Ackroyd JJ, Knapp B, Kramer A, Shewach DS. Late DNA Damage Mediated by Homologous Recombination Repair Results in Radiosensitization with Gemcitabine. Radiat Res 2016; 186:466-477. [PMID: 27740890 DOI: 10.1667/rr14443.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Gemcitabine (dFdCyd) shows broad antitumor activity in solid tumors in chemotherapeutic regimens or when combined with ionizing radiation (radiosensitization). While it is known that mismatches in DNA are necessary for dFdCyd radiosensitization, the critical event resulting in radiosensitization has not been identified. Here we hypothesized that late DNA damage (≥24 h after drug washout/irradiation) is a causal event in radiosensitization by dFdCyd, and that homologous recombination repair (HRR) is required for this late DNA damage. Using γ-H2AX as a measurement of DNA damage in MCF-7 breast cancer cells, we demonstrate that 10 or 80 nM dFdCyd alone produced significantly more late DNA damage compared to that observed within 4 h after treatment. The combination of dFdCyd treatment followed by irradiation did not produce a consistent increase in DNA damage in the first 4 h after treatment, however, there was a synergistic increase 24-48 h later relative to treatment with dFdCyd or radiation alone. RNAi suppression of the essential HRR protein, XRCC3, significantly decreased both radiosensitization and late DNA damage. Furthermore, inhibition of HRR with the Rad51 inhibitor B02 prevented radiosensitization when added after, but not during, treatment with dFdCyd and radiation. To our knowledge, this is the first published study to show that radiosensitization with dFdCyd results from a synergistic increase in DNA damage at 24-48 h after drug and radiation treatment, and that this damage and radiosensitization require HRR. These results suggest that tumors that overexpress HRR will be more vulnerable to chemoradiotherapy, and treatments that increase HRR and/or mismatches in DNA will enhance dFdCyd radiosensitization.
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Affiliation(s)
- Michael M Im
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Sheryl A Flanagan
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Jeffrey J Ackroyd
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Brendan Knapp
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Aaron Kramer
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
| | - Donna S Shewach
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
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Lamm N, Maoz K, Bester AC, Im MM, Shewach DS, Karni R, Kerem B. Folate levels modulate oncogene-induced replication stress and tumorigenicity. EMBO Mol Med 2016. [PMID: 26197802 PMCID: PMC4568948 DOI: 10.15252/emmm.201404824] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Chromosomal instability in early cancer stages is caused by replication stress. One mechanism by which oncogene expression induces replication stress is to drive cell proliferation with insufficient nucleotide levels. Cancer development is driven by alterations in both genetic and environmental factors. Here, we investigated whether replication stress can be modulated by both genetic and non-genetic factors and whether the extent of replication stress affects the probability of neoplastic transformation. To do so, we studied the effect of folate, a micronutrient that is essential for nucleotide biosynthesis, on oncogene-induced tumorigenicity. We show that folate deficiency by itself leads to replication stress in a concentration-dependent manner. Folate deficiency significantly enhances oncogene-induced replication stress, leading to increased DNA damage and tumorigenicity in vitro. Importantly, oncogene-expressing cells, when grown under folate deficiency, exhibit a significantly increased frequency of tumor development in mice. These findings suggest that replication stress is a quantitative trait affected by both genetic and non-genetic factors and that the extent of replication stress plays an important role in cancer development.
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Affiliation(s)
- Noa Lamm
- Department of Genetics, The Alexander Silberman Institute of Life Sciences Edmond J. Safra Campus The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Karin Maoz
- Department of Genetics, The Alexander Silberman Institute of Life Sciences Edmond J. Safra Campus The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Assaf C Bester
- Department of Genetics, The Alexander Silberman Institute of Life Sciences Edmond J. Safra Campus The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Michael M Im
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Donna S Shewach
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI, USA
| | - Rotem Karni
- Department of Biochemistry and Molecular Biology, Institute for Medical Research Israel-Canada The Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Batsheva Kerem
- Department of Genetics, The Alexander Silberman Institute of Life Sciences Edmond J. Safra Campus The Hebrew University of Jerusalem, Jerusalem, Israel
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7
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Harrabi SB, Adeberg S, Winter M, Haberer T, Debus J, Weber KJ. S-phase-specific radiosensitization by gemcitabine for therapeutic carbon ion exposure in vitro. JOURNAL OF RADIATION RESEARCH 2016; 57:110-114. [PMID: 26747201 PMCID: PMC4795954 DOI: 10.1093/jrr/rrv097] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Revised: 08/27/2015] [Accepted: 10/19/2015] [Indexed: 06/05/2023]
Abstract
Densely ionizing charged particle irradiation offers physical as well as biological advantages compared with photon irradiation. Radiobiological data for the combination of such particle irradiation (i.e. therapeutic carbon ions) with commonly used chemotherapeutics are still limited. Recent in vitro results indicate a general prevalence of additive cytotoxic effects in combined treatments, but an extension of established multimodal treatment regimens with photons to the inclusion of particle therapy needs to evaluate possible peculiarities of using high linear energy transfer (LET) radiation. The present study investigates the effect of combined radiochemotherapy using gemcitabine and high-LET irradiation with therapeutic carbon ions. In particular, the earlier observation of S-phase specific radiosensitization with photon irradiation should be evaluated with carbon ions. In the absence of the drug gemcitabine, carbon ion irradiation produced the typical survival behavior seen with X-rays-increased relative biological efficiency, and depletion of the survival curve's shoulder. By means of serum deprivation and subsequent replenishment, ∼70% S-phase content of the cell population was achieved, and such preparations showed radioresistance in both treatment arms-,photon and carbon ion irradiation. Combined modality treatment with gemcitabine caused significant reduction of clonogenic survival especially for the S-phase cells. WIDR cells exhibited S-phase-specific radioresistance with high-LET irradiation, although this was less pronounced than for X-ray exposure. The combined treatment with therapeutic carbon ions and gemcitabine caused the resistance phenomenon to disappear phenotypically.
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Affiliation(s)
- Semi B Harrabi
- Department of Radiation Oncology, University Hospital of Heidelberg, Im Neuenheimer Feld 400, Heidelberg 69120, Germany Heidelberg Ion Therapy Center (HIT), Im Neuenheimer Feld 450, Heidelberg 69120, Germany
| | - Sebastian Adeberg
- Department of Radiation Oncology, University Hospital of Heidelberg, Im Neuenheimer Feld 400, Heidelberg 69120, Germany
| | - Marcus Winter
- Heidelberg Ion Therapy Center (HIT), Im Neuenheimer Feld 450, Heidelberg 69120, Germany
| | - Thomas Haberer
- Heidelberg Ion Therapy Center (HIT), Im Neuenheimer Feld 450, Heidelberg 69120, Germany
| | - Jürgen Debus
- Department of Radiation Oncology, University Hospital of Heidelberg, Im Neuenheimer Feld 400, Heidelberg 69120, Germany Heidelberg Ion Therapy Center (HIT), Im Neuenheimer Feld 450, Heidelberg 69120, Germany
| | - Klaus-Josef Weber
- Department of Radiation Oncology, University Hospital of Heidelberg, Im Neuenheimer Feld 400, Heidelberg 69120, Germany
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8
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Im MM, Flanagan SA, Ackroyd JJ, Shewach DS. Drug metabolism and homologous recombination repair in radiosensitization with gemcitabine. Radiat Res 2015; 183:114-23. [PMID: 25564718 DOI: 10.1667/rr13807.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Gemcitabine (difluorodeoxycytidine; dFdCyd) is a potent radiosensitizer, noted for its ability to enhance cytotoxicity with radiation at noncytotoxic concentrations in vitro and subchemotherapeutic doses in patients. Radiosensitization in human tumor cells requires dFdCyd-mediated accumulation of cells in S phase with inhibition of ribonucleotide reductase, resulting in ≥80% deoxyadenosine triphosphate (dATP) depletion and errors of replication in DNA. Less is known of the role of specific DNA replication and repair pathways in the radiosensitization mechanism. Here the role of homologous recombination (HR) in relationship to the metabolic and cell cycle effects of dFdCyd was investigated using a matched pair of CHO cell lines that are either proficient (AA8 cells) or deficient (irs1SF cells) in HR based on expression of the HR protein XRCC3. The results demonstrated that the characteristics of radiosensitization in the rodent AA8 cells differed significantly from those in human tumor cells. In the AA8 cells, radiosensitization was achieved only under short (≤4 h) cytotoxic incubations, and S-phase accumulation did not appear to be required for radiosensitization. In contrast, human tumor cell lines were radiosensitized using noncytotoxic concentrations of dFdCyd and required early S-phase accumulation. Studies of the metabolic effects of dFdCyd demonstrated low dFdCyd concentrations did not deplete dATP by ≥80% in AA8 and irs1SF cells. However, at higher concentrations of dFdCyd, failure to radiosensitize the HR-deficient irs1SF cells could not be explained by a lack of dATP depletion or lack of S-phase accumulation. Thus, these parameters did not correspond to dFdCyd radiosensitization in the CHO cells. To evaluate directly the role of HR in radiosensitization, XRCC3 expression was suppressed in the AA8 cells with a lentiviral-delivered shRNA. Partial XRCC3 suppression significantly decreased radiosensitization [radiation enhancement ratio (RER) = 1.6 ± 0.15], compared to nontransduced (RER = 2.7 ± 0.27; P = 0.012), and a substantial decrease compared to nonspecific shRNA-transduced (RER = 2.5 ± 0.42; P = 0.056) AA8 cells. Although the results support a role for HR in radiosensitization with dFdCyd in CHO cells, the differences in the underlying metabolic and cell cycle characteristics suggest that dFdCyd radiosensitization in the nontumor-derived CHO cells is mechanistically distinct from that in human tumor cells.
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Affiliation(s)
- Michael M Im
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109
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9
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Xie M, Yen Y, Owonikoko TK, Ramalingam SS, Khuri FR, Curran WJ, Doetsch PW, Deng X. Bcl2 induces DNA replication stress by inhibiting ribonucleotide reductase. Cancer Res 2013; 74:212-23. [PMID: 24197132 DOI: 10.1158/0008-5472.can-13-1536-t] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
DNA replication stress is an inefficient DNA synthesis process that leads replication forks to progress slowly or stall. Two main factors that cause replication stress are alterations in pools of deoxyribonucleotide (dNTP) precursors required for DNA synthesis and changes in the activity of proteins required for synthesis of dNTPs. Ribonucleotide reductase (RNR), containing regulatory hRRM1 and catalytic hRRM2 subunits, is the enzyme that catalyzes the conversion of ribonucleoside diphosphates (NDP) to deoxyribonucleoside diphosphates (dNDP) and thereby provides dNTP precursors needed for the synthesis of DNA. Here, we demonstrate that either endogenous or exogenous expression of Bcl2 results in decreases in RNR activity and intracellular dNTP, retardation of DNA replication fork progression, and increased rate of fork asymmetry leading to DNA replication stress. Bcl2 colocalizes with hRRM1 and hRRM2 in the cytoplasm and directly interacts via its BH4 domain with hRRM2 but not hRRM1. Removal of the BH4 domain of Bcl2 abrogates its inhibitory effects on RNR activity, dNTP pool level, and DNA replication. Intriguingly, Bcl2 directly inhibits RNR activity by disrupting the functional hRRM1/hRRM2 complex via its BH4 domain. Our findings argue that Bcl2 reduces intracellular dNTPs by inhibiting ribonucleotide reductase activity, thereby providing insight into how Bcl2 triggers DNA replication stress.
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Affiliation(s)
- Maohua Xie
- Authors' Affiliations: Departments of Radiation Oncology, Hematology and Medical Oncology, and Biochemistry, Emory University School of Medicine and Winship Cancer Institute of Emory University, Atlanta, Georgia; and Department of Clinical and Molecular Pharmacology, City of Hope National Medical Center, Duarte, California
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Sidorova JM, Kehrli K, Mao F, Monnat R. Distinct functions of human RECQ helicases WRN and BLM in replication fork recovery and progression after hydroxyurea-induced stalling. DNA Repair (Amst) 2012; 12:128-39. [PMID: 23253856 DOI: 10.1016/j.dnarep.2012.11.005] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 10/15/2012] [Accepted: 11/18/2012] [Indexed: 12/21/2022]
Abstract
Human WRN and BLM genes are members of the conserved RECQ helicase family. Mutations in these genes are associated with Werner and Bloom syndromes. WRN and BLM proteins are implicated in DNA replication, recombination, repair, telomere maintenance, and transcription. Using microfluidics-assisted display of DNA for replication track analysis (ma-RTA), we show that WRN and BLM contribute additively to normal replication fork progression, and non-additively, in a RAD51-dependent pathway, to resumption of replication after arrest by hydroxyurea (HU), a replication-stalling drug. WRN but not BLM is required to support fork progression after HU. Resumption of replication by forks may be necessary but is not sufficient for timely completion of the cell cycle after HU arrest, as depletion of WRN or BLM compromises fork recovery to a similar degree, but only BLM depletion leads to extensive delay of cell division after HU, as well as more pronounced chromatin bridging. Finally, we show that recovery from HU includes apparent removal of some of the DNA that was synthesized immediately after release from HU, a novel phenomenon that we refer to as nascent strand processing, NSP.
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Affiliation(s)
- Julia M Sidorova
- Department of Pathology, University of Washington, Seattle, WA 98195-7705, United States.
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11
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Walton MI, Eve PD, Hayes A, Valenti MR, De Haven Brandon AK, Box G, Hallsworth A, Smith EL, Boxall KJ, Lainchbury M, Matthews TP, Jamin Y, Robinson SP, Aherne GW, Reader JC, Chesler L, Raynaud FI, Eccles SA, Collins I, Garrett MD. CCT244747 is a novel potent and selective CHK1 inhibitor with oral efficacy alone and in combination with genotoxic anticancer drugs. Clin Cancer Res 2012; 18:5650-61. [PMID: 22929806 PMCID: PMC3474704 DOI: 10.1158/1078-0432.ccr-12-1322] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
PURPOSE Many tumors exhibit defective cell-cycle checkpoint control and increased replicative stress. CHK1 is critically involved in the DNA damage response and maintenance of replication fork stability. We have therefore discovered a novel potent, highly selective, orally active ATP-competitive CHK1 inhibitor, CCT244747, and present its preclinical pharmacology and therapeutic activity. EXPERIMENTAL DESIGN Cellular CHK1 activity was assessed using an ELISA assay, and cytotoxicity a SRB assay. Biomarker modulation was measured using immunoblotting, and cell-cycle effects by flow cytometry analysis. Single-agent oral CCT244747 antitumor activity was evaluated in a MYCN-driven transgenic mouse model of neuroblastoma by MRI and in genotoxic combinations in human tumor xenografts by growth delay. RESULTS CCT244747 inhibited cellular CHK1 activity (IC(50) 29-170 nmol/L), significantly enhanced the cytotoxicity of several anticancer drugs, and abrogated drug-induced S and G(2) arrest in multiple tumor cell lines. Biomarkers of CHK1 (pS296 CHK1) activity and cell-cycle inactivity (pY15 CDK1) were induced by genotoxics and inhibited by CCT244747 both in vitro and in vivo, producing enhanced DNA damage and apoptosis. Active tumor concentrations of CCT244747 were obtained following oral administration. The antitumor activity of both gemcitabine and irinotecan were significantly enhanced by CCT244747 in several human tumor xenografts, giving concomitant biomarker modulation indicative of CHK1 inhibition. CCT244747 also showed marked antitumor activity as a single agent in a MYCN-driven neuroblastoma. CONCLUSION CCT244747 represents the first structural disclosure of a highly selective, orally active CHK1 inhibitor and warrants further evaluation alone or combined with genotoxic anticancer therapies.
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Affiliation(s)
- Mike I Walton
- Cancer Research UK Cancer Therapeutics Unit, Division of Cancer Therapeutics, The Institute of Cancer Research, Sutton, United Kingdom.
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12
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Flanagan SA, Cooper KS, Mannava S, Nikiforov MA, Shewach DS. Short hairpin RNA suppression of thymidylate synthase produces DNA mismatches and results in excellent radiosensitization. Int J Radiat Oncol Biol Phys 2012; 84:e613-20. [PMID: 22867891 DOI: 10.1016/j.ijrobp.2012.06.050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 06/22/2012] [Accepted: 06/22/2012] [Indexed: 02/06/2023]
Abstract
PURPOSE To determine the effect of short hairpin ribonucleic acid (shRNA)-mediated suppression of thymidylate synthase (TS) on cytotoxicity and radiosensitization and the mechanism by which these events occur. METHODS AND MATERIALS shRNA suppression of TS was compared with 5-fluoro-2'-deoxyuridine (FdUrd) inactivation of TS with or without ionizing radiation in HCT116 and HT29 colon cancer cells. Cytotoxicity and radiosensitization were measured by clonogenic assay. Cell cycle effects were measured by flow cytometry. The effects of FdUrd or shRNA suppression of TS on dNTP deoxynucleotide triphosphate imbalances and consequent nucleotide misincorporations into deoxyribonucleic acid (DNA) were analyzed by high-pressure liquid chromatography and as pSP189 plasmid mutations, respectively. RESULTS TS shRNA produced profound (≥ 90%) and prolonged (≥ 8 days) suppression of TS in HCT116 and HT29 cells, whereas FdUrd increased TS expression. TS shRNA also produced more specific and prolonged effects on dNTPs deoxynucleotide triphosphates compared with FdUrd. TS shRNA suppression allowed accumulation of cells in S-phase, although its effects were not as long-lasting as those of FdUrd. Both treatments resulted in phosphorylation of Chk1. TS shRNA alone was less cytotoxic than FdUrd but was equally effective as FdUrd in eliciting radiosensitization (radiation enhancement ratio: TS shRNA, 1.5-1.7; FdUrd, 1.4-1.6). TS shRNA and FdUrd produced a similar increase in the number and type of pSP189 mutations. CONCLUSIONS TS shRNA produced less cytotoxicity than FdUrd but was equally effective at radiosensitizing tumor cells. Thus, the inhibitory effect of FdUrd on TS alone is sufficient to elicit radiosensitization with FdUrd, but it only partially explains FdUrd-mediated cytotoxicity and cell cycle inhibition. The increase in DNA mismatches after TS shRNA or FdUrd supports a causal and sufficient role for the depletion of dTTP thymidine triphosphate and consequent DNA mismatches underlying radiosensitization. Importantly, shRNA suppression of TS avoids FP-mediated TS elevation and its negative prognostic role. These studies support the further exploration of TS suppression as a novel radiosensitizing strategy.
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Affiliation(s)
- Sheryl A Flanagan
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan, USA.
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Perspectives for tailored chemoprevention and treatment of colorectal cancer in Lynch syndrome. Crit Rev Oncol Hematol 2011; 80:264-77. [DOI: 10.1016/j.critrevonc.2010.11.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2010] [Revised: 11/03/2010] [Accepted: 11/18/2010] [Indexed: 12/22/2022] Open
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Targeting the Large Subunit of Human Ribonucleotide Reductase for Cancer Chemotherapy. Pharmaceuticals (Basel) 2011; 4:1328-1354. [PMID: 23115527 PMCID: PMC3483043 DOI: 10.3390/ph4101328] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Ribonucleotide reductase (RR) is a crucial enzyme in de novo DNA synthesis, where it catalyses the rate determining step of dNTP synthesis. RRs consist of a large subunit called RR1 (α), that contains two allosteric sites and one catalytic site, and a small subunit called RR2 (β), which houses a tyrosyl free radical essential for initiating catalysis. The active form of mammalian RR is an αnβm hetero oligomer. RR inhibitors are cytotoxic to proliferating cancer cells. In this brief review we will discuss the three classes of RR, the catalytic mechanism of RR, the regulation of the dNTP pool, the substrate selection, the allosteric activation, inactivation by ATP and dATP, and the nucleoside drugs that target RR. We will also discuss possible strategies for developing a new class of drugs that disrupts the RR assembly.
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Gemcitabine-mediated radiosensitization of human soft tissue sarcoma. Transl Oncol 2011; 1:50-6. [PMID: 18607508 DOI: 10.1593/tlo.07121] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2007] [Revised: 11/20/2007] [Accepted: 11/21/2007] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND/PURPOSE Local and systemic control of soft tissue sarcoma (STS) remains a clinical challenge, particularly for retroperitoneal, deep truncal, or advanced extremity disease. 2',2'-Difluoro-2'-deoxycytidine (gemcitabine) is a potent radiosensitizer in many tumor types, but it has not been studied in human STS. The purpose of this study was to determine the radiosensitizing potential of gemcitabine in preclinical models of human STS. MATERIALS AND METHODS The in vitro radiosensitizing activity of gemcitabine was assessed with clonogenic survival assay on three human STS cell lines: SK-LMS-1 (leiomyosarcoma), SW-872 (liposarcoma), and HT-1080 (fibrosarcoma). Cell cycle distribution was determined using dual-channel flow cytometry. The in vivo radiosensitizing activity of gemcitabine was assessed with subcutaneous SK-LMS-1 nude mice xenografts. Tumor-bearing mice were treated with concurrent weekly gemcitabine and fractionated daily radiotherapy (RT) (2 Gy daily) for 3 weeks (a total dose of 30 Gy). RESULTS The 50% inhibitory concentration (IC(50)) of gemcitabine for the human STS cell lines ranged from 10 to 1000 nM. Significant in vitro radiosensitization was demonstrated in all three human STS cell lines using gemcitabine concentrations at and below the IC(50). Maximal radiosensitization was associated with accumulation of cells in early S-phase. SK-LMS-1 xenografts displayed significant tumor growth delay with combined gemcitabine and RT compared to either treatment alone. Treatment related toxicity was greatest in the gemcitabine plus RT arm, but remained at an acceptable level. CONCLUSIONS Gemcitabine is a potent radiosensitizer in preclinical models of human STS. Clinical trials combining gemcitabine and RT in human STS are warranted.
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Nucleotide deficiency promotes genomic instability in early stages of cancer development. Cell 2011; 145:435-46. [PMID: 21529715 DOI: 10.1016/j.cell.2011.03.044] [Citation(s) in RCA: 623] [Impact Index Per Article: 47.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 01/18/2011] [Accepted: 03/29/2011] [Indexed: 12/28/2022]
Abstract
Chromosomal instability in early cancer stages is caused by stress on DNA replication. The molecular basis for replication perturbation in this context is currently unknown. We studied the replication dynamics in cells in which a regulator of S phase entry and cell proliferation, the Rb-E2F pathway, is aberrantly activated. Aberrant activation of this pathway by HPV-16 E6/E7 or cyclin E oncogenes significantly decreased the cellular nucleotide levels in the newly transformed cells. Exogenously supplied nucleosides rescued the replication stress and DNA damage and dramatically decreased oncogene-induced transformation. Increased transcription of nucleotide biosynthesis genes, mediated by expressing the transcription factor c-myc, increased the nucleotide pool and also rescued the replication-induced DNA damage. Our results suggest a model for early oncogenesis in which uncoordinated activation of factors regulating cell proliferation leads to insufficient nucleotides that fail to support normal replication and genome stability.
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Huang Y, Rachid Z, Jean-Claude BJ. MGMT Is a Molecular Determinant for Potency of the DNA-EGFR–Combi-Molecule ZRS1. Mol Cancer Res 2011; 9:320-31. [DOI: 10.1158/1541-7786.mcr-10-0407] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Sandvold ML, Galmarini C, Myhren F, Peters G. The activity of the lipophilic nucleoside derivatives elacytarabine and CP-4126 in a panel of tumor cell lines resistant to nucleoside analogues. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2010; 29:386-93. [PMID: 20544524 DOI: 10.1080/15257771003729625] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The clinical activity of pyrimidine analogues (araC and gemcitabine) is impaired by different mechanisms of resistance and several efforts to overcome this problem have been undertaken. Elacytarabine (CP-4055, araC-5'elaidic acid ester) and CP-4126 (gemcitabine-5'elaidic acid ester) are lipophilic fatty acid derivatives of the nucleoside analogues araC and gemcitabine, respectively, that are currently investigated in clinical trials in solid tumors and hematological malignancies. Here, we present results on the activity of elacytarabine and CP-4126 in a panel of tumor cell lines that are resistant to araC and gemcitabine and we discuss the potential use of these agents in the treatment of patients with drug resistance phenotypes. We conclude that elacytarabine and CP-4126 are active in cells with deficient nucleoside membrane transport and altered mismatch repair. These results should be taking into consideration for future clinical development of elacyatrabine and CP-4126.
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Wouters A, Pauwels B, Lardon F, Pattyn GGO, Lambrechts HAJ, Baay M, Meijnders P, Vermorken JB. In vitro study on the schedule-dependency of the interaction between pemetrexed, gemcitabine and irradiation in non-small cell lung cancer and head and neck cancer cells. BMC Cancer 2010; 10:441. [PMID: 20723210 PMCID: PMC2931492 DOI: 10.1186/1471-2407-10-441] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Accepted: 08/19/2010] [Indexed: 12/14/2022] Open
Abstract
Background Based on their different mechanisms of action, non-overlapping side effects and radiosensitising potential, combining the antimetabolites pemetrexed (multitargeted antifolate, MTA) and gemcitabine (2',2'-difluorodeoxycytidine, dFdC) with irradiation (RT) seems promising. This in vitro study, for the first time, presents the triple combination of MTA, dFdC and irradiation using various treatment schedules. Methods The cytotoxicity, radiosensitising potential and cell cycle effect of MTA were investigated in A549 (NSCLC) and CAL-27 (SCCHN) cells. Using simultaneous or sequential exposure schedules, the cytotoxicity and radiosensitising effect of 24 h MTA combined with 1 h or 24 h dFdC were analysed. Results Including a time interval between MTA exposure and irradiation seemed favourable to MTA immediately preceding or following radiotherapy. MTA induced a significant S phase accumulation that persisted for more than 8 h after drug removal. Among different MTA/dFdC combinations tested, the highest synergistic interaction was produced by 24 h MTA followed by 1 h dFdC. Combined with irradiation, this schedule showed a clear radiosensitising effect. Conclusions Results from our in vitro model suggest that the sequence 24 h MTA → 1 h dFdC → RT is the most rational design and would, after confirmation in an in vivo setting, possibly provide the greatest benefit in the clinic.
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Affiliation(s)
- An Wouters
- Laboratory of Cancer Research and Clinical Oncology, Department of Medical Oncology, University of Antwerp, 2610 Wilrijk, Belgium.
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O'Konek JJ, Ladd B, Flanagan SA, Im MM, Boucher PD, Thepsourinthone TS, Secrist JA, Shewach DS. Alteration of the carbohydrate for deoxyguanosine analogs markedly changes DNA replication fidelity, cell cycle progression and cytotoxicity. Mutat Res 2010; 684:1-10. [PMID: 20004674 DOI: 10.1016/j.mrfmmm.2009.11.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2009] [Revised: 10/29/2009] [Accepted: 11/17/2009] [Indexed: 11/17/2022]
Abstract
Nucleoside analogs are efficacious cancer chemotherapeutics due to their incorporation into tumor cell DNA. However, they exhibit vastly different antitumor efficacies, suggesting that incorporation produces divergent effects on DNA replication. Here we have evaluated the consequences of incorporation on DNA replication and its fidelity for three structurally related deoxyguanosine analogs: ganciclovir (GCV), currently in clinical trials in a suicide gene therapy approach for cancer, D-carbocyclic 2'-deoxyguanosine (CdG) and penciclovir (PCV). GCV and CdG elicited similar cytotoxicity at low concentrations, whereas PCV was 10-100-fold less cytotoxic in human tumor cells. DNA replication fidelity was evaluated using a supF plasmid-based mutation assay. Only GCV induced a dose-dependent increase in mutation frequency, predominantly GC-->TA transversions, which contributed to cytotoxicity and implicated the ether oxygen in mutagenicity. Activation of mismatch repair with hydroxyurea decreased mutations but failed to repair the GC-->TA transversions. GCV slowed S-phase progression and CdG also induced a G2/M block, but both drugs allowed completion of one cell cycle after drug treatment followed by cell death in the second cell cycle. In contrast, PCV induced a lengthy early S-phase block due to profound suppression of DNA synthesis, with cell death in the first cell cycle after drug treatment. These data suggest that GCV and CdG elicit superior cytotoxicity due to their effects in template DNA, whereas strong inhibition of nascent strand synthesis by PCV may protect against cytotoxicity. Nucleoside analogs based on the carbohydrate structures of GCV and CdG is a promising area for antitumor drug development.
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Affiliation(s)
- Jessica J O'Konek
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI 48109, USA
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Chemoradiotherapy for Inoperable Non-small Cell Lung Cancer. Lung Cancer 2010. [DOI: 10.1007/978-1-60761-524-8_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Radivoyevitch T. Automated mass action model space generation and analysis methods for two-reactant combinatorially complex equilibriums: an analysis of ATP-induced ribonucleotide reductase R1 hexamerization data. Biol Direct 2009; 4:50. [PMID: 20003203 PMCID: PMC2799446 DOI: 10.1186/1745-6150-4-50] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Accepted: 12/09/2009] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Ribonucleotide reductase is the main control point of dNTP production. It has two subunits, R1, and R2 or p53R2. R1 has 5 possible catalytic site states (empty or filled with 1 of 4 NDPs), 5 possible s-site states (empty or filled with ATP, dATP, dTTP or dGTP), 3 possible a-site states (empty or filled with ATP or dATP), perhaps two possible h-site states (empty or filled with ATP), and all of this is folded into an R1 monomer-dimer-tetramer-hexamer equilibrium where R1 j-mers can be bound by variable numbers of R2 or p53R2 dimers. Trillions of RNR complexes are possible as a result. The problem is to determine which are needed in models to explain available data. This problem is intractable for 10 reactants, but it can be solved for 2 and is here for R1 and ATP. RESULTS Thousands of ATP-induced R1 hexamerization models with up to three (s, a and h) ATP binding sites per R1 subunit were automatically generated via hypotheses that complete dissociation constants are infinite and/or that binary dissociation constants are equal. To limit the model space size, it was assumed that s-sites are always filled in oligomers and never filled in monomers, and to interpret model terms it was assumed that a-sites fill before h-sites. The models were fitted to published dynamic light scattering data. As the lowest Akaike Information Criterion (AIC) of the 3-parameter models was greater than the lowest of the 2-parameter models, only models with up to 3 parameters were fitted. Models with sums of squared errors less than twice the minimum were then partitioned into two groups: those that contained no occupied h-site terms (508 models) and those that contained at least one (1580 models). Normalized AIC densities of these two groups of models differed significantly in favor of models that did not include an h-site term (Kolmogorov-Smirnov p < 1 x 10(-15)); consistent with this, 28 of the top 30 models (ranked by AICs) did not include an h-site term and 28/30 > 508/2088 with p < 2 x 10(-15). Finally, 99 of the 2088 models did not have any terms with ATP/R1 ratios >1.5, but of the top 30, there were 14 such models (14/30 > 99/2088 with p < 3 x 10(-16)), i.e. the existence of R1 hexamers with >3 a-sites occupied by ATP is also not supported by this dataset. CONCLUSION The analysis presented suggests that three a-sites may not be occupied by ATP in R1 hexamers under the conditions of the data analyzed. If a-sites fill before h-sites, this implies that the dataset analyzed can be explained without the existence of an h-site.
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Affiliation(s)
- Tomas Radivoyevitch
- Department of Epidemiology and Biostatistics, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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Heffeter P, Popovic-Bijelic A, Saiko P, Dornetshuber R, Jungwirth U, Voevodskaya N, Biglino D, Jakupec MA, Elbling L, Micksche M, Szekeres T, Keppler BK, Gräslund A, Berger W. Ribonucleotide reductase as one important target of [Tris(1,10-phenanthroline)lanthanum(III)] trithiocyanate (KP772). Curr Cancer Drug Targets 2009; 9:595-607. [PMID: 19508176 DOI: 10.2174/156800909789056962] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2008] [Accepted: 04/15/2009] [Indexed: 12/11/2022]
Abstract
KP772 is a new lanthanum complex containing three 1,10-phenathroline molecules. Recently, we have demonstrated that the promising in vitro and in vivo anticancer properties of KP772 are based on p53-independent G(0)G(1) arrest and apoptosis induction. A National Cancer Institute (NCI) screen revealed significant correlation of KP772 activity with that of the ribonucleotide reductase (RR) inhibitor hydroxyurea (HU). Consequently, this study aimed to investigate whether KP772 targets DNA synthesis in tumor cells by RR inhibition. Indeed, KP772 treatment led to significant reduction of cytidine incorporation paralleled by a decrease of deoxynucleoside triphosphate (dNTP) pools. This strongly indicates disruption of RR activity. Moreover, KP772 protected against oxidative stress, suggesting that this drug might interfere with RR by interaction with the tyrosyl radical in subunit R2. Additionally, several observations (e.g. increase of transferrin receptor expression and protective effect of iron preloading) indicate that KP772 interferes with cellular iron homeostasis. Accordingly, co-incubation of Fe(II) with KP772 led to generation of a coloured iron complex (Fe-KP772) in cell free systems. In electron paramagnetic resonance (EPR) measurements of mouse R2 subunits, KP772 disrupted the tyrosyl radical while Fe-KP772 had no significant effects. Moreover, coincubation of KP772 with iron-loaded R2 led to formation of Fe-KP772 suggesting chelation of RR-bound Fe(II). Summarizing, our data prove that KP772 inhibits RR by targeting the iron centre of the R2 subunit. As also Fe-KP772 as well as free lanthanum exert significant -though less pronounced- cytotoxic/static activities, additional mechanisms are likely to synergise with RR inhibition in the promising anticancer activity of KP772.
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Affiliation(s)
- P Heffeter
- Institute of Cancer Research, Department of Medicine I, Medical University of Vienna, 1090 Vienna, Austria
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Bischoff P, Altmeyer A, Dumont F. Radiosensitising agents for the radiotherapy of cancer: advances in traditional and hypoxia targeted radiosensitisers. Expert Opin Ther Pat 2009; 19:643-62. [DOI: 10.1517/13543770902824172] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Katz D, Ito E, Liu FF. On the path to seeking novel radiosensitizers. Int J Radiat Oncol Biol Phys 2009; 73:988-96. [PMID: 19251086 DOI: 10.1016/j.ijrobp.2008.12.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 11/29/2008] [Accepted: 12/02/2008] [Indexed: 10/21/2022]
Abstract
Radiation therapy is a highly effective cancer treatment modality, and extensive investigations have been undertaken over the years to augment its efficacy in the clinic. This review summarizes the current understanding of the biologic bases underpinning many of the clinically used radiosensitizers. In addition, this review illustrates how the advent of innovative, high-throughput technologies with integration of different disciplines could be harnessed for an expeditious discovery process for novel radiosensitizers, providing an exciting future for such pursuits in radiation biology and oncology.
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Affiliation(s)
- David Katz
- Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada
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Jensen A, Debus J, Weber KJ. S-phase cell-specific modification by gemcitabine of PFGE-analyzed radiation-induced DNA fragmentation and rejoining. Int J Radiat Biol 2009; 84:770-7. [PMID: 18821391 DOI: 10.1080/09553000802317752] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE To assess the cell cycle-dependent influence of gemcitabine on ionizing radiation-induced DNA double-strand breakage (DSB) and rejoining measured by pulsed-field gel electrophoresis (PFGE). MATERIALS AND METHODS WIDR cells (human colon carcinoma) were synchronized by serum starvation/stimulation providing populations with 7% (G1) or 50% S-phase cells, respectively. Following drug treatment (0.5 microg/ml for 2 hours) cells were irradiated (up to 90 Gy) or incubated for repair (up to 6 h after 40 Gy). Cell cycle changes were monitored by flow cytometry, DNA fragmentation was assessed by PFGE as fraction of electrophoretically mobile DNA. RESULTS Without drug treatment, irradiated S-phase cells exhibited lower PFGE signals than the G1 cells due to the well known electrophoretic immobility of replicative DNA fragments, but DSB rejoining was not different. Gemcitabine pretreatment increased the apparent initial radiation-induced DNA fragmentation specifically for S-phase cells. This effect was rapidly reversed (1 h) during incubation for repair. CONCLUSIONS The data indicate that gemcitabine causes the formation of additional radiation-induced DSB in S-phase cells or destabilizes the replicative structures that otherwise prevent DNA fragment migration during PFGE. The latter would be rapidly restituted superimposing DSB rejoining. This is discussed in relation to the recently proposed role of mismatch repair in gemcitabine radiosensitization.
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Flanagan SA, Krokosky CM, Mannava S, Nikiforov MA, Shewach DS. MLH1 deficiency enhances radiosensitization with 5-fluorodeoxyuridine by increasing DNA mismatches. Mol Pharmacol 2008; 74:863-71. [PMID: 18535288 DOI: 10.1124/mol.107.043349] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The antitumor drug 5-fluoro-2'-deoxyuridine (FdUrd) also sensitizes tumor cells to ionizing radiation in vitro and in vivo. Although radiosensitization with FdUrd requires dTTP depletion and S-phase arrest, the exact mechanism by which these events produce radiosensitization remains unknown. We hypothesized that the depletion of dTTP produces DNA mismatches that, if not repaired before irradiation, would result in radiosensitization. We evaluated this hypothesis in mismatch repair (MMR)-deficient HCT116 0-1 cells that lack the expression of the required MMR protein MLH1 (inactive MLH1), and in MMR-proficient (wild-type MLH1) HCT116 1-2 cells. Although HCT116 0-1 cells were less sensitive to FdUrd (IC(50) = 3.5 microM) versus HCT116 1-2 cells (IC(50) = 0.75 microM), when irradiation followed FdUrd (IC(50)) the MLH1-inactivated cells exhibited greater radiosensitization compared with MMR-wild-type cells [radiation enhancement ratio (RER) = 1.8 +/- 0.28 versus 1.1 +/- 0.1, respectively] and an increase (> or =8-fold) in nucleotide misincorporations. In SW620 cells and HCT116 1-2 MLH1-wild-type cells, FdUrd (IC(50)) did not produce radiosensitization nor did it increase the mutation frequency, but after short hairpin RNA-directed suppression of MLH1 this concentration produced excellent radiosensitization (RER = 1.6 +/- 0.10 and 1.5 +/- 0.06, respectively) and an increase in nucleotide misincorporations (8-fold and 6-fold, respectively). Incubation with higher concentrations of FdUrd (IC(90)) after suppression of MLH1 produced a further increase in ionizing radiation sensitivity in both SW620 and HCT116 1-2 cells (RER = 1.8 +/- 0.03 and 1.7 +/- 0.13, respectively) and nucleotide misincorporations (>10-fold in both cell lines). These results demonstrate an important role for MLH1 and implicate mismatches in radiosensitization by FdUrd.
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Affiliation(s)
- Sheryl A Flanagan
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI 48109-0504, USA
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Abstract
Radiosensitization with antimetabolites has improved clinical outcome for patients with solid malignancies, especially cancers of the GI tract, cervix, and head and neck. Fluorouracil (FU) and hydroxyurea have been widely used clinically during the last four decades, and promising results have been observed more recently with gemcitabine. Although the antimetabolites all target DNA replication, they differ with respect to the mechanisms by which they produce radiosensitization. The antimetabolite radiosensitizers may inhibit thymidylate synthase (TS) or ribonucleotide reductase, and the nucleoside/nucleobase analogs can be incorporated into DNA. Radiosensitization can result from chemotherapy-induced increase in DNA double-strand breaks or inhibition of their repair. Studies of repair pathways involved in radiosensitization with antimetabolites implicate base excision repair with the TS inhibitors, homologous recombination with gemcitabine, and mismatch repair with FU and gemcitabine. Gemcitabine can also stimulate epidermal growth factor receptor (EGFR) phosphorylation; inhibiting this effect with EGFR inhibitors can potentiate cytotoxicity and radiosensitization. Additional work is necessary to determine more precisely the processes by which antimetabolites act as radiation sensitizers and to define the optimal sequencing of these agents with EGFR inhibitors to provide better guidance for clinical protocols combining these drugs with radiotherapy.
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Affiliation(s)
- Donna S Shewach
- Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, MI 48109-0504, USA.
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