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Hume J, Lowry K, Whiley DM, Irwin AD, Bletchly C, Sweeney EL. Application of the ViroKey® SQ FLEX assay for detection of cytomegalovirus antiviral resistance. J Clin Virol 2023; 167:105556. [PMID: 37566984 DOI: 10.1016/j.jcv.2023.105556] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Revised: 07/13/2023] [Accepted: 08/03/2023] [Indexed: 08/13/2023]
Abstract
BACKGROUND Cytomegalovirus (CMV) is a viral infection which establishes lifelong latency, often reactivating and causing disease in immunosuppressed individuals, including haematopoietic stem cell transplant (HSCT) recipients. Treatment can be problematic due to antiviral resistance which substantially increases the risk of patient mortality. Diagnostic testing capabilities for CMV antiviral resistance in Australia and elsewhere have traditionally relied on gene-specific Sanger sequencing approaches, however, are now being superseded by next generation sequencing protocols. OBJECTIVE Provide a snapshot of local mutations and explore the feasibility of the ViroKeyࣨ® SQ FLEX Genotyping Assay (Vela Diagnostics Pty Ltd) by examining sequencing success. METHOD Performed sequencing on adult (n = 38) and paediatric (n = 81) plasma samples, over a large range of viral loads (above and below the assay recommended threshold of ≥1,000 International Units (IU)/mL; noting most of our paediatric samples have loads <1,000 IU/mL). RESULTS Eleven test runs (including three repeat runs; 14 to 15 samples per run) were conducted, and four runs were deemed valid. The overall individual sample success rate for the four evaluable test runs was 71.2% (42/59 samples); 80.4% (37/46) samples ≥1,000 IU/mL were valid. Ten clinically important antiviral resistance mutations were detected, the most common being A594V in the UL97 gene, found in 6 (5%) samples. CONCLUSIONS A range of technical issues were experienced, however with improvement this platform could be a useful addition to routine pathology workflows, providing timely antiviral resistance results for patients undergoing HSCT.
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Affiliation(s)
- Jocelyn Hume
- Faculty of Medicine, The University of Queensland Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Queensland, Australia; Pathology Queensland Central Laboratory, Brisbane, Queensland, Australia
| | - Kym Lowry
- Faculty of Medicine, The University of Queensland Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Queensland, Australia; Queensland Paediatric Infectious Diseases (QPID) Sakzewski Laboratory, Centre for Children's Health Research, Queensland Children's Hospital, Brisbane, Queensland, Australia
| | - David M Whiley
- Faculty of Medicine, The University of Queensland Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Queensland, Australia; Pathology Queensland Central Laboratory, Brisbane, Queensland, Australia
| | - Adam D Irwin
- Faculty of Medicine, The University of Queensland Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Queensland, Australia; Infection Management and Prevention Service, Queensland Children's Hospital, Brisbane, Queensland, Australia
| | - Cheryl Bletchly
- Pathology Queensland Central Laboratory, Brisbane, Queensland, Australia
| | - Emma L Sweeney
- Faculty of Medicine, The University of Queensland Centre for Clinical Research (UQCCR), The University of Queensland, Brisbane, Queensland, Australia.
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2
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Ismail MMF, Ayoup MS. Review on fluorinated nucleoside/non-nucleoside FDA-approved antiviral drugs. RSC Adv 2022; 12:31032-31045. [PMID: 36348998 PMCID: PMC9620415 DOI: 10.1039/d2ra05370e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2022] [Accepted: 10/13/2022] [Indexed: 11/07/2022] Open
Abstract
FDA-approved antiviral agents represent an important class that has attracted attention in recent years to combat current and future threats of viral pandemics. Fluorine ameliorates the electronic, lipophilic and steric problems of drugs. Additionally, fluorine can prolong drug activity and improve metabolic stability, thereby, modifying their pharmacodynamic and pharmacokinetic character. Herein, we summarized the fluorinated FDA-approved antiviral agents, dealing with biological aspects, mechanisms of action, and synthetic pathways.
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Affiliation(s)
- Magda M F Ismail
- Department of Pharmaceutical Medicinal Chemistry and Drug Design, Faculty of Pharmacy (Girls), Al-Azhar University Cairo 11754 Egypt
| | - Mohammed Salah Ayoup
- Department of Chemistry, Faculty of Science, Alexandria University P. O. Box 426 Alexandria 21321 Egypt
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Majewska A, Mlynarczyk-Bonikowska B. 40 Years after the Registration of Acyclovir: Do We Need New Anti-Herpetic Drugs? Int J Mol Sci 2022; 23:ijms23073431. [PMID: 35408788 PMCID: PMC8998721 DOI: 10.3390/ijms23073431] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2022] [Revised: 03/10/2022] [Accepted: 03/18/2022] [Indexed: 01/17/2023] Open
Abstract
Herpes simplex virus types 1 and 2 HSV1 and 2, namely varicella-zoster VZV and cytomegalovirus CMV, are among the most common pathogens worldwide. They remain in the host body for life. The course of infection with these viruses is often asymptomatic or mild and self-limiting, but in immunocompromised patients, such as solid organ or bone marrow transplant recipients, the course can be very severe or even life-threatening. Unfortunately, in the latter group, the highest percentage of infections with strains resistant to routinely used drugs is observed. On the other hand, frequent recurrences of genital herpes can be a problem even in people with normal immunity. Genital herpes also increases the risk of acquiring sexually transmitted diseases, including HIV infection and, if present in pregnant women, poses a risk to the fetus and newborn. Even more frequently than herpes simplex, congenital infections can be caused by cytomegalovirus. We present the most important anti-herpesviral agents, the mechanisms of resistance to these drugs, and the associated mutations in the viral genome. Special emphasis was placed on newly introduced drugs such as maribavir and brincidofovir. We also briefly discuss the most promising substances in preclinical testing as well as immunotherapy options and vaccines currently in use and under investigation.
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Affiliation(s)
- Anna Majewska
- Department of Medical Microbiology, Medical University of Warsaw, Chałubińskiego 5, 02-004 Warsaw, Poland;
| | - Beata Mlynarczyk-Bonikowska
- Department of Dermatology, Immunodermatology and Venereology, Medical University of Warsaw, Koszykowa 82a, 02-008 Warsaw, Poland
- Correspondence: ; Tel.: +48-225021313
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Abstract
Human herpesviruses are large double-stranded DNA viruses belonging to the Herpesviridae family. The main characteristics of these viruses are their ability to establish a lifelong latency into the host with a potential to reactivate periodically. Primary infections and reactivations with herpesviruses are responsible for a large spectrum of diseases and may result in severe complications in immunocompromised patients. The viral DNA polymerase is a key enzyme in the replicative cycle of herpesviruses, and the target of most antiviral agents (i.e., nucleoside, nucleotide and pyrophosphate analogs). However, long-term prophylaxis and treatment with these antivirals may lead to the emergence of drug-resistant isolates harboring mutations in genes encoding viral enzymes that phosphorylate drugs (nucleoside analogs) and/or DNA polymerases, with potential cross-resistance between the different analogs. Drug resistance mutations mainly arise in conserved regions of the polymerase and exonuclease functional domains of these enzymes. In the polymerase domain, mutations associated with resistance to nucleoside/nucleotide analogs may directly or indirectly affect drug binding or incorporation into the primer strand, or increase the rate of extension of DNA to overcome chain termination. In the exonuclease domain, mutations conferring resistance to nucleoside/nucleotide analogs may reduce the rate of excision of incorporated drug, or continue DNA elongation after drug incorporation without excision. Mutations associated with resistance to pyrophosphate analogs may alter drug binding or the conformational changes of the polymerase domain required for an efficient activity of the enzyme. Novel herpesvirus inhibitors with a potent antiviral activity against drug-resistant isolates are thus needed urgently.
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Affiliation(s)
| | - Guy Boivin
- CHU de Québec-Université Laval, Quebec City, QC, Canada.
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Impact of Amino Acid Substitutions in Region II and Helix K of Herpes Simplex Virus 1 and Human Cytomegalovirus DNA Polymerases on Resistance to Foscarnet. Antimicrob Agents Chemother 2021; 65:e0039021. [PMID: 33875432 DOI: 10.1128/aac.00390-21] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Amino acid substitutions conferring resistance of herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV) to foscarnet (PFA) are located in the genes UL30 and UL54, respectively, encoding the DNA polymerase (pol). In this study, we analyzed the impact of substitutions located in helix K and region II that are involved in the conformational changes of the DNA pol. Theoretical substitutions were identified by sequences alignment of the helix K and region II of human herpesviruses (susceptible to PFA) and bacteriophages (resistant to PFA) and introduced in viral genomes by recombinant phenotyping. We characterized the susceptibility of HSV-1 and HCMV mutants to PFA. In UL30, the substitutions I619K (helix K), V715S, and A719T (both in region II) increased mean PFA 50% effective concentrations (EC50s) by 2.5-, 5.6-, and 2.0-fold, respectively, compared to the wild type (WT). In UL54, the substitution Q579I (helix K) conferred hypersusceptibility to PFA (0.17-fold change), whereas the substitutions Q697P, V715S, and A719T (all in region II) increased mean PFA EC50s by 3.8-, 2.8- and 2.5-fold, respectively, compared to the WT. These results were confirmed by enzymatic assays using recombinant DNA pol harboring these substitutions. Three-dimensional modeling suggests that substitutions conferring resistance/hypersusceptibility to PFA located in helix K and region II of UL30 and UL54 DNA pol favor an open/closed conformation of these enzymes, resulting in a lower/higher drug affinity for the proteins. Thus, this study shows that both regions of UL30 and UL54 DNA pol are involved in the conformational changes of these proteins and can influence the susceptibility of both viruses to PFA.
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6
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Zarrouk K, Zhu X, Goyette N, Piret J, Shi R, Boivin G. Differential impact of various substitutions at codon 715 in region II of HSV-1 and HCMV DNA polymerases. Antiviral Res 2021; 188:105046. [PMID: 33588012 DOI: 10.1016/j.antiviral.2021.105046] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 02/05/2021] [Accepted: 02/08/2021] [Indexed: 01/13/2023]
Abstract
This study aimed at understanding the impact of different substitutions at codon 715 localized in the region II of the palm domain of herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV) DNA polymerases (pol). Here, we report a new theoretical mutation V715S that confers resistance of HSV-1 to foscarnet/acyclovir (5.6- and 9.2-fold increases EC50 values compared to wild type, respectively) and of HCMV to foscarnet/ganciclovir (2.8- and 2.9-fold increases in EC50 values compared to wild type, respectively). To further analyze the importance of this amino acid, we investigated the impact of the already known mutations V715M and V715G on the replicative capacities and drug susceptibilities of both viruses as well as on the activity and drug inhibition of the DNA pol. The V715G recombinant HSV-1 mutant was resistant to foscarnet and acyclovir (3.4- and 4.6-fold EC50 increase, respectively) whereas the V715M mutant was susceptible to foscarnet and resistant to acyclovir (3.4-fold EC50 increase). The V715G recombinant HCMV mutant did not grow and the V715M mutant was resistant to foscarnet (3.7-fold EC50 increase) and susceptible to ganciclovir. Finally, we showed by three-dimensional modeling that the differential impact of these mutations on the viral replicative capacity and drug resistance profile was related to different hydrophobic local environments for V715 in the DNA pol of the two viruses. Furthermore, we hypothesize that the DNA pol of HSV-1 is more tolerant to changes at this residue compared to that of HCMV because of a more hydrophobic environment stabilizing the region.
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Affiliation(s)
- Karima Zarrouk
- Research Center in Infectious Diseases, CHU de Québec- Laval University, Quebec City, QC, Canada
| | - Xiaojun Zhu
- Department of Biochemistry, Microbiology and Bioinformatics, PROTEO, And Institute of Integrative and Systems Biology, Laval University, Quebec City, QC, Canada
| | - Nathalie Goyette
- Research Center in Infectious Diseases, CHU de Québec- Laval University, Quebec City, QC, Canada
| | - Jocelyne Piret
- Research Center in Infectious Diseases, CHU de Québec- Laval University, Quebec City, QC, Canada
| | - Rong Shi
- Department of Biochemistry, Microbiology and Bioinformatics, PROTEO, And Institute of Integrative and Systems Biology, Laval University, Quebec City, QC, Canada
| | - Guy Boivin
- Research Center in Infectious Diseases, CHU de Québec- Laval University, Quebec City, QC, Canada.
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Hypersusceptibility of Human Cytomegalovirus to Foscarnet Induced by Mutations in Helices K and P of the Viral DNA Polymerase. Antimicrob Agents Chemother 2020; 64:AAC.01910-19. [PMID: 32015044 DOI: 10.1128/aac.01910-19] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 01/28/2020] [Indexed: 12/31/2022] Open
Abstract
Herein, we phenotypically and enzymatically characterize the theoretical mutation Q579I in helix K and the already described clinical mutation K805Q in helix P of cytomegalovirus DNA polymerase for susceptibility to foscarnet. Q579I and K805Q recombinant viruses were hypersusceptible to foscarnet (respective mean 50% effective concentrations [EC50] of 0.12- and 0.19-fold that of the wild type). Three-dimensional modeling analysis suggested that both mutations favor the closed conformation of the enzyme to which foscarnet binds with a higher affinity.
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WANG C, RUAN S, GU X, ZHU B. Antiviral activities of Radix Isatidis polysaccharide against type II herpes simplex virus in vitro. FOOD SCIENCE AND TECHNOLOGY 2018. [DOI: 10.1590/1678-457x.19317] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
| | - Shiman RUAN
- Jinan Center for Disease Control and Prevention, China
| | - Xunmei GU
- Jinan Infectious Disease Hospital, China
| | - Bin ZHU
- The Second People's Hospital of Jinan, China
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9
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Zhang L. New Insights into DNA Polymerase Function Revealed by Phosphonoacetic Acid-Sensitive T4 DNA Polymerases. Chem Res Toxicol 2017; 30:1984-1992. [PMID: 28872853 DOI: 10.1021/acs.chemrestox.7b00132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The bacteriophage T4 DNA polymerase (pol) and the closely related RB69 DNA pol have been developed into model enzymes to study family B DNA pols. While all family B DNA pols have similar structures and share conserved protein motifs, the molecular mechanism underlying natural drug resistance of nonherpes family B DNA pols and drug sensitivity of herpes DNA pols remains unknown. In the present study, we constructed T4 phages containing G466S, Y460F, G466S/Y460F, P469S, and V475W mutations in DNA pol. These amino acid substitutions replace the residues in drug-resistant T4 DNA pol with residues found in drug-sensitive herpes family DNA pols. We investigated whether the T4 phages expressing the engineered mutant DNA pols were sensitive to the antiviral drug phosphonoacetic acid (PAA) and characterized the in vivo replication fidelity of the phage DNA pols. We found that G466S substitution marginally increased PAA sensitivity, whereas Y460F substitution conferred resistance. The phage expressing a double mutant G466S/Y460F DNA pol was more PAA-sensitive. V475W T4 DNA pol was highly sensitive to PAA, as was the case with V478W RB69 DNA pol. However, DNA replication was severely compromised, which resulted in the selection of phages expressing more robust DNA pols that have strong ability to replicate DNA and contain additional amino acid substitutions that suppress PAA sensitivity. Reduced replication fidelity was observed in all mutant phages expressing PAA-sensitive DNA pols. These observations indicate that PAA sensitivity and fidelity are balanced in DNA pols that can replicate DNA in different environments.
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Affiliation(s)
- Likui Zhang
- Marine Science & Technology Institute Department of Environmental Science and Engineering, Yangzhou University , No. 196 Huayang West Road, Hanjiang, Yangzhou, Jiangsu 225127, China.,Department of Biological Sciences, University of Alberta , Edmonton, Alberta T6G 2R3, Canada
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10
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Zarrouk K, Piret J, Boivin G. Herpesvirus DNA polymerases: Structures, functions and inhibitors. Virus Res 2017; 234:177-192. [PMID: 28153606 DOI: 10.1016/j.virusres.2017.01.019] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 01/10/2017] [Accepted: 01/22/2017] [Indexed: 11/25/2022]
Abstract
Human herpesviruses are large double-stranded DNA viruses belonging to the Herpesviridae family. These viruses have the ability to establish lifelong latency into the host and to periodically reactivate. Primary infections and reactivations of herpesviruses cause a large spectrum of diseases and may lead to severe complications in immunocompromised patients. The viral DNA polymerase is a key enzyme in the lytic phase of the infection by herpesviruses. This review focuses on the structures and functions of viral DNA polymerases of herpes simplex virus (HSV) and human cytomegalovirus (HCMV). DNA polymerases of HSV (UL30) and HCMV (UL54) belong to B family DNA polymerases with which they share seven regions of homology numbered I to VII as well as a δ-region C which is homologous to DNA polymerases δ. These DNA polymerases are multi-functional enzymes exhibiting polymerase, 3'-5' exonuclease proofreading and ribonuclease H activities. Furthermore, UL30 and UL54 DNA polymerases form a complex with UL42 and UL44 processivity factors, respectively. The mechanisms involved in their polymerisation activity have been elucidated based on structural analyses of the DNA polymerase of bacteriophage RB69 crystallized under different conformations, i.e. the enzyme alone or in complex with DNA and with both DNA and incoming nucleotide. All antiviral agents currently used for the prevention or treatment of HSV and HCMV infections target the viral DNA polymerases. However, long-term administration of these antivirals may lead to the emergence of drug-resistant isolates harboring mutations in genes encoding viral enzymes that phosphorylate drugs (i.e., nucleoside analogues) and/or DNA polymerases.
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Affiliation(s)
- Karima Zarrouk
- Research Center in Infectious Diseases, CHU de Québec and Laval University, Quebec City, Quebec, Canada
| | - Jocelyne Piret
- Research Center in Infectious Diseases, CHU de Québec and Laval University, Quebec City, Quebec, Canada
| | - Guy Boivin
- Research Center in Infectious Diseases, CHU de Québec and Laval University, Quebec City, Quebec, Canada.
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11
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Topalis D, Gillemot S, Snoeck R, Andrei G. Distribution and effects of amino acid changes in drug-resistant α and β herpesviruses DNA polymerase. Nucleic Acids Res 2016; 44:9530-9554. [PMID: 27694307 PMCID: PMC5175367 DOI: 10.1093/nar/gkw875] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 09/13/2016] [Accepted: 09/21/2016] [Indexed: 12/15/2022] Open
Abstract
Emergence of drug-resistance to all FDA-approved antiherpesvirus agents is an increasing concern in immunocompromised patients. Herpesvirus DNA polymerase (DNApol) is currently the target of nucleos(t)ide analogue-based therapy. Mutations in DNApol that confer resistance arose in immunocompromised patients infected with herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV), and to lesser extent in herpes simplex virus 2 (HSV-2), varicella zoster virus (VZV) and human herpesvirus 6 (HHV-6). In this review, we present distinct drug-resistant mutational profiles of herpesvirus DNApol. The impact of specific DNApol amino acid changes on drug-resistance is discussed. The pattern of genetic variability related to drug-resistance differs among the herpesviruses. Two mutational profiles appeared: one favoring amino acid changes in the Palm and Finger domains of DNApol (in α-herpesviruses HSV-1, HSV-2 and VZV), and another with mutations preferentially in the 3′-5′ exonuclease domain (in β-herpesvirus HCMV and HHV-6). The mutational profile was also related to the class of compound to which drug-resistance emerged.
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Affiliation(s)
- D Topalis
- Rega Institute for Medical Research, Department Microbiology and Immunology, KU Leuven, Minderbroedersstraat 10, 3000, Leuven, Belgium
| | - S Gillemot
- Rega Institute for Medical Research, Department Microbiology and Immunology, KU Leuven, Minderbroedersstraat 10, 3000, Leuven, Belgium
| | - R Snoeck
- Rega Institute for Medical Research, Department Microbiology and Immunology, KU Leuven, Minderbroedersstraat 10, 3000, Leuven, Belgium
| | - G Andrei
- Rega Institute for Medical Research, Department Microbiology and Immunology, KU Leuven, Minderbroedersstraat 10, 3000, Leuven, Belgium
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12
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Abstract
Since the first antiviral drug, idoxuridine, was approved in 1963, 90 antiviral drugs categorized into 13 functional groups have been formally approved for the treatment of the following 9 human infectious diseases: (i) HIV infections (protease inhibitors, integrase inhibitors, entry inhibitors, nucleoside reverse transcriptase inhibitors, nonnucleoside reverse transcriptase inhibitors, and acyclic nucleoside phosphonate analogues), (ii) hepatitis B virus (HBV) infections (lamivudine, interferons, nucleoside analogues, and acyclic nucleoside phosphonate analogues), (iii) hepatitis C virus (HCV) infections (ribavirin, interferons, NS3/4A protease inhibitors, NS5A inhibitors, and NS5B polymerase inhibitors), (iv) herpesvirus infections (5-substituted 2'-deoxyuridine analogues, entry inhibitors, nucleoside analogues, pyrophosphate analogues, and acyclic guanosine analogues), (v) influenza virus infections (ribavirin, matrix 2 protein inhibitors, RNA polymerase inhibitors, and neuraminidase inhibitors), (vi) human cytomegalovirus infections (acyclic guanosine analogues, acyclic nucleoside phosphonate analogues, pyrophosphate analogues, and oligonucleotides), (vii) varicella-zoster virus infections (acyclic guanosine analogues, nucleoside analogues, 5-substituted 2'-deoxyuridine analogues, and antibodies), (viii) respiratory syncytial virus infections (ribavirin and antibodies), and (ix) external anogenital warts caused by human papillomavirus infections (imiquimod, sinecatechins, and podofilox). Here, we present for the first time a comprehensive overview of antiviral drugs approved over the past 50 years, shedding light on the development of effective antiviral treatments against current and emerging infectious diseases worldwide.
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Affiliation(s)
- Erik De Clercq
- KU Leuven-University of Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Leuven, Belgium
| | - Guangdi Li
- KU Leuven-University of Leuven, Rega Institute for Medical Research, Department of Microbiology and Immunology, Leuven, Belgium Department of Metabolism and Endocrinology, Metabolic Syndrome Research Center, Key Laboratory of Diabetes Immunology, Ministry of Education, National Clinical Research Center for Metabolic Diseases, The Second Xiangya Hospital, Central South University, Changsha, Hunan, China
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Contrasting effects of W781V and W780V mutations in helix N of herpes simplex virus 1 and human cytomegalovirus DNA polymerases on antiviral drug susceptibility. J Virol 2015; 89:4636-44. [PMID: 25673718 DOI: 10.1128/jvi.03360-14] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED DNA polymerases of the Herpesviridae and bacteriophage RB69 belong to the α-like DNA polymerase family. In spite of similarities in structure and function, the RB69 enzyme is relatively resistant to foscarnet, requiring the mutation V478W in helix N to promote the closed conformation of the enzyme to make it susceptible to the antiviral. Here, we generated recombinant herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV) mutants harboring the revertant in UL30 (W781V) and UL54 (W780V) DNA polymerases, respectively, to further investigate the impact of this tryptophan on antiviral drug susceptibility and viral replicative capacity. The mutation W781V in HSV-1 induced resistance to foscarnet, acyclovir, and ganciclovir (3-, 14-, and 3-fold increases in the 50% effective concentrations [EC50s], respectively). The recombinant HCMV mutant harboring the W780V mutation was slightly resistant to foscarnet (a 1.9-fold increase in the EC50) and susceptible to ganciclovir. Recombinant HSV-1 and HCMV mutants had altered viral replication kinetics. The apparent inhibition constant values of foscarnet against mutant UL30 and UL54 DNA polymerases were 45- and 4.9-fold higher, respectively, than those against their wild-type counterparts. Structural evaluation of the tryptophan position in the UL54 DNA polymerase suggests that the bulkier phenylalanine (fingers domain) and isoleucine (N-terminal domain) could induce a tendency toward the closed conformation greater than that for UL30 and explains the modest effect of the W780V mutation on foscarnet susceptibility. Our results further suggest a role of the tryptophan in helix N in conferring HCMV and especially HSV-1 susceptibility to foscarnet and the possible contribution of other residues localized at the interface between the fingers and N-terminal domains. IMPORTANCE DNA polymerases of the Herpesviridae and bacteriophage RB69 belong to the α-like DNA polymerase family. However, the RB69 DNA polymerase is relatively resistant to the broad-spectrum antiviral agent foscarnet. The mutation V478W in helix N of the fingers domain caused the enzyme to adopt a closed conformation and to become susceptible to the antiviral. We generated recombinant herpes simplex virus 1 (HSV-1) and human cytomegalovirus (HCMV) mutants harboring the revertant in UL30 (W781V) and UL54 (W780V) DNA polymerases, respectively, to further investigate the impact of this tryptophan on antiviral drug susceptibility. The W781V mutation in HSV-1 induced resistance to foscarnet, whereas the W780V mutation in HCMV slightly decreased drug susceptibility. This study suggests that the different profiles of susceptibility to foscarnet of the HSV-1 and HCMV mutants could be related to subtle conformational changes resulting from the interaction between residues specific to each enzyme that are located at the interface between the fingers and the N-terminal domains.
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DFT study on foscarnet as an antiviral drug: Conformer analysis, gas phase acidity, metal ion affinity and influence of metal complexation on gas phase acidity. J Mol Struct 2015. [DOI: 10.1016/j.molstruc.2014.09.075] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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15
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Utility of the bacteriophage RB69 polymerase gp43 as a surrogate enzyme for herpesvirus orthologs. Viruses 2013; 5:54-86. [PMID: 23299784 PMCID: PMC3564110 DOI: 10.3390/v5010054] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2012] [Revised: 12/16/2012] [Accepted: 12/17/2012] [Indexed: 01/09/2023] Open
Abstract
Viral polymerases are important targets in drug discovery and development efforts. Most antiviral compounds that are currently approved for treatment of infection with members of the herpesviridae family were shown to inhibit the viral DNA polymerase. However, biochemical studies that shed light on mechanisms of drug action and resistance are hampered primarily due to technical problems associated with enzyme expression and purification. In contrast, the orthologous bacteriophage RB69 polymerase gp43 has been crystallized in various forms and therefore serves as a model system that provides a better understanding of structure–function relationships of polymerases that belong the type B family. This review aims to discuss strengths, limitations, and opportunities of the phage surrogate with emphasis placed on its utility in the discovery and development of anti-herpetic drugs.
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16
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Zahn KE, Tchesnokov EP, Götte M, Doublié S. Phosphonoformic acid inhibits viral replication by trapping the closed form of the DNA polymerase. J Biol Chem 2011; 286:25246-55. [PMID: 21566148 DOI: 10.1074/jbc.m111.248864] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Phosphonoformic acid (PFA, foscarnet) belongs to a class of antiviral drugs that inhibit the human cytomegalovirus DNA polymerase (UL54) by mimicking the pyrophosphate leaving group of the nucleotide transfer reaction. Difficulties expressing UL54 have hampered investigation of the precise structural requirements rendering inhibition by this drug. However, a previously engineered chimeric DNA polymerase, constructed by mutating the homologous polymerase from bacteriophage RB69 (gp43) to express several variable elements from UL54, can bypass this obstacle because of its favorable expression and acquired sensitivity to PFA (Tchesnokov, E. P., Obikhod, A., Schinazi, R. F., and Götte, M. (2008) J. Biol. Chem. 283, 34218-34228). Here, we compare two crystal structures that depict the chimeric DNA polymerase with and without PFA bound. PFA is visualized for the first time in the active site of a DNA polymerase, where interactions are resolved between the PP(i) mimic and two basic residues absolutely conserved in the fingers domain of family B polymerases. PFA also chelates metal ion B, the cation that contacts the triphosphate tail of the incoming nucleotide. These DNA complexes utilize a primer-template pair enzymatically chain-terminated by incorporation of acyclo-GMP, the phosphorylated form of the anti-herpes drug acyclovir. We postulate that the V478W mutation present in the chimera is critical in that it pushes the fingers domain to more readily adopt the closed conformation whether or not the drug is bound. The closed state of the fingers domain traps the variant polymerase in the untranslocated state and increases affinity for PFA. This finding provides a model for the mechanism of UL54 stalling by PFA.
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Affiliation(s)
- Karl E Zahn
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405, USA
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Chevillotte M, von Einem J, Meier BM, Lin FM, Kestler HA, Mertens T. A new tool linking human cytomegalovirus drug resistance mutations to resistance phenotypes. Antiviral Res 2010; 85:318-27. [DOI: 10.1016/j.antiviral.2009.10.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Revised: 10/02/2009] [Accepted: 10/10/2009] [Indexed: 11/25/2022]
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Martin M, Azzi A, Lin SX, Boivin G. Opposite effect of two cytomegalovirus DNA polymerase mutations on replicative capacity and polymerase activity. Antivir Ther 2010; 15:579-86. [DOI: 10.3851/imp1565] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Tchesnokov EP, Obikhod A, Schinazi RF, Götte M. Engineering of a chimeric RB69 DNA polymerase sensitive to drugs targeting the cytomegalovirus enzyme. J Biol Chem 2009; 284:26439-46. [PMID: 19622750 PMCID: PMC2785332 DOI: 10.1074/jbc.m109.012500] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Revised: 06/19/2009] [Indexed: 11/06/2022] Open
Abstract
Detailed structural and biochemical studies with the human cytomegalovirus (HCMV UL54) DNA polymerase are hampered by difficulties to obtain this enzyme in large quantities. The crystal structure of the related RB69 DNA polymerase (gp43) is often used as a model system to explain mechanisms of inhibition of DNA synthesis and drug resistance. However, here we demonstrate that gp43 is approximately 400-fold less sensitive to the pyrophosphate analog foscarnet, when compared with UL54. The RB69 enzyme is also able to discriminate against the nucleotide analog inhibitor acyclovir. In contrast, the HCMV polymerase is able to incorporate this compound with similar efficiency as observed with its natural counterpart. In an attempt to identify major determinants for drug activity, we replaced critical regions of the nucleotide-binding site of gp43 with equivalent regions of the HCMV enzyme. We show that chimeric gp43-UL54 enzymes that contain residues of helix N and helix P of UL54 are resensitized against foscarnet and acyclovir. Changing a region of three amino acids of helix N showed the strongest effects, and changes of two segments of three amino acids in helix P further contributed to the reversal of the phenotype. The engineered chimeric enzyme can be produced in large quantities and may therefore be a valuable surrogate system in drug development efforts. This system may likewise be used for detailed structural and biochemical studies on mechanisms associated with drug action and resistance.
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Affiliation(s)
- Egor P. Tchesnokov
- From the Department of Microbiology and Immunology, McGill University, Montreal, Quebec H3A 2B4, Canada and
| | - Aleksandr Obikhod
- the Center for AIDS Research, Department of Pediatrics, Emory University School of Medicine and Veterans Affairs Medical Research, Atlanta, Georgia 30322
| | - Raymond F. Schinazi
- the Center for AIDS Research, Department of Pediatrics, Emory University School of Medicine and Veterans Affairs Medical Research, Atlanta, Georgia 30322
| | - Matthias Götte
- From the Department of Microbiology and Immunology, McGill University, Montreal, Quebec H3A 2B4, Canada and
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Picard-Jean F, Bougie I, Bisaillon M. Characterization of the DNA- and dNTP-binding activities of the human cytomegalovirus DNA polymerase catalytic subunit UL54. Biochem J 2007; 407:331-41. [PMID: 17672827 PMCID: PMC2275067 DOI: 10.1042/bj20070853] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The catalytic subunit of the human cytomegalovirus DNA polymerase is critical for the replication of the virus. In the present study, we report the expression and purification of a recombinant catalytic subunit of the human cytomegalovirus DNA polymerase expressed in bacteria which retains polymerase activity. As a first step towards elucidating the nature of the interaction between the enzyme, DNA and dNTPs, we have utilized endogenous tryptophan fluorescence to evaluate the binding of ligands to the enzyme. Using this technique, we demonstrate that the minimal DNA-binding site of the enzyme is 6 nt. We also report the first detailed study of the binding kinetics and thermodynamic parameters involved in the interaction between the enzyme, DNA and dNTPs. Our thermodynamic analyses indicate that the initial formation of the enzyme-DNA binary complex is driven by a favourable entropy change, but is also clearly associated with an unfavourable enthalpic contribution. In contrast, the interaction of dNTPs to the binary complex was shown to depend on a completely different mode of binding that is dominated by a favourable enthalpy change and associated with an unfavourable entropy change. In order to provide additional insights into the structural modifications that occur during catalysis, we correlated the effect of DNA and dNTP binding on protein structure using CD. Our results indicate that the enzyme undergoes a first conformational change upon the formation of the protein-DNA binary complex, which is followed by a second structural modification upon dNTP binding. The present study provides a better understanding of the molecular basis of DNA and dNTP recognition by the catalytic subunit of the human cytomegalovirus DNA polymerase.
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Affiliation(s)
- Frédéric Picard-Jean
- Département de Biochimie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC, Canada J1H 5N4
| | - Isabelle Bougie
- Département de Biochimie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC, Canada J1H 5N4
| | - Martin Bisaillon
- Département de Biochimie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC, Canada J1H 5N4
- To whom correspondence should be addressed (email )
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Bonnafous P, Naesens L, Petrella S, Gautheret-Dejean A, Boutolleau D, Sougakoff W, Agut H. Different Mutations in the HHV-6 DNA Polymerase Gene Accounting for Resistance to Foscarnet. Antivir Ther 2007. [DOI: 10.1177/135965350701200608] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Background Human herpesvirus 6 (HHV-6), which is closely related to human cytomegalovirus, is sensitive to foscarnet (PFA). Up to now, the resistance of HHV-6 to PFA has not been investigated. Objectives The goal of the study was to isolate and characterize PFA-resistant HHV-6 mutants in order to determine the mechanisms of resistance to the drug. Methods PFA-resistant viruses, isolated in MT4 cell culture under increasing concentrations of PFA, were characterized phenotypically and genotypically. The mutations identified in the HHV-6 DNA polymerase gene were evaluated in a functional assay using recombinant mutated forms of the enzyme, and their effect on protein structure was analysed in a three-dimensional model derived from available structures of DNA polymerases. Results Two mutants were selected and were 8- and 15-fold more resistant to PFA than the wild-type strain. Four amino acid changes were detected in the HHV-6 DNA polymerase in association with PFA resistance: T435R, H507Y, C525S, located in the δC conserved domain, and F292S. Either alone or in combination, these substitutions significantly decreased the inhibitory effect of PFA at the level of the polymerase, as measured by the incorporation of radiolabeled nucleotides in a DNA elongation assay. In the three-dimensional model of HHV-6 DNA polymerase structure the four changes were not located within the putative catalytic site, but they might induce either a disturbance of local conformation or a restricted access of PFA to its target site. Conclusion This first characterization of HHV-6 resistance to PFA highlights the role of distinct DNA polymerase gene mutations.
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Affiliation(s)
- Pascale Bonnafous
- Université Pierre et Marie Curie-Paris 6, EA2387, Groupe hospitalier Pitié-Salpêtrière, Paris, France
| | - Lieve Naesens
- Laboratory of Virology and Chemotherapy Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Stéphanie Petrella
- INSERM, U655-LRMA, Site Pitié-Salpêtrière AP-HP, Université Pierre et Marie Curie-Paris 6, Paris, France
| | - Agnès Gautheret-Dejean
- Université Pierre et Marie Curie-Paris 6, EA2387, Groupe hospitalier Pitié-Salpêtrière, Paris, France
- Laboratoire de Microbiologie, Faculté des Sciences Pharmaceutiques et Biologiques, Paris, France
| | - David Boutolleau
- Université Pierre et Marie Curie-Paris 6, EA2387, Groupe hospitalier Pitié-Salpêtrière, Paris, France
| | - Wladimir Sougakoff
- INSERM, U655-LRMA, Site Pitié-Salpêtrière AP-HP, Université Pierre et Marie Curie-Paris 6, Paris, France
| | - Henri Agut
- Université Pierre et Marie Curie-Paris 6, EA2387, Groupe hospitalier Pitié-Salpêtrière, Paris, France
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Scalzo AA, Corbett AJ, Rawlinson WD, Scott GM, Degli-Esposti MA. The interplay between host and viral factors in shaping the outcome of cytomegalovirus infection. Immunol Cell Biol 2006; 85:46-54. [PMID: 17146464 DOI: 10.1038/sj.icb.7100013] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cytomegalovirus (CMV) remains a major human pathogen causing significant morbidity and mortality in immunosuppressed or immunoimmature individuals. Although significant advances have been made in dissecting out certain features of the host response to human CMV (HCMV) infection, the strict species specificity of CMVs means that most aspects of antiviral immunity are best assessed in animal models. The mouse model of murine CMV (MCMV) infection is an important tool for analysis of in vivo features of host-virus interactions and responses to antiviral drugs that are difficult to assess in humans. Important studies of the contribution of host resistance genes to infection outcome, interplays between innate and adaptive host immune responses, the contribution of virus immune evasion genes and genetic variation in these genes to the establishment of persistence and in vivo studies of resistance to antiviral drugs have benefited from the well-developed MCMV model. In this review, we discuss recent advances in the immunobiology of host-CMV interactions that provide intriguing insights into the complex interplay between host and virus that ultimately facilitates viral persistence. We also discuss recent studies of genetic responses to antiviral therapy, particularly changes in DNA polymerase and protein kinase genes of MCMV and HCMV.
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Affiliation(s)
- Anthony A Scalzo
- Immunology and Virology Program, Centre for Ophthalmology and Visual Science, The University of Western Australia, Nedlands, Western Australia, Australia.
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Marchand B, Tchesnokov EP, Götte M. The pyrophosphate analogue foscarnet traps the pre-translocational state of HIV-1 reverse transcriptase in a Brownian ratchet model of polymerase translocation. J Biol Chem 2006; 282:3337-46. [PMID: 17145704 DOI: 10.1074/jbc.m607710200] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The pyrophosphate (PPi) analogue phosphonoformic acid (PFA or foscarnet) inhibits the reverse transcriptase (RT) of the human immunodeficiency virus type 1 (HIV-1); however, the mechanisms of drug action and resistance remain elusive. Here we studied the effects of the translocational status of HIV-1 RT on drug binding and inhibition of DNA synthesis. We identified "hot spots" for inhibition during active elongation. Site-specific footprinting analyses revealed that the corresponding complexes exist predominantly in the pre-translocational state. The sensitivity to PFA is significantly reduced with sequences that show a bias toward the post-translocational state. Binding studies showed that PFA stabilizes selectively the complex in the pre-translocated configuration. These findings are consistent with a Brownian ratchet model of polymerase translocation. The enzyme can rapidly shuttle between pre- and post-translocated states. The bound inhibitor acts like a pawl of a ratchet and prevents the forward motion of HIV-1 RT, whereas the bound nucleotide binds to the post-translocated complex and prevents the reverse motion. The proposed mechanisms of RT translocation and drug action are consistent with the PFA-resistant phenotypes. We show that certain sequences and the PFA-resistant E89K mutant diminishes the stability of the pre-translocated complex. In these cases, the enzyme is seen at multiple positions around the 3' end of the primer, which provides a novel mechanism for resistance. These findings validate the pre-translocated complex as a target for the development of novel, perhaps less toxic and more potent inhibitors that block HIV-1 RT translocation.
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Affiliation(s)
- Bruno Marchand
- Department of Microbiology & Immunology, McGill University, Montréal, Québec H3A 2B4, Canada
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Scott GM, Weinberg A, Rawlinson WD, Chou S. Multidrug resistance conferred by novel DNA polymerase mutations in human cytomegalovirus isolates. Antimicrob Agents Chemother 2006; 51:89-94. [PMID: 17043128 PMCID: PMC1797699 DOI: 10.1128/aac.00633-06] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The emergence of antiviral-resistant cytomegalovirus (CMV) strains is a continuing clinical problem, with increased numbers of immunocompromised patients given longer-duration antiviral prophylaxis. Two previously unrecognized CMV DNA polymerase mutations (N408K and A834P) identified separately and together in at-risk lung and kidney transplant recipients and a third mutation (L737M) identified in a liver transplant recipient were characterized by marker transfer to antiviral-sensitive laboratory strains AD169 and Towne. Subsequent phenotypic analyses of recombinant strains demonstrated the ability of mutation N408K to confer ganciclovir (GCV) and cidofovir (CDV) resistance and of mutation A834P to confer GCV, foscarnet, and CDV resistance. Mutation L737M did not confer resistance to any of the antiviral agents tested. A recombinant strain containing both N408K and A834P demonstrated increased GCV and CDV resistance compared to the levels of resistance of the virus containing only the A834P mutation. The addition of mutation N408K in combination with A834P also partially reconstituted the replication impairment of recombinant virus containing only A834P. This suggests that perturbation of both DNA polymerization (A834P) and exonuclease (N408K) activities contributes to antiviral resistance and altered replication kinetics in these mutant strains. The identification of these multidrug-resistant CMV strains in at-risk seronegative recipients of organs from seropositive donors suggests that improved prophylactic and treatment strategies are required. The additive effect of multiple mutations on antiviral susceptibility suggests that increasing antiviral-resistant phenotypes can result from different virus-antiviral interactions.
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Affiliation(s)
- Gillian M Scott
- Virology Research, POWH and UNSW Research Laboratories, Level 3 Clinical Sciences Building, Prince of Wales Hospital, Avoca Street, Randwick, NSW 2031, Australia.
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Cruchaga C, Ansó E, Rouzaut A, Martínez-Irujo JJ. Selective excision of chain-terminating nucleotides by HIV-1 reverse transcriptase with phosphonoformate as substrate. J Biol Chem 2006; 281:27744-52. [PMID: 16829515 DOI: 10.1074/jbc.m603360200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A major mechanism for human immunodeficiency virus 1 (HIV-1) reverse transcriptase (RT) resistance to nucleoside analogs involves the phosphorolytical removal of the chain-terminating nucleotide from the 3'-end of the primer. In this work, we analyzed the effect of phosphonoformate (PFA) and other pyrophosphate (PP(i)) analogs on PP(i)- and ATP-dependent phosphorolysis catalyzed by HIV-1 RT. Our experimental data demonstrated that PFA did not behave as a linear inhibitor but as an alternative substrate, allowing RT to remove AZT from a terminated primer through a PFA-dependent mechanism. Interestingly, in non-terminated primers, PFA was not a substrate for this reaction and competitively inhibited PP(i)- and ATP-dependent phosphorolysis. In fact, binding of PFA to the RT.template/primer complex was hindered by the presence of a chain terminator at the 3'-end of the primer. Other pyrophosphate analogs, such as phosphonoacetate, were substrates for the excision reaction with both terminated and nonterminated primers, whereas pamidronate, a bisphosphonate that prevents bone resorption, was not a substrate for these reactions and competitively inhibited the phosphorolytic activity of RT. As expected from their mechanisms of action, pamidronate (but not PFA) synergistically inhibits HIV-1 RT in combination with AZT-triphosphate in the presence of PP(i) or ATP. These results provide new clues about the mechanism of action of PFA and demonstrate that only certain pyrophosphate analogs can enhance the effect of nucleosidic inhibitors by blocking the excision of chain-terminating nucleotides catalyzed by HIV-1 RT. The relevance of these findings in combined chemotherapy is discussed.
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Affiliation(s)
- Carlos Cruchaga
- Departamento de Bioquímica y Biología Molecular, Universidad de Navarra, Calle Irunlarrea s/n, 31008 Pamplona, Spain
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