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Title of the Thesis In vitro Inhibition of Feline Leukaemia Virus Infection by Synthetic Peptides Derived from the Transmembrane Domain Graduate School for Cellular and Biomedical Sciences University of Bern PhD Thesis Submitted by Eva Johanna Bönzli from Tschugg (BE) Thesis advisor Prof. Dr. Hans Lutz Clinical Laboratory Vetsuisse Faculty of the University of Zürich Original document saved on the web server of the University Library of Bern This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 2.5 Switzerland License. To see the licence go to http://creativecommons.org/licenses/by-nc- nd/2.5/ch/ or write to Creative Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA. Copyright Notice This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 2.5 Switzerland License. http://creativecommons.org/licenses/by-nc-nd/2.5/ch/ You are free: to copy, distribute, display, and perform the work Under the following conditions: Attribution. You must give the original author credit. Non-Commercial. You may not use this work for commercial purposes. No derivative works. You may not alter, transform, or build upon this work. For any reuse or distribution, you must take clear to others the license terms of this work. Any of these conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author‟s moral rights according to Swiss law. The detailed license agreement can be found at: http://creativecommons.org/licenses/by-nc-nd/2.5/ch/legalcode.de Accepted by the Faculty of Medicine, the Faculty of Science and the Vetsuisse Faculty of the University of Bern at the request of the Graduate School for Cellular and Biomedical Sciences Bern, Dean of the Faculty of Medicine Bern, Dean of the Faculty of Science Bern, Dean of the Vetsuisse Faculty Bern “The cat is domestic only as far as suits its own ends” Saki (Hector H. Munro, 1870-1916) TABLE OF CONTENTS i SUMMARY ............................................................................................................................ 1 INTRODUCTION & AIM ........................................................................................................ 4 The Feline Leukaemia Virus (FeLV) .................................................................................. 5 Retroviruses .................................................................................................................. 5 Origin & Structure of FeLV ............................................................................................. 5 FeLV Entry into the Host Cell............................................................................................. 6 “Competitor” Peptides Interfering with the FeLV Entry Step ............................................... 9 Aims of the Thesis ............................................................................................................11 Motivation and Significance ..............................................................................................11 Importance of FeLV in Veterinary Medicine ..................................................................11 Importance of FeLV in Human Medicine .......................................................................13 References .......................................................................................................................14 RESULTS: MANUSCRIPT ...................................................................................................20 DISCUSSION .......................................................................................................................39 References .......................................................................................................................41 PERSPECTIVES & OUTLOOK ............................................................................................43 Perspectives in Veterinary Medicine .................................................................................44 Perspectives in Human Medicine ......................................................................................45 Future Antiviral Peptides ...................................................................................................46 References .......................................................................................................................47 ACKNOWLEDGEMENTS .....................................................................................................52 CURRICULUM VITAE ..........................................................................................................54 DECLARATION OF ORIGINALITY .......................................................................................57 ii SUMMARY 1 Introduction. Exposure to the feline leukaemia virus (FeLV), a naturally occurring gammaretrovirus of felines worldwide, may cause persistent viraemia and associated fatal diseases in a portion of infected cats. Several effective vaccines exist today, but currently there is no therapy for FeLV-viraemic cats. Infected cats consequently are either euthanized or die painfully. Peptides derived from the viral transmembrane (TM) protein, which effectively inhibit viral entry in vitro, have been identified for human and animal lentiviruses (e.g. human immunodeficiency virus (HIV), and feline immunodeficiency virus (FIV)), which are closely related to FeLV. It has been shown that these peptides interfere with some early steps in the viral replication cycle, the fusion of the viral and the cell membrane, which is crucial for a virus to infect a host cell. Aim. In this thesis, the insight gained with the synthetic peptides against HIV and FIV were intended to be transferred to the design and in vitro testing of synthetic peptides to block infection of feline cells by FeLV. Materials and Methods. Nine overlapping peptides from the FeLV TM were selected and modified. Their sequences were between 15 and 37 amino acids (aa) long. Peptides were challenged with FeLV subtype A on different feline cells as a substrate. Results were evaluated by enzyme-linked immunosorbent assay (ELISA) by quantifying the viral protein p27 in the cell culture supernatants after one week. Results. A 37 aa wildtype peptide EPK364 with sequence homology to the known HIV fusion inhibitor T20, displayed inhibitory effect of up to 88% if added to a culture of cat fibroblasts several hours after infection by FeLV subtype A. None of the shorter peptides decreased the viral replication. Further studies were performed with modifications of the sequence of EPK364 to support its stability, amphiphilic characteristics, and to increase its solubility. These modified variants of EPK364 indeed showed good inhibitory activity (58% and 27%, respectively), but less than the wildtype peptide. A cell viability test in the presence or absence of the three peptides was also performed. It revealed that the presence of peptide is not toxic for the cells; the cellular growth was neither influenced by EPK364, EPK397, nor by EPK398. Discussion. The inhibitory potential of the three 37 aa peptides may be due to the fact that longer peptides are in general more stable compared to short peptides. The reduced inhibitory effect of the modified variants may be due to loss of essential amino acids in both peptide sequences, generating a trade-off between increasing peptide stability/solubility due to modifications, and peptide binding capacity. It might be also considered that either the peptide working mechanism or the entry mechanism of gammaretroviruses is different from lentiviruses. 2 Perspectives. Inhibitory peptides might become important not only for veterinary use as therapeutic agent for viraemic cats, but also for the human medicine. Today, xenotransplantation is a method to fill the gap of the shortage of appropriate human organs. Animal (e.g. pig, baboon) organs serve as substitutes, but the transfer to the human acceptor is threatened by undetected gammaretroviruses that may induce infections and possibly tumours in humans. An antiviral therapy that inhibits these types of infections in immunosuppressed patients may increase the safety in xenotransplantations. 3 INTRODUCTION & AIM 4 The Feline Leukaemia Virus (FeLV) Retroviruses Viruses are small infectious agents that replicate in living cells of all organisms, animals (including humans), plants, bacteria, and even archaea [1]. Viral particles consist of genetic material made from either DNA or RNA, a capsid (protein coat) that encloses the genetic material, and in some cases an envelope of a lipid bilayer, i.e. a membrane, which surrounds the capsid. The envelope is typically derived from portions of the host cell membranes but include some viral glycoproteins. Among the viruses, the family of the Retroviridae (retroviruses) is a large and diverse group of enveloped viruses with an RNA genome. They are found in all vertebrates including humans. A common attribute of all retroviruses is a virus-transcribed enzyme, the reverse transcriptase (RNA-dependent DNA polymerase) [2] which is needed for an important replication step within the host: after entry into the host cell cytosol, the genomic single- stranded RNA of the retrovirus is first reverse-transcribed by the reverse transcriptase into double-stranded DNA, and then inserted by another viral enzyme, the integrase, into the host chromosomal DNA located in the nucleus of the cell. Integration is crucial for the “survival”
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