De Novo Design of α-Helical Lipopeptides Targeting Viral Fusion Proteins: A Promising Strategy for Relatively Broad-Spectrum Antiviral Drug Discovery
Identifieur interne : 000131 ( Pmc/Corpus ); précédent : 000130; suivant : 000132De Novo Design of α-Helical Lipopeptides Targeting Viral Fusion Proteins: A Promising Strategy for Relatively Broad-Spectrum Antiviral Drug Discovery
Auteurs : Chao Wang ; Lei Zhao ; Shuai Xia ; Tianhong Zhang ; Ruiyuan Cao ; Guodong Liang ; Yue Li ; Guangpeng Meng ; Weicong Wang ; Weiguo Shi ; Wu Zhong ; Shibo Jiang ; Keliang LiuSource :
- Journal of Medicinal Chemistry [ 0022-2623 ] ; 2018.
Abstract
Class I enveloped viruses share similarities in their apparent use of a hexameric coiled-coil assembly to drive the merging of virus and host cell membranes. Inhibition of coiled coil-mediated interactions using bioactive peptides that replicate an α-helical chain from the viral fusion machinery has significant antiviral potential. Here, we present the construction of a series of lipopeptides composed of a de novo heptad repeat sequence-based α-helical peptide plus a hydrocarbon tail. Promisingly, the constructs adopted stable α-helical conformations and exhibited relatively broad-spectrum antiviral activities against Middle East respiratory syndrome coronavirus (MERS-CoV) and influenza A viruses (IAVs). Together, these findings reveal a new strategy for relatively broad-spectrum antiviral drug discovery by relying on the tunability of the α-helical coiled-coil domains present in all class I fusion proteins and the amphiphilic nature of the individual helices from this multihelix motif.
Url:
DOI: 10.1021/acs.jmedchem.8b00890
PubMed: 30192544
PubMed Central: 7075651
Links to Exploration step
PMC:7075651Le document en format XML
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<author><name sortKey="Wang, Weicong" sort="Wang, Weicong" uniqKey="Wang W" first="Weicong" last="Wang">Weicong Wang</name>
<affiliation><nlm:aff id="aff5">Department of Clinical Trial Center, China National Clinical Research Center for Neurological Diseases, Beijing Tiantan Hospital,<institution>Capital Medical University</institution>
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<sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">De Novo Design
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Targeting Viral Fusion Proteins: A Promising Strategy for Relatively
Broad-Spectrum Antiviral Drug Discovery</title>
<author><name sortKey="Wang, Chao" sort="Wang, Chao" uniqKey="Wang C" first="Chao" last="Wang">Chao Wang</name>
<affiliation><nlm:aff id="aff1">State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
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<author><name sortKey="Zhao, Lei" sort="Zhao, Lei" uniqKey="Zhao L" first="Lei" last="Zhao">Lei Zhao</name>
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, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
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<author><name sortKey="Xia, Shuai" sort="Xia, Shuai" uniqKey="Xia S" first="Shuai" last="Xia">Shuai Xia</name>
<affiliation><nlm:aff id="aff2">Key Laboratory of Medical Molecular Virology of MOE/MOH, School of Basic Medical Sciences & Shanghai Public Health Clinical Center,<institution>Fudan University</institution>
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<author><name sortKey="Zhang, Tianhong" sort="Zhang, Tianhong" uniqKey="Zhang T" first="Tianhong" last="Zhang">Tianhong Zhang</name>
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<author><name sortKey="Cao, Ruiyuan" sort="Cao, Ruiyuan" uniqKey="Cao R" first="Ruiyuan" last="Cao">Ruiyuan Cao</name>
<affiliation><nlm:aff id="aff1">State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
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<author><name sortKey="Liang, Guodong" sort="Liang, Guodong" uniqKey="Liang G" first="Guodong" last="Liang">Guodong Liang</name>
<affiliation><nlm:aff id="aff1">State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
</nlm:aff>
</affiliation>
</author>
<author><name sortKey="Li, Yue" sort="Li, Yue" uniqKey="Li Y" first="Yue" last="Li">Yue Li</name>
<affiliation><nlm:aff id="aff3">Key Laboratory of Structure-Based Drug Design & Discovery of the Ministry of Education,<institution>Shenyang Pharmaceutical University</institution>
, Shenyang 110016,<country>China</country>
</nlm:aff>
</affiliation>
</author>
<author><name sortKey="Meng, Guangpeng" sort="Meng, Guangpeng" uniqKey="Meng G" first="Guangpeng" last="Meng">Guangpeng Meng</name>
<affiliation><nlm:aff id="aff3">Key Laboratory of Structure-Based Drug Design & Discovery of the Ministry of Education,<institution>Shenyang Pharmaceutical University</institution>
, Shenyang 110016,<country>China</country>
</nlm:aff>
</affiliation>
</author>
<author><name sortKey="Wang, Weicong" sort="Wang, Weicong" uniqKey="Wang W" first="Weicong" last="Wang">Weicong Wang</name>
<affiliation><nlm:aff id="aff5">Department of Clinical Trial Center, China National Clinical Research Center for Neurological Diseases, Beijing Tiantan Hospital,<institution>Capital Medical University</institution>
, Beijing 100050,<country>China</country>
</nlm:aff>
</affiliation>
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<author><name sortKey="Shi, Weiguo" sort="Shi, Weiguo" uniqKey="Shi W" first="Weiguo" last="Shi">Weiguo Shi</name>
<affiliation><nlm:aff id="aff1">State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
</nlm:aff>
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<author><name sortKey="Zhong, Wu" sort="Zhong, Wu" uniqKey="Zhong W" first="Wu" last="Zhong">Wu Zhong</name>
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, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
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<author><name sortKey="Jiang, Shibo" sort="Jiang, Shibo" uniqKey="Jiang S" first="Shibo" last="Jiang">Shibo Jiang</name>
<affiliation><nlm:aff id="aff2">Key Laboratory of Medical Molecular Virology of MOE/MOH, School of Basic Medical Sciences & Shanghai Public Health Clinical Center,<institution>Fudan University</institution>
, 130 Dong An Road, Shanghai 200032,<country>China</country>
</nlm:aff>
</affiliation>
<affiliation><nlm:aff id="aff4">Lindsley F. Kimball Research Institute,<institution>New York Blood Center</institution>
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;</nlm:aff>
</affiliation>
</author>
<author><name sortKey="Liu, Keliang" sort="Liu, Keliang" uniqKey="Liu K" first="Keliang" last="Liu">Keliang Liu</name>
<affiliation><nlm:aff id="aff1">State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
</nlm:aff>
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<series><title level="j">Journal of Medicinal Chemistry</title>
<idno type="ISSN">0022-2623</idno>
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<front><div type="abstract" xml:lang="en"><p content-type="toc-graphic"><graphic xlink:href="jm8b00890_0008" id="ab-tgr1"></graphic>
</p>
<p>Class I enveloped viruses share similarities
in their apparent
use of a hexameric coiled-coil assembly to drive the merging of virus
and host cell membranes. Inhibition of coiled coil-mediated interactions
using bioactive peptides that replicate an α-helical chain from
the viral fusion machinery has significant antiviral potential. Here,
we present the construction of a series of lipopeptides composed of
a de novo heptad repeat sequence-based α-helical peptide plus
a hydrocarbon tail. Promisingly, the constructs adopted stable α-helical
conformations and exhibited relatively broad-spectrum antiviral activities
against Middle East respiratory syndrome coronavirus (MERS-CoV) and
influenza A viruses (IAVs). Together, these findings reveal a new
strategy for relatively broad-spectrum antiviral drug discovery by
relying on the tunability of the α-helical coiled-coil domains
present in all class I fusion proteins and the amphiphilic nature
of the individual helices from this multihelix motif.</p>
</div>
</front>
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</TEI>
<pmc article-type="research-article" xml:lang="EN"><pmc-dir>properties open_access</pmc-dir>
<front><journal-meta><journal-id journal-id-type="nlm-ta">J Med Chem</journal-id>
<journal-id journal-id-type="iso-abbrev">J. Med. Chem</journal-id>
<journal-id journal-id-type="publisher-id">jm</journal-id>
<journal-id journal-id-type="coden">jmcmar</journal-id>
<journal-title-group><journal-title>Journal of Medicinal Chemistry</journal-title>
</journal-title-group>
<issn pub-type="ppub">0022-2623</issn>
<issn pub-type="epub">1520-4804</issn>
<publisher><publisher-name>American Chemical
Society</publisher-name>
</publisher>
</journal-meta>
<article-meta><article-id pub-id-type="pmid">30192544</article-id>
<article-id pub-id-type="pmc">7075651</article-id>
<article-id pub-id-type="doi">10.1021/acs.jmedchem.8b00890</article-id>
<article-categories><subj-group><subject>Article</subject>
</subj-group>
</article-categories>
<title-group><article-title>De Novo Design
of α-Helical Lipopeptides
Targeting Viral Fusion Proteins: A Promising Strategy for Relatively
Broad-Spectrum Antiviral Drug Discovery</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" id="ath1"><name><surname>Wang</surname>
<given-names>Chao</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
<xref rid="notes3" ref-type="notes">¶</xref>
</contrib>
<contrib contrib-type="author" id="ath2"><name><surname>Zhao</surname>
<given-names>Lei</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
<xref rid="notes3" ref-type="notes">¶</xref>
</contrib>
<contrib contrib-type="author" id="ath3"><name><surname>Xia</surname>
<given-names>Shuai</given-names>
</name>
<xref rid="aff2" ref-type="aff">‡</xref>
<xref rid="notes3" ref-type="notes">¶</xref>
</contrib>
<contrib contrib-type="author" id="ath4"><name><surname>Zhang</surname>
<given-names>Tianhong</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
<xref rid="notes3" ref-type="notes">¶</xref>
</contrib>
<contrib contrib-type="author" id="ath5"><name><surname>Cao</surname>
<given-names>Ruiyuan</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
</contrib>
<contrib contrib-type="author" id="ath6"><name><surname>Liang</surname>
<given-names>Guodong</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
</contrib>
<contrib contrib-type="author" id="ath7"><name><surname>Li</surname>
<given-names>Yue</given-names>
</name>
<xref rid="aff3" ref-type="aff">#</xref>
</contrib>
<contrib contrib-type="author" id="ath8"><name><surname>Meng</surname>
<given-names>Guangpeng</given-names>
</name>
<xref rid="aff3" ref-type="aff">#</xref>
</contrib>
<contrib contrib-type="author" id="ath9"><name><surname>Wang</surname>
<given-names>Weicong</given-names>
</name>
<xref rid="aff5" ref-type="aff">∥</xref>
</contrib>
<contrib contrib-type="author" id="ath10"><name><surname>Shi</surname>
<given-names>Weiguo</given-names>
</name>
<xref rid="aff1" ref-type="aff">†</xref>
</contrib>
<contrib contrib-type="author" corresp="yes" id="ath11"><name><surname>Zhong</surname>
<given-names>Wu</given-names>
</name>
<xref rid="cor3" ref-type="other">*</xref>
<xref rid="aff1" ref-type="aff">†</xref>
</contrib>
<contrib contrib-type="author" corresp="yes" id="ath12"><name><surname>Jiang</surname>
<given-names>Shibo</given-names>
</name>
<xref rid="cor2" ref-type="other">*</xref>
<xref rid="aff2" ref-type="aff">‡</xref>
<xref rid="aff4" ref-type="aff">§</xref>
</contrib>
<contrib contrib-type="author" corresp="yes" id="ath13"><name><surname>Liu</surname>
<given-names>Keliang</given-names>
</name>
<xref rid="cor1" ref-type="other">*</xref>
<xref rid="aff1" ref-type="aff">†</xref>
</contrib>
<aff id="aff1"><label>†</label>
State Key Laboratory of Toxicology and Medical Countermeasures,<institution>Beijing Institute of Pharmacology and Toxicology</institution>
, 27 Tai-Ping Road, Beijing 100850,<country>China</country>
</aff>
<aff id="aff2"><label>‡</label>
Key Laboratory of Medical Molecular Virology of MOE/MOH, School of Basic Medical Sciences & Shanghai Public Health Clinical Center,<institution>Fudan University</institution>
, 130 Dong An Road, Shanghai 200032,<country>China</country>
</aff>
<aff id="aff3"><label>#</label>
Key Laboratory of Structure-Based Drug Design & Discovery of the Ministry of Education,<institution>Shenyang Pharmaceutical University</institution>
, Shenyang 110016,<country>China</country>
</aff>
<aff id="aff4"><label>§</label>
Lindsley F. Kimball Research Institute,<institution>New York Blood Center</institution>
, New York, New York 10065,<country>United States</country>
;</aff>
<aff id="aff5"><label>∥</label>
Department of Clinical Trial Center, China National Clinical Research Center for Neurological Diseases, Beijing Tiantan Hospital,<institution>Capital Medical University</institution>
, Beijing 100050,<country>China</country>
</aff>
</contrib-group>
<author-notes><corresp id="cor1"><label>*</label>
For
K.L.: phone, <phone>86-10-6816-9363</phone>
; fax, <fax>86-10-6821-1656</fax>
; E-mail, <email>keliangliu55@126.com</email>
.</corresp>
<corresp id="cor2"><label>*</label>
For S.J.: phone, <phone>86-21-54237673</phone>
; fax, <fax>86-21-54237465</fax>
; E-mail, <email>shibojiang@fudan.edu.cn</email>
.</corresp>
<corresp id="cor3"><label>*</label>
For W.Z.: phone, <phone>86-10-6816-9363</phone>
; fax, <fax>86-10-6821-1656</fax>
, E-mail, <email>zhongwu@bmi.ac.cn</email>
.</corresp>
</author-notes>
<pub-date pub-type="epub"><day>07</day>
<month>09</month>
<year>2018</year>
</pub-date>
<pub-date pub-type="ppub"><day>11</day>
<month>10</month>
<year>2018</year>
</pub-date>
<volume>61</volume>
<issue>19</issue>
<fpage>8734</fpage>
<lpage>8745</lpage>
<history><date date-type="received"><day>05</day>
<month>06</month>
<year>2018</year>
</date>
</history>
<permissions><copyright-statement>Copyright © 2018 American Chemical
Society</copyright-statement>
<copyright-year>2018</copyright-year>
<copyright-holder>American Chemical
Society</copyright-holder>
<license license-type="open-access"><license-p>This article is made available via the PMC Open Access Subset for unrestricted RESEARCH re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.</license-p>
</license>
</permissions>
<abstract><p content-type="toc-graphic"><graphic xlink:href="jm8b00890_0008" id="ab-tgr1"></graphic>
</p>
<p>Class I enveloped viruses share similarities
in their apparent
use of a hexameric coiled-coil assembly to drive the merging of virus
and host cell membranes. Inhibition of coiled coil-mediated interactions
using bioactive peptides that replicate an α-helical chain from
the viral fusion machinery has significant antiviral potential. Here,
we present the construction of a series of lipopeptides composed of
a de novo heptad repeat sequence-based α-helical peptide plus
a hydrocarbon tail. Promisingly, the constructs adopted stable α-helical
conformations and exhibited relatively broad-spectrum antiviral activities
against Middle East respiratory syndrome coronavirus (MERS-CoV) and
influenza A viruses (IAVs). Together, these findings reveal a new
strategy for relatively broad-spectrum antiviral drug discovery by
relying on the tunability of the α-helical coiled-coil domains
present in all class I fusion proteins and the amphiphilic nature
of the individual helices from this multihelix motif.</p>
</abstract>
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<meta-value>jm8b00890</meta-value>
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<custom-meta><meta-name>document-id-new-14</meta-name>
<meta-value>jm8b00890</meta-value>
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<notes id="notes-d1e21-autogenerated"><fn-group><fn fn-type="" id="d30e284"><p>This article is made available for a limited time sponsored by ACS under the <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/page/policy/freetoread/index.html">ACS Free to Read License</ext-link>
, which permits copying and redistribution of the article for non-commercial scholarly purposes.</p>
</fn>
</fn-group>
</notes>
</front>
<body><sec id="sec1"><title>Introduction</title>
<p>The traditional “one
bug–one drug” paradigm
for the development of antiviral therapeutics has yielded laudable
successes to control the emerging and re-emerging threat of viral
pathogens.<sup><xref ref-type="bibr" rid="ref1">1</xref>
−<xref ref-type="bibr" rid="ref3">3</xref>
</sup>
However, a broad-spectrum antiviral strategy that
affords timely and effective pharmacological agents that can respond
to an increasing diversity of highly pathogenic viruses remains elusive.<sup><xref ref-type="bibr" rid="ref4">4</xref>
</sup>
A commonality in the viral life cycle, i.e.,
the fusion of enveloped viruses with the host cell membrane, represents
a viable target for the discovery of broad-spectrum therapeutics.<sup><xref ref-type="bibr" rid="ref5">5</xref>
,<xref ref-type="bibr" rid="ref6">6</xref>
</sup>
In this fusion process, the triggered formation of a leucine zipper-like
α-helical hexamer,<sup><xref ref-type="bibr" rid="ref7">7</xref>
,<xref ref-type="bibr" rid="ref8">8</xref>
</sup>
either at the cell surface
or within some later endosomes, is the typical structural feature
of class I fusion glycoproteins used by enveloped viruses such as
human immunodeficiency virus type 1 (HIV-1),<sup><xref ref-type="bibr" rid="ref9">9</xref>
−<xref ref-type="bibr" rid="ref11">11</xref>
</sup>
influenza A
viruses (IAVs),<sup><xref ref-type="bibr" rid="ref12">12</xref>
</sup>
Middle East respiratory
syndrome coronavirus (MERS-CoV),<sup><xref ref-type="bibr" rid="ref13">13</xref>
</sup>
and
Ebola virus (EboV)<sup><xref ref-type="bibr" rid="ref14">14</xref>
</sup>
(<xref rid="fig1" ref-type="fig">Figure <xref rid="fig1" ref-type="fig">1</xref>
</xref>
A).</p>
<fig id="fig1" position="float"><label>Figure 1</label>
<caption><p>Six-helix bundle (6HB)
fusion core structure and the design of
a lipopeptide template based on the interaction between the NHR and
CHR domains. (A) Cartoon representations of the HIV (PDB 1AIK), MERS-CoV (PDB 4NJL), and influenza
H3N2 (PDB 1QU1) 6HBs, in which the NHR trimers and CHR segments are colored in
gray and green, respectively. (B) Helical wheel representation of
a 6HB. The residues at the <italic>a</italic>
, <italic>d</italic>
,
and <italic>e</italic>
positions (yellow) form the buried face that
interacts with the NHR trimers, while those at the <italic>b</italic>
, <italic>c</italic>
, <italic>f</italic>
, and <italic>g</italic>
positions
(blue) are solvent-accessible sites. (C) The de novo designed lipopeptide
template, in which the critical residues at the <italic>a</italic>
, <italic>d</italic>
, and <italic>e</italic>
positions are highlighted
in red font. The dotted lines show the predicted intramolecular salt
bridges formed by the acidic amino acids at the <italic>i</italic>
positions and the basic residues at the <italic>i</italic>
+ 4 positions.</p>
</caption>
<graphic xlink:href="jm8b00890_0001" id="gr1" position="float"></graphic>
</fig>
<p>During the coiled-coil six-helix
bundle (6HB) assembly, three N-terminal
heptad repeat (NHR) regions of viral fusion proteins initially form
a central trimeric helix scaffold that becomes temporarily exposed,
creating a metastable prehairpin conformation; three C-terminal heptad
repeat (CHR) regions then pack onto the periphery of the trimeric
NHR inner core in an antiparallel orientation.<sup><xref ref-type="bibr" rid="ref15">15</xref>
</sup>
Bioactive peptides derived from the CHR motif of class
I viral fusion proteins, designated as C-peptides, act as decoy α-helices
and are able to bind to their corresponding NHR helical trimers to
form a heterologous nonfunctional 6HB structure in a virus-specific
manner, thereby antagonizing the refolding of the endogenous CHR region
and competitively inhibiting virus–host cell membrane fusion.<sup><xref ref-type="bibr" rid="ref16">16</xref>
</sup>
In 1993, Jiang and colleagues discovered a highly
potent HIV-1 fusion inhibitory peptides derived from the CHR region
of HIV-1 gp41, designated SJ-2176; in 1994, Wild et al. reported another
CHR-peptide, DP-178 (also named T20 later).<sup><xref ref-type="bibr" rid="ref17">17</xref>
,<xref ref-type="bibr" rid="ref18">18</xref>
</sup>
T20 (brand name, Fuzeon; generic name, enfuvirtide) was finally
approved by the U.S. Food and Drug Administration in 2003 for clinical
use as the first fusion inhibitor-based anti-HIV drug. The discovery
of these anti-HIV peptides spurred the identification of antiviral
peptides against other viruses that utilize class I fusion proteins,
including the recently identified MERS-CoV. After the emergence of
MERS-CoV infection, Gao’s group and Jiang’s group independently
solved the crystal structure of MERS-CoV’s 6HB fusion core.<sup><xref ref-type="bibr" rid="ref13">13</xref>
,<xref ref-type="bibr" rid="ref19">19</xref>
</sup>
On the basis of the 6HB structure, Jiang’s group reported
the highly effective anti-MERS-CoV peptide HR2PM2. Most recently,
we identified a hydrocarbon-stapled short α-helical peptide
that could inhibit MERS-CoV infection at the low micromolar level.<sup><xref ref-type="bibr" rid="ref20">20</xref>
</sup>
Considering the universal 6HB fusion mechanism
employed by class I enveloped viruses, inhibition of NHR/CHR coiled
coil-mediated interactions has significant potential for the development
of broad-spectrum therapeutic interventions.</p>
<p>Coiled coils are
ubiquitous protein folding motifs found in nature,
and they orchestrate the association of numerous complexes implicated
in biological processes.<sup><xref ref-type="bibr" rid="ref21">21</xref>
</sup>
A wealth of
structural information has provided a relatively detailed understanding
of the sequence-to-structure relationships for this supercoiled scaffold.<sup><xref ref-type="bibr" rid="ref22">22</xref>
</sup>
In structural terms, amphipathic α-helices
encode canonical coiled coils via burial of their hydrophobic faces
to drive the multimerization of constituent helices.<sup><xref ref-type="bibr" rid="ref23">23</xref>
</sup>
The hexameric coiled-coil assembly present in HIV-1 is
arguably the best characterized class I viral fusion apparatus,<sup><xref ref-type="bibr" rid="ref24">24</xref>
,<xref ref-type="bibr" rid="ref25">25</xref>
</sup>
in which the C-helices are divided into a hydrophobic buried binding
interface and hydrophilic solvent-accessible sites (<xref rid="fig1" ref-type="fig">Figure <xref rid="fig1" ref-type="fig">1</xref>
</xref>
B). Structural analysis has
demonstrated that a high variability in the primary sequence of CHR
motifs within the HIV-1 6HB is allowed as long as the driving force
for coiled-coil assembly, i.e., amphiphilic characteristics of the
individual helices, is maintained.<sup><xref ref-type="bibr" rid="ref26">26</xref>
,<xref ref-type="bibr" rid="ref27">27</xref>
</sup>
Accordingly,
α-helix-constrained HIV-neutralizing C-peptides, engineered
by strategies such as salt bridges,<sup><xref ref-type="bibr" rid="ref28">28</xref>
,<xref ref-type="bibr" rid="ref29">29</xref>
</sup>
helix-favoring
amino acids,<sup><xref ref-type="bibr" rid="ref30">30</xref>
</sup>
and hydrophobic mutations
in buried residues,<sup><xref ref-type="bibr" rid="ref31">31</xref>
</sup>
can significantly
enhance the bundle stability compared with their corresponding wild-type
ligands despite the substitution of approximately half of the parent
residues.</p>
<p>Incorporation of an alkyl hydrocarbon tail onto a
peptide represents
another promising α-helix-promoting technique. Recent studies
on HIV-1 fusion inhibitors have revealed that lipid-conjugated C-peptides
have a greatly increased α-helicity and NHR-binding capability.<sup><xref ref-type="bibr" rid="ref32">32</xref>
,<xref ref-type="bibr" rid="ref33">33</xref>
</sup>
Moreover, for viruses that fuse at the cell surface, lipidation
also provides the critical advantage of endowing C-peptides with the
membrane-tropic feature. Enrichment of the local concentration of
helical peptides at the membrane level further facilitates their assembly
with the intermediate-stage NHR-helical trimers.<sup><xref ref-type="bibr" rid="ref34">34</xref>
</sup>
For intracellularly fusing viruses, lipidation allows antiviral
peptides to internalize along with viruses into host cells, thereby
arresting 6HB formation in the endosomes.<sup><xref ref-type="bibr" rid="ref12">12</xref>
</sup>
</p>
<p>Taking advantage of the adjustability and tractability of
α-helix-mediated
interactions in the 6HB core structure typical of class I viral fusion
proteins, we herein describe a rational approach for the design of
relatively broad-spectrum inhibitors against infection of MERS-CoV,
of the family <italic>Coronaviridae</italic>
, that primarily employs
the cell surface pathway,<sup><xref ref-type="bibr" rid="ref13">13</xref>
,<xref ref-type="bibr" rid="ref35">35</xref>
</sup>
and IAV, of the family <italic>Orthomyxoviridae</italic>
, that uses the endocytic route,<sup><xref ref-type="bibr" rid="ref6">6</xref>
,<xref ref-type="bibr" rid="ref7">7</xref>
</sup>
based on replicating the topography of CHR helices by using de novo
designed amphiphilic α-helical peptides with the addition of
a fatty acid tail.</p>
</sec>
<sec id="sec2"><title>Design</title>
<p>In terms of the sequence,
coiled-coil domains share a characteristic
heptad repeat, usually denoted as <italic>a</italic>
-<italic><italic>b</italic>
</italic>
-<italic>c</italic>
-<italic>d</italic>
-<italic>e</italic>
-<italic>f</italic>
-<italic>g</italic>
, with hydrophobic
residues at the core <italic>a</italic>
-<italic>d</italic>
positions
and hydrophilic residues at the other sites.<sup><xref ref-type="bibr" rid="ref20">20</xref>
,<xref ref-type="bibr" rid="ref21">21</xref>
</sup>
In the helix wheel model of the NHR/CHR 6HB structure, the residues
at the <italic>a</italic>
-<italic>d</italic>
-<italic>e</italic>
sites
on the C-helices face the inner N-helices and are largely buried;
these residues are primarily responsible for CHR–NHR interaction.
Meanwhile, the residues at the <italic>b</italic>
-<italic>c</italic>
-<italic>f</italic>
-<italic>g</italic>
sites are located away from
the interaction center. Therefore, we adopted the heptad repeat approach
to design amphiphilic peptides based on the sequence Ac-(X<sub>a</sub>
E<sub>b</sub>
E<sub>c</sub>
X<sub>d</sub>
Z<sub>e</sub>
K<sub>f</sub>
K<sub>g</sub>
)<sub>5</sub>
-βAla-K(C16)-NH<sub>2</sub>
. In the
repeated heptapeptide sequence, we placed hydrophobic residues at
the “X” positions and polar/charged residues at the
“Z” positions. With the <italic>foreground</italic>
<italic>a</italic>
-<italic>d</italic>
and <italic>e</italic>
positions of
the model sequence set, the <italic>background</italic>
<italic>b</italic>
-<italic>c</italic>
-<italic>f</italic>
-<italic>g</italic>
sites were
populated with combinations of glutamic acid and lysine to form double
Glu-Lys intrastrand salt bridges at the <italic>i</italic>
to <italic>i</italic>
+ 4 positions to favor the overall α-helicity and
solubility of the heptad repeat peptides. Seminal work investigating
the structural characterization of coiled coils suggests that the
stability of helical bundles is directly proportional to the number
of heptad repeats. Combined with the optimal peptide length paradigm
established by current peptidic fusion inhibitors, the designed sequence
was made with five heptads, i.e., 35 residues, and an β-alanine
(βAla) was additionally appended outside of the heptad repeat
region in order to link an extra lysine residue,<sup><xref ref-type="bibr" rid="ref36">36</xref>
,<xref ref-type="bibr" rid="ref37">37</xref>
</sup>
which was capped by a palmitoyl group (C16), thus providing its
membrane-tropic feature and favorable safety profile for drug development
(<xref rid="fig1" ref-type="fig">Figure <xref rid="fig1" ref-type="fig">1</xref>
</xref>
C).</p>
</sec>
<sec id="sec3"><title>Results
and Discussion</title>
<p>Initially, we aimed to establish combinations
of <italic>foreground</italic>
<italic>a</italic>
-<italic>d</italic>
residues in the heptad repeat
moiety. As previous experiments have indicated that alanine residues
are strongly biased toward helix formation in peptides,<sup><xref ref-type="bibr" rid="ref38">38</xref>
</sup>
the design of the novel lipopeptide began with
the peptide named AAS (<xref rid="tbl1" ref-type="other">Table <xref rid="tbl1" ref-type="other">1</xref>
</xref>
), in which hydrophobic alanine residues were placed at the <italic>a</italic>
and <italic>d</italic>
positions of the heptad, and a
small helix-favoring polar residue, i.e., serine, which has been widely
utilized in protein functional scanning strategies,<sup><xref ref-type="bibr" rid="ref39">39</xref>
</sup>
was populated at the <italic>e</italic>
positions. To explore
the influence of hydrophobic residue contact at α-helix-mediated
coiled-coil interaction sites on antiviral activity, substitutions
at the <italic>a</italic>
-<italic>d</italic>
positions of the peptide
AAS were made with different hydrophobic residues, including Val,
Phe, Tyr, Leu, and Ile. We used our previously developed MERS-CoV
S protein-mediated cell–cell fusion assay to test the biological
activity of these peptides.<sup><xref ref-type="bibr" rid="ref40">40</xref>
</sup>
As shown
in <xref rid="tbl1" ref-type="other">Table <xref rid="tbl1" ref-type="other">1</xref>
</xref>
, all of
the lipopeptides potently inhibited cell–cell fusion mediated
by MERS-CoV S protein, with 50% effective concentration (EC<sub>50</sub>
) values ranging from 0.1 to >10.0 μM. Of the six lipopeptides
we designed, both LLS and IIS were found to be potent MERS-CoV fusion
inhibitors, with EC<sub>50</sub>
values of 0.24 and 0.10 μM,
respectively. The possible reasons for this activity include the evolutionary
preference for Leu and Ile in the heptad positions <italic>a</italic>
-<italic>d</italic>
for viral fusion glycoprotein sequences and the
significance of creating enough hydrophobicity/amphiphilicity to yield
a stable coiled-coil structure.<sup><xref ref-type="bibr" rid="ref41">41</xref>
</sup>
Compared
to LLS, IIS possessed obviously lower cytotoxicity in Huh-7 cells,
which were used as target cells in the cell–cell fusion assay.
Therefore, in the next round of analogues, we further mutated residues
at the <italic>e</italic>
position of the heptad of IIS with different
types of polar residues, including cationic Lys, anionic Glu, and
uncharged Gln, as well as aromatic/heterocyclic amino acids such as
Tyr, Trp, and His, expecting that these optimizations would provide
further improvement in potency and cytotoxicity. Strikingly, Gln-containing
IIQ and Tyr-containing IIY had EC<sub>50</sub>
values of 0.11 and
0.52 μM, respectively, even reaching the potencies of the MERS-CoV-specific
fusion inhibitor HR2PM2 peptide.<sup><xref ref-type="bibr" rid="ref42">42</xref>
</sup>
In addition,
both IIQ and IIY possessed lower cytotoxicity values than the selected
lead IIS, with a 50% cytotoxicity concentration (CC<sub>50</sub>
)
value of >100 μM. Subsequently, we tested the inhibitory
activity
of the peptide IIQ on the entry of pseudovirus carrying the wild-type
MERS-CoV S protein. As shown in Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S1</ext-link>
, IIQ was effective against MERS-CoV
pseudovirus infection, with an EC<sub>50</sub>
value of 0.13 μM;
this finding was in close agreement with the cell–cell fusion
assay results. These data imply that the de novo designed peptides
that are nonhomologous with the naturally occurring MERS-CoV S protein
sequence could effectively inhibit MERS-CoV infection by targeting
virus–host cell membrane fusion. Moreover, we explored the
structural properties of these lipopeptides by circular dichroism
(CD) spectroscopy to determine if their propensities to adopt α-helical
structure were correlated with anti-MERS-CoV activity. The relationships
between the EC<sub>50</sub>
s of lipopeptides and their α-helical
content are shown in <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S2</ext-link>
in the Supporting
Information. We found that the potency was not strictly dependent
on their α-helicity (<italic>r</italic>
<sup>2</sup>
= 0.2439),
suggesting that other factors, such as solubility and target binding
affinity and kinetics, may be involved in their biological activity.
This phenomena has also been observed in the studies on HIV-1 fusion
inhibitors, where several C-peptides exhibited no anti-HIV-1 potency
despite they have fully α-helical structure in solution.<sup><xref ref-type="bibr" rid="ref29">29</xref>
,<xref ref-type="bibr" rid="ref43">43</xref>
</sup>
</p>
<table-wrap id="tbl1" position="float"><label>Table 1</label>
<caption><title>Inhibitory Activities of Lipopeptides
on MERS-CoV S Protein-Mediated Cell–Cell Fusion<xref rid="t1fn1" ref-type="table-fn">a</xref>
</title>
</caption>
<graphic xlink:href="jm8b00890_0007" id="GRAPHIC-d7e755-autogenerated" position="float"></graphic>
<table-wrap-foot><fn id="t1fn1"><label>a</label>
<p>The number of 293T/MERS/EGFP cells
fused or unfused with Huh-7 cells were countered, and the percentage
of inhibition was calculated as described in the <xref rid="sec5" ref-type="other">experimental section</xref>
. Data were derived from the results of
three independent experiments and are expressed as the mean ±
standard deviation.</p>
</fn>
<fn id="t1fn2"><label>b</label>
<p>These
peptides have an acetyl group
at the N-terminus and carboxyamide at the C-terminus. The letters <italic>a</italic>
-<italic>g</italic>
indicate the positions of the corresponding
residues in a helical wheel presentation. βA, β-alanine.</p>
</fn>
<fn id="t1fn3"><label>c</label>
<p>Cytotoxicity to Huh-7 cells.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>The ongoing threat of the emergence
of resistant variants that
diminish or ablate the effectiveness of the currently available anti-IAV
drugs underscores the demand for new antiviral strategies targeting
other proteins in the influenza virus life cycle.<sup><xref ref-type="bibr" rid="ref44">44</xref>
</sup>
Therefore, we employed a cytopathic effect inhibition assay
to evaluate the inhibition effect of compounds IIS, IIY, and IIQ,
which exhibited promising potency in inhibiting MERS-CoV infection,
against IAVs. Surprisingly, one of the lipopeptides, IIQ, displayed
potent inhibitory activity toward both strains A/Puerto Rico/8/34
(H1N1) and A/Hong Kong/8/68 (H3N2), with EC<sub>50</sub>
values of
1.73 and 0.70 μM, respectively (<xref rid="tbl2" ref-type="other">Table <xref rid="tbl2" ref-type="other">2</xref>
</xref>
). Furthermore, none of these peptides displayed
a cytotoxic effect against Madin–Darby canine kidney (MDCK)
cells at concentrations up to 100 μM. The selective index of
IIQ was larger than 143, indicating a safe profile for further exploration.
The data presented in <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Table S1</ext-link>
in the Supporting
Information show that IIQ was also potent against oseltamivir-resistant
strains, including LN/1109 (H1N1) and TJ/15 (H1N1), with EC<sub>50</sub>
values of 4.36 and 3.03 μM, respectively, whereas oseltamivir
was much less effective (EC<sub>50</sub>
= 21.7 μM) against
LN/1109 (H1N1) and inactive against TJ/15 (H1N1) at concentrations
up to 100 μM. In addition, IIQ also exerted remarkable inhibitory
activity against B/Lee/40 strain infection with an EC<sub>50</sub>
value of 1.87 ± 0.95 μM. As expected, MERS-CoV HR2PM2
displayed no inhibition effect against A/Puerto Rico/8/34 (H1N1) and
A/Hong Kong/68 (H3N2) infection at the concentration up to 20 μM.
The life cycle of influenza virus is divided into three steps, i.e.,
virus entry, viral genome replication, and progeny virion release.<sup><xref ref-type="bibr" rid="ref45">45</xref>
</sup>
Currently, several anti-influenza drugs have
been developed for interruption of specific processes in influenza
infection. Among them, oseltamivir (Tamiflu) targets neuraminidase
(NA) protein, thus preventing release of tethered progeny virus from
its host cells.<sup><xref ref-type="bibr" rid="ref46">46</xref>
</sup>
Favipiravir that selectively
inhibits RNA-dependent RNA polymerase has been approved in Japan as
an inhibitor of influenza virus replication for the treatment of influenza
virus infection in 2014.<sup><xref ref-type="bibr" rid="ref47">47</xref>
</sup>
We then asked
if the IIQ peptide acts by inhibiting the entry step of IAV into host
cells. To address this question, a viral replicon assay and a neuraminidase
inhibition assay were performed to rule out any effect of IIQ on viral
replication and progeny virion release, respectively. In the mini-replicon
system, viral RNA polymerase protein expression plasmids mediate the
expression of a reporter genome encoding firefly luciferase. Through
determination of the normalized firefly luminescence/<italic>Renilla</italic>
luminescence ratio, we found that favipiravir
could inhibit influenza replicon activity in a dose-dependent manner,
with a 50% inhibitory concentration (IC<sub>50</sub>
) value of 26.2
± 3.7 μM, whereas IIQ and the neuraminidase inhibitor oseltamivir
exhibited no significant inhibition at concentrations up to 100 μM
(<xref rid="fig2" ref-type="fig">Figure <xref rid="fig2" ref-type="fig">2</xref>
</xref>
A). As shown
in <xref rid="fig2" ref-type="fig">Figure <xref rid="fig2" ref-type="fig">2</xref>
</xref>
B,C, neither
IIQ nor favipiravir was able to disturb cleavage of the substrate
by neuraminidase from the two IAV strains A/Puerto Rico/8/34 (H1N1)
and A/Hong Kong/8/68 (H3N2) in the test range. In contrast, oseltamivir
could inhibit neuraminidase of these two viruses, with IC<sub>50</sub>
values of 1.71 ± 0.2 and 0.51 ± 0.01 nM, respectively.
Taken together, these results suggest IIQ may affect the entry stage
of viral life cycle to block virus infection. Moreover, using a time-of-addition
assay, we found that the viral load at intervals of 0–10 h
(covering the whole life cycle) and 0–2 h (covering the entry
step) was reduced by approximately 60%, with the addition of 10 μM
IIQ, as compared with the PBS control, and no antiviral activity was
observed for the remaining three time intervals (2–5, 5–8,
and 8–10 h). However, favipiravir continued to exert its full
effect, even at the interval of 5–8 h. These results further
confirmed that IIQ targets the entry step in the IAV life cycle (<xref rid="fig2" ref-type="fig">Figure <xref rid="fig2" ref-type="fig">2</xref>
</xref>
D–F). Hemagglutination
inhibition (HI) assay is well-established to determine whether the
sialic acid-binding site on HA1 subunit acts as potential drug target;
meanwhile, hemolysis inhibition assay is commonly used to determine
whether the HA2 subunit can be a possible target.<sup><xref ref-type="bibr" rid="ref48">48</xref>
</sup>
Thus, an HI assay was first performed to determine the
potential effect of IIQ peptide on the HA1 subunit sialic acid-binding
site. The result showed that no apparent inhibition of influenza virus-induced
aggregation of chicken erythrocytes was observed in the test range,
indicating IIQ has no effect on the interaction of HA1 subunit with
its sialic acid receptor (Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S3A</ext-link>
). Moreover, the hemolysis inhibition assay showed
that the lysis of erythrocytes caused by the conformational rearrangements
of HA2 subunit under acidic condition was decreased compared with
the hemolytic effect of virus only (Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S3B</ext-link>
). The combined results indicate that
IIQ may bind to the HA2 subunit to interrupt the conformational changes
in HA2 rather than interacting with HA1 subunit via inhibiting the
absorption of viruses into host cells, consistent with our design
rationale.</p>
<table-wrap id="tbl2" position="float"><label>Table 2</label>
<caption><title>Inhibitory Activities of Lipopeptides
against Influenza A Virus Strains Infection in Cell Culture<xref rid="t2fn1" ref-type="table-fn">a</xref>
</title>
</caption>
<table frame="hsides" rules="groups" border="0"><colgroup><col align="left"></col>
<col align="char" char="±"></col>
<col align="char" char="±"></col>
<col align="char" char="."></col>
</colgroup>
<thead><tr><th style="border:none;" align="center"> </th>
<th colspan="2" align="center" char="±">EC<sub>50</sub>
(μM) for inhibiting<hr></hr>
</th>
<th style="border:none;" align="center" char="."> </th>
</tr>
<tr><th style="border:none;" align="center">compd</th>
<th style="border:none;" align="center" char="±">A/Puerto Rico/8/34 (H1N1)</th>
<th style="border:none;" align="center" char="±">A/Hong Kong/8/68 (H3N2)</th>
<th style="border:none;" align="center" char=".">CC<sub>50</sub>
(μM)<xref rid="t2fn2" ref-type="table-fn">b</xref>
</th>
</tr>
</thead>
<tbody><tr><td style="border:none;" align="left">IIS</td>
<td style="border:none;" align="char" char="±">1.96 ± 0.28</td>
<td style="border:none;" align="char" char="±">6.38 ± 1.06</td>
<td style="border:none;" align="char" char=".">>100</td>
</tr>
<tr><td style="border:none;" align="left">IIY</td>
<td style="border:none;" align="char" char="±">3.15 ± 1.79</td>
<td style="border:none;" align="char" char="±">12.9 ± 5.55</td>
<td style="border:none;" align="char" char=".">>100</td>
</tr>
<tr><td style="border:none;" align="left">IIQ</td>
<td style="border:none;" align="char" char="±">1.73 ± 0.81</td>
<td style="border:none;" align="char" char="±">0.70 ± 0.09</td>
<td style="border:none;" align="char" char=".">>100</td>
</tr>
<tr><td style="border:none;" align="left">oseltamivir</td>
<td style="border:none;" align="char" char="±">1.48 ± 0.05</td>
<td style="border:none;" align="char" char="±">0.01 ± 0.004</td>
<td style="border:none;" align="char" char=".">>100</td>
</tr>
</tbody>
</table>
<table-wrap-foot><fn id="t2fn1"><label>a</label>
<p>Data were derived from the results
of three independent experiments and are expressed as the mean ±
standard deviation.</p>
</fn>
<fn id="t2fn2"><label>b</label>
<p>The
cytotoxicity of compounds on
MDCK cells.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<fig id="fig2" position="float"><label>Figure 2</label>
<caption><p>Exploration of the viral
life cycle stage in which IIQ performed
its inhibitory activity. (A) The inhibitory effect of IIQ on IAV polymerase
activity was tested by a mini-replicon assay. Data represent the average
of three independent measurements and are shown as the mean with standard
deviation (bars). Oseltamivir and favipiravir were employed as negative
and positive controls, respectively. Inhibition of the neuraminidase
of influenza virus strains (B) A/Puerto Rico/8/34 and (C) A/Hong Kong/8/68
by IIQ as determined by chemiluminescence-based enzyme inhibition
assays. The results are from three independent experiments. Oseltamivir
and favipiravir were employed as positive and negative controls, respectively.
(D) Strategy for the time-of-addition assay. The life cycle of IVA
is divided into three steps, i.e., viral entry (0–2 h), viral
genome replication and translation (2–8 h), and progeny virion
release (8–10 h). MDCK cells were treated with inhibitor at
five time intervals (0–10, 0–2, 2–5, 5–8,
and 8–10 h) postinfection. The blue lines indicate the exposure
intervals of inhibitor during the first viral life cycle. Time-of-addition
assay to analyze the life cycle step specifically targeted by (E)
IIQ and (F) favipiravir. Quantitative real-time PCR was used to detect
the viral load at the indicated times. Data are expressed as the mean
± standard deviation of triplicate experiments. Statistical significance
was evaluated with MANOVA. *, <italic>p</italic>
< 0.05 compared
to PBS treatment. **, <italic>p</italic>
< 0.01 compared to PBS
treatment.</p>
</caption>
<graphic xlink:href="jm8b00890_0002" id="gr2" position="float"></graphic>
</fig>
<p>After identifying that the entry/fusion
process phase of the life
cycle of MERS-CoV and IAV was the point of interference, we explored
whether the IIQ peptide would interact with the corresponding NHR
region of viral fusion proteins with a mechanism of action similar
to virus-specific C-peptides. The first piece of evidence came from
native polyacrylamide gel electrophoresis (N-PAGE) of equimolar mixtures
of IIQ plus synthetic peptides containing the NHR segments of the
MERS-CoV spike (S) protein S2 subunit, designated as HR1P,<sup><xref ref-type="bibr" rid="ref13">13</xref>
</sup>
and the postfusion structure of the H3N2 hemagglutinin
(HA) HA2 subunit, namely N66,<sup><xref ref-type="bibr" rid="ref49">49</xref>
</sup>
respectively.
The mixtures of IIQ/HR1P and IIQ/N66 showed new bands at the upper
positions in the gel, demonstrating that tightly associated complexes
were formed (<xref rid="fig3" ref-type="fig">Figure <xref rid="fig3" ref-type="fig">3</xref>
</xref>
A). These findings are consistent with the results obtained from
circular dichroism (CD) spectroscopy, in which the signal of these
mixtures was dramatically greater than that of the mathematical sum
of the corresponding isolated peptides, suggesting induction of a
large α-helical structure resulting from their interaction (<xref rid="fig3" ref-type="fig">Figure <xref rid="fig3" ref-type="fig">3</xref>
</xref>
B,C).<sup><xref ref-type="bibr" rid="ref50">50</xref>
</sup>
Moreover, data from CD analysis indicated that
the IIQ/HR1P and IIQ/N66 helical bundles showed strong thermal stability,
with melting temperature values of >90 and 83.1 °C, respectively
(<xref rid="fig3" ref-type="fig">Figure <xref rid="fig3" ref-type="fig">3</xref>
</xref>
D and Supporting
Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Table S2</ext-link>
). In CD analysis,
N36/C34 6HB,<sup><xref ref-type="bibr" rid="ref31">31</xref>
</sup>
which has an available crystal
structure and is widely used to represent the HIV-1 fusion core, was
used as a positive control (Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S4</ext-link>
). Finally, sedimentation velocity analysis demonstrated
the heterogeneous 6HB states of the IIQ/HR1P complex and the IIQ/N66
complex (Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Table S3</ext-link>
and <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Figure S5</ext-link>
). Together, these data
suggest that the active IIQ peptide does indeed associate with a site
in the NHR region and forms heterogeneous 6HB structures that interfere
with the fusion between virus and target cell membrane.</p>
<fig id="fig3" position="float"><label>Figure 3</label>
<caption><p>Identification
of the NHR region of viral fusion proteins as the
potential target of IIQ. (A) Association of IIQ with HR1P, a synthetic
peptide spanning residues 998–1039 of the MERS-CoV S2 subunit
(PDB 4NJL),
and N66 peptide, which corresponds to residues 40–105 of IAV
H3 (X31) HA (PDB 1QU1), respectively, as determined by N-PAGE. The final peptide concentration
in each preparation was 75 μM. Left panel: Peptides were electrophoresed
in a 15% native polyacrylamide continuous gel at pH 3.4. HR1P alone
showed no band in the gel, likely because of its tendency to aggregate
when sample was prepared in PBS (pH 7.4) before analysis in the acidic
electrophoresis system. Right panel: Peptides were loaded on a 15%
Tris-glycine gel with Tris−glycine running buffer (pH 8.8).
IIQ alone showed no band in the gel, probably because the pH of the
gel buffer is only slightly higher than the isoelectric point value
of IIQ, thus it carries few net charges and cannot migrate into the
gel. CD spectra for (B) IIQ, HR1P, and the IIQ/HR1P complex at neutral
pH (solid lines) and for (C) IIQ, N66, and the IIQ/N66 complex at
pH 5.0 (the pH of endosomes, solid lines). The theoretical noninteracting
spectra of the related isolated peptides ((IIQ + HR1P) and (IIQ +
N66), dashed lines) are shown for comparison. All spectra were obtained
with 10 μM peptide at 25 °C. (D) CD signals at 222 nm for
IIQ/HR1P (pH 7.4) and IIQ/N66 (pH 5.0) mixtures as a function of temperature.</p>
</caption>
<graphic xlink:href="jm8b00890_0003" id="gr3" position="float"></graphic>
</fig>
<p>We used the palmitoyl-2-oleoyl-<italic>sn</italic>
-glycero-3-phospholcholine
large unilamellar vesicle (POPC LUV) liposome system to examine the
ability of IIQ to interact with a lipid bilayer by measuring the heat
generated during the peptide–lipid binding in an isothermal
titration calorimetry assay.<sup><xref ref-type="bibr" rid="ref51">51</xref>
</sup>
As shown
in <xref rid="fig4" ref-type="fig">Figure <xref rid="fig4" ref-type="fig">4</xref>
</xref>
, a huge
amount of released heat was observed after the titration of POPC LUVs
into solutions containing IIQ peptide, with a binding constant of
1.04 × 10<sup>5</sup>
M<sup>–1</sup>
. In comparison, the
unconjugated peptide IIQΔ, which exhibited no significant inhibitory
activity at the concentration up to 40 μM on both MERS-CoV pseudovirus
and A/Puerto Rico/8/34 (H1N1) infection, did not show lipid vesicle
binding. These observations indicate that IIQ can bind to a lipid
bilayer. Although HIV-1-neutralizing CHR peptides provide a classic
paradigm for the rational design of fusion inhibitors that interfere
with the interaction between the heptad-repeat regions of class I
viral fusion proteins, the development of such drugs with novel modes
of action against IAV remains a challenge, mainly by the inaccessibility
of exogenously added C-peptides to the endocytic compartment, where
fusogenic 6HB formation takes place. Thus, we next appended the fluorescent
probe nitrobenzoxadiazole (NBD) to the N-terminus of IIQ via a β-alanine
spacer to generate IIQ<sub>NBD</sub>
and monitored its cellular uptake.
IIQ<sub>NBD</sub>
was found to be similar to IIQ in terms of its α-helicity
and inhibitory potency against IAV infection, indicating that the
addition of the fluorophore did not dramatically affect the biophysical/biological
properties of IIQ (Supporting Information, <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Table S4</ext-link>
). To demonstrate cellular uptake, MDCK cells treated with
IIQ<sub>NBD</sub>
were observed after incubation for 0.5, 1, and 4
h by confocal microscopy. The lysotracker probe specifically fluoresces
in acidic vesicles.<sup><xref ref-type="bibr" rid="ref52">52</xref>
</sup>
As shown in <xref rid="fig5" ref-type="fig">Figure <xref rid="fig5" ref-type="fig">5</xref>
</xref>
, MDCK cells exposed
to IIQ<sub>NBD</sub>
for 0.5 h showed that the lipopeptides were distributed
on the periphery of the cell membrane. After 1 h, the accumulation
of IIQ<sub>NBD</sub>
within the MDCK cells was detected in the acidic
intracellular compartments, colocalized with LysoTracker Red. Moreover,
after 4 h, an increasing amount of IIQ<sub>NBD</sub>
was internalized
and colocalized extensively with LysoTracker Red. Taken together,
these results suggest that the α-helical lipopeptide could cross
the plasma membrane efficiently via endocytosis and trap IAV fusion
proteins in their prehairpin intermediate state, thereby blocking
membrane fusion.</p>
<fig id="fig4" position="float"><label>Figure 4</label>
<caption><p>Analysis of the binding of IIQ to a lipid bilayer. (A)
The sequences
IIQ and the negative control IIQΔ. (B) POPC LUVs (10 mg/mL)
were injected into a chamber containing 15 μM IIQ (left) or
IIQΔ (right) at 25 °C. Data acquisition and analysis were
performed using MicroCal Origin software (version 7.0). The upper
panels show the titration traces, and the lower panels show the binding
affinity when POPC LUVs were injected into IIQ or IIQΔ solution.</p>
</caption>
<graphic xlink:href="jm8b00890_0004" id="gr4" position="float"></graphic>
</fig>
<fig id="fig5" position="float"><label>Figure 5</label>
<caption><p>Uptake of the fluorescein-labeled peptide IIQ<sub>NBD</sub>
in
MDCK cells. Confocal microscopy images were obtained for IIQ<sub>NBD</sub>
after 0.5 h (A1–A3), 1 h (B1–B3), and 4 h (C1–C3)
of cell treatment. IIQ peptide was labeled with the fluorescein tag
NBD (green signal, A1–C1), and intracellular acidic vesicles
were stained with LysoTracker Red (red signal, A2–C2). The
yellow punctate staining demonstrates the electronic merging (Merge,
A3–C3) of IIQ<sub>NBD</sub>
and LysoTracker. The white and
yellow arrows indicate the cell nuclear region and the cell membrane,
respectively. Scale bar: 50 μm.</p>
</caption>
<graphic xlink:href="jm8b00890_0005" id="gr5" position="float"></graphic>
</fig>
<p>Subsequently, IIQ peptide was assessed for essential druglike
properties,
including water solubility and in vivo pharmacokinetic properties.
IIQ showed solubility value of 8.87 ± 0.4 mg/mL in pure water.
The pharmacokinetic behavior of IIQ was evaluated in rats (<xref rid="fig6" ref-type="fig">Figure <xref rid="fig6" ref-type="fig">6</xref>
</xref>
and <xref rid="tbl3" ref-type="other">Table <xref rid="tbl3" ref-type="other">3</xref>
</xref>
). Sprague–Dawley rats
were injected intravenously with 5 mg/kg of IIQ peptide, and blood
was withdrawn after 2 min, 5 min, 15 min, 30 min, 1 h, 2 h, 4 h, 8
h 12 h, and 24 h, respectively (three animals at each time point).
The LC/MS/MS method showed satisfactory results for the determination
of IIQ in rat plasma and was used for the pharmacokinetic study. Inspection
of the plasma concentration–time profile for IIQ revealed that
the mean value of the maximum plasma concentration (<italic>C</italic>
<sub>max</sub>
) obtained 2 min after dosing was 97.6 μg/mL
and the area under the plasma concentration–time curve extrapolated
to the last time point (AUC<sub>0–<italic>t</italic>
</sub>
)
was 234.7 (μg/mL)·h. The elimination kinetics of IIQ demonstrated
durable plasma half-life of 6.6 h, and the concentration of IIQ in
plasma remained well above the 0.1 μg/mL limit of quantitation
of the analytical method at 24 h. Furthermore, IIQ peptide has a low
rate of clearance of 20.7 mL·h<sup>–1</sup>
·kg<sup>–1</sup>
. Together, the favorable pharmacokinetic of IIQ,
including the efficacious exposure level, the low clearance, and the
relatively extended half-life in vivo, suggest IIQ is suitable for
further study as a drug candidate.</p>
<fig id="fig6" position="float"><label>Figure 6</label>
<caption><p>Pharmacokinetic studies of IIQ in plasma
following the administration
of a single intravenous dose (5 mg/kg) to Sprague–Dawley rats
(<italic>n</italic>
= 3).</p>
</caption>
<graphic xlink:href="jm8b00890_0006" id="gr6" position="float"></graphic>
</fig>
<table-wrap id="tbl3" position="float"><label>Table 3</label>
<caption><title>Pharmacokinetic Parameters of IIQ
in Rats Following a Single Dose iv Administration Calculated by Noncompartmental
Analysis by Using DAS, Version 3.2.8<xref rid="t3fn1" ref-type="table-fn">a</xref>
</title>
</caption>
<table frame="hsides" rules="groups" border="0"><colgroup><col align="left"></col>
<col align="char" char="±"></col>
<col align="char" char="±"></col>
<col align="char" char="±"></col>
<col align="char" char="±"></col>
<col align="char" char="±"></col>
<col align="center"></col>
</colgroup>
<thead><tr><th style="border:none;" align="center">compd</th>
<th style="border:none;" align="center" char="±">AUC (0–<italic>t</italic>
) ((μg/mL)·h)</th>
<th style="border:none;" align="center" char="±">MRT (0–<italic>t</italic>
) (h)</th>
<th style="border:none;" align="center" char="±"><italic>t</italic>
<sub>1/2</sub>
(h)</th>
<th style="border:none;" align="center" char="±">CL ((mL/h)/kg)</th>
<th style="border:none;" align="center" char="±"><italic>C</italic>
<sub>max</sub>
(μg/mL)</th>
<th style="border:none;" align="center"><italic>V</italic>
<sub>d</sub>
(mL/kg)</th>
</tr>
</thead>
<tbody><tr><td style="border:none;" align="left">IIQ</td>
<td style="border:none;" align="char" char="±">234.7 ± 7.8</td>
<td style="border:none;" align="char" char="±">4.1 ± 0.1</td>
<td style="border:none;" align="char" char="±">6.6 ± 0.2</td>
<td style="border:none;" align="char" char="±">20.7 ± 0.6</td>
<td style="border:none;" align="char" char="±">97.6 ± 8.4</td>
<td style="border:none;" align="center">197.8 ± 9.3</td>
</tr>
</tbody>
</table>
<table-wrap-foot><fn id="t3fn1"><label>a</label>
<p>MRT, mean residence
time; CL, clearance; <italic>V</italic>
<sub>d</sub>
, volume of distribution.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>To investigate whether our
engineered lipopeptides exert broad
antiviral spectrum beyond <italic>Coronaviridae</italic>
and <italic>Orthomyxoviridae</italic>
families, IIQ peptide was further evaluated
against HIV-1 envelope glycoprotein (Env)-mediated cell–cell
fusion and Ebola virus (EboV) envelope glycoprotein (GP)-mediated
cell entry. We found that IIQ inhibited HIV-1 Env-mediated cell fusion
with an EC<sub>50</sub>
of 3.63 ± 0.54 μM and exhibited
low cytotoxicity, with CC<sub>50</sub>
> 100 μM, on the TZM-b1
cell that was used for the fusion assay. Encouragingly, IIQ also inhibited
the entry of pseudovirus carrying the GP of the EboV Sudan species,
with EC<sub>50</sub>
value of 1.02 ± 0.54 μM. To our knowledge,
the formation of a hexameric coiled-coil complex is believed to be
a common element in type I fusion events. However, the fusion rates
vary significantly between viruses from different families, between
viruses within a family, and even between isolates of the same species,
thus leading to the different window periods during which inhibitory
peptides access to the target fusion protein and thereby impacting
entry inhibitor efficacy.<sup><xref ref-type="bibr" rid="ref5">5</xref>
</sup>
Furthermore,
the stability of the corresponding fusogenic 6HB of different type
I viral fusion proteins was also correlated with the inhibitory potency
of peptides.<sup><xref ref-type="bibr" rid="ref7">7</xref>
</sup>
Therefore, the engineered
lipopeptides with simple repeating units of the heptad in our study
could not be effective against all of the class I viruses entry, but
first provide a proof-of-concept prototype for broad-spectrum antiviral
agents design. Moreover, these lipopeptides may also be used as lead
compounds for further optimization to design inhibitors with a broader
antiviral spectrum.</p>
</sec>
<sec id="sec4"><title>Conclusions</title>
<p>On the basis of common
features of the fusogenic 6HB structure
formed between the CHR and NHR regions of the class I viral fusion
glycoproteins, we report an effective strategy to expedite the development
of relatively broad-spectrum antiviral drugs. Our study reveals that
the de novo designed α-helical lipopeptides, which are nonhomologous
with naturally occurring protein sequences, can interact with both
MERS-CoV and IAV NHR trimeric coiled coils to prevent virus–cell
membrane fusion. One of the designed peptides showed a high potency
against MERS-CoV infection and effectively neutralized H1N1 A/Puerto
Rico/8/34 (influenza A group 1), H3N2 A/Hong Kong/8/68 (influenza
A group 2), and even the influenza B virus (B/Lee/40). The relatively
broad-spectrum antiviral peptides were designed based on the secondary
structure at the hexameric coiled-coil complex interface. We anticipate
that this approach could also be extended to other pathogenic viruses
with class I fusion proteins because they undergo fusion catalysis
in a manner similar to that of MERS-CoV and IAVs.</p>
</sec>
<sec id="sec5"><title>Experimental Section</title>
<sec id="sec5.1"><title>General Peptide Synthesis</title>
<p>Peptides
were synthesized
by using standard Fmoc solid-phase synthesis techniques with a CS
Bio polypeptide synthesizer. Rink amide resin, with a resin loading
of 0.44 mmol/g, was selected as the solid support. <italic>N</italic>
,<italic>N</italic>
-Dimethylformamide (DMF), dichloromethane (DCM), <italic>N</italic>
-methyl-2-pyrrolidone (NMP), methanol, piperidine, and
other reagents used in the reaction process were anhydrous reagents
or dried prior to use. The synthetic steps were as follows: (1) The
resin was first swelled in a reaction vessel by the addition of 5
mL of DMF and 5 mL of DCM, followed by stirring for 20 min. (2) The
Fmoc protecting group was removed using 20% piperidine/DMF. The deprotection
reaction was performed twice; the first reaction was 5 min, and the
second reaction was 2 min. (3) The next amino acid was coupled with
the addition of 5 mL of amino acid solution (0.25 M), 5 mL of condensing
reagents [0.2 M <italic>O</italic>
-benzotriazole-<italic>N</italic>
,<italic>N</italic>
,<italic><italic>N</italic>
</italic>
′,<italic>N</italic>
′-tetramethyluronium hexafluorophosphate (HBTU)/DMF
and 0.2 M 1-hydroxybenzotriazole (HOBt)/DMF], and 5 mL of active base
solution [0.4 M <italic>N</italic>
,<italic>N</italic>
-diisopropylethylamine
(DIEA)/DMF] to the reactor; the reaction was stirred at room temperature
for 60 min. After completion of the coupling reaction or Fmoc removal,
the resin was washed with DMF (5 × 1 min) and DCM (3 × 1
min). For lipopeptides, the template peptides containing a Dde-protected
lysine residue at their C-terminus required a special deprotection
step (four 3 min washes of 2% hydrazinehydrate in DMF). This enabled
the conjugation of a palmityl moiety, which was performed by the addition
of 3 equiv of palmic acid, 3 equiv of HBTU, and 6 equiv of DIEA in
DMF to the resin, followed by stirring for 2 h. Conjugation of a fluoride
[4-fluoro-7- nitrobenzofurazan (NBD)] fluorescent probe to the N-terminus
of the peptide was performed by the addition of 6 equiv of NBD-Cl
dissolved in DMF together with 6 equiv of DIEA to the peptide resin,
followed by stirring for 12 h. The peptides were cleaved from the
resin and deprotected with reagent K, which contained 85% trifluoroacetic
acid, 5% thioanisole, 5% <italic>m</italic>
-cresol, and 5% water.
The carboxyl termini were amidated upon cleavage from the resin, and
the amino termini were capped with acetic acid anhydride, except NBD-conjugated
peptides. All lyophilized crude peptides were purified by reversed-phase
high-performance liquid chromatography (RP-HPLC; Shimadzu preparative
HPLC system), and the purity of each peptide was confirmed to be ≥95%
by analytical RP-HPLC (Shimadzu analytical HPLC system). Such information
is provided in the Supporting Information (<ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Table S5–S6</ext-link>
). The molecular weight of the peptides was characterized
by matrix-assisted laser desorption ionization–time-of-flight
mass spectrometry (Autoflex III, Bruker Daltonics Inc., Billerica,
MA).</p>
</sec>
<sec id="sec5.2"><title>MERS-CoV S Protein-Mediated Cell–Cell Fusion Assay</title>
<p>The target cells were Huh-7 cells expressing the MERS-CoV receptor
dipeptidyl peptidase 4. The effector cells were 293T/MERS/enhanced
GFP protein (EGFP) cells.<sup><xref ref-type="bibr" rid="ref13">13</xref>
</sup>
The 293T/MERS/EGPF
cells contained the MERS-CoV S protein gene and the EGFP gene transfected
with plasmid. The 293T/EGFP cells expressing only EGFP were employed
as negative control cells. Huh-7 cells were plated in 96-well plates
(5 × 10<sup>4</sup>
cells/well) at 37 °C for 5 h. Then,
serially diluted peptide samples were added, followed by the addition
of 293T/MERS/EGPF cells or 293T/EGFP cells (1 × 10<sup>4</sup>
cells/well). After coculturing at 37 °C for 4 h, the 293T/MERS/EGFP
cells and 293T/EGFP cells, either fused or unfused, with Huh-7 cells
were counted under an inverted fluorescence microscope (Nikon Eclipse
Ti-S).</p>
</sec>
<sec id="sec5.3"><title>Inhibition of Pseudotyped MERS-CoV Infection</title>
<p>Inhibition
of MERS-CoV pseudovirus infection was assessed using a previously
described method.<sup><xref ref-type="bibr" rid="ref42">42</xref>
</sup>
Briefly, the serially
diluted tested peptides were added to a 96-well plate and incubated
with MERS-CoV pseudovirus for 30 min at 37 °C. Then, the pseudovirus/peptide
mixture was added to the Huh-7 cells. Cultures were refed with fresh
medium at 12 h postinfection and incubated for an additional 48 h
at 37 °C. Fluorescence was determined using a luciferase kit
(Promega) and an Ultra 384 luminometer (Tecan).</p>
</sec>
<sec id="sec5.4"><title>Cytopathic
Effect Reduction Assay</title>
<p>Madin–Darby
canine kidney (MDCK) cells were seeded in a 96-well plate (Nunc MicroWell)
at a density of 1.5 × 10<sup>4</sup>
cells/well in Dulbecco’s
Modified Eagle’s Medium/Ham’s F-12 medium (DF-12) and
were incubated overnight to adhere to the plate.<sup><xref ref-type="bibr" rid="ref53">53</xref>
</sup>
A 3-fold dilution series of tested compounds in DF-12 with
tosylsulfonyl phenylalanyl chloromethyl ketone (TPCK)-trypsin was
added to cells infected with influenza virus A/Puerto Rico/8/1934
(H1N1) or A/Hong Kong/8/68 (H3N2) at a final multiplicity of infection
(MOI) of 0.003 Pfu/cell suspended in DF-12 medium with TPCK-trypsin.
After incubation at 37 °C for 72 h, the antiviral effect of the
tested compounds was measured using a CellTiter-Glo cell viability
assay (Promega, USA), as described by the manufacturer. The plates
were read by a SpectraMax M5 microplate reader (Molecular Devices,
USA).</p>
</sec>
<sec id="sec5.5"><title>Cytotoxicity Assays</title>
<sec id="sec5.5.1"><title>Cytotoxicity of Compounds on Huh-7 Cells</title>
<p>Briefly, 100
μL of a Huh-7 cell suspension (1 × 10<sup>5</sup>
cells/mL)
were added to each well of a 96-well culture plate. The plate was
incubated at 37 °C in 5% CO<sub>2</sub>
for 12 h. Next, 5 μL
of serially diluted peptide solution were added. At the same time,
a blank control group without peptide and a positive control group
with 5 μL of 10% Triton X-100 were cultured for 48 h under the
conditions of 5% CO<sub>2</sub>
at 37 °C. To each well were added
10 μL of Cell Counting Kit 8 solution, and the plate was incubated
for an additional 2 h. The absorbance at 450 nm was determined by
a microplate reader.</p>
</sec>
<sec id="sec5.5.2"><title>Cytotoxicity of Compounds on MDCK Cells</title>
<p>MDCK cells
were seeded in a 96-well plate at a density of 1.5 × 10<sup>4</sup>
cells/well in DF-12 medium and incubated overnight before a 3-fold
dilution series of tested compounds in DF-12 medium with TPCK-trypsin
was added to the cells. At 72 h after treatment, the cytotoxicity
was measured by a CellTiter-Glo cell viability assay (Promega, USA).
The 50% cytotoxicity concentration data were fit and determined by
Origin 8 software.</p>
</sec>
</sec>
<sec id="sec5.6"><title>Influenza Virus Replication Assay</title>
<p>Human embryonic kidney
293T cells were seeded in a 96-well plate (Nunc MicroWell) at a density
of 2.5 × 10<sup>4</sup>
cells/well in DF-12 medium and were incubated
overnight. The plasmid encoding the influenza replication complex
component (NP, PB1, PB2, and PA) and that encoding the luciferase
reporter (polI-NS-Luc and pRL<sub>SV40</sub>
) were transfected into
the cells using Lipofectamine 3000 (Invitrogen, USA). At 6 h post-transfection,
serially diluted oseltamivir or favipiravir or IIQ was added at the
indicated concentration. After 30 h, the luciferase activities were
measured using a SpectraMax M5 microplate reader (Molecular Devices,
USA) and a Dual-Glo luciferase assay kit (Promega, USA), according
to the standard protocol. The replicon activities were represented
by the ratio of firefly luciferase activity relative to <italic>Renilla luciferase</italic>
activity. The replicon activity
inhibition of the tested compounds was calculated using the following
formula: Inhibition of replicon activity (%) = (experimental sample
ratio – negative control ratio)/(positive control ratio –
negative control ratio) × 100%. Curve fitting was performed by
Origin 8.0 software.</p>
</sec>
<sec id="sec5.7"><title>Neuraminidase Inhibition Assay</title>
<p>The
NA-Star Influenza
Neuraminidase Inhibitor Resistance Detection Kit (Applied Biosystems,
USA) was used to measure the inhibition of neuraminidase activity
according to the manufacturer’s instructions. Neuraminidase
from influenza A/Hong Kong/8/68 (H3N2) and neuraminidase from influenza
A/Puerto Rico/8/1934 (H1N1) virus were used for this assay. The chemiluminescent
signal intensity of the assay plate was measured immediately after
accelerator injection, and the read time was set to 1 s. The inhibitory
activity of oseltamivir or favipiravir or IIQ was calculated using
the following formula: inhibitory activity (%) = (fluorescence of
virus control – fluorescence of sample)/(fluorescence of virus
control – fluorescence of substrate control) × 100%. Curve
fitting and IC<sub>50</sub>
calculation were accomplished by Origin
8.0 software.</p>
</sec>
<sec id="sec5.8"><title>Time of Addition Experiment and Real-Time
Reverse Transcription–Polymerase
Chain Reaction (RT-qPCR)</title>
<p>MDCK cells were seeded in a 12-well
plate at a density of 2.0 × 10<sup>5</sup>
cells/well and incubated
overnight. The cells were washed three times with phosphate-buffered
saline (PBS) prior to virus (MOI of 0.05 PFU/mL) adsorption at 4 °C
for 60 min. After adsorption, the cells were washed with PBS, treated
with favipiravir or IIQ at different time intervals (0–10 h,
0–2 h, 2–5 h, 5–8 h, 8–10 h postinfection,
respectively), harvested, and then applied to qPCR for viral load
analysis. Cells were continuously cultured in fresh medium after removal
of test compounds at 37 °C until 10 h postinfection, and then
viral load was analyzed. Total RNA of the cell samples was extracted
using an RNeasy Mini Kit (QIAGEN). Absolute RT-qPCR was performed
using the ABI Step One Plus platform by using a One-Step PrimeScript
RT-PCR Kit (Takara). All samples were run in triplicate. The details
of the primers, probe sequences, and reaction system can be found
in the <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Supporting Information</ext-link>
. The mRNA
expression profiles at different time intervals of IIQ or favipiravir
or PBS treatment were analyzed, and the mRNA expression profiles under
IIQ or favipiravir treatment were presented relative to the PBS control.
Statistical significance of the data was determined by MANOVA method
using SPSS 20.0 software.</p>
</sec>
<sec id="sec5.9"><title>Circular Dichroism (CD) Spectroscopy</title>
<p>CD spectra were
acquired on a MOS-450 system (BioLogic, Claix, France) with the following
parameters: bandwidth, 4.0 nm; resolution, 0.1 nm; path length, 0.1
cm; response time, 4.0 s; and scanning speed, 50 nm/min. HR1P was
incubated with IIQ at 25 °C for 30 min in 10 mM phosphate buffer
(pH 7.4). N66 was incubated with IIQ at 30 °C for 30 min in 10
mM sodium acetate buffer (containing 10 mM sodium phosphate and 150
mM sodium chloride, pH 5.0). All samples were prepared with the buffer
solution at a final concentration of 10 μM and cooled to 25
°C for measurement. The CD data were presented as the mean residue
ellipticity. The α-helical content for these peptides was calculated
by assuming that 100% helicity corresponds to −33000 degrees
cm<sup>2</sup>
dmol<sup>–1</sup>
. For the thermal unfolding
experiments, the CD absorbance was monitored at 222 nm with the temperature
for the peptide solutions ranging from 10 to 90 °C at a scan
speed of 2 °C/min. Samples at pH 5.0 contained 10 μM peptide
in 10 mM sodium acetate buffer (containing 10 mM sodium phosphate
and 150 mM sodium chloride). Samples at pH 7.4 contained 10 μM
peptide in 10 mM phosphate buffer.</p>
</sec>
<sec id="sec5.10"><title>Native Polyacrylamide Gel
Electrophoresis</title>
<p>An equimolar
mixture of IIQ and HR1P in 10 mM phosphate buffer (pH 7.4) was incubated
at 25 °C for 30 min (final concentration of each peptide: 150
μM). After the addition of 2× β-alanine–formic
acid native sample buffer to samples at a ratio of 1:1, all samples
were loaded on a 15% β-alanine–formic acid gel with a
β-alanine–formic acid running buffer (pH 3.4). After
sample loading, the samples were concentrated at a constant voltage
of 90 V. When the samples reached the boundary of the two gels, the
voltage was raised to 150 V, and the samples were electrophoresed
for 2.5 h until the indicator was within 1–2 cm of the leading
edge. The gel was subsequently stained with Coomassie Blue R250. An
equimolar mixture of IIQ and N66 in 10 mM sodium acetate buffer (containing
10 mM sodium phosphate and 150 mM sodium chloride, pH 5.0) was incubated
at 30 °C for 30 min (final concentration of each peptide: 150
μM). After incubation, the solutions were equilibrated at room
temperature, and the pH was neutralized by the addition of 200 mM
Tris buffer (pH 8.5). After the addition of 2× Tris-glycine native
sample buffer (Invitrogen, USA) to the samples at a ratio of 1:1,
all samples were loaded onto a 15% Tris-glycine gel with Tris−glycine
running buffer (pH 8.8). After sample loading, the samples were concentrated
at a constant voltage of 90 V. When the samples reached the boundary
of the two gels, the voltage was raised to 150 V and the samples were
electrophoresed for 2.5 h until the indicator was within 1–2
cm of the leading edge. The gel was subsequently stained with Coomassie
Blue R250.</p>
</sec>
<sec id="sec5.11"><title>Sedimentation Velocity Analysis (SVA)</title>
<p>A Beckman XL-A-type
ultracentrifuge was used for the SVA experiments. HR1P was incubated
with IIQ at 25 °C for 30 min in 10 mM phosphate buffer (pH 7.4).
N66 was incubated with IIQ at 30 °C for 30 min in 10 mM sodium
acetate buffer (containing 10 mM phosphate and 150 mM sodium chloride,
pH 5.0). All samples were prepared at a final concentration of 150
μM, which was measured by a UV absorption experiment. Data were
collected at 280 nm at a rotor speed of 3000 rpm initially and then
60000 rpm in continuous mode at 25 °C. The sedimentation coefficient
distribution, <italic>c</italic>
(s), was measured, and the molecular
weight distribution was calculated by SEDFIT software.</p>
</sec>
<sec id="sec5.12"><title>Isothermal
Titration Calorimetry (ITC)</title>
<p>ITC was performed
to detect the IIQ and lipid-binding activity, as described previously.<sup><xref ref-type="bibr" rid="ref51">51</xref>
</sup>
The solutions were degassed under vacuum prior
to use. To detect the IIQ and lipid-binding activity, large unilamellar
vesicles (LUVs) of 1-palmitoyl-2-oleoyl-<italic>sn</italic>
-glycero-3-phosphocholine
(POPC) liposomes were used. LUVs of POPC (13 mM) were injected into
the cell containing peptide solution (15 μM, 300 μL).
The experiments used a MicroCal ITC200 system (GE, Alpharetta, GA
USA) for titration, with the following experimental parameters: total
injection, 20 drops; drop volume, 2 μL; syringe concentration,
13 mM; cell concentration, 15 μM; cell temperature, 25 °C;
energy reference, 3 μCal/s; titration delay, 60 s; stirring
speed, 750 rpm; drop volume, 2 μL; titration time, 4 s; two-drop
interval, 120 s; data collection interval, 5 s. Data acquisition and
analyses were performed using Origin software (Version 8.5, MicroCal).</p>
</sec>
<sec id="sec5.13"><title>Immunofluorescence Assay</title>
<p>MDCK cells were pretreated
with LysoTracker Red DND-99 (L7528), which was purchased from Thermo
Fisher Scientific (Shanghai, China). LysoTracker solution (1 μL,
1 mM) was added to 10 mL of growth medium to obtain a working solution
of 100 nM. Cells in a 96-well plate were incubated with 50 μL
of 100 nM LysoTracker working solution for 1.5 h, and then they were
washed twice with PBS. DF-12 medium without phenol red containing
5 μM IIQ<sub>NBD</sub>
was added to the cells (time point of
0 h), and then the cells were cultured at 37 °C under 5% CO<sub>2</sub>
. At time points of 10 min, 30 min, 1 h, 2 h, and 4 h, the
cells were scanned with the Operetta confocal imaging system (provided
by PerkinElmer) with a 20× objective lens. The following filters
were used: Alexa Fluor 548 for acidic intracellular compartments and
FITC for IIQ<sub>NBD</sub>
.</p>
</sec>
<sec id="sec5.14"><title>Pharmacokinetic Assessments</title>
<p>Sprague–Dawley
rats
weighing 210 ± 10 g each were obtained from the Animal Center
of Beijing Institute of Pharmacology and Toxicology and were used
for pharmacokinetic assessments. Animals were treated in accordance
with the Animal Welfare Act and the “Guide for the Care and
Use of Laboratory Animals” (NIH Publication 86-23, revised
1985). Complete pharmacokinetic experimental procedures are provided
in the <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">Supporting Information</ext-link>
.</p>
</sec>
</sec>
</body>
<back><notes id="notes1" notes-type="si"><title>Supporting Information Available</title>
<p>The Supporting
Information is
available free of charge on the <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org">ACS Publications website</ext-link>
at DOI: <ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/abs/10.1021/acs.jmedchem.8b00890">10.1021/acs.jmedchem.8b00890</ext-link>
.<list id="silist" list-type="simple"><list-item><p>Inhibitory activity
of compounds on oseltamivir-resistant
strains; biophysical properties of the IIQ peptide; summary of the
SVA results of IIQ/HR1P and IIQ/N66 complexes; biological and biophysical
properties of IIQ<sub>NBD</sub>
; HPLC method used for the purification
of peptide compounds; HPLC method used for the analysis of peptide
compounds; IIQ peptide as inhibitor of MERS-CoV infection; correlation
between α-helical contents of lipopeptides with their observed
EC<sub>50</sub>
s; identification of HA2 subunit as the potential target
of IIQ compound; interaction between C34 and N36; the molecular mass
of IIQ/HR1P and IIQ/N66 as determined by SVA; pharmacokinetic assessments;
aqueous solubility determination; HIV-1 Env-mediated cell–cell
fusion assay; inhibition of pseudotyped Ebola virus infection; hemagglutination
inhibition assay; hemolysis inhibition assay; as well as MALDI-TOF-MS
and analytical HPLC of designed peptides (<ext-link ext-link-type="uri" xlink:href="http://pubs.acs.org/doi/suppl/10.1021/acs.jmedchem.8b00890/suppl_file/jm8b00890_si_001.pdf">PDF</ext-link>
)</p>
</list-item>
</list>
</p>
</notes>
<sec sec-type="supplementary-material"><title>Supplementary Material</title>
<supplementary-material content-type="local-data" id="sifile1"><media xlink:href="jm8b00890_si_001.pdf"><caption><p>jm8b00890_si_001.pdf</p>
</caption>
</media>
</supplementary-material>
</sec>
<notes notes-type="" id="notes3"><title>Author Contributions</title>
<p><sup>¶</sup>
C.W., L.Z.,
S.X., and T.Z. contributed equally to this work. Dr.
Chao Wang, Prof. Keliang Liu, Prof. Shibo Jiang, and Prof. Wu Zhong
conceived and designed the study. Guodong Liang, Guangpeng Meng, and
Yue Li performed synthesis. Dr. Lei Zhao, Dr. Shuai Xia, and Dr. Ruiyuan
Cao performed biological evaluation. Dr. Weiguo Shi and Guodong Liang
performed biophysical analysis. Dr. Tianhong Zhang and Weicong Wang
performed pharmacokinetics study. Dr. Chao Wang, Prof. Keliang Liu,
Prof. Shibo Jiang, and Prof. Wu Zhong analyzed the data and wrote
the manuscript.</p>
</notes>
<notes notes-type="COI-statement" id="NOTES-d7e1480-autogenerated"><p>The authors declare no
competing financial interest.</p>
</notes>
<ack><title>Acknowledgments</title>
<p>This research
was supported, in part, by grants
from the National Science Foundation of China (81573266 and 81630090),
Beijing Nova Program (Z181100006218115), National Science and Technology
Major Project of China (2018ZX09711003), and the National Key Research
and Development Program of China (2016YFC1201000 and 2016YFC1200400).</p>
</ack>
<glossary id="dl1"><def-list><title>Abbreviations Used</title>
<def-item><term>CHR</term>
<def><p>C-terminal heptad repeat</p>
</def>
</def-item>
<def-item><term>NHR</term>
<def><p>N-terminal heptad repeat</p>
</def>
</def-item>
<def-item><term>6HB</term>
<def><p>six-helix bundle</p>
</def>
</def-item>
<def-item><term>Da</term>
<def><p>Dalton</p>
</def>
</def-item>
<def-item><term>SVA</term>
<def><p>sedimentation velocity
analysis.</p>
</def>
</def-item>
</def-list>
</glossary>
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, <volume>5</volume>
, <fpage>e41</fpage>
<pub-id pub-id-type="doi">10.1038/emi.2016.64</pub-id>
.</mixed-citation>
</ref>
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