Effects of polyphenol compounds on influenza A virus replication and definition of their mechanism of action

Article abstract of DOI:10.1016/j.bmc.2012.05.062

A set of polyphenol compounds was synthesized and assayed for their ability in inhibiting influenza A virus replication. A sub-set of them showed low toxicity. The best compounds within this sub-set were 4 and 6g, which inhibited the viral replication in a dose-dependent manner. The antiviral activity of these molecules was demonstrated to be caused by their interference with intracellular pathways exploited for viral replication: (1) MAP kinases controlling nuclear-cytoplasmic traffic of viral ribonucleoprotein complex; (2) redox-sensitive pathways, involved in maturation of viral hemagglutinin protein.

Full text of DOI:10.1016/j.bmc.2012.05.062

Bioorganic & Medicinal Chemistry 20 (2012) 5046–5052
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Effects of polyphenol compounds on influenza A virus replication
and definition of their mechanism of action
Rossella Fioravanti a,1, Ignacio Celestino b,1, Roberta Costi a, , Giuliana Cuzzucoli Crucitti a, Luca Pescatori a,
⇑
Leonardo Mattiello c, Ettore Novellino d, Paola Checconi b, Anna Teresa Palamara b,e, Lucia Nencioni b,1
Roberto Di Santo a,1
,
a Istituto Pasteur Cenci Bolognetti - Dip. Chimica e Tecnologie del Farmaco, ‘‘Sapienza’’ University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy
b Istituto Pasteur Cenci Bolognetti - Dip. Sanità Pubblica e Malattie Infettive, ‘‘Sapienza’’ University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy
c Dipartimento di Dip. di Scienze di Base e Applicate per l’Ingegneria, ‘‘Sapienza’’ University of Rome, Via del Castro Laurenziano 7, 00161 Rome, Italy
d Dipartimento di Chimica Farmaceutica e Tossicologica, Università di Napoli ‘‘Federico II’’, Via D. Montesano 49, 80131 Napoli, Italy
e San Raffaele Pisana Istituto Scientifico di Ricerca e Cura, Via della Pisana 235, 00166 Rome, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
A set of polyphenol compounds was synthesized and assayed for their ability in inhibiting influenza A
virus replication. A sub-set of them showed low toxicity. The best compounds within this sub-set were
4 and 6g, which inhibited the viral replication in a dose-dependent manner. The antiviral activity of these
molecules was demonstrated to be caused by their interference with intracellular pathways exploited for
viral replication: (1) MAP kinases controlling nuclear-cytoplasmic traffic of viral ribonucleoprotein com-
plex; (2) redox-sensitive pathways, involved in maturation of viral hemagglutinin protein.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 21 March 2012
Revised 16 May 2012
Accepted 25 May 2012
Available online 4 June 2012
Keywords:
Influenza
Antivirals
Polyphenols
Resveratrol
Curcumin
1. Introduction
These agents block the ion-channel activity of the viral matrix (M2)
protein, which is mainly required for virus uncoating.6 Currently,
Each year influenza A viruses (IAV) cause thousands of deaths
and hospitalizations. The pandemic caused by the 2009 influenza
A (H1N1) virus—the first of the 21st century—was characterized
mainly by mild-moderate infections similar to those seen with
seasonal influenza,1 but several cases of acute respiratory distress
syndrome and pneumonia in previously healthy persons were also
reported.2 Influenza A viruses are enveloped, negative strand RNA
viruses belonging to the Orthomyxoviridae family. Their genome
consists of eight single-stranded RNA segments encoding 11 pro-
teins including hemagglutinin (HA), one of the main surface glyco-
proteins.3 The receptor binding site of HA is necessary for the virus
to bind galactose-bound sialic acid on the surface of host-cells, and
16 different subtypes have been isolated thus far from different
hosts.4 Influenza virus replication has been studied in depth, and
several antiviral agents all targeting viral structures, have been
developed.5 Among them, amantadine and rimantadine have a spe-
cific inhibitory effect on type A but not on type B influenza viruses.6
the viral neuraminidase (NA) inhibitors such as oseltamivir, zanam-
ivir, and peramivir are the mainstay of pharmacological protocols to
fight global influenza pandemics.7 However, the long-term efficacy
of these inhibitors is often limited by their toxicity and by the high
incidence in the selection of drug-resistant viral mutants that is al-
most certain.8–10 Actually, the main effort of the preclinical research
is addressed to block the viral replication by interfering with path-
ogen-exploited host-cell machinery.11 This approach could give
important advantages, including the broad-spectrum efficacy, the
antigenic properties, and the reduced probability to select drug-
resistant viral strains.11 In particular, a very promising and innova-
tive strategy to develop new antiviral agents could be based on the
inhibition of intracellular pathways that are specifically activated
by influenza virus to ensure its replication.12,13 Interestingly, many
of these pathways are highly sensitive to changes in the intracellu-
lar redox state,14,15 and as a matter of fact their activation is induced
by the oxidative stress caused by infections by DNA or RNA virus,
including influenza.11,15
Dietary polyphenols, such as resveratrol (RV) [5-[(1E)-2-(4-
hydroxyphenyl)ethenyl]-1,3-benzenediol (found in red wine) and
curcumin [diferuloyl methane; 1,7-bis-(4-hydroxy-3-methoxy-
⇑
Corresponding author. Tel.:+39 6 49693247.
E-mail address: roberta.costi@uniroma1.it (R. Costi).
Authors to indicate that they contributed equally to the work.
1
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.05.062

R. Fioravanti et al. / Bioorg. Med. Chem. 20 (2012) 5046–5052
5047
phenyl)-1,6-heptadiene-3,5-dione] (found in curry powder), were
2. Chemistry
reported to posses anticancer,16,17 anti-inflammatory,18,19 and
antiviral properties.20–22
All derivatives tested except 6b, were prepared as reported in
literature.45a–f Method of synthesis of compound 6b, chemical
and physical data are reported in Supplementary data.
Curcumin is a colouring compound present in the rhizome of Cur-
cuma longa L. It has been used for thousands of years in Southeast
Asia and Indian folk medicine to treat various diseases and eradicate
health problems.23 It shows many pharmacological properties
including anti-inflammatory,24 antioxidant, iron-chelating, and
some other activities.25 For example, the antioxidant activity of cur-
cumin is responsible for its ability to decrease the incidence of colon
cancer, and for its anti-atherogenic property.26 It has cytoprotective
effect on PC12 cells against 1-methyl-4-phenylpridinium ions-in-
duced neurotoxicity through the anti-apoptotic and anti-oxidative
properties of the Bcl-2-mitochondria-ROS-iNOS pathway.27 Re-
cently, curcumin has been proven to exert anti-influenza activity
by inhibition of the virus-cell attachment. These studies demon-
strated that treatment of cells with curcumin greatly reduced the
yield of IAV at sub-cytotoxic doses. Pre-incubation of virus with cur-
cumin pronouncedly inhibited influenza virus plaque formation.28
Unfortunately, curcumin is water insoluble, poorly dissolves in
organic phase, and shows low bioavailability in vivo after oral
administration.29,30 It is unstable at neutral-basic pH values and
in serum-free medium degrading to vanillin, ferulic acid, feruloyl
methane and trans-6-(40-hydroxy-30-methoxy-phenyl)-2,4-di-
oxo-5-hexenal.31
3. Result
In a first set of experiments the cytotoxicity of the compounds
has been evaluated in a test on confluent monolayers of MDCK cells.
Cells were plated at concentration of 2 ꢀ 105/ml, treated after 24 h
with various concentrations (range 5–40 lg/ml) of the synthesized
compounds ( 1, 2, 3, 4, 5, 6a–m), and incubated for the following
24 h. Microscopical examination, Trypan blue exclusion and cells
counts demonstrated that the compounds 1, 2, 3, 5, 6a, 6b, 6d,
6e, 6h, 6i, 6l and 6m, produced a dose-dependent toxic effect.
Indeed, morphological alterations, loss of cells viability and modifi-
cation of cell multiplication rate in treated cells were observed
(data not shown). These substances have been excluded for the fol-
lowing experiments. On the contrary, the treatment with the other
compounds did not induce any toxicity on cell monolayer, even if
the compound 6g caused a slight alteration of cell morphology
starting from 20
l
g/ml and the compounds 4, 6c, and 6f starting
from 40
lg/ml. These results were further confirmed using the
RV is a very interesting polyphenol belonging to the stilbene
family. It is found in several fruits, vegetables and beverages
including red wine. It is one of the most important plant polyphe-
nols with proven salutary activity on animal health. The most
important source of polyphenols and in particular RV for human
diet is grape (Vitis vinifera).32
O
OH
H3CO
HO
OCH3
OH
Curcumin
In the last two decades the potential protective effects of RV
against cardiovascular33 and neurodegenerative diseases,34 as well
as the chemo-preventive properties against cancer,35 have been
largely investigated. RV appears to be capable of interfering with
several intracellular signaling pathways, including those activated
by protein kinase C (PKC) and by mitogen-activated protein kinases
(MAPKs).36
RV has been also reported to exert an antiviral activity in differ-
ent experimental systems.37–39 A few years ago, we showed that
RV inhibits influenza virus replication in vitro and it is also effec-
tive in increasing the survival of influenza virus-infected mice.22
Surprisingly, these effects are not related to its well-known antiox-
idant activity. They are rather related to the inhibition of intracel-
lular pathways JNK (c-Jun N-terminal kinase) and p38MAPK
involved in regulation of viral ribonucleoprotein (vRNP) complex
traffic across the nuclear membrane, a key step of viral replication
cycle that precedes viral assembly and release.12
O
O
HO
HO
OH
OH
HO
HO
OH
OH
X
1
2-5
Comp.
X
2
3
4
5
CH2
CH2-COOCH2CH3
O
N-(CH2)2-CH3
OH
R3
R
R4
R2
R1
R5
R6
HO
O
OH
Resveratrol
6a-m
The biological activity of RV is limited by its low bioavailability
and metabolic instability. In fact, stilbene double bond is readily
oxidized by cytochrome P450 monooxygenases into highly reac-
tive epoxides, that may act as carcinogenic metabolites.40,41 Fur-
ther, under UV irradiation, RV converts to the (Z)-isomer42,43 and
this was claimed as one of the reason for the presence of small
amounts of (Z)-resveratrol in wines. The conversion from (E)- to
(Z)-configuration makes resveratrol less stable44 and consequently
decreases its biological activity.
Therefore, pursuing our studies on compounds active against
influenza and taking advantage of our experience in the synthesis
of polyhydroxylated analogues,45 we decided to synthesize a num-
ber of curcumin and resveratrol analogues with the aim of obtain-
ing compounds with improved ability in interfering with the cell
pathways exploited by the virus for its replication, such as kinase
pathways and intracellular redox state. These compounds were
evaluated for their antiviral activity and their structures are
reported in Figure 1.
Comp.
6a
R
H
H
H
H
R1
H
R2
H
R3
R4
R5
OH
H
OH
OH
OH
Cl
R6
H
H
OH
OH
H
OH
H
6b
H
OH
6c
6d
6e
6f
6g
6h
6i
OH
H
NH2
H
H
H
H
H
H
H
OH
H
OH
H
OH
OH
H
H
H
H
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OH
OH
OH
OH
OH
OH
H
OH
OH
OH
OH
OCH3
OH
OCH3
CH3
OH
F
6l
6m
Figure 1. Structures of curcumin and resveratrol analogues.

5048
R. Fioravanti et al. / Bioorg. Med. Chem. 20 (2012) 5046–5052
3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazoliumbromide (MTT)
proliferation assay (data not shown).
viral challenge (data not shown). Then, 4 and 6g were added to
MDCK cells immediately after virus challenge and afterwards re-
moved at different time points (Fig. 2B). Post-infection treatment
with both compounds for 2 or 4 h produced no significant antiviral
effect, which confirmed that they did not act by preventing virus
entry into the cells. In MDCK exposed to 4 or 6g for the first 6 h
after infection, slight decreases (about 30%) in viral replication
were noted 24 h p.i. More substantial inhibition was observed
when exposure was extended to the first 8 h (55%) or 24 h (75%)
p.i. In other experiments, the treatment was started at different
times after PR8 infection, and the compounds remained in the cell
culture medium through 24 h after infection (Fig. 2C).
The highest inhibition (about 79%) of viral replication was
achieved when treatment began 2 and 4 h after viral challenge.
When treatment was delayed until 6 h after infection, effects were
more limited but still observable and finally, when two compounds
were added 8 h p.i., no significant inhibition was noted. These data
indicate that the antiviral activity of the compounds is largely re-
lated to their inhibition of virus life-cycle steps occurring 2-8 h
p.i., and possibly related to post-transcriptional events.
3.1. Compounds 4 and 6g inhibit late phases of influenza virus
life-cycle
First, to assess whether the compounds that did not cause toxic
effect on cells, could exert an antiviral effect on influenza virus rep-
lication, confluent monolayers of MDCK cells highly permissive to
influenza virus replication, were infected with influenza A/Puerto
Rico/8/34 H1N1 (PR8) virus at low multiplicity of infection (0.01
M.O.I.) to allow multi-cycle replication. One hr after adsorption
the cells were washed and different concentrations of compounds
or DMSO (control infected CI cells) were added to MDCK and main-
tained for the duration of the experiment. As shown in Figure 2A,
24 h post infection (p.i.) virus titer, measured as the amount of virus
released into the cell supernatant by means of hemagglutinating
unit (HAU) assay, was dose-dependently (range 5–20
inhibited by compounds 4 and 6g. In particular, viral replication
was markedly reduced by 10 g/ml of 6g (75% vs CI cells) and
by 20 g/ml of 4 (75% vs CI cells) while the concentration of
20 g/ml of 6g was able to completely inhibit viral replication.
lg/ml)
l
l
l
3.2. Compound 4 inhibits expression of late viral proteins
However, since it induced some alteration of the monolayer, we
chose to not use it for the following experiments. The compounds
6c and 6f were able to inhibit influenza virus in a dose-dependent
manner (data not shown), however the molecular mechanisms
underlying their anti-influenza activity are still under investigation.
Next, to identify the step(s) of the influenza virus life-cycle that
were affected by compounds 4 and 6g, we first evaluated the effect
of these compounds on the PR8 virus alone. No significant antiviral
effect was detected when a stock solution of PR8 virus was incu-
bated for 1 h with 4 or 6g and then used for infection. Similarly,
virus production was not affected when compounds were present
in cell culture medium only during the 1 h phase of viral adsorp-
tion or when MDCK cells underwent a overnight pre-infection
treatment with two compounds, with drugs washout right before
Nucleoprotein (NP) is the most abundant influenza A viral pro-
tein that is synthesized immediately after infection, whereas the
major external glycoprotein hemagglutinin (HA), neuraminidase
(NA) and matrix protein 1 (M1) are late gene products.3 In order
to determine whether the inhibition of viral replication was related
to the modulation of viral protein synthesis, the cells were infected
with PR8, and compounds 6g (10 lg/ml) or 4 (20 lg/ml) were
immediately added after PR8 adsorption. Twenty-four hours after
infection, protein from cell lysates were separated by sodium
dodecyl sulfate-polyacrylammide gel electrophoresis in reducing
conditions and immunoblotted with anti-influenza Abs. As shown
in Figure 3 (left panel), while the treatment with 6g did not cause
any effect on the expression on viral proteins, except for NA
Figure 2. Compounds 4 and 6g inhibit specific steps of influenza virus life-cycle. (A) Different concentrations of each compound were added to PR8-infected (M.O.I = 0.01)
MDCK cells. Viral yields 24 h p.i. are expressed as percentages of those recorded for control infected (CI) cells treated with 0.02% dimethyl sulfoxide (DMSO; the concentration
present in culture medium containing the highest dose of compounds). Values shown are means of four experiments, each run in duplicate. ⁄P <0.01; ⁄⁄P <0.001; ⁄⁄⁄P <0.0001
vs CI. Viral yields 24 h p.i. for CI cells and cells infected/treated as follows: (B) 4 and 6g (20 and 10 lg/ml, respectively) were added to cell cultures immediately after PR8
challenge and removed at different time points (2, 4, 6, 8 or 24 h) after infection; (C) 4 and 6g were added 2, 4, 6, or 8 h p.i., and maintained in the culture medium for 24 h
after infection. Values shown are means of two experiments, each run in duplicate. ⁄P <0.01 vs CI.

R. Fioravanti et al. / Bioorg. Med. Chem. 20 (2012) 5046–5052
5049
Figure 3. Compound 4 inhibits expression of late viral proteins. (Left panel) expression of viral proteins in influenza A/PR8/34 H1N1 infected cells untreated or treated with
6g or 4, respectively. After 24 h, cells were lysed and cell homogenates were separated in reducing conditions by 12% gel, transferred to nitrocellulose membrane and
immunostained with goat polyclonal anti-influenza Abs. PR8 virus protein molecular weights are indicated to the right of the figure. HA, hemagglutinin; NP, nucleoprotein;
NA, neuraminidase; M1, matrix protein 1. Results are shown for one representative experiment of three performed. (Right panel) densitometric analysis of viral proteins
expression shown in (left panel). Results are expressed as ratio of each viral protein to actin.
protein (by 42% vs untreated cells), a significant inhibition of some
viral proteins was observable after treatment with 4.
Therefore to determine the underlying mechanism for the
inhibitory effect of 4 and 6g on nuclear translocation of vRNP com-
plexes, the possible involvement of the PKC pathway in the antivi-
ral activity of the compounds was investigated in human NCI-H292
infected cells. As shown in Figure 6, the phosphorylation of PKD,
the PKC downstream effector,47 was observed in infected cells
6 h p.i., and this event was markedly reduced by compounds 4
and 6g. Then, the phosphorylation of p38MAPK, JNK, and ERK path-
ways was analyzed. As shown in Figure 6, the compound 6g
strongly diminished p38MAPK and JNK phosphorylation, but had
no effect on that of ERK 1 and 2. Similar results were obtained in
cells treated with 4, although the inhibition of p38MAPK phos-
phorylation was less pronounced. These results indicate that the
strong inhibition of p38MAPK phosphorylation by 6g leads to vRNP
retaining in the nucleus of infected cells.
In particular, densitometric analysis (Fig. 3, right panel) re-
vealed decreased expression of HA (by 25% vs untreated), NA (by
56% vs untreated) and M1 (by 62% vs untreated), even if the
expression of NP protein was slight inhibited. These results suggest
that the antiviral activity exerted by 4 could be due to an interfer-
ence with viral protein synthesis, while the effect of 6g to the inhi-
bition of other steps of virus life-cycle.
3.3. Compounds 6g and 4 retain viral NP in the nucleus of
infected cells
During influenza virus replication, viral RNAs are packaged into
helical ribonucleoprotein (RNP) complexes with polymerase and
NP in the host-cell nucleus and are subsequently exported into
the cytosol to be assembled with the other structural proteins.3
Our previous studies demonstrated that RV blocks the nuclear-
cytoplasmic translocation of RNP complexes.22 To determine
whether the same mechanism was involved in 4 and 6g inhibition
of influenza virus replication, immunofluorescence analysis of
vRNP trafficking was performed. MDCK cells were infected with
PR8 at a high M.O.I. to allow single-cycle replication. Eight hours
after infection, cells were fixed, permeabilized and stained with
40,60-diamidino-2-phenylindole hydrochloride (DAPI), and then
incubated in turn with primary anti-NP antibody and with fluores-
cein isothiocyanate-conjugated secondary antibody. As shown in
Figure 4 in the untreated cells, NP was located predominantly in
the cytosol, and addition of compounds 4 and 6g led to the inhibi-
tion of viral RNP export from nucleus to cytoplasm. In particular,
the treatment with 6g caused a strong inhibition of nuclear-cyto-
plasmic traffic of NP, suggesting that this compound could inter-
fere with some pathways that regulate this important step of
influenza virus replication. These results were confirmed by wes-
tern blot analysis of NP localization in the nuclear and cytoplasmic
extracts after 8 h p.i. As shown in Figure 5 the treatment with the
compounds, especially with 6g, caused an inhibition of NP levels in
the cytosol, while the protein was mainly expressed in the nucleus
of the cells. Several kinase cascades, such as PKC and MAPKs are
activated during influenza virus infection.11 Pleschka et al.46 dem-
onstrated that ERK (extracellular signal-regulated kinase) phos-
phorylation promotes vRNP traffic and virus production. Our
previous studies demonstrated the role of p38MAPK activity in nu-
clear export of RNP complexes of influenza virus. In particular, the
inhibition of this kinase decreased vRNP traffic, phosphorylation of
viral NP (a key event for the export in the cytoplasm), and viral
titers in cells supernatants.12 Moreover, it is known that RV inter-
feres with several intracellular pathways including those activated
by PKC and MAPKs.36
3.4. Compound 4 restores the intracellular redox balance during
viral infection and affects viral HA localization
Influenza virus infection is associated with redox changes char-
acteristic of oxidative stress, including depletion of GSH levels and
a general oxidative stress in both in vivo and in vitro experimental
models.15 Our recent studies have demonstrated a key role of GSH
levels in the regulation of viral HA maturation. Indeed, the addition
of a GSH derivative was able to restore the reduced environment in
infected cells and, as a consequence, to interfere with intracellular
redox-regulated pathways responsible for the folding of viral pro-
teins. The final effect on viral replication was an impairment of vir-
al propagation by impeding HA plasma-membrane insertion.13
Therefore we evaluated the potential antioxidant activity of these
compounds. Twenty-four hours after infection, as expected influ-
enza virus-induced a significant depletion of intracellular GSH con-
tent (Fig. 7A). On the contrary, in infected cells treated with 4, GSH
levels did not diminish during viral infection, and GSH content was
similar to that measured in control (mock-infected) cells. The
treatment with 6g was also able to restore the intracellular GSH
content, even if in less extent. A confirmation of this difference
was obtained by measuring the redox potentials of 4 and 6g. Com-
pound 4 showed Epa1 = 0.75 V compared to Epa1 = 1,35 V found
for 6g. It is evident the higher reducing property of 4 compared
to that of 6g.
Next, we evaluated whether these compounds could interfere
with HA maturation, especially with HA localization on the plas-
ma-membrane. Immunofluorescence studies of HA localization
were performed 8 h after PR8 infection with high M.O.I. Cells were
fixed and stained with anti-HA antibody and with secondary anti-
body conjugated with phycoerythrin. As shown in Figure 7B, viral
protein HA was highly expressed, diffused into the cells and local-
ized predominantly on the plasma-membrane of infected cells.

5050
R. Fioravanti et al. / Bioorg. Med. Chem. 20 (2012) 5046–5052
Figure 4. Compounds 6g and 4 block the nuclear-cytoplasmic vRNP traffic. MDCK cells were infected with 1 M.O.I. to allow single-cycle replication. Cells were fixed,
permeabilized and stained with monoclonal anti-NP Ab and analyzed by fluorescence microscopy. Nuclei were stained with DAPI. Merged images are shown in the third
column.
Figure 5. Compounds 6g and 4 retain the NP in the nucleus of infected cells.
Cytosolic and nuclear extracts from 4 or 6g treated and untreated cells were
subjected to SDS-PAGE and immunoblotted with anti-NP Abs. The same nitrocel-
lulose filters were then stripped and restained with anti-a-tubulin or anti-lamin A/
C. Above each blot, densitometric analysis expressed as the ratio of viral NP/tubulin
or lamin is reported. Results are shown for one representative experiment of three
performed.
On the contrary, the treatment with the compounds, especially
with 4, inhibited HA expression, and viral protein localization on
the plasma-membrane was impaired. In particular, in these latter
cells HA was localized on the peri-nuclear zone (see white arrows,
Fig. 7B). These results suggest that 4 could exert its antiviral activ-
ity through regulation of some redox-sensitive pathways involved
in HA maturation. Further studies are in progress to better charac-
terize the molecular mechanism involved in this inhibition.
Figure 6. Compounds 4 and 6g interfere with PKC pathway. NCI-H292 cells were
mock- or PR8-infected (1 M.O.I.), treated with 4 or 6g and lysed 6 h p.i. Proteins
were separated by 10% SDS–PAGE and gels were blotted onto nitrocellulose
membranes and immunostained with rabbit anti-phospho-PKD, anti-phospho-ERK
1/2, anti-phospho-p38MAPK or anti-phospho-JNK Abs. The same nitrocellulose
filters were then stripped and restained with anti-PKD, anti-ERK1/2, anti-p38MAPK,
or anti-JNK Abs, respectively. Results are shown for one representative experiment
of three performed.
4. Discussion
In the present study we have demonstrated the antiviral activ-
ity of compounds 4 and 6g. These compounds inhibited the influ-
enza A virus replication in a dose-dependent manner without
inducing any cytotoxic effect. The antiviral activity of these mole-
cules is due to inhibition of two key steps of influenza virus life-
cycle: (1) nuclear-cytoplasmic traffic of vRNP; (2) maturation of
viral HA protein.
These fundamental steps are finely regulated by redox-sensitive
intracellular pathways that are activated during viral infection. In
particular, vRNP traffic is regulated by several intracellular kinases,
including PKC and MAPKs.11 In our previous paper we have dem-
onstrated that influenza virus-activated p38MAPK phosphorylated
viral NP, an event needed for vRNP nuclear export. Inhibition of
p38MAP led to retention of NP in the nucleus of infected cells.12
Here, we demonstrate that the two compounds were able to inhibit
p38MAPK and, as consequence, to impede the export of vRNP from
the nucleus to the cytoplasm, confirming the role of p38MAPK in
the regulation of this step of viral replication.
Viral infection is often associated with redox changes character-
istic of oxidative stress, and these alterations are mainly due to
virus-induced depletion of intracellular GSH levels.48 A decrease
in GSH content and general oxidative stress have been also demon-
strated during influenza virus infection in both in vivo and in vitro
experimental models.49–52 We have recently demonstrated a key
role of GSH levels in the regulation of viral HA maturation. Indeed
the addition of a GSH derivative impairs viral propagation by

R. Fioravanti et al. / Bioorg. Med. Chem. 20 (2012) 5046–5052
5051
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levels of GSH in influenza virus-infected cells.22 Here, the addition
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when HA redox-regulated maturation process is completed.13
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some redox-sensitive intracellular pathways involved in matura-
tion of viral HA. Further studies are in progress to evaluate the
molecular mechanisms underlying this process.
5. Conclusion
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Overall the data demonstrated that the compounds 4 and 6g
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Acknowledgments
This work was partially supported by the Italian Ministry of
Instruction, Universities, and Research (Progetto PON), and PRIN
n° 2008 CE75SA the Italian Ministry of Health, and Fondazione
Roma Grants.
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