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R A
Published June 26, 2017
DOI
10.20411/pai.v2i2.200
C C (CPC)
E P, R A A
I V in vitro in vivo
AUTHORS
Daniel L. Popkin1, Sarah Zilka2, Matthew Dimaano3, Hisashi Fujioka4, Cristina Rackley5, Robert
Salata6, Alexis Grith1, Pranab K. Mukherjee2, Mahmoud A. Ghannoum2, Frank Esper7
AFFILIATED INSTITUTIONS
1Department of Dermatology, University Hospitals Cleveland Medical Center and Case Western
Reserve University, Cleveland, Ohio
2Center for Medical Mycology, Department of Dermatology, University Hospitals Cleveland Med-
ical Center and Case Western Reserve University, Cleveland, Ohio
3Department of Medicine, e University of Chicago, Chicago, Illinois
4Electron Microscopy Core Facility, Case Western Reserve University School of Medicine
5Hathaway Brown Science Research and Engineering Program, Cleveland, Ohio
6Division of Infectious Diseases and HIV Medicine, University Hospitals Cleveland Medical Cen-
ter and Case Western Reserve University, Cleveland, Ohio
7Division of Pediatric Infectious Diseases, University Hospitals Cleveland Medical Center and
Case Western Reserve University, Cleveland, Ohio
Presented in part at IDWeek 2015San Diego, CA – October 7-11, 2015
CORRESPONDING AUTHOR
Frank Esper
Assistant Professor, Department of Pediatrics
Rainbow Babies and Children’s Hospital; Case Western Reserve University
Cleveland, OH
Phone: (216) 844-4939
Fax: (216) 844-8362
Frank.Esper@Uhhospitals.org
SUGGESTED CITATION
Popkin DL, Zilka S, Dimaano M, Fujioka H, Rackley C, Salata R, Grith A, Mukherjee PK,
Ghannoum MA, Esper F. Cetylpyridinium chloride (CPC) exhibits potent, rapid activity against
inuenza viruses in vitro and in vivo. Pathogens and Immunity. 2017;2(2):252-69. doi: 10.20411/
pai.v2i2.200
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ABSTRACT
Background: ere is a continued need for strategies to prevent inuenza. While cetylpyridinium
chloride (CPC), a broad-spectrum antimicrobial agent, has an extensive antimicrobial spectrum,
its ability to aect respiratory viruses has not been studied in detail.
Objectives: Here, we evaluate the ability of CPC to disrupt inuenza viruses in vitro and in vivo.
Methods: e virucidal activity of CPC was evaluated against susceptible and oseltamivir- re-
sistant strains of inuenza viruses. e eective virucidal concentration (EC) of CPC was deter-
mined using a hemagglutination assay and tissue culture infective dose assay. e eect of CPC
on viral envelope morphology and ultrastructure was evaluated using transmission electron mi-
croscopy (TEM). e ability of inuenza virus to develop resistance was evaluated aer multiple
passaging in sub-inhibitory concentrations of CPC. Finally, the ecacy of CPC in formulation to
prevent and treat inuenza infection was evaluated using the PR8 murine inuenza model.
Results: e virucidal eect of CPC occurred within 10 minutes, with mean EC50 and EC2log rang-
ing between 5 to 20 µg/mL, for most strains of inuenza tested regardless of type and resistance to
oseltamivir. Examinations using TEM showed that CPC disrupted the integrity of the viral enve-
lope and its morphology. Inuenza viruses demonstrated no resistance to CPC despite prolonged
exposure. Treated mice exhibited signicantly increased survival and maintained body weight
compared to untreated mice.
Conclusions: e antimicrobial agent CPC possesses virucidal activity against susceptible and
resistant strains of inuenza virus by targeting and disrupting the viral envelope. Substantial viru-
cidal activity is seen even at very low concentrations of CPC without development of resistance.
Moreover, CPC in formulation reduces inuenza-associated mortality and morbidity in vivo.
Keywords: Cetylpyridinium Chloride, CPC, Inuenza, Respiratory tract illness, respiratory virus,
quaternary ammonium compound
INTRODUCTION
Inuenza is responsible for substantial morbidity and mortality worldwide [1-5]. Globally, inu-
enza is estimated to adversely aect up to 5% to 10% of adults and 20% to 30% of children each
year [6]. Annual inuenza epidemics in the United States result in nearly 600,000 life-years lost,
3.1 million days of hospitalization, and 31.4 million outpatient visits [7]; in addition, the total
economic burden of inuenza exceeds $80 billion. Current prevention strategies for inuenza are
dependent on the use of anti-inuenza medications and vaccines.
Neuraminidase inhibitors (NAIs, eg oseltamivir) are approved in the United States to prevent and
treat inuenza [8, 9]. However, the use of antiviral medications for pre-exposure prophylaxis has
a very limited role and is generally not recommended for the majority of the population [10].
Also, NAIs confer only modest decreases in symptom duration for individuals presenting with
uncomplicated illness [11-13], and this treatment suers from the selection of resistant strains,
adverse eects, and high cost [14-16]. While the most eective way to prevent inuenza disease
and its severe outcomes is by vaccination, current coverage estimates are well below the Healthy
People 2020 goal of 70% [17, 18]. Additionally, vaccine/strain mismatch can result in low vaccine
ecacy [19-22]. Vaccines may also be contraindicated, unavailable, less eective in immuno-
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compromised individuals, and suer from perceived risks leading to “vaccine hesitancy” [23, 24].
erefore, the development of eective novel strategies to prevent and treat inuenza disease is a
signicant unmet need.
Cetylpyridinium chloride (CPC) has been used for decades against a variety of pathogens [25-
28], and it disrupts the microbial lipid bilayer through physicochemical interactions, a mecha-
nism that is unlikely to be aected by mutations in addition to being pathogen independent [29].
For this reason, CPC and other quaternary ammonium compounds are commonly employed
in the prevention of bacterial and fungal infections within healthcare settings. Yet there is little
evidence demonstrating their eectiveness against respiratory viruses. Here, we evaluated CPC
ecacy against the prototypical respiratory inuenza virus demonstrating: (1) direct virucidal
activity against inuenza, (2) rapid activity following exposure, (3) viral ultrastructure disruption,
(4) absence of inuenza resistance following prolonged exposure, and (5) prevention and treat-
ment of inuenza infection in a murine model.
MATERIALS AND METHODS
Viral Strains: Inuenza strains were obtained from national inuenza repositories: inuen-
za A/Victoria/3/1975 (H3N2), A/Virginia/1/2009 (H1N1), B/Lee/40, oseltamivir-resistant A/
California/08/2009 (H1N1)pdm09 and B/Memphis/20/1996 (corresponding ATCC num-
bers:VR-822,VR-1736, VR-1535,IRR# FR-202, IRR# FR-486), and a clinical strain of inuenza A
(H1N1pdm09) virus which was propagated from a patient sample hereaer referred to as ‘iso-
late 40’. Both oseltamivir-resistant strains contain the NA H275Y substitution. Inuenza A virus
(strain A/Puerto Rico/8/1934 H1N1) was obtained from ATCC and propagated in chicken eggs.
Cytotoxic Concentration (CC50) of CPC: Madin Darby canine kidneycells (MDCK, ATCC
number CCL-34) were cultured at 37°C and in 5% CO2 to 90% conuence in DMEM supple-
mented with penicillin/streptomycin, L-glutamine, and 10% fetal calf serum (Gibco, N.Y., USA).
Increasing concentrations of CPC (10µg/mL to 250µg/ml, Sigma-Aldrich, St. Louis, MO) diluted
in phosphate buered saline (PBS) were added to media and incubated at room temperature for
10 minutes. Following exposure, cells were washed 3 times in DMEM to remove residual CPC.
Complete media was then reapplied and cells were returned to 37°C, 5% CO2. Viability was quan-
titated by neutral red uptake at 48 hours as previously described [30]. Toxicity data were used to
determine the 50% cytotoxic concentration (CC50, Prism; v6.0 soware).
Inuenza Cell Culture: Growth of the inuenza virus was performed as previously described
[31]. Briey, MDCK were grown to 90% conuence followed by inoculation with inuenza virus
at a multiplicity of infection (MOI)of 0.1 for 1 hour. e inoculum was then removed and 500 µL
of optiMEM (Sigma-Aldrich, St Louis, MO)] was applied. Infected cells were grown at 32°C for 72
hours at 5% CO2. Tissue Culture Infective Dose 50% (TCID50) analysis was performed as detailed
elsewhere [32]. e TCID50 was dened as the amount of virus required to produce a cytopathic
eect in 50% of culture wells. e cytopathic eect was dened as focal rounding, degenerative
changes, and detachment of cell monolayers.
Hemagglutination Assay: Hemagglutination assays were performed as described previously [33].
Briey, 25 µL of viral sample was added to 25 µL of CPC diluted in PBS and subsequently incu-
bated at room temperature for 5 minutes. Serial 2-fold dilutions were mixed with 50 µL of 0.5%
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suspension of chicken RBCs (Lampire Biological Laboratories, Pipersville PA) and incubated at
room temperature for 30 minutes. Data were then presented as the percentage reduction in HA
titer. e RBCs were exposed to CPC only to ensure CPC did not have a direct lysing eect on
RBCs. Hemagglutination titers were determined as an end point dilution where no pellet was
observed. e concentration of chicken RBCs was standardized using a hemocytometer.
Transmission electron microscopy (TEM): Inuenza virus (B/Lee/40) was chosen as a prototyp-
ical inuenza virus and was treated with 50 µg/mL CPC for 5 minutes. A CPC concentration of 50
µg/mL was employed to ensure adequate visualization of CPC activity on TEM analysis while still
remaining below CC50 toxicity levels. Fiy microliters of sample were placed on glass slides and
formvar/carbon -coated TEM nickel grids (400 mesh) were placed over the samples face down for
1 minute. Inuenza virus treated with PBS only was used as a sham control. Next, the grid was
removed, blotted with lter paper and exposed to 2.0% uranyl acetate solution for an additional
1 minute. Excess uranyl acetate was removed, grids were air-dried, and examined under an FEI
Tecnai Spirit (T12) electron microscope (TEI, Hillsboro, Oregon). Images were captured using
a Gatan US4000 4kx4k CCD camera. e reviewer of TEM analysis was masked to treatment vs
control slides.
Inuenza Nucleoprotein (NP) ELISA: Samples were adsorbed overnight at 4°C in Costar 96-
well plates. Wells were washed with PBS and 0.1% Tween 20-PBS, followed by blocking with
BSA (1 g BSA in 50 ml PBS). Next, wells were exposed to mouse anti-inuenza B NP antibody
(diluted 1:1000, ABCAM) for 2 hours followed by secondary horseradish peroxidase-conjugated
goat anti-mouse antibody (diluted 1:10,000, ABCAM) for 2 hours and nally tetramethylbenzi-
dine (TMB ) ELISA substrate (ABCAM) for 15 minutes; all incubations were performed at 37°C.
Washes were performed between each incubation and reactions were terminated with ELISA
stopping solution. Absorbance at 450 nm was quantied with a Biorad microplate reader. OD
values were normalized with unexposed controls.
Inuenza challenge and evaluation of CPC in mice: Wildtype mice (C57/BL6, Jackson Labs,
Bar Harbor, ME) were infected intranasally (LD50, 8.0 x 103 pfu/mouse) with the mouse-adapt-
ed inuenza strain A/Puerto Rico/8/1934 H1N1 (PR8, ATCC). Viral stocks were propagated in
embryonated chicken eggs and titered by hemagglutination assay as described above. Viral stocks
were then titered in vivo to determine the LD50. e clinical formulation of CPC (ARMS-1 for-
mulated with glycerine and xanthan gum for human use [34]) was given orally. To determine
the prophylactic ecacy of ARMS-I, mice were treated with ARMS-1 (5 µL, applied orally) 15
minutes before the challenge and then twice a day for 5 consecutive days. Results were compared
with oseltamivir phosphate (1 mg in PBS, applied IP) twice a day for 5 consecutive days or phos-
phate buered saline (PBS) alone. Animals were observed daily for general appearance and body
weight (calculated as percentage of initial weight on day 0). For assessment of therapeutic ecacy
of ARMS-I, mice were challenged with inuenza virus as above, and then treated with ARMS-I
(10 μL orally) either 4 or 24 hours post infection (hpi), 3 times a day for 5 days. is dosage was
chosen to match recommended label usage. Survival and body weight measurements were used to
evaluate the eect of ARMS-1, as described above. All experiments were approved by Case West-
ern Reserve University Institutional Animal Care and Use Committee (IACUC) protocol #2011-
0200.
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Statistical Analysis: Pairwise comparisons were performed by a 2-tailed Student’s t test. e
statistical signicance between multiple groups was determined by one-way analysis of variance
(ANOVA) followed by Tukey-Kramer multiple comparison tests. Kaplan-Meier survival curves
were compared using the Mantel-Cox log rank test, followed by pairwise comparisons using the
Wilcoxon/Bonferroni’s correction for multiple groups. All statistical analyses were performed
with Prism, version 6.0 (Graph Pad Soware, San Diego, CA). A P value < 0.05 was considered
statistically signicant.
RESULTS
CPC exhibits direct virucidal activity against Inuenza A and B virus, including oseltami-
vir-resistant virus
We found that the percentage eective concentration of CPC (EC50) against all inuenza viruses
ranged between 5 μg/mL and 12.5 μg/mL (Table 1) by hemagglutination assay. is was well be-
low the 50% cytotoxic concentration of CPC (CC50) of 96 µg/mL (Figure 1) demonstrating pro-
tection vs general cell cytotoxicity, conrmed by microscopic visualization. Inuenza A required
higher concentrations of CPC to reduce the titer by 50% (H1N1:12.5 ± 5.6 μg/mL, H3N2: 10 ± 5.0
μg/mL), whereas inuenza B was signicantly more susceptible to the disrupting eects of CPC
(5 ± 1.9 μg/mL, P = 0.001). Based on these data, we determined that the therapeutic index (CC50/
EC50) of CPC ranges between 7.7 and 19.2 (Table 1).
Figure 1. MDCK cell viability following treatment with increasing concentrations of CPC for 10 minutes.
e cell viability was determined using the neutral red assay and the absorbance was measured at 450 nm,
n = 4 experimental replicates; data represent mean ± SD.
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Table 1. Eective virucidal concentration (EC50) and therapeutic index of CPC against inu-
enza viruses.
Virus (ATCC Strain Number) EC50 (Range) erapeutic Index**
Inuenza A H3N2 10 µg/mL ( 2-17 µg/mL) 9.6
Inuenza A H1N1 12.5 µg/mL (6 – 17 µg/mL) 7.7
Inuenza B 5 µg/mL (2 – 8 µg/mL) 19.2
Clinical Isolate 40 6 µg/mL (6 - 6 µg/mL)* 16
Oseltamivir Resistant Inuenza
A
8 µg/mL (6 - 6 µg/mL)* 12
Oseltamivir Resistant Inuenza B 8 µg/mL (6 - 6 µg/mL)* 12
EC50 was calculated by hemagglutination assay titer performed with n = 6 experimental replicates. Data
represent mean ± SD.
* All experiments were repeated 6 times and resulted in the same value.
** erapeutic Index was calculated by CC50 / EC50; CC50 was determined to be 96µg/mL by neutral red
assay
Hemagglutination assay results were next conrmed with an infectious assay. Specically, we
determined the EC2Log by TCID50. Concordant with hemagglutination data, we observed that CPC
conferred a 2 log reduction in inuenza virus by TCID50 (EC2log) at ≤20 µg/mL (EC2log) for all
inuenza strains tested. Again, inuenza B appeared more susceptible to CPC than inuenza A (4
μg/mL vs 20 μg/mL respectively).
To assess if the susceptibility to CPC is dierent in oseltamivir-resistant inuenza strains, we
compared the virucidal activity of CPC against oseltamivir-resistant virus to that of oseltami-
vir-susceptible strains. Our data showed that CPC was eective against both susceptible and re-
sistant inuenza strains. Table 1 shows the EC50 for resistant inuenza A and B viruses were both
8 μg/mL, while the EC50 for susceptible isolates ranged between 5 and 12.5 μg/mL. Notably, these
EC50 values were all close to one another suggesting that CPC is equally eective against both
susceptible and resistant viral strains.
Likewise, CPC conferred protection against both susceptible and resistant strains, as measured
by time to inactivation (Figure 2B). Virus infectivity was reduced by 50% following 5 minutes
of exposure to CPC and 90% reduction at 90 minutes. Taken together, these results indicate that
CPC has substantial and rapid (within minutes of exposure) antiviral activity against susceptible
and resistant inuenza virus.
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Figure 2. Semi-logarithmic time-kill curves of inuenza exposed to EC50 concentrations of CPC at
increasing exposure times are shown. e resulting percentage of hemagglutination compared to control
is shown over time with mean and standard deviation reported at the indicated time post CPC at EC50.
e trend line displays the rate of inactivation for each virus. A) Fiy percent of infectious virus was
inactivated in the rst 5 minutes of exposure for all isolates except for FluB. Isolate 40 is a clinical strain of
inuenza A (H1N1pdm09) virus propagated from a patient sample. B) Time-kill curve between oseltami-
vir-resistant and susceptible strains. No dierence in CPC susceptibility was seen between strains, n = 3
experimental replicates.
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Mechanism of action of CPC against inuenza virus involves rapid disruption of the viral
envelope
e mechanism of action of CPC against inuenza virus was evaluated using time-course and
TEM analyses. First, inuenza virus was exposed to CPC for increasing periods of exposure and
the remaining intact virus was titered by HA. Exposure of inuenza virus to CPC for more than 5
minutes caused ≥ 50% decrease of viability in all viral strains tested except H3N2 which attained
50% reduction following 10-minute exposure. Moreover, continued exposure to CPC for 90 min-
utes led to a 90% decrease in inuenza titer (Figure 2A). Second, TEM analyses showed that while
the viral envelope of untreated inuenza viruses was intact, exposure to CPC led to disruption of
the envelope and gross distortion of viral ultrastructure (eg cavitation, Figure 3). e presence of
negative stain in the interior of virions treated with CPC, but not in untreated virions, suggested
permeabilization of the viral membrane. Quantication of the number of intact and disrupted
viruses aer treatment revealed that 86% (172/200) of the viruses were disrupted or lacked the
envelope in CPC-treated samples, while 4.5% (9/200) of untreated virus preparations (in PBS)
displayed disrupted or non-enveloped morphologies.
Figure 3. Transmission electron microscopy (TEM) demonstrating CPC disrupts the integrity of the viral
envelope and morphology of inuenza virus. (A) Untreated inuenza virus, (B, C) inuenza virus treat-
ed with 50 µg/mL CPC for 5 minutes. Viral particles exposed to CPC demonstrate disrupted envelope or
cavitation (arrows) of viral units. e presence of negative stain inside the virions indicates membrane
permeabilization. e scale bar is in the lower le corner at 100 nm (A) or 50 nm (B,C). We quantied
the number of intact and disrupted viruses aer treatment, and found that in CPC-treated samples, 86%
(172/200) of the viruses were disrupted while in untreated samples only 4.5% (9/200) were disrupted.
To further conrm that CPC disrupts the inuenza virus envelope, we used ELISA to monitor the
release of nucleoprotein from viruses in response to increasing concentrations of CPC. We found
that exposure of virus to increasing concentrations of CPC (7.5, 10, and 20 µg/mL) resulted in
signicantly increased levels of viral nucleoprotein into the media supernatant (P ≤ 0.05, Figure
4). e level of released nucleoprotein reached a plateau at CPC concentrations above 10 µg/mL.
Taken together, these results demonstrate that CPC acts against inuenza virus by rapid disrup-
tion of the viral envelope.
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Figure 4. Inuenza nucleoprotein release from the virus in response to increasing concentrations of CPC
was measured by ELISA. Exposure to CPC concentrations above 7.5 µg/mL produced signicant eleva-
tions in nucleoprotein release compared to control, n = 8 experimental replicates, shown as mean ± SD.
Mean inuenza nucleoprotein levels in the presence of CPC were compared to control (0 µg/mL) using
independent samples t test (IBM SPSS ver 24, IBM Corp).
Exposure to CPC does not induce the development of resistance in inuenza virus
To evaluate the potential of CPC to induce drug resistance, inuenza virus was exposed to sub-in-
hibitory concentrations of CPC, and the EC50 following 10 passages of drug exposure was deter-
mined (Figure 5).
We dened CPC resistance as EC50 values > 2-fold the mean EC50 between treatment and control.
is denition is more stringent than that used for other inuenza medications [35].
No increase in EC50 was noted at any concentration for either H1N1 or H3N2. Inuenza B
demonstrated a slight increase in EC50 when exposed to CPC for 10 passages that was not signif-
icant. Of note, inuenza B susceptibility to CPC continued to be comparable to that of inuenza
A. ese results suggested that CPC has a low potential to select for inuenza virus resistance
consistent with its mechanism of action.
Orally applied CPC formulation exhibits prophylactic and therapeutic efcacy against inuen-
za infection in a murine model
e clinical formulation of CPC named “ARMS-1” is used prophylactically for upper respiratory
infections. In a randomized, double-blind clinical trial, we demonstrated that this topical oral
CPC formulation was well-tolerated and reduced the severity and duration of cough and sore
throat in the enrolled study participants vs the control group [34]. Although clinical ecacy met
statistical signicance, this study was not powered to address ecacy against specic pathogens
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(ie, inuenza). To determine the physiological relevance of CPC against inuenza, we evaluat-
ed the ecacy of the CPC-based clinical formulation ARMS-1 containing 0.1% CPC w/v as the
active ingredient [34]. We tested whether ARMS-1 conferred protection from the widely used
mouse-adapted inuenza H1N1 strain PR8 [36] in both prophylactic and therapeutic models of
inuenza infection.
Figure 5. Exposure of inuenza to 3 sub-inhibitory concentrations of CPC for 10 passages shows an ab-
sence of resistance to CPC. Inuenza A (H1N1, H3N2) and Inuenza B strains were continuously grown
in 3 sub-inhibitory concentrations of CPC: 0.2, 0.02, and 0.002 μg/mL. Viral titer was determined at the
end of each passage by hemagglutination assay to ensure an adequate inoculation for each subsequent
passage. Ten passages, with 3–4 days exposure per passage, of each inuenza strain were performed for all
concentrations of CPC. e EC50 was then determined for each virus at the 10th passage and compared to
the original strain (baseline control). No development of resistance to CPC (dened as over 2-fold change
in EC50) was seen in any strain of inuenza at any tested concentration of CPC, n = 3 experimental repli-
cates, shown as mean ± SD.
Evaluation of the prophylactic ecacy of ARMS-I showed that body weights of PBS-treated mice
were signicantly reduced at 3, 4, 5, and 6 days post infection (dpi), compared to ARMS-I treated
mice (P ≤ 0.046, Figure 6A). e increase in relative body weight between ARMS-I-treated and
untreated mice ranged between 14% on day 3 and 24.8% on day 6 post-infection. Of note, ARMS-
I-treated animals tended to exhibit higher body weights than oseltamivir-treated mice, with a
signicant dierence noted on day 3 (95.7% vs 86.8%, respectively; P = 0.033). Increased weight
in ARMS-I-treated animals was consistent with increased activity (decreased morbidity) noted
during daily observation. Survival analysis demonstrated that ARMS-I-treated mice exhibited
signicantly increased survival compared to untreated mice (P = 0.0102, Figure 6B). ere was no
signicant dierence in survival between the ARMS-I-treated vs oseltamivir-treated groups.
Given the promising protection observed prophylactically, we next asked whether ARMS-I might
be protective aer infectious challenge. We found that animals treated 4 hpi with ARMS-I did not
have signicant weight loss in contrast to animals which were untreated or treated 24 hpi and ex-
hibited up to 10% reduction in body weight, during the rst 7 days (Figure 6C). Survival analysis
demonstrated that ARMS-I treatment 24 hpi signicantly increased survival compared to untreat-
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ed mice (P = 0.047, Figure 6D). Mice treated 24 hpi with ARMS-I also had increased survival at
the termination of the experiment (14 dpi). However, this dierence was not statistically signi-
cant (P = 0.08, Figure 6D).
ese in vivo studies provide physiological evidence that CPC-based treatments may be eca-
cious in the prevention and treatment of inuenza-associated morbidity and mortality.
Figure 6. CPC formulation (ARMS-I, 0.1% CPC w/v) reduced inuenza-associated pathogenicity in vivo.
ARMS-I prophylactic protection from morbidity and mortality was demonstrated by (A) body weight
(percentage of initial weight on Day 0) and (B) Kaplan-Meier survival curve, respectively. e ARMS-I
and oseltamivir groups were treated 15 minutes before the challenge and then twice a day for 5 consecutive
days.
Similarly, ARMS-I therapeutic protection was demonstrated when given 4 or 24 hours post infection by
(C) body weight (percentage of initial weight on Day 0) and (D) Kaplan-Meier survival curve. Weights
were not reported aer > = 50% of mice died. Asterisk (*) indicates P < 0.05 between indicated ARMS-1
and either vehicle or no treatment group in prophylactic (A, B) and therapeutic (C,D) studies, respectively,
n = 8 to 10 mice/group. One of 2 similar experiments is shown
DISCUSSION:
We found that CPC is active against susceptible and oseltamivir-resistant inuenza strains. CPC
disrupted inuenza particles rapidly, within minutes of exposure, analogous to CPC’s eects on
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other pathogens [29]. Viral resistance was not observed aer prolonged exposure over multiple
passages in vitro, consistent with the physicochemical mechanism of action of CPC. is study
demonstrates that CPC can directly disrupt the membranes and subsequently inhibit infection
of pathogenic inuenza viruses. Lastly, we found that the clinical formulation of CPC reduced
inuenza-associated morbidity and mortality in vivo. ese ndings have signicant implications
for the prevention of inuenza.
Cetylpyridinium chloride is one of the more active quaternary ammonium compounds (QACs)
but, despite its use in the food, pharmaceutical, and medical industries for over y years, there is
little data specically detailing its mechanism of action against viruses. It is assumed that CPC has
direct action against lipid bilayer membranes, particularly the cytoplasmic membrane, leading to
leakage of cytoplasmic contents and lysis of the microbial cell [29, 37]. is mechanism allows for
a broad but varied spectrum of activity among dierent types of microorganisms with bacteria,
fungi, and enveloped viruses such as HIV described as highly susceptible [27, 38]. ere have
been no studies published to date on the eectiveness of CPC against respiratory viral pathogens
such as inuenza. Here we demonstrate that the EC50 of CPC against inuenza viruses is within a
clinically meaningful range.
All inuenza strains had CPC-associated EC50 and EC2log well below the CC50 of MDCK cells
consistent with a clinically viable therapeutic index. Interestingly, inuenza B had lower EC50
and EC2log compared to inuenza A suggesting that this strain is more susceptible to the eects of
CPC. e reasons for this remain unclear as both inuenza A and B derive their envelope from
the host cell. However, reports have shown that the phospholipid composition of puried virions
diers from that of the host cells. Whereas phosphatidylcholine is the major component in most
mammalian cell membranes, in puried virions phosphatidylethanolamine dominates. In addi-
tion, analysis of lipid species of the viral envelope revealed subtle dierences between inuenza
A and B strains [39]. As these bilayers are the target for QACs, such dierences may lead to an
alteration of CPC anity resulting in changes of susceptibility to CPC.
e ability of CPC to perturb viral envelopes allows for a broad spectrum of activity. However,
historical concerns over the toxicity of CPC may have resulted in it being underused clinically. In
our study, the therapeutic index (EC50/CC50) of CPC was between 7.7 and 19.2, within the range
for consideration of drug development. However, it is important to note that MDCK cells are
quite robust; further cytotoxicity testing of CPC in human-derived cells, such as A549 cells, may
add to our understanding of potential toxicity. We expect that longer exposure may also portend
increased toxicity. Importantly, CPC has been deemed safe for human use when applied at con-
centrations up to 1000 µg/mL [25, 27, 28]. Additionally, extensive safety studies have already been
conducted with CPC, including animal pharmacokinetic absorption, distribution, metabolism
and excretion (ADME), carcinogenicity, developmental toxicity, and reproductive toxicity studies
[25, 26, 28]. ese studies were conducted in a wide array of animal models (mice, rats, hamsters,
rabbits, cats, and dogs) and humans demonstrating that CPC is safe for human use at the doses
used in this study, including the 0.1% w/v clinical formulation. Lastly, a randomized double-blind
clinical trial demonstrated that the CPC formulation (ARMS-I) was safe, well tolerated, and had a
high acceptability with a protective signal [34].
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e virucidal kinetics of CPC against inuenza viruses sensitive or resistant to oseltamivir were
similar to the rapid antimicrobial activity described for bacteria and fungi [29]. Similar ndings
were reported by Maillard et al who found that disruption of bacteriophage F116 structure oc-
curred within minutes following CPC exposure [40]. For prevention of viral invasion and devel-
opment of disease, CPC with its broad spectrum and rapid virucidal activity may be preferred.
Our TEM and nucleoprotein release studies showed that CPC disrupts the viral envelope. Al-
though these experiments were performed using inuenza B as a prototype virus, we expect the
results to be similar with inuenza A. is observation is in agreement with the known mech-
anism of action of CPC. Importantly, it is likely that CPC would also have substantial activity
against other enveloped viruses such as RSV, parainuenza, and coronavirus. e common annu-
al epidemic of these viral pathogens in addition to inuenza highlight the unmet need for broad
anti-virals. e potential activity of CPC against non-enveloped pathogens including rhinovirus,
bocavirus, or adenovirus remains unclear. However, since CPC has been shown to cause structur-
al damage in non-enveloped bacteriophage [40], this agent may have activity against non-envel-
oped human viral pathogens as well. us, further evaluation of CPC eectiveness against viral
pathogens other than inuenza, both enveloped and non-enveloped, has potential clinical value.
Overuse of NAIs throughout the world has quickly led to the spread of neuraminidase resistance
[41]. In contrast, QACs, including CPC, have been actively deployed since the 1930s with no ap-
parent reduction in their eectiveness against bacteria and fungi [29]. e reason that resistance
to CPC has not been observed is likely attributable to its mechanism of action, which involves
binding to the microbial lipid bilayer, and CPC acts against inuenza by disrupting the lipid enve-
lope, which is analogous to the activity against bacteria and fungi. Since the viral envelope is host
derived, the physicochemical mechanism of CPC is independent of intrinsic viral proteins and
unlikely to be inuenced by mutation. We have shown that inuenza strains had no signicant
increase in EC50 aer 10 passages in the presence of sub-inhibitory CPC concentrations. is lack
of resistance potentiation by CPC contrasts with the dramatic development of oseltamivir resis-
tance aer as little as 4 to 6 passages under similar conditions [42, 43]. In this regard subthera-
peutic oseltamivir exposure can result in > 1000-fold increase in IC50 [43, 44]. However, continued
exposure of inuenza to CPC beyond 10 passages should be performed to ensure that there is no
late development of resistance.
Lastly, we demonstrated protection conferred by the CPC-based ARMS-1 clinical formulation
in a mouse model of inuenza. Oen, drug candidates possess potent in vitro inhibitory activity
but fail when tested in vivo. We found that mice treated with ARMS-1 either before or following
infectious challenge exhibited signicantly increased survival compared to vehicle control mice
and comparable to oseltamivir-treated mice. In addition, no toxicity was detected in the mice
treated with ARMS-1 in our experimental mouse model. In fact, the ARMS-1 treatment group
had higher weights and normal activity when compared with untreated, PBS-treated and osel-
tamivir-treated groups. is protection was most prominent when ARMS-1 was given either 15
minutes before or 4 hours aer infection. Both of these time points are prior to clinical symptoms.
ese ndings support prophylactic use and indicate that a CPC-based treatment would probably
not work aer infection is established. Future studies are needed, including similar in vivo trials
in ferrets, another important animal model for inuenza infection, to assess the potential of CPC-
based therapies to protect against inuenza disease.
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In conclusion, we demonstrated that CPC shows signicant activity against inuenza via direct
virucidal activity by disruption of the viral envelope and no indication of resistance selection. In-
creased survival was observed in mice treated with the CPC formulation, compared to untreated
mice, a nding similar to the anti-inuenza agent oseltamivir. We submit that CPC has the ability
to protect against inuenza respiratory tract infections and should be considered for further clini-
cal development.
FUNDING
is work was supported by ARMS Pharmaceutical LLC, National Institutes of Health grants
number R01DE024228 and RO1DE17846, the Oral HIV AIDS Research Alliance (OHARA,
BRSACURE-S-11-000049-110229), and a Cleveland Digestive Diseases Research Core Center
(DDRCC) Pilot and Feasibility project (supported by NIH/NIDDK P30 DK097948). DP was
supported by an American Skin Association Carson Scholar Award and VA Merit award IBX
IBX002719A. DP and MG are members of the CWRU/UH Center for AIDS Research: NIH Cen-
ter for AIDS Research grant P30 AI036219.
TRANSPARENCY DECLARATIONS
MAG acts as Chief Scientic Ocer and Consultant for ARMS Pharmaceutical LLC. PKM acts
as a Consultant for ARMS Pharmaceutical LLC. ere is no conict of interest for the remaining
authors regarding the publication of this paper.
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