Preclinical Considerations for Long-acting Delivery of Tenofovir Alafenamide from Subdermal Implants for HIV Pre-exposure Prophylaxis.

PURPOSE: Long-acting formulations of the potent antiretroviral prodrug tenofovir alafenamide (TAF) hold potential as biomedical HIV prevention modalities. Here, we present a rigorous comparison of three animal models, C57BL/6 J mice, beagle dogs, and merino sheep for evaluating TAF implant pharmacokinetics (PKs). METHODS: Implants delivering TAF over a wide range of controlled release rates were tested in vitro and in mice and dogs. Our existing PK model, supported by an intravenous (IV) dosing dog study, was adapted to analyze mechanistic aspects underlying implant TAF delivery. RESULTS: TAF in vitro release in the 0.13 to 9.8 mg d-1 range with zero order kinetics were attained. Implants with equivalent fabrication parameters released TAF in mice and sheep at rates that were not statistically different, but were 3 times higher in dogs. When two implants were placed in the same subcutaneous pocket, a two-week creep to Cmax was observed in dogs for systemic drug and metabolite concentrations, but not in mice. Co-modeling IV and TAF implant PK data in dogs led to an apparent TAF bioavailability of 9.6 in the single implant groups (compared to the IV group), but only 1.5 when two implants were placed in the same subcutaneous pocket. CONCLUSIONS: Based on the current results, we recommend using mice and sheep, with macaques as a complementary species, for preclinical TAF implant evaluation with the caveat that our observations may be specific to the implant technology used here. Our report provides fundamental, translatable insights into multispecies TAF delivery via long-acting implants.

The role of immunophilins in viral infection.

BACKGROUND: Tremendous progress has been made in the past 20 years in understanding the roles played by immunophilins, and in particular the cyclophilins, in supporting the replication cycles of human viruses. A growing body of genetic and biochemical evidence and data from clinical trials confirm that cyclophilins are essential cofactors that contribute to establishing a permissive environment within the host cell that supports the replication of HIV-1 and HCV. Cyclophilin A regulates HIV-1 replication kinetics and infectivity, modulates sensitivity to host restriction factors, and cooperates in the transit of the pre-integration complex into the nucleus of infected cells. Cyclophilin A is an essential cofactor whose expression supports HCV-specific RNA replication in human hepatocytes. GENERAL SIGNIFICANCE: Peptidyl-prolyl isomerase inhibitors have been used in clinical trials to validate cyclophilins as antiviral targets for the treatment of HIV-1 and Chronic Hepatitis C virus infection and as molecular probes to identify the roles played by immunophilins in supporting the replication cycles of human viruses. SCOPE OF REVIEW: This review summarizes emerging research that defines the functions of immunophilins in supporting the replication cycles of HIV-1, HCV, HBV, coronaviruses, and other viral pathogens and describes new information that suggests a role for immunophilins in regulating innate immune responses against chronic viral infection. MAJOR CONCLUSIONS: The dependence on cyclophilins by evolutionarily distinct viruses for accomplishing various steps in replication such as viral entry, initiation of genomic nucleic acid replication, viral genome uncoating, nuclear import and nuclear entry, emphasizes the potential of cyclophilin inhibitors as therapeutic agents. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

C5A Protects Macaques from Vaginal Simian-Human Immunodeficiency Virus Challenge.

A safe and effective vaginal microbicide could decrease human immunodeficiency virus (HIV) transmission in women. Here, we evaluated the safety and microbicidal efficacy of a short amphipathic peptide, C5A, in a rhesus macaque model. We found that a vaginal application of C5A protects 89% of the macaques from a simian-human immunodeficiency virus (SHIV-162P3) challenge. We observed no signs of lesions or inflammation in animals vaginally treated with repeated C5A applications. With its noncellular cytotoxic activity and rare mechanism of action, C5A represents an attractive microbicidal candidate.

Cyclophilin and NS5A inhibitors, but not other anti-hepatitis C virus (HCV) agents, preclude HCV-mediated formation of double-membrane-vesicle viral factories.

Although the mechanisms of action (MoA) of nonstructural protein 3 inhibitors (NS3i) and NS5B inhibitors (NS5Bi) are well understood, the MoA of cyclophilin inhibitors (CypI) and NS5A inhibitors (NS5Ai) are not fully defined. In this study, we examined whether CypI and NS5Ai interfere with hepatitis C virus (HCV) RNA synthesis of replication complexes (RCs) or with an earlier step of HCV RNA replication, the creation of double-membrane vesicles (DMVs) essential for HCV RNA replication. In contrast to NS5Bi, both CypI and NS5Ai do not block HCV RNA synthesis by way of RCs, suggesting that they exert their antiviral activity prior to the establishment of enzymatically active RCs. We found that viral replication is not a precondition for DMV formation, since the NS3-NS5B polyprotein or NS5A suffices to create DMVs. Importantly, only CypI and NS5Ai, but not NS5Bi, mir-122, or phosphatidylinositol-4 kinase IIIα (PI4KIIIα) inhibitors, prevent NS3-NS5B-mediated DMV formation. NS3-NS5B was unable to create DMVs in cyclophilin A (CypA) knockdown (KD) cells. We also found that the isomerase activity of CypA is absolutely required for DMV formation. This not only suggests that NS5A and CypA act in concert to build membranous viral factories but that CypI and NS5Ai mediate their early anti-HCV effects by preventing the formation of organelles, where HCV replication is normally initiated. This is the first investigation to examine the effect of a large panel of anti-HCV agents on DMV formation, and the results reveal that CypI and NS5Ai act at the same membranous web biogenesis step of HCV RNA replication, thus indicating a new therapeutic target of chronic hepatitis C.

The combination of alisporivir plus an NS5A inhibitor provides additive to synergistic anti-hepatitis C virus activity without detectable cross-resistance.

Alisporivir (ALV), a cyclophilin inhibitor, is a host-targeting antiviral (HTA) with multigenotypic anti-hepatitis C virus (HCV) activity and a high barrier to resistance. Recent advances have supported the concept of interferon (IFN)-free regimens to treat chronic hepatitis C. As the most advanced oral HTA, ALV with direct-acting antivirals (DAAs) represents an attractive drug combination for IFN-free therapy. In this study, we investigated whether particular DAAs exhibit additive, synergistic, or antagonistic effects when combined with ALV. Drug combinations of ALV with NS3 protease, NS5B polymerase, and NS5A inhibitors were investigated in HCV replicons from genotypes 1a, 1b, 2a, 3, and 4a (GT1a to -4a). Combinations of ALV with DAAs exerted an additive effect on GT1 and -4. A significant and specific synergistic effect was observed with ALV-NS5A inhibitor combination on GT2 and -3. Furthermore, ALV was fully active against DAA-resistant variants, and ALV-resistant variants were fully susceptible to DAAs. ALV blocks the contact between cyclophilin A and domain II of NS5A, and NS5A inhibitors target domain I of NS5A; our data suggest a molecular basis for the use of these two classes of inhibitors acting on two distinct domains of NS5A. These results provide in vitro evidence that ALV with NS5A inhibitor combination represents an attractive strategy and a potentially effective IFN-free regimen for treatment of patients with chronic hepatitis C. Due to its high barrier and lack of cross-resistance, ALV could be a cornerstone drug partner for DAAs.

Correlation between NS5A dimerization and hepatitis C virus replication.

Hepatitis C virus (HCV) is the main agent of acute and chronic liver diseases leading to cirrhosis and hepatocellular carcinoma. The current standard therapy has limited efficacy and serious side effects. Thus, the development of alternate therapies is of tremendous importance. HCV NS5A (nonstructural 5A protein) is a pleiotropic protein with key roles in HCV replication and cellular signaling pathways. Here we demonstrate that NS5A dimerization occurs through Domain I (amino acids 1-240). This interaction is not mediated by nucleic acids because benzonase, RNase, and DNase treatments do not prevent NS5A-NS5A interactions. Importantly, DTT abrogates NS5A-NS5A interactions but does not affect NS5A-cyclophilin A interactions. Other reducing agents such as tris(2-carboxyethyl)phosphine and 2-mercaptoethanol also abrogate NS5A-NS5A interactions, implying that disulfide bridges may play a role in this interaction. Cyclophilin inhibitors, cyclosporine A, and alisporivir and NS5A inhibitor BMS-790052 do not block NS5A dimerization, suggesting that their antiviral effects do not involve the disruption of NS5A-NS5A interactions. Four cysteines, Cys-39, Cys-57, Cys-59, and Cys-80, are critical for dimerization. Interestingly, the four cysteines have been proposed to form a zinc-binding motif. Supporting this notion, NS5A dimerization is greatly facilitated by Zn(2+) but not by Mg(2+) or Mn(2+). Importantly, the four cysteines are vital not only for viral replication but also critical for NS5A binding to RNA, revealing a correlation between NS5A dimerization, RNA binding, and HCV replication. Altogether our data suggest that NS5A-NS5A dimerization and/or multimerization could represent a novel target for the development of HCV therapies.

HCV NS5A and IRF9 compete for CypA binding.

BACKGROUND & AIMS: Cyclophilin A (CypA) is vital for HCV replication. Cyp inhibitors successfully decrease viral loads in HCV-infected patients. However, their mechanisms of action remain unknown. Since interferon (IFN) can also suppress HCV replication, we asked whether a link between CypA and the IFN response exists. METHODS: We used cellular and recombinant pulldown approaches to investigate the possibility of a specific association of CypA with host ligands. RESULTS: We found for the first time that CypA binds to a major component of the IFN response - the IFN regulatory factor 9 (IRF9). IRF9 is the DNA-binding component of the transcriptional IFN-stimulated gene factor 3 (ISGF3). CypA binds directly to IRF9 via its peptidyl-prolyl isomerase (PPIase) pocket. Cyp inhibitors such as cyclosporine A (CsA) or non-immunosuppressive derivates such as alisporivir and SCY-635, prevent IRF9-CypA complex formation. CypA binds to the C-terminal IRF-association-domain (IAD), but not to the DNA-binding or linker domains of IRF9. Remarkably, CypA associates with the multimeric ISGF3 complex. We also obtained evidence that CypA neutralization enhances IFN-induced transcription. Interestingly, the hepatitis C virus (HCV) non-structural 5A (NS5A) protein, which is known to modulate the IFN response, competes with IRF9 for CypA binding and can prevent the formation of IRF9-CypA complexes. CONCLUSIONS: This study demonstrates for the first time that CypA binds specifically to a component of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, IRF9. This study also reveals a novel opportunity of HCV to modulate the IFN response via NS5A.

Acute antagonism in three-drug combinations for vaginal HIV prevention in humanized mice.

Adolescent girls and young women in low- to middle-income countries are disproportionately at risk of becoming HIV-1 infected. New non-vaccine biomedical products aimed at overcoming this global health challenge need to provide a range of safe, effective, and discreet dosage forms based on the delivery of one or more antiviral compounds. An overarching strategy involves vaginal drug administration through inserts/tablets, gels, films, and intravaginal rings. The approach derives its appeal from being women-controlled and topical, there-by potentially minimizing systemic exposure to the agents and their metabolites. Oral regimens based on tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) are established and effective in HIV-1 pre-exposure prophylaxis (PrEP), and form a promising basis for vaginal PrEP. Here, we used bone marrow/liver/thymus humanized mice to measure the in vivo efficacy against HIV-1 of single and combination antiviral compounds applied vaginally, coupled with data analysis using the Chou-Talalay mathematical model to study the dose-effect characteristics. Unexpectedly, strong antagonism was observed in drug combinations composed of TDF-FTC coupled with a third agent using a different mode of action against HIV-1. The antagonistic effect was remedied when TDF was omitted from the regimen. Our approach provides a translational template for the preclinical, rational, and systematic evaluation of drug combinations for the prevention of HIV-1, and other viral diseases.

Sublimable C5A delivery provides sustained and prolonged anti-HIV microbicidal activities.

We have identified a short amphipathic helical peptide, called C5A, which exhibits potent microbicidal activities in vitro and which offers protection from vaginal HIV transmission in vivo in a humanized mouse model. However, there are many obstacles to overcome before C5A can be considered a true microbicidal candidate. First, it must be stabilized against enzymatic degradation in a continuously warm and moist environment. Second, it must be delivered in a controlled manner to achieve long-term and coitally independent efficacy. We demonstrate in this in vitro study that the combination of two matrices with different subliming properties ((hexamethylcyclotrisiloxane [HMCS] and cyclododecane [CDD]) containing 10% labile C5A yielded the best results in terms of controlled release and preserved anti-HIV activity of the peptide when pre-exposed to cell-free medium or cell culture at body temperature for up to 2 months.

The cyclophilin inhibitor SCY-635 disrupts hepatitis C virus NS5A-cyclophilin A complexes.

The nonimmunosuppressive cyclophilin (Cyp) inhibitor SCY-635 blocks hepatitis C virus (HCV) replication both in vitro and in vivo and represents a novel potent anti-HCV agent. However, its mechanism of action remains to be fully elucidated. A growing body of evidence suggests that cyclophilin A (CypA) is absolutely necessary for HCV replication and that the HCV nonstructural 5A (NS5A) protein serves as a main viral ligand for CypA. In this study, we examined the effect of SCY-635 on HCV replication. Specifically, we asked whether SCY-635 blocks HCV replication by targeting CypA-NS5A interactions. We also investigated the possibility that HCV can escape SCY-635 selection pressure and whether this resistance influences either CypA-NS5A interactions or the dependence of HCV on CypA. We found not only that SCY-635 efficiently inhibits HCV replication, but it is sufficient alone to clear HCV replicon-containing cells. We found that SCY-635 prevents CypA-NS5A interactions in a dose-dependent manner. SCY-635 prevents the contact between CypA and NS5A derived from genotypes 1 to 3. Together, these data suggest that NS5A-CypA interactions control HCV replication and that SCY-635 blocks viral replication by preventing the formation of these complexes. We also found that NS5A mutant proteins found in SCY-635-resistant HCV replicons behave similarly to wild-type NS5A in terms of both CypA binding and SCY-635-mediated dissociation and inhibition of CypA binding. However, the NS5A mutations found in SCY-635-resistant HCV replicons rescued viral replication in CypA-knockdown cells, suggesting that the NS5A mutations, which arose in vitro under SCY-635 selection, do not alter the binding affinity of CypA for NS5A. These specific mutations in NS5A eliminate the dependence of HCV RNA replication on the expression of host CypA.

Multiple mutations in hepatitis C virus NS5A domain II are required to confer a significant level of resistance to alisporivir.

Alisporivir is the most advanced host-targeting antiviral cyclophilin (Cyp) inhibitor in phase III studies and has demonstrated a great deal of promise in decreasing hepatitis C virus (HCV) viremia in infected patients. In an attempt to further elucidate the mechanism of action of alisporivir, HCV replicons resistant to the drug were selected. Interestingly, mutations constantly arose in domain II of NS5A. To demonstrate that these mutations are responsible for drug resistance, they were reintroduced into the parental HCV genome, and the resulting mutant viruses were tested for replication in the presence of alisporivir or in the absence of the alisporivir target, CypA. We also examined the effect of the mutations on NS5A binding to itself (oligomerization), CypA, RNA, and NS5B. Importantly, the mutations did not affect any of these interactions. Moreover, the mutations did not preserve NS5A-CypA interactions from alisporivir rupture. NS5A mutations alone render HCV only slightly resistant to alisporivir. In sharp contrast, when multiple NS5A mutations are combined, significant resistance was observed. The introduction of multiple mutations in NS5A significantly restored viral replication in CypA knockdown cells. Interestingly, the combination of NS5A mutations renders HCV resistant to all classes of Cyp inhibitors. This study suggests that a combination of multiple mutations in domain II of NS5A rather than a single mutation is required to render HCV significantly and universally resistant to Cyp inhibitors. This in accordance with in vivo data that suggest that alisporivir is associated with a low potential for development of viral resistance.

Sustained local delivery of structurally diverse HIV-1 microbicides released from sublimation enthalpy controlled matrices.

PURPOSE: Use of coital-dependent products to prevent HIV-1 transmission has resulted in mixed success. We hypothesize that incorporation of antiviral drug candidates into a novel controlled delivery system will prolong their activity, making their use coital independent, thus increasing their chance of prophylactic success. METHODS: Tenofovir, emtricitabine, and C5A peptide HIV microbicides were mechanically incorporated into matrices comprising a series of subliming solids. Matrix sublimation rates and drug release rates were measured in three in vitro and one in vivo environments intended to model human vaginal interior. Antiviral activity studies evaluating matrix incorporated microbicides were performed using in vitro cell cultures and human ectocervical explants. RESULTS: Drug release rates were identical to matrix sublimation rates, and were zero order. Differences in matrix material sublimation enthalpies determined drug release and matrix erosion rates in a thermodynamically definable manner, in vitro and in vivo. Durations of release ranging from several days to several months were readily achieved. Prolonged duration of anti HIV-1 activity was shown for matrix incorporated microbicides, using ectocervical explant and cell culture models of HIV-1 infection. CONCLUSION: Subliming solid matrices show promise as a delivery system providing multi month intravaginal release of a wide range of HIV-1 microbicides.

Fundamental aspects of long-acting tenofovir alafenamide delivery from subdermal implants for HIV prophylaxis.

Global efforts aimed at preventing human immunodeficiency virus type one (HIV-1) infection in vulnerable populations appear to be stalling, limiting our ability to control the epidemic. Long-acting, controlled drug administration from subdermal implants holds significant potential by reducing the compliance burden associated with frequent dosing. We, and others, are exploring the development of complementary subdermal implant technologies delivering the potent prodrug, tenofovir alafenamide (TAF). The current report addresses knowledge gaps in the preclinical pharmacology of long-acting, subdermal TAF delivery using several mouse models. Systemic drug disposition during TAF implant dosing was explained by a multi-compartment pharmacokinetic (PK) model. Imaging mass spectrometry was employed to characterize the spatial distribution of TAF and its principal five metabolites in local tissues surrounding the implant. Humanized mouse studies determined the effective TAF dose for preventing vaginal and rectal HIV-1 acquisition. Our results represent an important step in the development of a safe and effective TAF implant for HIV-1 prevention.

Early SARS-CoV-2 dynamics and immune responses in unvaccinated participants of an intensely sampled longitudinal surveillance study.

Background: A comprehensive understanding of the SARS-CoV-2 infection dynamics and the ensuing host immune responses is needed to explain the pathogenesis as it relates to viral transmission. Knowledge gaps exist surrounding SARS-CoV-2 in vivo kinetics, particularly in the earliest stages after exposure. Methods: An ongoing, workplace clinical surveillance study was used to intensely sample a small cohort longitudinally. Nine study participants who developed COVID-19 between November, 2020 and March, 2021 were monitored at high temporal resolution for three months in terms of viral loads as well as associated inflammatory biomarker and antibody responses. CD8 + T cells targeting SARS-CoV-2 in blood samples from study participants were evaluated. Results: Here we show that the resulting datasets, supported by Bayesian modeling, allowed the underlying kinetic processes to be described, yielding a number of unexpected findings. Early viral replication is rapid (median doubling time, 3.1 h), providing a narrow window between exposure and viral shedding, while the clearance phase is slow and heterogeneous. Host immune responses different widely across participants. Conclusions: Results from our small study give a rare insight into the life-cycle of COVID-19 infection and hold a number of important biological, clinical, and public health implications.

A virocidal amphipathic {alpha}-helical peptide that inhibits hepatitis C virus infection in vitro.

An amphipathic alpha-helical peptide (C5A) derived from the membrane anchor domain of the hepatitis C virus (HCV) NS5A protein is virocidal for HCV at submicromolar concentrations in vitro. C5A prevents de novo HCV infection and suppresses ongoing infection by inactivating both extra- and intracellular infectious particles, and it is nontoxic in vitro and in vivo at doses at least 100-fold higher than required for antiviral activity. Mutational analysis indicates that C5A's amphipathic alpha-helical structure is necessary but not sufficient for its virocidal activity, which depends on its amino acid composition but not its primary sequence or chirality. In addition to HCV, C5A inhibits infection by selected flaviviruses, paramyxoviruses, and HIV. These results suggest a model in which C5A destabilizes viral membranes based on their lipid composition, offering a unique therapeutic approach to HCV and other viral infections.

Hepatitis C virus NS5A anchor peptide disrupts human immunodeficiency virus.

In the absence of an effective vaccine, there is an urgent need for safe and effective antiviral agents to prevent transmission of HIV. Here, we report that an amphipathic alpha-helical peptide derived from the hepatitis C virus NS5A anchor domain (designated C5A in this article) that has been shown to be virocidal for the hepatitis C virus (HCV) also has potent antiviral activity against HIV. C5A exhibits a broad range of antiviral activity against HIV isolates, and it prevents infection of the three in vivo targets of HIV: CD4(+) T lymphocytes, macrophages, and dendritic cells by disrupting the integrity of the viral membrane and capsid core while preserving the integrity of host membranes. C5A can interrupt an ongoing T cell infection, and it can prevent transmigration of HIV through primary genital epithelial cells, infection of mucosal target cells and transfer from dendritic cells to T cells ex vivo, justifying future experiments to determine whether C5A can prevent HIV transmission in vivo.

The combination of the NS5A and cyclophilin inhibitors results in an additive anti-HCV inhibition in humanized mice without development of resistance.

We and others previously reported that the direct-acting agents (DAA) NS5A inhibitors (NS5Ai) and the host-targeting agents cyclophilin inhibitors (CypIs) inhibit HCV replication in vitro. In this study, we investigated whether the combination of NS5Ai and CypI offers a potent anti-HCV effect in vivo. A single administration of NS5Ai or CypI alone to HCV-infected humanized-mice inhibits HCV replication. The combination of NS5Ai with CypI suppresses HCV (GT1a, GT2a, GT3a and GT4a) replication in an additive manner. NS5Ai/CypI combinations provide a statistically more profound anti-HCV inhibition for GT2a and GT3a than GT1a and GT4a, leading to a fastest and deepest inhibition of GT2a and GT3a replications. Combining CypI with NS5Ai prevents the viral rebound normally observed in mice treated with NS5Ai alone. Results were confirmed in mice implanted with human hepatocytes from different donors. Therefore, the combination of NS5Ai with CypI may serve as a regimen for the treatment of HCV patients with specific genotypes and disorder conditions, which diminish sustain viral response levels to DAA, such as GT3a infection, cirrhosis, and DAA resistance associated with the selection of resistance-associated substitutions present at baseline or are acquired during treatment.

Protective Effects of Astodrimer Sodium 1% Nasal Spray Formulation against SARS-CoV-2 Nasal Challenge in K18-hACE2 Mice.

Strategies to combat COVID-19 require multiple ways to protect vulnerable people from infection. SARS-CoV-2 is an airborne pathogen and the nasal cavity is a primary target of infection. The K18-hACE2 mouse model was used to investigate the anti-SARS-CoV-2 efficacy of astodrimer sodium formulated in a mucoadhesive nasal spray. Animals received astodrimer sodium 1% nasal spray or PBS intranasally, or intranasally and intratracheally, for 7 days, and they were infected intranasally with SARS-CoV-2 after the first product administration on Day 0. Another group was infected intranasally with SARS-CoV-2 that had been pre-incubated with astodrimer sodium 1% nasal spray or PBS for 60 min before the neutralisation of test product activity. Astodrimer sodium 1% significantly reduced the viral genome copies (>99.9%) and the infectious virus (~95%) in the lung and trachea vs. PBS. The pre-incubation of SARS-CoV-2 with astodrimer sodium 1% resulted in a significant reduction in the viral genome copies (>99.9%) and the infectious virus (>99%) in the lung and trachea, and the infectious virus was not detected in the brain or liver. Astodrimer sodium 1% resulted in a significant reduction of viral genome copies in nasal secretions vs. PBS on Day 7 post-infection. A reduction in the viral shedding from the nasal cavity may result in lower virus transmission rates. Viraemia was low or undetectable in animals treated with astodrimer sodium 1% or infected with treated virus, correlating with the lack of detectable viral replication in the liver. Similarly, low virus replication in the nasal cavity after treatment with astodrimer sodium 1% potentially protected the brain from infection. Astodrimer sodium 1% significantly reduced the pro-inflammatory cytokines IL-6, IL-1α, IL-1ß, TNFα and TGFß and the chemokine MCP-1 in the serum, lung and trachea vs. PBS. Astodrimer sodium 1% nasal spray blocked or reduced SARS-CoV-2 replication and its sequelae in K18-hACE2 mice. These data indicate a potential role for the product in preventing SARS-CoV-2 infection or for reducing the severity of COVID-19.

Virucidal and antiviral activity of astodrimer sodium against SARS-CoV-2 in vitro.

An effective response to the ongoing coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will involve a range of complementary preventive modalities. The current studies were conducted to evaluate the in vitro SARS-CoV-2 antiviral and virucidal (irreversible) activity of astodrimer sodium, a dendrimer with broad spectrum antimicrobial activity, including against enveloped viruses in in vitro and in vivo models, that is marketed for antiviral and antibacterial applications. We report that astodrimer sodium inhibits replication of SARS-CoV-2 in Vero E6 and Calu-3 cells, with 50% effective concentrations (EC50) for i) reducing virus-induced cytopathic effect of 0.002-0.012 mg/mL in Vero E6 cells, and ii) infectious virus release by plaque assay of 0.019-0.032 mg/mL in Vero E6 cells and 0.030-0.037 mg/mL in Calu-3 cells. The selectivity index (SI) in these assays was as high as 2197. Astodrimer sodium was also virucidal, irreversibly reducing SARS-CoV-2 infectivity by >99.9% (>3 log10) within 1 min of exposure, and up to >99.999% (>5 log10) shown at astodrimer sodium concentrations of 10-30 mg/mL in Vero E6 and Calu-3 cell lines. Astodrimer sodium also inhibited infection in a primary human airway epithelial cell line. The data were similar for all investigations and were consistent with the potent antiviral and virucidal activity of astodrimer sodium being due to irreversible inhibition of virus-host cell interactions, as previously demonstrated for other viruses. Further studies will confirm if astodrimer sodium binds to SARS-CoV-2 spike protein and physically blocks initial attachment of the virus to the host cell. Given the in vitro effectiveness and significantly high SI, astodrimer sodium warrants further investigation for potential as a topically administered agent for SARS-CoV-2 therapeutic applications.

A robust SARS-CoV-2 replication model in primary human epithelial cells at the air liquid interface to assess antiviral agents.

There are, besides remdesivir, no approved antivirals for the treatment of SARS-CoV-2 infections. To aid in the search for antivirals against this virus, we explored the use of human tracheal airway epithelial cells (HtAEC) and human small airway epithelial cells (HsAEC) grown at the air-liquid interface (ALI). These cultures were infected at the apical side with one of two different SARS-CoV-2 isolates. Each virus was shown to replicate to high titers for extended periods of time (at least 8 days) and, in particular an isolate with the D614G in the spike (S) protein did so more efficiently at 35 °C than 37 °C. The effect of a selected panel of reference drugs that were added to the culture medium at the basolateral side of the system was explored. Remdesivir, GS-441524 (the parent nucleoside of remdesivir), EIDD-1931 (the parent nucleoside of molnupiravir) and IFN (ß1 and λ1) all resulted in dose-dependent inhibition of viral RNA and infectious virus titers collected at the apical side. However, AT-511 (the free base form of AT-527 currently in clinical testing) failed to inhibit viral replication in these in vitro primary cell models. Together, these results provide a reference for further studies aimed at selecting SARS-CoV-2 inhibitors for further preclinical and clinical development.