Bacteriophage-derived dsRNA, known as Larifan, is a nationally well-known broad-spectrum antiviral medication. This study aimed to ascertain the antiviral activity of Larifan against the novel SARS-CoV-2 virus. Larifan’s effect against SARS-CoV-2 in vitro was measured in human lung adenocarcinoma (Calu3) and primary human small airway epithelial cells (HSAEC), and in vivo in the SARS-CoV-2 infection model in golden Syrian hamsters. Larifan inhibited SARS-CoV-2 replication both in vitro and in vivo. Viral RNA copy numbers and titer of infectious virus in the supernatant of Calu3 cells dropped significantly: p = 0.0296 and p = 0.0286, respectively. A reduction in viral RNA copy number was also observed in HSAEC, especially when Larifan was added before infection (p = 0.0218). Larifan markedly reduced virus numbers in infected hamsters’ lungs post-infection, with a more pronounced effect after intranasal administration (p = 0.0032). The administration of Larifan also reduced the amount of infections virus titer in the lungs (p = 0.0039). Improvements in the infection-induced pathological lesion severity in the lungs of animals treated with Larifan were also demonstrated. The inhibition of SARS-CoV-2 replication in vitro and the reduction in the viral load in the lungs of infected hamsters treated with Larifan alongside the improved lung histopathology suggests a potential use of Larifan in also controlling the COVID-19 disease in humans.

The involvement of tissue-resident macrophages (TRMs) in health and diseases makes them unique therapeutic targets. TRMs are activated through their surface pattern recognition receptors, such as Toll-like receptors (TLRs) that are essential sensors of danger signals. Here, we determine the activation status of rat peritoneal macrophages (PMs) and microglia (MG) cells under normal and hypoxic conditions and investigate the effect of TLR3 agonist bacteriophage-derived dsRNA (Larifan) on the metabolic profile of TRMs in vitro. We implemented the phenotypic markers CD14 and CD206, arginine metabolism, phagocytic activity and reactive oxygen species generation as metabolic characteristics to evaluate TRMs activation. We showed that normoxic TRMs from different tissue niches responded to Larifan exposure in different ways. PM exhibited signs towards M1 polarisation. In contrast, the MG activation pattern could be considered as neither pro-inflammatory nor anti-inflammatory. We also showed that TRMs, regardless of the tissue niche, responded to hypoxia with a phenotypic shift towards an anti-inflammatory (M2) state. Larifan could attenuate hypoxia-induced TRMs metabolic programming. However, hypoxic conditions could negatively affect the interaction of TRMs with danger signals.

Purpose: Bacteriophage-derived dsRNA, also known as Larifan, is nationally well-known broad-spectrum antiviral medication. The goal of this study was to ascertain the antiviral activity of Larifan against the novel SARS-CoV-2. Methods: The antiviral activity of Larifan against SARS-CoV-2 in vitro was measured in human lung adenocarcinoma (Calu3) and primary human small airway epithelial cells (HSAEC) using cytopathic effect assay, viral RNA copy number detection by digital droplet PCR (ddPCR) and infectious virus titration in cells supernatants in Vero E6 cells by end-point titration method. The antiviral effect of Larifan in vivo was detected in SARS-CoV-2 infection model in Golden Syrian hamsters. Larifan (5 mg/kg) was administered either subcutaneously or intranasally twice before and after virus infection with a 24-hour interval between doses. The viral RNA copies and infectious virus titre were detected in animal lungs at day three and five post-infection using ddPCR and end-point titration in Vero E6 cells, respectively. Histopathology of lungs was analysed as well. Results: Larifan inhibited SARS-CoV-2 replication in Calu3 cells both after the drug addition pre- and pot-infection with a substantial drop in the supernatant viral RNA copy numbers from eight (p = 0.0013) to twenty (p = 0.0042) times, respectively. Similarly, infectious virus titre in Vero E6 cells dropped by 3.6log10 and 2.8log10 after the drug addition pre- and pot-infection, respectively. In HSAEC, Larifan inhibited SARS-CoV-2 replication at the similar level. Larifan also markedly reduced virus numbers in the lungs of infected hamsters (p = 0.0032) both at day three and five post-infection with a more pronounced effect after intranasal administration reaching a drop by 2.7log10 at day three and 2.0log10 at day five. The administration of Larifan also reduced the amount of infections virus titer in lungs (p = 0.0039) by 4.3log10 and 2.8log10 at day three and five post-infection, respectively. Improvements in the infection-induced pathological lesion severity in the lungs of animals treated with Larifan were also demonstrated by histological analyses. Conclusions: The inhibition of SARS-CoV-2 replication in vitro and the reduction of the viral load in the lungs of infected hamsters treated with Larifan alongside the improved lung histopathology, suggests a potential use of Larifan in controlling the COVID-19 disease in humans.