Nanchangmycin suppresses influenza A virus infection by blocking endosomal acidification

Abstract

Influenza A viruses (IAVs) constitute a major threat to human and animal health. Currently, M2 ion-channel inhibitors, neuraminidase (NA) inhibitors, RNA polymerase inhibitors, and cap-dependent endonuclease inhibitors have been applied clinically as therapeutics against IAVs. However, IAVs possess adaptive mutations to these inhibitors, especially M2 ion channel and NA inhibitors. Thus, novel antiviral agents should be developed. In the present study, we screen approximately 5500 compounds and identify an IAV inhibitor, nanchangmycin, which possesses a robust antiviral activity both in vitro and in vivo. In addition, it exhibits broad-spectrum antiviral activity for additional virus infections, including pseudorabies virus, herpes virus, porcine epidemic diarrhea virus, porcine reproductive and respiratory syndrome virus. Most importantly, it has antiviral activity against oseltamivir-resistant strains in sub-μM ranges and promotes the survival of MDCK cells infected with the oseltamivir-resistant influenza A virus strain. Further studies reveal that it blocks the nuclei migration of viral nuclear proteins (NPs), resulting in NP accumulation in the cytoplasm, particularly within perinuclear endosomes. Also, it inhibits IAVs by blocking endosomal acidification. Overall, nanchangmycin has the potential to be developed as an anti-influenza agent.

1. Introduction

Influenza viruses remain a serious and significant public health threat, causing human and animal respiratory infections [1]. Owing to seasonal influenza virus outbreaks and sporadic pandemics with the potential for widespread infection or disease, humans and animals are under continual assault [2,3]. The “Spanish” influenza pandemic has caused 50 million deaths worldwide [4,5]. The pandemic (pdm09) influenza A H1N1 strain, which originated in swine worldwide, and avian H5N1 and H7N9 influenza A viruses are highly pathogenic to humans [4–6]. The World Health Organization estimates that approximately 1 billion human influenza cases, of which 3‒5 million are considered severe and result in 290,000 to 650,000 deaths, are recorded annually [7]. Multiple strategies have been adopted to reduce the burden attributed to pandemic influenza. Vaccination is an appropriate option to combat the influenza virus, while its drawback is the difficulty of producing large quantities of vaccines within a short period, resulting in delayed protection [8]. Thus, drugs for controlling influenza virus infection constitute another strategy.

Influenza A viruses (IAVs), which are members of the family Orthomyxoviridae, are enveloped negative-strand RNA viruses that contain eight discrete single-stranded RNA gene segments encoding at least 11 open reading frames (ORFs) [1]. On the basis of the antigenicity of the hemagglutinin (HA) and neuraminidase (NA) surface glycoproteins, 18 HA (H1–H18) and 11 NA (N1–N11) subtypes have been identified. The typical viral cycle consists of five stages: attachment, entry, replication, assembly and release [9]. Advances in understanding the molecular mechanisms of the IAV life cycle have promoted the development of antiviral agents [10–15]. Currently, three major classes of antiviral drugs are available: M2 inhibitors [16,17], neuraminidase inhibitors [18,19] and polymerase inhibitors [20]. The potential of vast genetic variability within influenza viruses and highly error-prone RNA-dependent RNA polymerase does raise the chances of the emergence of drug-resistant strains [21,22]. Several mutant virus strains with resistance to these drugs have been reported [23–28], indicating that resistance is a serious public concern. In the 2009 pandemic influenza A/H1N1 virus background, H275Y, a histidine, was replaced by a tyrosine in the neuraminidase at the 275th residue, becoming the most frequently reported mutation, which renders oseltamivir (OSE)-resistance [26]. Recently, studies have reported that reassortment between swine influenza virus and 2009 influenza A virus in human has emerged [29], which emphasizes the discovery of novel influenza virus inhibitors to combat drug-resistant influenza virus strains.