In vitro inhibition of mumps virus replication by favipiravir (T-705)

Highlights

• Favipiravir inhibits the growth of wildtype and vaccine strains of mumps virus in vitro at low micro-molar concentration.

• Favipiravir inhibits viral growth by significantly reducing viral ribonucleic acid (RNA) and protein production.

• We did not observe the development of resistance.

Abstract

During the last decade multiple mumps outbreaks have occurred in the U.S. despite high two dose MMR coverage with most cases detected among two dose MMR vaccine recipients. Waning immunity, the evolution of wild-type virus strains, and settings with intense exposure have contributed to the resurgence of mumps. Typically, mumps virus infections resolve without serious clinical sequelae; however, serious complications may occur among unvaccinated or severely immunocompromised individuals. Favipiravir (T-705) has been shown to have in vitro anti-viral activity against a broad range of positive and negative strand RNA viruses. Here, we demonstrate that T-705 inhibits the growth of wildtype and vaccine strains of mumps virus in vitro at low micro-molar concentrations (EC₅₀ 8–10μM). We did not observe the development of resistance after five subsequent passages at low concentrations of drug. Both viral RNA and protein synthesis were selectively reduced compared to host mRNA and protein synthesis. Antiviral treatment options for mumps virus infection may be valuable, especially for areas with a high disease burden or for cases with severe complications. These results presented here suggest that further studies are warranted.

Introduction

Infection with mumps virus typically causes fever and swelling of the parotid salivary glands (parotitis). Additional complications may include orchitis, oophoritis, hearing loss, pancreatitis, myocarditis, meningitis or, rarely, encephalitis (Venkatesan and Murphy, 2018; MacRae and Varma, 2020). Following implementation of a routine two-dose vaccination schedule, annual mumps disease incidence in the U.S. dropped from >186,000 to <500 cases (Barskey et al., 2009). However, since 2006 there have been multiple outbreaks that have cumulatively affected >18,000 people, the majority of whom were two dose vaccine recipients (Marin et al., 2018). The two-dose effectiveness of MMR-II vaccine has been estimated to be approximately 88% for protection against mumps disease (McLean et al., 2010).

The immunologic basis for protection against symptomatic mumps disease and the reason for the mumps resurgence are not fully understood. Contributing factors may include waning immunity (LeBaron et al., 2009), ineffective antibody responses (Latner et al., 2017), antigenic differences between the vaccine and circulating wildtype strains (Rubin et al., 2008), high-density living and exposure settings (Barskey et al., 2009), and areas with sub optimal vaccine coverage (Hill et al., 2018). Importantly, even naturally acquired wildtype mumps virus infection does not necessarily provide life-long immunity in all individuals, as symptomatic re-infections are known to occur (Sakata et al., 2015).

Pharmacologic anti-viral treatment options for mumps virus infection may be of value for certain populations or special circumstances. For example, an effective anti-viral could potentially be used in cases of severe neurologic complications (Watanabe et al., 2013; Kanra et al., 2004). Mumps was a leading cause of viral meningitis in the U.S. prior to routine vaccination. Treatment may also provide benefit for individuals who are unable to be vaccinated for medical reasons. Treatment may be especially useful in countries where mumps vaccination is not routine or that have a high mumps disease burden, resulting in more frequent rates of serious complications (Griffith et al., 2018). Compounds that have shown antiviral activity against mumps virus include ribavirin (McCammon and Riesser, 1979), GS-5734 (Lo et al., 2017), and 4′-Azidocytidine (R1479) (Hotard et al., 2017). Favipiravir (T-705; 6-fluoro-3-hydroxy-2-pyrazinecarboxamide), has been reported to have antiviral activity against a growing list of viruses with positive or negative-sense RNA viruses (Delang et al., 2018). Among these viruses are members of the paramyxovirus family, including measles, human respirovirus 3 (formerly parainfluenza virus 3), respiratory syncytial virus, and human metapneumovirus (Jochmans et al., 2016). T-705 leads to C → U and G → A transition mutations following incorporation by virus encoded RNA-dependent RNA polymerases (RdRp) thus inhibiting accurate translation of mRNA and inducing lethal mutagenesis in the genome (Abdelnabi et al., 2017). It has been approved in Japan for treatment of infection with pandemic influenza virus, but use has been restricted due to concerns regarding the potential for teratogenicity (Delang et al., 2018). However, T-705 has been the subject of additional recent phase II and III clinical trials for treatment of influenza and Ebola virus infections (www.ClinicalTrials.Gov[w, 2019). Although results from the majority of these trials are still unpublished, clinical efficacy for treatment of Ebola infection in one report was encouraging, but not definitive, due to inherent limitations of the study design (Sissoko et al., 2016). Here, we examined the in vitro activity of favipiravir against mumps virus.