Potential Therapeutic Agents for Feline Calicivirus Infection.

Tulio M Fumian,Peter A White,Grace J H Yan,Natalie E Netzler,Jennifer H Lun,Daniel Enosi Tuipulotu,Alice G Russo

doi:10.3390/v10080433

Abstract

Feline calicivirus (FCV) is a major cause of upper respiratory tract disease in cats, with widespread distribution in the feline population. Recently, virulent systemic diseases caused by FCV infection has been associated with mortality rates up to 50%. Currently, there are no direct-acting antivirals approved for the treatment of FCV infection. Here, we tested 15 compounds from different antiviral classes against FCV using in vitro protein and cell culture assays. After the expression of FCV protease-polymerase protein, we established two in vitro assays to assess the inhibitory activity of compounds directly against the FCV protease or polymerase. Using this recombinant enzyme, we identified quercetagetin and PPNDS as inhibitors of FCV polymerase activity (IC50 values of 2.8 μM and 2.7 μM, respectively). We also demonstrate the inhibition of FCV protease activity by GC376 (IC50 of 18 µM). Using cell culture assays, PPNDS, quercetagetin and GC376 did not display antivirals effects, however, we identified nitazoxanide and 2′-C-methylcytidine (2CMC) as potent inhibitors of FCV replication, with EC50 values in the low micromolar range (0.6 μM and 2.5 μM, respectively). In conclusion, we established two in vitro assays that will accelerate the research for FCV antivirals and can be used for the high-throughput screening of direct-acting antivirals.

Highlights

Feline caliciviruses (FCV) are members of the Caliciviridae family and a major pathogen of cats worldwide
To confirm the RNA-dependent RNA polymerase (RdRp) activity of the Pro-Pol dual protein, we tested it using an in vitro fluorescence-based transcription assay, where the double-stranded RNA (dsRNA) product was detected with PicoGreen dye [35]
The RdRp activity was reduced by 50% in the presence of 60 mM NaCl, and completely inhibited at 200 mM (Figure 1B)

Summary

Introduction

Feline caliciviruses (FCV) are members of the Caliciviridae family (genus Vesivirus) and a major pathogen of cats worldwide. The virus has been associated with vesicular and upper respiratory tract disease, especially in multi-cat environments, such as shelters, colonies, and catteries, where. FCV is detected in up to 40% of cats [1,2,3]. Highly contagious virulent strains of FCV have emerged and were linked with severe disease (FCV-associated virulent systemic disease (VSD)) and high mortality rates (up to 50%) [6,7,8]. After the first description of FCV-VSD in 2000, outbreaks have occurred in the USA and Europe, which were associated with genetically distinct virulent FCV strains that have evolved locally [8,9,10,11,12,13]. The severe disease has a marked tropism for endothelial and epithelial cells of the skin and parenchymal organs and adult cats are often more severely affected than kittens [14,15]

Methods

Results

Conclusion