The Adenosine Analogue NITD008 has Potent Antiviral Activity against Human and Animal Caliciviruses

Abstract

The widespread nature of calicivirus infections globally has a substantial impact on the health and well-being of humans and animals alike. Currently, the only vaccines approved against caliciviruses are for feline and rabbit-specific members of this group, and thus there is a growing effort towards the development of broad-spectrum antivirals for calicivirus infections. In this study, we evaluated the antiviral activity of the adenosine analogue NITD008 in vitro using three calicivirus model systems namely; feline calicivirus (FCV), murine norovirus (MNV), and the human norovirus replicon. We show that the nucleoside analogue (NA), NITD008, has limited toxicity and inhibits calicivirus replication in all three model systems with EC50 values of 0.94 μM, 0.91 µM, and 0.21 µM for MNV, FCV, and the Norwalk replicon, respectively. NITD008 has a similar level of potency to the most well-studied NA 2′-C-methylcytidine in vitro. Significantly, we also show that continual NITD008 treatment effectively cleared the Norwalk replicon from cells and treatment with 5 µM NITD008 was sufficient to completely prevent rebound. Given the potency displayed by NITD008 against several caliciviruses, we propose that this compound should be interrogated further to assess its effectiveness in vivo. In summary, we have added a potent NA to the current suite of antiviral compounds and provide a NA scaffold that could be further modified for therapeutic use against calicivirus infections.

Feline Calicivirus Virulent Systemic Disease: Clinical Epidemiology, Analysis of Viral Isolates and in vitro Efficacy of Novel Antivirals in Australian Outbreaks

“…Accordingly, we investigated the in vitro efficacy of three antiviral compounds (NTZ, 2CMC, NITD-008) against representative strains of FCV-VSD. These molecules have demonstrated antiviral activity against the F9 vaccine strain with EC50s values in the low micromolar range [15], and showed dose-response inhibition against the replication of FCV-VSD strains at low micromolar concentrations. Nucleoside analogues, 2CMC and NITD-008, inhibit the viral RNA-dependent RNA polymerase.…”

“…4). NTZ showed a half maximal cytotoxic concentration (CC50) value of 12.7 µM, whilst 2CMC and NITD-008 demonstrated CC50 values of >100 µM [14,15]. Therefore, using the higher EC50 values obtained for each compound, the therapeutic index (TI = CC 50 /EC 50 ) values determined for NTZ, 2CMC and NITD-008 were 21, >18 and >111, respectively (Figure 3).…”

“…As vaccination does not fully protect against FCV-VSD there is interest in developing antivirals for use in the face of outbreaks. Three antiviral drugs (nitazoxanide, 2'-C-methylcytidine and NITD-008) have recently been shown to have efficacy against the FCV-F9 prototype vaccine strain but they have not yet been tested against viruses isolated from FCV-VSD outbreaks [14], [15].…”

Nitazoxanide protects cats from feline calicivirus infection and acts synergistically with mizoribine in vitro

“…NITD008, fexaramine and 2CMC are also candidate drugs to treat FCV infection. NTZ and 2CMC have been shown to have synergistic anti-FCV activity, and have been used to treat FCV-infected cats (Enosi Tuipulotu et al, 2019;Fumian et al, 2018;Kim and Chang, 2018). MZR has been shown to have antiviral activity against caprine alpha herpes virus 1 (CpHV-1), but it had not been determined whether it also has activity against FCV (Camero et al, 2017).…”

Current and Future Antiviral Strategies to Tackle Gastrointestinal Viral Infections

“…Jin et al showed that 2CMC triphosphate (2CMC-TP) inhibited the viral polymerases by competing directly with natural CTP during primer elongation, therefore acting as a classic chain terminator [ 139 ]. 7-deaza-2′ -C- methyladenosine (7DMA) and NITD008 are adenosine analogues that were initially developed as an inhibitor of HCV and dengue virus replication, respectively, but also possess anti-NoV activity [ 40 , 140 ].…”