Unraveling the Potential Antiviral Activity of Isoxazoline-Carbocyclic Monophosphate Nucleotides Against Echovirus 11

From July 2022, a novel Echovirus 11 (E11) variant has been associated with severe neonatal
infections and liver failure. Currently, there are no vaccines or antiviral options for the
targeted treatment of non-polio enterovirus (EV) infections; therefore, anti-EV drugs are
urgently needed. In this study, the putative anti-E11 activity of two isoxzoline-carbocyclic
monophosphate nucleotides (4a and 4b) was evaluated in vitro by cytopathic effect (CPE)
reduction in VERO 76 cells and qRT-PCR. Treatment with nucleotide 4a at 25 and 50 μM
successfully diminished the CPE caused by E11 by 90% and 75%, respectively, and induced
a reduction in viral RNA in the supernatant by 72% and 89%. In contrast, the treatment
with 25 and 50 μM of 4b caused a minor inhibition of CPE (58 and 38%), and no significant
E11 RNA level changes were observed. A time course viral progeny production assay
was performed to assess the inhibitory effect of nucleotide 4a on E11 infection progression.
Compared to the control, the treated group showed a significant drop in viral RNA levels,
with reductions of 43% at 10 h, 65% at 24 h, and 96% at 48 h post-infection. The results
showed the extensive antiviral properties of the monophosphate nucleotide 4a in vitro.
Moreover, a retrospective molecular docking study strongly supports that nucleotide 4a
is an RdRp inhibitor capable of decreasing E11 genome replication and virus particle
formation in VERO 76 cells.