Brequinar Exerts Antiviral Effects Against Aquareovirus via Host Pyrimidine Metabolism Modulation.

Grass carp reovirus (GCRV) causes hemorrhagic disease in aquaculture, necessitating novel antivirals. Host-targeted broad-spectrum agents represent a promising approach. We evaluated Brequinar, a dihydroorotate dehydrogenase (DHODH) inhibitor in pyrimidine de novo synthesis, against GCRV in vitro and in vivo. In grass carp kidney (CIK) cells, Brequinar (0-50 μM) showed no cytotoxicity, dose-dependently alleviated cytopathic effect, reduced viral titers and suppressed VP5/VP7 expression. Antiviral efficacy was observed under pre-treatment, post-treatment and 48 h pre-treatment regimens, with post-infection administration showing stronger inhibition at moderate concentrations. In grass carp, Brequinar significantly reduced GCRV-II-induced mortality and tissue viral loads; post-infection dosing conferred better survival. Pharmacokinetic analysis demonstrated markedly greater systemic and tissue exposure following intraperitoneal administration than oral gavage, with peak concentrations reaching 1493.09 ng/mL in blood and 931.13 ng/mL in liver after intraperitoneal injection, compared with only 114.8 and 105.6 ng/mL, respectively, following oral administration. Transcriptomics demonstrated broad downregulation of pyrimidine metabolism genes, validated by sorbitol dehydrogenase (SORD) suppression. In a 30-day rare minnow model, Brequinar reduced viral loads after an initial rise, suggesting its potential application in reducing viral burden in virus-infected broodstock. Collectively, Brequinar exerts anti-GCRV activity by interfering with pyrimidine metabolism via DHODH inhibition and shows potential as a host-targeted antiviral strategy, with possible application in reducing viral burden in high-value broodstock in aquaculture.