Host oxidative folding pathways offer novel anti-chikungunya virus drug targets with broad spectrum potential

- Alphaviruses feature multiple disulfide bonds in their envelope proteins.
- Several endoplasmic reticulum proteins-PDI, TRX-R, and ERO-1- participate in disulfide bond formation and isomerization.
- The TRX-R inhibitor auranofin inhibited chikungunya virus replication in vitro and reduced morbidity in a murine model.
- Protein disulfide isomerase and ERO-1 inhibitors reduced replication in vitro, but with notable toxicity.
- 16F16 and auranofin also impacted Venezuelan equine encephalitis and Zika virus replication in vitro, but with toxicity.

Alphaviruses require conserved cysteine residues for proper folding and assembly of the E1 and E2 envelope glycoproteins, and likely depend on host protein disulfide isomerase-family enzymes (PDI) to aid in facilitating disulfide bond formation and isomerization in these proteins. Here, we show that in human HEK293 cells, commercially available inhibitors of PDI or modulators thereof (thioredoxin reductase, TRX-R; endoplasmic reticulum oxidoreductin-1, ERO-1) inhibit the replication of CHIKV chikungunya virus (CHIKV) in vitro in a dose-dependent manner. Further, the TRX-R inhibitor auranofin inhibited Venezuelan equine encephalitis virus and the flavivirus Zika virus replication in vitro, while PDI inhibitor 16F16 reduced replication but demonstrated notable toxicity. 16F16 significantly altered the viral genome: plaque-forming unit (PFU) ratio of CHIKV in vitro without affecting relative intracellular viral RNA quantities and inhibited CHIKV E1-induced cell-cell fusion, suggesting that PDI inhibitors alter progeny virion infectivity through altered envelope function. Auranofin also increased the extracellular genome:PFU ratio but decreased the amount of intracellular CHIKV RNA, suggesting an alternative mechanism of action. Finally, auranofin reduced footpad swelling and viremia in the C57BL/6 murine model of CHIKV infection. Our results suggest that targeting oxidative folding pathways represents a potential new anti-alphavirus therapeutic strategy.