Targeting the human protein disulfide isomerase A3 as a broad-spectrum antiviral approach against human respiratory viruses

Objectives: The recent emergence of new respiratory virus infections in humans with epidemic or pandemic potential has reiterated the urgent need for effective broad-spectrum antivirals (BSAs) as part of a strategic framework for preventing and preparing pandemics. The cellular machinery involved in the maturation of Viral Proteins in the endoplasmic reticulum (ER) can be considered in the search for host-targeting agents (HTAs) with potential BSA activity. In this context, human protein disulfide isomerase A3 (PDIA3) catalyzes the formation and isomerization of disulfide bonds in the ER pathway specific for folding N-glycosylated proteins. Here, we investigated the feasibility of pharmacological targeting of PDIA3 to identify BSAs against respiratory viruses.

Methods: The relevance of PDIA3 in viral infections was evaluated using siRNA knockdown. A disulfide bond assay was used to evaluate the content of disulfide bridges in viral glycoproteins.

Results: LOC14, a small molecule prototype PDIA3 inhibitor, exhibited Antiviral activity in the sub-micromolar range against a panel of representative human respiratory viruses, including the coronaviruses hCoV-OC43 and hCoV-229E, clinical isolates of influenza A and B viruses, and respiratory syncytial virus (RSV), even in a primary human airway epithelial cell model. Using hCoV-OC43 as a model respiratory virus with envelope N-linked glycoproteins to confirm the mechanistic mode of action, LOC14 was observed to affect the folding of the spike glycoprotein by reducing the formation of disulfide bonds, thereby hampering the production of infectious viral particles.

Conclusions: These findings validate PDIA3 as a target for developing HTAs with BSA activity against respiratory virus infections.

Broad-Spectrum Antivirals; Envelope glycoproteins; Host-Targeting Agents; Human respiratory viruses; LOC14; Protein Disulfide Isomerase A3.