Mechanism of Action of a Prostaglandin E₂Receptor Antagonist with antimicrobial activity againstStaphylococcus aureus

AbstractOur laboratory recently reported that the EP4receptor antagonist, L-161,982, had direct growth-inhibitory effects onStaphylococcus aureus in vitroand in vivo, reducing microbial burden and providing significant protection against lethality in models ofS. aureusmonomicrobial and polymicrobial intra-abdominal infection. This antimicrobial activity was observed with both methicillin-sensitive and methicillin-resistantS. aureus(MRSA), as well as other Gram-positive bacteria. The antimicrobial activity of L-161,982 was independent of EP4receptor inhibitory activity. In this study, we investigated the mechanism of action (MOA) of L-161,982, which contains a sulfonamide functional group. However, results demonstrate L-161,982 does not affect folate synthesis (sulfonamide MOA), oxidative stress, or membrane permeability. Instead, our results suggest that the inhibitor works via effects on inhibition of the electron transport chain (ETC). Similar to other ETC inhibitors, L-161,982 exposure results in a small colony size variant phenotype and inhibition of pigmentation, as well as significantly reduced hemolytic activity, and ATP production. In addition, L-161,982 potentiated the antimicrobial activity of another ETC inhibitor and inhibition was partially rescued by supplementation with nutrients required for ETC auxotrophs. Taken together, these findings demonstrate that L-161,982 exerts antimicrobial activity against MRSA via inhibition the ETC, representing a new member of a potentially novel antimicrobial drug class.