Neutrophil granulocytes play an important role in regulating and fine-tuning inflammatory reactions. FPRs can recognize danger signals during microbial infections, inflammation, cancer, and tissue injury.
In general, FPR recognizes formyl peptides, it also can recognize some small compounds and lipopeptides.

Today, we will introduce a first-in-class, potent and selective and agonist of formyl peptide receptor type 2 (FPR2)/Lipoxin A4 receptor (ALX), ACT-389949.

In neutrophils, ACT-389949 (10 nM) can induce a transient rise in [Ca²⁺]_i  at a low concentration, at the same time, another FPR2 selective peptide agonist WKYMVM erects similar result.

Most researchers have demonstrated that FPR agonists can activate the PLC-PIP2-IP3 signaling route, and then IP3 triggers a release of Ca²⁺ from intracellular stores. This signal pathway is independent of the extracellular concentration of Ca²⁺.Since EGTA (ca²⁺ chelator; 2.5  mM) has no effects on ACT-389949-activated [Ca²⁺]_i  rise, ACT-389949 activity is dependent on a release of Ca²⁺ from intracellular stores.
Furthermore, to determine the precise receptor preference of ACT-389949. researchers determine two selective antagonists, Cyclosporin H (FPR2 specific antagonist) and PBP10 (FPR2 specific antagonist). PBP10 (1 µM) rather than Cyclosporin H can completely inhibit ACT-389949 activity, therefore, ACT-389949 is selective for FPR2.
Nextly, researchers investigate the ability of ACT-389949 to induce the release of NADPH-oxidase generated superoxide anions.

ACT-389949 (100 nM) induces neutrophil respiratory burst responses. It triggers a rapid increase of superoxide release after around one minute. Besides, comparing with WKYMVM (EC₅₀=40 nM), ACT-389949 induces the respiratory burst with an EC₅₀ value of 10 nM.

Agonist binding can induce the recruitment of cytosolic β-arrestin, it plays an important role in subsequent receptor desensitization and internalization.

Some FPR2 agonist lacks the ability to recruit β-arrestin 2 and to trigger chemotaxis. But ACT-389949 can trigger β-arrestin 2 recruitment in cells expressing FPR2. ACT-389949 induces this kind of recruitment with an EC₅₀ of 20 nM and reaches maximum response at 100 nM. Meanwhile, ACT-389949 has no effect on β-arrestin recruitment in FPR1 expressing cells.

In conclusion, in this article, the researchers provide certain molecular insights into ACT-389949 induced FPR2 signaling and activation in human neutrophils.
A has the potential to be a valuable research tool for mechanistic studies as a selective and potent FPR2 agonist.

reference:

Lind S, et al. Biochem Pharmacol. 2019 Aug;166:163-173.