Researchers tested three lab-made chemicals that block a brain‑immune receptor called P2X7. They found that two of them work as expected against ATP, but none of them stop the peptide LL‑37 from turning the receptor on. This suggests that current P2X7 blockers might not stop all inflammation pathways linked to LL‑37.

Antagonists of the P2X7 receptor (P2X7R) have the potential to treat diseases where neuroinflammation is present such as depression, chronic pain and Alzheimer's disease. We recently developed a structural hybrid (C1; 1-((adamantan-1-yl)methyl)-2-cyano-3-(quinolin-5-yl)guanidine) of a purported competitive P2X7R antagonist (C2; 2-cyano-1-((1S)-1-phenylethyl)-3-(quinolin-5-yl)guanidine) and a likely negative allosteric modulator (NAM) of the P2X7R (C3; N-((adamantan-1-yl)methyl)-2-chloro-5-methoxybenzamide). Here we aimed to pharmacologically characterize C1, to gain insights into how select structural components impact antagonist interaction with the P2X7R. A second aim was to examine the role of the peptide LL-37, an apparent activator of the P2X7R, and compare the ability of multiple P2X7R antagonists to block its effects. Compounds 1, 2 and 3 were characterised using washout, Schild and receptor protection studies, all using dye uptake assays in HEK293 cells expressing the P2X7R. LL-37 was examined in the same HEK293 cells and THP-1 monocytes. Compounds 2 and 3 acted as a BzATP-competitive antagonist and NAM of the P2X7R respectively. Compound 1 was a slowly reversible NAM of the P2X7R suggesting the incorporation of an appropriately positioned adamantane promotes binding to the allosteric site of the P2X7R. LL-37 was shown to potentiate the ability of ATP to induce dye uptake at low concentrations (1-3 μg mL^-1) or induce dye uptake alone at higher concentrations (10-20 μg mL^-1). None of the P2X7R antagonists studied were able to block LL-37-induced dye uptake bringing in to question the ability of current P2X7R antagonists to inhibit the inflammatory action of LL-37 in vivo.