TNF-α antagonist is an exocyclic peptide that mimics the critical TNF-α recognition loop on TNF receptor I complex and, thus, prevents ligand interaction with the receptor. By blocking the TNF receptor ligand contact site, this peptide interferes with both activating receptor activator of NF-κB (RANK) and TNF-α's recruitment and activation of osteoclasts. TNF-α antagonist has been used to block bone resorption in the study of systemic bone loss in rheumatoid arthritis and inflammatory bone destruction.

NCI 126224, a toll-like receptor 4 (TLR4) antagonist, demonstrates selective inhibition of nitric oxide (NO) production in RAW 264.7 macrophages, triggered by the TLR4 agonist LPS (IC50 = 0.31 µM), as opposed to minimal effects on NO production induced by agonists for TLR7/8 (R-848), TLR1/2 (Pam3CSK4), and TLR3 (poly(I:C)). Nevertheless, it also effectively inhibits NO production initiated by the TLR2/6 agonist FSL-1 at an IC50 of 0.6 µM in the same cell line. Moreover, NCI 126224 suppresses LPS-induced NF-κB activity in BV-2 microglial cells and reduces LPS-triggered increases in IL-1β and TNF-α levels in RAW 264.7 macrophages with IC50 values of 5.92, 0.42, and 1.54 µM, respectively.

PMX-53, a macrocyclic complement 5a (C5a) peptidomimetic and C5a receptor antagonist (IC50 = 0.3 µM), effectively inhibits the C5a-induced secretion of myeloperoxidase (MPO) in isolated human polymorphonuclear leukocytes (PMNs). Administered orally at 10 mg/kg, PMX-53 mitigates vascular leakage, PMN infiltration, and the production of TNF-α and IL-6 in a rat peritoneal Arthus reaction model. Additionally, in a 3-nitropropionic acid (3-NP)-induced Huntington’s disease rat model, it alleviates body weight loss, anorexia, and striatal degeneration. Furthermore, at a dose of 3 mg/kg, PMX-53 decreases atherosclerotic lesion size and lipid content in ApoE-/- mice.