S100 calcium-binding protein A8 (MRP-8) (S100A8)

S100 calcium-binding protein A8 (S100A8), historically identified as Migration inhibitory factor-related protein-8 (MRP-8), is a low-molecular-weight alarmin and member of the S100 protein family [1, 7]. It is highly expressed in the cytosol of neutrophils and monocytes, where it modulates calcium signaling, cytoskeletal organization, and inflammatory cell activation [1, 8]. Under pathological conditions, S100A8 is released as a damage-associated molecular pattern (DAMP) and typically functions as a heterodimer with S100A9, forming the pro-inflammatory complex known as calprotectin [5, 14]. Extracellular S100A8 serves as an endogenous ligand for pattern recognition receptors, including Toll-like receptor 4 (TLR4) and the Receptor for Advanced Glycation End-products (RAGE), activating signaling cascades like NF-κB that drive the production of pro-inflammatory cytokines [2, 10, 15]. S100A8 is a critical mediator in diverse diseases, including rheumatoid arthritis, inflammatory bowel disease, and sepsis, and it is increasingly recognized for its role in promoting the cancer premetastatic niche and the recruitment of myeloid-derived suppressor cells [3, 9, 14]. Therapeutic targeting of S100A8 via neutralizing antibodies, specific inhibitory peptides, or small molecules like quinoline-3-carboxamides (e.g., tasquinimod) represents a promising strategy for treating chronic inflammation and cancer metastasis [2, 3, 11].

Other names

Migration inhibitory factor-related protein-8MRP-8Calgranulin-AMyeloid-related protein 8Cystic fibrosis antigenCFAGP8Protein S100-A8CAGA

Drugs targeting S100A8 primarily act by competitively inhibiting its binding to extracellular receptors, notably the TLR4/MD-2 complex and RAGE [2, 3]. Small molecule inhibitors such as tasquinimod and paquinimod bind to the S100A8/S100A9 complex, preventing receptor cross-linking and subsequent downstream signaling through the MyD88-dependent pathway [11, 14]. This inhibition reduces the secretion of pro-inflammatory cytokines like IL-6, IL-8, and TNF-α and prevents the accumulation of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment [1, 3, 9]. Research peptides like peptide3A5 also provide specific blockade of S100A8 homodimers or monomers, further attenuating the alarmin-driven inflammatory response [2, 3].