101 compounds significantly decreased adhesion (50% inhibition) of K562 CD11b/CD18 cells to immobilized Fg in the presence of agonist Mn2+ions in duplicate wells and were identified as main positives from this screen (hit-rate of <1%). CD11d), which with each other form four unique receptors. The 2 2 integrin CD11b/CD18 (also known as complement receptor type 3 (CR3), Mac-1 and M2) is definitely primarily indicated on neutrophils, macrophages and monocytes, is critical for the normal function of these cells and plays an important part in the development of inflammatory response [2;3;4]. Integrin CD11b/CD18 recognizes a wide variety of physiologic ligands, including Fibrinogen (Fg), the complement fragment iC3b and CD54 (ICAM-1). Binding of integrin CD11b/CD18 H-1152 to its ligands is dependent on divalent cations and is tightly regulatedin vivo. Integrin CD11b/CD18 is definitely expressed inside a low-affinity, inactive conformation in circulating leukocytes, but is definitely H-1152 rapidly upregulated on cell surface and triggered to high-affinity, active conformation on a sub-second timescale [5]. A loss of practical 2 integrins in humans leads to leukocyte adhesion deficiency type 1, where circulating neutrophils fail to abide by or migrate across the endothelium and the individuals are susceptible to recurrent, life-threatening bacterial infections [2;3;4]. Conversely, improper excessive activation of leukocyte integrins is also harmful, which contributes to sustained swelling, ischemia-reperfusion injury [1;2], tissue damage [6], stroke [7], neointimal thickening in response to vascular injury [8] and the development of various autoimmune diseases [9], making it an important therapeutic target [10]. Indeed, obstructing antibodies that prevent cell adhesion have been effective in animal models of a number of inflammatory diseases [11;12]. However, the humanized antiintegrin obstructing antibodies failed to show much benefit in a number of clinical studies [13]. Additionally, adverse effects due to the nonselective blockade of various other leukocyte functions by mAbs further complicates their use as a restorative agent [14]. Similarly, ligand mimics, such as recombinant glycoprotein neutrophil inhibitory element (NIF) while effective in animals, was clinically ineffective in a phase II trial and was left behind [15]. Recombinant proteins, such as the ligand-binding A-domain (also known as I-domain) of CD11b that act as competitive Rabbit polyclonal to baxprotein antagonists have shown encouraging results in animals, but have yet to be tested in human studies [16]. Competitive ligandmimetic peptides derived either from CD11b/CD18 ligands or anti-CD11b/CD18 mAbs were reported to be ineffective in H-1152 obstructing ligand bindingin vitro[17]. Therefore, integrin CD11b/CD18 selective small molecules may be more encouraging restorative agents, especially compounds that target allosteric regulatory sites, such as the hydrophobic pocket known as site-for-isoleucine (SILEN) in CD11b/CD18 [18] (termed lovastatin binding site (L-site) [19] or I website allosteric site (IDAS) [20] in related integrin CD11a/CD18). In fact, several small molecule antagonists focusing on IDAS in integrin CD11a/CD18 have been reported (examined in [21]). Although a number of integrin CD11a/CD18 antagonists cross-react with integrin CD11b/CD18 and prevent its function, there are very few reports of antagonists focusing on integrin CD11b/CD18 [22], primarily due to the lack of good high-throughput testing (HTS) assays with integrin CD11b/CD18. We recently described a novel cell-adhesion based HTS assay using the 384-well plate format that is ideal for the finding of small molecule integrin CD11b/CD18 antagonists [23]. With this communication, we describe the finding of several novel small molecule antagonists of integrin CD11b/CD18 using a modification of this HTS assay. Many of the newly identified compounds show high potency (IC50of <1M). The compounds show little structural similarity to known integrin CD11a/CD18 antagonists. Using chemical clustering analyses, we also recognized potential.