αvβ3 Integrin Binding Affinity and Specificity of SM256 in Various Species

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Abstract
This study was undertaken to define the αvβ3 binding affinity and specificity of the low-molecular-weight nonpeptide integrin antagonist, SM256. SM256 demonstrated high potency (IC50, 0.057 ± 0.030 nM) in inhibiting vitronectin binding to purified human αvβ3 receptors. Additionally, SM256 inhibited αvβ3-mediated human umbilical vein endothelial cell (HUVEC) or 293/β3 (β3-transfected cell line) adhesion to fibrinogen with IC50 values of 0.0054 ± 0.0058 and 0.0023 ± 0.0012 μM, respectively. SM256 demonstrated a relatively high degree of specificity for human αvβ3-mediated functions as compared with other human integrins including αvβ5 (IC50, 0.92 ± 0.69 μM), αIIbβ3 (IC50, 0.72 ± 0.07 μM), α4/β1 (IC50, >100 μM) and α5/β1 (IC50, 2.3 ± 2.1 μM). SM256 demonstrated different degree of species specificity in blocking αvβ3-mediated cellular adhesion with relatively higher affinity to dog (IC50, 0.005 ± 0.002 μM), rabbit (IC50, 0.021 ± 0.01 μM), mouse (IC50, 0.035 ± 0.01 μM), and pig (IC50, 0.41 ± 0.24 μM) endothelial or smooth-muscle cell αvβ3-mediated adhesion. Additionally, SM256 demonstrated high degree of αvβ3 specificity as compared with αvβ5, α5β1, or αIIbβ3-mediated binding in these species. SM256 is a potent αvβ3 antagonist with high affinity and specificity for αvβ3-mediated functions. Additionally, a comparable αvβ3 affinity for SM256 was demonstrated with endothelial cells obtained from various species (dog, mouse, rabbit, and pig) as compared with that from human.