alpha(v)beta(3) integrin binding affinity and specificity of SM256 in various species

This study was undertaken to define the alpha(v)beta(3) binding affinity an d specificity of the low-molecular-weight nonpeptide integrin antagonist, S M256. SM256 demonstrated high potency (IC50, 0.057 +/- 0.030 nM) in inhibit ing vitronectin binding to purified human alpha(v)beta(3) receptors. Additi onally, SM256 inhibited alpha(v)beta(3)-mediated human umbilical vein endot helial cell (HUVEC) or 293/beta 3 (beta 3-transfected cell line) adhesion t o fibrinogen with IC50 values of 0.0054 +/- 0.0058 and 0.0023 +/- 0.0012 mu M, respectively. SM256 demonstrated a relatively high degree of specificit y for human alpha(v)beta(3)-mediated functions as compared with other human integrins including alpha(v)beta(5) (IC50, 0.92 +/- 0.69 mu M), alpha(IIb) beta(3) (IC50, 0.72 +/- 0.07 mu M), alpha(4)/beta(1) (IC50, >100 mu M) and alpha(5)/beta(1) (IC50, 2.3 +/- 2.1 mu M). SM256 demonstrated different deg ree of species specificity in blocking alpha(v)beta(3)-mediated cellular ad hesion with relatively higher affinity to dog (IC50, 0.005 +/- 0.002 mu M), rabbit (IC50, 0.021 +/- 0.01 mu M), mouse (IC50, 0.035 +/- 0.01 mu M), and pig (IC50, 0.41 +/- 0.24 mu M) endothelial or smooth-muscle cell alpha(v)b eta(3)-mediated adhesion. Additionally, SM256 demonstrated high degree of a lpha(v)beta(3) specificity as compared with alpha(v)beta(5), alpha(5)beta(1 ), or alpha(IIb)beta(3)-mediated binding in these species. SM256 is a poten t alpha(v)beta(3) antagonist with high affinity and specificity for alpha(v )beta(3)-mediated functions. Additionally, a comparable alpha(v)beta(3) aff inity for SM256 was demonstrated with endothelial cells obtained from vario us species (dog, mouse, rabbit, and pig) as compared with that from human.