XJ-735

Several platelet alpha(IIb)beta(3) integrin antagonists have been designed as preventive agents against the formation of arterial thrombi. Although the potency of these compounds in inhibiting platelet aggregation is in the nanomolar range, their specificity on other integrins that can bind ligands through an arginine-glycine-aspartic acid (RGD) motif is far from being well established. For instance, some cyclic RGD peptides can also interact with alpha(v)beta(3) integrin. We used a novel pharmacological assay, based on SDS-stable interaction between (125)I-echistatin and RGD-dependent integrins, to evaluate the specificity of several RGD compounds on integrins present on rat cardiac fibroblasts and human skin fibroblasts. None of the RGD peptidomimetics tested (L-734,217, lamifiban, Ro 44-3888, SR 121566A, BIBU-52, XV459) could interact with either alpha(v)beta(3) and alpha(8)beta(1) on rat fibroblasts or with alpha(v)beta(3) and alpha(v)beta(1) on human fibroblasts. Cyclic RGD peptides showed some potency (3-80 microM) on rat and human integrins with an alpha(v) subunit. We also compared the potency of these compounds on platelets. All RGD compounds demonstrated IC(50) between 0.6 and 530 nM on basal human platelets. Activation of the receptor with thrombin resulted in a 2- to 60-fold increase in potency, with L-734,217 and BIBU-52 showing the largest difference. On basal and thrombin-activated rat platelets, only eptifibatide, DMP728, and XJ735 could displace (125)I-echistatin (IC(50) approximately 0.1-1.5 microM). These results indicate that RGD peptidomimetics have a specificity limited to alpha(IIb)beta(3) integrin, whereas cyclic RGD peptides can also interact with other RGD-dependent integrins, particularly those of the alpha(v) subunit family.

We hypothesized that cell-matrix adhesion, migration, and differentiation events that underlie restenosis are mediated by alpha v beta 3 integrin-ligand interactions.

Using immunohistochemistry and in situ hybridization, we examined the spatial and temporal vessel wall expression of alpha v beta 3 and osteopontin following deep coronary arterial injury. Cell migration and adhesion assays were performed to demonstrate the affinity and specificity of XJ 735 for various vessel wall integrins. The effects of XJ 735 (a selective cyclic Arg-Gly-Asp (RGD) peptidomimetic alpha v beta 3 antagonist) on neointimal hyperplasia and lumen stenosis were tested in a porcine coronary injury model. Normolipemic swine underwent oversized stent injury followed by XJ 735 administration (9 animals, 28 lesions; 1 mg/kg bolus + 7 days 4 mg/kg/d infusion + 21 days 2 mg/kg i.v. bolus 12 hourly) or placebo (10 animals, 30 arterial lesions).

Maximal alpha v beta 3 immunoreactivity was observed between 7-14 days following injury in the neointima, media, and adventitia. Maximal osteopontin mRNA signal in the neointima, media, and adventitia was observed at 14, 7 and 28 days respectively. IC50 for XJ 735 alpha v beta 3-mediated inhibition of human and porcine endothelial cell adhesion, and vascular smooth muscle cell migration, ranged from 0.6 to 4.4 microM. In contrast, IC50 for porcine or human alpha IIb/beta 3, alpha 4 beta 1, alpha v beta 5, and alpha 5 beta 1 inhibition exceeded 100 microM. Steady state XJ 735 plasma levels exceeded 5 microM. Despite slightly higher injury scores in XJ 735 treated animals, significant reductions in mean neointima area (43% reduction; p = 0.0009), and mean percent lumen stenosis (approximately 2.9 fold reduction; p = 0.04) were observed in XJ 735 treated animals. XJ 735 treatment did not significantly alter the relative size of the arterial injury and reference sites (geometric remodeling). Comparison of neontima area vs. injury score regression lines revealed significant reductions in slope (p = 0.0001) and intercept (p = 0.0001) for XJ 735.

Selective alpha v beta 3 blockade is an effective anti-restenosis strategy that potently limits neointimal growth and lumen stenosis following deep arterial injury. The co-ordinate spatial and temporal upregulation of alpha v beta 3 expression following vessel wall injury, and the high affinity and specificity of XJ 735 for alpha v beta 3, confirms the importance of this integrin in adhesive and migratory cell-matrix events underlying coronary restenosis.