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Synthetic Vß3 Antagonists Inhibit Insulin-Like Growth Factor-I-Stimulated Smooth Muscle Cell Migration and Replication¹

Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599; and Monsanto/Searle Discovery Research, Chesterfield, Missouri 63198

Address all correspondence and requests for reprints to: David R. Clemmons, M.D., Division of Endocrinology, University of North Carolina School of Medicine, CB No. 7170, Chapel Hill, North Carolina 27599-7170. E-mail: dpm{at}med.unc.edu

Porcine aortic smooth cells respond to insulin-like growth factor-I (IGF-I) with increases in DNA synthesis and cell migration. Because ligand occupancy of the Vß3 integrin has been shown to be necessary for IGF-I to stimulate maximal increases in both processes, we determined whether synthetic Vß3 antagonists could inhibit IGF-I-stimulated actions on this cell type. Low-molecular-weight compounds that had been selected based on their ability to compete with vitronectin for binding to purified human Vß3 in vitro were analyzed for their ability to compete with ¹²⁵I-kistrin (a known ligand for porcine Vß3) for binding to porcine Vß3. Nine compounds were screened, and five were found to be potent competitive inhibitors. The most potent compound, SC-69000, resulted in 88% competition at 10^-7 M and was nearly equipotent with echistatin. The compounds that were the most potent inhibitors of kistrin binding were tested for their capacity to inhibit the cell migration response to IGF-I. Three compounds caused between 81–88% inhibition of IGF-I-stimulated migration at 10^-7 M. To determine whether these compounds could inhibit other IGF-I-stimulated actions, their ability to inhibit IGF-I-stimulated [³H]-thymidine incorporation into DNA was analyzed. The four compounds that were the most potent inhibitors of cell migration also inhibited IGF-I-stimulated DNA replication. IGF-I stimulates the synthesis of IGF binding protein-5 by these cells. Preincubation with the four most active compounds also resulted in significant inhibition of the ability of IGF-I to stimulate IGF binding protein-5 synthesis. Vß3 occupancy by the ligand vitronectin has been shown to enhance the capacity of IGF-I to activate its receptor tyrosine kinase. The four most active compounds were shown to inhibit IGF-I-stimulated IGF-I receptor autophosphorylation. These findings suggest that blockade of ligand occupancy of the Vß3 integrin globally inhibits several IGF-I-stimulated biologic actions and that synthetic inhibitors are very active in this regard. Because these compounds can be administered to whole animals, they should be very useful in determining whether blocking Vß₃ occupancy in vivo results in alteration in responsiveness to IGF-I.

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