APPROACH TO DISCOVERING NOVEL THERAPEUTIC AGENTS FOR OSTEOPOROSIS BASED ON INTEGRIN RECEPTOR BLOCKADE

On a global scale, osteoporosis is a major and growing public health p roblem. In the United States, osteoporosis is present in 24 million pe ople (mostly women) and contributes to more than 1.3 million fractures /year. Serious morbidity and mortality results from these fractures, C urrent therapies for osteoporosis are few, efficacy is limited, and si de effects problematic. Fundamental to the pathophysiology of osteopor osis is an imbalance between the tightly, coupled processes of bone re sorption and bone formation that characterize normal bone remodeling. Our laboratory is engaged in a research effort focused on elucidating the role of the osteoclast integrin in bone resorption, defining the n ature of ligand-integrin interactions, and developing antagonists for cell surface adhesion molecules, particularly the alpha(v) beta(3) vit ronectin-like integrin receptor, present on the surface of human osteo clasts. Peptides containing the internal arginine-glycine-aspartic aci d (RGD) motif have been shown to inhibit osteoclast-mediated bone reso rption in vivo. We are now designing more potent and selective inhibit ors of bone resorption as a potential new mechanism-based therapeutic approach to osteoporosis based on a novel mechanism. In an effort to r apidly identify the highest affinity ligand's for the human alpha(v) b eta(3) integrin, we have generated combinatorial peptide libraries con taining substantial structural diversity. For instance, based on all p ossible sequence combinations of extracellular matrix proteins known t o bind alpha(v) beta(3) we recently synthesized and chemically analyze d a library of 4360,000 peptides, all of which contain RGD. Human alph a(v) beta(3) receptors are now available in a clonal cell line that ex presses high levels of recombinant receptor, these cells can serve as a very important research tool in this project because of the limited number of bone-derived osteoclasts that can be harvested for experimen tation. The library of peptides will be screened by ''affinity selecti on '': the highest binding affinity peptide(s) will be isolated and mi crosequenced. Receptor-favored sequences will be synthesized and evalu ated in a battery of in vitro and in vivo bioassays. Through these inv estigations insight will be gained into the role of integrins in bone biology and pathophysiology, and new directions will be developed for the design of potent human alpha(v) beta(3)-selective antagonists for the treatment of osteoporosis. (C) 1995 John Wiley & Sons, Inc.