Developing Synthetic Cell Targeting System

Robey, F

Abstract

The goals of the work performed for this project are the syntheses and uses of new biologically active materials that specifically interact with cell surface receptors and to use the newly designed materials for a variety of functions that include drug and gene delivery, vaccines and substrata for implant materials. New assay systems have to be developed and much of the work effort for this project includes new methods development. The primary focus of the work is not in the methods development but in the uses of the new materials in defined biological systems. In addition, much of the work effort emphasizes structure-function relationships. To make a targeted anti-viral vaccine, the knowledge of what components on the virus' surface bind to the cells receptor is necessary. When that information is not available as is the case for gp120 of HIV-1, we construct materials based on theoretical considerations. We have focussed on three proteins: serum amyloid P component (SAP), bone sialoprotein (BSP) and CD4, the cell surface receptor for HIV-1. All three proteins are known to be involved in the interactions of extracellular components having nonspecific characteristics. SAP is known to be involved in binding sulfated polysaccharides and active subunits derived from the parent SAP may find a use in the receptor clustering experiments we are performing to get active genetic materials into a cell. We previously found that a synthetic peptide from SAP can support the attachment of many cell types to polystyrene surfaces by binding to cell surface sulfated polysaccharides. We now have identified two peptides from native SAP that bind heparin. The peptides are formed by digesting native SAP with cathepsin D. BSP, in addition to being involved in cell adhesion through an integrin, is a highly phosphorylated protein that probably plays a role in mineralization of bone. That certain integrins have been implicated in relocation of metastasizing cancer cells implied that the cyclic RGD motif in BSP can block the adhesion of breast cancer cells to bone cells in culture. CD4, in addition to binding strongly and specifically to gp120 of HIV-1 interacts closely with the beta chain of MHC Class II and in this role, CD4 allows the cells to function in a helper role during certain events in which the immune system is activated. It is unknown if the gp120 binding part of CD4 is actually used in the everyday activities of CD4 or if, through some chance, CD4 simply has a region on its surface that is specifically recognized by gp120. We now can inhibit the binding of gp120 to CD4 with conformationally constrained peptides and peptomers that have been constructed.