Electroactive monolayer substrates that selectively release adherent cells.

This communication describes a dynamic substrate that can selectively release immobilized ligands and hence can regulate, in real-time, the ligand ± receptor interactions between a cell and the substrate to which it is attached. The aim of this work is to provide model substrates for mechanistic studies of cell adhesion and migration. The adhesion of cells is mediated by the binding of cell-surface receptorsÐoften, the integrin family of receptorsÐto ligands of the insoluble protein matrix (also known as the extracellular matrix). In many cases, cells respond to changes in the composition of ligands presented within the matrix. Examples are found in the growth or differentiation of cells, and in tumor metastasis, where malignant cells migrate through the endothelial barrier. The development of dynamic substrates which can modulate the composition of ligands that interact with adherent cells would provide new opportunities for studying many important cellular processes. In this paper, we describe a chemical strategy to develop a dynamic substrate that can selectively release immobilized ligands under electrochemical control. Our approach is based on a self-assembled monolayer (SAM) of alkanethiolates on gold that presents peptide ligands tethered to the monolayer through an electroactive quinone ester moiety (Scheme 1 B). The quinone ester undergoes a twoelectron reduction on application of an electrical potential to the underlying gold substrate to give the corresponding hydroquinone, which then rapidly cyclizes to give a lactone with release of the peptide ligand. 5] We use as a model system, a monolayer that can release the tripeptide Arg-Gly-Asp (RGD). This peptide is a ligand found within many extracellular matrix proteins and which mediates cell adhesion through integrin receptors. With this system, the application of an electrical potential results in the release of RGD and, therefore, of cells that are attached to the monolayer. This model system has the benefits that the dynamic property can be easily visualized, and that it establishes the compatibility of the electroactive substrate with the conditions of cell culture. The tri(ethylene glycol) C.S. thanks the state Nordrhein-Westfalen for a Lise Meitner habilitation fellowship and A.J. the DFG for a habilitation fellowship (JA 963 1/1). The authors are very much indebted to R. Kamischke and Prof. A. Bennighoven for providing the TOF-SIMS images and to Prof. H.-J. Galla for his support.