Small Molecule Agonist of Very Late Antigen-4 (VLA-4) Integrin Induces Progenitor Cell Adhesion

Activation of the integrin family of cell adhesion receptors on progenitor cells may be a viable approach to enhance the effects of stem cell-based therapies by improving cell retention and engraftment. Here, we describe the synthesis and characterization of the first small molecule agonist identified for the integrin alpha 4 beta 1 (also known as very late antigen-4 or VLA-4). The agonist, THI0019, was generated via two structural modifications to a previously identified alpha 4 beta 1 antagonist. THI0019 greatly enhanced the adhesion of cultured cell lines and primary progenitor cells to alpha 4 beta 1 ligands VCAM-1 and CS1 under both static and flow conditions. Furthermore, THI0019 facilitated the rolling and spreading of cells on VCAM-1 and the migration of cells toward SDF-1 alpha. Molecular modeling predicted that the compound binds at the alpha/beta subunit interface overlapping the ligand-binding site thus indicating that the compound must be displaced upon ligand binding. In support of this model, an analog of THI0019 modified to contain a photoreactive group was used to demonstrate that when cross-linked to the integrin, the compound behaves as an antagonist instead of an agonist. In addition, THI0019 showed cross-reactivity with the related integrin alpha 4 beta 7 as well as alpha 5 beta 1 and alpha L beta 2. When cross-linked to alpha L beta 2, the photoreactive analog of THI0019 remained an agonist, consistent with it binding at the alpha/beta subunit interface and not at the ligand-binding site in the inserted ("I") domain of the L subunit. Co-administering progenitor cells with a compound such as THI0019 may provide a mechanism for enhancing stem cell therapy.