Small molecule antagonists of alpha4 integrins: novel drugs for asthma

The alpha4 integrins, alpha4beta1 (VLA-4) and alpha4beta7, are heterodimeric cell-surface proteins expressed on leukocytes involved in both cell-cell and cell-matrix interactions. These two integrins are key regulators of physiologic and pathologic responses in inflammation and autoimmune disease. In particular, their central role in animal models of allergic lung disease has been well documented, and suggests a key role in human asthma. In addition, integrins are proven valid targets for small molecule drugs, following the development of both parenteral and orally active antagonists of platelet integrin alphaIIbbeta3, and more recently, integrin alphaVbeta3. Therefore, there is a significant drive to develop small molecule inhibitors of alpha4 integrins for autoimmune diseases in general, and asthma in particular. The biology of alpha4 integrins in asthma has been recently reviewed, as has early work on the chemistry of alpha4 integrin antagonists. Here we summarise the recent rapid advances in this arena, particularly in the chemistry of alpha4 integrin small molecule antagonists, with emphasis on asthma as a clinical target.