Targeting α4β1 integrin: from cyclic to linear ligands, effects of chemical modifications

The immune system depends on integrins for adhesion and migration during leukocyte trafficking and for intracellular signalling. There is a causal relationship between dysregulation of integrin expression and the onset of pathological conditions, such as autoimmune diseases, inflammation, cancer, and infections. Therefore, integrins, such as α₄β₁, are considered important therapeutic targets. In this study, a series of novel compounds were synthesized and evaluated for affinity and potency towards α₄β₁, and selectivity towards α₅β₁, and α_Mβ₂ integrins. Three compounds 3, 4, and 8 showed excellent binding affinities (K_i < 10 nM) for α₄β₁. In cell adhesion assays these three ligands behaved as antagonists of α₄β₁, as confirmed by integrin-mediated intracellular signalling with a functional selectivity over ERK1/2 signalling pathway. Notably, compound 4, a proline derivative, was an antagonist against α₄β₁ (IC₅₀ 15 ± 3 nM) and an agonist against α_Mβ₂ integrin (EC₅₀ 23 ± 5 nM). Compound 2, a fluorinated β-lactam derivative, was a selective and potent agonist of α₅β₁ (EC₅₀ 45.98 ± 7.92 nM). Compound 5, although it seems to bind to a different site compared to LDV in α₄β₁ integrin, showed an agonist behaviour in cell adhesion mediated by α₄β₁ and α₅β₁ integrin (EC₅₀ 25 ± 3 and 4.8 ± 3.4 nM, respectively) and in activating α₄β₁ integrin-mediated ERK1/2 and Akt phosphorylation. Compound 8 was the most potent agonist of the series against α_Mβ₂ (EC₅₀ 1.4 ± 0.2 nM). Overall, the present study provides new insights into the effects of new integrin ligands that could be considered as potential lead compounds for therapeutic applications in inflammatory diseases and cancer.