Biological and transductional effects of allosteric antagonists on the activity of chemoattractant receptors

There are two major chemokine receptors expressed on the surface of neutrophils, CXCR1 and CXCR2.It is thought that targeting both receptors may be necessary for optimal inhibition of PMN influx in several inflammation disorders such as post-ischemia reperfusion injury, pulmonary fibrosis, sepsis, psoriasis among other.
DF 2156A is a potent dual inhibitor of CXCR1 and CXCR2 and was derived from a specific lead optimization program (Moriconi et al., 2007). Because it blocks both CXCR1 and CXCR2, it may overcome the problem of redundancy generated by the ELR+ CXC chemokine-CXCR1/R2 axis. The present study demonstrated, that DF 2156A is a potent blocker of both CXCR1 and CXCR2 expressed on PMNs, lymphocytes, and cells transfectants with a IC50 in the range of 1 to 2 nM. Despite its potency on both CXCL8 receptors, the effect of DF 2156A was highly specific. DF 2156A did not affect the activity of several related chemokine receptor belonging to both CC and CXC subfamilies. Our evidences show that DF 2156A is able to block different signaling pathway activated by CXCL8. Here we describe the molecular mechanism exerted by this compound. In particular it unaffected CXCL8- induced both receptors internalization but also both receptors recycling to the cell membrane after CXCL removal, indicating that it does not interfere more in general with the trafficking of both CXCL8 receptors. By contrats DF 2156A significantly suppressed CXCL8- induced cofilin phosphorylation and subsequent failure of CXCR1/R2 cells to migrate in response to CXCL8. Cofilin is protein that is postulated regulates cell migration and chemotaxis, in chemokine responses.
This model of concerted type of allosteric antagonists raises the possibility to stabilize slightly different active receptor conformations, which might interact preferentially with distinct tranducer molecules or signaling pathway. Moreover, this class of antagonists would offer untapped advantages for drug development programs.