Pharmacological evidence for complex and multiple site interaction of CXCR4 with SDF-1 alpha: implications for development of selective CXCR4 antagonists

The C-X-C chemokine SDF-1 and its receptor CXCR4, mediate a pivotal role in the pathophysiology of HIV-1 infection and vascular inflammatory diseases. in this study, we investigated the pharmacological properties of SDF-1 alp ha interaction with CXCR4 in human leukemia cell lines. Our data, based on [I-125]-SDF-1 alpha radioligand binding, SDF-1 alpha -induced [S-35]-GTP ga mmaS binding and use of specific CXCR4 antagonist AMD3100 reveals the compl ex nature of SDF-1 alpha -CXCR4 interaction. Firstly, homologous competitio n with cold SDF-1 alpha revealed a bimodal ligand displacement curve and se condly, although AMD3100 inhibited both SDF-1 alpha -mediated chemotaxis (I C50=4.7 nM) and [S-35]-GTP gammaS binding (IC50=7.4 nM) with high affinity, it was intriguingly upto 3000-fold less potent (IC50 = 15.2 muM) in the ra dioligand binding assay. These results provide pharmacological evidence for the recently described two-site model for SDF-1 alpha -CXCR4 interaction. Accordingly, inhibition of SDF-l alpha binding to one of the receptor sites is sufficient to antagonize function, without causing its complete displac ement from the receptor. Furthermore, these findings have important implica tions in the development and evaluation or CXCR4-selective small molecule a ntagonists for therapeutic use. (C) 2001 Elsevier Science B.V. All rights r eserved.