Interleukin-8 antagonists generated by N-terminal modification.

We have previously shown that the residues Glu4-Leu5-Arg6 (ELR) preceding the first cysteine at the N terminus of the 72-residue form of interleukin-8 (IL-8) are essential for receptor binding and neutrophil activation (Clark-Lewis, I., Schumacher, C., Baggiolini, M., and Moser, B. (1991) J. Biol. Chem. 266, 23128-23134). We have now synthesized a series of analogs of IL-8(4-72), the truncated form of IL-8 with the N-terminal sequence ELRC, as potential IL-8 antagonists. Among 26 analogs with deletions or amino acid replacements in the ELR region several inhibited IL-8 function. The most potent were IL-8(6-72), with Arg6 at the N terminus, and IL-8,AAR(7-72) with N-terminal Ala4-Ala5 instead of Glu4-Leu5. They inhibited IL-8 receptor binding, exocytosis (IC50 0.3 microM), as well as chemotaxis and the respiratory burst. Inhibition was restricted to responses elicited by IL-8, GRO alpha, or NAP-2, and no effect was observed when the unrelated agonists fMet-Leu-Phe or C5a were used as stimuli. These results demonstrate that selective antagonists that prevent or attenuate the action of IL-8 and its related chemotactic cytokines are obtained by modification of the ELR sequence at the N terminus.