SELECTIVE-INHIBITION OF N-FORMYLPEPTIDE-INDUCED NEUTROPHIL ACTIVATIONBY CARBAMATE-MODIFIED PEPTIDE ANALOGS

Stimulation Of the leukocyte N-formylpeptide receptor (FPR) induces ch emotaxis, cell adhesion, free radical release, and degranulation, resp onses associated with infection and inflammation. Under conditions whe re continuous activation of the receptor prevails, neutrophil-dependen t tissue damage ensues. Antagonists of the FPR have potential for use as diagnostic and therapeutic agents. Hence, we have synthesized and e valuated a series of amino-terminal carbamate analogues of the peptide Met-Leu-Phe (MLF) in order to determine the structural requirements f or imparting agonist or antagonist activity at the human neutrophil FP R, Peptides were evaluated in three in vitro assays: receptor binding, superoxide anion release, and cell adhesion. Unbranched carbamates (m ethoxycarbonyl, ethoxycarbonyl, and n-butyloxycarbonyl) resulted in ag onist activity, whereas branched carbamates (iso-butyloxycarbonyl, ter t-butyloxycarbonyl, and benzyloxycarbonyl) were antagonists. The pepti de antagonists were more potent inhibitors of superoxide anion release than cell adhesion by 4-7-fold. When iso-butyloxycarbonyl-MLF (i-Boc- MLF) was further modified at the carboxy terminus with Lys, antagonist potency was retained but without functional selectivity. Further C-te rminal modification with the radionuclide linker diethylenetriaminepen taacetic acid did not alter the potency of i-Boc-MLFK. These results i ndicate that the switch from agonist to antagonist activity can be ach ieved by modifying the overall size and shape of the aminoterminal gro up; that modifications at both the amino and carboxy termini can alter the functional selectivity of the peptide; and that modifications can be tolerated at the carboxy terminus to allow for development of an a ntagonist for diagnostic applications.