Inhibitory effect of ONO-1078 on specific binding of peptide leukotrienes to human lung crude membrane

Abstract

We investigated the effects of ONO-1078, a newly synthesized peptide leukotriene (p-LT) antagonist, on the specific binding of radiolabelled [ 3H]-LTC 4, [ 3H]-LTD 4 and [ 3H]-LTE 4 to a human lung crude membrane fraction (HLMF). The binding assay was performed under conditions in which [ 3H]-LTC 4 and [ 3H]-LTD 4 were not metabolized by HLMF; that is, the metabolism of LTC 4 to LTD 4 or LTE 4 was almost completely prevented by pretreating HLMF with 5 mM acivicin at 37°C for 180 min, and metabolism of LTD 4 to LTE 4 was inhibited by including 5 mM l-cysteine and 5 mM glycine in the assay. [ 3H]-LTD 4 specific binding was potently and concentration-dependently dissociated by ONO-1078. Its potency was 180-fold stronger than that of FPL 55712, a standardized p-LT antagonist, whereas high concentrations of ONO-1078 similar to those of FPL 55712 were required to inhibit [ 3H]-LTC 4 specific binding. The rank order of the inhibitory potencies of p-LT agonists and antagonists for [ 3H]-LTD 4 specific binding was LTD 4 > ONO-1078 > LTE 4 > LTC 4 > FPL 55712. On the other hand, not only high concentrations of ONO-1078 and FPL 55712 but also more than a 100-fold excess of unlabelled LTE 4 was required to inhibit [ 3H]-LTE 4 specific binding, indicating that the binding sites do not appear to be receptors of LTE 4. From these results, it is suggested that ONO-1078 is a highly potent LTD 4 antagonist which is expected to be very effective on bronchial asthma.