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Inhibition of 3H-leukotriene D4 binding to guinea pig lung receptors by the novel leukotriene antagonist ICI 198,615

D Aharony, RC Falcone and RD Krell

Department of Pharmacology, Stuart Pharmaceuticals, Division of ICI American Inc., Wilmington, Delaware.

The specific binding of [3H]5(S)hydroxy-6(R)-S-cysteinylglycyl - 7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid ([3H]LTD4) to receptors on guinea pig lung parenchymal membranes and its inhibition by ICI 198,615, a representative example of a new class of leukotriene antagonists, was characterized by a receptor-ligand binding assay. [3H]LTD4 bound specifically and rapidly (Kon = 0.29 +/- 0.6 nM-1.min-1) reaching equilibrium within 15 min. The rate of binding was greatly inhibited in the presence of ICI 198,615. Excess LTD4 or ICI 198,615 slowly (t1/2 = 20 min) dissociated about 70% of the receptor-bound [3H]LTD4, whereas in combination with GTP analogs, both induced a rapid (t1/2 less than 5 min) and full dissociation. Equilibrium saturation analysis of [3H]LTD4 binding demonstrated a saturable (Bmax = 1014 +/- 174 fmol/mg) and high affinity (Kd = 0.43 +/- 0.09 nM) binding site. A high degree of stereoselectivity was demonstrated with inhibition of binding by the stereoisomers of LTD4: S,R much greater than R,R greater than R,S much greater than S,S. The rank order for inhibition of binding by peptide leukotriene was: LTD4 greater than 5(S)-hydroxy-6(R)- S-cysteinyl-7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid much greater than 5(S)hydroxy-6(R)-S-glutathionyl-7(E),9(E),11(Z),14(Z)- eicosatetraenoic acid (potency ratios were: 1:4:590). In competition assays, ICI 198,615 competitively inhibited binding of [3H]LTD4 (Ki = 0.27 +/- 0.16 nM) and was 2300-fold and 3100-fold more potent than LY171883 or FPL55712. These data, together with results obtained previously in functional receptor assays, illustrate that this new class of leukotriene antagonists are the most potent and selective competitive antagonists of LTD4 receptors yet described.

Volume 243, Issue 3, pp. 921-926, 12/01/1987
Copyright © 1987 by American Society for Pharmacology and Experimental Therapeutics






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Copyright © 1987 by the American Society for Pharmacology and Experimental Therapeutics.