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MK 287: a potent, specific, and orally active receptor antagonist of platelet-activating factor
S B Hwang1, M H Lam, D M Szalkowski
1Merck Sharp and Dohme Research Laboratories, Rahway, NJ 07065.
Abstract:
MK 287 (L-680,573), a tetrahydrofuran analog, potently inhibited [3H]C18-PAF binding to human platelet, polymorphonuclear leukocyte (PMN) and lung membranes with K1 values of 6.1 +/- 1.5, 3.2 +/- 0.7, and 5.49 +/- 2.3 nM, respectively. The inhibitory effects are stereospecific and competitive. The racemate, L-668,750 is less potent and the enantiomer, L-680,574 is 20-fold less potent than MK 287. Inhibition of the binding of [3H]C18-PAF to human PMN membranes by MK 287 was associated with the reduction of the affinity of the radioligand but not the number of the receptor sites. Binding of other radioligands (e.g., LTB4, LTC4, C5a, FMLP) to their specific receptors was unaltered at 1-10 microM MK 287. [3H]MK 287 bound to membranes from human platelets and PMNs: KD = 2.1 +/- 0.6 and 2.9 +/- 1.2 nM, respectively. When examined on isolated human cells, MK 287 potently and selectively inhibited PAF-induced aggregation of platelets in plasma (ED50 = 56 +/- 38 nM) or gel-filtered platelets (ED50 = 1.5 +/- 0.5 nM) and elastase release from PMNs (ED50 = 4.4 +/- 2.6 nM). In studies in vivo, MK 287 inhibited PAF-induced lethality in mice (ED50 = 0.8 mg/kg orally) and PAF-induced bronchoconstriction in guinea pigs (ED50 = 0.18 mg/kg intraduodenally and 0.19 mg/kg intravenously). Inhibition of PAF-induced bronchoconstriction was accompanied by parallel rightward shifts in concentration-response curves for PAF-induced platelet aggregation measured ex vivo.
Insights
MK 287, a potent tetrahydrofuran analog, effectively blocks platelet-activating factor (PAF) binding and inhibits PAF-induced responses. This compound shows promise in treating PAF-mediated conditions by selectively targeting PAF receptors.
Area of Science:
- Pharmacology
- Biochemistry
- Immunology
Background:
- Platelet-activating factor (PAF) is a potent lipid mediator involved in inflammatory and allergic responses.
- PAF receptors are implicated in various physiological and pathological processes, including platelet aggregation and leukocyte activation.
Purpose of the Study:
- To characterize MK 287 (L-680,573), a novel tetrahydrofuran analog, as a selective inhibitor of PAF.
- To evaluate the binding affinity, stereospecificity, and functional effects of MK 287 in vitro and in vivo.
Main Methods:
- Radioligand binding assays using [3H]C18-PAF and [3H]MK 287 to human platelet, polymorphonuclear leukocyte (PMN), and lung membranes.
- Functional assays measuring PAF-induced platelet aggregation and elastase release from PMNs.
- In vivo studies assessing PAF-induced lethality in mice and bronchoconstriction in guinea pigs.
Main Results:
- MK 287 demonstrated potent and stereospecific inhibition of [3H]C18-PAF binding to human platelet, PMN, and lung membranes (K1 values in nanomolar range).
- MK 287 selectively inhibited PAF-induced platelet aggregation and PMN elastase release in vitro.
- In vivo, MK 287 effectively inhibited PAF-induced lethality in mice and bronchoconstriction in guinea pigs.
Conclusions:
- MK 287 is a highly potent and selective PAF receptor antagonist.
- The findings suggest MK 287 has therapeutic potential for PAF-mediated inflammatory and allergic diseases.