Antiplatelet mechanism of 2-chloro-3-(4-hexylphenyl)amino-1,4-naphthoquinone (NQ304), an antithrombotic agent

Abstract

The effects of 2-chloro-3-(4-hexylphenyl)-amino-1,4-napthoquinone (NQ304), an antithrombotic agent, on aggregation, binding of fibrinogen to glycoprotein IIb/IIIa and intracellular signals were investigated using human platelets. NQ303 inhibited thrombin-, arachidonic acid- and thapsigargin-induced aggregation of washed human platelets with the IC50 values of 22.2 +/- 0.7, 6.5 +/- 0.2, and 7.6 +/- 0.1 muM, respectively. NQ304 significantly inhibited fluorescein isothiocyanate-conjugated fibrinogen binding to human platelet surface glycoprotein IIb/IIa receptor by 75%, but failed to inhibit the fibrinogen binding to purified glycoprotein IIb/IIIa receptor. This result suggests that NQ304 inhibit platelet aggregation by suppression of an intracellular pathway that involves exposure of the glycoprotein IIb/IIIa receptor, rather than by direct inhibition of fibrinogen-glycoprotein IIb/IIa binding. NQ304 significantly inhibited thrombin-induced increase in intracellular Ca2+ mobilization at the dose of 30 muM and ATP secretion in a dose-dependent manner, it also inhibited thrombin- and arachidonic acid-induced thromboxane A? formation in human platelet dose-dependently. In conclusion, the antiplatelet mechanism of NQ304 may be due to the reduction of the thromboxane A(2) formation, inhibition of adenosine triphosphate release and intracellular calcium mobilization.