MK-383 (L-700,462), a selective nonpeptide platelet glycoprotein IIb/IIIa antagonist, is active in man

Background. Fibrinogen-dependent cross-linking of glycoprotein (GP) IIb/IIIa on activated platelets is the final mechanism leading to platelet aggregation. Inhibition of this mechanism may result in a novel antithrombotic agent. We studied the activity of MK-383 (L-700,462), a new, nonpeptide GPIIb/IIIa antagonist, in vitro and in vivo, in man. Methods and Results. MK-383, a nonpeptide tyrosine derivative, dose-dependently inhibited fibrinogen-dependent platelet aggregation, in vitro. Binding of ¹²⁵I-labeled fibrinogen to activated platelets was prevented in a competitive manner with an IC₅₀ of 10±4.2 nmol/L. The activity and tolerability of MK-383 were evaluated in a two-part double-blind, placebo-controlled, dose-escalation study in healthy male subjects using 1- and 4-hour intravenous infusions. Effects on ADP- and collagen-induced ex vivo platelet aggregation (APA or CPA) and template bleeding time (TBT) were evaluated. Twenty-four subjects participated in the 1-hour part. Six received placebo and 18 MK-383 in doses ranging from 0.05 to 0.40 μg · kg^-1 · min^-1. MK-383 inhibited platelet aggregation and prolonged bleeding time in a dose-dependent manner. APA and CPA were totally inhibited at the end of infusion of 0.4 μg · kg^-1 · min^-1 and returned to 55% and 89% of baseline, respectively, at 3 hours after infusion. TBT was prolonged at this dose from 5.0±1.3 minutes predose to 22.7±6 minutes at the end of the infusion (P<.01) and was normalized by 3 hours after infusion. In the 4-hour infusion part, 15 subjects received MK-383 (0.1 to 0.2 μg · kg^-1 · min^-1, and five received placebo. Complete inhibition of ex vivo platelet aggregation was seen at 0.15 and 0.2 μg · kg^-1 · min^-1. At 0.2 μg · kg^-1 · min^-1, TBT was prolonged from 4.4±1.2 to 23.9+4.3 minutes at the end of infusion (P<.01) and remained slightly prolonged 3 hours after infusion (7.2±1.8 minutes). No adverse effects were observed in any of the 33 subjects receiving MK-383. Conclusions. The results from this study indicate that MK-383 appears to be well tolerated and active in man. It is the first nonpeptide GPIIb/IIIa antagonist that can be used to investigate the antithrombotic potential of this new class of antiplatelet agents.