Neutralization of alpha(2)-antiplasmin by microplasmin: a randomized, double-blind, placebo-controlled, ascending-dose study in healthy male volunteers.
BACKGROUND
Microplasmin is the isolated proteinase domain of plasmin. Administration of microplasmin has been found to neutralize alpha(2)-antiplasmin (alpha(2)-AP) activity, which has been associated with reduced infarct size in various preclinical models of stroke.


OBJECTIVE
The goals of this first-in-man study were to investigate the ability of microplasmin to neutralize alpha(2)-AP activity and to monitor its tolerability in healthy male volunteers.


METHODS
This Phase I, double-blind, placebo-controlled, ascending-dose study included 10 groups, each containing 6 subjects who were randomized to receive microplasmin or placebo in a 2:1 ratio. The study had 3 parts. In part 1, subjects received a single intravenous bolus of microplasmin 0.1, 0.5, 1, 1.5, or 2 mg/kg or placebo over 15 minutes. In part 2, subjects received a bolus of microplasmin 1 mg/kg or placebo, followed by an infusion of 1, 2, 3, or 4 mg/kg or placebo over 60 minutes. In part 3, subjects, all of whom were aged >55 years, received a bolus of mi-croplasmin 1 mg/kg or placebo, followed by an infusion of 1 mg/kg or placebo. The primary pharmaco-dynamic end point was the change in alpha(2)-AP activity, measured at different time points up to 4 days after dosing using a chromogenic assay. All adverse events were monitored based on spontaneous reports and nondirected questioning at study visits up to the post-study visit 21 days after administration of study drug.


RESULTS
The mean (SD) age of subjects in parts 1, 2, and 3 was 30 (8), 30 (8), and 64 (8) years, respectively. All groups receiving microplasmin had a dose-dependent decrease in alpha(2)-AP activity. In part 1, the mean maximal inhibition of alpha(2)-AP was 11.8% (6.0%), 27.7% (4.3%), 53.0% (4.8%), 65.3% (4.3%), and 84.0% (6.0%) after bolus administration of microplasmin 0.1, 0.5, 1, 1.5, and 2 mg/kg, respectively, and 7.4% (6.9%) after administration of placebo. In part 2, the mean maximal inhibition of alpha(2)-AP was 74.6% (11.2%), 95.5% (3.3%), 99.0% (1.0%), and 88.0% (12.5%) after bolus administration of microplasmin 1 mg/kg followed by an infusion of 1, 2, 3, and 4 mg/kg, respectively, compared with 12.9% (6.8%) after administration of placebo. In part 3, the mean maximal inhibition was 69.7% (3.4%) after bolus administration of microplasmin 1 mg/kg followed by an infusion of 1 mg/kg, compared with 8.8% (4.1%) with placebo. One subject in the highest dose group in part 1 (2 mg/kg) and 2 subjects in the highest dose group in part 2 (1 + 4 mg/kg) had an urticarial reaction. All 3 subjects also had a decrease in total hemolytic complement and an increase in complement 5a.


CONCLUSIONS
Neutralization of alpha(2)-AP activity by microplasmin was feasible in these healthy male volunteers. The urticarial reactions observed in the highest dose groups were considered dose-limiting adverse events. Further trials are needed to investigate the tolerability of this therapy and whether it is neuroprotective in patients with acute ischemic stroke.
Pakola
Steve
S
ThromboGenics NV, 3001 Leuven, Belgium. Steve.Pakola@thrombogenics.com
Cahillane
Geraldine
G
Stassen
Jean-Marie
JM
Lijnen
H Roger
HR
Verhamme
Peter
P
D000328:Adult; D000368:Aged; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005341:Fibrinolysin / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D013997:Time Factors; D014581:Urticaria / Q000139:chemically induced*; D055815:Young Adult; D000979:alpha-2-Antiplasmin / Q000187:drug effects* / Q000378:metabolism
D010446:Peptide Fragments; D000979:alpha-2-Antiplasmin; C054561:microplasmin; D005341:Fibrinolysin