Novel low-molecular-weight inhibitor of PAI-1 (XR5118) promotes endogenous fibrinolysis and reduces postthrombolysis thrombus growth in rabbits.
BACKGROUND
Elevated levels of plasminogen activator inhibitor 1 (PAI-1) have been associated with the occurrence of thrombotic disease, and inhibition of PAI-1 activity in vivo resulted in enhanced thrombolysis and a reduction in reocclusion. Besides monoclonal antibodies and peptides, no suitable agents that are able to block PAI-1 activity are available to date. The present study was designed to test the interaction between a nonantibody, nonpeptide, diketopiperazine-based inhibitor of PAI-1, XR5118, and PAI-1 and to assess the effect of XR5118 on PAI-1 activity in vitro and on in vivo thrombolysis and thrombus growth in an experimental thrombosis model in rabbits.


RESULTS
The binding site of XR5118 on the PAI-1 molecule was studied by competitive binding experiments with mapped anti-PAI-1 monoclonal antibodies by use of surface plasmon resonance experiments. XR5118 selectively and competitively inhibited binding of the PAl-1-inhibiting monoclonal antibody CLB-2C8, indicating that binding of XR5118 to PAI-1 takes place at the area between amino acids 110 and 145 of the PAI-1 molecule, which is known to be involved with the binding of PAI-1 to tissue plasminogen activator (TPA). Incubation of plasma or platelet releasate with XR5118 resulted in a dose-dependent inhibition of PAI-1 activity. Systemic infusion of XR5118 induced a significant reduction in plasma PAI-1 activity levels from 23.7+/-4.9 to 10.9+/-3.4 IU/mL. Administration of XR5118 resulted in a significant, twofold increase in endogenous thrombolysis compared with the control. Thrombus growth in rabbits receiving both XR5118 and rTPA was significantly attenuated compared with rabbits receiving rTPA alone (13.5+/-2.7% versus 19.9+/-3.8%, respectively).


CONCLUSIONS
XR5118 binds to PAI-1 and reduces plasma PAI-1 activity levels. Furthermore, XR5118 promotes endogenous thrombolysis and inhibits thrombus accretion and is the first nonpeptide compound with significant anti-PAI-1 activity in vivo in these models.
Friederich
P W
PW
Center for Hemostasis, Thrombosis, Atherosclerosis, and Inflammation Research, Academic Medical Center, University of Amsterdam, Netherlands.
Levi
M
M
Biemond
B J
BJ
Charlton
P
P
Templeton
D
D
van Zonneveld
A J
AJ
Bevan
P
P
Pannekoek
H
H
ten Cate
J W
JW
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D005342:Fibrinolysis / Q000187:drug effects*; D006801:Humans; D007601:Jugular Veins; D008970:Molecular Weight; D010879:Piperazines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010949:Plasma / Q000378:metabolism; D017395:Plasminogen Activator Inhibitor 1 / Q000097:blood* / Q000378:metabolism; D011817:Rabbits; D013917:Thrombin / Q000494:pharmacology*; D013924:Thrombophlebitis / Q000097:blood / Q000517:prevention & control*
D010879:Piperazines; D017395:Plasminogen Activator Inhibitor 1; C107761:XR 5118; D013917:Thrombin