Inhibitors of Human Factor XIIIa as New Anticoagulants

SUMMARY
The long-term goal of our research is to develop effective anticoagulants that do not cause bleeding
complications to be safely used for a wider range of patients suffering from venous thromboembolism (VTE).
This project aims at developing effective and safer anticoagulants by targeting human factor XIIIa (FXIIIa). All
available anticoagulants are associated with a significant risk of bleeding. Current anticoagulants inhibit directly
or indirectly thrombin and/or factor Xa. This is the reason why they are clinically effective, but it is also the
reason why they cause bleeding. The central hypothesis is that inhibiting FXIIIa will result in effective
protection against VTE without causing significant bleeding. In contrast to all other clotting factors which are
serine proteases, FXIIIa is a transglutaminase that catalyzes the last step in the coagulation process. This
unique biochemical aspect of FXIIIa has been under investigation in the context of VTE. In vitro experiments
showed that treating normal human blood with an experimental transglutaminase inhibitor increases RBC
extrusion from contracting clots and reduces clot size. Various studies also suggested that a certain FXIIIa
polymorphism provides significant protection against VTE and that heterozygous FXIII-deficient mice do not
show signs of excessive bleeding. Thus, FXIIIa may serve as a potential therapeutic target to develop a new
effective treatment for VTE that does not significantly increase the bleeding risk. Despite this promise, very few
FXIIIa inhibitors have been developed, all of which lack substantial selectivity as they can also inhibit other
transglutaminases by blocking their active sites. Thus, I have proposed sulfonated non-saccharide glycos-
aminoglycan mimetics as a platform to develop FXIIIa inhibitors. The sulfonated molecules are to inhibit FXIIIa
potently and selectively through allosteric modulation. In preliminary studies, I discovered two sulfonated
molecules that inhibit FXIIIa with low micromolar potencies. The two molecules inhibited FXIIIa-mediated
polymerization of fibrin. The two molecules did not affect other clotting factors and did not affect the viability of
three cell lines. Molecular modeling projected a plausible binding site for these molecules on FXIIIa. In this
proposal, I specifically aim at using a multidisciplinary approach to establish the principles of effective and
selective inhibition of FXIIIa by sulfonated molecules. I will synthesize advanced libraries of two “lead”
molecules and evaluate their biochemical and biological potential as anticoagulants. The proposal is
innovative because i) it puts forward a novel approach to overcome the limitations of current VTE treatment; ii)
it exploits a multidisciplinary approach to investigate the specific aims; and iii) it introduces new technologies
with proprietary structural and mechanistic aspects. The project is also significant because it will: i) identify
2-3 potent, specific, and allosteric FXIIIa inhibitors for future evaluation in animal models of VTE and bleeding;
ii) offer new tools to better understand FXIIIa role in the coagulation physiology and pathology; iii) investigate
an alternative approach to modulate FXIIIa via allostery to pave the way to transforming anticoagulants.

Grant Number: 5R16GM149412-03
NIH Institute/Center: NIH
Principal Investigator: Rami Al-Horani