Active site-inhibited seven: mechanism of action including signal transduction

Vascular injury brings tissue factor (TF) into contact with blood and its natural ligands, factors VII (FVII) and VIIa (FVIIa). This results in localized FVIIa activity on TF-expressing cells, initiating coagulation, and nonhemostatic activities. Activation of transcription factors, expression of genes for inflammation, tissue remodeling, and wound healing follow, but these mechanisms for maintaining vascular integrity may lead to pathophysiologic states. Recombinant FVIIa is converted into a catalytically inert protein by reactive site residues reacting with Phe-Phe-Arg-chloromethyl ketone. Active site-inhibited FVIIa (ASIS) retains its affinity for TF and competes for FVIIa and FVII binding to TF, blocking FVIIa activity and FVII to FVIIa activation. It therefore acts as an antithrombotic agent and has been shown in previous studies on animal models of sepsis to prevent organ failure associated with fibrin deposition. Mitigation of inflammatory response and prolonged survival were remarkable and additional effects of TF blockage by ASIS not observed with inhibitors of downstream coagulation factors Xa and thrombin. This suggests that FVIIa/TF exerts a noncoagulopathic effect on cellular activities, attenuated by ASIS blocking FVIIa-induced signaling. The precise mechanism remains elusive but blockade of TF/FVIIa activity provides an attractive possibility for pharmaceutical intervention. In vitro measurements of ASIS-TF binding and FVIIa/TF inhibition are described, together with investigation of the FVIIa-induced signaling pathway and gene expression. Additionally, possible implications of ASIS blockage for hemostatic and nonhemostatic aspects of the pathophysiology associated with vascular stress and injury are discussed.