AVE5026: A Novel, Extractive Heparinoid with Enriched Anti-Xa Activity and Enhanced Antithrombotic Activity.

Abstract

AVE5026 represents a new generation of antithrombotic with high anti-Xa and low anti-IIa activities (anti Xa/IIa ratio > 30) when compared to heparin and low molecular weight heparins. This new heparin is a polydisperse mixture of oligomeric heparin fragments with an average molecular weight of 2000–3000 daltons prepared by partial and controlled depolymerization of porcine mucosal heparin. Unlike other depolymerized heparins where the antithrombin (AT) affinity components and anti-Xa activity is decreased with the decrease in the molecular weight, AVE5026 exhibits a relatively higher proportion of AT components which translates into a higher anti-Xa activity. A great majority of the oligosaccharide components in AVE5026 are composed of tetra-, hexa-, octa-and deca-saccharides. Heparinase is capable of digesting AVE5026 into mainly tetrasaccharide components. Despite its lower antithrombin actions, AVE5026 produces its anticoagulant effect in such whole blood assays as ACT and TEG. In the whole blood based global anticoagulant assays such as PT, APTT, AVE5026 produces modest anticoagulant effects in comparison to enoxaparin and heparin. Similarly in the plasma base system its anticoagulant effects are relatively weaker than enoxaparin and heparin. In the amidolytic anti-Xa assay, AVE5026 produced stronger inhibitory effects in comparison to enoxaparin (IC50 = 2.5 and 4.1 μg/ml, respectively). In the amidolytic anti-IIa assays AVE5026 produced modest inhibitory effects (IC50 = 38 μg/ml). Interestingly, in the AT deficient plasma in the APTT, AVE5026 produced comparable anticoagulant effects as in the NHP, indicating a stronger thrombin generation effect. Such an effect was not observed in the heptest and anti-Xa assays. In the purified AT system, AVE5026 produced a relatively stronger anti-Xa effect than enoxaparin (IC50 = 2.0 and 3.8 μg/ml, respectively). Interestingly in the thrombin generation assays using both intrinsic and extrinsic activators, AVE5026 produced concentration dependent inhibition of Xa (IC50=7–8 μg/ml) and IIa generation (IC50=>10 μg/ml), whereas fondaparinux did not produce any effect. In the agonist induced platelet aggregation studies with agonists such as ADP, collagen, epinephrine and arachidonic acid, AVE5026 did not produce any inhibitory effects. However, it strongly blunted TF mediated activation of microparticles and p-selectin expression (IC50=8 μg/ml). In comparison to enoxaparin, AVE5026 showed no cross reactivity with the HIT antibodies in the platelet aggregation system. AVE5026 produced a dose dependent antithrombotic response after IV and SC administration in the rat laser model. In the rabbit stasis thrombosis model AVE5026 produced a dose dependent antithrombotic effect by both IV and SC routes. The relative bleeding effects of AVE5026 in a rat tail bleeding and rabbit blood loss model were negligible in comparison to enoxaparin and heparin by both IV and SC routes. Repeated administration of AVE5026 in dose ranges of 1–5 mg/kg od, sc for 14 days did not result in accumulation effect of the Xa actions. Furthermore, in contrast to enoxaparin, there was no enhancement of the hemorrhagic profile. This superior safety efficacy index in animal models in comparison to other LMWH may translate into improved antithrombotic efficacy with decreased bleeding risk.