A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

Lu G, Deguzman FR, Hollenbach SJ, et al.Department of Biology, Portola Pharmaceuticals Inc., South San Francisco, California, USA

Nature Medicine, April 2013, Volume 19 No 4 pp446 - 451

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa 2

Background

• Noval oral anticoagulants (factor Xa & IIa inhibitors) widely used

• Higher incidence for (GI-)bleeding• Until now no antidote for nOAC• Management of bleeding difficult; Vitamin

K, tranexamin acid, FFP, rfVIIa, PCC not effective

-> presentation of a recombinant agent antagonizing factor Xa

-> proof of concept with in vitro & in vivo investigations

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa 3

Recombinant Antidote (r-antidote)

• Truncated form of enzymatically inactive fXa• Lacks GLA domain, catalytically inactive due to mutation in serine

residue• Mature functional form, expressed in chinese hamster ovary

Aspects to prove:•Specific binding to fXa?•Reversal of anticoagulation?•pro- or antithrombotic properties?•Reduce loss of bleeding?

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa 4

r-Antidote: in vitro-essays

• Reversal of anticoagulation in human plasma:

• clotting assay & thrombin generation assay:

• high affinity for fXa-inhibitors

• Inhibitory activity dose-dependently and completely reversed by r-Antidote

• no pro- or anticoagulant activity

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

In vivo rat model - reversal of anticoagulation

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•Rapid normalisation of INR after r-antidote infusion

•Reversal of anticoagulation correlates to reduction of unbound fXa-inhibitor-fraction

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

Mouse model of blood loss (tail transection)

• ASS+Rivar.+r-antidote reduced blood loss by 85%• After r-antidote rivaroxaban activity reduced by >80%

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Treat-I: vehicle + vehicle + vehicle Treat-II: vehicle + rivaroxaban + vehicleTreat-III: ASA + vehicle + vehicle Treat-IV: ASA + rivaroxaban + vehicle Treat-V: ASA + rivaroxaban + r- Antidote

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

Rabbit model of blood loss (liver laceration model)• Laceration of 2 liver lobes and blood loss collection over 15min after injection of

vehicle or rivaroxaban and r-antidote

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• PT & aPTT increased 2.3x resp. 1.9x after rivaroxaban, blood loss 3.2x higher

• r-Antidote reduced blood loss by >85%, decreased anti-fXa activity by 98%

• Correlation of blood loss with reduction in anti-fXa-activity an free fXa-inhibiton

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

Reversal of ATIII-dependent fXa inhibitors by r-antidote

• r-antidote mimicking binding-site of fXa for ATIII

• Enoxaparin (LMWH) & Fondaparinux (pentasaccharide) indirect fXa inhibitor (increase affinity of ATIII for fXa)

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FondaparinuxEnoxaparin

• anti-fXa activitiy of enoxaparin & fondaparinux dose-dependently reversed with r-antidote

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa

Reversal of ATIII-dependent fXa inhibitors by r-antidote

• Animal model (rat tail transection)

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Treat-I: vehicleTreat-II: Enoxaparin & vehicleTreat-III Enoxaparin & r-antidote 2mg/hTreat-IV: Enoxaparin & r-antidote 4mg/h

Enoxaparin

Treat-I: vehicleTreat-II: Fondaparinux & vehicleTreat-III Fondaparinux & r-antidoteTreat-IV: fondaparinux & Protamine

• Normalisation of hemostasis after r-antidote administration

• Complete reversal of ATIII-dependent fXa inhibition

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa 10

Discussion

• r-antidote does not interfere with normal fXa function • r-antidote with no anticoagulant or procoagulant activity • Rapid onset of action & complete reversal of fXa-inhibitors activity• Normalises hemostasis from anticoagulant drugs targeting fXa• Universal antidote for direct & indirect fXa inhibition

Limitations• Possible that used in vitro system are not sensitive enough• Preclinical data based on animal model, difficulties to extrapolate to

humans• unidentified interactions with other proteins• immunogenicity

A specific antidote for reversal of anticoagulation by direct and indirect inhibitors of coagulation factor Xa 11

Conclusion

• r-antidote capable to reverse nOAC-induced bleedings• Rapid onset of action will have major impact in future daily practice

(bleeding management, surgical procedures)• Increase safety of using fXa-inhibiting drugs.

• Phase II-study running• Further studies (antidote IIa-inhibitor, unviversal fIIa & fXa-antidote) on

the way