Abstract

Abstract 2101

Poster Board II-78

The absence of abnormal bleeding associated with congenital deficiencies of the intrinsic coagulation pathway factor, FXI, suggests that this pathway is not important for normal blood coagulation in vivo. However, recent work in mice and higher species demonstrates that the intrinsic pathway is an important contributor to pathologic intravascular thrombosis, suggesting that targeting this pathway may yield effective antithrombotic agents with high safety.

We have previously demonstrated that second generation antisense oligonucleotides (ASOs) targeting the intrinsic pathway member FXI were potent antithrombotic agents and that this activity was achieved in several mouse models of thrombosis without any increase in bleeding risk (Zhang et al. ASH 2008).

Here we characterize the pharmacological activity, chemical SAR and safety profile of FXI antisense oligonucleotides administered subcutaneously in Cynomologus monkeys. Our first monkey study was designed to address the PK/PD kinetics of FXI ASOs from a single chemical series (20 mers, 5-10-5 MOE Gapmers). Two dose escalation regimes were evaluated (1) 5mg/kg (3wks), 10mg/kg (3 wks) followed by 25 mg/kg (6wks) and (2) 5mg/kg (3wks) followed by 10mg/kg (9 wks). The subsequent study was designed to evaluate chemical SAR around the active ASOs identified in the study 1. FXI antisense oligonucleotides FXI-AS1, FXI-AS2 demonstrated dose and time dependent pharmacologic activity, including, decreased FXI mRNA in liver (up to 90%), decreased FXI protein levels and FXI activity measured in plasma, with a maximal inhibition of >80% observed at 25mg/kg on both schedules, prolonged activated partial thromboplastin times (aPTT), maximal aPTT ratio of 2.O, but no change in prothrombin time (PT) as expected. Similar to previous studies in mouse the anticoagulant activity observed from FXI depletion in monkeys was not associated with increased bleeding risk as assessed in a skin bleeding time test. Additionally, FXI ASOs had no deleterious effects on organ weights, platelets, or on measures of liver and kidney function. The second study confirmed the effects of FXI-AS1 and FXI-AS2 and demonstrated that shorter ASOs with decreased gap size were equally potent.

These results further support the development of FXI ASOs as human therapeutics for the treatment of coagulation related disorders with the potential for improved safety profiles.

Disclosures:

MacLeod:Isis Pharmaceuticals: Employment. Crosby:Isis Pharmaceuticals, Inc.: Employment. Zhao:Isis Pharmaceuticals, Inc.: Employment. Gao:Isis Pharmaceuticals, Inc.: Employment. May:Isis Pharmaceuticals, Inc.: Employment. Zhang:Isis Pharmaceuticals, Inc.: Consultancy. Lowenberg:Isis Pharmaceuticals, Inc.: Consultancy. Levi:Isis Pharmaceuticals, Inc.: Consultancy. Monia:Isis Pharmaceuticals, Inc.: Employment.

Author notes

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Asterisk with author names denotes non-ASH members.