Abstract 36: Factor XII RNAi-based Therapeutic as a Prophylactic Anti-thrombotic Therapy

Abstract

Introduction: Current anticoagulants effectively prevent thromboembolic (TBE) events, but unmet medical need remains due to elevated risk of major bleeding events, particularly where Factor Xa inhibitors are contraindicated. Factor XII (F12) zymogen initiates the intrinsic coagulation pathway through both autocleavage and Factor XI cleavage. F12 deficient mice show protection from induced thrombosis without increased bleeding risk. F12 deficiency in humans is not associated with increased bleeding risk, suggesting F12 is not essential for hemostasis. Methods: Hepatocyte-targeted RNA interference (RNAi) triggers for reducing liver F12 expression were developed for subcutaneous (SQ) administration. Specific rodent/human/non-human primate (NHP) cross-reactive RNAi triggers were designed in silico and screened for knockdown activity in vitro and in wild-type mice. Structure activity relationship (SAR) studies of active RNAi triggers identified optimal modifications for lead identification. Candidate RNAi triggers were evaluated for activity and safety in NHPs. In addition, candidate RNAi triggers were evaluated for activity in two rodent models of thrombosis and bleeding risk. Results: F12 RNAi triggers exhibited significant and sustained knockdown of serum F12 levels in both mice and NHPs. SAR studies enabled identification of a candidate lead molecule that demonstrated >95% knockdown after a single 1 mg/kg dose in mice. Evaluation of two SQ doses of this RNAi trigger in NHPs demonstrated >93% knockdown of serum F12 levels at nadir with durable knockdown of >90% for over 5 weeks after the final dose. Concomitant increases in coagulation biomarker aPTT were observed, consistent with functional F12 depletion. Both arteriovenous shunt studies in rats and FeCl 3 -induced TBE studies in mice exhibited prevention of clot formation after F12 knockdown. Importantly, F12 knockdown did not increase bleeding times in explicit hemostasis studies in mice. Conclusions: Development of a SQ-administered F12-specific RNAi trigger offers potential for a novel, infrequently dosed prophylactic treatment for TBE without increased bleeding risk. Administration by medical personnel would eliminate adherence concerns inherent to current therapies.