Inhibition of Factor XI using a GalNAc-siRNA RBD5049: a novel antithrombotic drug with high potency and long duration

Abstract

Abstract Introduction Bleeding risk remains a major concern of the existing anticoagulants. Inhibition Factor XI (FXI) using small molecule inhibitors, antibodies or antisense oligonucleotides (ASOs) to inactive intrinsic pathway of coagulation have been developed as a safer treatment option over the last decade. siRNA is a nucleic acid drug with class advantages of high selectivity, long duration and benign safety profiles. The current abstract summarizes key preclinical efficacy and safety data supporting the first-in-human study. Purpose To evaluate efficacy and safety, of a GalNAc-siRNA molecule RBD4059, for development of a novel antithrombotic treatment. Methods In vitro potency of several siRNAs were assessed and screened in HepG2 cells. Upon selection of the lead candidate, the siRNA was conjugated with a GalNAc molecule, using RIBO-GalSTAR liver targeting system. In vivo efficacy of RBD4059 was tested in C57BL/6J mice and cynomolgus non-human primates (NHPs). The antithrombotic effect of RBD4059 was determined in arterial and venous thrombosis models induced by FeCl3. Enoxaparin sodium (Lovenox) with clinical equivalent dose (4 mg/kg) was used as a control. Single- and repeated- dose GLP toxicology studies were performed in both CD-1 mice and NHPs. Results IC50 values of RBD4059 was 0.56 nM HepG2 cells. Dose-dependent and long-lasting effects of RBD4059 on the inhibition of plasma FXI activity (FXIa) were observed in mice and in NHPs. RBD4059 at a single dose of 9 mg/kg achieved a maximum of 89% plasma FXIa reduction and 1.38-fold APTT prolongation in mice, and the inhibitory effects could be maintained until Day 64. RBD4059 at 3 mg/kg or 9 mg/kg significantly prevented flow reduction due to FeCl3-induced thrombosis in both arterial and venous thrombosis models, and efficacy was superior than enoxaparin. In NHPs, the inhibitory effects of FXIa were maintained until Day 71 with the maximum effect of 77% FXIa reduction and 1.34-fold APTT prolongation. GLP toxicology studies showed good safety profile without any signs of increased bleeding despite supra-physiological doses and the NOAEL was considered 600 mg/kg in mice and 400 mg/kg in NHPs. Conclusions RBD4059 has demonstrated high potency/efficacy and long duration regarding FXI inhibition and with large safety margin. As the first siRNA based molecule targeting FXI, RBD4059 has now entered Phase 1 trial in human healthy volunteers.Figure 1