fesomersen (Ionis Pharmaceuticals)

Fesomersen (IONIS-FXI-Rx) is a second-generation 2-O-methoxyethyl (2-MOE) modified antisense oligonucleotide (ASO) designed to inhibit the synthesis of coagulation Factor XI (FXI) in the liver. By binding to the messenger RNA (mRNA) of FXI, fesomersen triggers RNase H-mediated degradation, leading to a significant reduction in circulating FXI protein levels. Factor XI is a key component of the intrinsic pathway of the coagulation cascade, and its inhibition is hypothesized to decouple thrombosis from hemostasis, potentially offering antithrombotic efficacy with a lower risk of bleeding compared to traditional anticoagulants. Developed by Ionis Pharmaceuticals and formerly partnered with Bayer, fesomersen was primarily investigated for the prevention of thromboembolic events in patients with end-stage renal disease (ESRD) undergoing hemodialysis. Following Phase 2 clinical results, development was discontinued by Bayer, and Ionis has since focused on a ligand-conjugated version (IONIS-FXI-L_Rx) for improved potency.

Other names

Factor XI antisense oligonucleotide