Factor XI

Class

Factor XI siRNA anticoagulant

Factor XI is a plasma protein produced by the liver that participates in the coagulation cascade, the sequence of enzymatic reactions that converts circulating clotting factors into a stable fibrin clot. It sits within the so-called intrinsic pathway, where it is activated and in turn activates Factor IX, amplifying thrombin generation. Genetic and epidemiological studies show that people born with low Factor XI activity are substantially protected from venous thromboembolism and ischemic stroke while experiencing only mild bleeding, mostly after significant trauma or surgery. This observation has made Factor XI an attractive anticoagulant target: reducing its activity is expected to lower pathological clot formation without disabling the separate pathway that maintains normal hemostatic plugging of injured vessels. Two distinct strategies are represented here: small interfering RNA (siRNA), which suppresses hepatic production of Factor XI protein at the genetic level, and a monoclonal antibody, which binds circulating or membrane-associated Factor XI to block its activation or enzymatic function. Both approaches aim to lower functional Factor XI below the threshold needed to sustain excessive clotting, while sparing the parallel tissue-factor-driven pathway responsible for stopping bleeding at a wound. This mechanism is relevant to conditions such as atrial fibrillation, venous thromboembolism, and other settings where long-term anticoagulation is needed.