Factor XI as an Anticoagulation Target
Coagulation factor XI (FXI) is an enzyme in the clotting cascade, regulated by factor XIIa (FXIIa) and thrombin. Excessive FXI activation contributes to thrombotic disease, including myocardial infarction, stroke, and venous thrombosis. FXI is therefore a candidate anticoagulant target, since blocking it can prevent and treat thrombosis with little bleeding risk.
A paper in Research and Practice in Thrombosis and Haemostasis describes BJTJ-1837, an antibody that blocks FXI activation and produces anticoagulant and antithrombotic effects without increasing bleeding risk. The authors are from Beijing TUO JIE Biopharmaceutical Co Ltd (BJTJ Biotech) and Peking University Third Hospital.
Study Design and Regulatory Compliance
Prisys ran the animal studies reported for BJTJ-1837 as a contract research organization (CRO). The work followed CFDA/AAALAC guidelines and IACUC standards for animal care, and the in vivo work was performed in cynomolgus monkeys.
Effects of FXI antibodies on aPTT, PT, and TGA in human plasma. (A) Effects of BJTJ-1837 (n = 3), MAA868 (n = 2), AB023 (n = 2), and BAY-1213790 (n = 2) on aPTT in human plasma. Human plasma was incubated with different concentrations of antibodies or PBS for 3 minute at 37 °C. For measurement, aPTT reagents were added, and the time to clot was determined. For data analysis, aPTT values were normalized to the PBS group, and the final concentrations of antibodies were plotted against the relative aPTT. ∗P < .05, ∗∗P < .01, vs BJTJ-1837. (B) Effects of BJTJ-1837 (n = 2), MAA868 (n = 1), AB023 (n = 2), and BAY-1213790 (n = 3) at the concentration of 50 μg/mL (except 33 μg/mL for BAY-1213790) on PT in human plasma. For measurement, PT reagents were added, and the time to clot was determined. For data analysis, PT values were normalized to the PBS group. Data represented mean ± SEM. (C) The dose-dependent effect of BJTJ-1837 on inhibiting thrombin generation. In the assay, the thrombin generation was triggered by low concentrations of tissue factor, and thrombin activity was measured by adding fluorogenic substrate to plasma. The IC50 of BJTJ-1837 was 4.14 μg/mL. aPTT, activated partial thromboplastin time; F, factor; PBS, phosphate-buffered saline; PT, prothrombin time; TGA, thrombin generation assay.
Arterial Venous Shunt Thrombosis Model
The A-V shunt model creates an artificial arteriovenous circuit in cynomolgus monkeys and then asks a single question: does thrombus form inside the circuit? Prisys used it to test BJTJ-1837 at several doses against marketed anticoagulants in cynomolgus monkeys. BJTJ-1837 significantly reduced shunt thrombus weight and prolonged bleeding time in a dose-dependent manner. Against the comparator anticoagulants, it produced a stronger antithrombotic effect with lower bleeding risk.
Bleeding Time Measurement
Bleeding time is read from a standard-sized wound cut on the tail or ear, and the interval until bleeding stops reflects both bleeding tendency and hemostatic function. Prisys applied the measurement to BJTJ-1837 at several doses alongside marketed anticoagulants in cynomolgus monkeys. Bleeding time lengthened with dose, but the increase was small, and no severe or fatal bleeding occurred. Against the comparator anticoagulants, the safety profile of BJTJ-1837 was better, with bleeding that remained manageable.
BJTJ-1837 demonstrated efficacy and safety in a subacute toxicity study in cynomolgus monkeys. Two monkeys (from the 1.5 mg/kg and 3 mg/kg group after 1 month washing period) were dosed twice with 30 mg/kg at day 1 and day 14. aPTT (A) and PT (B) were measured at different time points. The blood samples were collected with a vacuum blood collection tube containing trisodium citrate at indicated time points after antibody dosing. The samples were centrifuged at 1500 g for 15 minutes at room temperature and plasma was collected for assays. For data analysis, aPTT and PT values were normalized to the predose baseline. Values were mean ± SEM. ∗P < .05 vs control. aPTT, activated partial thromboplastin time; ns, not significant; PT, prothrombin time
Histopathology Analysis
Organs and tissues are collected at necropsy, sectioned, stained, and examined microscopically for treatment-related damage. Prisys compared histopathology in BJTJ-1837-treated and control cynomolgus monkeys, with marketed anticoagulants as comparators. No treatment-related abnormality or tissue damage appeared in any organ examined. Toxicity and side effects were lower than with the comparator anticoagulants.
Across the three studies, BJTJ-1837 showed antithrombotic activity in the shunt model, modest bleeding prolongation, and unremarkable organ histology in cynomolgus monkeys. The aPTT, PT, and TGA results in human plasma, together with the in vivo data, appear in the published paper.
BJTJ-1837, a novel FXI activation-blocking antibody, https://doi.org/10.1016/j.rpth.2023.100067
