Controlled Long-Term Knockdown of Plasminogen in Mice and Dogs Using siRNA: Assessment of Phenotype and Toxicity
Amy Wong Strilchuk, Ph.D. Candidate
University of British Columbia
Vancouver, British Columbia, Canada
The fibrinolytic system, and in particular the protease plasmin, play an important role in the maintenance of vascular patency by dissolving fibrin‐rich thrombi. With the critical role of this process related to fibrinolysis and hemostasis, there have been several attempts to discover ways to achieve long-lasting modulation, largely through the control of plasmin or its precursor plasminogen. Plasmin inhibitors such as tranexamic acid have a short half-life, while murine models of plasminogen genetic knockout show deleterious phenotypes by five months of age. siRNA targeting plasminogen may provide a more flexible tool to knock down plasminogen and modulate fibrinolysis long term. Amy Strilchuk from the University of British Columbia in Vancouver, Canada, presented findings on Sunday, July 18, 2021, regarding a new tool to reduce plasminogen levels. Lipid nanoparticles were used to deliver siRNA targeting plasminogen in wild-type mice and dogs. To evaluate efficacy of knockdown, blood and tissues were collected for protein analysis, mRNA quantification, and coagulation assessment by thromboelastography. After multiple doses in dogs, and eight months of sustained knockdown in mice, tests were done to examine drug toxicity, duration of knockdown, and other variables.
Doses of 1.0 and 0.054 mg siRNA/kg body weight in mice and dogs, respectively, caused >90% knockdown of plasminogen and resulted in prolonged clot stability for three weeks after administration. Periodontal bone loss and fibrin deposition in the liver, pathological phenotypes that develop in plasminogen-deficient mice by five months of age, were not observed in mice after eight months of plasminogen knockdown. Strilchuk commented, based on the findings yielded from this study, that siRNA targeting plasminogen is a promising tool for effective and long-lasting control of fibrinolysis. This work also represents the first use and optimization of lipid nanoparticle gene therapy in canine models.