Potential for Recombinant ADAMTS13 as an Effective Therapy for Acquired Thrombotic Thrombocytopenic Purpura

Abstract

Objective-The metalloprotease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) regulates the size of von Willebrand factor multimers. A deficiency in ADAMTS13 activity is associated with the life-threatening disease thrombotic thrombocytopenic purpura (TTP). The vast majority of patients have acquired TTP, where circulating anti-ADAMTS13 autoantibodies are causative for the decreased ADAMTS13 activity. Current treatment consists of plasma exchange, but improved therapies are highly warranted. Approach and Results-We have developed a new rat model mimicking various aspects of acquired TTP to investigate the therapeutic efficacy of human recombinant ADAMTS13. A polyclonal antibody against ADAMTS13 completely blocked endogenous rat ADAMTS13 activity in Sprague-Dawley rats. When TTP was triggered using recombinant von Willebrand factor, the animals displayed severe TTP-like symptoms, such as thrombocytopenia, hemolytic anemia, and von Willebrand factor-rich thrombi in the kidneys and brain. Subsequent injection of 400, 800, or 1600 U/kg recombinant ADAMTS13 prevented full development of these symptoms. Analysis of plasma samples confirmed that recombinant ADAMTS13 was able to override circulating anti-ADAMTS13 inhibitory antibodies, resulting in restoration of ADAMTS13 activity and degradation of ultralarge von Willebrand factor multimers. Conclusions-Recombinant ADAMTS13 was shown to be effective in averting severe acquired TTP-like symptoms in rats and holds promising value for the treatment of this severe and life-threatening disease in humans. rADAMTS13 therapy seems to be a promising treatment opportunity for this patient group. In the presented study, we developed a rat model mimicking various aspects of acquired TTP, with which we further explored the feasibility of rAD-AMTS13 treatment in acquired TTP. Materials and MethodsMaterials and Methods are available in the online-only Data Supplement. Results Establishing a Rat Model Resembling Acquired TTPFirst, rats were injected with polyclonal anti-ADAMTS13 antibodies (650 U/kg) to block endogenous rat ADAMTS13 activity and to establish a robust inhibitor titer of ≈10 BU/ mL. Then, animals were administered 2000 U/kg recombinant VWF (rVWF) to trigger TTP symptoms.11 Control animals received either control IgG instead of anti-ADAMTS13 antibodies or saline instead of rVWF. Animals were followed for 24 h, and blood samples were analyzed after 3 and 24 h. The normal platelet count at baseline was 650±177×10 3 platelets/μL blood ( Figure 1A). Rats injected with anti-ADAMTS13 antibodies and triggered with rVWF developed thrombocytopenia, with a platelet count of 427±111×10 3 /μL after 3 h and 218±40×10 3 /μL after 24 h ( Figure 1A). Neither injection of anti-ADAMTS13 antibodies without additional rVWF nor injection of control IgG with rVWF resulted in thrombocytopenia (652±146×10 3 /μL and 766±63×10 3 /μL after 24 h, respectively; Figure 1A). Hemoglobin levels also decreased significantly after 24 h when rats developed TTP ...

Mechanisms of Autoantibody-Induced Pathology

“…It is effective to treat congenital TTP symptoms in mice (312) and acquired TTP symptoms in rats, where rADAMTS13 was able to overcome circulating inhibitors and reconstitute ADAMTS13 activity (313). A Phase I clinical study is currently going on to assess rADAMTS13 in the treatment and prophylaxis of congenital TTP (NCT02216084).…”

Quality Assessment of Established and Emerging Blood Components for Transfusion

“…Fibrinogen concentrates and PCCs may provide superior therapy compared to plasma in bleeding patients without genetic deficits due to the possibility of rapid restoration of hemostasis and are under active investigation. Even in TTP, a recombinant ADAMTS13 is in preclinical development, a product that may in future supplement the most evidence-supported indication for plasma transfusion [98]. Given the paucity of evidence of benefit for the medical use of transfusable plasma and the existence of high-level clinical evidence of efficacy for some of the indications for which fractionated products are employed, it is likely that an increasing proportion of plasma will be fractionated rather than transfused.…”

Novel therapies in thrombotic thrombocytopenic purpura

“…showed that rADAMTS13 can neutralize autoantibodies and reconstitute the ADAMTS13 activity in vitro 28. Moreover, pre‐clinical studies using Sprague‐Dawley rats, showed that rADAMTS13 can restore the ADAMTS13 activity by forming ADAMTS‐13 specific immune complexes 29, 30. These data collectively suggest a role for rADAMTS13 in iTTP and may be the rationale for future studies.…”