Ablynx Develops Nano Antibody for Treatment of Rare Clotting Disorder

Last week, Ablynx announced substantial progress in the development of the nano antibody drug caplicizumab to treat acquired thrombotic thrombocytopenic purpura (aTTP), a rare, but life-threatening autoimmune disease. The Belgian biopharmaceutical company has submitted a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) for approval. If accepted, caplicizumab will not only be the first therapeutic specifically indicated for the treatment of aTTP, but also the first approved nano antibody drug on the market.

aTTP is characterized by the autoimmune impairment of ADAMTS13, an enzyme that normally cleaves multimeric von Willebrand factor (vWF) into its functional form. Without the function of ADAMTS13, multimeric vWF forms aggregates with platelets in the blood. Low free platelet count and excess clotting result in thrombotic complications and a significant risk of organ damage due to the blockages of blood flow to tissues.

The current standard of care for aTTP involves immunosuppression and daily plasma exchange transfusion, in which a patient’s plasma is replaced with donor plasma to remove platelet-vWF aggregates. Caplicizumab is an anti-vWF nano antibody that prevents the formation of aggregates by blocking the interaction of multimeric vWF complexes with platelets.

While dozens of monoclonal antibodies have been approved by the FDA for therapeutic use (with hundreds more undergoing clinical trials), caplicizumab is the first therapeutic nano antibody. Nano antibodies are single-domain antibody fragments that bear full antigen binding capacity like monoclonal antibodies, but have a smaller size and unique structure, giving them features of small-molecule drugs. Nano antibodies are more stable than conventional monoclonal antibodies, allowing for multiple administration routes, and can be humanized to lower toxicity and immunogenicity. Because they are encoded by single genes, nano antibodies are easier and more cost-effective than traditional antibodies to engineer and manufacture.

Currently, caplicizumab is undergoing Phase III clinical trials and a three-year follow-up study has been initiated to determine the long-term safety and efficacy of this drug. Ablynx aims to commercialize caplicizumab in North America and Europe upon the trial’s conclusion and approval of BLA filing in 2018.

With the obvious advantages of nano antibodies over conventional monoclonal antibodies as biological drugs, caplicizumab is likely only the first of many to come.

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