An experimental therapy in development by Shire for patients with the rare blood disorder hereditary thrombotic thrombocytopenic purpura (hTTP) has been granted a fast track designation by the US Food and Drug Administration.

The company is targeting its therapy SHP655 (recombinant ADAMTS13) towards treatment of acute episodes of hTTP in patients with a constitutional deficiency of the von Willebrand factor-cleaving (VWF) protease ADAMTS13.

A deficiency in this enzyme can cause clotting in the microvasculature with associated organ morbidities.

Currently, between 3,000 to 4,000 patients around the globe have hTTP, and there are no approved treatment options although various other therapies are used off label and have a range of severe complications for patients, Shire noted.

The FDA’s Fast Track designation is supported by preclinical data and a Phase I study of the drug, and is designed to facilitate the development, and expedite the review of drugs to treat serious conditions and fill an unmet medical need. If approved, SHP655 would be the world's first recombinant ADAMTS13 enzyme replacement therapy.

Shire now plans to initiate a Phase III global trial to evaluate the safety and efficacy of the therapy in the treatment and prevention of acute TTP events in patients with severe hereditary ADAMTS13 deficiency.