Rigel Submits NDA for Fostamatinib

Rigel Pharmaceuticals today announced that it has submitted a New Drug Application (NDA) to the United States Food and Drug Administration for its experimental drug fostamatinib for the treatment of chronic and persistent immune thrombocytopenia (ITP).

ITP is an autoimmune condition in which body attacks its own blood platelets, resulting in excessive bruising and bleeding. The condition is rare, only impacting between 60,000 and 125,000 people in the United States, according to the company. “Current therapies for ITP include steroids, blood platelet production boosters (TPOs) and splenectomy. However, a portion of patients do not derive a benefit from existing therapies,” according to a Rigel press release.

Fostamatinib is a spleen tyrosine kinase (SYK) inhibitor. SYK plays a wide role in the body, mediating “unexpectedly diverse biological functions, including cellular adhesion, innate immune recognition, osteoclast maturation, platelet activation and vascular development,” according to a 2010 Nature Reviews Immunology study. Rigel believes their drug “may address the underlying autoimmune cause of ITP by impeding platelet destruction.”

The NDA submitted contains phase 3 clinical studies of fostamatinib in 163 ITP patients: two randomized placebo-controlled studies and one open-label extension study. Results from the placebo-controlled Fostamatinib in ITP, or FIT, studies were released in late summer of 2016 and early winter of 2017. Defining “stable” as “achieving platelet counts of ≥ 50,000/μL on ≥ 4 of the 6 visits between weeks 14 and 24” and “transient” as “achieving at least 2 consecutive median platelet counts over 50,000/μL during the trial without rescue” but not otherwise meeting stable criteria, 29% of fostamatinib patients (18% stable, 11% transient) saw some form of improvement over the course of the studies, compared with only 2% of the placebo groups.

The company expects to receive word of the FDA’s acceptance of the NDA sometime in June; In 2015, the agency granted Rigel Orphan Drug status for fostamatinib.

The drug maker’s press release notes that the NDA includes data from other, non-ITP related studies, since “across all indications, fostamatinib has been evaluated in over 4,600 subjects.”

Those additional thousands of study patients had other conditions: the drug is neither new nor specifically intended for ITP. Throughout the past decade, it has been investigated in the treatment of other autoimmune diseases, notably rheumatoid arthritis (RA). AstraZeneca worked in a partnership with Rigel for years to attempt to develop fostamatinib as an RA drug. While extensive trials showed it to be relatively safe, definitive data never emerged showing that it was an effective treatment for that condition. In 2013, AstraZeneca walked away from that program.