Rigel shaken after fostamatinib misses phase III trial target

Shares in Rigel Pharmaceuticals fell yesterday after it revealed its lead drug candidate fostamatinib had failed a phase III trial in chronic/persistent immune thrombocytopenia (ITP), a disease leading to reduced platelet counts.

The FIT 2 trial showed that 18% of patients treated with fostamatinib achieved a stabilisation of their platelet levels, with just 4% of those on placebo hitting that objective. The difference between the two groups was not however significant.

Down more than 30% at one point, the stock rallied on comments from chief executive Raul Rodriguez, who said he believed the results of FIT 2 and the earlier FIT 1 trial - taken together - "support a clear treatment effect" with the drug, which is an orally-active spleen tyrosine kinase (SYK) inhibitor.

"Our next step is to receive feedback from the FDA," he added, saying the company would "continue to pursue this opportunity". The company has previously said it hopes to file for approval of fostamatinib in the US in the first quarter of 2017.

That positive view was backed up by analysts at Piper Jaffray, who said: "With one positive trial and one near-miss and strong pooled data, we believe fostamatinib is still in good shape."

ITP is an autoimmune disease where the immune system attacks and destroys platelets in the blood, and affects around 50,000 people in the US. Fostamatinib has a novel mechanism of action, blocking antibody receptor signalling in white blood cells in a bid to interrupt the immune destruction.

In August, Rigel reported the same 18% response rate for fostamatinib in the FIT 1 trial. However, in that study no patient on placebo achieved stable platelet levels. In FIT 2, the difference between the groups came down to just one patient in the placebo group.

Despite the trial meeting its targets, at the time analysts expressed a little disappointment with the result, saying they had been hoping for a response rate above 20% that would have made a stronger case for prescribing the drug. Estimates for peak sales are in the $300m-400m range.

Fostamatinib is also in phase II trials for two other rare diseases - autoimmune haemolytic anaemia and IgA nephropathy. It was formerly partnered with AstraZeneca (AZ), but the UK pharma group handed back rights after it failed a trial comparing it to AbbVie's TNF inhibitor Humira (adalimumab) in rheumatoid arthritis.