Rigel Pharmaceuticals continues to be plagued by a low response rate in its big Phase III program for fostamatinib. But unlike its first late-stage data drop, which scored a hit on the primary endpoint, the biotech now has to explain why its second confirmatory study failed.
It’s not an enviable task. At the end of August the South San Francisco-based biotech’s share price $RIGL went on a roller coaster ride with a positive but unimpressive 18% response rate for immune thrombocytopenia patients who achieved a stable platelet response. That was exactly the same rate seen in the second Phase III, only this time one patient on a placebo also achieved a stable platelet response, and that scuttled any shot at hitting the primary endpoint. For analysts who had been looking for a response rate at least in the low 20s with clear signs of efficacy, this stumble will not play well.
Investors didn’t care for news, either. Rigel’s shares plunged 33% in early trading Thursday.
Rigel CEO Raul Rodriguez, though, says if you add all the data from both Phase III studies together, you still come up with a positive outcome. And that’s what they want to take to the FDA.
“We believe that the totality and consistency of data from the FIT Phase III program, which included two Phase III studies and one long-term extension study, strongly supports a clear treatment effect, with a sustained clinical benefit of fostamatinib,” said Rodriguez in a statement. “We are encouraged by these results and believe that the risk/benefit ratio for fostamatinib is positive for patients with chronic/persistent ITP, a population with a serious unmet medical need. As a result, we will continue to pursue this opportunity. Our next step is to seek feedback from the FDA.”
The therapy is a spleen tyrosine kinase (Syk) inhibitor, which should help stop the bleeding that occurs when someone has a low platelet count. But in a small proof-of-concept study for thrombocytopenia, the therapy scored a 50% response rate, which had whetted appetites for something solid in Phase III.
There’s no turning back now, though. Rigel laid off close to half of its staff last month as it cleared the decks for an FDA application and launch plans.
Back in 2013 fostamatinib flopped in a Phase III study of rheumatoid arthritis, forcing AstraZeneca to wash its hands of their partnership and leaving Rigel to undergo an overhaul, shedding staff and reorganizing around dry eye diseases (R348) and lupus (R333). They both quickly failed Phase II. Another drug, R118, had to be abandoned after investigators tracked some serious side effects.
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