Rigel Pharmaceuticals ($RIGL) fell about 35% in early trading on news that a second Phase III trial for its fostamatinib missed the primary endpoint. Already, Wall Street had reacted poorly in August to a first Phase III trial that reported barely positive data for fostamatinib in immune thrombocytopenia (ITP).
The latest news has pulled its valuation all the way down to only $200 million. Rigel said in a statement that it would continue to pursue the candidate in this indication and that it will “seek feedback from the FDA.”
The second trial failed because of a stronger placebo response than in the first Phase III study. In fact, Rigel said that only one patient responded to placebo in the trial. But that was enough to edge the study out of meeting its primary endpoint of stable platelet response in four of the last six visits between trial weeks 14 and 24 of treatment.
"The totality and consistency of data from the FIT Phase 3 program, which included two Phase 3 studies and one long-term extension study, strongly supports a clear treatment effect, with a sustained clinical benefit of fostamatinib," said Rigel President and CEO Raul Rodriguez in the 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."
Like in the prior study, the fostamatinib response rate was 18%. In pooled data for responders from both Phase III trials, Rigel noted that platelet counts improved to a median of more than 100,000/uL from a median at baseline of 18,500/uL.
Fostamatinib is an oral spleen tyrosine kinase inhibitor that’s in testing to treat adult chronic/persistent immune thrombocytopenia, a bleeding disorder that impairs clotting. This is the company’s lead candidate, which is also in Phase II testing to treat autoimmune hemolytic anemia and nephropathy.
"Given the heterogeneity of ITP, it is currently almost impossible to predict how patients will respond to available therapies, which is why it is so important for physicians and patients to have treatment options," said the studies’ lead investigator, Dr. James Bussel, a professor of pediatrics, pediatrics in obstetrics and gynecology, and pediatrics in medicine at Weill Cornell Medicine. "This heterogeneity means that treatments that work by different mechanisms can make important contributions in certain patients, such as those who might be especially responsive to fostamatinib because of its unique mechanism of action. The FIT Phase 3 studies have both demonstrated that fostamatinib provided a robust and enduring benefit for those patients who responded to the drug."