- Rigel Pharmaceuticals’ hopes for its low-platelet drug took a hit on Thursday, after a single placebo response caused the second of two Phase 3 studies to miss its primary endpoint.
- Shares in the South San Francisco-based biotech fell by nearly 30% in early trading on the news. Despite the setback, Rigel tried to spin the data to show that the combined results from both studies show evidence of a clinical benefit for the drug, known as fostamatinib.
- A little over a month ago Rigel announced a substantial restructuring to trim costs and focus on development and potential commercialization of fostamatinib, cutting 46 jobs in the process.
Both Phase 3 studies, which were designed to be identical, measured platelet responses among adult patients with chronic/persistent immune thrombocytopenia. In each, the primary endpoint was defined as a stable platelet count greater than 50,000/uL of blood on a minimum of four of the last six clinic visits between weeks 14 and 24 of treatment.
A response rate of 18% among patients receiving fostamatinib was seen in both trials. Statistical significance was met in the first study, but a stable response from one of the 24 patients on placebo derailed the second.
Even before Thursday’s news, some analysts had been disappointed by the 18% response rate, having hoped to see results in the mid-20% range.
In a statement on the results, Rigel said combining the data from both trials showed a statistically significant clinical benefit.
"We believe that 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 Raul Rodriguez, CEO of Rigel.
Rodriguez indicated the company’s next step would be discussions with the Food and Drug Administration.
The safety profile of fostamatinib was consistent with the previous trial, Rigel said. The most common adverse events were gastrointestinal-related.
Patients from both studies were invited to enroll in an open-label extension study after completion. Among the 43 placebo non-responders who signed up, six patients achieved a stable platelet response after treatment with fostamatinib in the open-label study.
Rigel said its current holdings of cash and equivalents would be sufficient to fund operations through the end of 2017, even accounting for a potential commercial launch in ITP. Rigel also indicated it was looking for companies to partner with for ex-U.S. development and commercialization of fostamatinib.