- Rigel Pharmaceuticals, Inc. plans to push into the second stage of a Phase 2 trial testing its lead drug in patients with a rare blood disorder, after top-line results from the initial phase showed some promise.
- Treatment with Rigel's drug, called fostamatinib, helped raise hemoglobin levels in six of 17 patients with warm antibody autoimmune hemolytic anemia (AIHA), meeting the pre-specified primary endpoint for the first stage of the study.
- Rigel has already submitted fostamatinib for U.S. approval to treat chronic or persistent immune thrombocytopenia, or ITP, despite a near miss in the second of two late-stage studies for that indication. Investor hopes for a regulatory OK received a boost this week, when the company said the Food and Drug Administration would not hold an advisory committee meeting to review the drug's profile.
Rigel's SOAR study was set up as a two-stage study to test the potential of fostamatinib to treat AIHA. Success in the first stage, which involved 17 patients, clears the way for Rigel to begin enrolling for the second phase.
In stage one, six of the 17 patients experienced at least a 2 g/dl increase in hemoglobin levels from baseline and surpassed a minimum threshold of 10 g/dl — the criteria by which Rigel defined a response.
Two of those six patients, however, only saw a response in an extension study after the 12-week evaluation period of the trial.
Another two individuals withdrew from SOAR for non-treatment related reasons and will be replaced, Rigel said. On the whole, safety was consistent with past studies of fostamatinib. Two patients died due to non-treatment related adverse events.
AIHA is a rare blood disorder that affects an estimated 40,000 adults in the U.S., according to the company. In patients with the condition, antibodies produced by the immune system mistakenly destroy the body's red blood cells, resulting in severe anemia. No treatments are currently approved.
Jefferies analyst Eun Yang sees both news events as a positive and said in a note to clients that each indication represents about $190 million to $200 million in revenues, respectively.
Investors appeared unenthusiastic on the news, pushing Rigel shares down more than 8% in value Tuesday. But company stock still remains up on the month, buoyed by news this week that the FDA would not convene an advisory panel meeting to review fostamatinib's risk/benefit profile in ITP.
Rigel expects the FDA to decide on approval in that indication by April 17 of next year. While no advisory committee hearing can be seen as a positive signal, a regulatory OK is still not a sure thing.
Last fall, the second of two Phase 3 studies testing fostamatinib in ITP failed on a single placebo response that pushed the results out of the range of statistical significance. Rigel maintains that looking at the data from both trials together shows a clear benefit, but analysts were already lukewarm on the positive results from the first study.