Rigel Touts Late-Stage Data for Platelet Drug

Xconomy San Francisco — 

Back in 2013, Rigel Pharmaceuticals, having seen a few drugs fail in clinical trials, decided to go after less common health problems rather than the major diseases, including asthma and rheumatoid arthritis, it had before. There’s still more to be done before that decision pays off with Rigel’s first approved drug, but the South San Francisco, CA, company claims to have taken a step in that direction this morning.

Rigel (NASDAQ: RIGL) said this morning that its experimental drug fostamatinib succeeded in the first of two Phase 3 trials in patients with adult chronic immune thrombocytopenia purpura (ITP), a disease in which the body attacks platelets in the blood needed for clotting and wound healing. Rigel said 18 percent of patients on fostamatinib met the study’s primary goal of having “stable” platelet numbers, or more than 50,000 platelets per microliter of blood, on at least four clinical visits between 14 and 24 weeks after treatment. None of the patients on placebo met that goal. Rigel enrolled 76 patients in the trial: 51 got the drug, the other 25 a placebo.

The most common side effects were gastrointestinal-related, including nausea, vomiting, diarrhea, and stomach pain—31 patients (61 percent) of those on Rigel’s drug, experienced such side effects, compared to five (20 percent) on placebo. Rigel said no new safety problems popped up in the study.

The results weren’t as striking as those Rigel had seen in an earlier, smaller trial, which were published in the journal Blood in 2009. In that study, Rigel had enrolled 16 ITP patients who hadn’t responded to at least two other treatments, and found that its drug led to a sustained response in at least half of them. But Rigel noted today that two patients who participated in the earlier trial have now been on fostamatinib for more than seven years and have maintained stable platelet levels over that time, demonstrating the drug’s potential as a chronic therapy for ITP patients.

Rigel will need to build that case with more data. It has a second Phase 3 trial of fostamatinib ongoing that should produce data in October or November. Rigel also enrolled all the responders from the first Phase 3 trial in an extension study to see how the drug fares over time. If data from both of those studies hold up, Rigel could file for FDA approval early next year.

Shares of Rigel closed at $2.64 apiece and were up 25 percent, to $3.30 apiece, during pre-market trading on Tuesday.

Chronic ITP affects about 50,000 to 60,000 adult in the U.S., according to Rigel. They’re currently treated with steroids or drugs that can boost platelet count —drugs like romiplostim (Nplate) and eltrombopag (Promacta)—or surgery to remove the spleen. Not all of these treatments are effective, however, leaving room for improvement. Rigel’s drug, a so-called spleen tyrosine kinase inhibitor, interferes with immune cells that destroy platelets.

“We believe that fostamatinib has significant commercial potential given that it has a unique mechanism of action that may work where other products have failed,” said Rigel president and CEO Raul Rodriguez, in a statement.

Fostamatinib was once the focus of a partnership between Rigel and AstraZeneca, but the British drugmaker ended the deal in 2013 after the drug failed a trial in rheumatoid arthritis. Another Rigel drug failed in asthma in 2013 as well, leading the company to restructure and turn its attention to less common disorders like ITP, the kidney disease iGa nephropathy, and a rare form of anemia. Here’s more on Rigel’s strategic shift, and the rationale behind its decision to go after ITP.