Rigel falls on disappointing RA data

Rigel Pharmaceuticals Inc. (NASDAQ:RIGL) fell $3.03 (40%) to $4.50 on Friday after partner AstraZeneca plc (LSE:AZN; NYSE:AZN) reported that fostamatinib plus methotrexate met one co-primary endpoint but missed the other in the Phase III OSKIRA-1 trial to treat rheumatoid arthritis. Fostamatinib missed the endpoint of structural preservation as measured by modified total Sharp score (mTSS) on radiographic scans from baseline to week 24 vs. placebo plus methotrexate, but met the co-primary endpoint of improving ACR20 response rate at week 24 vs. placebo. The ACR20 response rate for fostamatinib was 44-49% at week 24 vs. 34% for placebo. The double-blind, international trial enrolled 923 RA patients with an inadequate response to methotrexate.

According to the label of competing RA drug Xeljanz tofacitinib from Pfizer Inc. (NYSE:PFE), the drug led to ACR20 response rates of 50-62% at month 6 vs. 25% for placebo in a Phase III trial in patients with an inadequate response to methotrexate. FDA approved the oral Janus kinase (JAK) inhibitor in November, though the label does not include language on preventing structural damage or disease progression. The agency questioned the efficacy of Xeljanz on the mTSS endpoint at a May 2012 advisory committee meeting (see BioCentury, May 14, 2012). ...