Rigel Pharma Shares Sink as Fostamatinib Fails to Hit Secondary Endpoint

Shares of Rigel Pharma RIGL have plunged more than 30 percent Thursday following news from its development partner AstraZeneca AZN that fostamatinib achieved its primary endpoint but failed to achieve the secondary endpoint. Volume in Rigel is very heavy Thursday. AstraZeneca today announced top-line results of OSKIRA-4, a Phase IIb monotherapy study of fostamatinib, the first kinase inhibitor with selectivity for SYK (spleen tyrosine kinase) in development as an oral treatment for rheumatoid arthritis (RA). OSKIRA-4 was a six month study evaluating improvements in signs and symptoms of RA in 280 patients who had never previously used a disease-modifying anti-rheumatic drug (DMARD), were DMARD intolerant or had an inadequate response to DMARDs and were randomised to receive fostamatinib as a monotherapy, adalimumab as a monotherapy, or placebo. Three dose regimens of fostamatinib were evaluated in OSKIRA-4: 100mg twice daily, 100mg twice daily for a month followed by 150mg once daily, and 100mg twice daily for a month followed by 100mg once daily. OSKIRA-4 had two primary objectives – a superiority comparison to placebo at 6 weeks and a non-inferiority analysis against adalimumab monotherapy at 24 weeks as measured by change from baseline in DAS28 score (a composite endpoint assessing signs and symptoms of RA). In the OSKIRA-4 study, fostamatinib as a monotherapy met the first primary objective, showing a statistically significant superior DAS28 score change from baseline compared to placebo at 6 weeks at the 100mg twice daily dose and the 100mg twice daily for a month followed by 150mg once daily dose, but not at the 100mg twice daily for a month followed by 100mg once daily dose. The OSKIRA-4 study did not meet its second primary objective as all fostamatinib monotherapy doses were inferior to adalimumab monotherapy at week 24 based on DAS28. The adalimumab monotherapy ACR20 result at the 24 week endpoint was 59%. The safety and tolerability findings for fostamatinib as reported in the OSKIRA-4 study were generally consistent with that previously observed in the TASKi Phase II programme.