Rigel Completes Phase I Clinical Trial of R406 in Rheumatoid Arthritis

April 1, 2005

Rigel Pharmaceuticals has completed a Phase I clinical study of R406, an orally delivered product candidate for the treatment of rheumatoid arthritis (RA), a chronic inflammatory disease that progressively destroys joint cartilage and bone.

The Phase I study evaluated the safety and pharmacokinetics of R406. Based on the preliminary results of the study, R406 was well-tolerated at the dose levels Rigel plans to use moving forward. The study also generated valuable pharmacokinetic/pharmacodynamic data establishing a strong correlation between R406 plasma levels and the inhibition of its target. This data will be helpful in guiding the future development of R406.

The study at Guy's Drug Research Unit in London was conducted in two sequential parts. The first was a placebo-controlled, escalating single-dose, human safety/pharmacokinetic clinical trial that included 35 volunteers. This was followed by a placebo-controlled, multiple-dose human safety clinical trial with an additional 24 volunteers.

Based on the trial's favorable safety data, Rigel believes it can enter into broader, longer-term safety and efficacy trials with R406 for the treatment of RA.