SOUTH SAN FRANCISCO, Calif., May 6, 2011 /PRNewswire/ -- Rigel Pharmaceuticals, Inc. (Nasdaq: RIGL) today announced that the company will assume development of R343, its inhaled syk inhibitor for allergic asthma that recently completed several Phase 1 clinical trials. Pfizer Inc. is returning full rights to the R343 program as a result of its decision to exit the allergy and respiratory therapeutic area within R&D. Rigel is evaluating the details of R343's development to date and expects to design a Phase 2 clinical trial with R343 later this year. "It is rare in our business that one has the opportunity to develop an asset which is both promising and on which the research and development has been as well done as the package that Pfizer is transferring to us. R343 will now become Rigel's most advanced in-house project," said James M. Gower, chairman and chief executive officer of Rigel. "The introduction of a therapeutic that would target a possible underlying cause of allergic asthma, such as R343's inhibition of syk in the immune cascade, may provide a significant advancement in the treatment of this disorder." In 2005, Rigel licensed its portfolio of inhaled small molecule syk inhibitors to Pfizer. A year later, Pfizer identified R343 as the lead product candidate for intrapulmonary delivery in the potential treatment of allergic asthma. R343 is highly selective to syk and has exhibited limited full body (systemic) exposure. In 2007, Pfizer began the first in a series of Phase 1 clinical trials of R343 in normal healthy adults and then later in mildly asthmatic adults. The initial results from these clinical trials, which have not yet been published, showed R343 to be well tolerated and with beneficial improvement in both the early and late phase asthmatic responses following an allergen challenge.