Pfizer Inc, New York, has returned full rights of R343, an inhaled syk inhibitor for allergic asthma, to Rigel Pharmaceuticals Inc, South San Francisco, following its decision to exit the allergy and respiratory therapeutic area within R&D. Rigel will assume development of R343, which recently completed several phase 1 clinical trials. Currently, 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.

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. Syk is a protein tyrosine kinase that plays a pivotal role in IgE receptor signaling in mast cells. R343 is designed to bind to the syk in mast cells to interrupt the signal from the IgE receptors. The ability of R343 to inhibit syk potentially prevents or stops the immune response to the allergen and may be effective in the short and long-term control of allergic asthma.

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.

Source: Rigel Pharmaceuticals Inc