R343

R343 is a small molecule drug developed as an inhaled therapy targeting allergic asthma. It acts as a dual inhibitor of immunoglobulin E (IgE) and spleen tyrosine kinase (Syk), both of which play key roles in the allergic inflammatory cascade. By inhibiting Syk kinase activity in mast cells—downstream of IgE receptor activation—R343 aims to block intracellular signaling that leads to airway inflammation and obstruction characteristic of allergic asthma. The drug was initially developed by Rigel Pharmaceuticals and later licensed to Pfizer for clinical development. Clinical trials included Phase 1 and Phase 2 studies in patients with mild to moderate allergic asthma; however, the compound did not meet primary or secondary endpoints in these studies.