Inhibitors of phosphodiesterase type 4 (PDE4) act by increasing intracellular concentrations of cyclic AMP, which has a broad range of anti-inflammatory effects on various key effector cells involved in asthma and chronic obstructive pulmonary disease (COPD).

HPP737, a novel, potent and selective PDE4 inhibitor, has shown activity in vivo in animal models of airway inflammation. HPP737 is undergoing IND-enabling toxicology studies. Preclinical data suggests HPP737 may not have the side effects common to other PDE4 inhibitors in development.