Anti-inflammatory and immunomodulatory potential of the novel PDE4 inhibitor roflumilast in vitro

From a series of benzamide derivatives, roflumilast (3-cyclo-propylmethoxy- 4- difluoromethoxy-N-[3,5-di-chloropyrid-4-yl] benzamide) was identified as a potent and selective PDE4 inhibitor. It inhibits PDE4 activity from huma n neutrophils with an IC50 of 0.8 nM without affecting PDE1 (bovine brain), PDE2 (rat heart), and PDE3 and PDE5 (human platelets) even at 10,000-fold higher concentrations. Roflumilast is almost equipotent to its major metabo lite formed in vivo (roflumilast N-oxide) and piclamilast (RP 73401), howev er, more than 100-fold more potent than rolipram and Ariflo (cilomilast; SB 207499). The anti-inflammatory and immunomodulatory potential of roflumila st and the reference compounds was investigated in various human leukocytes using cell-specific responses: neutrophils [N-formyl-methyl-leucyl-phenyla lanine (fMLP)-induced formation of LTB4 and reactive oxygen species (ROS)], eosinophils (fMLP- and C5a-induced ROS formation), monocytes, monocyte-der ived macrophages, and dendritic cells (lipopolysaccharide- induced tumor ne crosis factor-alpha synthesis), and CD4+ T cells (anti-CD3/anti-CD28 monocl onal antibody-stimulated proliferation, IL-2, IL-4, IL-5, and interferon-ga mma release). Independent of the cell type and the response investigated, t he corresponding IC values (for half-maximum inhibition) of roflumilast wer e within a narrow range (2-21 nM), very similar to roflumilast N-oxide (3-4 0 nM) and piclamilast (2-13 nM). In contrast, cilomilast (40-3000 nM) and r olipram (10-600 nM) showed greater differences with the highest potency for neutrophils. Compared with neutrophils and eosinophils, representing the t erminal inflammatory effector cells, the relative potency of roflumilast an d its N-oxide for monocytes, CD4+ T cells, and dendritic cells is substanti ally higher compared with cilomilast and rolipram, probably reflecting an i mproved immunomodulatory potential. The efficacy of roflumilast in vitro an d in vivo (see accompanying article in this issue) suggests that roflumilas t will be useful in the treatment of chronic inflammatory disorders such as asthma and chronic obstructive pulmonary disease.