Preclinical Evaluation of an Inhibitor of Cytosolic Phospholipase A2α for the Treatment of Asthma

Asthma is a chronic inflammatory lung disease with considerable unmet medical needs for new and effective therapies. Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) is the rate-limiting enzyme that is ultimately responsible for the production of eicosanoids implicated in the pathogenesis of asthma. We investigated a novel cPLA(2)alpha inhibitor, PF-5212372, to establish the potential of this drug as a treatment for asthma. PF-5212372 was a potent inhibitor of cPLA(2)alpha (7 nM) and was able to inhibit prostaglandin (PG)D-2 and cysteinyl leukotriene release from anti-IgE-stimulated human lung mast cells (0.29 and 0.45 nM, respectively). In a mixed human lung cell population, PF-5212372 was able to inhibit ionomycin-stimulated release of leukotriene B-4, thromboxane A(2), and PGD(2) (2.6, 2.6, and 4.0 nM, respectively) but was significantly less effective against PGE(2) release (>301 nM; p < 0.05). In an in vitro cell retention assay, PF-5212372 retained its potency up to 24 h after being washed off. In a sheep model of allergic inflammation, inhalation of PF-5212372 significantly inhibited late-phase broncho-constriction (78% inhibition; p < 0.001) and airway hyper-responsiveness (94% inhibition; p < 0.001), and isolated sheep lung mast cell assays confirmed species translation via effective inhibition of PGD(2) release (0.78 nM). Finally, PF-5212372 was assessed for its ability to inhibit the contraction of human bronchi induced by AMP. PF-5212372 significantly inhibited AMP-induced contraction of human bronchi (81% inhibition; p < 0.001); this finding, together with the ability of this drug to be effective in a wide range of preclinical asthma models, suggests that inhibition of cPLA(2)alpha with PF-5212372 may represent a new therapeutic option for the treatment of asthma.