In vitro and in vivo pharmacological profile of PL-3994, a novel cyclic peptide (Hept-cyclo(Cys-His-Phe-d-Ala-Gly-Arg-d-Nle-Asp-Arg-Ile-Ser-Cys)-Tyr-[Arg mimetic]-NH(2)) natriuretic peptide receptor-A agonist that is resistant to neutral endopeptidase and acts as a bronchodilator.

The pharmacological and airways relaxant profiles of PL-3994 (Hept-cyclo(Cys-His-Phe-d-Ala-Gly-Arg-d-Nle-Asp-Arg-Ile-Ser-Cys)-Tyr-[Arg mimetic]-NH(2)), a novel natriuretic peptide receptor-A (NPR-A) agonist, were evaluated. PL-3994, a full agonist, has high affinity for recombinant human (h), dog, or rat NPR-As (K(i)s of 1, 41, and 10 nm, respectively), and produced concentration-dependent cGMP generation in human, dog and rat NPR-As (respective EC(50)s of 2, 3 and 14 nm). PL-3994 has a K(i) of 7 nm for hNPR-C but was without effect on cGMP generation in hNPR-B. PL-3994 (1 µm) was without significant effect against 75 diverse molecular targets. PL-3994 or BNP, a natural NPR ligand, produced concentration-dependent relaxation of pre-contracted guinea-pig trachea (IC(50)s of 42.7 and 10.7 nm, respectively). PL-3994, and also BNP, (0.1 nm-100 µm) elicited a potent, concentration-dependent but small relaxation of pre-contracted human precision-cut lung slices (hPCLS). Intratracheal PL-3994 (1-1000 µg/kg) produced a dose-dependent inhibition of the bronchoconstrictor response evoked by aerosolized methacholine, but was without significant effect on cardiovascular parameters. PL-3994 was resistant to degradation by human neutral endopeptidase (hNEP) (92% remaining after 2 h), whereas the natural ligands, ANP and CNP, were rapidly metabolized (≤1% remaining after 2 h). PL-3994 is a potent, selective NPR agonist, resistant to NEP, with relaxant effects in guinea-pig and human airway smooth muscle systems. PL-3994 has the profile predictive of longer clinical bronchodilator activity than observed previously with ANP, and suggests its potential utility in the treatment of asthma, in addition to being a useful research tool to evaluate NPR biology.

Antiinflammatory effects of the phosphodiesterase-4 inhibitor cilomilast (Ariflo) in chronic obstructive pulmonary disease.

Cilomilast (Ariflo), a new oral phosphodiesterase-4 selective inhibitor, improves lung function in chronic obstructive pulmonary disease (COPD). We have evaluated its antiinflammatory effects in 59 patients with COPD randomized to receive cilomilast, 15 mg two times a day, or placebo for 12 weeks. Induced sputum differential cell counts were obtained at baseline and at five further visits. Interleukin-8 and neutrophil elastase were measured in sputum supernatant. Bronchial biopsies obtained at baseline and at Week 10 were immunostained and counted for neutrophils, CD8+ and CD4+ T-lymphocyte subsets, and CD68+ macrophages. Cells expressing the genes for interleukin-8 and tumor necrosis factor-alpha were identified by in situ hybridization and quantified. Compared with placebo, analysis of variance (ANOVA) of the change from baseline showed that cilomilast did not alter any sputum endpoint or FEV1. However, bronchial biopsies demonstrated that cilomilast treatment was associated with reductions in CD8+ (p = 0.001; ANOVA) and CD68+ cells (p < 0.05; ANOVA). In addition, by Poisson analysis, comparison of cell counts analyzed as a ratio of active to placebo demonstrated reductions of CD8+ (48% p < 0.01) and CD68+ (47% p = 0.001) cells. This is the first demonstration of reduction by any agent of airway tissue inflammatory cells characteristic of COPD. Phosphodiesterase-4 inhibitors represent a promising new class of substances for use in antiinflammatory treatment of this disease.