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A strategy to overcome the side effect liabilities of oral PDE4 inhibitors has been to deliver the drugs by inhalation. In this report, we identify 1-[[5-(1(S)-aminoethly)-2-[8-methoxy-2-(triflurormethyl)-5-quinolinyl]-4-oxazolyl] carbonyl]-4(R)-[(cyclopropylcarbonyl)amino]-L-proline, ethyl ester xinafoate salt, (COMPOUND 1) as a potent and selective inhibitor of PDE4 with biological and pharmacokinetic properties suitable for delivery by the inhaled route. COMPOUND 1 potently inhibits human PDE4 (IC(50)=70pM) with little or no activity against other PDEs. It is highly potent against PDE4B and PDE4D which are important isoforms of PDE4 controlling inflammation and airway functions. In an allergen-challenged Brown Norway rat model of asthma, COMPOUND 1 inhibited the late phase influx of inflammatory cells and reductions in lung function following its administration by the intratracheal or nose-only routes of administration. Important differences were seen between intratracheal COMPOUND 1 and our previously published results with the oral PDE4 inhibitor roflumilast (Celly et al., 2005), as COMPOUND 1 rapidly (within 1h) reversed the decline in lung function when it was given therapeutically to rats already challenged with antigen. COMPOUND 1 was weakly active by the oral route which is a finding consistent with results showing this compound has poor oral bioavailability in animals. Positive interactions between COMPOUND 1 and albuterol, and COMPOUND 1 and mometasone furoate were seen on the improvement in lung functions in allergen-challenged rats. These results identify COMPOUND 1 as a potent and selective inhibitor of PDE4 with properties suitable for delivery by inhalation.

Orally active phosphodiesterase 4 (PDE4) inhibitors have been developed for the treatment of asthma and chronic obstructive pulmonary disorders (COPD) although their full development has been limited by adverse side effects. Administration of PDE4 inhibitors by inhalation may improve their therapeutic index, but limited information exists on the efficacy of inhaled PDE4 inhibitors to improve lung function. In this study in ovalbumin-sensitized Brown Norway rats, roflumilast was given either intratracheally or by nose-only inhalation and changes in lung function (forced vital capacity, FVC; peak expiratory flow, PEF) and inflammatory cell influx (total cells, eosinophils and neutrophils) into the bronchoalveolar lavage (BAL) fluid were evaluated 24 h after allergen challenge. Intratracheal roflumilast, given 5 h before antigen challenge, inhibited the antigen-induced reductions in FVC (ED50 = 140 microg/kg, i.t.) and total cells appearing in the bronchoalveolar lavage fluid (ED50 = 50 microg/kg, i.t.). By the nose-only inhalation route, roflumilast reduced the bronchoalveolar lavage fluid total cells (ED50 = 10 microg/kg, estimated pulmonary deposition). Intratracheal roflumilast (600 microg/kg, i.t.) was also given to rats 24 h after the antigen challenge and reversed the antigen-induced reductions of FVC by 38% at 1 h, 54% at 5 h and 71% by 16 h. Intratracheal roflumilast also reduced the number of inflammatory cells in the bronchoalveolar lavage fluid and reduced the interstitial airway edema caused by the antigen challenge. These results support the development of inhaled PDE4 inhibitors for the treatment of asthma and COPD, particularly for the improvement of lung function.