The influx of leukocytes (eosinophils, lymphocytes, and monocytes) into the airways and their production of proinflammatory cytokines contribute to the severity of allergic asthma. We describe here the synthesis and pharmacological evaluation of a series of triazinylphenylalkylthiazolecarboxylic acid esters that were designed to act as lung-specific antedrugs and inhibitors of the production of interleukin (IL)-5, a primary eosinophil-activating and proinflammatory cytokine. Closer examination of the hydroxypropyl ester, 15, indicated its high metabolic stability (t(1/2) > 240 min) in human lung S9 fraction but rapid conversion (t(1/2) = 15 min) into the pharmacologically inactive carboxylic acid by human liver preparations. In stimulated human whole blood cultures, 15 reduced not only the production of IL-5 (IC(50) = 78 nM) but also the biosynthesis of the monocyte chemotactic proteins MCP-1 (IC(50) = 220 nM), MCP-2 (IC(50) = 580 nM), and MCP-3 (IC(50) = 80 nM). In vivo, intratracheal administration of 15 (6 mg/animal) to allergic sheep, either before (-4 h) or after (+1.5 h) the pulmonary allergen challenge, completely abrogated the late-phase airway response and reduced the bronchial hyperreactivity to inhaled carbachol.