Pharamcological Characterization of a Novel Long-acting Histamine H₁ Receptor Antagonist, KAA-276

Abstract

The pharmacological profile of a newly synthesized histamine H₁ receptor antagonist, KAA-276 (1-[1-(4-fluorophenylmethyl)-1H-benzimidazol-2-yl]-5-[2-[4-(2-carboxyethyl)-phenyl]ethyl]-1, 5-diazacyclooctane sulfate), was characterized. In a H₁ receptor binding assay in vitro, KAA-276 inhibited [³H]mepyramine binding to guinea pig cerebellar membrane preparations with an IC₅₀ of 0.66 nM. The inhibitory potency of KAA-276 was greater than that of terfenadine, but similar to that of astemizole and letotifen. KAA-276 antagonized the histamine-induced constriction of ileum and trachea isolated from guinea pigs in a dose-dependent manner with a concomitant reduction in the maximum response. Furthermore, the inhibitory effect of KAA-276 on histamine induced contraction was potentiated depending on the duration of preincubation time and revealed an irreversible property. KAA-276 given orally, intraduodenally, and by inhalation significantly inhibited histamine-induced bronchoconstriction dose-dependently in guinea pigs. Inhalation of KAA-276 exhibited inhibitory activity with a rapid onset and long duration, while intraduodenal administration resulted in action with a slow onset. Therefore, KAA-276, an irreversible and selective histamine, H₁ receptor antagonist, was shown to be a useful drug for therapeutic strategies against bronchial asthma when administered by the aerosol route.