The effect of RG 12525 on leukotriene D4-mediated pulmonary responses in guinea pigs.

RG 12525 (5-(2-[4-quinolin-2-yl)methoxyl] phenoxymethyl)benzyl tetrazole) is under investigation as a specific inhibitor of leukotriene D4 (LTD4). The present studies examine the effect of orally administered RG 12525 on LTD4 mediated pulmonary responses in three separate guinea pig models. The compound inhibited antigen-induced mortality in the systemic anaphylaxis model with an ED50 (95% confidence interval) = 2.2 (0.8-6.4) mg/kg. In this model, the activity half-life of RG 12525 was shown to be 6.5 hours and the compound offered significant protection within 15 minutes of administration. RG 12525 also protected against LTD4-induced bronchoconstriction in a model measuring changes in pulmonary function with an ED50 = 0.6 (0.4-1.0) mg/kg. The same level of activity was observed in a similar model which monitored changes in pulmonary function in response to exogenous antigen in actively-sensitized guinea pigs. Together, these data indicate that RG 12525 is a potent, orally active LTD4 antagonist which possesses the requisite profile for potential clinical development.