Stereoselective inhibition of the binding of [ 3H]PK 11195 to peripheral-type benzodiazepine binding sites by a quinolinepropanamide derivative

Abstract

The specific binding of [ 3H]PK 11195 to the peripheral-type benzodiazepine binding site is inhibited by the 1-enantiomer of N,N-diethyl-α-methyl-2-phenyl-4-quinolinepropanamide ((−)Q 1) but not by its d-enantiomer ((+)Q 1). (−)Q 1 inhibited [ 3H]PK 11195 binding to several rat tissues with an IC 50 of less than 10nM whereas (+)Q 1 was at least 500 times less potent. This stereoselectivity was observed in all the tissues tested (brain, heart, kidney and adrenals). The same stereoselectivity was found for the displacement of the binding of [ 3H]PK 11195 in vivo, where (−)Q 1 had an ID 50 between 4–15 mg/kg and (+)Q 1 was completely inactive at all doses tested (i.e. up to 40 mg/kg). Neither isomer had appreciable affinity for central-type benzodiazepine binding sites ([ 3H]diazepam) nor for voltage-sensitive calcium channels ([ 3H]PN 200210 and [ 3H]verapamil).