Pharmacological characterization of the benz[ d ]indolo[2,3- g ]azecine LE300, a novel type of a nanomolar dopamine receptor antagonist

Abstract

LE300 (7-methyl-6,7,8,9,14,15-hexahydro-5 H-benz[d]indolo[2,3-g]azecine), a previously reported subnanomolar antagonist at rat striatal dopamine D1 receptors, and three of its azecine-N-substituted congeners combining structural elements of serotonin and dopamine were comprehensively characterised (binding and function) at recombinant human dopamine receptors. Radioligand competition experiments at D1 and D2L receptors were performed by using [(3)H]SCH23390 and [(3)H]spiperone, respectively. Functional assays included measurements of cAMP, intracellular [Ca(2+)], and [(35)S]GTPgammaS-binding. LE300 was the most potent compound with a 10- to 20-fold selectivity for D1 over D2L receptors as measured in equilibrium binding experiments [competition radioligand binding: K(i)(D1)=1.9 nM, K(i)(D2L)=44.7 nM; [(35)S]GTPgammaS-binding: K(i)(D1)=1.8 nM, K(i)(D2L)=21.5 nM]. In functional (non-equilibrium) experiments, LE300 did not reveal a D1 over D2L selectivity but retained nanomolar K(i) values at human dopamine receptors (measurement of cAMP: K(i)(D1)=25.9 nM, K(i)(D2L)=5.2 nM; measurement of intracellular [Ca(2+)]: K(i)(D1)=60.4 nM, K(i)(D2L)=19.0 nM). LE300 is currently under investigation for usefulness as positrone emission tomography ligand. In conclusion, LE300 is a novel type of a nanomolar dopamine receptor antagonist combining structural core elements of dopamine and serotonin, and may become useful as positrone emission tomography ligand.

Dopamine Receptor Ligands. Part VII [1]: Novel 3‐Substituted 5‐Phenyl‐1, 2, 3, 4, 5, 6‐hexahydro‐azepino‐[4, 5‐b]indoles as Ligands for the Dopamine Receptors

“…In summary, cyclic compounds with micromolar affinities were synthesized (3 a-e), that showed some selectivity for the hD 1 receptor (3 c had~eight times higher affinity to hD 1 than to hD 2L or hD 5 ).Interestingly, in contrast to the azepine N-H compound (3 a) which is an agonist, the data suggests that compounds 3 c and 3 e are a partial and an inverse agonist, respectively.…”

“…Preincubation was necessary to produce adequate levels of cAMP for detection. Cells that expressed the hD 1 and hD 5 receptors, could then be …”

“…The compounds were tested in radioligand binding studies using Chinese hamster ovary (CHO)-cells stably expressing hD 1 -, hD 2L -, hD 4 -and hD 5 -receptors. In an initial screen, the decrease in receptor-bound radioactivity, by a 10 µM solution of the test compound, was measured.…”

“…The methods used have been previously described in further detail with special regards to the pharmacological behaviour of compound 1 (LE 300) [5]. 2 : 95 % air in HAM/F12-medium (Sigma-Aldrich) supplemented with 10 % fetal bovine serum, 1mM L-glutamine, 20 U/ml penicillin G, 20 µg/ml streptomycin and 0,2 µg/ml G 418 (all by Sigma-Aldrich).…”

“…A number of compounds are known to interact selectively with the hD 1 -receptor including the well known hD 1 -selective antagonist SCH 23390 2 a [2], the agonist SKF 38393 2 b [3] and the indoloazezine LE 300 1, a new lead structure containing both a tryptamine unit and a β-phenylethylamine structure [4,5] (ç s please check sentence). We were interested in synthesizing corresponding indoloazepines 3 a-i with the goal of generating a new class of antipsychotics selective for the hD 1 -receptor family but which lack the extrapyramidal side effects of classical antipsychotic drugs [6] (Figure 1).…”