Rolf Hohlweg

NNC-112, NNC-687 and NNC-756, new selective and highly potent dopamine D1 receptor antagonists

The neurochemical properties of three novel benzazepine derivatives NNC-112, NNC-687 and NNC-756 were assessed. These compounds inhibited dopamine D1 receptor binding in vitro with low nanomolar to picomolar dissociation constants whereas those for the D2 receptor were in the micromolar range. Contrary to classical neuroleptics, but similar to the atypical neuroleptics, clozapine and fluperlapine, NNC-112, NNC-687 and NNC-756 were relatively more potent in inhibiting dopamine-stimulated adenylyl cyclase than [3H]SCH 23390 binding. Both NNC-112 and NNC-756 had high affinity for the 5-HT2 receptor whereas NNC-687 had low affinity for this receptor. The affinity for other receptors or neurotransmitter transporters was very low. In vivo, the dopamine D1 receptor selective profile of NNC-112, NNC-687 and NNC-756 was evident from the potent inhibition of D1 receptor binding whereas no effect on D2 receptor binding was apparent. In addition, the compounds blocked D1 receptor-mediated rotation in unilaterally 6-hydroxydopamine-lesioned rats, but had no effect on D2-induced rotation. Thus, NNC-112, NNC-687 and NNC-756 are potent and selective dopamine D1 receptor antagonists that may be useful in the treatment of schizophrenia.

(8-Naphthalen-1-ylmethyl-4-oxo-1-phenyl-1,3,8-triaza-spiro[4. 5]dec-3-yl)-acetic acid methyl ester (NNC 63-0532) is a novel potent nociceptin receptor agonist.

Spiroxatrine was identified as a moderately potent (Ki=118 nM) but non‐selective agonist at the human nociceptin/orphanin FQ receptor, ORL1. This compound was subject to chemical modification and one of the resulting compounds, (8‐naphthalen‐1‐ylmethyl‐4‐oxo‐1‐phenyl‐1,3,8‐triaza‐spiro[4.5]dec‐3‐yl)‐acetic acid methyl ester (NNC 63‐0532) was shown to have high affinity for ORL1 (Ki=7.3 nM). NNC 63‐0532 showed only moderate affinity for the following receptors (Ki values in parentheses): μ‐opioid (140 nM), κ‐opioid (405 nM), dopamine D2S (209 nM), dopamine D3 (133 nM) and dopamine D4.4 (107 nM) out of 75 different receptors, ion‐channels and transporters. In functional assays, NNC 63‐0532 was shown to be an agonist at ORL1 (EC50=305 nM), a much weaker agonist at the μ‐opioid receptor (EC50>10 μM) and an antagonist or weak partial agonist at dopamine D2S (IC50=2830 nM). Thus, NNC 63‐0532 is a novel non‐peptide agonist with ∼12 fold selectivity for ORL1 and may be useful for exploring the physiological roles of this receptor owing to its brain‐penetrating properties.

The preferential dopamine D3 receptor agonist cis-8-OH-PBZI induces limbic Fos expression in rat brain

The affinity, selectivity and agonistic properties of a constrained dopaminergic compound, the benz[e]indole cis-8-hydroxy-3-(n-propyl)1,2,3a.4,5,9b-hexahydro-1H-benz[e]indole (cis-8-OH-PBZI), for the dopamine D3 receptor were evaluated in competition binding experiments with cloned human dopamine receptor subtypes and, to further extend its profile, in in vitro radioligand binding assays. The Ki value measured for competition binding of this compound to the dopamine D3 receptor was 27.4+/-3.1 nM; this was 775-fold, 550-fold, 90-fold and 10-fold higher affinity than that measured at dopamine D1A, D5, D2s and D4 receptors, respectively. Evidence of dopamine receptor activation by cis-8-OH-PBZI was obtained by measuring dose-dependent increases in extracellular acidification rates and decreases in cAMP synthesis. In vivo, cis-8-OH-PBZI potently induced Fos protein immunoreactivity in the rat medial prefrontal cortex and shell region of the nucleus accumbens, but only marginally in the motor dorsolateral striatum, indicating a selective limbic site of action. In conclusion, the present data identify cis-8-OH-PBZI as having preference for the dopamine D3 receptor in vitro, and as having dopamine agonist activity and limbic sites of action in vivo.

Histamine h3 receptor antagonists

The SAR of H3 ligands has been difficult to evaluate because of species differences, multiple isoforms and constitutive activity, among other complicating factors. A review is given of the sometimes-conflicting affinity, activity and efficacy data of H3 agonists that has been described in literature to date.

Functional Differentiation of Multiple Dopamine D1-Like Receptors by NNC 01-0012

Abstract: Although members of the multiple vertebrate/mammalian dopamine D1 receptor gene family can be selectively classified on the basis of their molecular/phylogenetic, structural, and tissue distribution profiles, no subtype‐specific discriminating agents have yet been identified that can functionally differentiate these receptors. To define distinct pharmacological/functional attributes of multiple D1‐like receptors, we analyzed the ligand binding profiles, affinity, and functional activity of 12 novel NNC compounds at mammalian/vertebrate D1/D1A and D5/D1B, as well as vertebrate D1C/D1D, dopamine receptors transiently expressed in COS‐7 cells. Of all the compounds tested, only NNC 01‐0012 displayed preferential selectivity for vertebrate D1C receptors, inhibiting [3H]SCH‐23390 binding with an estimated affinity (∼0.6 nM) 20‐fold higher than either mammalian/vertebrate D1/D1A or D5/D1B receptors or the D1D receptor. Functionally, NNC 01‐0012 is a potent antagonist at D1C receptors, inhibiting to basal levels dopamine (10 µM)‐stimulated adenylyl cyclase activity. In contrast, NNC 01‐0012 (10 µM) exhibits weak antagonist activity at D1A receptors, inhibiting only 60% of maximal cyclic AMP production by dopamine, while acting as a partial agonist at vertebrate D1B and D1D receptors, stimulating adenylyl cyclase activity by ∼33% relative to the full agonist dopamine (10 µM), an effect that was blocked by the selective D1 receptor antagonist NNC 22‐0010. These data clearly suggest that the benzazepine NNC 01‐0012, despite lacking the N‐methyl residue in the R3 position, is a selective and potent D1C receptor antagonist. Moreover, the differential signal transduction properties exhibited by NNC 01‐0012 at these receptor subtypes provide further evidence, at least in vertebrates, for the classification of the D1C receptor as a distinct D1 receptor subtype.

Preparation of a potential positron emission tomographic radioligand for the dopamine transporter

NNC 12-0722 (1-[2-(bis(4-fluorophenyl)methoxy)ethyl]-4-methyl piperazine) is a new selective inhibitor of the dopamine transporter. [11C]NNC 12-0722 was prepared by N-methylation of the desmethyl compound with [11C]methyl iodide. The total radiochemical yield of [11C]NNC 12-0722 was 40%–50% with an overall synthesis time of 30–35 min. The radiochemical purity was higher than 99% and the specific radioactivity about 1500 Ci/mmol (55 GBq/μmol). Autoradiographic examination of [11C]NNC 12-0722 binding on whole hemisphere cryosections from human brain post mortem demonstrated specific binding in the caudate nucleus and putamen. In a positron emission tomographic examination of [11C]NNC 12-0722 in a cynomolgus monkey there was a rapid uptake of radioactivity in the brain. In the striatum, a region with a high density of dopamine transporters, the radioactivity was two times higher than in the cerebellum. These results indicate that [11C]NNC 12-0722 may be a useful radioligand for labelling of the dopamine transporter in man.

Synthesis and binding properties of [3H]NNC 12-0781, a new radioligand for the dopamine reuptake system

The tritiated dopamine reuptake inhibitor [3H]NNC 12-0781 ([1-[2-(bis(4-fluorophenyl)-methoxy)-ethyl]-4-(3-(2-furanyl)-2,3-[3H] - propyl)-piperazine) was radiolabelled in one step starting from 1-[2-(bis(4-fluorophenyl)-methoxy)-ethyl]-4-(3-(2-furanyl)-2-propenyl)- piperazine, using tritium gas and PdO as catalyst. The radiochemical purity of [3H]NNC 12-0781 was higher than 99% after HPLC purification with a specific radioactivity of 21 Ci/mmol. [3H]NNC 12-0781 bound specifically to rat striatum in vitro at +4 degrees C with a Kd of 1.76 nM and Bmax of 587 fmol/mg tissue. The nonspecific binding was about 10% at Kd. At +37 degrees C no acceptable binding was observed. The association of [3H]NNC 12-0781 thus has the characteristics of a radioligand for the dopamine transporter in vitro at +4 degrees C.