Characterization of binding sites of a new neurotensin receptor antagonist, [3H]SR 142948A, in the rat brain.

The present study describes the characterization of the binding properties and autoradiographic distribution of a new nonpeptide antagonist of neurotensin receptors, [3H]SR 142948A (2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methyl carbamoyl)-2-isopropylphenyl)-1H-pyrazole-3-carbonyl]-amino]-ad amantane-2-carboxylic acid, hydrochloride), in the rat brain. The binding of [3H]SR 142948A in brain membrane homogenates was specific, time-dependent, reversible and saturable. [3H]SR 142948A bound to an apparently homogeneous population of sites, with a Kd of 3.5 nM and a Bmax value of 508 fmol/mg of protein, which was 80% higher than that observed in saturation experiments with [3H]neurotensin. [3H]SR 142948A binding was inhibited by SR 142948A, the related nonpeptide receptor antagonist, SR 48692 (2-[[1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazole -3-carbonyl]amino]-adamantane-2-carboxylic acid) and neurotensin. Saturation and competition studies in the presence or absence of the histamine H1 receptor antagonist, levocabastine, revealed that [3H]SR 142948A bound with similar affinities to both the levocabastine-insensitive neurotensin NT1 receptors (20% of the total binding population) and the recently cloned levocabastine-sensitive neurotensin NT2 receptors (80% of the receptors) (Kd = 6.8 and 4.8 nM, respectively). The regional distribution of [3H]SR 142948A binding in the rat brain closely matched the distribution of [125I]neurotensin binding. In conclusion, these findings indicate that [3H]SR 142948A is a new potent antagonist radioligand which recognizes with high affinity both neurotensin NT1 and NT2 receptors and represents thus an excellent tool to study neurotensin receptors in the rat brain.

X-ray structural characterization of SR 142948, a novel potent synthetic neurotensin receptor antagonist.

SR 142948 is an original and extremely potent neurotensin receptor antagonist developed in a promising approach to novel antipsychotic drugs. The X-ray structure was elucidated and compared to SR 48692 and levocabastine, providing new informations about the possible recognition process of NT receptor subtypes.

Biochemical and pharmacological activities of SR 142948A, a new potent neurotensin receptor antagonist.

SR 142948A, 2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methylc arbamoyl)-2-isopropylphenyl)-1H-pyrazole3-carbonyl]amino] adamantane-2-carboxylic acid, hydrochloride, a new and extremely potent neurotensin (NT) receptor antagonist, has been characterized in comparison with SR 48692. This selective compound possesses nanomolar affinities for NT receptors, recognizes the two binding sites described for the NT receptor and fully displaces [3H]SR 48692 specific binding. SR 142948A antagonizes the classical in vitro NT effects, i.e., inositol monophosphate formation in HT 29 cells (IC50 = 3.9 nM) or intracellular calcium mobilization in Chinese hamster ovary cells transfected with the human receptor. It dose-dependently (0.04-640 x 10(-3) mg/kg p.o.) inhibits the turning behavior induced by unilateral intrastriatal injection of NT in mice, with the biphasic profile previously seen for SR 48692. At 0.1 mg/kg (i.p.), it completely antagonizes NT-evoked acetylcholine release in the rat striatum. In contrast to SR 48692, SR 142948A (p.o.) blocks both hypothermia and analgesia induced by i.c.v. injection of NT (mice and/or rats) but is unable to modify the dopamine release evoked by NT injection into the ventral tegmental area. In summary, SR 142948A retains the properties of the lead compound SR 48692 (no intrinsic agonist activity, oral bioavailability, long duration of action and good brain access), reveals a wider spectrum of activity than SR 48692 (probably due to the inhibition of NT receptor subtypes) and represents an additional tool for further exploration of the therapeutic potential of this class of compounds.

Biochemical and pharmacological properties of SR 46349B, a new potent and selective 5-hydroxytryptamine2 receptor antagonist.

A new potent, selective and p.o. active serotonergic [5-hydroxytryptamine (5-HT2)] receptor antagonist, SR 46349B [trans, 4-([3Z)3-(2-dimethylaminoethyl)oxyimino-3(2-flurophenyl++ +)propen-1-yl]phenol hemifumarate) has been characterized by a series of "in vitro" and "in vivo" methods. Based upon binding studies with 5-HT2 receptors in rat brain cortical membranes and blockade of 5-HT-induced contractions in isolated tissues (rabbit thoracic aorta, rat jugular vein, rat caudal artery, rat uterus and guinea pig trachea), SR 46349B showed high affinity for 5-HT2 receptors. Furthermore, SR 46349B displayed moderate affinity for the 5-HT1C receptor and had no affinity for the other 5-HT1 subclass (5-HT1A, 5-HT1B or 5-HT1D), dopamine (D1 or D2), "alpha" adrenergic (alpha-1 or alpha-2), sodium and calcium channel and histamine (H1) receptors. It did not interact with histamine (H1), alpha-1 adrenergic and 5-HT3 receptors in smooth muscle preparations. No inhibition of the uptake of norepinephrine, dopamine or 5-HT was seen. Based upon blockade of pressor responses to 5-HT in pithed rats and in vivo binding studies in mice, SR 46349B was found to be a potent and p.o. active 5-HT2 receptor antagonist with a relatively long duration of action. Behavioral experiments, including mescaline- and 5-hydroxytryptophan-induced head twitches and learned helplessness, as well as sleep-waking cycle and EEG spectral parameter studies, indicated that SR 46349B has a classical 5-HT2 psychopharmacological antagonist profile.