ARC 239 dihydrochloride

ARC 239 dihydrochloride is a selective antagonist of α2B adrenoceptor with pKD value of 8.8 [1].

α2B adrenoceptor is a G-protein coupled receptor. α2-adrenergic receptors include three subtypes: α2A, α2B and α2C, which play an important role in regulating neurotransmitter release from adrenergic neurons in the central nervous system and from sympathetic nerves.

ARC 239 dihydrochloride is a selective α2B adrenoceptor antagonist. In rat brain, ARC 239 inhibited the binding of 5-HTIA receptor radioligands 8-OH-DPAT and RX 821002 to cortical membranes with Ki values of 63.1 and 136 nM respectively, which suggested that ARC 239 recognized 5-HT1A receptor [2]. Treatment human platelets with ARC 239 significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), epinephrine and arachidonic acid and increased collagen/epinephrine closure time, which suggested that α2B adrenoceptor play a critical role in platelet aggregation [3]. In cervical samples isolated from pregnant rats, ARC 239 effectively inhibited noradrenaline-stimulated contractions [4].

In C57BL/6 mice with gastric mucosal damage induced by acidified ethanol, ARC 239 (10.4 nM) antagonized gastroprotective effect induced by α2-adrenoceptor agonists [5].

References:
[1].  Bylund DB, Ray-Prenger C, Murphy TJ. Alpha-2A and alpha-2B adrenergic receptor subtypes: antagonist binding in tissues and cell lines containing only one subtype. J Pharmacol Exp Ther, 1988, 245(2): 600-607.
[2].  Meana JJ, Callado LF, Pazos A, et al. The subtype-selective alpha 2-adrenoceptor antagonists BRL 44408 and ARC 239 also recognize 5-HT1A receptors in the rat brain. Eur J Pharmacol, 1996, 312(3): 385-388.
[3].  Marketou ME, Kintsurashvili E, Androulakis NE, et al. Blockade of platelet alpha2B-adrenergic receptors: a novel antiaggregant mechanism. Int J Cardiol, 2013, 168(3): 2561-2566.
[4].  Gál A, Kolarovszki-Sipiczki Z, et al. The effect of the ARC 239 on the myometrial and cervical action in the rat, in vitro. Acta Pharm Hung, 2009, 79(2): 75-80.
[5].  Zádori ZS, Shujaa N, Brancati SB, et al. Both α2B- and α2C-adrenoceptor subtypes are involved in the mediation of centrally induced gastroprotection in mice. Eur J Pharmacol, 2011, 669(1-3): 115-120.

Characterization of sensory neurotransmission and its inhibition via alpha 2B-adrenoceptors and via non-alpha 2-receptors in rabbit iris.[Pubmed:7685502]

Naunyn Schmiedebergs Arch Pharmacol. 1993 Apr;347(4):394-401.

To find out whether, and which type of, adrenoceptors mediate prejunctional inhibition of sensory neurotransmitter release from trigeminal fibres, the modulation of twitch response to electrical field stimulation on rabbit isolated iris was investigated. Evoked iris sphincter contractions consisted of a minor fast cholinergic and a large slow component. The latter was unaffected by atropine and guanethidine, hence nonadrenergic noncholinergic in nature (NANC), but nearly completely abolished by capsaicin pretreatment and by the neurokinin receptor antagonist spantide. The response was probably not mediated by NK2 receptors as SR 48,968, an NK2 selective nonpeptide antagonist, failed to reduce the response to the release of the endogenous neurokinin(s) (and exogenous substance P), but in part due to NK1 receptor activation as shown by a reduction of response by CP 96,345, an NK1 selective non-peptide antagonist, and in part perhaps mediated by NK3 receptors. A small neurokinin receptor antagonist- and capsaicin-insensitive NANC contraction is probably not mediated by CGRP receptors. The alpha 2-adrenoceptor agonist oxymetazoline inhibited the evoked NANC response (22 nmol/l, IC20; about 40%, maximum inhibition) without affecting the cholinergic response (up to 1 mumol/l) or the postjunctional iris sensitivity to exogenous substance P. The inhibition was antagonized by rauwolscine (apparent -log KB 8.04) and by the relatively alpha 2B-adrenoceptor selective antagonist ARC-239 (-log KB 8.51). The alpha 2- and imidazoline receptor agonist aganodine inhibited the evoked NANC response (0.25 mumol/l, IC20; about 30%, maximum inhibition) without affecting the postjunctional substance P responses. Rauwolscine 0.3 mumol/l failed to antagonize this effect. It is concluded that the release of sensory neurotransmitter(s) from trigeminal fibres in the rabbit eye may be inhibited by alpha 2B-adrenoceptors and by a non-alpha 2-receptor, perhaps an imidazoline receptor.

Alpha-2A and alpha-2B adrenergic receptor subtypes: antagonist binding in tissues and cell lines containing only one subtype.[Pubmed:2835476]

J Pharmacol Exp Ther. 1988 May;245(2):600-7.

The affinities of 34 adrenergic antagonists for alpha-2 adrenergic receptors were determined from homogenate radioligand binding studies using [3H]yohimbine and [3H]rauwolscine. It has been suggested that alpha-2 adrenergic receptors can be subdivided into alpha-2A and alpha-2B subtypes. Oxymetazoline is selective for alpha-2A receptors, whereas prazosin is alpha-2B selective. Five different tissues were used, each of which has only one of the two subtypes: human platelet (alpha-2A), HT29 cell line (alpha-2A), human cerebral cortex (alpha-2A), neonatal rat lung (alpha-2B), and NG108-15 cell line (alpha-2B). The drug affinities were highly correlated when alpha-2A tissues were compared with alpha-2A tissues (r = 0.97 to 0.98) or when the two alpha-2B tissues were compared (r = 0.99). By contrast, comparison of an alpha-2A tissue with an alpha-2B tissue resulted in poor correlations (r = 0.77 to -0.87). Three new subtype selective drugs were identified among these drugs on the basis of at least a 10-fold greater affinity for one subtype. All three were selective for the alpha-2B subtype: ARC-239 (100-fold selective), chlorpromazine (18-fold selective), and 7-hydroxychlorpromazine (17-fold selective). These studies, by demonstrating distinct pharmacological profiles for the two alpha-2 adrenergic receptor subtypes in several different tissues, further support the existence and definition of these subtypes. The identification of a cell line for each subtype should be useful in the further study of alpha-2 adrenergic receptor subtypes.