(-)-U-50488 hydrochloride

(-)-U-50488 hydrochloride is a selective agonist for κ-opioid receptor [1].

The κ-opioid receptor (KOR) is a type of opioid receptor for opioid peptide dynorphin and controls addiction. Also, KOR plays an important role in stress, anxiety, anhedonia, depression and increased drug-seeking behavior.

(-)-U-50488 hydrochloride is a selective KOR agonist [1]. In isolated rat DRG neurons, U-50488 (0.3-40 μM) inhibited voltage-independent Ca2+ channel currents. In HeLa cells that didn’t express KOR, U-50488 (20 μM) blocked Ca2+ channels [2].

In rhesus monkeys, U-50488 exhibited potent antinociceptive activity and produced diuresis [1]. U-50488 enhanced contraction of the rabbit vas deferens induced by electrically with IC50 value of 26.5 nM. In mice, U-50488 impaired motor function with ED50 value of 15.3 mg/kg and reduced spontaneous activity [3]. In adult rats, U-50488 increased the threshold required to maintain self-stimulation responding, a depressive-like effect. While, males were significantly more sensitive than females to the threshold-increasing effects [4].

References:
[1].  Tang AH, Collins RJ. Behavioral effects of a novel kappa opioid analgesic, U-50488, in rats and rhesus monkeys. Psychopharmacology (Berl), 1985, 85(3): 309-314.
[2].  Hassan B, Ruiz-Velasco V. The κ-opioid receptor agonist U-50488 blocks Ca2+ channels in a voltage- and G protein-independent manner in sensory neurons. Reg Anesth Pain Med, 2013, 38(1): 21-27.
[3].  Lu SN, Ma SC, Zhang KG, et al. Comparison of pharmacological profile of selective kappa-opioid agonist K-II and U-50488. Yao Xue Xue Bao, 1991, 26(3): 171-174.
[4].  Russell SE, Rachlin AB, Smith KL, et al. Sex differences in sensitivity to the depressive-like effects of the kappa opioid receptor agonist U-50488 in rats. Biol Psychiatry, 2014, 76(3): 213-222.

Agonist-induced desensitization and down-regulation of the human kappa opioid receptor expressed in Chinese hamster ovary cells.[Pubmed:9535991]

J Pharmacol Exp Ther. 1998 Apr;285(1):28-36.

In this study, we examined whether the human kappa opioid receptor stably expressed in Chinese hamster ovary cells underwent desensitization and down-regulation after prolonged exposure to the agonist (-)U50,488H. Pretreatment with (-)U50,488H led to a reduction in the magnitude of increase in [35S]GTPgammaS binding by the subsequent application of (-)U50,488H. The extent of desensitization was related to duration of exposure and (-)U50,488H concentration. Pretreatment with (-)U50,488H also reduced the potency of (-)U50,488H in inhibiting forskolin-stimulated adenylate cyclase. In membranes of (-)U50,488H-pretreated cells, the affinity of (-)U50,488H was lower than that in the untreated control, and GTPgammaS had no effect on (-)U50,488H affinity, consistent with the notion of uncoupling of the receptor-G protein complex by (-)U50, 488H treatment. Down-regulation of the kappa opioid receptor also occurred on exposure to (-)U50,488H. Higher (-)U50,488H concentrations and/or longer incubation periods were required for down-regulation than for desensitization. The degree of down-regulation depended on the agonist concentration and incubation time. (-)U50,488H-induced desensitization and down-regulation were blocked by naloxone. (+)U50,488H, an inactive stereoisomer, did not cause desensitization or down-regulation. These results indicate that both processes were receptor-mediated. After incubation with (-)U50,488H and removal of (-)U50,488H, both (-)U50,488H-induced [35S]GTPgammaS binding and receptor number returned to the control level, which indicates that both processes were reversible. Thus, desensitization and down-regulation of the kappa opioid receptor occur after agonist exposure and represent two different adaptation mechanisms.

Withdrawal contractures of guinea-pig isolated ileum after acute activation of kappa-opioid receptors.[Pubmed:8388301]

Br J Pharmacol. 1993 May;109(1):48-52.

1. The present study was undertaken to investigate firstly whether a brief exposure for 5 min of guinea-pig isolated ileum to the kappa-opioid agonist, U-50,488H produced a withdrawal contracture on addition of naloxone and secondly to ascertain whether the response was due to the activation of kappa-opioid receptors. 2. Naloxone (10(-6) M) did not elicit a response in preparations exposed to U-50,488H (5 x 10(-7) M-2 x 10(-6) M). However, after exposure to U-50,488H (5 x 10(-7) M), naloxone (10(-6) M) produced a strong contracture if the agonist was washed out 1 min before the addition of the antagonist. 3. The addition of naloxone (10(-6) M) to the ileum preparation exposed to U-50,488H (10(-7) M or lower) caused a response of similar intensity irrespective of whether the agonist had been washed out. 4. The selective kappa-opioid antagonist, nor-binaltorphimine (2.7 x 10(-9) M and 2.7 x 10(-7) M), injected before the opioid agonists, prevented the naloxone-induced contracture after exposure to U-50,488H (8 x 10(-8) M) but did not affect the contracture after exposure to morphine (5 x 10(-7) M). 5. Nor-binaltorphimine (2.7 x 10(-9) M) caused a contraction of the ileum preparation when injected 5 min after exposure to U-50,488H (8 x 10(-8) M) but not after morphine (5 x 10(-7) M). 6. The alpha 2-adrenoceptor agonist, clonidine (3 x 10-8 M) and the calcium channel blocker, nifedipine(3 x 10-8 M), injected 1 min before naloxone, blocked the ileum contraction to naloxone after exposure to U-50,488H (8 x 10-8 M). The results demonstrate that the stimulation of Kappa-opioid receptors can induce a similar dependence in guinea-pig ileum to that produced by activation of micro receptors.

Effect of chronic administration of U-50,488H, a kappa-opioid receptor agonist, on central dopamine D2 receptors of the rat.[Pubmed:8390939]

Eur J Pharmacol. 1993 Apr 22;235(1):23-30.

The effect of U-50,488H, a kappa-opiate agonist, induced tolerance and abstinence on the characteristics of dopamine D2 receptors of brain regions and spinal cord was determined in the rat. Male Sprague-Dawley rats were injected with U-50,488H (25 mg/kg i.p) or its vehicle twice a day for 4 days. This procedure resulted in the development of tolerance to the analgesic activity of U-50,488H. The binding characteristics (Bmax and Kd values) of [3H]spiroperidol to dopamine D2 receptors were determined in discrete brain regions (hypothalamus, hippocampus, cortex, pons and medulla, midbrain, corpus striatum and amygdala) and spinal cord of U-50,488H-tolerant and -abstinent rats. Rats labeled as tolerant to U-50,488H were injected with U-50,488H on day 5 and killed 1 h later, whereas those labeled abstinent were killed on day 5 without the injection of the drug. Vehicle-injected rats served as controls. [3H]Spiroperidol bound to brain regions and spinal cord membranes at a single high affinity site. The Bmax and Kd values of [3H]spiroperidol in brain regions and spinal cord of U-50,488H-tolerant and abstinent rats did not differ from their respective vehicle-injected controls. The behavioral responses (total distance travelled, horizontal activity, movement time, total number of movements, number of stereotypic movements, stereotypic time and rest time) to different doses of a selective dopamine D2 receptor agonist, 2-bromo-alpha-ergocryptine (bromocriptine) were also determined in rats treated chronically with U-50,488H.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and absolute configuration of optically pure enantiomers of a kappa-opioid receptor selective agonist.[Pubmed:2822490]

FEBS Lett. 1987 Nov 2;223(2):335-9.

The enantiomers of U50,488, ligands highly selective for kappa-opioid receptors, have been prepared by a refined procedure and their optical purity demonstrated. The absolute configuration of (+)-trans-2-pyrrolidinyl-N-methylcyclohexylamine, a chemically versatile intermediate for synthesis of analogs of kappa-opioid receptor ligands with defined chirality, has been determined to be 1S,2S by X-ray crystallographic analysis. This intermediate has been used to synthesize the optically pure U50,488 enantiomers with known absolute configuration.