A-71623

A-71623 is a selective agonist of CCKA receptor with an IC50 value of 3.7 nM in guinea pig pancreas [1, 2].

CCKA receptors belong to a subtype of cholecystokinin (CCK) receptors in the brain. CCK is a type of neuropeptide present throughout the central nervous system. CCK can act as a neurotransmitter in both normal and abnormal brain. CCK receptors exist in two forms in the brain. Another subtype of CCK receptors is CCKB subtype [1].

In NCI-H345 cells possessing CCKB/gastrin receptors, A-71623 was weak and behaved as a partial agonist in calcium studies [2]. A-71623 had very low affinity to CCK binding sites in C6 cells with an IC50 value of 1236 ± 81 nM [3]. It is hard to find the CCKA response result of the application of A-71623 in cells.

In radioligand binding assays, A-71623 showed IC50 values of 3.7 nM for CCKA in guinea pig pancreas and 4500 nM for CCKB in cerebral cortex. Data showed that A-71623 was an agonist in stimulating the release of pancreatic amylase, and this stimulatory effect was potently inhibited by L-364,718, a CCKA antagonist. Data showed that A-71623 acted as a full agonist in stimulating the breakdown of phosphoinositide in pancreas. In the ileum, A-71623 was also a potent agonist in stimulating CCKA receptors. In guinea pig gastric glands, the affinity of A-71623 for the CCK-B/gastrin receptor was 11 µM. This result demonstrated that A-71623 should be a potent and selective agonist at CCKA receptors [2].

References:
[1].  Gracey DJ, Bell R, King DJ. Differential effects of the CCKA receptor ligands PD-140,548 and A-71623 on latent inhibition in the rat. Progress in Neuro-Psychopharmacology and Biological Psychiatry, 2002, 26(3): 497-504.
[2].  Lin CW, Shiosaki K, Miller TR, et al. Characterization of two novel cholecystokinin tetrapeptide (30-33) analogues, A-71623 and A-70874, that exhibit high potency and selectivity for cholecystokinin-A receptors. Molecular pharmacology, 1991, 39(3): 346-351.
[3].  Kaufmann R, Lindschau C, Scho T, et al. Type B cholecystokinin receptors on rat glioma C6 cells. Binding studies and measurement of intracellular calcium mobilization. Brain research, 1994, 639(1): 109-114.

CCK-A receptor selective antagonists derived from the CCK-A receptor selective tetrapeptide agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623).[Pubmed:7837233]

J Med Chem. 1995 Jan 6;38(1):207-11.

Analogs of the CCK-A receptor selective agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623) were prepared in which the lysine residue was replaced with L-4-aminophenylalanine and D-or L-3-aminophenylalanine. These new analogs were moderately potent antagonists of CCK-8 in the isolated guinea pig gallbladder with exceptional CCK-A receptor selectivity as evaluated in membrane preparations from CHO K1 cells stably transfected with human CCK-A and CCK-B receptors.

Alternate drug delivery routes for A-71623, a potent cholecystokinin-A receptor agonist tetrapeptide.[Pubmed:8894966]

J Drug Target. 1996;4(2):69-78.

A-71623 (BOC-Trp-Lys(epsilon-N-2-methylphenylaminocarbonyl)- Asp-(N-methyl)-Phe-NH2) is a tetrapeptide which has high affinity and selectivity for cholecystokinin receptors; it is a potent appetite suppresser in animal studies. Because of its low (< 1%) oral bioavailability, studies were performed to assess the feasibility of delivery of A-71623 by pulmonary, sublingual, and transdermal routes of administration. The pKa was determined to be 4.2 by spectrophotometric titration; aqueous solubility is increased by increasing pH and by increasing ethanol content. The solubility of A-71623 in ethanol/propellant mixtures was investigated; solubility ranged from 1.0 to 2.5 mg/mL in mixtures of ethanol, propellant 11 (trichlorofluoromethane), and propellant 12 (dichlorodifluoromethane). The log apparent octanol/water partition coefficient was 2.8 at pH 5 and 1.0 at pH 8. Maximum stability at 70 degrees C was seen in the range of pH values of 5.5-7.5; hydrolysis of the N-terminal BOC group appears to be the primary route of degradation. Increasing ethanol content increases the stability; Arrhenius analysis indicated a t90 of 150 days under ambient conditions in 25% ethanol. Intratracheal delivery of 3 mumol/kg A-71623 in 50% ethanol to rats showed rapid and efficient absorption of drug from the lungs, with a Cmax of 2.7 microM and an AUC of 85 microM*min. Similar studies in dogs showed bioavailabilities of 59% and 46% for 2 and 3 mumol/kg intratracheal doses, respectively, relative to intravenous administration. Sublingual administration of 1 mumol/kg A-71623 in a vehicle of 80% ethanol/2% Klucel/2.5% peppermint oil gave high prolonged plasma levels of A-71623, with a Cmax of 0.37 microM, indicating high bioavailability and favorable partitioning and distribution effects from the sublingual cavity for this formulation. Transdermal delivery was examined by in vitro diffusion through human skin; the permeability coefficient of A-71623 in 40% ethanol was 2.6 x 10(-5) cm/hr, suggesting that transdermal delivery of up to 2 mg/day may be feasible. In conclusion, the results provide preliminary indications that delivery of efficacious doses of A-71623, and perhaps other CCK analogs, by alternate routes of delivery is probably feasible.

A-71623, a selective CCK-A receptor agonist, suppresses food intake in the mouse, dog, and monkey.[Pubmed:1513850]

Pharmacol Biochem Behav. 1992 Aug;42(4):699-704.

The anorectic actions of cholecystokinin (CCK)-8 and of a selective CCK-A agonist, A-71623, were examined in CD1 mice, beagle dogs, and cynomolgus monkeys. A-71623 suppressed intakes in all species tested, and the effects were blocked by a selective CCK-A antagonist, A-70104. In the dog only, CCK-8 was more potent on a molar basis compared to A-71623, although the effects of both CCK agonists were more short-lived in the dog compared to the other species tested. Our results support other evidence suggesting that the anorectic actions of exogenous application of CCK-8 in these species are mediated via stimulation of the CCK-A receptor subtype.

Differential effects of the CCKA receptor ligands PD-140,548 and A-71623 on latent inhibition in the rat.[Pubmed:11999900]

Prog Neuropsychopharmacol Biol Psychiatry. 2002 Apr;26(3):497-504.

Latent inhibition (LI) is a behavioural paradigm in which repeated exposure to a stimulus without consequence inhibits the formation of any new associations with that stimulus. To the extent that LI reflects a process of leaming to ignore irrelevant stimuli, disrupted LI has been suggested as an animal model for the attentional deficits observed in schizophrenia. The antipsychotic potential of cholecystokinin (CCK) stems from its colocalization with dopamine (DA) in the mesolimbic pathway, where it demonstrates both excitatory and inhibitory effects on dopaminergic activity. This may be explained by mediation through different receptor subtypes. A variety of hypotheses has emerged regarding the potential clinical application of subtype-selective CCK-based drugs. The present experiments examined the effects on LI of two selective CCK(A) ligands: PD-140,548 (a CCK(A) antagonist, Experiment 1: 0.001, 0.01, and 0.1 mg/kg) and A-71623 (a CCK(A) agonist, Experiment 2: 0.02, 0.05, and 0.1 mg/kg). In both experiments, the effects of haloperidol (0.1 mg/kg) were also investigated. Animals receiving 0.1 mg/kg of haloperidol or 0.001 or 0.1 mg/kg (but not 0.01 mg/kg) of PD-140,548 treated the preexposed stimulus as irrelevant after a low number of preexposures. In contrast, no facilitatory effect on LI was detectable at any of the A-71623 doses. The finding that A-71623 failed to enhance LI indicates that it is unlikely that this compound would have any antipsychotic effect within the clinical setting. Considering the facilitatory effect exerted by PD-140,548 on LI, it is probable that the inhibition of CCK activity might prove a more promising strategy for the pharmacological treatment of schizophrenia.