Cholecystokinin-27-32-amide. A member of a new class of cholecystokinin receptor antagonists

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and β-catenin in rat pancreatic acinar cells

PAK4 is the only member of the Group II p21-activated kinases (PAKs) present in rat pancreatic acinar cells and is activated by gastrointestinal hormones/neurotransmitters stimulating PLC/cAMP and by various pancreatic growth factors. However, little is known of the role of PAK4 activation in cellular signaling cascades in pancreatic acinar cells. In the present study, we examined the role of PAK4's participation in five different cholecystokinin-8 (CCK-8)-stimulated signaling pathways (PI3K/Akt, MAPK, focal adhesion kinase, GSK3, and β-catenin), which mediate many of its physiological acinar-cell effects, as well as effects in pathophysiological conditions. To define PAK4's role, the effect of two different PAK4 inhibitors, PF-3758309 and LCH-7749944, was examined under experimental conditions that only inhibited PAK4 activation and not activation of the other pancreatic PAK, Group I PAK2. The inhibitors' effects on activation of these five signaling cascades by both physiological and pathophysiological concentrations of CCK, as well as by 12-O-tetradecanoylphobol-13-acetate (TPA), a PKC-activator, were examined. CCK/TPA activation of focal adhesion kinases(PYK2/p125^FAK) and the accompanying adapter proteins (paxillin/p130^CAS), Mek1/2, and p44/42, but not c-Raf or other MAPKs (JNK/p38), were mediated by PAK4. Activation of PI3K/Akt/p70s6K was independent of PAK4, whereas GSK3 and β-catenin stimulation was PAK4-dependent. These results, coupled with recent studies showing PAK4 is important in pancreatic fluid/electrolyte/enzyme secretion and acinar cell growth, show that PAK4 plays an important role in different cellular signaling cascades, which have been shown to mediate numerous physiological and pathophysiological processes in pancreatic acinar cells.NEW & NOTEWORTHY In pancreatic acinar cells, cholecystokinin (CCK) or 12-O-tetradecanoylphobol-13-acetate (TPA) activation of focal adhesion kinases (p125^FAK,PYK2) and its accompanying adapter proteins, p130CAS/paxillin; Mek1/2, p44/42, GSK3, and β-catenin are mediated by PAK4. PI3K/Akt/p70s6K, c-Raf, JNK, or p38 pathways are independent of PAK4 activation.

Cyclic AMP-dependent protein kinase A and EPAC mediate VIP and secretin stimulation of PAK4 and activation of Na+,K+-ATPase in pancreatic acinar cells

Rat pancreatic acinar cells possess only the p21-activated kinase (PAKs), PAK4 of the group II PAK, and it is activated by gastrointestinal hormones/neurotransmitters stimulating PLC and by a number of growth factors. However, little is known generally of cAMP agents causing PAK4 activation, and there are no studies with gastrointestinal hormones/neurotransmitters activating cAMP cascades. In the present study, we examined the ability of VIP and secretin, which stimulate cAMP generation in pancreatic acini, to stimulate PAK4 activation, the signaling cascades involved, and their possible role in activating sodium-potassium adenosine triphosphatase (Na⁺,K⁺-ATPase). PAK4 activation was compared with activation of the well-established cAMP target, cyclic AMP response element binding protein (CREB). Secretin-stimulated PAK4 activation was inhibited by KT-5720 and PKA Type II inhibitor (PKI), protein kinase A (PKA) inhibitors, whereas VIP activation was inhibited by ESI-09 and HJC0197, exchange protein directly activated by cAMP (EPAC) inhibitors. In contrast, both VIP/secretin-stimulated phosphorylation of CREB (pCREB) via EPAC activation; however, it was inhibited by the p44/42 inhibitor PD98059 and the p38 inhibitor SB202190. The specific EPAC agonist 8-CPT-2- O-Me-cAMP as well 8-Br-cAMP and forskolin stimulated PAK4 activation. Secretin/VIP activation of Na⁺,K⁺-ATPase, was inhibited by PAK4 inhibitors (PF-3758309, LCH-7749944). These results demonstrate PAK4 is activated in pancreatic acini by stimulation of both VIP-/secretin-preferring receptors, as is CREB. However, they differ in their signaling cascades. Furthermore, PAK4 activation is needed for Na⁺,K⁺ATPase activation, which mediates pancreatic fluid secretion. These results, coupled with recent studies reporting PAKs are involved in both pancreatitis/pancreatic cancer growth/enzyme secretion, show that PAK4, similar to PAK2, likely plays an important role in both pancreatic physiological/pathological responses. NEW & NOTEWORTHY Pancreatic acini possess only the group II p21-activated kinase, PAK4, which is activated by PLC-stimulating agents/growth factors and is important in enzyme-secretion/growth/pancreatitis. Little information exists on cAMP-activating agents stimulating group II PAKs. We studied ability/effect of cyclic AMP-stimulating agents [vasoactive intestinal polypeptide (VIP), secretin] on PAK4 activity in rat pancreatic-acini. Both VIP/secretin activated PAK4/CREB, but the cAMP signaling cascades differed for EPAC, MAPK, and PKA pathways. Both hormones require PAK4 activation to stimulate sodium-potassium adenosine triphosphatase activity. This study shows PAK4 plays an important role in VIP-/secretin-stimulated pancreatic fluid secretion and suggests it plays important roles in pancreatic acinar physiological/pathophysiological responses mediated by cAMP-activating agents.

P21-activated kinase 4 in pancreatic acinar cells is activated by numerous gastrointestinal hormones/neurotransmitters and growth factors by novel signaling, and its activation stimulates secretory/growth cascades

p21-activated kinases (PAKs) are highly conserved serine/threonine protein kinases, which are divided into two groups: group-I (PAKs1-3) and group-II (PAKs4-6). In various tissues, Group-II PAKs play important roles in cytoskeletal dynamics and cell growth as well as neoplastic development/progression. However, little is known about Group-II PAK's role in a number of physiological events, including their ability to be activated by gastrointestinal (GI) hormones/neurotransmitters/growth factors (GFs). We used rat pancreatic acini to explore the ability of GI hormones/neurotransmitters/GFs to activate Group-II-PAKs and the signaling cascades involved. Only PAK4 was detected in pancreatic acini. PAK4 was activated by endothelin, secretagogues-stimulating phospholipase C (bombesin, CCK-8, and carbachol), by pancreatic GFs (insulin, insulin-like growth factor 1, hepatocyte growth factor, epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor), and by postreceptor stimulants (12-O-tetradecanoylphobol-13-acetate and A23187 ). CCK-8 activation of PAK4 required both high- and low-affinity CCK1-receptor state activation. It was reduced by PKC-, Src-, p44/42-, or p38-inhibition but not with phosphatidylinositol 3-kinase-inhibitors and only minimally by thapsigargin. A protein kinase D (PKD)-inhibitor completely inhibited CCK-8-stimulated PKD-activation; however, stimulated PAK4 phosphorylation was only inhibited by 60%, demonstrating that it is both PKD-dependent and PKD-independent. PF-3758309 and LCH-7749944, inhibitors of PAK4, decreased CCK-8-stimulated PAK4 activation but not PAK2 activation. Each inhibited ERK1/2 activation and amylase release induced by CCK-8 or bombesin. These results show that PAK4 has an important role in modulating signal cascades activated by a number of GI hormones/neurotransmitters/GFs that have been shown to mediate both physiological/pathological responses in acinar cells. Therefore, in addition to the extensive studies on PAK4 in pancreatic cancer, PAK4 should also be considered an important signaling molecule for pancreatic acinar physiological responses and, in the future, should be investigated for a possible role in pancreatic acinar pathophysiological responses, such as in pancreatitis. NEW & NOTEWORTHY This study demonstrates that the only Group-II p21-activated kinase (PAK) in rat pancreatic acinar cells is PAK4, and thus differs from islets/pancreatic cancer. Both gastrointestinal hormones/neurotransmitters stimulating PLC and pancreatic growth factors activate PAK4. With cholecystokinin (CCK), activation is PKC-dependent/-independent, requires both CCK1-R affinity states, Src, p42/44, and p38 activation. PAK4 activation is required for CCK-mediated p42/44 activation/amylase release. These results show PAK4 plays an important role in mediating CCK physiological signal cascades and suggest it may be a target in pancreatic acinar diseases besides cancer.

Substrate Specificity and Possible Heterologous Targets of Phytaspase, a Plant Cell Death Protease

Plants lack aspartate-specific cell death proteases homologous to animal caspases. Instead, a subtilisin-like serine-dependent plant protease named phytaspase shown to be involved in the accomplishment of programmed death of plant cells is able to hydrolyze a number of peptide-based caspase substrates. Here, we determined the substrate specificity of rice (Oryza sativa) phytaspase by using the positional scanning substrate combinatorial library approach. Phytaspase was shown to display an absolute specificity of hydrolysis after an aspartic acid residue. The preceding amino acid residues, however, significantly influence the efficiency of hydrolysis. Efficient phytaspase substrates demonstrated a remarkable preference for an aromatic amino acid residue in the P3 position. The deduced optimum phytaspase recognition motif has the sequence IWLD and is strikingly hydrophobic. The established pattern was confirmed through synthesis and kinetic analysis of cleavage of a set of optimized peptide substrates. An amino acid motif similar to the phytaspase cleavage site is shared by the human gastrointestinal peptide hormones gastrin and cholecystokinin. In agreement with the established enzyme specificity, phytaspase was shown to hydrolyze gastrin-1 and cholecystokinin at the predicted sites in vitro, thus destroying the active moieties of the hormones.

Gastrointestinal growth factors and hormones have divergent effects on Akt activation

Akt is a central regulator of apoptosis, cell growth and survival. Growth factors and some G-protein-coupled receptors (GPCR) regulate Akt. Whereas growth-factor activation of Akt has been extensively studied, the regulation of Akt by GPCR's, especially gastrointestinal hormones/neurotransmitters, remains unclear. To address this area, in this study the effects of GI growth factors and hormones/neurotransmitters were investigated in rat pancreatic acinar cells which are high responsive to these agents. Pancreatic acini expressed Akt and 5 of 7 known pancreatic growth-factors stimulate Akt phosphorylation (T308, S473) and translocation. These effects are mediated by p85 phosphorylation and activation of PI3K. GI hormones increasing intracellular cAMP had similar effects. However, GI-hormones/neurotransmitters [CCK, bombesin, carbachol] activating phospholipase C (PLC) inhibited basal and growth-factor-stimulated Akt activation. Detailed studies with CCK, which has both physiological and pathophysiological effects on pancreatic acinar cells at different concentrations, demonstrated CCK has a biphasic effect: at low concentrations (pM) stimulating Akt by a Src-dependent mechanism and at higher concentrations (nM) inhibited basal and stimulated Akt translocation, phosphorylation and activation, by de-phosphorylating p85 resulting in decreasing PI3K activity. This effect required activation of both limbs of the PLC-pathway and a protein tyrosine phosphatase, but was not mediated by p44/42 MAPK, Src or activation of a serine phosphatase. Akt inhibition by CCK was also found in vivo and in Panc-1 cancer cells where it inhibited serum-mediated rescue from apoptosis. These results demonstrate that GI growth factors as well as gastrointestinal hormones/neurotransmitters with different cellular basis of action can all regulate Akt phosphorylation in pancreatic acinar cells. This regulation is complex with phospholipase C agents such as CCK, because both stimulatory and inhibitory effects can be seen, which are mediated by different mechanisms.

Progress in developing cholecystokinin (CCK)/gastrin receptor ligands that have therapeutic potential

Gastrin and cholecystokinin (CCK) are two of the oldest hormones and within the past 15 years there has been an exponential increase in knowledge of their pharmacology, cell biology, receptors (CCK1R and CCK2R), and roles in physiology and pathological conditions. Despite these advances there is no approved disease indication for CCK receptor antagonists and only a minor use of agonists. In this review, the important factors determining this slow therapeutic development are reviewed. To assess this it is necessary to briefly review what is known about the roles of CCK receptors (CCK1R and CCK2R) in normal human physiology, their role in pathologic conditions, the selectivity of available potent CCKR agonists/antagonists as well as to review their use in human conditions to date and the results. Despite extensive studies in animals and in humans, recent studies suggest that monotherapy with CCK1R agonists will not be effective in obesity, nor CCK2R antagonists in panic disorders or CCK2R antagonists to inhibit growth of pancreatic cancer. Areas that require more study include the use of CCK2R agonists for imaging tumors and radiotherapy, CCK2R antagonists in hypergastrinemic states especially with long-term PPI use and for potentiation of analgesia as well as use of CCK1R antagonists for a number of gastrointestinal disorders [motility disorders (irritable bowel syndrome, dyspepsia, and constipation) and pancreatitis (acute and chronic)].

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

Moleular models for cholecystokinin-A receptor

Numerous techniques have been used to elucidate the structural basis for interaction of cholecystokinin (CCK)-related peptides with their hormone-binding receptor, the CCK-A receptor (CCK-AR), including structure-activity relationship studies, site-directed mutagenesis, photoaffinity-labeling, and solution NMR analysis of both CCK peptide ligands and peptide fragments derived from the CCK-A receptor. Different structural models have been developed for the peptide-receptor complexes using various subsets of the available experimental data (Giragossian & Mierke 2001; Ding et al. 2002; Escrieut et al. 2002). Here, we review details of the various models and evaluate the impact of selected experimental data sets on model development.

The biologically crucial C terminus of cholecystokinin and the non-peptide agonist SR-146,131 share a common binding site in the human CCK1 receptor. Evidence for a crucial role of Met-121 in the activation process

The cholecystokinin (CCK) receptor-1 (CCK1R) is a G protein-coupled receptor, which mediates important central and peripheral cholecystokinin actions. Our aim was to progress in mapping of the CCK1R binding site by identifying residues that interact with the methionine and phenylalanine residues of the C-terminal moiety of CCK because these are crucial for its binding and biological activity, and to determine whether CCK and the selective non-peptide agonist, SR-146,131, share a common binding site. Identification of putative amino acids of the CCK1R binding site was achieved by dynamics-based docking of the ligand CCK in a refined three-dimensional model of the CCK1R using, as constraints, previous results that identified contact points between residues of CCK and CCK1R (Kennedy, K., Gigoux, V., Escrieut, C., Maigret, B., Martinez, J., Moroder, L., Frehel, D., Gully, D., Vaysse, N., and Fourmy, D. (1997) J. Biol. Chem. 272, 2920-2926 and Gigoux, V., Escrieut, C., Fehrentz, J. A., Poirot, S., Maigret, B., Moroder, L., Gully, D., Martinez, J., Vaysse, N., and Fourmy, D. (1999) J. Biol. Chem. 274, 20457-20464). By this approach, a series of residues forming connected hydrophobic clusters were identified. Pharmacological and functional analysis of mutated receptors indicated that a network of hydrophobic residues including Cys-94, Met-121, Val-125, Phe-218, Ile-329, Phe-330, Trp-326, Ile-352, Leu-356, and Tyr-360, is involved in the binding site for CCK and in the activation process of the CCK1R. Within this hydrophobic network, the physico-chemical nature of residue 121 seems to be essential for CCK1R functioning. Finally, the biological properties of mutants together with dynamic docking of SR-146,131 in the CCK1R binding site demonstrated that SR-146,131 occupies a region of CCK1R binding site which interacts with the C-terminal amidated tripeptide of CCK, i.e. Met-Asp-Phe-NH(2). These new and important insights will serve to better understand the activation process of CCK1R and to design or optimize ligands.

Pharmacological profile of T-0632, a novel potent and selective CCKA receptor antagonist, in vivo

The pharmacological profile of a new CCKA receptor antagonist, T-0632 [sodium (S)-1-(2-fluorophenyl)-2,3-dihydro-3-[(3-isoquinolinylcarbonyl) amino]-6-methoxy-2-oxo-1H-indole-3-propanoate], was examined in in vivo studies and compared with those of L-364, 718 [3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1, 4-benzodiazepine-3-yl)-1 H-indole-2-carboxamide] and loxiglumide [D.L-4-(3,4-dichlorobenzoylamino)-5-(N-3-methoxypropyl-pentylam ino)-5- oxopentanoic acid]. In rats, intravenously administered T-0632, L-364,718 and loxiglumide dose dependently inhibited cholecystokinin octapeptide (CCK-8)-stimulated pancreatic exocrine secretion with estimated ED50 values of 0.025, 0.016 and 1.8 mg/kg, respectively. The ED50 values for intraduodenal administration of these compounds were 0.040, 0.26 and 3.0 mg/kg, respectively. In mice, orally administered T-0632 prevented caerulein-induced pancreatitis, CCK-8-induced inhibition of gastric emptying and CCK-8-induced gallbladder emptying in dose-dependent manners with ED50 values of 0.028, 0.04, and 0.12 mg/kg, respectively. The effect of T-0632 for caerulein-induced pancreatitis was 4-fold more potent than that for gallbladder emptying. In contrast, the effects of L-364,718 and loxiglumide for caerulein-induced pancreatitis were 2-4-fold weaker than those for gallbladder emptying. In dogs, T-0632 and loxiglumide maximally inhibited CCK-8-stimulated pancreatic amylase secretion at doses of 0.01 and 10 mg/kg, respectively. At these doses, the effect of T-0632 on CCK-8-induced increase in the gallbladder intraluminal pressure was weaker than that of loxiglumide. These results suggest that T-0632 has a potent antagonistic action on CCKA receptors in several animal species and the effects of T-0632 are more selective for the pancreas over the gallbladder compared with L-364,718 and loxiglumide.

Structure-affinity studies of C-terminally modified analogs of neuropeptide Y led to a novel class of peptidic Y1 receptor antagonist

A novel type of C-terminally modified analogs of the 36-mer peptide hormone neuropeptide Y has been synthesized, characterized and tested with respect to receptor affinity and biological activity in various systems. The compounds were obtained by synthesizing the fully protected peptide fragment NPY 1-35 or analogs of this, and coupling it in solution to various amines, alcohols, and modified tyrosine residues. It could be confirmed, that the C-terminal tyrosineamide of NPY is essential for its affinity to the Y1 receptor subtype. Obviously, the amino group of the amide part is more important than the oxygene atom of the carbonyl group, as NPY 1-35-tyrosinol has a lower affinity than NPY 1-35-tyrosinethioamide. NPY 1-35-tyramide could be shown to act as an antagonist in a Ca2+ release assay in human neuroblastoma cells. Analogs of NPY 1-35-tyramide showed the same structure-affinity relationships as NPY itself, suggesting, that there exists the same binding mode for the agonist and the antagonist.

Comparative conformational analysis of CCK-B agonist Boc-Trp-Phg-Asp-(1-Nal)-NH2 and CCK1-B antagonist Boc-Trp-Phg-Asp-(1-Nal)-N(Me)2 using 1HNMR spectroscopy and restrained molecular dynamics

The tetrapeptide Boc-Trp-Phg-Asp-(1-Nal)-NH2 is a potent CCK-B agonist. Interestingly, bis-methylation of the C-terminal carboxamide group of this compound leads to Boc-Trp-Phg-Asp-(1-Nal)-N(Me)2 which behaves as a CCK-B antagonist in electrophysiological studies on hippocampal neurones (Corringer et al., 1993). In order to ascertain whether bismethylation of the terminal carboxamide group has an influence on the conformational preferences of the peptide, we have undertaken a comparative conformational analysis of the two tetrapeptides by the combined use of 2D NMR spectroscopy and restrained molecular dynamics. The solution conformation of the two peptides were examined by 1H NMR in a d6-DMSO/H2O (80:20) mixture. 1H-1H distance constraints, derived from 2D NOESY and ROESY experiments, were used as inputs for subsequent restrained molecular dynamics simulations. Comparison of the NMR and molecular modeling data indicates different conformational preferences for these two peptides. Interestingly, the aromatic side chains of the CCK-B antagonist Boc-Trp-Phg-Asp-(1-Nal)-N(Me)2 in its preferential conformation, overlap their corresponding moieties in the two non peptide CCK-B antagonists L-362,260 and LY-288,513. The differences in conformational behaviour of the studied tetrapeptides could, at least in part, account for their opposite agonist/antagonist profile, a findings which could serve for the design of new conformationally restricted CCK-B analogs.

Binding of cholecystokinin-8 (CCK-8) peptide derivatives to CCKA and CCKB receptors

The structural requirements for the selective binding of cholecystokinin-8 (CCK-8)-related peptides to peripheral (CCKA) receptors are not sufficiently understood. In this study, the interaction of a series of newly shortened analogues of CCK-8 with both receptor subtypes was analyzed by displacement studies using [3H]-CCK-8 and 125I-Bolton-Hunter (BH)-CCK-8 as radioligands. The pentapeptide derivative of CCK-8, succinyl-Tyr (SO3H)-Met-Gly-Trp-Met-phenethylamide, was found to bind selectively with high affinity to the CCKA receptor. The replacement of Met28 and/or Met31 by norleucine and of L-Trp30 by its D-analogue had no significant effect on the binding properties of the peptide. Further C-terminal shortening resulted in a drastic loss of affinity and selectivity of the CCK receptor binding.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Pharmacological profile of KSG-504, a new cholecystokinin-A-receptor antagonist

Pharmacological effects of KSG-504, a newly synthetized compound, on the response induced by exogenous CCK-8 were investigated. KSG-504 inhibited 125I-CCK-8 binding to both rat pancreas and cerebral cortex with IC50 values of 2.0 x 10(-7) M and 8.0 x 10(-5) M, respectively. The selectivity ratio of KSG-504 for pancreatic CCK receptor (CCK-A) was estimated as 400. In the isolated pancreatic acini of rats, KSG-504 caused a parallel rightward shift of the concentration-response curve for CCK-8-stimulated amylase release with no change in its maximal response, indicating a competitive antagonism of the drug for the CCK-A receptor (Schild plot analysis; slope = 0.927, pA2 = 6.9). In addition, KSG-504 produced a significant inhibition of CCK-8-induced pancreatic amylase secretion when administered intravenously or intraduodenally to rats (ED50: 52 micrograms/kg/min by the i.v. route and 12.1 mg/kg by the i.d. route). KSG-504 had equipotent inhibitory effects on both CCK-8-stimulated pancreatic secretion and gallbladder contraction in dogs with ED50 values of 0.98 and 0.84 mg/kg, respectively. KSG-504 also inhibited the CCK-8-induced contraction of isolated guinea pig ileum in a concentration-dependent manner (IC50 = 3.0 x 10(-6) M). These results demonstrate that KSG-504 is a competitive and selective CCK-A-receptor antagonist that is effective in vivo after oral administration.

Modification of "peptoid" CCK-B antagonists to probe requirements for CCK-B agonist activity

This paper describes the use of the non-peptidal N-(2-adamantyloxycarbonyl)-alpha-methyl tryptophan phenylethylamide template of the "peptoid" CCK B antagonist compounds 1 as a basis to probe the functional group requirements of the CCK B receptor in order to produce an agonist response. Comparison of the peptoid template with inter-group distances in a fully extended conformation of the endogenous CCK-B agonist CCK 30-33 led to the design of a series of compounds 2 containing additional Ph, COOH and CONH2, functions at distances from the Trp indole ring that are able to mimic those in the natural ligand. The effect of these modifications was then assessed by measurement of CCK B binding affinities and potential agonist efficacy was investigated by comparison with contraction of guinea-pig isolated stomach corpus muscle strip stimulated by the CCK-B agonist pentagastrin. All compounds showed sub-micromolar binding affinities with each series displaying discernible dependence on intermediate chain length. All compounds (except 2f) were shown to be good CCK B antagonists; no compounds showed significant agonist activity up to a concentration of 1 microM.

Inhibitory effects of a cholecystokinin antagonist, loxiglumide (CR-1505), on the growth of freshly separated and xenografted human pancreatic cancer

The effects of cholecystokinin (CCK) and a CCK antagonist, loxiglumide (CR-1505), on four freshly separated and six xenografted human pancreatic cancers, were investigated. The level of DNA synthesis in only one of five tested pancreatic cancers was enhanced by CCK at concentrations of 0.01-10 nM, while in the other four cancers DNA synthesis was not affected. The levels of DNA, RNA, and protein synthesis (by 3H-thymidine, 3H-uridine, and 3H-leucine incorporation tests, respectively) in all the tested cancers were dose-dependently inhibited by loxiglumide at concentrations of 20-2000 microM, and the IC50 of loxiglumide for DNA synthesis in pancreatic cancers was 156 +/- 80 microM (means +/- SD). The in vivo effect of loxiglumide was assessed using a xenografted line (PC-HN) transplanted in nude mice. The in vivo 50% lethal dose of loxiglumide for nude mice was about 500 mg/kg. Death was caused by respiratory failure due to severe congestion of the lung after the administration of a large dose of loxiglumide. The growth of a PC-HN transplanted in the nude mice was significantly inhibited by subcutaneous loxiglumide at 250 mg/kg, twice a day for 28 days, which did not cause death. It is suggested that loxiglumide inhibits the in vivo and in vitro growth of human pancreatic cancer, perhaps independently of its action as a CCK antagonist, and this study also suggests that loxiglumide may be a new type of therapeutic agent to be used for the treatment of human pancreatic cancer.

2-Naphthalenesulphonyl L-aspartyl-(2-phenethyl)amide (2-NAP)--a selective cholecystokinin CCKA-receptor antagonist

1. The in vitro pharmacological characterization of the sodium salt of 2-naphthalenesulphonyl 1-aspartyl-(2-phenethyl)amide [2-NAP], a hydrophilic compound derived from the C-terminal aspartate-phenylalanine dipeptide of cholecystokinin (CCK), is described. 2. 2-NAP behaved as a competitive antagonist of sulphated cholecystokinin octapeptide (CCK-8) at CCKA-receptors in both intact tissue bioassays (guinea-pig gall bladder, pancreas and ileum, human and rabbit gall bladder) and a radioligand displacement assay (guinea-pig pancreatic cells). The mean pKB, over assays, was 6.5. 3. Compared to the other assays, the rabbit gall bladder assay gave a significantly higher pKB estimate [7.0] for 2-NAP and a significantly lower estimate [8.9] for devazepide (formerly L-364,718 and MK-329), a well-characterized CCKA-receptor antagonist; these anomalous results suggest that a different class of CCKA-receptors may be involved. 4. 2-NAP, was found to be highly selective, having at least 300 fold greater affinity for CCKA-receptors than for 50 other pharmacological loci, including gastrin/CCKB, as estimated by bioassay or radioligand displacement.

Examination of the effects of cholecystokinin 26-33 and neuropeptide Y on responses of visual cortical neurons of the cat

Extracellular recordings were made from 160 neurons in area 17 (n = 120) and area 18 (n = 40) of the visual cortex of anesthetized cats. Cells were classified according to their receptive field properties and their intracortical positions were evaluated histologically. Cholecystokinin 26-33, antagonists, (cholecystokinin 27-32, cholecystokinin 27-33 and proglumide), amino acids, neuropeptide Y and solvent vehicle (control), were administered to cells by microiontophoresis (cholecystokinin and neuropeptide Y) or by pressure (neuropeptide Y). The results of the tests with cholecystokinin 26-33 fell into four categories: enhancement (31%), suppression (24%), mixed, i.e. either biphasic responses or dose-related alterations in the direction of effect (20%), and no effect (25%). Enhancements of the visually elicited response were more prevalent in simple (43%) and unimodal/movement-sensitive (34%) cells than in complex (7%) cells. The converse was true for suppressions: 19% of simple cells, 24% of unimodal/movement-sensitive cells, and 31% of complex cells were suppressed. Thirty per cent of the unaffected cells were complex or unimodal/movement-sensitive; only 14% were simple. Cells in layers II-IV were more likely to have firing enhanced than suppressed by cholecystokinin 26-33. The converse was true for cells in layers V and VI, where 50% of responses were suppressed and only 22% were enhanced. Unaffected cells were found predominantly in layer III of areas 17, and the lower part of layer III and layer IV of area 18. Cholecystokinin 26-33 sometimes exerted delayed, response-suppressant effects; it also occasionally elevated responsiveness preferentially within the upper ranges (10-20 degrees/s) of velocity tuning curves. Cholecystokinin 26-33 altered the response-suppressant action of GABA in 11 of 19 visually sensitive cells. The peptide potentiated the visual responsiveness in half of the cells where cholecystokinin 26-33 diminished the GABA-induced suppressions (n = 8). The presumed antagonists either exerted no effect on firing or on cholecystokinin 26-33-induced effects, or had cholecystokinin 26-33-like actions themselves. There was a reversible partial antagonism of the effects of cholecystokinin 26-33 on only two of 11 cells tested. Neuropeptide Y injected by pressure or administered iontophoretically had variable and inconsistent effects on the visually evoked responses of 29 additional neurons from those described above. These effects were indistinguishable from those of the vehicle whether spontaneous activity, magnitude of the visually elicited response, spatial integrity of the RF substructure, orientation or velocity tuning was assessed.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure activity of C-terminal modified analogs of Ac-CCK-7

Previous work indicates that both the C-terminal phenylalanine amide and the tryptophan moieties of cholecystokinin (CCK) are critical pharmacophores for interaction with either the A or B receptor subtypes. We have examined a series of analogs of Ac-CCK-7 [Ac-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe33-NH2] (2) in which the phenyl ring of the C-terminal Phe-NH2 has been modified. Compounds were assessed in binding assays using homogenated rat pancreatic membranes and bovine striatum as the source of CCK-A and CCK-B receptors respectively and for anorectic activity after intraperitoneal administration to rats. Substitution of a number of cycloalkyl or bicyclic aryl moieties for the phenyl ring of phenylalanine33 including cyclopentyl (20), cyclohexyl (21), cyclooctyl (23), 2-(5,6,7,8-tetrahydro)naphthyl (26), 2-naphthyl (27), and 1-naphthyl (29) led to analogs with 10-70 times the anorectic potency of 2. The anorectic activity of 21 was blocked by the specific CCK-A receptor antagonist MK-329. Other bulky aliphatic groups in place of the phenylalanine33 aromatic ring such as isopropyl, 2-adamantyl and cyclohexylmethyl gave derivatives similar to 2 in potency. While most of the new compounds were comparable to CCK in binding assays, 23, 26, 27 and 29 were exceptionally potent with IC50s 10(-11)-10(-14) M in the pancreas. Compounds 23 and 29 were further evaluated for their ability to stimulate amylase secretion and found to have potencies similar to that of CCK. The dissociation between potency in the binding and amylase secretion assays suggests that they may interact with a high affinity binding site which is not coupled to amylase secretion. We conclude that CCK receptors possess a generous hydrophobic pocket capable of accommodating large alkyl groups in place of the side chain of phenylalanine33 and that the pharmacological profile of CCK analogs can be tailored by appropriate exploitation of this finding.

Perspectives of CCK antagonists in pancreatic research. Part II. Experimental studies

In this article, the effects of different classes of cholecystokinin (CCK) receptor antagonists in CCK-related physiological processes of the pancreas have been discussed. Both glutaramic acid derivatives and natural (benzodiazepine) analogs are potent, competitive antagonists of peripheral CCK receptors. These compounds thus provide a powerful tool for investigating the physiological and pharmacological actions of CCK in the gastrointestinal system, and have already clarified the role of CCK in pancreatic secretion and trophism or growth.

Perspectives of CCK antagonists in pancreatic research and clinical use. Part I

Cholecystokinin (CCK) is one of the most important regulators of pancreatic and digestive physiology. Its importance led to research and discovery of a number of CCK receptor antagonists. Some of them are experimentally and clinically used today in order to assess the relative contribution of CCK to different aspects of pancreatic physiology. Furthermore, clinical trials are running with the aim of determining their possible therapeutic indications in pancreatic diseases, such as acute and chronic pancreatitis or pancreatic carcinoma. The rationale and evidence for their use are discussed.

Progress in the development of potent bombesin receptor antagonists

Bombesin and the mammalian-related peptides gastrin-releasing peptide (GRP), GRP and neuromedin B have been shown to have numerous actions in the CNS, gastrointestinal tract and on growth. However, the role of the peptides in various physiological processes has remained unclear because of the lack of potent antagonists. Recent in vitro studies have described four different classes of bombesin receptor antagonist, some of which are active in the nanomolar range and in vivo. Robert Jensen and David Coy describe recent insights into peptide structural determinants of biological activity. Evidence from structure-function studies have resulted in identification of some analogues that function as potent antagonists in all systems examined. Furthermore, various subtypes of bombesin receptors can now be differentiated by these various classes of antagonist.

Pharmacological activity of cholecystokinin analogues modified in the Met28-Gly29 region

Analogues of the C-terminal octapeptide of cholecystokinin (CCK) modified in the Met28-Gly29 region, were tested for their ability to interact with peripheral cholecystokinin receptors on rat pancreatic acini and to stimulate amylase secretion. These analogues were further evaluated for their ability to recognize central CCK receptors on guinea pig brain membranes. The behavioral effect of these analogues was also tested after intrastriatal injection into mice. It appeared that these analogues were full CCK agonists in the peripheral system. Although some induced dopaminomimetic effects after intrastriatal injection into mice, being as potent as the C-terminal octapeptide of cholecystokinin (CCK-8), others did not have any effect and were able to antagonize CCK-8 actions in the striatum. The results of this study confirm that one can obtain very potent CCK analogues by modifying the peptide bond between Met28 and Gly29, and that this modification can produce either CCK agonists or antagonists of CCK-induced dopamine transmission in the striatum.

CCK antagonists interact with CCK-B receptors on human small cell lung cancer cells

The ability of cholecystokinin (CCK) receptor antagonists to interact with CCK receptors in small cell lung cancer (SCLC) cells was investigated. L-365,260, CCK-8, L-364,718, CBZ-CCK(27-32)-NH2 and proglumide analogue 10 inhibited specific 125I-CCK-8 binding to SCLC cells with IC50 values of 0.2, 2, 500, 100,000 and 500,000 nM, respectively. Gastrin-I and CCK-8 elevated the cytosolic Ca2+ when SCLC cells were loaded with Fura 2-AM. L-365,260 inhibited the cytosolic Ca2+ increase caused by 10 nM CCK-8 in a dose-dependent manner. The effects of 10 nM L-365,260 were reversed by high concentrations of CCK-8. These data indicate that L-365,260 functions as a reversible CCK-8 antagonist using SCLC cells.

Cholecystokinin antagonists proglumide, lorglumide and benzotript, but not L-364,718, interact with brain opioid binding sites

It has been reported that proglumide and L-364,718 potentiate opioid-induced antinociception. However, their mode of action in pain modulation is still not understood. To evaluate a possible interaction with opioid receptors, we determined the affinities of the CCK antagonists proglumide, lorglumide, benzotript and L-364,718 on mu, delta and kappa binding sites, using guinea pig brain crude synaptosome preparations. These affinities were compared to that of the central CCK binding site, using rat brain slide-mounted sections. At 100 microM, proglumide competed for 13% and 17% of mu and kappa binding sites, but did not interact with delta and CCK sites. At this concentration, lorglumide reduced mu, delta, kappa and CCK specific binding by 44%, 69%, 35% and 88%, whereas benzotript diminished it by 16%, 13%, 38% and 48%, respectively. L-364,718 did not interact with opioid receptors (assay limit of solubility, 10 microM) but had a high affinity for CCK binding sites (IC50, 126nM). The lack of selectivity of proglumide, lorglumide and benzotript for CCK receptors suggests that their reported ability to potentiate morphine analgesia may be related to an interaction with opioid receptors.

Oral administration of loxiglumide (CCK antagonist) inhibits postprandial gallbladder contraction without affecting gastric emptying

The effect of a single oral dose of loxiglumide, a cholecystokinin antagonist, on postprandial gallbladder contraction and on gastric emptying was evaluated in humans. Following a 12-hr fasting period, two tablets of loxiglumide (400 mg each) or placebo was administered on different days, in random order and in a double-blind fashion to 10 healthy volunteers 15 min before the ingestion of a 1050-kcal standard meal. Gallbladder and antral volumes were measured by real-time ultrasonography in basal conditions and at fixed time intervals after the meal. Oral loxiglumide administration was followed by a total inhibition of the gallbladder contraction for 60 min after the end of the meal ingestion. Thereafter, up to the end of the study period, gallbladder volume was larger than that of the placebo study (at 300 min after the meal 2.7 +/- 1.6 ml after placebo and 8.2 +/- 3.5 ml after loxiglumide; P less than 0.008). No difference between placebo and loxiglumide was found in the antral volumes at any time interval (postprandial 63.5 +/- 16.5 ml after placebo and 59.4 +/- 24 ml after loxiglumide; at 300 min after the meal 20.8 +/- 13.3 ml after placebo and 18.9 +/- 9.5 ml after loxiglumide). In conclusion, a single oral dose of loxiglumide at the dose of 800 mg can inhibit postprandial gallbladder contraction without affecting gastric emptying. It would therefore appear that in man endogenous CCK, released after a solid-liquid, caloric, nutrient-balanced meal, plays a major role in the contraction of the gallbladder but does not affect gastric emptying.

Loxiglumide. A new proglumide analog with potent cholecystokinin antagonistic activity in the rat pancreas

D,L-4-(3,4-dichlorobenzoylamino)-5-(N-3-methoxypropyl-pentylami no)-5- oxopentanoic acid (CR 1505; loxiglumide) is a newly developed analog of proglumide. We examined the inhibitory effects of loxiglumide on pancreatic exocrine function in the isolated pancreatic acini and the isolated perfused pancreata of rats. Loxiglumide inhibited cholecystokinin octapeptide (CCK-8)-stimulated amylase release and, similarly, binding of [125I]CCK-8 to isolated rat pancreatic acini. Loxiglumide was about 3000 times more potent than the reference substance proglumide, but was about 1000 times less potent than L-364,718, another new CCK antagonist having benzodiazepine ring, in inhibiting CCK-8-stimulated amylase release. The inhibitory effect of loxiglumide displayed competitive kinetics and was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. The inhibitory effect of loxiglumide was fully reversible in isolated acini. However, the pancreata perfused with 10 microM loxiglumide for 20 min did not respond to CCK-8 for more than 20 min even after the removal of loxiglumide infusion. In contrast, an immediate increase in pancreatic exocrine secretion was observed after proglumide removal. Loxiglumide appeared to be bound to the receptors on acinar cells in a slowly dissociating state. These results indicate that loxiglumide acts as a potent, competitive, and specific CCK antagonist on the exocrine pancreas and, because of its prolonged inhibitory action, may be useful as a therapeutic agent in pancreatic disease.

Effect of substitutions in position 12 of bombesin on antagonist activity

Recent studies show that substitutions for the His in position 12 of bombesin (Bn) are important in determining antagonist activity. The present study was designed to investigate the chemical properties of the substitution in position 12 of Bn that determined antagonist activity and affinity. Nine [Leu14]Bn analogues with a single amino acid substitution and two analogues with multiple substitutions in addition to position 12 were synthesized. Replacing His12 with Phe12 resulted in an agonist with 100-fold decrease in potency and as reported previously, replacement with D-Phe12 resulted in an antagonist, but with a 10,000-fold decrease in affinity. Substitution of D-beta-naphthylalanine (D-Nal12), a larger and more hydrophobic group than D-Phe, produced a complete loss of antagonist activity, whereas substitution of D-pyridylalanine (D-Pal12), a group more hydrophilic and similar in size to D-Phe, converted the analogue to a very weak agonist with 300-fold lower affinity than the D-Phe analogue. Antagonist activity depended on the nature of the aromatic moiety, with a D-Trp12 resulting in an inactive analogue, and with a D-Tyr12 resulting in a weak antagonist being 100-fold less potent than the D-Phe12 substitution. The addition of an electron withdrawing group to the D-Phe substitution (D-Cpa12) resulted in a minimal decrease in antagonist activity, whereas the addition of an electron donating group (p-hydroxy in D-Tyr12) resulted in a 30-fold decrease in antagonist activity. The addition of a basic group (D-Arg12 or D-Pal12) resulted in weak agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

L-364,718, a new CCK antagonist, inhibits postprandial pancreatic secretion and PP release in dogs

The effects of L-364,718, a new CCK receptor antagonist, on food-stimulated exocrine pancreatic secretion and plasma levels of PP, insulin, CCK, and gastrin were examined in four conscious dogs with pancreatic fistulas. Intravenous injections of L-364,718 (20 nmol/kg) significantly inhibited pancreatic protein and enzyme responses by food (33% inhibition) but not juice volume output. Both rapid and secondary prolonged postprandial rises of plasma PP were also significantly suppressed by L-364,718 (50% inhibition); however, plasma levels of insulin were not altered. Postprandial levels of gastrin were not affected by L-364,718 administration, whereas 3-hr integrated CCK response was significantly enhanced by L-364,718. This study indicates that L-364,718 inhibits pancreatic protein and enzyme secretion and the release of pancreatic polypeptide stimulated by food in conscious dogs. This inhibition might be due to the selective blockage of receptor binding of circulating CCK molecules. The results suggest that L-364,718 may be useful for the physiological and pathophysiological studies associated with CCK.

Cholecystokinin stimulates neuronal receptors to produce contraction of the canine colon

The motor effects of cholecystokinin 26-33-amide (CCK octapeptide; CCK-OP) and several purported CCK receptor antagonists on canine colonic circular muscle were determined in pentobarbital anesthetized dogs. Intravenous injections of CCK-OP had no effect on colonic motility at doses that contracted the gallbladder, stomach and duodenum. CCK-OP delivered by intraarterial injection to a small segment of the proximal colon produced a dose related increase in colonic motility with one-half maximum response at 12 ng/Kg and maximum response at 50 ng/Kg. The effects of intraarterial injections of several established CCK-receptor antagonists on proximal colonic responses to intraarterial injections of CCK-OP were determined. Proglumide, 10 mg/Kg, did not produce colonic contractions itself, but antagonized CCK-OP-induced responses. Carbobenzyloxy (CBZ)-CCK27-32-amide antagonized CCK-OP-induced colonic responses and also had no effect on basal colonic motility (0.1-1 and 5 micrograms/Kg). Neither compound antagonized acetylcholine- induced colonic responses. Butoxycarbonyl (BOC)-CCK31-33-amide increased basal colonic motility, but did not alter CCK-OP-induced responses at doses of 0.1 and 0.2 mg/Kg. Dibutyryl-cGMP at a dose of 0.1 mg/Kg did not affect basal motility or CCK-OP-induced contractions. At a dose of 1.0 mg/kg it increased basal colonic motility but did not affect CCK-OP-induced contractions. Pentagastrin increased colonic motor activity only at a dose of 5 micrograms/Kg, i.a., a much higher dose than effective doses of CCK-OP. The mechanism of CCK-OP-induced colonic motor effects also was determined. Atropine sulfate, 100 micrograms/Kg, i.v. significantly reduced both intraarterial acetylcholine-and CCK-OP-induced maximum colonic contractions. Tetrodotoxin, at intravenous doses that completely block neuronal activity, did not affect maximum acetylcholine-induced contractions but practically eliminated maximum CCK-OP-induced maximum colonic responses. In conclusion, intraarterial CCK-OP produces circular muscle contraction of the canine proximal colon that is mediated by stimulation of specific CCK receptors which produce the release of acetylcholine from cholinergic enteric neurons. Proglumide and CBZ-CCK27-32-amide are effective CCK receptor antagonists at these colonic neuronal receptors.

Synthesis and biological evaluation of pNPY fragments

Peptide fragments of pNPY corresponding to the C-terminal segments (13-36) and (25-36), the N-terminal segments (1-12) and (1-24), the segments (6-14) and (7-20), which contain a putative beta-turn, and the internal segments (13-24) and (20-30) were synthesized using solid phase methodology. These fragments were assayed for NPY receptor binding activity in the rat hypothalamus membrane preparation, enhancement of food intake in the rat following ivt administration and inhibition of electrically stimulated muscle contraction in the rat vas deferens. Only the C-terminal fragment (13-36) retained some of the activities of pNPY, appearing to act as a weak agonist, having an additive effect with pNPY on the inhibition of muscle contraction and prolonging the duration of action of pNPY in the feeding assay. It also had considerable alpha-helical character, as did pNPY. None of the other peptide fragments had any agonist or antagonist activity. These results suggest that the expression of full biological NPY activity requires both the C- and the N-terminal segments as well as a putative amphiphilic alpha-helical segment (14-31).

Cholecystokinic activity of N alpha-hydroxysulfonyl-[Nle28,31]CCK26-33 analogues modified at the C-terminal residue

Three new analogues of N alpha-hydroxysulfonyl-[Nle28,31]CCK26-33 are reported in which the C-terminal L-Phe33 residue has been replaced by L-Leu, D-Phe or N-methyl-L-Phe. Biological evaluation in a series of binding and bioassays demonstrates that both L-stereochemistry and an aromatic side chain at position-33 are essential for full agonist activity. While the L-Leu33 and D-Phe33 analogues had reduced potencies in stimulating contraction of the guinea pig ileum or gall bladder, the D-Phe33 analogue was fourfold selective for the ileum. This latter analogue also exhibited apparent partial agonism in the rat pancreatic amylase release assay. The N-methyl-L-Phe33 analogue was almost equipotent to the parent analogue in all bioassays, suggesting that this modification might be useful for introducing enzymatic stability in CCK analogues.

Pathogenesis of the impaired gall bladder contraction of coeliac disease

We have investigated the possibility that the abnormally decreased gall bladder contraction after meals in patients with coeliac disease might result in part from an abnormality in the gall bladder response to endogenous cholecystokinetic hormones--for example, cholecystokinin and motilin--rather than solely from decreased secretion of such hormones. Eight patients with untreated coeliac disease and nine controls received intravenous infusions of the pure synthetic cholecystokinin analogue caerulein, 2-16 ng/kg/hour. Gall bladder emptying was measured on a minute-by-minute basis using 99mTc-HIDA scans. In the patients with coeliac disease, gall bladder emptying was greatly decreased (34.6 +/- 9.9 v 61.5 +/- 7.5% at 60 minutes, p less than 0.02), and a much greater dose of caerulein was needed to initiate gall bladder contraction (3.80 +/- 1.08 v 1.49 +/- 0.56 ng/kg, p less than 0.02). These results suggest that the abnormal gall bladder contraction in coeliac disease is not simply because of impaired release of cholecystokinin. Although mechanical factors secondary to the increased gall bladder size in patients with coeliac disease might to some extent account for the findings, the alternative explanation is that the gall bladder muscle is for some reason resistant to the action of cholecystokinetic agents. A similar phenomenon affecting the pancreas might contribute to the abnormally decreased pancreatic secretion found in coeliac disease.

L364718, a new CCK antagonist, inhibits biological actions of CCK in conscious dogs

The effects of L364718, a new CCK receptor antagonist, on CCK-8 stimulated pancreatic secretion and PP release were examined in three conscious dogs with pancreatic fistulas. L364718 (20 nmol/kg) caused a potent inhibition of CCK-8 stimulated pancreatic protein, amylase and trypsin secretion but not of volume and bicarbonate secretion. Release of PP by CCK was also significantly suppressed by L364718. The degree of inhibition by L364718 was dependent upon the amount of CCK-8 infused. This study demonstrates that L364718 acts as a potent antagonist of CCK's action on pancreatic enzyme secretion and PP release in dogs and suggests that this agent might be a useful tool for studying the physiological role of CCK in conscious animals.

In vivo activities of peptide and pseudo-peptide analogs of the C-terminal octapeptide of cholecystokinin on pancreatic secretion in the rat

Most studies measuring the agonist and antagonist activities of CCK analogs and derivatives on the exocrine pancreas have been done with in vitro models. However, extrapolation to the in vivo situation may be sometimes hazardous, due to the catabolism of the peptides by circulating and tissue peptidases, and to their eventual interaction with various endogenous factors. The present experiments were organized to measure the efficacy and potency on pancreatic secretion of the rat in vivo of a series of CCK 8 analogs whose binding and activity had been previously measured on guinea-pig and rat isolated acini. The molecules tested were derivatives of Boc-(Nle 28-Nle 31)-CCK 26-33 (1), and comprised 2-phenylethylester derivatives, des-Phe derivatives, and a series of pseudo-peptides with a "reduced" bond CH2-NH replacing the peptide bond in position 28-29 to 32-33. They were perfused in anaesthetized rats, and the outputs of sodium, bicarbonate and total protein were measured. All of the derivatives studied had in vivo the same efficacy as (1) on the output of protein, and were 10 to 500 times less potent. For most compounds, the relative order of potencies measured in vivo was similar to that measured in vitro on amylase secretion by rat acini. However, the derivatives with reduced bonds in positions 28-29 and 29-30 were respectively 3 and 2 times less potent in vivo, relative to (1), while derivatives with reduced bonds in positions 30-31, 31-32 and 32-33 were 1.5 to 2.5 times more potent in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)