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Human ACE is a central component of the renin-angiotensin system and a major therapeutic target for cardiovascular diseases. The somatic form of the enzyme (sACE) comprises two homologous metallopeptidase domains (N and C), each bearing a zinc active site with similar but distinct substrate and inhibitor specificities. In this study, we present the biological activity of silacaptopril, a silylated analogue of captopril, and its binding affinity towards ACE. Based on the recently determined crystal structures of both the ACE domains, a series of docking calculations were carried out in order to study the structural characteristics and the binding properties of silacaptopril and its analogues with ACE.

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we have synthesized and characterized a new labeled gastrin ligand, 125I-BH-[Leu15]-gastrin-(5-17) [(3-[125I]iodo-4-hydroxyphenyl)-propionyl-[Leu15]-gastrin-(5-17)]. Binding of 125I-BH-[Leu15]-gastrin-(5-17) to isolated canine fundic mucosal cells was specific, saturable and of high affinity. 125I-BH-[Leu15]-gastrin- (5-17) and 125I-BH-CCK-8[(3-[125I]iodo-4-hydroxyphenyl)-propionyl-CCK-8] interact with isolated canine fundic mucosal cells with small differences in maximal binding capacities and affinities, 3800 +/- 900 binding sites/cell (Kd = 0.52 +/- 0.23 nM) and 6200 +/- 1100 binding sites/cell (Kd = 0.31 +/- 0.18 nM), respectively. The relative order of potencies for gastrin and CCK analogs in displacing 125I-BH-[Leu15]-gastrin-(5-17) binding correlated well with those obtained using 125I-BH-CCK-8. Selective CCK/gastrin antagonists L-364,718 (MK-329) and L-365,260 also inhibited 125I-BH-[Leu15]-gastrin-(5-17) binding. These results indicate that 125I-BH-[Leu15]-gastrin-(5-17) binds to gastrin receptors in isolated canine fundic mucosal cells. We have also characterized 125I-BH-[Leu15]-gastrin-(5-17) binding to the human Jurkat lymphoblastic cell line (Jurkat cells) known to express the CCK-B/gastrin receptor. Saturation experiments have shown that both 125I-BH-[Leu15]-gastrin-(5-17) and 125I-BH-CCK-8 interact with a single class of high-affinity binding sites in the Jurkat cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

A new series of growth hormone secretagogue (GHS) analogues based on the 1,2,4-triazole structure were synthesized and evaluated for their in vitro binding and their ability to stimulate intracellular calcium release to the cloned hGHS-1a ghrelin receptor expressed in LLC PK-1 cells. We have synthesized potent ligands of this receptor, some of them behaving as agonists, partial agonists, or antagonists. Some compounds among the most potent, i.e., agonist 29c (JMV2873), partial agonists including 21b (JMV2810), antagonists 19b (JMV2866) and 19c (JMV2844), were evaluated for their in vivo activity on food intake, after sc injection in rodents. Some compounds were found to stimulate food intake like hexarelin; some others were identified as potent hexarelin antagonists in this assay. Among the tested compounds, 21b was identified as an in vitro ghrelin receptor partial agonist, as well as a potent in vivo antagonist of hexarelin-stimulated food intake in rodents. Compound 21b was without effect on GH release from rat. However, in this series of compounds, it was not possible to find a clear correlation between in vitro and in vivo results.

1 The growth hormone secretagogue receptor 1a (GHSR-1a) is a G-protein coupled receptor, involved in the biological actions of ghrelin by triggering inositol phosphates and calcium intracellular second messengers. It has also been reported that ghrelin could activate the 44- and 42-kDa extracellular signal-regulated protein kinases (ERK1/2) in different cell lines, but it is not clear whether this regulation is GHSR-1a dependent or not. 2 To provide direct evidence for the coupling of GHSR-1a to ERK1/2 activation, this pathway has been studied in a heterologous expression system. 3 Thus, in Chinese hamster ovary (CHO) cells we showed that ghrelin induced, via the human GHSR-1a, a transient and dose-dependent activation of ERK1/2 leading to activation of the transcriptional factor Elk1. 4 We then investigated the precise mechanisms involved in GHSR-1a-mediated ERK1/2 activation using various specific inhibitors and dominant-negative mutants and found that internalization of GHSR-1a was not necessary. Our results also indicate that phospholipase C (PLC) was involved in GHSR-1a-mediated ERK1/2 activation, however, pathways like tyrosine kinases, including Src, and phosphoinositide 3-kinases were not found to be involved. GHSR-1a-mediated ERK1/2 activation was abolished both by a general protein kinase C (PKC) inhibitor, Go6983, and by PKC depletion using overnight pretreatment with phorbol ester. Moreover, the calcium chelator, BAPTA-AM, and the inhibitor of conventional PKCs, Go6976, had no effect on the GHSR-1a-mediated ERK1/2 activation, suggesting the involvement of novel PKC isoforms (ɛ, δ), but not conventional or atypical PKCs. Further analyses suggest that PKCɛ is required for the activation of ERK1/2. 5 Taken together, these data suggest that ghrelin, through GHSR-1a, activates the Elk1 transcriptional factor and ERK1/2 by a PLC- and PKCɛ-dependent pathway. British Journal of Pharmacology (2006) 148, 350–365. doi:10.1038/sj.bjp.0706727

In cells overexpressing active MEKK1 to enhance c-Jun trans-activation, expression of rat cholecystokinin 1 receptor increased the activity of c-Jun while in the same experimental conditions overexpression of mouse cholecystokinin 1 receptor repressed it. This differential trans-activation is specific, since it was not observed for either the other overexpressed kinases (MEK, PKA) or for other transcription factors (ATF2, ELK-1, CREB). This differential behaviour was also detected in a human colon adenocarcinoma cell-line naturally producing high levels of endogenous MEKK1. This differential behaviour between the two receptors on the MEKK1-induced c-Jun trans-activation was independent of the activation state of JNK, of the phosphorylation level of c-Jun and of its ability to bind its specific DNA responsive elements. Two amino acids (Val43 and Phe50 in the mouse cholecystokinin 1 receptor, replaced by Leu43 and Ileu50 in the rat cholecystokinin 1 receptor) localized in the first transmembrane domain were found to play a crucial role in this differential behaviour. MEKK1 probably activates a transcriptional partner of c-Jun whose activity is maintained or increased in the presence of the rat cholecystokinin 1 receptor but repressed in the presence of the mouse cholecystokinin 1 receptor. British Journal of Pharmacology (2006) 147, 951–958. doi:10.1038/sj.bjp.0706690

It has previously been reported that the cholecystokinin analog JMV-180 behaves differently on the rat and the mouse cholecystokinin-A receptor (CCK-AR). In mice this analog acts as an agonist on low- and high-affinity sites of the CCK-AR, whereas in rats this compound acts as an agonist on high-affinity sites and as an antagonist on low-affinity sites. In an attempt to understand why the same compound behaves differently on these two CCK-A receptors, we cloned the cDNA encoding the mouse CCK-AR. We then investigated a cellular model able to mimic the effect that was observed in rats and mice. HeLa cells were transiently cotransfected with plasmids leading to expression of the rat or mouse CCK-AR in the presence of pFos-Luc as reporter plasmid; such a plasmid placed the regulatory part of the human c-Fos gene upstream from the firefly luciferase structural gene (Luc). We then observed that the two CCK-A receptors behaved differently, not only in the presence of compound JMV-180 but also in the presence of cholecystokinin or even in absence of ligand; the rat CCK-AR was 2 to 3 times more potent than the mouse CCK-AR in inducing the reporter protein, whatever the ligand studied. This result was confirmed using the same kind of experiment with the reporter plasmid p(TRE)(3)-tk-Luc. Using various mutated receptors, we investigated the role of the putative third intracellular loop. We concluded that both the primary structure of the receptor and the cellular context are in part responsible for the differential behavior of these CCK-A receptors.

The aim of this study was to analyse the antisecretory mechanism of L-365,260 in vitro in isolated rabbit gastric glands. We showed that compound L-365,260, described as a non-peptide specific competitive CCK-B receptor antagonist, was able to dose-dependently inhibit [14C]-aminopyrine accumulation induced by histamine (10−4 M), carbachol (5×10−5 M), 3-isobutyl-1-methyl-xanthine (IBMX) (5×10−6 M) and forskolin (5×10−7 M) with similar IC50 values respectively of 1.1±0.6×10−7 M, 1.9±1.2×10−7 M, 4.2±2.0×10−7 M and 4.0±2.8×10−7 M. We showed that L-365,260 acted beyond receptor activation and production of intracellular second messengers and that it had no action on the H+/K+-ATPase. We found that L-365,260 inhibited cyclic AMP-induced [14C]-aminopyrine accumulation in digitonin-permeabilized rabbit gastric glands, suggesting that this compound acted, at least in part, as an inhibitor of the cyclic AMP-dependent protein kinase (PKA) pathway. Keywords: L-365,260; isolated rabbit gastric glands; [14C]-aminopyrine accumulation; H+/K+-ATPase; protein kinase inhibitor Introduction Acetylcholine, gastrin and histamine are the three most important mediators that stimulate gastric acid secretion by interacting with specific receptors located at the basolateral membrane of the parietal cells. Acetylcholine interacts with a muscarinic M3 receptor (Kajimura et al., 1992), gastrin with a CCK-B/gastrin receptor (Kopin et al., 1992) and histamine with a histamine H2 receptor (Black et al., 1972). It has been established that the gastric histamine H2 receptor is coupled to the formation of cyclic AMP (Chew et al., 1980). Activation of the parietal cell M3 cholinoceptor or the CCK-B/gastrin receptor leads to an elevation of [Ca2+]i (Chew et al., 1992). The observation that cholinergic or gastrin stimulation of acid secretion is potentiated by histamine (Berglindh et al., 1976; Soll, 1978; Chew & Hersey, 1982; Oiry et al., 1995) suggests that cyclic AMP and [Ca2+]i interact at some level. Whatever the complexity of the mechanism of acid secretion, the binding of these ligands to the receptors on the basolateral membrane of the parietal cell generates changes in second messengers and activation of protein kinase cascades that lead to final activation of the H+/K+-adenosine triphosphatase (H+/K+-ATPase) (EC 3.6.1.36) (Sachs et al., 1976; Forte & Soll, 1989). One role of cyclic AMP is the activation of cyclic AMP-dependent protein kinase (PKA) (Chew, 1985). PKA has specific functional targets and also initiates a phosphorylation cascade through activation of other downstream protein kinases the actions of which cause proton pump activation and cytoskeletal rearrangements which are characteristic of the stimulated parietal cell. It has been suggested that Ca2+/calmodulin-dependent kinase may play an important regulatory role in the modulation of cytoskeletal structure and function. Recently, Tsunoda et al. (1992) reported that Ca2+/calmodulin-dependent kinase II (CaMK II) mediates cholinergic-stimulated parietal cell secretion. In resting parietal cells, the H+/K+-ATPase is sequestered in the cytoplasmic membrane compartments of low K+ permeability: the tubulovesicles. Stimulation of the parietal cells causes a cytoskeletal reorganization and a fusion of the tubulovesicles with the apical plasma membrane, transferring the proton pump to that surface (Forte & Soll, 1989). The H+/K+-ATPase constitutes the final step common to each secretagogue in the production of acid by parietal cells and so provides a target for inhibitors used therapeutically as anti-ulcer agents such as omeprazole (Fellenius et al., 1981). In a previous study in which we compared the acid secretion induced by the C-terminal octapeptide of cholecystokinin (CCK-8) and [Leu11]gastrin(5–17) in isolated rabbit gastric glands (Oiry et al., 1995), we confirmed the ability of histamine to potentiate the action of CCK-8 (or [Leu11]gastrin(5–17)). To better understand the cooperativity between CCK and histamine, we tested the potency of various classes of CCK receptor antagonists (L-365,260; PD-135,158; YM-022; JMV-180 and L-364,718) as inhibitors of histamine-induced [14C]-aminopyrine accumulation. We found that PD-135,158; YM-022; JMV-180 and L-364,718 had no effect on histamine-induced [14C]-aminopyrine accumulation. Surprisingly, only compound L-365,260 appeared active and even more potent than cimetidine to inhibit histamine-induced [14C]-aminopyrine accumulation. Compound L-365,260, already described in the literature as a competitive and specific CCK-B/gastrin receptor antagonist (Lotti & Chang, 1989), presented a different and specific behaviour compared to other CCK-B/gastrin antagonists (PD-135,158, YM-022 and JMV-180). It has been mentioned that in the rat in vivo, low doses of L-365,260 inhibited pentagastrin-stimulated secretion (Hirst et al., 1991), whereas higher doses inhibited basal-, histamine- and carbachol-stimulated secretion (Hirst et al., 1991; Nishida et al., 1992; Pendley et al., 1993). In order to provide a better understanding of the role of L-365,260 in acid secretion in vitro, we decided to investigate further its antisecretory mechanism in isolated rabbit gastric glands.

In the present study we compared various CCK(B) receptor antagonists and tried to detect a difference in biological activity between the C-terminal octapeptides of cholecystokinin (CCK-8) and [Leu11]gastrin-(5-17) in isolated rabbit gastric glands. Binding experiments showed that different CCK(B)/gastrin receptor agonists bound with high affinity and that antagonists inhibited this binding in accordance with a CCK(B)/gastrin pharmacological profile. [Leu11]gastrin-(5-17), CCK-8 and cionin were found to induce [14C]aminopyrine accumulation to 25% above the basal level. Under the same experimental conditions, histamine induced a response twice as great as the response obtained with [Leu11]gastrin-(5-17) or CCK-8. [Leu11]gastrin-(5-17) (10(-7) M), CCK-8 (10(-8) M) and cionin (10(-8) M) appeared to be full agonists. CCK(B)/gastrin receptor antagonists including L-365,260 (3R-(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin++ +-3-yl)-N-(3-methylphenyl) urea), L-364,718 (3S-(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin++ +-3-yl)-1H-indole-2-carboximide) (a selective CCK(A) receptor antagonist), PD-135,158 (4([2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[[[1.7.7-trimethyl-bicyclo[2. 2.1]hept-2-yl)oxy]carbonyl]amino]propyl]amino]-1-phenylethyl] amino-4-oxo-[1S-1alpha.2beta[S*(S*)]4alpha]]-butano nate N-methyl-D-glucamine) (bicyclo system 1S-endo), YM-022 ((R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1,4-++ +benzodiazepin-3-yl]-3-(3-methylphenyl)urea) and JMV-180 (Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-O-CH2-CH2-C6H5) exhibited the same profile for inhibition of [Leu11]gastrin-(5-17) or CCK-8-induced [14C]aminopyrine accumulation in rabbit gastric glands. These results suggested that [Leu11]gastrin-(5-17) and CCK-8 induced [14C]aminopyrine accumulation by the same mechanism. [Leu11]gastrin-(5-17)- or CCK-8-induced [14C]aminopyrine accumulation was inhibited by about 40% by the histamine H2 receptor blocker cimetidine. These results are consistent with there being cooperativity between [Leu11]gastrin-(5-17) (or CCK-8) and histamine in the acid secretory pathway. Similarly, the CCK(B)/gastrin receptor antagonists were tested against histamine-induced [14C]aminopyrine accumulation and surprisingly, only compound L-365,260 appeared active and even more potent than cimetidine.

We have shown that gastrin and cholecystokinin octapeptide (CCK-8) are differently coupled to G protein (GTP-binding protein) through type B cholecystokinin receptors in guinea-pig brain membranes and Jurkat cells. Indeed, the gastrin-13 binding affinity is strongly reduced by stable guanyl nucleotides, whereas CCK-8 binding is only slightly affected. In order to determine the structural requirements regulating such coupling, we have synthesized several gastrin and cholecystokinin fragments (sulphated or unsulphated) elongated at the N-terminus of the common C-terminal tetrapeptide. We investigated their interaction with CCKB receptors in guinea pig brain membranes and Jurkat cells and their involvement in the G protein coupling. Their apparent binding affinities to CCKB receptors were measured by inhibition of [125I]Bolton Hunter-CCK-8 (3-[125I]iodo-4-hydroxyphenyl)propionyl-CCK-8) binding in the presence or absence of GTP gamma S (guanosine 5'-O-(3-thio)triphosphate) or aluminum tetrafluoride (AlF4-). Activation of the G proteins by GTP gamma S or AlF4- led to a decrease in binding affinity for the gastrin related peptides, the common CCK-gastrin C-terminal forms, the cholecystokinin hexapeptide and the unsulphated cholecystokinin heptapeptide. Sulphated CCK-7, CCK-8, and cionin apparent binding affinities were not affected. These finding indicated that the sulphated tyrosine in position 7 in CCK (as counted from the C-terminus), provides the cholecystokinin selectivity for the CCKB receptor compared to gastrin. The results are discussed with the aim to better clarify the physiological relevance of gastrin and cholecystokinin toward CCKB receptors and their related intracellular events.

International audience; The growth hormone secretagogue receptor type 1a (GHS-R1a) belongs to class A G-protein-coupled receptors (GPCR). This receptor mediates pleiotropic effects of ghrelin and represents a promising target for dysfunctions of growth hormone secretion and energy homeostasis including obesity. Identification of new compounds which bind GHS-R1a is traditionally achieved using radioactive binding assays. Here we propose a new fluorescence-based assay, called Tag-lite binding assay, based on a fluorescence resonance energy transfer (FRET) process between a terbium cryptate covalently attached to a SNAP-tag fused GHS-R1a (SNAP-GHS-R1a) and a high-affinity red fluorescent ghrelin ligand. The long fluorescence lifetime of the terbium cryptate allows a time-resolved detection of the FRET signal. The assay was made compatible with high-throughput screening by using prelabeled cells in suspension under a 384-well plate format. Ki values for a panel of 14 compounds displaying agonist, antagonist, or inverse agonist properties were determined using both the radioactive and the Tag-lite binding assays performed on the same batches of GHS-R1a-expressing cells. Compound potencies obtained in the two assays were nicely correlated. This study is the first description of a sensitive and reliable nonradioactive binding assay for GHS-R1a in a format amenable to high-throughput screening.

Human ACE is a central component of the renin-angiotensin system and a major therapeutic target for cardiovascular diseases. The somatic form of the enzyme (sACE) comprises two homologous metallopeptidase domains (N and C), each bearing a zinc active site with similar but distinct substrate and inhibitor specificities. In this study, we present the biological activity of silacaptopril, a silylated analogue of captopril, and its binding affinity towards ACE. Based on the recently determined crystal structures of both the ACE domains, a series of docking calculations were carried out in order to study the structural characteristics and the binding properties of silacaptopril and its analogues with ACE.

International audience; Ghrelin receptor ligands based on trisubstituted 1,2,4-triazole structure were synthesized and evaluated for their in vitro binding and biological activity. In this study, we explored the replacement of the R-aminoisobutyryl moiety by aromatic or heteroaromatic groups. Compounds 5 and 34 acted as potent in vivo antagonists of hexarelin-stimulated food intake. These two compounds did not stimulate growth hormone secretion in rodents and did not antagonize growth hormone secretion induced by hexarelin.

1. The growth hormone secretagogue receptor 1a (GHSR-1a) is a G-protein coupled receptor, involved in the biological actions of ghrelin by triggering inositol phosphates and calcium intracellular second messengers. It has also been reported that ghrelin could activate the 44- and 42-kDa extracellular signal-regulated protein kinases (ERK1/2) in different cell lines, but it is not clear whether this regulation is GHSR-1a dependent or not. 2. To provide direct evidence for the coupling of GHSR-1a to ERK1/2 activation, this pathway has been studied in a heterologous expression system. 3. Thus, in Chinese hamster ovary (CHO) cells we showed that ghrelin induced, via the human GHSR-1a, a transient and dose-dependent activation of ERK1/2 leading to activation of the transcriptional factor Elk1. 4. We then investigated the precise mechanisms involved in GHSR-1a-mediated ERK1/2 activation using various specific inhibitors and dominant-negative mutants and found that internalization of GHSR-1a was not necessary. Our results also indicate that phospholipase C (PLC) was involved in GHSR-1a-mediated ERK1/2 activation, however, pathways like tyrosine kinases, including Src, and phosphoinositide 3-kinases were not found to be involved. GHSR-1a-mediated ERK1/2 activation was abolished both by a general protein kinase C (PKC) inhibitor, Gö6983, and by PKC depletion using overnight pretreatment with phorbol ester. Moreover, the calcium chelator, BAPTA-AM, and the inhibitor of conventional PKCs, Gö6976, had no effect on the GHSR-1a-mediated ERK1/2 activation, suggesting the involvement of novel PKC isoforms (epsilon, delta), but not conventional or atypical PKCs. Further analyses suggest that PKCepsilon is required for the activation of ERK1/2. 5. Taken together, these data suggest that ghrelin, through GHSR-1a, activates the Elk1 transcriptional factor and ERK1/2 by a PLC- and PKCepsilon-dependent pathway.

International audience; It is well known that the amidated C-terminal part of gastrin is crucial for its interaction with the classical seven transmembrane domain receptors CCK-1 or CCK-2. Nevertheless, over the past 10 years, several groups have characterized new binding sites using peptides related to gastrin (particularly glycine-extended forms of gastrin) on various tumoral and nontumoral cell lines. In the present study, we focused on the human astrocytic tumoral cell line U373. Although it has been described that gastrin was able to inhibit the motility of these cells, we were unable to detect any classical CCK/gastrin receptor. On the other hand, by using the radiolabeled C-terminal heptapeptide of gastrin ((125)I-G-7), we evidenced a new binding site that possessed a pharmacological profile different from the classical CCK/gastrin receptors. This new gastrin binding site seemed to be coupled to G proteins and be implicated in c-Fos transcription gene. Moreover, we showed that G-7 was able to induce a strong inhibition of U373 cell migration, a crucial biological effect when we know that astrocytoma cells' migration in brain parenchyma constitutes a major feature of malignancy in astrocytic tumors.It is well known that the amidated C-terminal part of gastrin is crucial for its interaction with the classical seven transmembrane domain receptors CCK-1 or CCK-2. Nevertheless, over the past 10 years, several groups have characterized new binding sites using peptides related to gastrin (particularly glycine-extended forms of gastrin) on various tumoral and nontumoral cell lines. In the present study, we focused on the human astrocytic tumoral cell line U373. Although it has been described that gastrin was able to inhibit the motility of these cells, we were unable to detect any classical CCK/gastrin receptor. On the other hand, by using the radiolabeled C-terminal heptapeptide of gastrin ((125)I-G-7), we evidenced a new binding site that possessed a pharmacological profile different from the classical CCK/gastrin receptors. This new gastrin binding site seemed to be coupled to G proteins and be implicated in c-Fos transcription gene. Moreover, we showed that G-7 was able to induce a strong inhibition of U373 cell migration, a crucial biological effect when we know that astrocytoma cells' migration in brain parenchyma constitutes a major feature of malignancy in astrocytic tumors.

alpha-amidation of a peptide (which takes place from a glycine-extended precursor) is required to produce biologically active amidated hormones, such as gastrin-releasing peptide (GRP)/Pyr-Gln-Arg-Leu-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH(2) (bombesin). It was shown that glycine-extended gastrin mediates mitogenic effects on various cell lines by interacting with a specific receptor, different from the classical CCK(1) or CCK(2) receptors. On the basis of this observation, we have extended the concept of obtaining active glycine-extended forms of others amidated peptides to produce new active analogues. In this study, we have tested the biological behaviour of a synthetic analogue of the glycine-extended bombesin (para-hydroxy-phenyl-propionyl-Gln-Trp-Ala-Val-Gly-His-Leu-Met-Gly-OH or JMV-1458) on various in vitro models. We showed that compound JMV-1458 was able to inhibit specific (3-[125I]iodotyrosyl(15)) GRP ([125I]GRP) binding in rat pancreatic acini and in Swiss 3T3 cells with K(i) values of approximately 10(-8) M. In isolated rat pancreatic acini, we found that JMV-1458 induced inositol phosphates production and amylase secretion in a dose-dependent manner. In Swiss 3T3 cells, the glycine-extended bombesin analogue dose-dependently produced [3H]thymidine incorporation. By using potent GRP/bombesin receptor antagonists, we showed that this synthetic glycine-extended bombesin analogue induces its biological activities via the classical GRP/bombesin receptor.

We have investigated the potential role of gastrin in the regulation of cell growth in human astrocytic tumors. To this end we have used synthetic analogs of gastrin and cholecystokinin (CCK) which behave as gastrin and/or CCK antagonists, e.g. compounds JMV-97, JMV-209 and JMV-179. Their effects on astrocytic tumor cell proliferation was investigated by the use of the colorimetric MTT assay. The in vitro biological models used in the present study included the SW1088, U87 and U373 astrocytic tumor cell lines. The results demonstrated marked influence of gastrin and CCK antagonists in the regulation of astrocytic tumor growth. This suggests that gastrin and/or CCK antagonists might be tested in experimental glioblastoma.

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we synthesized and characterized a labelled gastrin ligand, [125I]BH[Leu15]gastrin-(5–17) (3-(3-[125I]iodo-4-hydroxyphenyl)propionyl[Leu15]gastrin-(5–17)). On isolated canine fundic mucosal cells and human Jurkat lymphoblastic cell line, known to express CCKB/gastrin receptors, the binding experiments performed indicate that [125I]BH[Leu15]gastrin-(5–17) provides a convenient biologically active ligand for cholecystokinin/gastrin receptor studies. We showed in this study that, on guinea-pig brain membranes known to possess CCKB and CCKA receptors, [125I]BH[Leu15]gastrin-(5–17) binds to a single class of high-affinity binding sites in a saturable and specific manner. [125I]BH[Leu15]gastrin-(5–17) interacts with guinea-pig brain membranes with a maximal binding capacity that is about three-fold lower than that of [125I]BHCCK8 (CCK8, the C-terminal octapeptide of cholecystokinin). The apparent affinities of CCK analogoues and selective CCK receptor antagonists L-365,260 and MK-329 for the sites labelled by both probes were in accordance with a CCKB-like profile. Association-dissociation kinetics of [125I]BH[Leu15]gastrin-(5–17) and [125I]BHCCK8 were performed and compared. They showed that [125I]BHCCK8 equilibrated more slowly than [125I]BH[Leu15]gastrin-(5–17). The effects of pH, monovalent and divalent cations on binding of both probes were investigated. The results obtained did not indicate strong differences between [125I]BH[Leu15]gastrin-(5–17) and [125I]BHCCK8 binding. Binding experiments in the presence of stable analogues of GTP showed a different behaviour between [125I]BH[Leu15]gastrin-(5–17) and [125I]BHCCK8. GTPγS strongly decreased [125I]BH[Leu15]gastrin-(5–17) binding whereas it weakly affected [125I]BHCCK8 binding. The 5′-adenylylimidodiphosphate was found to exert a similar effect than GTPγS on gastrin and CCK8 binding. The results of binding studies carried out with [125I]BH[Leu15]gastrin-(5–17) showed that gastrin binds specifically to guinea-pig brain membranes. Furthermore, the different effects of guanyl nucleotides on gastrin and CCK binding strongly suggested that gastrin and CCK trigger a differential G protein coupling through the same binding sites.