Type B cholecystokinin receptors on rat glioma C6 cells. Binding studies and measurement of intracellular calcium mobilization

Netazepide, an Antagonist of Cholecystokinin Type 2 Receptor, Prevents Vincristine-Induced Sensory Neuropathy in Mice

Among the vinca-alkaloid class, vincristine is a potent chemotherapeutic agent with significant neurotoxic effects and is employed to address a wide spectrum of cancer types. Recently, the therapeutic potential of the cholecystokinin type 2 receptor (CCK2R) as a target for vincristine-induced peripheral neuropathy (VIPN) was demonstrated. In this study, the impact of preventive CCK2R blockade using netazepide (Trio Medicines Ltd., London, UK) was investigated in a mouse model of vincristine-induced peripheral neuropathy. Netazepide is a highly selective CCK2R antagonist under development for the treatment of patients with gastric neuroendocrine tumors caused by hypergastrinemia secondary to chronic autoimmune atrophic gastritis. Vincristine-induced peripheral neuropathy was induced by intraperitoneal injections of vincristine at 100 µg/kg/d for 7 days (D0 to D7). Netazepide (2 mg/kg/d or 5 mg/kg/d, per os) was administered one day before vincristine treatment until D7. Vincristine induced a high tactile allodynia from D1 to D7. VIPN was characterized by dorsal root ganglion neuron (DRG) and intraepidermal nerve fiber (IENF) loss, and enlargement and loss of myelinated axons in the sciatic nerve. Netazepide completely prevented the painful symptoms and nerve injuries induced by vincristine. In conclusion, the fact that netazepide protected against vincristine-induced peripheral neuropathy in a mouse model strongly supports the assessment of its therapeutic potential in patients receiving such chemotherapy.

Intracellular interplay between cholecystokinin and leptin signalling for satiety control in rats

Cholecystokinin (CCK) and leptin are satiety-controlling peptides, yet their interactive roles remain unclear. Here, we addressed this issue using in vitro and in vivo models. In rat C6 glioma cells, leptin pre-treatment enhanced Ca²⁺ mobilization by a CCK agonist (CCK-8s). This leptin action was reduced by Janus kinase inhibitor (AG490) or PI3-kinase inhibitor (LY294002). Meanwhile, leptin stimulation alone failed to mobilize Ca²⁺ even in cells overexpressing leptin receptors (C6-ObRb). Leptin increased nuclear immunoreactivity against phosphorylated STAT3 (pSTAT3) whereas CCK-8s reduced leptin-induced nuclear pSTAT3 accumulation in these cells. In the rat ventromedial hypothalamus (VMH), leptin-induced action potential firing was enhanced, whereas nuclear pSTAT3 was reduced by co-stimulation with CCK-8s. To further analyse in vivo signalling interplay, a CCK-1 antagonist (lorglumide) was intraperitoneally injected in rats following 1-h restricted feeding. Food access was increased 3-h after lorglumide injection. At this timepoint, nuclear pSTAT3 was increased whereas c-Fos was decreased in the VMH. Taken together, these results suggest that leptin and CCK receptors may both contribute to short-term satiety, and leptin could positively modulate CCK signalling. Notably, nuclear pSTAT3 levels in this experimental paradigm were negatively correlated with satiety levels, contrary to the generally described transcriptional regulation for long-term satiety via leptin receptors.

Cholecystokinin (CCK) and CCK receptor expression by human gliomas: Evidence for an autocrine/paracrine stimulatory loop

Cholecystokinin (CCK) is a gut-brain peptide has been described to be able to induce mitosis according to recent studies. Additionally, conflicting data has been published on whether tumours of the central and peripheral nervous system in general, and gliomas in particular, express CCK receptors. In the present in vitro study we employed reverse transcription followed by the polymerase chain reaction (RT-PCR) to investigate whether mRNA for CCK-A and CCK-B receptors as well as CCK peptide itself is present in primary human gliomas and the U-87 MG GBM cell line. The data show that 14/14 (100%) of the primary gliomas exhibited mRNA expression for the CCK peptide gene and the B receptor including the U-87 MG cells, whereas, only 2/14 (14%) showed presence of the CCK-A receptor. The presence of CCK receptors together with CCK peptide expression itself suggests presence of an autocrine loop controlling glioma cell growth. In support of this conclusion, a neutralizing antibody against the CCK peptide exhibited a dose dependent inhibition of cell growth whereas, antagonists to CCK caused a dose depend inhibition of exogenous stimulated glioma cell growth in vitro, via the CCK-B receptor which is PKC activated. Assessment of apoptosis and proteasome activity were undertaken and we report that treatment with CCK antagonists decreased proteasome and increased caspase-3 activity. These data indicate that CCK peptide and CCK-B are abundant in human gliomas and they act to stimulate cell growth in an autocrine manner, primarily via the high affinity CCK-B receptor, which was blocked by antagonists to CCK, perhaps via apoptosis.

Thermodynamic analysis of ligands at cholecystokinin CCK2 receptors in rat cerebral cortex

BACKGROUND AND PURPOSE

Several studies using radioligand binding assays, have shown that measurement of thermodynamic parameters can allow discrimination of agonists and antagonists (Weiland et al., 1979; Borea et al., 1996a). Here we investigate whether agonists and antagonists can be thermodynamically discriminated at CCK(2) receptors in rat cerebral cortex.

EXPERIMENTAL APPROACH

The pK(L) of [(3)H]-JB93182 in rat cerebral cortex membranes was determined at 4, 12, 21 and 37 degrees C in 50 mM Tris-HCl buffer (buffer B pH 6.96; containing 0.089 mM bacitracin). pK(I) values of ligands of diverse chemical structure and with differing intrinsic activity (alpha), as defined by the lumen-perfused rat and mouse stomach bioassays, were determined in buffer B at 4, 12, 21 and 37 degrees C.

KEY RESULTS

[(3)H]-JB93182 labelled a homogeneous population of receptors in rat cerebral cortex at 4, 12, 21 and 37 degrees C and the pK(L) and B(max) were not altered by incubation temperature. [(3)H]-JB93182 binding reached equilibrium after 10, 50, 90 and 220 min at 37, 21, 12 and 4 degrees C, respectively. pK(I) values for R-L-365,260, R-L-740,093, YM220, PD134,308 and JB95008 were higher at 4 degrees C than at 37 degrees C. There was no effect of temperature on pK(I) values for pentagastrin, CCK-8S, S-L-365,260, YM022, PD140,376 and JB93242.

CONCLUSIONS AND IMPLICATIONS

CCK(2) receptor agonists and antagonists at rat CCK(2) receptors cannot be discriminated by thermodynamic analysis using [(3)H]-JB93182 as the radioligand.

Different signaling pathways are involved in CCK(B) receptor-mediated MAP kinase activation in COS-7 cells

Recently, the involvement of the MAP kinase ERK in mitogenic signaling of cholecystokininB (CCK(B)) receptors has been shown. However, the intracellular effector systems involved in this signaling pathway are poorly defined. In this study, we used COS-7 cells transiently transfected with the human CCK(B) receptor to investigate cholecystokinin-induced MAP kinase activation. CCK-8 induced activation of ERK2 which is associated with its phosphorylation and localization in the nucleus. The CCK-8-dependent ERK stimulation is sensitive to wortmannin an inhibitor of phosphoinositide 3-kinases (PI3Ks) indicating the involvement of PI3K activity. To identify the PI3K species involved in mitogenic signaling of the CCK(B) receptor several dominant-negative mutants of PI3K regulatory and catalytic subunits were transiently expressed. Surprisingly, different catalytically inactive mutants of the G protein-sensitive PI3Kgamma did not affect ERK stimulation induced by CCK, whereas a dominant-negative mutant of the regulatory p85 subunit induced significant inhibition of CCK-dependent ERK activity. These results indicate an involvement of PI3K class 1A species alpha, beta or/and delta in signal transduction via CCK(B) receptors. In addition, protein kinase C (PKC)-dependent signaling pathways contribute to CCK(B)-mediated MAP kinase signaling as shown by inhibition of CCK-8-induced ERK activation by the PKC inhibitor bisindolylmaleimide.

Cholecystokinin and psychiatric disorders : role in aetiology and potential of receptor antagonists in therapy

Cholecystokinin (CCK) is one of the most abundant neuropeptides in the brain. It is found in the highest levels in cortical and limbic structures and also in the basal ganglia. Two subtypes of CCK receptors have been described in the brain and gastrointestinal tissues. CCK(A) (alimentary subtype) receptors are mainly located in the gastrointestinal tract, regulating secretion of enzymes from the pancreas and emptying of the gallbladder. However, CCK(A) receptors are also found in several brain regions, with the highest densities in structures poorly protected by the haematoencephalic barrier (the area postrema, nucleus tractus solitarius and hypothalamus). The distribution of CCK(B) (brain subtype) receptors overlaps with the localisation of CCK and its mRNA in different brain areas, with the highest densities in the cerebral cortex, basal ganglia, nucleus accumbens and forebrain limbic structures.Both subtype of CCK receptor belong to the guanine nucleotide-binding protein-(G protein)-linked receptor superfamily containing 7 transmembrane domains. Signal transduction at CCK receptors is mediated via G(q) protein-related activation of phospholipase C and the formation of inositol 1,4,5-triphosphate (IP(3)) and 1,2-diacylglycerol (DAG). Recent cloning of CCK(A) and CCK(B) receptors has shown that mRNA for both receptors is distributed in the same tissues as established in radioligand binding and receptor autoradiography studies, with few exceptions.The existence of multiple CCK receptors has fuelled the development of selective CCK(A) and CCK(B) receptor antagonists. These antagonists belong to distinct chemical groups, including dibutyryl derivatives of cyclic nucleotides, amino acid derivatives, partial sequences and derivatives of the -COOH terminal sequence heptapeptides of CCK, benzodiazepine derivatives, 'peptoids' based on fragments of the CCK molecule, and pyrazolidinones. At the present time, the compounds of choice for blockade of the CCK(A) receptor are lorglumide, devazepide and lintitript (SR27897). L-365,260, CI-988, L-740,093 and LY288513 are the drugs most widely used to block CCK(B) receptors.Studies with CCK antagonists (and agonists) in animals and humans suggest a role for CCK in the regulation of anxiety and panic. The administration of CCK agonists [ceruletide (caerulein), CCK-4, pentagastrin] has an anxiogenic action in various animal models and in different animal species. However, the anxiogenic action of CCK agonists is restricted to nonconditioned (ethological) models of anxiety, with very limited activity in the 'classical' conditioned models. Pharmacological studies have revealed that CCK(B) receptors are the key targets in the anxiogenic action of CCK agonists. Nevertheless, CCK(B) antagonists displayed very little activity, if any at all, in these models, but strongly antagonised the effects of CCK(B) agonists. The anxiogenic/panicogenic action of CCK(B) agonists (CCK-4, pentagastrin) is even more pronounced in human studies, but the effectiveness of CCK(B) antagonists as anxiolytics remains unclear. Clinical trials performed to date have provided inconclusive data about the anxiolytic potential of CCK(B) receptor antagonists, probably because of limiting pharmacokinetic factors.The results of some animal experiments suggest a role for CCK in depression. The administration of CCK(B) antagonists causes antidepressant-like action in mouse models of depression. However, human studies replicating this result have yet to be carried out.A prominent biochemical alteration in schizophrenia is a reduction of CCK levels in the cerebral cortex. This change may be related to the loss of cortical neurons, due to the schizophrenic process itself. In animal studies (mainly in mice), administration of CCK agonists and antagonists has been shown to be effective in several models, reflecting a possible antipsychotic activity of these drugs. However, the data obtained in human studies suggest that CCK agonists and antagonists do not improve the symptoms of schizophrenia. Taking into account the reduced levels of CCK and its receptors found in schizophrenia, treatments increasing, but not blocking, brain CCK activity may be more appropriate.

CCK-B receptor-mediated stimulation of polyphosphoinositide turnover in GH3 pituitary cells in response to cholecystokinin and pentagastrin

CCK-B receptor-mediated polyphosphoinositide (PPI) turnover in GH3 pituitary cells has been examined and comparisons are made with Ca2+ mobilisation and receptor binding data, previously described. Sulphated cholecystokinin octapeptide (CCK-8s) and the CCK-B-selective agonist pentagastrin dose-dependently stimulated PPI turnover in GH3 cells with similar maximal increases of 3.0 fold and 3.3 fold, respectively, in production of [3H]inositol phosphates over control. Responses, measured over 30min periods in the presence of 10mM LiCl, were generally maximal for both agonists at 100nM. Consistent with their [125]Bolton Hunter CCK-8s (BHCCK) binding affinities and with effects on Ca2+ mobilisation, CCK-8s was slightly more potent than pentagastrin in stimulating PPI turnover (EC50s 1.3nM and 3.9nM respectively). Both peptides showed higher potency in the PPI assay than in Ca2+ studies. 100nM pentagastrin-induced PPI turnover was dose-dependently inhibited by the CCK-B receptor-selective antagonist L-365,260 (IC50 470nM) whilst the CCK-A receptor antagonist, devazepide, only produced weak partial inhibition (18% at 10,000nM). Antagonists alone were observed to depress control activity in PPI turnover but not in Ca2+ mobilisation assays. The selectivity of L-365,260 compared to devazepide was similar in binding studies to that for both 100nM pentagastrin-induced functional responses. Schild analysis of antagonism of PPI turnover by L-365,260 yielded a line with slope close to unity (1.07) and a pKB of 8.27+/-0.05.

Cholecystokinin excites neostriatal neurons in rats via CCKA or CCKB receptors

The effect of iontophoretically applied cholecystokinin (CCK) on neurons of the neostriatum was studied in rats anaesthetized with urethane. The most frequently observed effect of the sulphated octapeptide (CCK-8S) on striatal neurons was excitation. Spontaneously active neurons responded more often to CCK-8S than quiescent cells. Silent, primarily non-responsive neurons could often be stimulated with CCK-8S using glutamate to induce an ongoing discharge. Thus, 45.8% of the 177 neurons studied changed their discharge rate by more than 30%. Certain CCK receptor antagonists could prevent the effect of CCK-8S, fully or at least partly, in the majority of CCK-responsive neurons. The data suggest that cholecystokinin modulates the firing of active neostriatal neurons via the CCKA or the CCKB receptor type. Furthermore, we compared neuronal responses to glutamate with those recorded during concomitant administration of CCK-8S in order to study the interaction of both transmitters, which may be colocalized in striatal afferents. CCK-8S mainly enhanced the excitatory effect of glutamate on striatal neurons, but in several neurons the response to glutamate was reduced. The CCKB receptor antagonist could prevent CCK-8S from increasing the glutamate-induced activation.

Physiology of transformed glial cells

Much of our present knowledge of glial cell function stems from studies of glioma cell lines, both rodent (C6, C6 polyploid, and TR33B) and human (1321N1, 138MG, D384, R-111, T67, Tp-276MG, Tp-301MG, Tp-483MG, Tp-387MG, U-118MG, U-251MG, U-373MG, U-787MG, U-1242MG, and UC-11MG). New methods such as patch clamp and Ca2+ imaging have lead to rapid progress the last few years in our knowledge about glial cells, where an unexpected presence and diversity of receptors and ion channels have emerged. Basic mechanisms related to membrane potential and K+ transport and the presence of voltage gated ion channels (Na+, inwardly rectifying K+, Ca(2+)-activated K+, Ca2+, and Cl- channels) have been identified. Receptor function and intracellular signaling for glutamate, acetylcholine, histamine, serotonin, cathecolamines, and a large number of neuropeptides (bradykinin, cholecystokinin, endothelin, opioids, and tachykinins) have been characterized. Such studies are facilitated in cell lines which offer a more homogenous material than primary cultures. Although the expression of ion channels and receptors vary considerably between different cell lines and comparative studies are rare, a few differences (compared to astrocytes in primary culture) have been identified which may turn out to be characteristic for glioma cells. Future identification of specific markers for receptors on glial and glioma cells related to cell type and growth properties may have great potential in clinical diagnosis and therapy.

Effects of guanyl nucleotides on CCKB receptor binding in brain tissue and continuous cell lines: a comparative study

The effects of non-hydrolyzable guanyl nucleotide analogue GTP-gamma S on CCKB receptor binding in human and guinea-pig cortex, Jurkat T-cells, rat pituitary GH3 cells, rat glioma C6 cells and human small cell lung cancer NCI-H69 cells were investigated by using [3H]CCK-8S saturation and competition binding studies. GTP-gamma S caused inhibition of specific [3H]CCK-8S binding in a concentration dependent manner with a plateau at 10-25 microM. 25 microM GTP-gamma S resulted in a small but significant increase in Kd and IC50 values with amount very similar in all CCKB receptor models tested. However, the maximal number of specific [3H]CCK-8S binding sites (Bmax) was unaffected. Results suggest that CCKB receptors are G-protein coupled in a similar way to human and guinea-pig cortex, Jurkat cells, GH3 cells, C6 cells and NCI-H69 cells.

Cholecystokinin affects the neuronal discharge mode in the rat lateral geniculate body

Neurons of the dorsal lateral geniculate body (dLGB) discharge either continuously with single spikes or in bursts, that is, groups of action potentials with an interspike interval < or = 4 ms. The influence of the sulphated octapeptide of cholecystokinin (CCK-8S) on the discharge mode of dLGB neurons was studied in rats anesthetized with urethane. Unit activity was recorded during repeated stimulation with diffuse light. The occurrence of bursts was determined during control conditions and during iontophoretic administration of CCK-8S and its antagonists. CCK-8S frequently increased the number of bursts. The percentage of spikes involved in bursts was mainly augmented in neurons that responded after short latency to light or were excited by light-off. It was predominantly reduced in units responding to light after long latency with a primary excitation. CCKA receptors seem to contribute to burst induction, since CCK-8S reduced bursting in the presence of the CCKA receptor antagonist Ge 410 and increased bursting when applied with the CCKB receptor antagonist PD 135,158. These bursts were frequently related to light stimuli.

Comparative 3H-CCK-8S binding studies on CCKB-type receptors in guinea-pig cortex and continuous cell lines

The present study was undertaken to compare binding characteristics of CCKB-type receptors in guinea-pig cortex, Jurkat T-cells, GH3 cells and C6 cells. The rank order of potency of a variety of CCK agonists and antagonists in inhibiting specific [3H]CCK-8S binding was highly correlated for the 4 CCKB receptor models as demonstrated by a computer-assisted statistical analysis. Taking the ligand binding profiles as the criterion it is concluded that CCKB receptors in guinea-pig cortex, Jurkat T-cells, pituitary GH3 cells and rat glioma C6 cells share identical pharmacological properties.