Quantification of the bombesin/gastrin releasing peptide antagonist RC-3095 by liquid chromatography-tandem mass spectrometry

Bombesin (BN) and its mammalian equivalent, gastrin-releasing peptide (GRP), stimulate cell proliferation and are involved in the pathogenesis of several types of human cancer. BN/GRP and their receptors were shown to be critical for the growth of various human malignancies, such as small-cell lung, prostate, ovary, stomach and breast cancers in the human tumor xenograft model. In the present study, a fast, sensitive, robust method was developed for the determination and quantification of a BN/GRP receptor antagonist RC-3095 (D-Tpi-Gln-Trp-Ala-Val-Gly-His-Leupsi(CH2NH)Leu-NH2), in human plasma by liquid chromatography coupled with tandem mass spectrometry. RC-3095 was extracted from 0.2 ml human plasma by protein precipitation using cold acetonitrile (0.4 ml). The method has a chromatographic run of 10 min using a C(8) analytical column (150 mm x 4.6 mm i.d.) and the linear calibration curve over the range was linear from 20 to 10000 ng ml(-1) (r(2)>0.994). The between-run precision, based on the relative standard deviation replicate quality controls, was 5.7% (60 ng ml(-1)), 7.1% (600 ng ml(-1)) and 6.8% (8000 ng ml(-1)). The between-run accuracy was +/-0.0, 2.1 and 3.1% for the above-mentioned concentrations, respectively. The developed procedure allows the quantitative determination of peptide RC-3095 for pharmacokinetics studies in human plasma.     

The bombesin/gastrin releasing peptide receptor antagonist RC-3095 blocks apomorphine but not MK-801-induced stereotypy in mice

Bombesin (BN)-like peptides might be involved in the pathogenesis of neuropsychiatric disorders such as schizophrenia. Stereotyped behaviors induced by the dopamine receptor agonist apomorphine or the N-methyl-D-aspartate glutamate receptor antagonist dizocilpine (MK-801) in rodents have been proposed as animal models of schizophrenic psychosis. In the present study we evaluated the effects of the BN/gastrin-releasing peptide receptor (GRP) antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) on apomorphine and MK-801-induced stereotyped behavior in mice. An intraperitoneal (i.p.) injection of RC-3095 (1.0, 10.0 or 100.0 mg/kg) blocked apomorphine-induced stereotypy. The inhibitory effect of RC-3095 on apomorhine-induced stereotypy was similar to that induced by haloperidol (0.5 mg/kg). RC-3095 did not affect stereotyped behavior induced by MK-801 (0.5 mg/kg). The results provide the first evidence that BN/GRP receptor antagonism blocks stereotyped behavior induced by a dopamine agonist. Together with previous evidence, the present study indicates that the BN/GRP receptor can be considered a drug target in the investigation of potential new agents for treating neuropsychiatric disorders.     

Non-associative learning and anxiety in rats treated with a single systemic administration of the gastrin-releasing peptide receptor antagonist RC-3095

The gastrin-releasing peptide receptor (GRPR) has been implicated in the modulation of emotionally-motivated memory. In the present study, we investigated the role of the GRPR on non-emotional, non-associative memory, and anxiety. Adult male Wistar rats were given a systemic injection of the GRPR antagonist [D-Tpi⁶, Leu¹³ psi(CH₂NH)-Leu¹⁴] bombesin (6–14) (RC-3095) (0.2, 1.0 or 5.0 mg/kg) 30 min before exposure to an open field or an elevated plus maze. Habituation to the open field was tested in a retention trial carried out 24 h after the first exposure to the open field. Rats given RC-3095 at the doses of 1.0 or 5.0 mg/kg showed impaired habituation. Animals treated with 5.0 mg/kg of RC-3095 spent significantly more time in the closed arms of the elevated plus maze. No effects of RC-3095 on locomotion or exploratory behavior were observed. The results implicate the GRPR in the regulation of non-emotional, non-associative memory as well as in anxiety.     

Opposite effects of low and high doses of the gastrin-releasing peptide receptor antagonist RC-3095 on memory consolidation in the hippocampus: possible involvement of the GABAergic system

Although the gastrin-releasing peptide receptor (GRPR) has recently emerged as a system importantly involved in regulating memory formation, the role of hippocampal GRPRs in memory remains controversial. The present study examined the effects of GRPR antagonism on memory consolidation in area CA1 of the hippocampus. Male Wistar rats received bilateral infusions of the GRPR antagonist [D-Tpi6, Leu13 psi(CH2NH)-Leu14] bombesin (6-14) (RC-3095; 1, 3, or 10 microg/side) into the dorsal hippocampus immediately after inhibitory avoidance (IA) training. RC-3095 at 1 microg impaired, whereas the dose of 10 microg enhanced, 24-h IA retention. A second experiment showed that the RC-3095-induced enhancement of memory consolidation was prevented by pretraining infusion of an otherwise ineffective dose of the gamma-aminobutyric acid type A (GABA(A)) receptor agonist muscimol. The results indicate that high doses of GRPR antagonists can induce enhancement of memory consolidation in the hippocampus. In addition, the memory-enhancing effect of GRPR antagonists might be mediated by inhibition of GABAergic transmission.     

Effect of bombesin and gastrin-releasing peptide on the release of gastric inhibitory polypeptide and insulin in rats

The objective of this study was to determine whether bombesin- or gastrin-releasing peptide-induced release of insulin occurs before or after the release of gastric inhibitory polypeptide (GIP) in rats. The present results demonstrate that GIP release occurs before insulin release and suggest that bombesin-like peptides and GIP interact to stimulate insulin secretion.     

High potency of a new bombesin antagonist (RC-3095) in inhibiting serum gastrin levels; comparison of different routes of administration.

This study was performed to evaluate the efficacy and duration of action of a new bombesin antagonist D-Tpi6,Leu13 psi (CH2NH)Leu14-bombesin (6-14) (RC-3095), given by different routes of administration, in suppressing gastrin releasing-peptide (GRP(14-27))-stimulated gastrin release in rats. First, we showed that GRP(14-27) itself was highly active when administered by different routes. GRP(14-27), given to rats at a dose of 25 micrograms/100 g b.w. significantly increased serum gastrin levels 3 and 6 min after intravenous and for more than 30 min after subcutaneous administration or pulmonary inhalation. RC-3095 was then injected subcutaneously, intravenously and also delivered by pulmonary inhalation at a dose of 10 micrograms/100 g b.w. in each case to seven male rats 2, 30, 60 or 120 min prior to i.v. administration of 5 micrograms GRP(14-27). RC-3095 administered 2 min prior to GRP(14-27) decreased the gastrin response to GRP(14-27), measured as area under the curve, by 81% in the intravenously injected group and 64% in the pulmonary inhalation group in the first 6 min. When GRP(14-27), was given 30 min after administration of RC-3095, the gastrin response was decreased by 52% in the subcutaneous group, 49% in the pulmonary inhalation group and 11% in the intravenous group during the first 6 min. RC-3095 delivered subcutaneously or by pulmonary inhalation 1 h before GRP(14-27) was also able to significantly inhibit gastrin release. Analysis of the data revealed that the bioavailability of RC-3095 given by the pulmonary inhalation route was about 69% of the s.c. route.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and characterization of the bombesin/gastrin-releasing peptide receptor from Swiss 3T3 cells

The bombesin/gastrin-releasing peptide (GRP) receptor was solubilized from Swiss mouse 3T3 cell membranes in an active form and was purified about 90,000-fold to near homogeneity by a combination of wheat germ agglutinin-agarose and ligand affinity chromatography. The purified receptor displayed a single diffuse band with a Mr of 75,000-100,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After treatment of the receptor with N-glycanase, removing N-linked oligosaccharide moieties, the protein yielded a Mr = 38,000 band. These results agree with the Mr value estimated for the GRP receptor that was labeled on Swiss 3T3 cells by cross-linking to 125I-GRP1-27. GRP1-27 bound to the purified receptor with a Kd of 0.038 +/- 0.019 nM. By comparison, the soluble receptor in unfractionated extracts and intact membranes displayed a Kd for GRP1-27 of 0.036 +/- 0.003 nM and 0.13 +/- 0.04 nM, respectively. The relative potencies of a series of GRP analogs for the soluble receptor and intact membranes indicated that the extraction procedure did not significantly alter the receptor's ligand binding specificity. However coupling of the receptor to its guanyl nucleotide regulatory protein was not maintained in the soluble extract, and a G-protein did not co-purify with the receptor. Physiological concentrations of NaCl greatly inhibited the binding of some GRP analogs to the receptor, while the binding of other analogs was not affected. A domain on the GRP molecule involving Lys-13 or Arg-17 was identified which promoted binding to the GRP receptor under conditions of low ionic strength. These findings aided the development of an effective ligand affinity resin for the purification of the GRP receptor.     

Biotinylation of a bombesin/gastrin-releasing peptide analogue for use as a receptor probe.

The development of a biotinylated bombesin/gastrin-releasing peptide (GRP) for use as a receptor probe is reported. The lysine13 of a GRP-27 was substituted by arginine and lysine was added to the amino terminus. Biotinylation of the N-terminal lysine was performed. The biotinylated peptide was purified by HPLC and characterized by mass spectral analysis. Binding studies with murine Swiss 3T3 fibroblasts, cells known to express bombesin/GRP receptors, yielded a dissociation curve for the biotinylated GRP-27 analogue (biotin-Lysyl[Asp12,Arg13]GRP-27) which was nearly identical to that of native GRP. Using studies of gastrin release from isolated canine G cells, equipotent functional activity of the biotinylated probe and unmodified GRP was demonstrated. Measurements of retained 125I-avidin confirmed that the biotin/avidin interaction could occur once the biotin-peptide complex was bound. Applicability of the probe was demonstrated with fluorescent microscopy using avidin-FITC on Swiss 3T3 fibroblasts. In conclusion, a novel biotinylated bombesin/GRP analogue has been developed which retains the functional characteristics of the native peptide and is a useful probe for receptor studies.     

Pulmonary vascular effects of bombesin and gastrin-releasing peptide in conscious newborn lambs

A growing body of anatomic findings has led investigators to suggest that peptide-containing pulmonary neuroendocrine cells may control pulmonary vascular tone. One such peptide, bombesin, has been found in increased quantities in the lungs of infants with pulmonary disorders that cause pulmonary hypertension. Therefore we studied the effect on pulmonary vascular tone of bombesin, and its C-terminal analog, gastrin-releasing peptide (GRP). Normoxic and hypoxic unsedated newborn lambs with chronically implanted flow probes around the right and left pulmonary arteries were used. Bombesin and GRP were injected into one pulmonary artery only, and direct effects of these peptides were determined by comparing the flow changes in the injected vs. the uninjected lung. Bombesin had no measurable effect on pulmonary vascular resistance under any condition or at any dose (0.1-60 micrograms/kg). Systemic blood pressure increased significantly (12%) after a 10-micrograms/kg dose. GRP was devoid of any measurable hemodynamic effects, even at a dose of 10 micrograms/kg. If pulmonary neuroendocrine cells help regulate vascular resistance, bombesin does not appear to play a role.     

Comparison of the actions of bombesin, gastrin-releasing peptide-27, neuromedin B, and gastrin-releasing peptide-10 in causing release of gastrin and gastric inhibitory peptide in rats

The objective of this study was to compare the gastrin- and gastric inhibitory peptide (GIP)-releasing actions of bombesin, gastrin-releasing peptide (GRP)-27, neuromedin B, and GRP-10 in rats. Both bombesin and GRP-27 are potent stimulants of gastrin and GIP release, whereas neuromedin B and GRP-10 are less effective, on a molar basis.     

Comparative effect of chronic bombesin, gastrin-releasing peptide and caerulein on the rat pancreas

This study was designed to compare, on a molar basis, the effect of chronic bombesin, gastrin-releasing peptide (GRP) and caerulein on pancreatic growth in the rat. These 3 peptides were administered s.c. 3 times daily for 4 days at the following concentrations: 0.036, 0.36, 3.6 and 7.2 nmol/kg of body weight. Bombesin and GRP induced pancreatic growth in a dose-dependent manner from 3.6 nmol/kg. This growth was characterized by an increase in pancreatic weight, its protein and RNA contents but not in DNA content suggesting cellular hypertrophy. Caerulein exerted a biphasic effect on pancreatic growth, inducing cellular hypertrophy at low doses since 0.36 nmol/kg and atrophy with the highest dose (7.2 nmol/kg). Bombesin and caerulein (until 3.6 nmol/kg) increased the pancreatic content in chymotrypsin more than in amylase. The 7.2 nmol/kg caerulein treatment depressed all enzyme activities while the same dose of GRP increased pancreatic lipase content. It is concluded that (1) bombesin and GRP are equipotent trophic factors for the pancreas; (2) caerulein is the most potent factor and exerts a biphasic effect on pancreatic growth; (3) pancreatic growth and synthesis and/or secretion of enzymes are not regulated through the same mechanism.     

Isolation of the bombesin/gastrin-releasing peptide receptor from human small cell lung carcinoma NCI-H345 cells.

Purification of the gastrin-releasing peptide (GRP) or bombesin receptor has proved elusive in part due to technical difficulties. In the present studies, the problem of oxidized radioligand was avoided by the use of 125I-GRP, which was verified to be not oxidized by high performance liquid chromatography. Specific 125I-GRP binding (at 0 degrees C) to intact human small cell lung carcinoma NCI-H345 cells which had been subjected to a dilute acid wash was 6 fmol/10(6) cells. Inhibition of GRP degradation by human H345 cell membranes through the use of phenanthroline or phosphoramidon permitted the development of binding assays for the GRP receptor in detergent-solubilized crude membrane preparations. The solubilized GRP receptor exhibited saturable, high affinity (KD = 1.3 nM), temperature-dependent specific binding averaging 402 +/- 65 fmol/mg protein (mean +/- S.E. for eight separate membrane preparations with 125I-GRP concentration = 3 nM), with a Bmax = 434 fmol/mg protein using a gel filtration binding assay. That the GRP receptor had been solubilized was demonstrated by its failure to pellet when centrifuged at 100,000 x g for 60 min, its passage through a 0.22-micron filter without loss of binding activity, and its elution in the void volume of a Sephadex G-50 gel filtration column, but within the inclusion volume of a Sephacryl S-200 column (Ve/V0 = 1.1). Isolation of the GRP receptor from human H345 cell-solubilized membranes was achieved by ligand affinity chromatography. A unique 70-kDa band on silver-stained reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis was reproducibly eluted from GRP14-27 affinity columns by an acidic high salt buffer, but binding activity was denatured by these conditions. The protein nature of the GRP receptor was demonstrated by its sensitivity to proteases after isolation. In addition, two unique bands of 65 and 70 kDa were eluted from the GRP14-27 affinity column with GRP14-27 in neutral buffer, and this eluate possessed specific 125I-GRP binding with a stoichiometry of approximately 1:1. Thus, reported here is the isolation of a functional membrane-associated, saturable, high affinity GRP receptor with temperature-dependent binding from the solubilized membranes of human H345 cells.     

Solubilization of the receptor for the neuropeptide gastrin-releasing peptide (bombesin) with functional ligand binding properties

The receptor for the neuropeptide gastrin-releasing peptide, the mammalian homologue of bombesin, was solubilized from rat brain and Swiss 3T3 cells by using the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid (CHAPS) and the cholesteryl hemisuccinate ester (CHS). Only the combination of the detergent CHAPS and the cholesteryl ester CHS in a glycerol-containing buffer satisfactorily preserved the binding activity upon solubilization. Specific binding activity was only solubilized from cell lines and tissue preparations known to express the GRP receptor. The dissociation constant (Kd) for the receptor solubilized from rat brain and Swiss 3T3 cells was 0.6 nM, similar to the value of 0.8 nM calculated for the membrane-bound receptor. Binding was saturable and reached equilibrium after approximately 2 h at 4 degrees C. The identity of the solubilized receptor with the membrane-bound one was further confirmed by the concordance of the relative binding affinities of various established bombesin analogues.     

Primary structures of the bombesin-like neuropeptides in frog brain show that bombesin is not the amphibian gastrin-releasing peptide

Peptides displaying gastrin-releasing peptide/bombesin-like immunoreactivity were isolated in pure form from an extract of the brain of the European green frog, Rana ridibunda. The primary structure of the more abundant peptide was established as: Gly-Ser-His-Trp-Ala-Val-Gly-His-Leu-Met. NH2. This sequence shows one substitution (Ser for Asn) compared with mammalian gastrin-releasing peptide (18-27) (neuromedin C). The extract also contained gastrin-releasing peptide but bombesin was absent. The data indicate that bombesin is not the amphibian counterpart of gastrin-releasing peptide.     

Immunohistochemical localization of calcitonin gene-related peptide and bombesin/gastrin-releasing peptide in nerve fibers of the rat, guinea pig and pig female genital organs

The localization and distribution of calcitonin gene-related peptide (CGRP) and bombesin/gastrin-releasing peptide (GRP) immunoreactivity were studied in the rat, guinea pig and pig female genital organs with indirect immunohistochemical technique. In the rat, guinea pig and pig, CGRP and GRP immunoreactivities were localized in nerve fibers of the uterus, ovary and oviduct. Generally, CGRP-immunoreactive nerve fibers were intensely stained, while GRP-immunoreactive nerve fibers exhibited moderate immunoreactivity. The number of GRP-immunoreactive nerve fibers in these organs was lower in comparison with that of CGRP-immunoreactive nerve fibers. The pattern of distribution of these nerve fibers was very similar in different genital organs of all species studied. In the uterus of rat, guinea pig and pig, CGRP- and GRP-immunoreactive nerve fibers and nerve bundles were observed in the muscular membrane and around blood vessels. Some delicate CGRP- and GRP-immunoreactive nerve fibers were also present in the submucous layer of the uterus. In the oviduct, CGRP- and GRP-immunoreactive nerve fibers were seen in the muscular membrane, around blood vessels and in the submucous layer. In the ovary, CGRP- and GRP-immunoreactive nerve fibers were distributed in medullary stroma, in close contact with blood vessels and between follicles of different stages of development.