A nucleus-directed bombesin derivative for targeted delivery of metallodrugs to cancer cells

We have synthesized a set of bombesin derivatives with the aim of exploring their tumor targeting properties to deliver metal-based chemotherapeutics into cancer cells. Peptide QRLGNQWAVGHLL-NH₂ (BN3) was selected based on its high internalization in gastrin-releasing peptide receptor (GRPR)-overexpressing PC-3 cells. Three metallopeptides were prepared by incorporating the terpyridine Pt(II) complex [PtCl(cptpy)]Cl (1) (cptpy = 4'-(4-carboxyphenyl)-2,2':6,2″-terpyridine) at the N-terminus of BN3 or at the N^Ɛ- or N^α-amino group of an additional Lys residue (1-BN3, Lys-1-BN3 and 1-Lys-BN3, respectively). 1-Lys-BN3 displayed the best cytotoxic activity (IC₅₀: 19.2 ± 1.7 μM) and similar ability to intercalate into DNA than complex 1. Moreover, the polypyridine Ru(II) complex [Ru(bpy)₂)(cmbpy)](PF₆)₂ (2) (bpy = 2,2'-bipyridine; cmbpy = 4-methyl-2,2'-bipyridine-4'-carboxylic acid), with proven activity as photosensitizer, was coupled to BN3 leading to metallopeptide 2-Lys-BN3. Upon photoactivation, 2-Lys-BN3 displayed 2.5-fold higher cytotoxicity against PC-3 cells (IC₅₀: 7.6 ± 1.0 μM) than complex 2. To enhance the accumulation of the drugs into the cell nucleus, the nuclear localization signal (NLS) PKKKRKV was incorporated at the N-terminus of BN3. NLS-BN3 displayed higher cellular internalization along with nuclear biodistribution. Accordingly, metallopeptides 1-NLS-BN3 and 2-NLS-BN3 showed increased cytotoxicity (IC₅₀: 12.0 ± 1.1 μM and 2.3 ± 1.1 μM). Interestingly, the phototoxic index of 2-NLS-BN3 was 8-fold higher than that of complex 2. Next, the selectivity towards cancer cells was explored using 1BR3.G fibroblasts. Higher selectivity indexes were obtained for 1-NLS-BN3 and 2-NLS-BN3 than for the unconjugated complexes. These results prove NLS-BN3 effective for targeted delivery of metallodrugs to GRPR-overexpressing cells and for enhancing the cytotoxic efficacy of metal-based photosensitizers.

Preliminary studies of 68Ga-NODA-USPION-BBN as a dual-modality contrast agent for use in positron emission tomography/magnetic resonance imaging

The aim of this study was to propose a new dual-modality nanoprobe for positron emission tomography/magnetic resonance imaging (PET/MRI) for the early diagnosis of breast cancer. For synthesis of the nanoprobe, polyethylene glycol-coated ultra-small superparamagnetic iron-oxide nanoparticles (USPION) armed with NODA-GA chelate and grafted with bombesin (BBN) were radiolabeled with ⁶⁸Ga. After characterization, in vitro studies to evaluate the cell binding affinity of the nanoprobe were done by performing Perl's Prussian blue cell staining and MRI imaging. Finally, for in vivo studies, magnetic resonance images were taken in SCID mice bearing breast cancer tumor pre- and post-injection, and a multimodal nanoScan PET/computed tomography was used to perform preclinical imaging of the radiolabeled nanoparticles. Afterwards, a biodistribution study was done on sacrificed mice. The results showed that the highest r₁ and r₂ values were measured for USPIONs at 20 and 60 MHz, respectively. From the in vitro studies, the optical density of the cells after incubation increased with the increase of the iron concentration and the duration of incubation. However, the T₂ values decreased when the iron concentration increased. Furthermore, from in vivo studies, the T₂ and signal intensity decreased during the elapsed time post-injection in the tumor area. In this study, the in vitro studies showed that the affinity of cancer cells to nanoprobe increases meaningfully after conjugation with BBN, and also by increasing the duration of incubation and the iron concentration. Meanwhile, the in vivo results confirmed that the blood clearance of the nanoprobe happened during the first 120 min post-injection of the radiolabeled nanoprobe and also confirmed the targeting ability of that to a gastrin-releasing peptide receptor positive tumor.

Synthesis and exploration of novel radiolabeled bombesin peptides for targeting receptor positive tumor

Increasing evidence of peptide receptor overexpression in various cancer cells, warrant the development of receptor specific radiolabeled peptides for molecular imaging and therapy in nuclear medicine. Gastrin-releasing-peptide (GRP) receptor, are overexpressed in a variety of human cancer cells. The present study report the synthesis and biological evaluation of new bombesin (BBN) analogs, HYNIC-Asp-[Phe¹³]BBN(7-13)-NH-CH₂-CH₂-CH3:BA1, HYNIC-Pro-[Tyr¹³Met¹⁴]BBN(7-14)NH₂:BA2 as prospective tumor imaging agent with compare to BBN(7-14)NH₂:BS as standard. The pharmacophores were radiolabeled in high yields with ^99mTc, characterized for their stability in serum and saline, cysteine/histidine and were found to be substantially stable. Internalization/externalization and receptor binding studies were assessed using MDA-MB-231 cells and showed high receptor binding-affinity and favourable internalization. Fluorescence studies revealed that BA1 changed the morphology of the cells and could localize in the nucleus more effectively than BA2/BS. Cell-viability studies displayed substantial antagonistic and nuclear-internalization effect of BA1. BA1 also exhibited antiproliferative effect on MDA-MB-231 cell by inducing apoptosis. In vivo behaviour of the radiopeptides was evaluated in GRP receptor positive tumor bearing mice. The ^99mTc-BA1/^99mTc-BA2 demonstrated rapid blood/urinary clearance through the renal pathway and comparatively more significant tumor uptake image and favourable tumor-to-non-target ratios provided by ^99mTc-BA1. The specificity of the in vivo uptake was confirmed by co-injection with BS. Moreover, ^99mTc-BA1 provided a much clearer tumor image in scintigraphic studies than others. Thus the combination of favourable in vitro and in vivo properties renders BA1 as more potential antagonist bombesin-peptide for targeting GRP-receptor positive tumor. These properties are encouraging to carry out further experiments for non-invasive receptor targeting potential diagnostinc and therapeutic agent for tumors.

Bombesin Prevents the Atrophy of Peyer's Patches and the Dysfunction of M Cells in Rabbits Receiving Long-Term Parenteral Nutrition

BACKGROUND

Long-term parenteral nutrition (PN) induces atrophy of the gut-associated lymphoid tissue (GALT). We examined whether bombesin could ameliorate this atrophy of Peyer's patches and the down-regulation of particle transport by M cells, which was also observed in rabbits undergoing PN.

METHODS

Adult female rabbits were randomized into 6 groups to receive chow ad libitum, chow + bombesin, PN, or PN + bombesin (20 microg/kg, subcutaneously every 8 hours) for 2 or 4 weeks. At the end of each nutrition period, a laparotomy was performed under anesthesia and a suspension of 1 x 10(10)/mL of 0.5-microm fluorescent microspheres was injected into the lumen of intestinal segments containing Peyer's patches and incubated for 2 hours. After the incubation, segments were harvested and prepared for light microscopy, immunohistochemistry, fluorescent microscopy, and electron microscopy.

RESULTS

Long-term PN reduced the size of ileal Peyer's patches, the number of microspheres that was taken up into the follicle-associated epithelium of lymphoid nodules, and the area of Peyer's patch surface occupied by M cells. The number of intraepithelial lymphocytes within the follicle-associated epithelium near the perifollicular crypts of Peyer's patches was also reduced by long-term PN. These consequences were dramatically ameliorated by treatment with bombesin. No ultrastructural alteration of the M cells of Peyer's patches was found in the chow, the PN, or the PN + bombesin groups.

CONCLUSIONS

Bombesin prevents PN-induced atrophy of GALT, reduction of M cell numbers, and decrease in particulate transport by M cells during long-term PN. Bombesin may modulate the genesis of and particulate transport by M cells through stimulation of lymphoid cells in Peyer's patch epithelium near perifollicular crypts, where M cells and other constituents of lymphoid follicle epithelium are generated, thereby preserving mucosal immunity.

Effect of endogenous cholecystokinin on the course of acute pancreatitis in rats

AIM: To examine the effects of pancreatic rest, stimulation and rest/stimulation on the natural course of recovery after acute pancreatitis.

METHODS: Acute hemorrhagic pancreatitis (AP) was induced in male rats by intraductal infusion of 40 μL/100 g body weight of 3% sodium taurocholate. All rats took food ad libitum. At 24 h after induction of AP, rats were divided into four groups: control (AP-C), pancreas rest (AP-R), stimulation (AP-S), and rest/stimulation (AP-R/S). Rats in the AP-C, AP-R and AP-S groups received oral administration of 2 mL/kg body weight saline, cholecystokinin (CCK)-1 receptor antagonist, and endogenous CCK release stimulant, respectively, twice daily for 10 d, while those in the AP-R/S group received twice daily CCK-1 receptor antagonist for the first 5 d followed by twice daily CCK release stimulant for 5 d. Rats without any treatment were used as control group (Control). Biochemical and histological changes in the pancreas, and secretory function were evaluated on day 12 at 24 h after the last treatment.

RESULTS: Feeding ad libitum (AP-C) delayed biochemical, histological and functional recovery from AP. In AP-C rats, bombesin-stimulated pancreatic secretory function and HOMA-β-cell score were significantly lower than those in other groups of rats. In AP-R rats, protein per DNA ratio and pancreatic exocrine secretory function were significantly low compared with those in Control rats. In AP-S and AP-R/S rats, the above parameters recovered to the Control levels. Bombesin-stimulated pancreatic exocrine response in AP-R/S rats was higher than in AP-S rats and almost returned to control levels. In the pancreas of AP-C rats, destruction of pancreatic acini, marked infiltration of inflammatory cells, and strong expression of α-smooth muscle actin, tumor necrosis factor-α and interleukin-1β were seen. Pancreatic rest reversed these histological alterations, but not atrophy of pancreatic acini and mild infiltration of inflammatory cells. In AP-S and AP-R/S rats, the pancreas showed almost normal architecture.

CONCLUSION: The favorable treatment strategy for AP is to keep the pancreas at rest during an early stage followed by pancreatic stimulation by promoting endogenous CCK release.

Intravenous infusion of gastrin-releasing peptide-27 and bombesin in rats reveals differential effects on meal size and intermeal interval length

We have previously shown that the intraperitoneal (i.p.) administration of gastrin-releasing peptide-27 (GRP-27) or bombesin (BN) (at 0.21, 0.41 and 1.03nmol/kg) reduces meal size (MS) and prolongs the intermeal interval (IMI). Here, we hypothesized that the intravenous (i.v.) administration of the same doses of GRP-27 and BN will be as effective as the i.p. administration in evoking these feeding responses. To test this hypothesis, we administered GRP-27 and BN i.v. and measured first MS (10% sucrose), IMI, satiety ratio (SR, IMI/MS) and second MS in overnight food-deprived but not water-deprived male Sprague Dawley rats. We found that (1) only GRP-27 reduced the first MS, (2) BN prolonged the IMI, (3) GRP-27 and BN increased the SR and (4) only BN reduced the size of the second meal. Contrary to our hypothesis, the i.v. administration of GRP-27 and BN affected the MS and IMI differently than did the i.p. administration. In conclusion, this pharmacological study suggests that the MS and IMI are regulated at different sites.

Physiological function of gastrin-releasing peptide and neuromedin B receptors in regulating itch scratching behavior in the spinal cord of mice

Pruritus (itch) is a severe side effect associated with the use of drugs as well as hepatic and hematological disorders. Previous studies in rodents suggest that bombesin receptor subtypes i.e. receptors for gastrin-releasing peptide (GRPr) and neuromedin B (NMBr) differentially regulate itch scratching. However, to what degree spinal GRPr and NMBr regulate scratching evoked by intrathecally administered bombesin-related peptides is not known. The first aim of this study was to pharmacologically compare the dose-response curves for scratching induced by intrathecally administered bombesin-related peptides versus morphine, which is known to elicit itch in humans. The second aim was to determine if spinal GRPr and NMBr selectively or generally mediate scratching behavior. Mice received intrathecal injection of bombesin (0.01-0.3 nmol), GRP (0.01-0.3 nmol), NMB (0.1-1 nmol) or morphine (0.3-3 nmol) and were observed for one hour for scratching activity. Bombesin elicited most profound scratching over one hour followed by GRP and NMB, whereas morphine failed to evoke scratching response indicating the insensitivity of mouse models to intrathecal opioid-induced itch. Intrathecal pretreatment with GRPr antagonist RC-3095 (0.03-0.1 nmol) produced a parallel rightward shift in the dose response curve of GRP-induced scratching but not NMB-induced scratching. Similarly, PD168368 (1-3 nmol) only attenuated NMB but not GRP-induced scratching. Individual or co-administration of RC-3095 and PD168368 failed to alter bombesin-evoked scratching. A higher dose of RC-3095 (0.3 nmol) generally suppressed scratching induced by all three peptides but also compromised motor function in the rotarod test. Together, these data indicate that spinal GRPr and NMBr independently drive itch neurotransmission in mice and may not mediate bombesin-induced scratching. GRPr antagonists at functionally receptor-selective doses only block spinal GRP-elicited scratching but the suppression of scratching at higher doses is confounded by motor impairment.

Bombesin-like peptides stimulate growth hormone secretion mediated by the gastrin-releasing peptide receptor in cattle

This study was designed to determine the effects of bombesin-like peptides (BLPs) on the secretion of growth hormone (GH) and to characterize the receptor subtypes mediating these effects in cattle. Four experiments were conducted: (1) six steers were randomly assigned to receive intravenous (IV) bolus injections of 0, 0.2, 1.0, 12.5 and 50.0 μg/kg neuromedin C (NMC); (2) seven pre-weaned calves were IV injected with 1.0 μg/kg NMC; (3) six steers were IV injected with 2.5μg/kg bovine gastrin-releasing peptide (GRP), 1.0 μg/kg NMC combined with 20.0 μg/kg [d-Lys(3)]-GHRP-6 (an antagonist for the GH secretagogue receptor type 1a [GHS-R1a]), 1.0 μg/kg NMC combined with 20.0 μg/kg N-acetyl-GRP(20-26)-OCH(2)CH(3) (N-GRP-EE, an antagonist for the GRP receptor), 20.0 μg/kg N-GRP-EE alone, 1.0 μg/kg neuromedin B (NMB); and (4) four rats were IV injected 1.0 μg/kg NMC. A serial blood sample was collected before and after injection. Plasma GH levels dose-dependently increased at 5 min after NMC injection and the minimal effective dose was 1.0 μg/kg. Plasma GH level was elevated by GRP, but not by NMB. The NMC-induced elevation of GH was completely blocked by N-GRP-EE. The administration of NMC elevated GH level in pre-weaned calves but not in rats. Ghrelin level was unaffected by any treatments; and [d-Lys(3)]-GHRP-6 did not block the NMC-induced elevation of GH. The results indicate BLP-induced elevation of GH levels is mediated by the GRP receptor but not through a ghrelin/GHS-R1a pathway in cattle.

Possible involvement of S-nitrosylation of brain cyclooxygenase-1 in bombesin-induced central activation of adrenomedullary outflow in rats

We previously reported that both nitric oxide (NO) generated from NO synthase by bombesin and NO generated from SIN-1 (NO donor) activate the brain cyclooxygenase (COX) (COX-1 for bombesin), thereby eliciting the secretion of both catecholamines (CA) from the adrenal medulla by brain thromboxane A(2)-mediated mechanisms in rats. NO exerts its effects via not only soluble guanylate cyclase, but also protein S-nitrosylation, covalent modification of a protein cysteine thiol. In this study, we clarified the central mechanisms involved in the bombesin-induced elevation of plasma CA with regard to the relationship between NO and COX-1 using anesthetized rats. Bombesin (1 nmol/animal, i.c.v.)-induced elevation of plasma CA was attenuated by carboxy-PTIO (NO scavenger) (0.5 and 2.5 μmol/animal, i.c.v.), but was not influenced by ODQ (soluble guanylate cyclase inhibitor) (100 and 300 nmol/animal, i.c.v.). The bombesin-induced response was effectively reduced by dithiothreitol (thiol-reducing reagent) (0.4 and 1.9 μmol/kg/animal, i.c.v.) and by N-ethylmaleimide (thiol-alkylating reagent) (0.5 and 2.4 μmol/kg/animal, i.c.v.). The doses of dithiothreitol also reduced the SIN-1 (1.2 μmol/animal, i.c.v.)-induced elevation of plasma CA, but had no effect on the U-46619 (thromboxane A(2) analog) (100 nmol/animal, i.c.v.)-induced elevation of plasma CA even at higher doses (1.9 and 9.7 μmol/kg/animal, i.c.v.). Immunohistochemical studies demonstrated that the bombesin increased S-nitroso-cysteine-positive cells co-localized with COX-1 in the spinally projecting neurons of the hypothalamic paraventricular nucleus (PVN). Taken together, endogenous NO seems to mediate centrally administered bombesin-induced activation of adrenomedullary outflow at least in part by S-nitrosylation of COX-1 in the spinally projecting PVN neurons in rats.

Gastrin-releasing peptide induces itch-related responses through mast cell degranulation in mice

Gastrin-releasing peptide (GRP), secreted from the central terminals of primary afferents, is involved in the transmission of itch signals in the spinal dorsal horn. Although primary afferents containing GRP are distributed throughout the skin, the role of peripherally released GRP in the itch response is unknown. We investigated whether GRP acts on the skin to induce an itch response in mice. Intradermal injections of GRP(18-27) (1-300 nmol/site) elicited scratching. GRP(18-27)-induced scratching was inhibited by the μ-opioid receptor antagonist naltrexone hydrochloride, the BB(2) bombesin receptor antagonist RC-3095, the H(1) histamine receptor antagonists fexofenadine hydrochloride and chlorpheniramine maleate, and the PAR(2) proteinase-activated receptor antagonist FSLLRY-NH(2). Mast cell deficiency significantly, but not completely, reduced the GRP(18-27)-induced scratching. BB(2) bombesin receptors are present in mast cells in the skin, and intradermal injection of GRP(18-27), not only induced scratching, but also led to mast cell degranulation. GRP(18-27)-induced mast cell degranulation was inhibited by the BB(2) bombesin receptor antagonist RC-3095. These results suggest that peripherally released GRP can induce an itch response, at least partly, through activation of BB(2) receptors present in the mast cells, triggering their degradation and the release of histamine and the serine proteinase, tryptase.

Differential thresholds of neuromedins B-, C-, and bombesin-induced anorexia and crop-emptying rate in chicks

Neuromedin B (NMB) and neuromedin C (NMC) are homologs of bombesin and are distributed throughout both the brain and gastrointestinal tract. The physiological roles of these bombesin-like peptides in chicks (Gallus gallus) have not been documented. Therefore, the purpose of the present study was to measure the effects of these bombesin-like peptides on food intake, crop-emptying rate and body temperature in chicks, and then to compare these effects with those of bombesin. Intracerebroventricular (ICV, 5 nmol) and intraperitoneal (IP, 300 nmol/kg) injections of NMB, NMC, and bombesin significantly decreased food deprivation-induced food intake. When ICV injected (5 nmol), all three peptides significantly reduced crop-emptying rate. IP injection of NMC and bombesin (300 nmol/kg) also reduced crop-emptying rate while NMB did not. The magnitude of food intake suppression and crop-emptying rate reduction were greater for bombesin than NMB and NMC. ICV and IP injections of NMB, NMC and bombesin did not affect cloacal temperature. In sum, the present study suggests that central and peripheral NMB and NMC are associated with reduced food intake and crop-emptying of chicks, but these effects are weaker than those of bombesin.

A gastrin-releasing peptide receptor antagonist blocks D-amphetamine-induced hyperlocomotion and increases hippocampal NGF and BDNF levels in rats

The gastrin-releasing peptide receptor (GRPR) has emerged as a novel molecular target in neurological and psychiatric disorders, and previous animal studies suggest that GRPR antagonists might display cognitive-enhancing and antipsychotic properties. Hyperlocomotion produced by administration of D-amphetamine (D-AMPH) to rats has been put forward as a model of the manic phase of bipolar disorder (BD). In the present study, we examined the effects of a single systemic administration of the GRPR antagonist [D-Tpi(6), Leu(13) psi(CH(2)NH)-Leu(14)] bombesin (6-14) (RC-3095) on hyperlocomotion induced by a single systemic injection of D-AMPH in male rats. We also evaluated the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the hippocampus of rats treated with D-AMPH and RC-3095. Administration of RC-3095 at any of the doses used blocked D-AMPH-induced hyperlocomotion. Specific doses of RC-3095 increased the levels of NGF and BDNF in the dorsal hippocampus. Administration of D-AMPH did not affect NGF or BDNF levels by itself, but blocked the RC-3095 effects. The results suggest that GRPR antagonists might display anti-manic activity.

Neuromedin C microinjected into the amygdala inhibits feeding

Bombesin-like peptides including gastrin releasing peptide and neuromedin C are known to inhibit feeding. Bombesin receptors have been found in moderate to high densities in the amygdaloid body, which is essentially involved in the regulation of feeding and body weight. In the present experiments neuromedin C (15, 30, and 60 ng), a carboxyterminal decapeptid fragment of gastrin releasing peptide, was bilaterally microinjected into the central part of the amygdala in ad libitum fed male CFY rats. Food intake was measured every 5 min for 30 min and also 6 min following neuromedin C or vehicle microinjections. Fifteen nanograms neuromedin C significantly suppressed liquid food consumption for 5 min and 30 ng for 25 min. However, 60 ng was not effective. Neuromedin C effects were blocked by prior application of the bombesin receptor antagonist [Leu(13)-psi(CH(2)NH)-Leu(14)]-bombesin. Neuromedin C treatment increased latency to feeding, decreased food intake, decreased the time spent feeding and their ratio, the number and the duration of feeding episodes during the first 5 min, without modifying body temperature or stereotype activity. Results indicate that neuromedin C may decrease the efficiency of feeding and that activation of bombesin receptors in the central amygdala may reduce appetite.

Effects of oral preload, CCK or bombesin administration on short term food intake of melanocortin 4-receptor knockout (MC4RKO) mice

We investigated whether either heterozygous (HET) or homozygous (knockout, KO) disruption of the melanocortin type 4 receptor (MC4R) gene alters post ingestive responsiveness of mice. Specifically, we tested the hypothesis that hyperphagia in MC4RKO mice might be due to a deficit in processes that sustain intermeal intervals (satiety) and/or processes that terminate ongoing episodes of eating (satiation). To test satiety, mice drank an oral preload and then we monitored intake of a subsequent liquid diet test meal. To test satiation, we examined the effect of exogenous administration of cholecystokinin (CCK) and bombesin (BN) on the size of a liquid diet meal. Experiment 1 was comprised of two studies. In the first, we determined that the intake of all three genotypes following fasts of either 6, 12, or 24h were comparable, and so chose 12h deprivation for the subsequent studies. In the second, 12h fasted mice were allowed to consume a fixed preload, approximately 50% of their expected mean intake and, following delays of either 30 or 60 min, were allowed to consume to satiation. Compared with no preload, the preload significantly reduced meal size comparably in all three genotypes. The reduction in intake was greater when the test meal was presented 30 compared with 60 min after the preload, again with no genotype differences in this decay of satiety. In experiment 2, we administered either CCK or BN and examined suppression of meal size after a 12h fast. Mice were tested repeatedly with CCK-8 (2, 6, or 18 microg/kg ip) or BN (2, 4 or 8 microg/kg ip) with vehicle injection days intervening. The 30 min intakes of HET and KO mice were suppressed more than those of WT following either CCK or BN. These experiments suggest that diminished responsiveness to nutrients or gut satiety hormones is not responsible for hyperphagia in MC4RKO mice.

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.

Evaluation of combined (177)Lu-DOTA-8-AOC-BBN (7-14)NH(2) GRP receptor-targeted radiotherapy and chemotherapy in PC-3 human prostate tumor cell xenografted SCID mice

The focus of this study was to evaluate the therapeutic benefit of combined gastrin-releasing peptide (GRP) receptor-targeted radiotherapy (TRT) with chemotherapy, using the PC-3 xenograft severe combined immunodeficiency (SCID) mouse model. (177)Lu-DOTA-8-AOC-BBN(7-14)NH(2) is a radiotherapeutic peptide that specifically targets the gastrin-releasing peptide receptor overexpressed on primary and metastatic prostate cancer. The chemotherapeutic agents, docetaxel and estramustine, were administered as single agents or in combination with the receptor-targeted radiotherapeutic agent. Combination receptor TRT/chemotherapy studies were begun 21 days postxenografting and were conducted as multiple-dose trials. The GRP receptor TRT agent was administered every 14 days, and single and combination chemotherapy dose regimens were given weekly. Tumor size, body weight, and body condition score were evaluated twice-weekly and a hematology profile once-weekly. Therapy study tumor volumes were evaluated by way of a repeated measures analysis of variance (ANOVA). Tumor volume measurements at 12 days postdose administration demonstrated a statistically significant (two-tailed P-value <0.05) tumor growth suppression in all experimental groups receiving GRP receptor-targeted radiotherapy, when compared to the control group. The two combined GRP receptor TRT/chemotherapy treatment groups demonstrated the greatest tumor growth suppression of all treatment groups. In comparing the two combined GRP receptor TRT/chemotherapy groups to the GRP receptor TRT alone group, a statistically significant difference was demonstrated for the combined groups by day 30, postdose administration. These data demonstrate that GRP receptor-targeted radiation therapy, using (177)Lu-DOTA-8-AOC-BBN(7-14)NH(2), used either alone or in combination with conventional chemotherapy, can suppress the growth of androgen- independent prostate cancer (AIPC).

Bombesin inhibits alveolarization and promotes pulmonary fibrosis in newborn mice

RATIONALE

Bombesin-like peptides promote fetal lung development. Normally, levels of mammalian bombesin (gastrin-releasing peptide [GRP]) drop postnatally, but these levels are elevated in newborns that develop bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by arrested alveolarization. In premature baboons with BPD, antibombesin antibodies reduce lung injury and promote alveolarization.

OBJECTIVES

The present study tests whether exogenous bombesin or GRP given perinatally alters alveolar development in newborn mice.

METHODS

Mice were given peptides intraperitoneally twice daily on Postnatal Days 1-3. On Day 14 lungs were inflation-fixed for histopathologic analyses of alveolarization.

MEASUREMENTS AND MAIN RESULTS

Bombesin had multiple effects on Day 14 lung, when alveolarization was about half complete. First, bombesin induced alveolar myofibroblast proliferation and increased alveolar wall thickness compared with saline-treated control animals. Second, bombesin diminished alveolarization in C57BL/6 (but not Swiss-Webster) mice. We used receptor-null mice to explore which receptors might mediate these effects. Compared with wild-type littermates, bombesin-treated GRP receptor (GRPR)-null mice had increased interstitial fibrosis but reduced defects in alveolarization. Neuromedin B (NMB) receptor-null and bombesin receptor subtype 3-null mice had the same responses as their wild-type littermates. GRP had the same effects as bombesin, whereas neither NMB nor a synthetic bombesin receptor type 3 ligand had any effect. All effects of GRP were abrogated in GRPR-null mice.

CONCLUSIONS

Bombesin/GRP can induce features of BPD, including interstitial fibrosis and diminished alveolarization. GRPR appears to mediate all effects of GRP, but only part of the bombesin effect on alveolarization, suggesting that novel receptors may mediate some effects of bombesin in newborn lung.

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, Leu(13) psi(CH2NH)-Leu14] bombesin (6-14) (RC-3095) (0.2, 1.0 or 5.0mg/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 5.0mg/kg showed impaired habituation. Animals treated with 5.0mg/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.

The role of bombesin in the mechanism of pituitary hormones release

OBJECTIVES

Functional studies indicate that bombesin may be involved in many physiological functions, including sensory transmission, the regulation of central autonomic pathways, thermoregulation, secretion of pituitary hormones, gastric and pancreatic secretion, food intake and satiety.

MATERIAL AND METHODS

In order to evaluate the role of bombesin in the mechanism of pituitary hormones release the effects of bombesin on rGH, rTSH, rPRL, rFSH and rLH release were investigated in female Wistar-Kyoto rats. In studies 'in vitro' bombesin in a dose of 1nM, 10nM, 100nM was administered to pituitary cell culture. After 60, 120, 240 min. of incubation pituitary hormones were measured. In studies 'in vivo' bombesin was injected intraventricularly (icv) in a dose of 0.5 microg/5 microl aCSF (artificial cerebrospinal fluid) for 5 min. (experiment I). In experiment II bombesin was administered intravenously (iv) in a dose of 10 microg. After 60 min, 120 mins the animals were decapitated and serum rGH, rPRL, rTSH, rLH, rFSH concentrations were measured with RIA methods.

RESULTS

Bombesin stimulated rLH, rPRL, rTSH release from cultured pituitary cells. A slight increase of GH was also observed. After intravenous (iv) injection of bombesin an increase in serum rPRL and rGH levels was found. However, the intraventricular (icv) administration of bombesin leads to decrease of serum rGH, rPRL and rTSH concentrations.

CONCLUSION

Our studies 'in vitro' and 'in vivo' indicate that bombesin may be involved in the modulation of pituitary hormones release.

Sensitization of pulmonary chemosensitive neurons by bombesin-like peptides in rats

Small cell lung cancer (SCLC) patients suffer from pulmonary stresses such as dyspnea and chest pain, and the pathogenic mechanisms are not known. SCLC cells secrete a variety of bioactive neuropeptides, including bombesin-like peptides. We hypothesize that these peptides may enhance the sensitivity of the pulmonary chemosensitive nerve endings, contributing to the development of these pulmonary stresses in SCLC patients. This study was therefore carried out to determine the effects of bombesin and gastrin-releasing peptide (GRP), a major bombesin-like peptide, on the sensitivities of pulmonary chemoreflex and isolated pulmonary vagal chemosensitive neurons. In anesthetized, spontaneously breathing rats, intravenous infusion of bombesin or GRP significantly amplified the pulmonary chemoreflex responses to chemical stimulants such as capsaicin and ATP. The enhanced responses were completely abolished by perineural capsaicin treatment of both cervical vagi, suggesting the involvement of pulmonary C-fiber afferents. In isolated pulmonary vagal chemosensitive neurons, pretreatment with bombesin or GRP potentiated the capsaicin-induced Ca(2+) transient. This sensitizing effect was further demonstrated in patch-clamp recording studies; the sensitivities of these neurons to both chemical (capsaicin and ATP) and electrical stimuli were significantly enhanced by the presence of either bombesin or GRP. In summary, our results have demonstrated that bombesin and GRP upregulate the pulmonary chemoreflex sensitivity in vivo and the excitability of isolated pulmonary chemosensitive neurons in vitro.

Periprandial changes in growth hormone release in goldfish: role of somatostatin, ghrelin, and gastrin-releasing peptide

In goldfish, growth hormone (GH) transiently rises 30 min after meals, returning to baseline at 1 h postmeal. Somatostatin (SRIF) is the major inhibitor of GH release. Three cDNAs encoding pre-pro-SRIF (PSS) have been previously cloned from goldfish brain: PSS-I, which encodes SRIF-14; PSS-II, which is potentially processed into gSRIF-28 that has [Glu1,Tyr7,Gly10]SRIF-14 at the COOH terminus; and PSS-III, which encodes [Pro2]SRIF-14 at its COOH terminus. In goldfish, bombesin (BBS), mimicking the endogenous gastrin-releasing peptide (GRP), acutely suppresses food intake and also stimulates GH release. Ghrelin was recently characterized in goldfish as a GH secretagogue and an orexigen. In this paper, we studied the changes in SRIF mRNA levels during feeding and analyzed the influences of BBS and ghrelin peptides on forebrain PSS expression. The results showed a 60% reduction in PSS-II mRNA after meals, but no changes in the expression of PSS-I and PSS-III were found. Intraperitoneal injections of 100 ng/g body wt of BBS increased GH secretion and decreased PSS-I and PSS-II gene expression. Intraperitoneal injection of goldfish ghrelin (100 ng/g body wt) transiently increased the serum GH levels and increased PSS-I, while decreasing PSS-II mRNA levels. Ghrelin (50 ng/g body wt) blocked the effects of BBS (100 ng/g body wt) on PSS-I but not on PSS-II expression. Coadministration of BBS and ghrelin decreased only the PSS-II gene expression. We conclude that the interactions between BBS/GRP and ghrelin can account for the postprandial variations in serum GH levels and the forebrain expression of PSS-II. Furthermore, we demonstrate that intraperitoneal administration of BBS reduces the ghrelin expression levels in the gut. Thus the inhibition of production of ghrelin in the gut may contribute to the satiety effects of BBS/GRP peptides.

[respiratory responses to microinjections of bombesin into the solitary tract nucleus, and the mechanism of their realization]

We investigated the respiratory effects of 10-(13)-10(-4) M bombesin microinjected into the solitary tract nucleus of adult anaesthetized rats. Bombesin markedly increased ventilation, tidal volume and electric activity of inspiratory muscles. The respiratory response was most pronounced when bombesin administered in mean concentrations (10(-10)-10(-7) M). We found that the respiratory effects ofbombesin could be based on its capacity for inhibition of Hering-Breuer inspiratory termination reflex at the level of the solitary tract nucleus. These results in aggregate with pattern of the distribution of endogenous bombesin and its receptors in the solitary tract nucleus area suggest the involvement of bombesin in the respiratory control via dorsal structures of the respiratory center.

Brain prostanoid TP receptor-mediated adrenal noradrenaline secretion and EP3 receptor-mediated sympathetic noradrenaline release in rats

Sympathetic nerves release noradrenaline, whereas adrenal medullary chromaffin cells secrete noradrenaline and adrenaline. Therefore, plasma noradrenaline reflects the secretion from adrenal medulla in addition to the release from sympathetic nerves, however the exact mechanisms of adrenal noradrenaline secretion remain to be elucidated. The present study was designated to characterize the source of plasma noradrenaline induced by intracerebroventricularly (i.c.v.) administered bombesin and prostaglandin E2 in urethane-anesthetized rats. Bombesin (1.0 nmol/animal, i.c.v.) elevated plasma noradrenaline and adrenaline, while prostaglandin E2 (0.3 nmol/animal, i.c.v.) elevated only plasma noradrenaline. The bombesin-induced elevations of both catecholamines were attenuated by pretreatments with furegrelate (an inhibitor of thromboxane A2 synthase) [250 and 500 microg (0.9 and 1.8 micromol)/animal, i.c.v.)] and [(+)-S-145] [(+)-(1R,2R,3S,4S)-(5Z)-7-(3-[4-3H]-phenylsulphonyl-aminobicyclo[2.2.1]hept-2-yl)hept-5-enoic acid sodium salt] (an antagonist of prostanoid TP receptors) [100 and 250 microg (250 and 625 nmol)/animal)], and abolished by acute bilateral adrenalectomy. On the other hand, the prostaglandin E2-induced elevation of plasma noradrenaline was not influenced by acute bilateral adrenalectomy. These results suggest that adrenal noradrenaline secretion and sympathetic noradrenaline release are mediated by differential central mechanisms; brain prostanoid TP receptors activated by bombesin are involved in the adrenal noradrenaline secretion, while brain prostanoid EP (probably EP3) receptors activated by prostaglandin E2 are involved in the sympathetic noradrenaline release in rats. Brain prostanoid TP receptors activated by bombesin are also involved in the adrenal adrenaline secretion.

Targeting Cytotoxic Conjugates of Somatostatin, Luteinizing Hormone- Releasing Hormone and Bombesin to Cancers Expressing Their Receptors: A “Smarter” Chemotherapy

Chemotherapy is one of the main modalities in the therapy of cancer. However, an improvement in the efficacy and a reduction in the toxicity of chemotherapeutic agents remains a great challenge to oncologists. A specific delivery of cytotoxic drugs to cancerous cells may help improving both aspects. Peptide hormones, for which receptors have been found in various human cancers, can serve as carriers for a local delivery of cytotoxic agents or radiopharmaceuticals to the tumors, as demonstrated by the successful clinical use of radiolabeled somatostatin analog Octreoscan for the detection and treatment of some somatostatin receptor-positive tumors. Thus, in recent years we developed a series of cytotoxic peptide hormone conjugates based on derivatives of hypothalamic hormones such as somatostatin and luteinizing hormone-releasing hormone (LHRH), and the brain-gut hormone bombesin. To create targeted conjugates with high cytotoxic activity, a derivative of doxorubicin (DOX), 2-pyrrolino-DOX (AN-201), which is 500-1, 000 times more active than its parent compound, was developed. This agent was coupled to somatostatin octapeptide RC-121 to form cytotoxic conjugate AN-238, and to [D-Lys6]LHRH carrier to produce analog AN-207. Cytotoxic bombesin hybrid AN-215 also contains AN-201. DOX was likewise linked to [D-Lys6]LHRH to form AN-152. A comprehensive testing of these cytotoxic conjugates in experimental models of various human and rodent cancers led to their selection as candidates for clinical trials.

Mechanisms underlying anorexia after microinjection of bombesin into the lateral cerebroventricle

Intracerebroventricular (i.c.v.) injections of bombesin (BN) and gastrin-releasing peptide (GRP) dose-dependently decreased food intake in male Wistar rats fasted for 17 h. Neuromedin B (NMB) did not show any effect on food intake. After BN administration, locomotor activity did not significantly change, compared with a vehicle-injected group. The anorexia induced by BN (0.3 microg) was perfectly inhibited by pretreatment with a GRP-receptor antagonist, [D-Tyr(6)]BN(6-13) methyl ester (10 microg), an NO synthase inhibitor, L-nitro-arginine (30 microg), and a PKG inhibitor, H-9 (2 microg). The cGMP concentration in the hypothalamus increased 1 h after administration when compared with the vehicle-injected group. On the other hand, an NMB-receptor antagonist, BIM23127 (10 microg), and the protein kinase (PK) C inhibitors, chelerythrine (2 microg) and Go6983 (2 microg), inhibited only the late phase of the anorexia. A PKC activator, phorbol 12, 13-dibutyrate (3 microg), injected into the ventricle decreased food intake. These findings suggest that BN suppresses food intake mainly mediated through the GRP receptor and NO-cGMP-PKG pathway, and NMB receptor and PKC is partly involved in the late phase of the anorexia.

Effects of cholecystokinin and bombesin on the expression of preprosomatostatin-encoding genes in goldfish forebrain

It was previously demonstrated that both cholecystokinin (CCK) and bombesin (BBS) stimulate growth hormone (GH) secretion in goldfish. Both peptides induce satiety and it was speculated that they integrate satiation and the postprandial increase in GH circulating levels. In the present paper we investigated the effects of CCK and BBS on the forebrain expression of the somatostatin gene family in goldfish to analyze if somatostatin peptides may be part of the effector mechanisms of CCK and BBS. We found that peripherally as well as centrally administered CCK decreases mRNA levels of preprosomatostatin (PSS)-I that encodes for SRIF-14, having no effects on PSS-II and PSS-III, which encode for gSRIF-28 and [Pro2] SRIF-14, respectively. In addition, a direct action on the pituitary to stimulate GH release, this inhibition of PSS-I expression provides a possible mechanism for CCK to increase postprandial GH levels. On the other hand, BBS inhibits the forebrain expression of PSS-I and PSS-II but does not affect PSS-III regardless of the route of administration. We conclude that this could be the most likely mechanism of action of BBS to increase GH secretion, since there are few BBS-immunoreactive (IR) fibers and BBS binding sites in the anterior pituitary of goldfish.

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.

Intrahippocampal infusion of the bombesin/gastrin-releasing peptide antagonist RC-3095 impairs inhibitory avoidance retention

Bombesin (BN)-like peptides regulate cell proliferation and cancer growth as well as neuroendocrine and neural functions. We evaluated the effects of the BN/gastrin-releasing peptide (GRP) antagonist RC-3095 on memory formation. Male Wistar rats were given a bilateral infusion of saline or RC-3095 (0.2, 1.0 or 5.0 microg) into the dorsal hippocampus either immediately or 2 h after training in an inhibitory avoidance (IA) task. Retention test trials were carried out 1.5 h (short-term memory) and 24 h (long-term memory) after training. RC-3095 impaired both short- and long-term retention only when given immediately after training. The results suggest that the hippocampal BN/GRP receptor system modulates IA memory formation.

Somatostatin receptor type 2 mediates bombesin-induced inhibition of gastric acid secretion in mice

Studies in isolated mouse stomach showed that bombesin releases somatostatin. We characterized the effects of exogenous bombesin on gastric acid secretion in mice and determined the involvement of somatostatin and somatostatin receptor type 2 (SSTR2) by using somatostatin immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. Gastric acid secretion was monitored under basal and pentagastrin-, histamine- or bethanechol-stimulated conditions in urethane-anaesthetized mice. Bombesin (10-40 micro g kg-1 h-1) and somatostatin-14 (20 micro g kg-1 h-1) were infused I.V. 10 and 30 min after PRL-2903 or somatostatin antibody pretreatment, respectively. Urethane-anaesthetized wild-type mice had low basal acid secretion (0.12 +/- 0.01 micro mol (10 min)-1) compared with SSTR2 knockout mice (1.43 +/- 0.10 micro mol (10 min)-1). Somatostatin antibody and PRL-2903 increased basal secretion in wild-type mice but not in SSTR2 knockout animals. In wild-type mice, bombesin inhibited secretagogue-stimulated acid secretion in a dose-dependent manner, and somatostatin-14 inhibited pentagastrin-stimulated secretion. In wild-type mice pretreated with somatostatin antibody or PRL-2903 and in SSTR2 knockout mice, bombesin and somatostatin-14 I.V. infusion did not alter the increased gastric acid secretion. These results indicate that, in mice, bombesin inhibits gastric acid secretion through the release of somatostatin and the activation of SSTR2. These observations strengthen the important role of SSTR2 in mediating somatostatin inhibitory actions on gastric acid secretion.

Pharmacological characteristics of bombesin receptor mediating hypothermia in the central nervous system of rats

Bombesin (BN) and structurally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), injected into the lateral ventricle produce multiple effects such as hypothermia, anorexia and hormone release. In this study, the pharmacological characteristics of BN receptors mediating hypothermia in the central nervous system (CNS) were investigated using free-moving male Wistar rats. Intracerebroventricular injections of BN, GRP and NMB produced hypothermia in a dose-dependent manner. The BN (0.3 microg)-induced effect showed a short latency and a 4-h duration with a potency increased by more than 100 times compared to the NMB-induced effect. Pretreatment with [D-Tyr(6)]BN(6-13)methylester, a GRP receptor antagonist, inhibited the BN (0.3 microg)- and NMB (7 microg)-induced hypothermia. On the other hand, BIM23127, an NMB receptor antagonist, did not influence the hypothermia. Of the protein kinase C (PKC) inhibitors, chelerythrine, Go6983, staurosporine and GF109203X, the first two partially blocked the BN-induced hypothermia. A PKC activator, phorbol-12,13-dibutyrate, decreased the rectal temperature. Genistein (a tyrosine kinase inhibitor), Y-27632 (a Rho kinase inhibitor) and PD98059 (a MAPK inhibitor) tended to suppress the BN-induced hypothermia, however, these were not significant. The inhibitory effect of a mixture of the three inhibitors, chelerythrine, genistein and Y-27632, on the BN-induced hypothermia was of a similar degree to that of chelerythrine alone. The BN receptor mediating the hypothermia seem to be the GRP subtype, and the effect involves activation of PKC.

Small bowel allografts maintained by administration of bombesin while under immunosuppression

BACKGROUND/PURPOSE

The aim of this study was to determine if Bombesin (BBS) could help maintain the mucosal villus state in small bowel allografts without inducing acute rejection under immunosuppression.

METHODS

Allogeneic small bowel transplantation was performed heterotopically in rats (n = 12). All rats received daily administration of FK506 from postoperative day 0 to day 28. On postoperative day 14, rats were divided into 2 groups of 6 rats each, and administered BBS or normal saline as a control. After 2 weeks of treatment, the rats were killed, and the graft mucosal villus state was evaluated by H&E staining, and crypt cell proliferation analysis was performed using immunohistochemistry with proliferative cell nuclear antigen (PCNA).

RESULTS

Villi were thin, and villus blunting was marked in the control group. The BBS group showed that the villi of the grafts were well maintained, and the volume of the lamina propria mucosa was adequately preserved. The PCNA labeling index of crypt cells in the control group was 40.06 +/- 3.36 (mean +/- SD) and that in the BBS group was 61.02 +/- 4.27. There was a significant difference (P <.001) between the 2 groups.

CONCLUSIONS

BBS maintained allograft epithelial cells and the volume of the lamina propria intestinal mucosa, stimulating proliferation of crypt cells under immunosuppression without inducing acute rejection.

Healing-promoting effect of bombesin treatment on chronic gastric ulcer in rats

To evaluate whether bombesin treatment has a facilitatory effect on the healing of chronic gastric ulcer, following the induction of ulcer by serosal application of acetic acid, rats were given bombesin (30 microg/kg/day; subcutaneously) or vehicle three times a day for 7, 14 or 21 days until they were decapitated. Neither food intake nor gastric emptying rate in either vehicle-treated or bombesin-treated groups was not statistically different from control rats. Similarly, ulcer indices and gastric myeloperoxidase (MPO) activities at the first and second weeks of injury were not different among the groups. However, in the 3-week ulcer group, bombesin treatment reduced tissue MPO level significantly back to control levels. Moreover, the analysis of the surface epithelium by scanning electron and light microscopy demonstrated a significant reduction in the severity of ulcers by bombesin treatment. Pretreatment with CCK antagonists (L-364,718 or L365,260; 25 micromol/kg/day) before bombesin treatment showed that neither of the CCK antagonists had a significant effect on the bombesin-mediated healing process, suggesting that CCK receptors are not involved in the action of bombesin. In accordance with the previous studies that show its acute gastroprotective effects, bombesin is also effective in promoting the healing process of chronic gastric ulcer in rats.

Tobacco smoke exposure and bombesin-like peptides in guinea pigs

Bombesin-like peptides (BLPs) are associated with tobacco smoke (TS)-induced diseases. We sought to determine if acute TS exposure releases BLPs into the pulmonary circulation. Sensitized and non-sensitized guinea pigs were chronically exposed to TS or compressed air. Thereafter, the lungs were acutely challenged with TS while perfused. Perfusates were analyzed for BLPs. TS increased BLPs in non-sensitized guinea pigs. A separate study determined daily bombesin exposure increased lung cell counts but not airway hyperresponsivensess. TS exposure releases BLPs into the pulmonary circulation but can be modified by host factors and bombesin itself does not induce airway hyperresponsiveness.

Octreotide-induced suppression of the hyperglycemic response to neostigmine or bombesin: relationship to hypothalamic noradrenergic drive

Neostigmine (cholinesterase inhibitor) or bombesin, when injected into the third cerebral ventricle of awake rat, dose-dependently increased serum glucose with the simultaneous rise in hypothalamic noradrenergic neuronal activity (NAA). Co-administration of octreotide with neostigmine or bombesin suppressed the hypothalamic NNA response with the simultaneous inhibition of the hyperglycemic response. There was a close relationship between hypothalamic NNA and serum glucose in these studies. On the basis of the concept that hypothalamic noradrenergic drive plays an important role in mediating the hyperglycemic response to stressful stimuli, the present findings suggest that the hyperglycemic response to neostigmine or bombesin is mediated via the interaction with hypothalamic noradrenergic neurons.

Secretion of the trefoil factor TFF3 from the isolated vascularly perfused rat colon

The trefoil factor TFF3 is a peptide predominantly produced by mucus-secreting cells in the small and large intestines. It has been implicated in intestinal protection and repair. The mechanisms that govern TFF3 secretion are poorly understood. The aim of this study was, therefore, to evaluate the influence of neurotransmitters, hormonal peptides and mediators of inflammation on the release of TFF3. For this purpose, an isolated vascularly perfused rat colon preparation was used. After a bolus administration of 1 ml isotonic saline into the lumen, TFF3 secretion was induced by a 30-min intra-arterial infusion of the compounds to be tested. TFF3 was evaluated in the luminal effluent using a newly developed radioimmunoassay. TFF3 was barely detected in crude luminal samples. In contrast, dithiothreitol (DTT) treatment of the effluent revealed TFF3 immunoreactivity, which amounted to about 0.3 pmol min(-1) cm(-1) in the basal state. Gel chromatography of DTT-treated luminal samples revealed a single peak that co-eluted with the monomeric form of TFF3. TFF3 was not detected in the portal effluent. Bethanechol (10(-6)-10(-4) M), vasoactive intestinal peptide (VIP, 10(-8)-10(-7) M) or bombesin (10(-8)-10(-7) M) induced a dose-dependent release of TFF3. In contrast, substance P evoked a modest release of TFF3, whereas calcitonin gene-related peptide (CGRP), somatostatin, neurotensin or peptide YY (PYY) did not modify TFF3 secretion. The degranulator compound bromolasalocid, 16,16-dimethyl PGE2 (dmPGE2) or interleukin-1-beta (IL-1-beta) also evoked a marked release of TFF3. In conclusion, TFF3 in the colonic effluent is present in a complex. This association presumably involves a disulfide bond. Additionally, the present results suggest a role for enteric nervous system and resident immune cells in mediation of colonic TFF3 secretion.

Blockade of GRP receptors inhibits gastric emptying and gallbladder contraction but accelerates small intestinal transit

BACKGROUND & AIMS

This study was designed to characterize [D-F(5)Phe(6)D-Ala(11)]Bn(6-13)OMe (BIM26226) as a gastrin-releasing peptide (GRP)-preferring bombesin receptor antagonist and to determine whether GRP physiologically regulates gastrointestinal motility. Intravenous BIM26226 (5-500 microg. kg(-1). h(-1)) inhibits GRP-induced gallbladder contraction and plasma cholecystokinin (CCK) release in a dose-dependent fashion.

METHODS

Gastric emptying and small bowel transit of a solid meal were quantified using scintigraphy. Meal-stimulated gallbladder contraction was measured by sonography in a 2-period crossover design.

RESULTS

Intravenous BIM26226 potently inhibited gastric lag time (114 +/- 7 vs. 41 +/- 6 minutes [control]) and gastric emptying rate (0.11 +/- 0.02%/min vs. 0.26 +/- 0.04%/min [control]), whereas concomitant infusion of BIM26226 accelerated small bowel transit time (153 +/- 41 vs. 262 +/- 20 minutes [control]). A continuous liquid meal perfusion into the duodenum induced complete gallbladder contraction (t(50%), 35 +/- 4 minutes), which BIM26226 inhibited significantly (t(50%), 64 +/- 8 minutes). BIM26226 did not alter plasma CCK response, indicating that circulating CCK did not mediate these effects.

CONCLUSIONS

These data show that BIM26226 is a potent antagonist of exogenous and endogenous GRP and suggest that GRP is a major physiologic regulator of gastric emptying, small bowel transit, and gallbladder contraction.

Attenuation of the anorectic effects of cholecystokinin and bombesin by the specific amylin antagonist AC 253

Previous studies provided evidence for an interaction between the satiety effects of cholecystokinin (CCK), bombesin (BBS), and amylin. Amylin released in response to CCK (or BBS) was supposed to mediate part of CCK's (or BBS's) anorectic effect since the amylin and calcitonin gene-related peptide (CGRP) antagonist CGRP 8-37 attenuated their anorectic action. Due to the low specificity of CGRP 8-37 for amylin vs. CGRP binding sites, the aim of the present study was to test whether the specific amylin antagonist AC 253 also influenced the anorectic effects of CCK and BBS. Injections took place at dark onset in 24-h food-deprived rats. At a dose that attenuated the anorectic effect of amylin (5 microg/kg), the amylin antagonist AC 253 (500 microg/kg) significantly attenuated the anorectic effects of CCK and BBS (0.5 microg/kg). It can therefore be concluded that amylin, rather than CGRP, mediates part of the anorectic effects of CCK and BBS.

Central bombesin inhibits food intake and the orexigenic effect of neuropeptide Y in the neonatal chick

It is well known that central injection of bombesin (BN) suppresses feeding in mammalian and avian species, but the anorexigenic effect of central BN are still open with special reference to the chick. The dose response (0, 0.1 and 0.5 microg) of intracerebroventricular (ICV) injection of BN was examined in Experiment 1. ICV injection of BN inhibited food intake in a dose-dependent manner. Experiment 2 was done to determine whether BN interacts with the orexigenic effect of neuropeptide Y (NPY) in the neonatal chick. Central administration of NPY (2.5 microg) greatly enhanced food intake, but co-injection of BN (0.5 microg) suppressed food intake. The dose response of NPY (2.5 microg) co-injected with three levels of BN (0, 0.1 and 0.5 microg) was examined in Experiment 3. ICV injection of BN attenuated the hyperphagia by NPY in a dose-related fashion. It is suggested that central BN may interact with NPY for the regulation of feeding in the neonatal chick.

Impact of gastrin-releasing peptide on intestinal microcirculation after ischemia-reperfusion in rats

We investigated the effect of gastrin-releasing peptide (GRP) and its antagonist RC-3095 on intestinal microcirculation after ischemia-reperfusion. Intestinal ischemia was induced in female Wistar rats by occlusion of the superior mesenteric artery for 40 min. Ten minutes prior to reperfusion, infusion of GRP or RC-3095 was started. A jejunal segment was exteriorized and the microhemodynamics of the mucosa and submucosa were examined by intravital microscopy and compared both with normal and ischemic controls (without application of the regulatory peptide). Ischemia-reperfusion significantly decreased functional capillary density from 891.2 +/- 14.1 to 398.3 +/- 11.4 cm(-1). Capillary red blood cell velocity was reduced from 0.46 +/- 0.01 to 0.37 +/- 0.01 mm/s (p < 0.05). Furthermore, both sticking and rolling of leukocytes were enhanced. 3.4 +/- 1.1% of the villi were not perfused at all. GRP infusion reversed the microcirculatory ischemia-reperfusion injury by increasing functional capillary density to 669.8 +/- 8.3 cm(-1) and red blood cell velocity to 0.62 +/- 0.01 mm/s (p < 0.05). In addition, application of GRP resulted in a complete absence of stasis (0%) in the villi. Leukocyte-endothelium adherence remained unchanged when compared to the ischemic controls. In contrast, application of RC-3095 caused an aggravation of microcirculatory disturbances demonstrated by a markedly increased number of non-perfused villi (42.5 +/- 4.2%; p < 0.05 vs. ischemic controls) and a significantly reduced functional capillary density (346.2 +/- 8.4 cm(-1), p < 0.05 vs. ischemic controls). In addition, RC-3095 led to an increased permanent leukocyte adherence in postcapillary venules whereas rolling was significantly reduced when compared to normal controls. We conclude that GRP in pharmacological doses has a protective effect on intestinal microcirculation during reperfusion. Furthermore, these data suggest that endogenous GRP may play a decisive role in the maintenance of microvascular integrity during reperfusion.

Inhibition of growth of MDA-MB-468 estrogen-independent human breast carcinoma by bombesin/gastrin-releasing peptide antagonists RC-3095 and RC-3940-II

BACKGROUND

The growth of breast carcinoma is promoted by autocrine growth factors such as the bombesin (BN)-like peptides and epidermal growth factor (EGF). The stimulatory action of BN-like peptides can be blocked by the use of BN/gastrin-releasing peptide (GRP) antagonists.

METHODS

The authors investigated the effects of synthetic BN/GRP antagonists RC-3095 and RC-3940-II on tumor growth and the expression of mRNA for EGF receptors and three BN receptor subtypes in MDA-MB-468 human breast carcinoma. Athymic nude mice with xenografts of MDA-MB-468 human breast carcinoma were injected subcutaneously for 6 weeks with RC-3940-II at doses of 20 or 40 microg/day. In another study, the effects of RC-3940-II and RC-3095 were compared.

RESULTS

RC-3940-II caused a significant and dose-dependent growth inhibition of MDA-MB-468 tumors in nude mice; therapy with either dose of RC-3940-II significantly (P<0.01) reduced the mean final tumor volume and weight compared with controls. RC-3940-II induced a persistent regression of > 50% of all tumors. One of 3 tumors treated with 20 microg of RC-3940-II and 3 of 5 tumors treated with 40 microg were found to have regressed completely by the end of the study. When RC-3940-II and RC-3095 were compared at the dose of 20 microg/day, both powerfully suppressed growth of MDA-MB-468 tumors, with RC-3940-II causing a complete regression of 2 tumors and RC-3095 a complete regression of 1 tumor. Receptor analyses of untreated MDA-MB-468 tumors revealed an overexpression of EGF receptors and two classes of binding sites for BN/GRP. mRNAs for receptors of GRP, neuromedin B, and BN receptor subtype-3 were detected by reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

A virtual arrest of growth or regression of MDA-MB-468 human breast carcinoma after therapy with RC-3940-II and RC-3095 indicates that these BN/GRP antagonists could provide a new treatment modality for breast tumors expressing BN and EGF receptors.

Role of central oxytocin in the inhibition by endotoxin of distension-stimulated gastric acid secretion

The gastric acid hyposecretory state associated with endotoxemia is mediated by a nervous reflex involving the central nervous system. The aim of the present study was to analyse the central effects of different peptides on distension-stimulated gastric acid secretion and the endogenous role of such peptides on the hyposecretory effects of endotoxin. The effect of an intracisternal (i.c.) administration of oxytocin, vasopressin, corticotropin releasing factor (CRF), bombesin, somatostatin and the opioid receptor agonist BW443C or an intravenous (i.v.) injection of a small dose of endotoxin on distension-stimulated gastric acid secretion was studied in the continuously perfused stomach of anaesthetised rats. In some animals, specific receptor antagonists for oxytocin (Compound VI [d(CH2)5, Tyr(Me)2, Thr4, Tyr-NH2(9)]-OVT, 0.01-1 microg/rat), vasopressin (des-Gly9-[beta-Mercapto-beta,beta-cyclopentamethylene-propiony l1, O-Et-Tyr2, Val4, Arg8]-VP, 20 microg/rat), CRF (alpha-helical CRF [9-41], 50 microg/rat) or bombesin (D-Phe12-Bombesin, 20 microg/rat) were administered i.c. before endotoxin. Distension-stimulated acid secretion was significantly inhibited by central oxytocin (0.2, 2 or 4 nmol/rat, 45+/-16%, 69+/-10% and 79+/-5% reduction, respectively), CRF (0.5, 1 or 2 nmol/rat, 52.2+/-15.6%, 74.3+/-9.1% and 93.2+/-1.6% reduction, respectively) and bombesin (2 nmol/rat, 79.1+/-5.8% reduction). The hyposecretory effect induced by endotoxin (5 microg/kg, 60.2+/-2.3% reduction) was reversed in a dose-dependent manner by pretreatment with the oxytocin receptor antagonist (0.01, 0.1 and 1 microg/rat, 65.2+/-14.4%, 88.0+/-22.5% and 112.4+/-25.2% of control response, respectively) while the vasopressin (20 microg/rat), CRF (50 microg/rat) or bombesin (20 microg/rat) receptor antagonists had no effect. The present results support a role for the endogenous release and action in the central nervous system of oxytocin in the inhibitory effect of endotoxin on gastric acid secretion.

Synthesis of nitric oxide in the dorsal motor nucleus of the vagus mediates the inhibition of gastric acid secretion by central bombesin

1. Central administration of bombesin inhibits gastric acid production independently of the centrally or peripherally-acting stimuli employed. This study evaluates the role and location of the cerebral nitric oxide (NO) implicated in the inhibitory effect of central bombesin on in vivo rat gastric acid secretion, as induced by distension with 15 cm H2O, insulin (0.75 u.i. kg-1 i.p.) TRH (1.2 microg kg-1, i.c.) or pentagastrin (100 microg kg-1, i.p.). 2. The acid-inhibitory effect of i.c. bombesin (40 ng kg-1) was prevented by prior administration of L-NAME (80 microg kg-1) in the dorsal motor nucleus of the vagus (DMN). This dose of L-NAME when administered into the nucleus of the tractus solitarious (NTS) did not influence the effects of bombesin. Administration of L-arginine (400 microg kg-1) into the DMN restored the acid-inhibitory effect of i.c. bombesin in animals treated with L-NAME. 3. Microinjection of bombesin (12 ng kg-1) into the paraventricular nucleus of the hypothalamus (PvN) inhibits acid secretion stimulated by pentagastrin. This inhibitory effect was prevented by a previous injection of L-NAME (80 microg kg-1) into the DMN. 4. The release of NO in the DMN following i.c. administration of bombesin was confirmed by in vivo electrochemical detection. 5. Administration by microdialysis in the DMN of the NO-donor SNAP (25 mM in 1.5 microl min-1) into the DMN inhibits pentagastrin-stimulated gastric acid secretion. 6. The present study suggests that nNOS-containing neurons in the DMN have an inhibitory role in the control of gastric acid responses.

Capsaicin-sensitive fibers are required for the anorexic action of systemic but not central bombesin

Bombesin (BN) suppresses food intake in rats whether given centrally or systemically. Although the brain BN-sensitive receptors are known to be essential for the anorexic effect of systemic BN, the mode of communication between the gut and the brain remains unclear. This study assessed whether the anorexic effect of systemic BN is mediated humorally or via neural circuits. Afferent neurons were lesioned using capsaicin (50 mg/kg sc) on postnatal day 2, and responses to BN were assessed during adulthood. Capsaicin treatment decreased body weight gain significantly from postnatal age 4-7 wk. Peripheral BN (4-16 micrograms/kg ip) dose dependently suppressed food intake in control animals. However, this effect was completely blocked in capsaicin-treated rats. In contrast to systemic effects, feeding-suppressant effects of centrally administered BN (0.01-0.5 microgram icv) were not affected by capsaicin treatment. This research suggests that peripheral BN communicates with the brain via a neuronal system(s) whose afferent arm is constituted of capsaicin-sensitive C and/or Adelta-fibers, whereas the efferent arm of this satiety- and/or anorexia-mediating circuitry is capsaicin resistant.

Effect of bombesin at low doses on the secretion of the exocrine pancreas and on plasma gastrin concentration in the conscious pig

We investigated the role of low-doses of bombesin in the regulation of exocrine secretion in the pancreas of the conscious pig. In ten growing castrated male Large White pigs, bombesin was infused intravenously for 1 h at doses of 0 to 500 pmol/kg/h under a stimulation of secretin (36 pmol/kg/h). In six pigs, bombesin (50 pmol/kg/h) was administered alone for 2 h and its effect on pancreatic secretion was compared to that of an infusion of secretin. The pancreatic juice and the blood were collected at 15-min intervals for use in assays of protein in the juice and gastrin in the plasma. When bombesin was infused alone or in combination with secretin, the volume secreted was not altered. The protein output was not altered by secretin, but was increased by the infusion of bombesin, in a dose-dependent manner, reaching a plateau at 250 pmol/kg/h. The plasma gastrin levels were increased by bombesin, starting with the 50 pmol/kg/h dose. This effect was maximal at a dose of 100 pmol/kg/h. The levels remained below those measured after a standard meal, demonstrating that the effect of bombesin on the studied parameters is of physiological significance.

Effect of the gastrin-releasing peptide antagonist BIM 26226 and lanreotide on an acinar pancreatic carcinoma

The effects of a potent specific gastrin-releasing peptide receptor antagonist, BIM 26226 ([D-F5 Phe6, D-Ala11] bombesin (6-13) OMe), and the long-acting somatostatin analogue, lanreotide (BIM 23014), on the growth of an acinar pancreatic adenocarcinoma growing in the rat or cultured in vitro were investigated. Lewis rats bearing a pancreatic carcinoma transplanted s.c. in the scapular region, were treated with gastrin-releasing peptide (30 microg/kg per day), BIM 26226 (30 and 100 microg/kg per day) and lanreotide (100 microg/kg per day) alone or in combination for 14 successive days. Chronic administration of BIM 26226 and lanreotide significantly inhibited the growth of pancreatic tumours stimulated or not by gastrin-releasing peptide (GRP), as shown by a reduction in tumour volume, protein, ribonucleic acid, amylase and chymotrypsin contents. This effect was more pronounced with 100 microg/kg per day BIM 26226 than with 30 microg/kg per day. However, BIM 26226 and lanreotide, given together, did not exert any additive effect on GRP-treated and -untreated tumours. In cell cultures, both BIM 26226 and lanreotide (10(-6) M) inhibited [3H]thymidine incorporation in tumour cells induced or not by GRP, but no increased effect was observed after combined treatment with both agents. Binding studies showed that BIM 26226 had a high affinity for GRP receptors in tumour cell membranes (IC50 = 6 nM). These results from in vivo and in vitro experiments suggest that BIM 26226 and lanreotide are able to reduce the growth of an experimental acinar pancreatic tumour. Thus, these agents represent interesting steps toward the development of new approaches for treatment of pancreatic carcinomas.

Effect of cerebroventricular perfusion of bombesin on gastrointestinal myoelectric activity

The effect of intracerebroventricular (i.c.v.) perfusion of bombesin (BBS) on the interdigestive migrating myoelectric complex (MMC) activity was examined in conscious dogs with electrodes implanted on the stomach and small intestine. Cannulas and a catheter were chronically positioned in the lateral and fourth cerebral ventricles, respectively. i.c.v. perfusion of BBS, which failed to increase plasma BBS levels, replaced phase I activity in the stomach and duodenum by intense irregular spike activity and decreased the occurrence rate of MMCs, whereas intravenous infusion of BBS evoked phase II-like activity, mainly in the jejunum and ileum, and suppressed phase III activity. These data suggest that the effect of i.c.v. administration of BBS was mediated by direct activation of central brain structures. During i.c.v. perfusion of BBS, cycling in plasma levels of motilin persisted even when phase III activity was absent and plasma levels of epinephrine rose significantly. Epinephrine infusion, however, did not affect myoelectric gastrointestinal activity except for prolonging phase II. Thus it is unlikely that the central action of BBS is exerted by motilin or epinephrine.

Plasma cholecystokinin and gallbladder responses to increasing doses of bombesin in celiac disease

Impaired postprandial gallbladder emptying in celiac disease has been attributed to an absence of appropriate cholecystokinin release. To determine if a flat jejunal mucosa in celiac patients is related to a reduced cholecystokinin-secreting capacity, increasing doses of bombesin were infused into six patients with celiac disease and a flat jejunal mucosa (group A), in seven celiac patients with a normal jejunal mucosa while on a gluten-free diet (group B), and in seven healthy controls (group C). Bombesin induced significant (P < 0.05) increments of plasma CCK to a maximum value of 1.0 +/- 0.3 pM in group A, to 1.5 +/- 0.3 pM in group B, and to 1.2 +/- 0.3 pM in group C (NS between groups), that were accompanied by significant (P < 0.05) gallbladder emptying responses of 70 +/- 4% in group A, 47 +/- 10% in group B and 65 +/- 5% in group C. Dose-response relationships were not different between groups. We conclude that there is no major impairment of gallbladder responsiveness to bombesin or of cholecystokinin-secreting capacity in patients with a flat jejunal mucosa due to celiac disease.

Brain histamine mediates the bombesin-induced central activation of sympatho-adrenomedullary outflow

Intracerebroventricular (i.c.v.) administration of bombesin (0.3 nmol) increased plasma levels of both adrenaline and noradrenaline in urethane anesthetized rats. These bombesin-induced increases were inhibited by i.c.v. pretreatment with pyrilamine, an H1-receptor antagonist. Ranitidine, an H2-receptor antagonist also inhibited the increase of adrenaline, however, its effective dose was much larger than that of pyrilamine. Furthermore, the bombesin-induced increase of noradrenaline was not effectively inhibited by ranitidine. In the next series, turnover of histamine was assessed by measuring accumulation of tele-methylhistamine (t-MH), a major metabolite of brain histamine. I.c.v. administration of bombesin (0.3-3 nmol) increased turnover of hypothalamic histamine, while its intravenous administration was without effect. The present results suggest that the bombesin-induced central activation of sympatho-adrenomedullary outflow is probably, at least in part, mediated through brain histaminergic neurons.