Bombesin Receptor Antagonist Research Articles

Two novel bombesin-like neuropeptides from the skin secretion of Pelophylax kl. esculentus: Ex vivo pharmacological characterization on rat smooth muscle types.

Mammalian bombesin-like neuropeptides (BLPs) play an important role in regulation of physiological and pathophysiological processes. Frog skin-derived BLPs, of smaller size and diverse lengths and sequences at their N-terminus, have attracted the attention of many researchers. However, these N-terminal variants and the receptors modulating their pharmacological actions are poorly studied and less understood. In this study, two BLPs, namely, [Asn3, Lys6, Thr10, Phe13]3–14-bombesin and [Asn3, Lys6, Phe13]3–14-bombesin with primary structures NLGKQWATGHFM and NLGKQWAVGHFM were isolated from the skin secretion of hybrid Pelophylax kl. esculentus. Both BLPs share a similar primary structure with only a single amino acid substitution at the eighth position (threonine to valine), while they have quite different myotropic potencies with EC50 values in the range of 22.64 ± 9.7 nM (N = 8) to 83.93 ± 46.9 nM (N = 8). The potency of [Asn3, Lys6, Thr10, Phe13]3–14-bombesin was approximately 3-fold higher than that of [Asn3, Lys6, Phe13]3–14-bombesin. Through the investigation of receptor selectivity using a canonical bombesin receptor antagonist, it was found that [Asn3, Lys6, Thr10, Phe13]3–14-bombesin and [Asn3, Lys6, Phe13]3–14-bombesin had an affinity to both BB1 and BB2 receptors. Their contractile functions are mainly modulated by both BB1 and BB2 receptors on rat urinary bladder and BB2 alone on rat uterus smooth muscle preparations. These data may provide new insights into the design of potent and selective ligands for bombesin receptors. Moreover, [Asn3, Lys6, Thr10, Phe13]3–14-bombesin and [Asn3, Lys6, Phe13]3–14-bombesin did not induce significant hemolysis and toxicity in normal human cells, suggesting that these two natural novel BLPs have great potential for development into new drug candidates.

A prospective study of 68Ga-RM2 PET/MRI in patients with biochemically recurrent prostate cancer and negative conventional imaging.

e17536 Background: 68Ga-RM2 is a synthetic bombesin receptor antagonist targeting gastrin-releasing peptide receptors (GRPr) that are overexpressed in several human tumors, including prostate cancer (PC). Methods: We enrolled 114 men with BCR PC, 45-83-year-old (mean±SD: 68.2±7.0). Imaging started at 40-89 minutes (mean±SD: 51.3±9.2 after injection of 113.8-152.6 MBq (mean±SD: 140.7±6.4) of 68Ga-RM2 using a time-of-flight (TOF)-enabled simultaneous positron emission tomography (PET) / magnetic resonance imaging (MRI) scanner. Twenty-four and 23 patients also underwent 68Ga-PSMA11 and 18F-DCFPyL PET/CT, respectively. Results: All patients had rising PSA and negative conventional imaging prior to enrollment. 68Ga-RM2 PET identified recurrent PC in 78 of the 114 participants, while the simultaneous MRI was positive for PC in 45 of the 103 patients. Positivity rate of 68Ga-RM2 PET was: 31.8% for PSA < 0.5 ng/dl ( n= 22), 60% for PSA 0.5 – 1.0 ng/dl ( n= 15), 64.7% for PSA 1.0 – 2.0 ng/dl ( n= 17), 81.8% for PSA 2.0 – 5.0 ng/dl ( n= 22) and 87.2% for PSA > 5.0 ng/dl ( n= 38). PSA velocity values were 1.9±2.7 ng/ml/year (range: 0-9.1) in patients with negative PET scans and 5.8±9 ng/ml/year (range: 0.2-45.4) in patients with positive PET scans ( P: 0.01). Twenty-eight and 34 lesions were detected by 68Ga-RM2 PET and 68Ga-PSMA11 PET, respectively, while 25 lesions in 13 patients were identified by both radio-pharmaceuticals. The mean SUVmax ranged 1.6-51.2 (mean±SD:14.7±12.5) for PSMA and ranged 2.5-52.5 (mean±SD: 10.7±11.6) for RM2 ( P= 0.096). Three lesions in 2 patients were RM2-avid only (all lymph nodes) and 9 lesions in 7 patients were PSMA avid only (7 lymph nodes, 1 skeletal and 1 lung nodule). 32 and 48 lesions were detected by 68Ga-RM2 PET and 18F-DCFPyL PET, respectively. 28 lesions in 12 patients were identified by both radio-pharmaceuticals. The mean SUVmax ranged 1.7-79.3 (mean±SD: 22.2±23) for DCFPyL and ranged 1.7-46.8 (mean±SD: 7±9.2) for RM2 (P < 0.01). Four lesions in 2 patients were RM2 avid only (1 adrenal and 3 skeletal); 17 lesions in 6 patients were DCFPyL avid only (7 lymph nodes, 9 skeletal and 1 prostate). Conclusions: 68Ga-RM2 may identify higher risk patients given the highly statistically significant difference PSA velocity values between patients with negative and positive scans and may be a complementary radiopharmaceutical to the PSMA-targeting tracers to ultimately allow for personalized medicine. Clinical trial information: NCT02624518 .

LBA02-09 INTERIM ANALYSIS RESULTS OF A PROSPECTIVE STUDY OF 68 GA-RM2 PET/MRI IN PATIENTS WITH BIOCHEMICALLY RECURRENT PROSTATE CANCER AND NEGATIVE CONVENTIONAL IMAGING

Introduction:68Ga-RM2 is a synthetic bombesin receptor antagonist targeting gastrin-releasing peptide receptors (GRPr) that are overexpressed in several human tumors, including prostate cancer (PC)...

Prospective Evaluation of 68Ga-RM2 PET/MRI in Patients with Biochemical Recurrence of Prostate Cancer and Negative Findings on Conventional Imaging.

68Ga-labeled DOTA-4-amino-1-carboxymethyl-piperidine-d-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 (68Ga-RM2) is a synthetic bombesin receptor antagonist that targets gastrin-releasing peptide receptor (GRPr). GRPr proteins are highly overexpressed in several human tumors, including prostate cancer (PCa). We present data from the use of 68Ga-RM2 in patients with biochemical recurrence (BCR) of PCa and negative findings on conventional imaging. Methods: We enrolled 32 men with BCR of PCa, who were 59-83 y old (mean ± SD, 68.7 ± 6.4 y). Imaging started at 40-69 min (mean, 50.5 ± 6.8 min) after injection of 133.2-151.7 MBq (mean, 140.6 ± 7.4 MBq) of 68Ga-RM2 using a time-of-flight-enabled simultaneous PET/MRI scanner. T1-weighted, T2-weighted, and diffusion-weighted images were acquired. Results: All patients had a rising level of prostate-specific antigen (PSA) (range, 0.3-119.0 ng/mL; mean, 10.1 ± 21.3 ng/mL) and negative findings on conventional imaging (CT or MRI, and a 99mTc-methylene diphosphonate bone scan) before enrollment. The observed 68Ga-RM2 PET detection rate was 71.8%. 68Ga-RM2 PET identified recurrent PCa in 23 of the 32 participants, whereas the simultaneous MRI scan identified findings compatible with recurrent PCa in 11 of the 32 patients. PSA velocity was 0.32 ± 0.59 ng/mL/y (range, 0.04-1.9 ng/mL/y) in patients with negative PET findings and 2.51 ± 2.16 ng/mL/y (range, 0.13-8.68 ng/mL/y) in patients with positive PET findings (P = 0.006). Conclusion:68Ga-RM2 PET can be used for assessment of GRPr expression in patients with BCR of PCa. High uptake in multiple areas compatible with cancer lesions suggests that 68Ga-RM2 is a promising PET radiopharmaceutical for localization of disease in patients with BCR of PCa and negative findings on conventional imaging.

68Ga-DOTA-Bombesin (68Ga-RM2 or 68Ga-Bombesin) PET versus 68Ga-PSMA PET: A pilot prospective evaluation in patients with biochemical recurrence of prostate cancer.

331 Background: Detection of prostate cancer (PC) after biochemical recurrence (BCR) remains a great challenge. RM2 is a synthetic bombesin receptor antagonist, which targets gastrin-releasing peptide receptors (GRPr). PSMA is a membrane antigen expressed on prostate cancer cells. Here we present a comparison of 2 novel PET tracers, 68Ga-RM2 and 68Ga-PSMA, in patients with BCR with prior non-contributory conventional imaging. Methods: Ten men (67-83 year-old; mean ± SD: 74.3 ± 5.9) with BCR PC were imaged with 68Ga-RM2 and 7 of them also had 68Ga-PSMA PET. The SUVmax and SUVmean measurements were recorded in normal tissues and areas of uptake outside the expected physiologic biodistribution. Results: All 7 patients who had both scans had rising PSA (range: 3.5-36.5 ng/mL; mean±SD: 13.5 ± 11.5) and non-contributory conventional imaging (CT, MRI, 18F FDG PET/CT, 18F NaF PET/CT, 99mTc MDP bone scan). 68Ga-PSMA had the highest physiologic uptake in the salivary glands and small bowel, with hepatobiliary and renal clearance noted, while 68Ga-RM2 had the highest physiologic uptake in the pancreas, with renal clearance noted. Uptake values uptake outside the expected physiologic biodistribution were not statistically different between 68Ga-PSMA and 68Ga-RM2. 68Ga-PSMA localized in a lymph node and seminal vesicle in one patient with no abnormal 68Ga-RM2 uptake. In 2 patients abdominal peri-aortic lymph nodes were more easily visualized by 68Ga-RM2 due to lack of interference by radioactivity accumulation in the small intestine. Conclusions: 68Ga-PSMA and 68Ga-RM2 have distinct biodistribution in this small cohort of patients with BCR PC. High uptake in multiple areas outside the expected physiologic biodistribution suggests that both 68Ga-PSMA and 68Ga-RM2 are promising PET radiopharmaceuticals for localization of disease in patients with BCR PC and non-contributory conventional imaging. The differences in target density, biodistribution and clearance pathways may result in the superiority of one of the two tracers in different patients. 68Ga-RM2 shows similar sensitivity to 68Ga-PSMA and has the potential for being FDA-approved in the future. Clinical trial information: NCT02440308.

Viability of D283 medulloblastoma cells treated with a histone deacetylase inhibitor combined with bombesin receptor antagonists.

Medulloblastoma (MB) comprises four distinct molecular subgroups, and survival remains particularly poor in patients with Group 3 tumors. Mutations and copy number variations result in altered epigenetic regulation of gene expression in Group 3 MB. Histone deacetylase inhibitors (HDACi) reduce proliferation, promote cell death and neuronal differentiation, and increase sensitivity to radiation and chemotherapy in experimental MB. Bombesin receptor antagonists potentiate the antiproliferative effects of HDACi in lung cancer cells and show promise as experimental therapies for several human cancers. Here, we examined the viability of D283 cells, which belong to Group 3 MB, treated with an HDACi alone or combined with bombesin receptor antagonists. D283 MB cells were treated with different dosesof the HDACi sodium butyrate (NaB), the neuromedin B receptor (NMBR) antagonist BIM-23127, the gastrin releasing peptide receptor (GRPR) antagonist RC-3095, or combinations of NaB with each receptor antagonist. Cell viability was examined by cell counting. NaB alone or combined with receptor antagonists reduced cell viability at all doses tested. BIM-23127 alone did not affect cell viability, whereas RC-3095 at an intermediate dose significantly increased cell number. Although HDACi are promising agents to inhibit MB growth, the present results provide preliminary evidence that combining HDACi with bombesin receptor antagonists is not an effective strategy to improve the effects of HDACi against MB cells.

Copper-64 Labeled Macrobicyclic Sarcophagine Coupled to a GRP Receptor Antagonist Shows Great Promise for PET Imaging of Prostate Cancer.

The gastrin-releasing peptide receptor (GRPr) is an important molecular target for the visualization and therapy of tumors and can be targeted with radiolabeled bombesin derivatives. The present study aims to develop statine-based bombesin receptor antagonists suitable for labeling with 64Cu for imaging by positron emission tomography (PET). The potent GRPr antagonist D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2 was conjugated to the sarcophagine (3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane=Sar) derivative 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid (MeCOSar) via PEG4 (LE1) and PEG2 (LE2) spacers and radiolabeled with 64Cu2+ with >95% yield and specific activities of about 100 MBq/nmol. Both Cu(II) conjugates have high affinity for GRPr (IC50: natCu-LE1, 1.4±0.1 nM; natCu-LE2, 3.8±0.6 nM). The antagonistic properties of both conjugates were confirmed by Ca2+-flux measurements. Biodistribution studies of Cu-64-LE1 exhibited specific targeting of the tumor (19.6±4.7% IA/g at 1 h p.i.) and GRPr-positive organs. Biodistribution and PET images at 4 and 24 h postinjection showed increasing tumor-to-background ratios with time. This was illustrated by the acquisition of PET images showing high tumor-to-normal tissue contrast. This study demonstrates the high affinity of the MeCOSar-PEGx-bombesin conjugates to GRPr. The stability of 64Cu complexes of MeCOSar, the long half-life of 64Cu, and the suitable biodistribution profile of the 64Cu-labeled peptides lead to PET images of high contrast suitable for potential translation into the clinic.

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 GRP18–27 (1–300nmol/site) elicited scratching. GRP18–27-induced scratching was inhibited by the μ-opioid receptor antagonist naltrexone hydrochloride, the BB2 bombesin receptor antagonist RC-3095, the H1 histamine receptor antagonists fexofenadine hydrochloride and chlorpheniramine maleate, and the PAR2 proteinase-activated receptor antagonist FSLLRY-NH2. Mast cell deficiency significantly, but not completely, reduced the GRP18–27-induced scratching. BB2 bombesin receptors are present in mast cells in the skin, and intradermal injection of GRP18–27, not only induced scratching, but also led to mast cell degranulation. GRP18–27-induced mast cell degranulation was inhibited by the BB2 bombesin receptor antagonist RC-3095. These results suggest that peripherally released GRP can induce an itch response, at least partly, through activation of BB2 receptors present in the mast cells, triggering their degradation and the release of histamine and the serine proteinase, tryptase.

Novel dimeric DOTA-coupled peptidic Y1-receptor antagonists for targeting of neuropeptide Y receptor-expressing cancers

BackgroundSeveral peptide hormone receptors were identified that are specifically over-expressed on the cell surface of certain human tumors. For example, high incidence and density of the Y1 subtype of neuropeptide Y (NPY) receptors are found in breast tumors. Recently, we demonstrated that the use of potent radiolabeled somatostatin or bombesin receptor antagonists considerably improved the sensitivity of in vivo imaging when compared to agonists. We report here on the first DOTA-coupled peptidic Y1 receptor affine dimer antagonists.MethodsBased on a Y1 affine dimeric peptide scaffold previously reported to competitively antagonize NPY-mediated processes, we have developed new dimeric DOTA-coupled Y1 receptor affine antagonists for scintigraphy and radiotherapy. These dimeric peptides were tested for their specific binding to Y1 expressed in SK-N-MC cells and Y2 expressed in SH-SY5Y as well as for their ability to mediate cAMP production in SK-N-MC cells.ResultsIntroduction of two DOTA moieties at the N-termini of the dimeric NPY analogs as well as the double Asn29 replacement by Dpr(DOTA) or Lys(DOTA) (6 and 10) moiety dramatically reduced binding affinity. However, asymmetric introduction of the DOTA moiety in one segment of the peptidic heterodimer (8 and 11) resulted in suitable antagonists for receptor targeting with high binding affinity for Y1. All compounds were devoid of Y2 binding affinity.ConclusionsThe design and the in vitro characterization of the first DOTA-coupled dimeric NPY receptor antagonist with high affinity and selectivity for Y1 over Y2 are described. This compound may be an excellent candidate for the imaging of Y1-positive tumors and their treatment.

To B or not to B: Fat is the question

To B or not to B: Fat is the question

Modulation of 11β-Hydroxysteroid Dehydrogenase Expression by Bombesin: A Possible Mechanism for Glucocorticoid Resistance in Androgen Independent Prostate Cancer

Treatment with glucocorticoids is one of a limited number of options for androgen independent prostate cancer. Neuroendocrine differentiation has been shown to contribute to androgen-independent prostate cancer progression. To study the potential link between neuroendocrine differentiation and the glucocorticoid action, we investigated the effects of the product of neuroendocrine differentiation--bombesin on glucocorticoid metabolizing enzymes--11beta-hydroxysteroid dehydrogenases in PC-3 cells. Our Western analysis, RT-PCR, and activity assays demonstrate that while 18-hour exposure to bombesin reduces 11beta-hydroxy-steroid dehydrogenases-1 profiles (activities 25% less, protein level 29% lower, mRNA levels 45% lower), contrarily it increases 11beta-hydroxysteroid dehydrogenases-2 profiles (activities 34%, protein levels 100%, mRNA levels 120%). Blockade bombesin action with bombesin receptor antagonists and the enzyme degrading bombesin prevented these changes, suggesting the observed modulations were bombesin receptor-specific. In addition, bombesin increased the amounts of interleukin-8 and mRNA of vascular endothelial growth factor receptor 2, which were lowered in the presence of cortisol, suggesting that neuropeptide blockade may extend the benefits of glucocorticoids in treating androgen-independent prostate cancer.

Bombesin Receptor Antagonists May Be Preferable to Agonists for Tumor Targeting

Two bombesin analogs, Demobesin 4 and Demobesin 1, were characterized in vitro as gastrin-releasing peptide (GRP) receptor agonist and antagonist, respectively, and were compared as (99m)Tc-labeled ligands for their in vitro and in vivo tumor-targeting properties. N(4)-[Pro(1),Tyr(4),Nle(14)]Bombesin (Demobesin 4) and N(4)-[d-Phe(6),Leu-NHEt(13),des-Met(14)]bombesin(6-14) (Demobesin 1) were characterized in vitro for their binding properties with GRP receptor autoradiography using GRP receptor-transfected HEK293 cells, PC3 cells, and human prostate cancer specimens. Their ability to modulate calcium mobilization in PC3 and transfected HEK293 cells was analyzed as well as their ability to trigger internalization of the GRP receptor in transfected HEK293 cells, as determined qualitatively by immunofluorescence microscopy and quantitatively by enzyme-linked immunosorbent assay (ELISA). Further, their internalization properties as (99m)Tc-labeled radioligands were tested in vitro in both cell lines. Finally, their biodistribution was analyzed in PC3 tumor-bearing mice. A comparable binding affinity with the 50% inhibitory concentration (IC(50)) in the nanomolar range was measured for Demobesin 4 and Demobesin 1 in all tested tissues. Demobesin 4 behaved as an agonist by strongly stimulating calcium mobilization and by triggering GRP receptor internalization. Demobesin 1 was ineffective in stimulating calcium mobilization and in triggering GRP receptor internalization. However, in these assays, it behaved as a competitive antagonist as it reversed completely the agonist-induced effects in both systems. (99m)Tc-Labeled Demobesin 1 was only weakly taken up by PC3 cells or GRP receptor-transfected HEK293 cells (10% and 5%, respectively, of total added radioactivity) compared with (99m)Tc-labeled Demobesin 4 (45% of total added radioactivity in both cell lines). Remarkably, the biodistribution study revealed a much more pronounced uptake at 1, 4, and 24 h after injection of (99m)Tc-labeled Demobesin 1 in vivo into PC3 tumors than (99m)Tc-labeled Demobesin 4. In vivo competition experiments demonstrated a specific uptake in PC3 tumors and in physiologic GRP receptor-expressing tissues. The tumor-to-kidney ratios were 0.7 for Demobesin 4 and 5.2 for Demobesin 1 at 4 h. This comparative in vitro/in vivo study with Demobesin 1 and Demobesin 4 indicates that GRP receptor antagonists may be superior targeting agents to GRP receptor agonists, suggesting a change of paradigm in the field of bombesin radiopharmaceuticals.

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 60 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-ψ(CH 2NH)-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.

Activation of p300 histone acetyltransferase activity and acetylation of the androgen receptor by bombesin in prostate cancer cells

Androgen receptor signaling in prostate cancer cells is augmented by the androgen receptor (AR) coactivator p300, which transactivates and acetylates the AR in the presence of dihydrotestosterone (DHT). As prostate cancer (PC) cells progress to androgen independence, AR signaling remains intact, indicating that other factors stimulate AR activities in the absence of androgen. We previously reported that neuropeptide growth factors could transactivate the AR in the presence of very low concentrations of DHT. Here, we examine the involvement of p300 in neuropeptide activation of AR signaling. Transfection of increasing concentrations of p300 in the presence of bombesin into PC-3 cells resulted in a linear increase in AR transactivation, suggesting that p300 acts as a coactivator in neuropeptide-mediated AR transactivation. P300 is endowed with histone acetyltransferase (HAT) activity. Therefore, we examine the effect of bombesin on p300 HAT activity. At 4 h after the addition of bombesin, p300 HAT activity increased 2.0-fold (P<0.01). Incubation with neutral endopeptidase, which degrades bombesin, or bombesin receptor antagonists blocked bombesin-induced p300 HAT activity. To explore the potential signaling pathways involved in bombesin-induced p300 HAT activity, we examined Src and PKCdelta pathways that mediate bombesin signaling. Inhibitors of Src kinase activity or Src kinase siRNA blocked bombesin-induced p300 HAT activity, whereas PKCdelta inhibitors or PKCdelta siRNA significantly increased bombesin-induced p300 HAT activity suggesting that Src kinase and PKCdelta kinase are involved in the regulation of p300 HAT activity. As AR is acetylated in the presence of 100 nM DHT, we next examined whether bombesin-induced p300 HAT activity would result in enhanced AR acetylation. Bombesin-induced AR acetylation at the same motif KLKK observed in DHT-induced acetylation. Elimination of p300 using p300 siRNA reduced AR acetylation, demonstrating that AR acetylation was mediated by p300. AR acetylation results in AR transactivation and the expression of the AR-regulated gene prostate-specific antigen (PSA). Therefore, we examined bombesin-induced AR transactivation and PSA expression in the presence and absence of p300 siRNA and found inhibition of p300 expression reduced bombesin-induced AR transactivation and PSA expression. Together these results demonstrate that bombesin, via Src and PKCdelta signaling pathways, activates p300 HAT activity which leads to enhanced acetylation of AR resulting in increased expression of AR-regulated genes.

Agonist function of the neurokinin receptor antagonist, [ d-Arg1, d-Phe5, d-Trp7,9,Leu11]substance P, in monocytes

G-protein-coupled bombesin receptors are capable of signaling through the G i protein even when receptor-coupling to G q is blocked by [ d-Arg1, d-Phe5, d-Trp7,9,Leu11]substance P (SpD), a neurokinin-1 receptor antagonist and “biased” agonist to bombesin receptors. As bombesin is a monocyte and tumor cell attractant, we were interested in the effects of SpD on cell migration. Chemotaxis of monocytes was tested in micropore filter assays. SpD was a dose-dependent agonist in monocyte migration and was not inhibited by antagonists to neurokinin-1 or -2 receptors. SpD failed to inhibit chemotaxis toward bombesin, suggesting that inhibition of bombesin receptor coupling to G q with SpD does not impair migratory responses elicited by bombesin. As pertussis toxin inhibited migration, coupling of receptors to G i may signal migration. Chemotaxis toward SpD was inhibited by bombesin receptor antagonists as well as by blocking signaling enzymes downstream of G q (phospholipase-3 and protein kinase C with wortmannin and bisindolylmaleimide, respectively), suggesting transactivation of G q-mediated chemotaxis signaling by SpD via bombesin receptors. Protein kinase C that induces sphingosine kinase activation and production of sphingosine-1-phosphate, which may lead to G q-dependent chemoattraction, was involved in SpD-dependent migration. Inhibition of sphingosine-1-phosphate production with dimethylsphingosine inhibited monocyte migration toward SpD. Data suggest that SpD induces migration in monocytes and signaling events involving activation of sphingosine kinase in a G i protein- and protein kinase C-dependent fashion. “Biased” agonism of SpD at bombesin receptors may affect normal and tumor cell migration.

Gastrin-releasing peptide microinjected into the amygdala inhibits feeding

Bombesin (BN)-like peptides including gastrin-releasing peptide (GRP) are known to inhibit feeding. In the amygdaloid body BN receptors have been found in moderate to high densities. The central part of the amygdala (ACE) is essentially involved in the regulation of feeding and body weight. In the present experiments GRP was injected into the ACE and liquid food intake, general behavioural activity, as well as core temperature, were examined in male CFY rats. Food intake was measured every 5 min for 30 min and at the 40th and the 60th min following GRP or vehicle microinjections. Bilateral application of 50, 100 or 150 ng GRP resulted in transient inhibition of food intake while bilateral injection of 25 or 300 ng GRP did not modify feeding. Effect of GRP was eliminated by prior application of BN receptor antagonist [Leu 13-ψ(CH 2NH)-Leu 14]BN. After GRP or vehicle treatments animals were video-monitored and food intake, the first meal latency (FML), intermeal intervals (IMI), the time spent feeding (FT), grooming, resting and exploration were analysed at 5-min intervals for 30 min. However, FML did not change after GRP, the first IMI increased and intake, FT and intake/FT significantly decreased during the first 5 min. Duration of resting gradually increased after GRP and animals spent less time with exploration after GRP treatment than after vehicle injection. These differences were significant during the 25–30-min period. In body temperature, no significant changes were observed. Our results show that GRP in the ACE inhibits feeding and that GRP may decrease the efficiency of eating and may act as a satiety signal.

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

Background & Aims: This study was designed to characterize [D-F5Phe6D-Ala11]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 μg · 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 (t50%, 35 ± 4 minutes), which BIM26226 inhibited significantly (t50%, 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.GASTROENTEROLOGY 2001;120:361-368

Bombesin Receptors in Distinct Tissue Compartments of Human Pancreatic Diseases

Overexpression of receptors for regulatory peptides in various human diseases is reportedly of clinical interest. Among these peptides, bombesin and gastrin-releasing peptide (GRP) have been shown to play a physiological and pathophysiological role in pancreatic tissues. Our aim has been to localize bombesin receptors in the human diseased pancreas to identify potential clinical applications of bombesin analogs in this tissue. The presence of bombesin receptor subtypes has been evaluated in specimens of human pancreatic tissues with chronic pancreatitis (n = 23) and ductal pancreatic carcinoma (n = 29) with in vitro receptor autoradiography on tissue sections incubated with 125I-[Tyr4]-bombesin or the universal ligand 125I-[D-Tyr6, β-Ala11, Phe13, Nle14]-bombesin(6–14) as radioligands and displaced by subtype-selective bombesin receptor agonists and antagonists. GRP receptors were identified in the pancreatic exocrine parenchyma in 17 of 20 cases with chronic pancreatitis. No measurable bombesin receptors were found in the tumor tissue of ductal pancreatic carcinomas, however, GRP receptors were detected in a subset of peritumoral small veins in 19 of 29 samples. Moreover, residual pancreatic islets in these tissues were shown to express the BB3 receptor subtype. These data demonstrate the presence of bombesin receptors in three distinct tissue compartments of the pancreas, namely GRP receptors in the exocrine parenchyma in chronic pancreatitis and in peritumoral vessels around ductal pancreatic carcinomas, and BB3 receptors in residual pancreatic islets. Such a selective expression of bombesin receptor subtypes in pancreatic tissues may not only be of pathophysiological significance but may represent the basis for potential diagnostic and therapeutic clinical applications of bombesin analogs, including GRP receptor scintigraphy to differentiate chronic pancreatitis from ductal pancreatic carcinoma.

Presence of receptors for bombesin/gastrin-releasing peptide and mRNA for three receptor subtypes in human prostate cancers.

Bombesin-like peptides can function as autocrine or paracrine growth factors and stimulate the growth of some cancer cells, including human prostate cancer. Three bombesin receptor subtypes, termed gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3), have been identified in rodents and humans. We investigated the presence and characteristics of the functional receptors for bombesin/GRP in human prostate adenocarcinoma specimens by radio-receptor assay and the mRNA expression of the three bombesin receptor subtypes by RT-PCR. Of the 80 specimens of primary prostate cancer examined by receptor binding assays, 50 ( approximately 63%) showed high-affinity, low-capacity binding sites for bombesin/GRP, and 12 of these 50 receptor-positive specimens also showed a second binding site. Of the 22 prostate cancer specimens analyzed by RT-PCR, 20 (91%) expressed GRPR mRNA, 3 (14%) showed NMBR mRNA, and 2 ( approximately 9%) revealed BRS-3 mRNA. No correlation was observed between receptor expression and patients' age or pathological data. The detection of a wide distribution of bombesin/GRP receptors in human prostate carcinomas supports the view that they may be involved in modulation of tumor progression and suggests that approaches based on binding of bombesin receptor antagonists or new targeted cytotoxic bombesin analogs to prostate cancers could be considered for the therapy.

Presence of receptors for bombesin/gastrin-releasing peptide and mRNA for three receptor subtypes in human prostate cancers

BACKGROUND Bombesin-like peptides can function as autocrine or paracrine growth factors and stimulate the growth of some cancer cells, including human prostate cancer. Three bombesin receptor subtypes, termed gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3), have been identified in rodents and humans. METHODS We investigated the presence and characteristics of the functional receptors for bombesin/GRP in human prostate adenocarcinoma specimens by radio-receptor assay and the mRNA expression of the three bombesin receptor subtypes by RT-PCR. RESULTS Of the 80 specimens of primary prostate cancer examined by receptor binding assays, 50 (∼63%) showed high-affinity, low-capacity binding sites for bombesin/GRP, and 12 of these 50 receptor-positive specimens also showed a second binding site. Of the 22 prostate cancer specimens analyzed by RT-PCR, 20 (91%) expressed GRPR mRNA, 3 (14%) showed NMBR mRNA, and 2 (∼9%) revealed BRS-3 mRNA. No correlation was observed between receptor expression and patients' age or pathological data. CONCLUSIONS The detection of a wide distribution of bombesin/GRP receptors in human prostate carcinomas supports the view that they may be involved in modulation of tumor progression and suggests that approaches based on binding of bombesin receptor antagonists or new targeted cytotoxic bombesin analogs to prostate cancers could be considered for the therapy. Prostate 42:295–303, 2000. © 2000 Wiley-Liss, Inc.