Ultra-high-frequency radio-frequency acoustic molecular imaging with saline nanodroplets in living subjects.

Molecular imaging is a crucial technique in clinical diagnostics but it relies on radioactive tracers or strong magnetic fields that are unsuitable for many patients, particularly infants and pregnant women. Ultra-high-frequency radio-frequency acoustic (UHF-RF-acoustic) imaging using non-ionizing RF pulses allows deep-tissue imaging with sub-millimetre spatial resolution. However, lack of biocompatible and targetable contrast agents has prevented the successful in vivo application of UHF-RF-acoustic imaging. Here we report our development of targetable nanodroplets for UHF-RF-acoustic molecular imaging of cancers. We synthesize all-liquid nanodroplets containing hypertonic saline that are stable for at least 2 weeks and can produce high-intensity UHF-RF-acoustic signals. Compared with concentration-matched iron oxide nanoparticles, our nanodroplets produce at least 1,600 times higher UHF-RF-acoustic signals at the same imaging depth. We demonstrate in vivo imaging using the targeted nanodroplets in a prostate cancer xenograft mouse model expressing gastrin release protein receptor (GRPR), and show that targeting specificity is increased by more than 2-fold compared with untargeted nanodroplets or prostate cancer cells not expressing this receptor.

Sensitization of spinal itch transmission neurons in a mouse model of chronic itch requires an astrocytic factor.

BACKGROUND: Chronic itch is a highly debilitating symptom among patients with inflammatory skin diseases. Recent studies have revealed that gastrin-releasing peptide (GRP) and its receptor (gastrin-releasing peptide receptor [GRPR]) in the spinal dorsal horn (SDH) play a central role in itch transmission. OBJECTIVE: We aimed to investigate whether GRP-GRPR signaling is altered in SDH neurons in a mouse model of chronic itch and to determine the potential mechanisms underlying these alterations. METHODS: Patch-clamp recordings from enhanced green fluorescent protein (EGFP)-expressing (GRPR+) SDH neurons were used to examine GRP-GRPR signaling in spinal cord slices obtained from Grpr-EGFP mice. Immunohistochemical, genetic (gene expression and editing through adeno-associated virus vectors), and behavioral approaches were also used for in vivo experiments. RESULTS: We observed potentiation of GRP-evoked excitation in the GRPR+ SDH neurons of mice with contact dermatitis, without concomitant changes in GRPR expression. Interestingly, increases in excitation were attenuated by suppressing the reactive state of SDH astrocytes, which are known to be reactive in patients with chronic itch conditions. Furthermore, CRISPR-Cas9-mediated astrocyte-selective in vivo editing of a gene encoding lipocalin-2 (LCN2), an astrocytic factor implicated in chronic itch, suppressed increases in GRP-induced excitation of GRPR+ neurons, repetitive scratching, and skin damage in mice with contact dermatitis. Moreover, LCN2 potentiated GRP-induced excitation of GRPR+ neurons in normal mice. CONCLUSION: Our findings indicate that, under chronic itch conditions, the GRP-induced excitability of GRPR+ SDH neurons is enhanced through a non-cell-autonomous mechanism involving LCN2 derived from reactive astrocytes.

Role of neuromedin B and its receptor in the innate immune responses against influenza A virus infection in vitro and in vivo.

The peptide neuromedin B (NMB) and its receptor (NMBR) represent a system (NMB/NMBR) of neuromodulation. Here, it was demonstrated that the expression of NMBR in cells or murine lung tissues was clearly upregulated in response to H1N1/PR8 influenza A virus infection. Furthermore, the in vitro and in vivo activities of NMB/NMBR during PR8 infection were investigated. It was observed that A549 cells lacking endogenous NMBR were more susceptible to virus infection than control cells, as evidenced by the increased virus production in the cells. Interestingly, a significant decrease in IFN-α and increased IL-6 expression were observed in these cells. The role of this system in innate immunity against PR8 infection was probed by treating mice with NMB. The NMB-treated mice were less susceptible to virus challenge, as evidenced by increased survival, increased body weight, and decreased viral NP expression compared with the control animals. Additionally, the results showed that exogenous NMB not only enhanced IFN-α expression but also appeared to inhibit the expression of NP and IL-6 in PR8-infected cells and animals. As expected, opposing effects were observed in the NMBR antagonist-treated cells and mice, which further confirmed the effects of NMB. Together, these data suggest that NMB/NMBR may be an important component of the host defence against influenza A virus infection. Thus, these proteins may serve as promising candidates for the development of novel antiviral drugs.

Cloning of neuromedin B and its receptor in the rabbit and generating a polyclonal antibody to the neuromedin B protein.

Neuromedin B (NMB) is a highly conserved bombesin-related neuropeptide found in mammals. Neuromedin B (NMB) executes its effect by binding to the cell surface receptor, neuromedin B receptor (NMBR). In this study, we cloned the rabbit NMB and NMBR genes. The similarity and phylogenetic analyses of NMB and NMBR gene sequences were performed. The expression of NMB and NMBR mRNA in the rabbit was investigated using real-time RT-PCR. Our bioinformatic analysis demonstrated that the cloned rabbit NMB precursor cDNA encoded Gly-His-Phe-Met-NH2 amino acids at the C-terminus, and that its receptor possessed typical transmembrane features. The NMB mRNA was highly expressed in the CNS, while the NMBR mRNA was widely expressed in many tissues, with the highest expression in the gastrointestinal tract. The studies on the NMB distribution and function are limited by the lack of a specific antibody to this neuropeptide. In this paper, polyclonal NMB antibody was generated in mice. Western blotting analysis revealed that the prepared antibody could specifically recognize the recombinant and the endogenous NMB proteins. Immunohistochemistry analysis indicated that the NMB protein was localized in the cytoplasm of the pituitary cells. The existence of NMB protein in the hypothalamic-pituitary-gonadal axis suggests that NMB might function in rabbit reproduction.

Gastrin-releasing peptide receptor (GRPR) mediates chemotaxis in neutrophils.

Neutrophil migration to inflamed sites is crucial for both the initiation of inflammation and resolution of infection, yet these cells are involved in perpetuation of different chronic inflammatory diseases. Gastrin-releasing peptide (GRP) is a neuropeptide that acts through G protein coupled receptors (GPCRs) involved in signal transmission in both central and peripheral nervous systems. Its receptor, gastrin-releasing peptide receptor (GRPR), is expressed by various cell types, and it is overexpressed in cancer cells. RC-3095 is a selective GRPR antagonist, recently found to have antiinflammatory properties in arthritis and sepsis models. Here we demonstrate that i.p. injection of GRP attracts neutrophils in 4 h, and attraction is blocked by RC-3095. Macrophage depletion or neutralization of TNF abrogates GRP-induced neutrophil recruitment to the peritoneum. In vitro, GRP-induced neutrophil migration was dependent on PLC-ß2, PI3K, ERK, p38 and independent of Gαi protein, and neutrophil migration toward synovial fluid of arthritis patients was inhibited by treatment with RC-3095. We propose that GRPR is an alternative chemotactic receptor that may play a role in the pathogenesis of inflammatory disorders.

Immunohistochemical detection of bombesin receptor subtypes GRP-R and BRS-3 in human tumors using novel antipeptide antibodies.

Bombesin (BN)-like peptides can stimulate cancer cell growth through binding to their specific G protein-coupled receptors. It is well established that BN receptors are being overexpressed in a subset of human tumors; however, little is known about the cellular and subcellular localization of individual BN receptor subtypes in these tissues. In this study, we developed and characterized novel antipeptide antibodies to the carboxy terminal regions of the gastrin-releasing peptide-preferring bombesin receptor (GRP-R) and the bombesin receptor subtype-3 (BRS-3). Specificity of the antisera was demonstrated by (1) detection of broad bands migrating at Mr 50,000-70,000 in Western blots of membranes from receptor-expressing tissues; (2) cell surface staining of transfected cells; (3) translocation of GRP-R receptor immunostaining after BN exposure; and (4) abolition of tissue immunostaining by preadsorbtion of the antibodies with their immunizing peptides. The distribution of BN receptors was investigated in 74 formalin-fixed, paraffin-embedded human tumors. GRP-R receptors were most frequently detected in breast and prostate carcinomas. BRS-3 receptors were often detected in prostate and pancreatic carcinomas and in pituitary adenomas. Immunoreactive GRP-R and BRS-3 receptors were in many cases predominantly confined to the plasma membrane and uniformly present on nearly all tumor cells. The development of these novel antipeptide antibodies will facilitate the identification of those tumors, which may be targets for diagnostic or radiotherapeutic application of subtype-selective BN analogs.

Targeting gastrin-releasing peptide receptors on small cell lung cancer cells with a bispecific molecule that activates polyclonal T lymphocytes.

PURPOSE: Gastrin-releasing peptide (GRP) is a growth factor for small cell lung cancer (SCLC). GRP belongs to the bombesin peptide family and has significant homology to bombesin. We constructed a bispecific molecule, OKT3xAntag2, by conjugating a monoclonal antibody OKT3 (anti-CD3) with a bombesin/GRP antagonist (Antag2) and evaluated cytotoxicity against SCLC cells. EXPERIMENTAL DESIGN: We tested binding of the bispecific molecule to SCLC cell lines and T cells by flow cytometry, antibody-dependent cellular cytotoxicity (ADCC) of SCLC cells in vitro and in a murine SCLC xenograft model. We studied SCLC apoptosis and necrosis during ADCC and the activity and cleavage of caspase-3, caspase-9, and poly(ADP-ribose) polymerase (PARP). RESULTS: The bispecific molecule functions as a cross-linker between T cells and SCLC cells, induces T cell activation, and mediates ADCC of SCLC cells; 40% to 80% growth inhibition of SCLC cells mediated by the bispecific molecule at low effector to target cell ratios was achieved. Activation of T cells by the bispecific molecule resulted in significant increases in IFNgamma production and apoptosis and necrosis of SCLC cells associated with cleavage of PARP and caspase-3. Targeted immunotherapy with the bispecific molecule-armed human T cells significantly reduced SCLC tumor burdens in a mouse model. CONCLUSION: The bispecific molecule OKT3xAntag2 mediates growth inhibition and apoptosis of SCLC cells by activated T cells through activation and cleavage of caspase-3 and PARP in vitro and in vivo. Clinical trials of this bispecific molecule through adoptive transfer of ex vivo activated T cells in GRP receptor-positive tumors, such as SCLC, are warranted.

Gastrin-releasing peptide receptor antagonist effects on an animal model of sepsis.

RATIONALE: Several new therapeutic strategies have been described for the treatment of sepsis, but to date none are related to alterations in the bombesin/gastrin-releasing peptide (GRP) receptor pathways. OBJECTIVES: To determine the effects of a selective GRP receptor antagonist, RC-3095, on cytokine release from macrophages and its in vivo effects in the cecal ligation and puncture (CLP) model of sepsis and in acute lung injury induced by intratracheal instillation of LPS. METHODS: We determined the effects of RC-3095 in the CLP model of sepsis and in acute lung injury induced by intratracheal instillation of LPS. In addition, we determined the effects of RC-3095 on tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-10, and nitric oxide release from activated macrophages. MEASUREMENTS AND MAIN RESULTS: The GRP antagonist attenuated LPS- or CLP-induced TNF-alpha, IL-1beta, and nitric oxide release in cultured macrophages and decreased the mRNA levels of inducible nitric oxide synthase. The administration of RC-3095 (0.3 mg/kg) 6 h after sepsis induction improved survival in the CLP model, and diminished lung damage after intratracheal instillation of LPS. These effects were associated with attenuation on the circulating TNF-alpha and IL-1beta levels and decreased myeloperoxidase activity in several organs. CONCLUSIONS: We report that a selective GRP receptor antagonist attenuates the release of proinflammatory cytokines in vitro and in vivo and improves survival in "established" sepsis. These are consistent with the involvement of a new inflammatory pathway relevant to the development of sepsis.

Immunohistochemical localization of gastrin-releasing peptide receptor in the mouse brain.

Gastrin-releasing peptide (GRP) is a mammalian bombesin (BN)-like peptide that binds with high affinity to the GRP receptor (GRP-R). Previous behavioral studies using mice and rats showed that the GRP/GRP-R system mediates learning and memory by modulating neurotransmitter release in the local GABAergic network of the amygdala and the nucleus tractus solitarius (NTS). To date, the precise distribution of GRP-R in the brain has not been elucidated. We used a synthetic peptide derived from mouse GRP-R to generate affinity-purified antibodies to GRP-R and used immunohistochemistry to determine the distribution of GRP-R in the mouse brain. The specificity of anti-GRP-R antibody was confirmed in vitro using COS-7 cells transiently expressing GRP-R and in vivo using GRP-R-deficient and wild-type mouse brain sections. GRP-R immunoreactivity was widely distributed in the isocortex, hippocampal formation, piriform cortex, amygdala, hypothalamus, and brain stem. In particular, GRP-R immunoreactivity was observed in the lateral (LA), central, and basolateral amygdaloid (BLA) nuclei and NTS, which are important regions for memory performance. Double-labeling immunohistochemistry demonstrated that subpopulations of GRP-R are present in GABAergic neurons in the amygdala. Consequently, GRP-R immunoreactivity was observed in the GABAergic neurons of the limbic region. These anatomical results provide support for the idea that the GRP/GRP-R system mediates memory performance by modulating neurotransmitter release in the local GABAergic network.

Gastrin-releasing peptide is a mitogen and a morphogen in murine colon cancer.

Little is known about the factors involved in regulating the appearance, or differentiation, of solid tumors including those arising from the colon. We herein demonstrate that the mitogen gastrin-releasing peptide (GRP) is a morphogen, critically important in regulating the differentiation of murine colon cancer. Although epithelial cells lining the mouse colon do not normally express GRP and its receptor (GRP-R), both are aberrantly expressed by all better differentiated cancers in wild-type C57BL/6J mice treated with the carcinogen azoxymethane. Whereas small tumors in both wild-type and GRP-R-deficient (i.e., GRP-R-/-) mice are histologically similar, larger tumors become better differentiated in the former but degenerate into more poorly differentiated mucinous adenocarcinomas in the latter. This alteration in phenotype is attributable to GRP increasing focal adhesion kinase expression in GRP-R-expressing tumors. Consistent with GRP acting as a mitogen, GRP/GRP-R coexpressing tumors in wild-type animals also contain more proliferating cells than those occurring in GRP-R-/- mice. Yet tumors are similarly sized in animals of either genotype receiving azoxymethane for identical times, a finding attributable to the significantly higher number of apoptotic cells detected in GRP/GRP-R coexpressing cancers. Thus, these findings indicate that although GRP is a mitogen, aberrant expression does not result in increased tumor growth. Rather, the mitogenic properties of GRP are subordinate to it acting as a morphogen, where it and its receptor are critically involved in regulating colon cancer histological progression by promoting a well-differentiated phenotype.

Bombesin-like peptides stimulate somatostatin release from rat fundic D cells in primary culture.

In several species, bombesin-like neuropeptides stimulate somatostatin release in in vitro preparations of gastric mucosa. We sought to determine if this response is due to a direct effect on fundic D cells. Rat fundic mucosal cells were isolated by pronase E (1% D cells). D cells were separated by counterflow elutriation and subsequent density-gradient centrifugation (Nycodenz) (15% D cells) and grown in primary culture for 48 h (46% D cells). Cultured cells were double stained with affinity-purified rabbit-anti-gastrin-releasing peptide (GRP) receptor antibody and mouse monoclonal antibody to human somatostatin. After incubation with rhodamine-labeled anti-rabbit and fluorescein isothiocyanate-labeled anti-mouse antibodies, reactions were visualized by fluorescence microscopy. All cells positive for somatostatin had GRP receptors, whereas all non-D cells showed no expression in this G cell-free culture system. Somatostatin release from cultured cells was stimulated by sulfated cholecystokinin octapeptide (CCK-8; EC50 3 X 10(-10) M) and epinephrine (EC50 4 X 10(-8) M), which are established stimuli for canine fundic D cells. Bombesin (EC50 6 X 10(-11) M), its mammalian analog GRP-27, and neuromedin C (GRP-10) (EC50 1 X 10(-10) M, for both) were almost equally potent stimuli of somatostatin release, eliciting maximal response at 10(-9) M (400-550% above basal). Neuromedin B was less potent and effective (maximal response at 10(-8) M, 230% above basal). [D-Phe6]bombesin-(6-13)-OMe, a specific bombesin receptor antagonist, inhibited bombesin-stimulated somatostatin release in a competitive manner (IC50 9 X 10(-8) M). Potentiating interactions were observed between bombesin and dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) or epinephrine, but not between bombesin and CCK-8. We conclude that bombesin-like peptides directly stimulate somatostatin release by interacting with specific receptors on rat fundic D cells. Bombesin-like peptides appear to induce Ca(2+)-phospholipid-dependent signal-response transduction, as is indirectly suggested by potentiating interactions with DBcAMP or epinephrine.

The gastrin-releasing peptide receptor is rapidly phosphorylated by a kinase other than protein kinase C after exposure to agonist.

Several guanine nucleotide-binding protein-coupled receptors are known to be rapidly phosphorylated after agonist exposure. In this study we show that the gastrin-releasing peptide receptor (GRP-R) is rapidly phosphorylated in response to agonist exposure. When [32P]orthophosphate-labeled cells were exposed to bombesin, the receptor was maximally phosphorylated on serine and threonine residues within 1 min. Although addition of 12-O-tetradecanoylphorbol 13-acetate also resulted in phosphorylation of the GRP-R, elimination of protein kinase C activity using the inhibitor 7-hydroxystaurosporine did not prevent bombesin-induced GRP-R phosphorylation. We conclude that a kinase other than protein kinase C is principally responsible for the rapid, agonist-induced phosphorylation of the GRP-R.

The conserved NPXnY motif present in the gastrin-releasing peptide receptor is not a general sequestration sequence.

Exposure of the gastrin-releasing peptide (GRP) receptor to agonists causes a rapid desensitization of the receptor-stimulated mobilization of intracellular calcium. Homologous desensitization occurs by uncoupling the G-proteins from the receptor and by ligand induced internalization. The molecular determinants of desensitization of the GRP receptor are not well known. The importance of tyrosine 324 which is located in a highly conserved NPX2-3 Y motif of the GRP receptor was investigated. Kirsten murine sarcoma virus-transformed rat kidney (KNRK) cells were transfected with expression vectors encoding either the wild type or the mutant (tyrosine 324 to alanine 324) rat GRP receptor. The wild type and mutant GRP receptors were expressed at a high level in the KNRK cells, 2.0 x 10(6) and 0.5 x 10(6) receptors per cell, respectively. The wild type and mutant GRP receptors bound GRP with the same affinity (Kd = 6-7 nM). KNRK cells expressing the wild type or mutant GRP receptor had similar [Ca2+]i, dose response to GRP. KNRK cells expressing the GRP receptor rapidly internalized bound 125I-GRP at 37 degree C. Internalization was inhibited at 4 degrees C and by 0.45 m sucrose. The internalization of bound 125I-GRP by the mutant GRP receptor was identical to the wild type receptor. Fluorescent microscopy was used to directly observe the GRP receptor expressed on the surface of the KNRK cells and to visualize its ligand induced internalization. There was no difference in the pattern of internalization between the wild type and mutant GRP receptors expressed in KNRK cells. Therefore, the highly conserved tyrosine 324 does not have a role in GRP binding, receptor-G-protein interaction, or initial events of ligand induced receptor internalization. The NPXnY motif is not a general sequestration sequence for seven transmembrane G-protein linked receptors.