Early events elicited by bombesin and structurally related peptides in quiescent Swiss 3T3 cells. I. Activation of protein kinase C and inhibition of epidermal growth factor binding

How Gastrin-Releasing Peptide Opens the Spinal Gate for Itch

Spinal transmission of pruritoceptive (itch) signals requires transneuronal signaling by gastrin-releasing peptide (GRP) produced by a subpopulation of dorsal horn excitatory interneurons. These neurons also express the glutamatergic marker vGluT2, raising the question of why glutamate alone is insufficient for spinal itch relay. Using optogenetics together with slice electrophysiology and mouse behavior, we demonstrate that baseline synaptic coupling between GRP and GRP receptor (GRPR) neurons is too weak for suprathreshold excitation. Only when we mimicked the endogenous firing of GRP neurons and stimulated them repetitively to fire bursts of action potentials did GRPR neurons depolarize progressively and become excitable by GRP neurons. GRPR but not glutamate receptor antagonism prevented this action. Provoking itch-like behavior by optogenetic activation of spinal GRP neurons required similar stimulation paradigms. These results establish a spinal gating mechanism for itch that requires sustained repetitive activity of presynaptic GRP neurons and postsynaptic GRP signaling to drive GRPR neuron output.

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Spinal itch relay requires effective communication from GRP to GRP receptor neurons

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Single action potentials in GRP neurons fail to release sufficient GRP

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Only burst firing releases enough GRP to prime GRP receptor neurons for activation

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GRP acts as a volume transmitter probably explaining why itch is hard to localize

RC-3095, a gastrin-releasing peptide receptor antagonist, synergizes with gemcitabine to inhibit the growth of human pancreatic cancer CFPAC-1 in vitro and in vivo

OBJECTIVES

Pancreatic cancer remains a lethal disease. In this study, we investigated the efficacy of a combination of gastrin-releasing peptide receptor antagonist RC-3095 and gemcitabine on pancreatic cancer CFPAC-1.

METHODS

The antiproliferation effects of RC-3095, gemcitabine, or the combination on pancreatic cancer were monitored in vitro. Nude mice bearing xenografts of CFPAC-1 cell received injections of the vehicle (control), RC-3095 (20 μg, subcutaneously, daily), gemcitabine (15 mg/kg, intraperitoneally, every 3 days), or the combination of RC-3095 and gemcitabine for 4 weeks. The histological changes and protein expression were tested using immunohistochemistry and Western blotting.

RESULTS

Treatment with the combination in culture exhibited a powerful inhibition effect on CFPAC-1 cell proliferation. In xenograft mice model, RC-3095 or gemcitabine significantly reduced the volume and weight of tumors after 4 weeks of treatment, as compared with controls. The combination more potently inhibited the tumor growth than either agent used individually. Immunohistochemistry and Western blotting showed gastrin-releasing peptide receptor/bombesin receptor subtype-3 positive cells and protein expression in tumors decreased by treatment with RC-3095 or gemcitabine alone or greater in combination.

CONCLUSIONS

Our data suggested that the combination could be considered for the possible new approaches for treatment of pancreatic cancers.

Mitogenic signaling pathways induced by G protein-coupled receptors

G protein-coupled receptor (GPCR) agonists, including neurotransmitters, hormones, chemokines, and bioactive lipids, act as potent cellular growth factors and have been implicated in a variety of normal and abnormal processes, including development, inflammation, and malignant transformation. Typically, the binding of an agonistic ligand to its cognate GPCR triggers the activation of multiple signal transduction pathways that act in a synergistic and combinatorial fashion to relay the mitogenic signal to the nucleus and promote cell proliferation. A rapid increase in the activity of phospholipases C, D, and A2 leading to the synthesis of lipid-derived second messengers, Ca2+ fluxes and subsequent activation of protein phosphorylation cascades, including PKC/PKD, Raf/MEK/ERK, and Akt/mTOR/p70S6K is an important early response to mitogenic GPCR agonists. The EGF receptor (EGFR) tyrosine kinase has emerged as a transducer in the signaling by GPCRs, a process termed transactivation. GPCR signal transduction also induces striking morphological changes and rapid tyrosine phosphorylation of multiple cellular proteins, including the non-receptor tyrosine kinases Src, focal adhesion kinase (FAK), and the adaptor proteins CAS and paxillin. The pathways stimulated by GPCRs are extensively interconnected by synergistic and antagonistic crosstalks that play a critical role in signal transmission, integration, and dissemination. The purpose of this article is to review recent advances in defining the pathways that play a role in transducing mitogenic responses induced by GPCR agonists.

The combination of antagonists of LHRH with antagonists of GHRH improves inhibition of androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancers

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) could extend the duration of response of androgen sensitive prostate cancers to androgen deprivation.

METHODS

We investigated the effect of new GHRH antagonists MZ-J-7-118 and MZ-J-7-138 and luteinizing hormone-releasing hormone (LHRH) antagonist Cetrorelix or castration on androgen sensitive MDA-PCa-2b and LuCaP-35 prostate cancer models xenografted into nude mice. Animals bearing androgen-independent LuCaP-35V prostatic cancer model were also treated with MZ-J-7-118.

RESULTS

Receptors for LHRH and GHRH were present in MDA-PCA-2b, LuCaP-35, and LuCaP-35V tumors. GHRH antagonists increased the inhibitory effect of surgical castration and LHRH antagonists on androgen sensitive MDA-PCa-2b and LuCaP-35 tumors. The time to relapse of androgen-dependent LuCaP-35 tumors was extended by GHRH antagonists. Growth of androgen-independent LuCaP-35V xenografts was also significantly inhibited by MZ-J-7-118. In MDA-PCa-2b tumors treatment with MZ-J-7-118 caused a significant decrease of VEGF and Cetrorelix or its combination with MZ-J-7-118 reduced EGF. The B(max) of EGF receptors was significantly reduced by Cetrorelix, MZ-J-7-118 and their combination.

CONCLUSIONS

Our findings suggest that the use of a combination of antagonists of GHRH and LHRH could improve the therapy for androgen sensitive prostate cancer. Antagonists of GHRH could be also considered for treatment of androgen-independent prostate cancers.

Protein kinase Calpha mediates feedback inhibition of EGF receptor transactivation induced by Gq-coupled receptor agonists

While a great deal of attention has been focused on G-protein-coupled receptor (GPCR)-induced epidermal growth factor receptor (EGFR) transactivation, it has been known for many years that the tyrosine kinase activity of the EGFR is inhibited in cells treated with tumor-promoting phorbol esters, a process termed EGFR transmodulation. Because many GPCR agonists that elicit EGFR transactivation also stimulate the Gq/phospholipase C (PLC)/protein kinase C (PKC) pathway, we hypothesized that PKC-mediated inhibition of EGFR transactivation operates physiologically as a feedback loop that regulates the intensity and/or duration of GPCR-elicited EGFR transactivation. In support of this hypothesis, we found that treatment of intestinal epithelial IEC-18 cells with the PKC inhibitors GF 109203X or Ro 31-8220 or chronic exposure of these cells to phorbol-12,13-dibutyrate (PDB) to downregulate PKCs, markedly enhanced the increase in EGFR tyrosine phosphorylation induced by angiotensin II or vasopressin in these cells. Similarly, PKC inhibition enhanced EGFR transactivation in human colonic epithelial T84 cells stimulated with carbachol, as well as in bombesin-stimulated Rat-1 fibroblasts stably transfected with the bombesin receptor. Furthermore, cell treatment with inhibitors with greater specificity towards PKCalpha, including Gö6976, Ro 31-7549 or Ro 32-0432, also increased GPCR-induced EGFR transactivation in IEC-18, T84 and Rat-1 cells. Transfection of siRNAs targeting PKCalpha also enhanced bombesin-induced EGFR tyrosine phosphorylation in Rat-1 cells. Thus, multiple lines of evidence support the hypothesis that conventional PKC isoforms, especially PKCalpha, mediate feedback inhibition of GPCR-induced EGFR transactivation.

G protein-coupled receptor activation rapidly stimulates focal adhesion kinase phosphorylation at Ser-843. Mediation by Ca2+, calmodulin, and Ca2+/calmodulin-dependent kinase II

A rapid increase in the tyrosine phosphorylation of focal adhesion kinase (FAK) has been extensively documented in cells stimulated by multiple signaling molecules, but little is known about the regulation of FAK phosphorylation at serine residues. Stimulation of Swiss 3T3 cells with the G protein-coupled receptor agonists bombesin, vasopressin, or bradykinin induced an extremely rapid (within 5 s) increase in FAK phosphorylation at Ser-843. The phosphorylation of this residue preceded FAK phosphorylation at Tyr-397, the major autophosphorylation site, and FAK phosphorylation at Ser-910. Treatment of intact cells with ionomycin stimulated a rapid increase in FAK phosphorylation at Ser-843, indicating that an increase in intracellular Ca2+ concentration ([Ca2+]i) is a potential pathway leading to FAK-Ser-843 phosphorylation. Indeed, treatment with agents that prevent an agonist-induced increase in [Ca2+]i (e.g. thapsigargin or BAPTA (1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)), interfere with calmodulin function (e.g. trifluoperazine, W13, and W7), or block Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation (KN93) or expression (small interfering RNA) abrogated the rapid FAK phosphorylation at Ser-843 induced by bombesin, bradykinin, or vasopressin. Furthermore, activated CaMKII directly phosphorylated the recombinant COOH-terminal region of FAK at a residue equivalent to Ser-843. Thus, our results demonstrate that G protein-coupled receptor activation induces rapid FAK phosphorylation at Ser-843 through Ca2+, calmodulin, and CaMKII.

Antagonists of bombesin/gastrin-releasing peptide decrease the expression of angiogenic and anti-apoptotic factors in human glioblastoma

We have investigated the antitumor effects and the mechanism of action of antagonists of bombesin/gastrin-releasing peptide (GRP), RC-3940-II and RC-3940-Et, on the growth of U-118MG human malignant glioma xenografted into nude mice. Tumors volume was measured weekly, and after 6 weeks of treatment with GRP antagonists the tumors were analyzed by Western blot assays for the expression of vascular endothelial growth factor (VEGF), protein kinase C (PKC)-alpha, the anti-apoptotic protein Bcl-2 and the pro-apoptotic protein Bax. A radioreceptor assay was used to characterize the receptors for bombesin/GRP. Specific high-affinity receptors for bombesin were found in U-118MG tumors, and their growth was reduced by 52.5% by RC-3940-II and 72.6% by RC-3940-Et (both p<0.01). The tumor doubling time was prolonged by 4.6 and 12 days after treatment with RC-3940-II and RC-3940-Et, respectively, compared to controls (p<0.05). Both antagonists caused a significant (p<0.05) decrease of about 28% in the levels of VEGF protein and a reduction of approximately 35% in the expression of PKCalpha. The relative ratio of Bcl-2:Bax was also diminished by around 70% by both analogs, indicating a net apoptotic gain and the efficacy of treatment. Our results suggest that bombesin/GRP antagonists, RC-3940-II and RC-3940-Et, could be of value for the treatment of human glioblastomas.

Protein kinase D potentiates DNA synthesis induced by Gq-coupled receptors by increasing the duration of ERK signaling in swiss 3T3 cells

Protein kinase D (PKD) potentiates cellular DNA synthesis in response to G protein-coupled receptor (GPCR) agonists but the mechanism(s) involved has not been elucidated. Here, we examined whether PKD overexpression in Swiss 3T3 cells regulates the activation/inactivation kinetics of the extracellular-regulated protein kinase (ERK) in response to the mitogenic GPCR agonists bombesin and vasopressin. Addition of bombesin or vasopressin to Swiss 3T3 cells overexpressing PKD induced a striking increase in the duration of MEK/ERK/RSK activation as compared with cultures of either control Swiss 3T3 cells or Swiss 3T3 cells expressing a kinase-inactive PKD mutant. In contrast, the duration of ERK activation in response to epidermal growth factor, which acts via protein kinase C/PKD-independent pathways, was not increased. Furthermore, bombesin or vasopressin promoted a striking increase in phosphorylation (at Ser-374) and accumulation of c-Fos (the c-fos proto-oncogene product) in Swiss 3T3 cells overexpressing wild-type (but not kinase-inactive) PKD. Inhibition of the sustained phase of ERK/RSK activation abrogated the increase in c-Fos accumulation and DNA synthesis induced by bombesin or vasopressin in PKD-overexpressing cells. Our results demonstrate that PKD selectively potentiates mitogenesis induced by bombesin or vasopressin in Swiss 3T3 cells by increasing the duration of MEK/ERK/RSK signaling.

Transcriptional down-regulation of MARCKS gene expression in immortalized hippocampal cells by lithium

The gene (Macs) for the mouse myristoylated alanine-rich C kinase substrate (MARCKS) encodes a prominent substrate for protein kinase C that has been implicated in processes requiring signal dependent changes in actin-membrane plasticity and cytoskeletal restructuring. We have previously demonstrated that MARCKS protein is significantly down-regulated in rat hippocampus and in an immortalized hippocampal cell line (HN33.dw) following long-term exposure to lithium at clinically relevant concentrations (1 mM). Our current studies have examined transcriptional and post-transcriptional events that may underlie the lithium-induced down-regulation of MARCKS protein in the cultured hippocampal cell model system. MARCKS mRNA and protein expression were found to be concomitantly down-regulated following exposure of the HN33.dw cells to chronic lithium. Whereas the stability of MARCKS mRNA remained unchanged in the presence of lithium, nuclear run-off assay indicated that the transcription of nascent MARCKS mRNA was significantly reduced (approximately 50%) in the cells that had been treated with lithium for 7 days. Transient transfection of HN33.dw cells with a mouse cloned Macs promoter (993-bp) showed that the Macs promoter activity was attenuated to the same extent after chronic (7-10 days), but not subacute (24 h), lithium exposure. The inhibition of the Macs promoter was found to be dependent upon the presence of a 280-bp promoter region between -993-bp and -713-bp relative to the translation start site, suggesting that this region is a potential lithium-responsive region of Macs promoter (LRR). Mutant promoter lacking the LRR not only did not respond to chronic lithium exposure but also had significantly reduced promoter activity, suggesting that chronic lithium exposure represses the transcriptional activity of activator(s) bound to the promoter. Taken together, our data indicate that transcriptional inhibition of the Macs gene underlies the lithium-induced down-regulation of MARCKS expression in the immortalized hippocampal cells.

Bombesin and substance P analogues differentially regulate G-protein coupling to the bombesin receptor. Direct evidence for biased agonism

Substance P analogues including [d-Arg1,d-Phe5,d-Trp7,9,Leu11]substance P (SpD) act as "broad spectrum neuropeptide antagonists" and are potential anticancer agents that inhibit the growth of small cell lung cancer cells in vitro and in vivo. However, their mechanism of action is controversial and not fully understood. Although these compounds block bombesin-induced mitogenesis and signal transduction, they also have agonist activity. The mechanism underlying this agonist activity was examined. SpD binds to the ligand-binding site of the bombesin/gastrin-releasing peptide receptor and blocks the bombesin-stimulated increase in [Ca2+]i within the same concentration range that causes sustained activation of c-Jun N-terminal kinase and extracellular signal-regulated protein kinase (ERK). The activation of c-Jun N-terminal kinase by SpD and bombesin is blocked by dominant negative inhibition of G(alpha12). The ERK activation by SpD is pertussis toxin-sensitive in contrast to ERK activation by bombesin, which is pertussis toxin-insensitive but dependent on epidermal growth factor receptor phosphorylation. SpD does not simply act as a partial agonist but differentially modulates the activation of the G-proteins G(alpha12), G(i), and G(q) compared with bombesin. This unique ability allows the bombesin receptor to couple to G(i) and at the same time block receptor activation of G(q). Our results provide direct evidence that SpD is acting as a "biased agonist" and that this has physiological relevance in small cell lung cancer cells. This validation of the concept of biased agonism has important implications in the development of novel pharmacological agents to dissect receptor-mediated signal transduction and of highly selective drugs to treat human disease.

Neuromedin B

Neuromedin B (NMB) is one of the bombesin (BN)-related peptides in mammals. It was originally purified from pig spinal cords, and it has been shown to be present in central nervous system as well as in gastrointestinal tract. BN and its related peptides have various physiological effects. These include regulation of exocrine and endocrine secretions, smooth muscle contraction, feeding, blood pressure, blood glucose, body temperature and cell growth. NMB exerts its effect by binding to the cell surface receptor. A high affinity receptor, NMB receptor (NMB-R) has been identified. This is a G-protein coupled receptor with seven membrane-spanning regions. Upon agonist binding, several intracellular signaling cascades including phospholipase activation, calcium mobilization and protein kinase C (PKC) activation lead to expression of several genes, DNA synthesis or cellular effects such as secretion. Existence of NMB-R has been demonstrated in several brain regions, notably in olfactory and thalamic regions, and in gastrointestinal tracts. Recent analysis using NMB-R-deficient mice, generated by gene-targeting technique, enables to distinguish functional properties of NMB-R from GRP-R. In this review, molecular characterization, anatomical distribution and pharmacological properties of NMB and NMB-R will be presented. Moreover, physiological roles of NMB and its receptor demonstrated by the analysis of NMB-R-deficient mice will be reported. Comparison with GRP/GRP-R system will provide important information about BN-like peptide systems in mammals.

Involvement of calmodulin and protein kinase C in cholecystokinin release by bombesin from STC-1 cells

The mouse intestinal neuroendocrine tumor cell line STC-1 secretes cholecystokinin (CCK) and other hormones. We investigated the role of Ca2+, calmodulin (CaM), and protein kinase C (PKC) in the regulation of CCK release from STC-1 cells. Phorbol 12-myristate 13-acetate (TPA) significantly stimulated CCK release. Staurosporine significantly inhibited CCK release from STC-1 cells stimulated by TPA in a dose-dependent manner. The absence of extracellular calcium completely inhibited CCK release from TPA-stimulated STC-1 cells. Neurotensin did not stimulate CCK release from these cells. W-7, a CaM antagonist, reduced CCK release from STC-1 cells stimulated by bombesin in a dose-dependent manner. These findings suggest that CaM and PKC play an important role in the regulation of CCK release from STC-1 cells stimulated by bombesin.

[Arg6,D-Trp7,9,NmePhe8]-substance P (6-11) activates JNK and induces apoptosis in small cell lung cancer cells via an oxidant-dependent mechanism

[Arg6,D-Trp7,9,NmePhe8]-substance P (6-11) (antagonist G) is a novel class of anti-cancer agent that inhibits small-cell lung cancer (SCLC) cell growth in vitro and in vivo and is entering phase II clinical investigation for the treatment of SCLC. Although antagonist G blocks SCLC cell growth (IC50 = 24.5 +/- 1.5 and 38.5 +/- 1.5 microM for the H69 and H510 cell lines respectively), its exact mechanism of action is unclear. This study shows that antagonist G stimulates apoptosis as assessed by morphology (EC50 = 5.9 +/- 0.1 and 15.2 +/- 2.7 microM for the H69 and H510 cell lines respectively) and stimulates c-jun-N-terminal kinase (JNK) activity in SCLC cells (EC50 = 3.2 +/- 0.1 and 15.2 +/- 2.7 microM). This activity is neuropeptide-independent, but dependent on the generation of reactive oxygen species (ROS) and is inhibited by the free radical scavenger n-acetyl cysteine. Furthermore, antagonist G itself induces inflammation (59% increase in oedema volume compared to control) and potentiates (by 35-40%) bradykinin-induced oedema formation in vivo. In view of these results we show that, as well as acting as a 'broad-spectrum' neuropeptide antagonist, antagonist G stimulates basal G-protein activity in SCLC cell membranes (81 +/- 12% stimulation at 10 microM), thereby displaying a unique ability to stimulate certain signal transduction pathways by activating G-proteins. This novel activity may be instrumental for full anti-cancer activity in SCLC cells and may also account for antagonist G activity in non-neuropeptide-dependent cancers.

A single in vivo administration of bombesin antagonist RC-3095 reduces the levels and mRNA expression of epidermal growth factor receptors in MXT mouse mammary cancers

Epidermal growth factor (EGF) and its receptors (EGFR) play important roles in tumorigenesis. In various experimental cancers, treatment with antagonists of bombesin/gastrin-releasing peptide (BN/GRP) produces a reduction in EGFRs, concomitant to inhibition of tumor growth. To investigate the mechanisms involved, we monitored concentrations of BN/GRP antagonist RC-3095 in serum of mice, rats, and hamsters given a single subcutaneous or intravenous injection of this analog. In parallel studies, we measured levels and mRNA expression of EGFRs in estrogen-dependent and independent MXT mouse mammary cancers, following a single subcutaneous administration of RC-3095 to tumor-bearing mice. Peak values of RC-3095 in serum were detected 2 min after intravenous or 15 min after subcutaneous injection. The levels of RC-3095 declined rapidly and became undetectable after 3-5 hr. In the estrogen-dependent MXT tumors, the concentration of EGF receptors was reduced by about 60% 6 hr following injection and returned to original level after 24 hr. Levels of mRNA for EGFR fell parallel with the receptor number and were nearly normal after 24 hr. In the hormone-independent MXT cancers, the number of EGFRs decreased progressively, becoming undetectable 6 hr after injection of RC-3095, and returned to normal values at 24 hr, but EGFR mRNA levels remained lower for 48 hr. Thus, in spite of rapid elimination from serum, BN/GRP antagonist RC-3095 can induce a prolonged decrease in levels and mRNA expression of EGFRs. These findings may explain how single daily injections of BN/GRP antagonists can maintain tumor growth inhibition.

Bombesin, vasopressin, endothelin, bradykinin, and platelet-derived growth factor rapidly activate protein kinase D through a protein kinase C-dependent signal transduction pathway

Protein kinase D (PKD) is a serine/threonine protein kinase that is activated by phorbol esters via protein kinase C in intact cells. To assess the physiological significance of this putative pathway, we examined the regulation of PKD in living cells by mitogenic regulatory peptides and by platelet-derived growth factors (PDGF). Our results demonstrate that bombesin rapidly induces PKD activation in Swiss 3T3 cells, as shown by autophosphorylation and syntide-2 phosphorylation assays. Maximum PKD activation (14-fold above base-line levels) was obtained 90 s after bombesin stimulation. Bombesin also induced PKD activation in Rat-1 cells stably transfected with the bombesin/gastrin releasing peptide (GRP) receptor and in COS-7 cells transiently co-transfected with PKD and bombesin/GRP receptor expression constructs. No inducible kinase activity was demonstrated when COS-7 cells were transfected with a kinase-deficient PKD mutant. Bombesin-mediated PKD activation was prevented by treatment of Swiss 3T3 cells with the protein kinase C inhibitors GF 1092030X and Ro 31-8220. In contrast, these compounds did not inhibit PKD activity when added directly in vitro. Vasopressin, endothelin, and bradykinin also activated PKD in Swiss 3T3 cells through a PKC-dependent pathway. Platelet-derived growth factor-stimulated PKD activation in Swiss 3T3 cells and in porcine aortic endothelial cells stably transfected with PDGF-beta receptors. Treatment with GF 1092030X or Ro 31-8220 inhibited PKD activation induced by PDGF. Thus, our results indicate that PKD is activated by multiple signaling peptides through a protein kinase C-dependent signal transduction pathway in a variety of cell types.

Reduction in receptors for bombesin and epidermal growth factor in xenografts of human small-cell lung cancer after treatment with bombesin antagonist RC-3095

Antagonists of bombesin/gastrin-releasing peptide (BN/GRP) have been developed to inhibit the stimulatory effects of BN/GRP on the mitogenesis of tumor cells such as human small-cell lung carcinoma (SCLC). The mode of action of these antagonists is not completely understood. In this study, we evaluated the effect of BN/GRP antagonist RC-3095 on receptors for BN/GRP and epidermal growth factor (EGF) in H-128 human SCLC line xenografted into nude mice. Treatment with RC-3095, administered s.c. at a dose of 20 microg/day per animal for 4 weeks caused a 70% reduction in tumor volume and weight. Membrane receptors for BN/GRP and EGF were characterized in untreated and treated animals. In the control group, [125I-Tyr4]BN was bound to a single class of specific, high affinity binding sites with a dissociation constant (Kd) = 6.55 +/- 0.93 nM and maximal binding capacity (Bmax) = 512.8 +/- 34.8 fmol/mg membrane protein. Therapy with RC-3095 decreased the concentration of BN/GRP receptors on H-128 SCLC tumor membranes. Specific, high affinity binding sites for EGF with Kd = 1.78 +/- 0.26 nM and Bmax = 216.8 +/- 19.6 fmol/mg membrane protein were also found on the untreated H-128 SCLC tumors. Treatment with RC-3095 significantly decreased Bmax of receptors for EGF. Our results indicate that the suppression of growth of H-128 SCLC by BN antagonist RC-3095 is accompanied by a decrease in the number of receptors for both BN/GRP and EGF. These observations are in agreement with the results obtained in other experimental cancers. The findings on antagonist RC-3095 reinforce the view that both BN/GRP and EGF receptors participate in a cascade of events involved in the growth of SCLC and other cancers. Although the complete mechanisms of action of antagonist RC-3095 remain to be elucidated, the antitumor effect could be the result of the fall in the EGF receptor number, which might lead to a decrease in EGF receptor autophosphorylation.

[D-Arg1,D-Trp5,7,9,Leu11]Substance P coordinately and reversibly inhibits bombesin- and vasopressin-induced signal transduction pathways in Swiss 3T3 cells

The novel substance P (SP) analogue, [D-Arg1,D-Trp5,7,9,Leu11]SP like [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP inhibited DNA synthesis induced by bombesin, vasopressin, and bradykinin, but did not interfere with the mitogenic response induced by other growth factors or pharmacological agents in Swiss 3T3 cells. [D-Arg1,D-Trp5, 7,9,Leu11]SP reversibly inhibited bombesin-induced DNA synthesis, causing a 6-fold greater rightward shift in the bombesin dose response than [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP at identical concentrations (10 microM). We found that the new, more potent, SP analogue coordinately and reversibly inhibited bombesin-induced Ca2+ mobilization and protein kinase C (PKC) and mitogen-activated protein (MAP) kinase activation. The dose-response curves for bombesin-induced Ca2+ mobilization and MAP kinase activation were similarly displaced (51- and 40-fold, respectively) by [D-Arg1, D-Trp5,7,9,Leu11]SP. In addition, [D-Arg1,D-Trp5,7,9,Leu11]SP reversibly inhibited bombesin-induced tyrosine phosphorylation of Mr 110,000-130,000 and 70,000-80,000 bands as well as p125 focal adhesion kinase. [D-Arg1,D-Trp5,7,9,Leu11]SP also reversibly and coordinately inhibited vasopressin-induced Ca2+ mobilization, PKC stimulation, MAP kinase activation, tyrosine phosphorylation, and DNA synthesis in Swiss 3T3 cells. Surprisingly, deletion of the terminal Leu of [D-Arg1,D-Phe5,D-Trp7,9,Leu11]SP to yield [D-Arg1, D-Phe5,D-Trp7,9]SP1-10 resulted in a selective loss of inhibitory activity of this analogue against bombesin- but not vasopressin-stimulated DNA synthesis, Ca2+ mobilization, and MAP kinase activation. Collectively, these results suggest that SP analogues act at the receptor level to coordinately and reversibly antagonize bombesin- or vasopressin-induced signal transduction in Swiss 3T3 cells.

Bombesin, bradykinin, vasopressin, and phorbol esters rapidly and transiently activate Src family tyrosine kinases in Swiss 3T3 cells. Dissociation from tyrosine phosphorylation of p125 focal adhesion kinase

Treatment of quiescent Swiss 3T3 cells with bombesin induces a rapid (</=40 s) and transient increase in the kinase activity of the Src family of tyrosine kinases, as determined by autophosphorylation in immune complex kinase assays (4.6 +/- 0.2-fold stimulation, n = 44) and phosphorylation of exogenous substrates. Phorbol 12, 13-dibutyrate increased the activity of Src family kinases with similar kinetics but was less effective than bombesin. However, Src family kinase activation by bombesin is not dependent either on protein kinase C or Ca2+. Bombesin stimulation of Src family kinase activity could also be dissociated from p125 focal adhesion kinase tyrosine phosphorylation. Neither treatment with cytochalasin D nor placement of the cells in suspension prevented the stimulation of Src family kinase activity induced by bombesin, but both abolished bombesin-induced tyrosine phosphorylation of p125 focal adhesion kinase. The stimulation of the Src family kinase activity by bombesin was completely prevented by treatment with vanadate, a potent inhibitor of protein-tyrosine phosphatases. Bradykinin and vasopressin also stimulated Src family kinase activity transiently, and this stimulation was also inhibited by vanadate. Our results dissect two separate pathways that lead to protein tyrosine phosphorylation in neuropeptide-stimulated Swiss 3T3 cells.

Pulmonary Neuroendocrine Cells and Lung Development

Pulmonary neuroendocrine cells produce bioactive peptides such as gastrin-releasing peptide (GRP) at high levels in developing fetal lung. The role of GRP and other peptides in promoting branching morphogenesis, cell proliferation, and cell differentiation during lung organogenesis is reviewed. Possible roles for bioactive peptides derived from these cells in the pathophysiology of perinatal lung disorders are discussed.

Bombesin receptor structure and expression in human lung carcinoma cell lines

Mammalian bombesin-like peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) are regulatory neuropeptides involved in numerous physiologic processes, and have been implicated as autocrine and/or paracrine growth factors in human lung carcinoma. Three structurally and pharmacologically distinct bombesin receptor subtypes have been isolated and characterized: the gastrin releasing peptide receptor (GRP-R), the neuromedin B receptor (NMB-R), and bombesin receptor subtype-3 (BRS-3). The three receptors are structurally related, sharing about 50% amino acid identity. They are members of the G-protein coupled receptor superfamily with a seven predicted transmembrane segment topology characteristic of receptors in this family. The signal transduction pathway for GRP-R and NMB-R involves coupling to a pertussis-toxin insensitive G-protein, activation of phospholipase C (PLC), generation of inositol trisphosphate (IP3), release of intracellular calcium, and activation of protein kinase C. While all three bombesin receptors are activated by bombesin agonists, GRP-R, NMB-R, and BRS-3 have very different affinities for the mammalian bombesin-like peptides GRP and NMB, as well as bombesin receptor antagonists. The three bombesin receptor subtypes are expressed in an overlapping subset of human lung carcinoma cell lines. Any therapeutic strategy based on modulation of bombesin growth responses in human lung carcinoma would be well served to take into account the pharmacologic heterogeneity of the relevant receptors.

GRP receptors are present in non small cell lung cancer cells

Previously, GRP receptors were characterized in small cell lung cancer cells and here non-small cell lung cancer (NSCLC) cells were investigated: (125I-Tyr4) bombesin (BN) or 125I-GRP bound with high affinity to NCI-H720 (lung carcinoid) and NCI-H1299 (large cell carcinoma) cells. Binding was specific, time dependent, and saturable. Specific (125I-Tyr4)BN binding to NCI-H1299 cells was inhibited with high affinity by GRP, BN, GRP14-27, (D-Phe6)BN6-13methyl ester, moderate affinity by NMB, and low affinity by GRP1-16. BN (10 nM) transiently elevated cytosolic calcium in a dose dependent manner. BN caused translocation of protein kinase C from the cytosol to the membrane and the translocation caused by BN was reversed by (D-Phe6)BN6-13methylester. BN stimulated arachidonic acid release and the increase caused by BN was reversed by (D-Phe6)BN6-13methylester. Using a clonogenic assay, BN stimulated the growth of NCI-H720 cells, and the number of colonies was reduced using (D-Phe6)BN6-13methylester. These data suggest that GRP receptors that are present in lung carcinoid and NSCLC cells may regulate proliferation.

Cloning of a receptor for amphibian [Phe13]bombesin distinct from the receptor for gastrin-releasing peptide: identification of a fourth bombesin receptor subtype (BB4)

Bombesin is a tetradecapeptide originally isolated from frog skin and demonstrated to have a wide range of actions in mammals. Based on structural homology and similar biological activities, gastrin-releasing peptide (GRP) has been considered the mammalian equivalent of bombesin. We previously reported that frogs have both GRP and bombesin, which therefore are distinct peptides. We now report the cloning of a bombesin receptor subtype (BB4) that has higher affinity for bombesin than GRP. PCR was used to amplify cDNAs related to the known bombesin receptors from frog brain. Sequence analysis of the amplified cDNAs revealed 3 classes of receptor subtypes. Based on amino acid homology, two classes were clearly the amphibian homologs of the GRP and neuromedin B receptors. The third class was unusual and a full-length clone was isolated from a Bombina orientalis brain cDNA library. Expression of the receptor in Xenopus oocytes demonstrated that the receptor responded to picomolar concentrations of [Phe13]-bombesin, the form of bombesin most prevalent in frog brain. The relative rank potency of bombesin-like peptides for this receptor was [Phe13]bombesin > [Leu13]bombesin > GRP > neuromedin B. In contrast, the rank potency for the GRP receptor is GRP > [Leu13]bombesin > [Phe13]bombesin > neuromedin B. Transient expression in CHOP cells gave a Ki for [Phe13]bombesin of 0.2 nM versus a Ki of 2.1 nM for GRP. Distribution analysis showed that this receptor was expressed only in brain, consistent with the distribution of [Phe13]-bombesin. Thus, based on distribution and affinity, this bombesin receptor is the receptor for [Phe13]bombesin. Phylogenetic analysis suggests that this receptor separated prior to separation of the GRP and neuromedin B receptors; thus, BB4 receptors and their cognate ligands may also exist in mammals.

Differential modulation of bombesin-stimulated phospholipase C beta and mitogen-activated protein kinase activity by [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P

Mitogenic stimulation of Swiss 3T3 fibroblasts with bombesin results in receptor-mediated activation of a complex array of effectors, including phospholipase C beta and mitogen-activated protein (MAP) kinase. Incubation of Swiss 3T3 fibroblasts with the 11-amino acid [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide inhibited bombesin-stimulated cell proliferation and phospholipase C beta activation even at high bombesin concentrations. The peptide did not inhibit the activation of phospholipase C beta by a GTPase-deficient form of the Gq-like protein, G16, indicating that the peptide does not inhibit phospholipase C beta and is acting at a point upstream of the activated form of the G protein alpha subunit. The peptide inhibited MAP kinase activation at low bombesin concentrations, but unlike phospholipase C beta, this inhibition could be overcome with 30 nM bombesin. In control Swiss 3T3 cells, bombesin did not measurably activate Ras or Raf-1 above basal levels. Following incubation of the cells with the [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide, 50 nM bombesin activated Raf-1 4-6-fold over basal levels. Platelet-derived growth factor-stimulated activities of PLC, Ras, Raf-1, and MAP kinase were unaltered after incubation of Swiss 3T3 cells with the [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide, as was platelet-derived growth factor-stimulated growth of the Swiss 3T3 cells. Thus, the peptide behaves as an antagonist that differentially inhibited phospholipase C beta and MAP kinase signal transduction pathways. The growth arrest observed with the peptide indicates that the bombesin-stimulated activation of MAP kinase is not sufficient to support mitogenesis in Swiss 3T3 cells.

Substance P-related antagonists inhibit vasopressin and bombesin but not 5'-3-O-(thio)triphosphate-stimulated inositol phosphate production in Swiss 3T3 cells

The substance P (SP) analogues [DArg1, DPhe5, DTrp7,9, Leu11] SP (AntD) and [Arg6, DTrp7,9, MePhe8] SP (6-11) (AntG) inhibit the action of many different neuropeptides including SP. These analogues might be useful in the treatment of small cell lung cancer but their mechanism of action is unclear. Here, we analyzed the effect of AntD and AntG on neuropeptide vs. guanosine 5'-3-O-(thio) triphosphate (GTP gamma S)-stimulated inositol phosphate generation in permeabilized Swiss 3T3 cells. AntD inhibited vasopressin and bombesin stimulated inositol phosphate formation (IC50 of 0.75 microM and 2 microM, respectively). Similarly, AntG inhibited vasopressin-stimulated inositol phosphate generation with an IC50 of 1 microM. Strikingly, neither AntD up to 10 microM nor AntG up to 20 microM was able to inhibit GTP gamma S-stimulated inositol phosphate generation. Dose-response curves of neuropeptide-induced inositol phosphate generation were dramatically displaced to the right by either 10 microM AntD or 20 microM AntG. However, neither antagonist affected the dose response of GTP gamma S-stimulated inositol phosphate generation. Furthermore, 20 microM AntD had no effect on AIF-4-induced inositol phosphates in COS-1 cells transfected with G alpha q. AntD inhibited [3H]vasopressin binding competitively in intact Swiss 3T3 cells and both AntD and AntG inhibited [3H]vasopressin binding in Swiss 3T3 and rat liver membranes. Scatchard analysis revealed that AntD inhibited vasopressin binding by reducing receptor affinity without affecting receptor number in both intact and membrane preparations of Swiss 3T3 cells. The results strongly suggest that SP analogues AntD and AntG block the action of the Ca2+ mobilizing neuropeptides at the receptor level, rather than inhibiting G protein-stimulated inositol phosphate production.

Calcium, calmodulin and cell cycle progression

Proliferation of mammalian cells both in vivo and in vitro is dependent upon physiological concentrations of extracellular Ca2+. Growth factor stimulation of quiescent cells at the G0/G1 border usually results in a rapid mobilization of Ca2+ from both intra- and extracellular pools. However, Ca2+ influx is also required for later phases of cell cycle transition, especially in the late G1 phase for initiation of DNA synthesis. Available evidence indicates that calmodulin plays the major and essential roles in the Ca(2+)-dependent regulation of cell proliferation. Ca2+ and calmodulin act at multiple points in the cell cycle, including the initiation of the S phase and both initiation and completion of the M phase. Ca2+ and calmodulin stimulate the expression of genes involved in the cell cycle progression, leading to activation of cyclin-dependent kinases p33cdk2 and p34cdc2. Ca2+ and calmodulin are also involved in activation of enzymes participating in nucleotide metabolism and DNA replication, as well as nuclear envelope breakdown and cytokinesis. Ca2+/calmodulin-dependent protein kinase II and protein phosphatase calcineurin are both involved in the Ca2+ and calmodulin-mediated signalling of growth regulation. As compared to normal cells, growth of transformed cells is independent of extracellular Ca2+ and much less sensitive to calmodulin antagonists, suggesting the existence of derangements in the Ca2+ and calmodulin-mediated growth regulation mechanisms.

Effects of vinorelbine on epidermal growth factor-receptor binding of human breast cancer cell lines in vitro

Epidermal Growth Factor (EGF) is a mitogenic peptide that binds to surface membrane receptors (EGFR) of breast cancer cells. After binding, secondary transmitter molecules are activated by tyrosine phosphorylation of the intracellular receptor domaine. The activity of the EGF/EGFR system can be modulated by a variety of chemically unrelated compounds including cytostatic agents. The purpose of our present study was to determine the effects of vinorelbine, a novel semisynthetic vinca alkaloid on EGF receptor binding on human breast cancer cells. We have found that MDA-231 and MDA-468 cells bind substantially more [125I]-EGF after preincubation with vinorelbine. This effect was concentration- and time-dependent reaching a maximum at 100 ng/ml and 24 h incubation. Subsequent experiments showed an increase in the rate of EGF binding as well as maximal binding capacity. Scatchard analysis of binding experiments under equilibrium conditions indicated that this was mainly due to an increase in the number of apparent EGF binding sites. Modulation of EGF receptor binding by vinorelbine was not detectable when isolated membranes were used indicating that intact cytoplasmatic mechanisms are required for the upregulation of EGF receptors.

Effects of somatostatin analogue RC-160 and bombesin/gastrin-releasing peptide antagonists on the growth of human small-cell and non-small-cell lung carcinomas in nude mice

We investigated the effects of our synthetic bombesin/gastrin-releasing peptide (GRP) antagonists and somatostatin analogue RC-160 on the growth of human small-cell lung carcinoma (SCLC) and non-small-cell lung carcinoma (non-SCLC) lines in nude mice. Athymic nude mice bearing xenografts of the SCLC NCl-H69 line or non-SCLC NCl-H157 line were treated for 5 and 4 weeks, respectively, with somatostatin analogue RC-160 or various bombesin/GRP antagonists. RC-160, administered s.c. peritumorally at a dose of 100 micrograms per animal per day, inhibited the growth of H69 SCLC xenografts as shown by more than 70% reduction in tumour volumes and weights, as compared with the control group. Bombesin/GRP antagonists, RC-3440, RC-3095 and RC-3950-II, given s.c. peritumorally at a dose of 20 micrograms per animal per day, also inhibited the growth of H69 SCLC tumours. RC-3950-II had the greatest inhibitory effect and decreased tumour volume and weights by more than 80%. The growth of H-157 non-SCLC xenografts was significantly reduced by treatment with RC-160, but not with bombesin/GRP antagonist RC-3095. In mice bearing either tumour model, administration of RC-160 significantly decreased serum growth hormone and gastrin levels. Specific high-affinity receptors for bombesin and somatostatin were found on membranes of SCLC H69 tumours, but not on non-SCLC H157 tumours. Receptor analyses demonstrated high-affinity binding sites for epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on the membranes of H69 and H157 tumours. EGF receptors were down-regulated on H69 tumours after treatment with RC-160 and bombesin/GRP antagonists. The concentration of binding sites for EGF and IGF-I on the H157 tumours was decreased after treatment with RC-160, but bombesin/GRP antagonist RC-3095 had no effect. These results demonstrate that bombesin/GRP antagonists inhibit the growth of H-69 SCLC, but not of H-157 non-SCLC xenografts in nude mice, whereas somatostatin analogue RC-160 is effective in both tumour models. This raises the possibility that these peptide analogues could be used selectively in the treatment of various subclasses of lung cancer.

Bombesin, endothelin and platelet-derived growth factor induce rapid translocation of the myristoylated alanine-rich C-kinase substrate in Swiss 3T3 cells

We analyzed the effect of growth factors on the localization of the 80-kDa acidic myristoylated alanine-rich C-kinase substrate (80-kDa MARCKS), the major protein kinase C (PKC) substrate, in Swiss 3T3 fibroblasts. Virtually all 80-kDa MARCKS of quiescent cultures of these cells was membrane bound. However, within 40 min after addition of bombesin (10 nM) to these cells, the content of 80-kDa MARCKS in the cytoplasmic fraction increased 25-fold. Phosphorylated 80-kDa MARCKS was detectable in the cytoplasmic fraction as early as 30 s after addition of bombesin and the translocation was sustained for 6 h i.e. until 80-kDa MARCKS became down-regulated. The ability of bombesin to stimulate translocation of 80-kDa MARCKS was dose-dependent (concentration required to produce 50% of the effect was 0.6 nM bombesin) and was abolished by the specific antagonist [Leu14,13 psi 14CH2NH]bombesin. Furthermore, platelet-derived growth factor (PDGF) stimulated a dose-dependent (concentration required to produce 50% of the effect was 3 ng/ml) translocation which was comparable to that induced by bombesin in terms of kinetics and magnitude. Translocation was independent of continuous protein synthesis, but dependent on active PKC. Depletion or inhibition of PKC activity abolished the 80-kDa MARCKS translocation induced by either bombesin or PDGF. Furthermore, the neuropeptides beta-endothelin, bradykinin, and vasopressin, which are known to stimulate PKC activity, also promoted translocation. In contrast, epidermal growth factor, insulin and forskolin, which do not activate PKC, failed to cause such an effect. Translocation of 80-kDa MARCKS was also observed in Rat1 cells treated with phorbol ester, PDGF and beta-endothelin. We conclude that the translocation of 80-kDa MARCKS from the membrane to the cytosol is an early response to a variety of growth-promoting factors that stimulate PKC through different signal-transduction pathways.

Association of guinea pig lung bombesin receptors with pertussis toxin-sensitive guanine nucleotide binding proteins

The possible interaction of bombesin receptors with guanine nucleotide binding protein in guinea pig lung was studied. The non-hydrolysable GTP analogue guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) was shown to decrease [125I-Tyr4]bombesin binding in a concentration-dependent manner. The specificity of this effect was assessed by examining the effects of other guanine nucleotides on this binding at a concentration of 1 mM. GMP and GDP weakly inhibited [125I-Tyr4]bombesin binding (2 and 19%, respectively), whereas GTP, guanosine-5'-[beta-thio]triphosphate (GDP beta S), and 5-guanylylimidodiphosphate (GppNHp) exhibited similar potencies, inducing 52%, 46%, and 43% inhibition of [125I-Tyr4]bombesin binding respectively. Saturation experiments performed in the absence and presence of 100 microM GTP gamma S indicated the presence of a single population of receptors in both cases. However, the addition of GTP gamma S induced a marked decrease in the number of receptors (from 1.76 fmol/mg protein to 0.78 fmol/mg protein) without significantly altering the dissociation constant (Kd). These results provide evidence that bombesin receptors are coupled to a G-protein signal transduction pathway in guinea pig lung. We have further characterised this G-protein on the basis of its toxin sensitivity. Pretreatment of the lung membranes with either pertussis (10 micrograms/ml) or cholera toxin (50 micrograms/ml) was performed. Cholera toxin treatment did not affect the ability of GTP gamma S to inhibit [125I-Tyr4]bombesin binding to guinea pig lung membranes. However, pertussis toxin treatment induced a decrease in binding and resulted in the inability of GTP gamma S to inhibit [125I-Tyr4]bombesin binding in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of growth of MKN45 human gastric-carcinoma xenografts in nude mice by treatment with bombesin/gastrin-releasing-peptide antagonist (RC-3095) and somatostatin analogue RC-160

Nude mice bearing xenografts of the gastrin-responsive human gastric carcinoma MKN45 cell line were treated for 4 to 5 weeks with bombesin/gastrin-releasing-peptide(GRP) antagonist (RC-3095), somatostatin analogues RC-160 and SMS 201-995, or the combination of RC-3095 and RC-160. Tumor volumes and weights were reduced significantly to a similar extent by RC-160 and SMS 201-995, administered by daily s.c. injections at a dose of 100 micrograms/day. Bombesin/GRP antagonist RC-3095, given s.c. at a dose of 20 micrograms/day, had the greatest inhibitory effect on tumor growth. The combination of RC-3095 with RC-160 did not further potentiate the suppression of tumor growth. Histologically, the number of mitotic cels decreased significantly in the groups treated with RC-160 or the combination of RC-3095 with RC-160. Serum gastrin levels were significantly diminished in all treated groups. Therapy with RC-160 or the combination also significantly decreased levels of serum growth hormone. Receptor assays on tumor membranes showed that bombesin was bound to 2 classes of receptor sites, one with high affinity and low capacity, the other with low affinity and high capacity. Binding sites for epidermal growth factor (EGF) were down-regulated in tumor cells after treatment with RC-3095, RC-160 or the combination of RC-3095 with RC-160. In studies in vitro, both RC-160 and RC-3095 significantly inhibited the proliferation of MKN45 cells in culture as measured by cell number. These data demonstrate, for the first time, that the growth of human gastric cancer in nude mice can be inhibited not only by somatostatin analogues, but also by administration of modern bombesin/GRP antagonists, such as RC-3095.

Map kinase activation in Swiss 3T3 cells stimulated with gastrin-releasing peptide is associated with increased phosphorylation of a 78,000 M(r) protein immunoprecipitated by anti-raf kinase anti-serum

Addition of 10 nM gastrin-releasing peptide (GRP) to Swiss 3T3 fibroblasts induced a transient (1-2 min) tyrosine phosphorylation and activation of mitogen-activated protein kinase (MAP kinase). Increased activity of 42,000 M(r) MAP kinase was detected with immunochemical methods; however, in situ kinase detection on renaturated SDS-polyacrylamide electrophoresis gel revealed activation of both 42,000 and 44,000 M(r) MAP kinase species. Furthermore, stimulation of 32P-labelled cells with 10 nM GRP for 2 min resulted in an increased phosphorylation of a protein with an approximate molecular mass of 78,000 M(r) in anti-raf kinase and anti-MAP kinase kinase immunoprecipitates of cytosolic extracts from 32P-labelled cells. The presented data demonstrated that GRP induces MAP kinase activation in Swiss 3T3 fibroblasts, and furthermore suggest a role for raf kinase in this process.

Effects of the microtubule-disturbing agents docetaxel (Taxotere), vinblastine and vincristine on epidermal growth factor-receptor binding of human breast cancer cell lines in vitro

Epidermal growth factor (EGF) is a mitogenic peptide that binds to surface membrane receptors (EGFR) of breast cancer cells. After binding, secondary transmitter molecules are activated by tyrosine phosphorylation of the intracellular receptor domaine. The activity of the EGF/EGFR system can be modulated by a variety of chemically unrelated compounds including cytostatic agents. The purpose of our present study was to determine the effects of mitotic inhibitors on EGF receptor binding on human breast cancer cells. We found that MDA-231 and MDA-468 cells bind substantially more [125I]EGF after preincubation with docetaxel, vinblastine and vincristine. This effect was concentration- and time-dependent, reaching a maximum at 3000 ng/ml and 48 h incubation for docetaxel, and 100 ng/ml and 48 h incubation for vinca alcaloids. Subsequent experiments showed an increase in the rate of EGF binding as well as maximal binding capacity. Scatchard analysis of binding experiments under equilibrium conditions indicated that this was due to an increase in the number of apparent EGF binding sites. Modulation of EGF receptor binding by docetaxel, vinblastine, and vincristine was not detectable when isolated membranes were used, indicating that intact cytoplasmatic mechanisms are required for the upregulation of EGF receptors.

Novel soluble, high-affinity gastrin-releasing peptide binding proteins in Swiss 3T3 fibroblasts

Swiss 3T3 cells contained substantial amounts of soluble and specific [125I]GRP binders. Like the membrane-associated GRP receptor, they were of high affinity, saturable, bound to GRP(14-27) affinity gels, and exhibited specificity for GRP(14-27) binding. They differed in that acid or freezing destroyed specific binding, specific binding exhibited different time and temperature effects, no detergent was required for their solubilization, ammonium sulfate fractionation yielded different profiles, the M(rs) were lower, GRP(1-16) also blocked binding, and a polyclonal anti-GRP receptor antiserum did not bind on Western blots. The isolated, soluble GRP binding protein(s) rapidly degraded [125I]GRP. These soluble GRP binding proteins may play a role in the regulation of the mitogenic effects of GRP on these cells.

Inhibitory effects of antagonists of bombesin/gastrin releasing peptide (GRP) and somatostatin analog (RC-160) on growth of HT-29 human colon cancers in nude mice

Nude mice bearing xenografts of HT-29 human colon cancer cell line were treated for 4 weeks with somatostatin analog (RC-160), bombesin/gastrin releasing peptide (GRP) antagonists (RC-3095 and RC-3440). In three separate experiments somatostatin analog RC-160 (50 micrograms/day) released from microgranules significantly reduced tumor growth. Bombesin/GRP antagonists, RC-3095 and RC-3440 injected subcutaneously (s.c.) twice daily at a dose of 10 micrograms had the greatest and consistently significant inhibitory effect on tumor growth. RC-3095 given once daily s.c. at a dose of 20 micrograms was less effective. RC-3095 also inhibited metastatic tumor growth after intrasplenic injection of HT-29 cells in nude mice. Specific binding sites of somatostatin, bombesin and epidermal growth factor (EGF) were detected on intact HT-29 cells or on the membranes from HT-29 tumor xenografts. The inhibitory effects of bombesin antagonists on tumor growth were consistently linked with a significant down-regulation of EGF receptors. Bombesin/GRP antagonists and somatostatin analogs could be considered for the development of new hormonal therapies for colon cancer.

Antagonists of bombesin/gastrin-releasing peptides as adjuncts to agonists of luteinizing hormone-releasing hormone in the treatment of experimental prostate cancer

BACKGROUND

Palliative methods for treatment of advanced prostatic carcinoma, including those based on luteinizing hormone-releasing hormone (LH-RH) agonists, cannot prevent the ultimate growth of hormone-independent cells, and the duration of disease remission in patients with prostate cancer is limited. New therapeutic approaches combining androgen ablation therapy with other compounds must be explored. Various studies suggest that bombesin or gastrin-releasing peptide (GRP) act as autocrine growth factors and may play a role in the initiation and progression of some cancers, including those of the prostate.

METHODS

The effects of treatment with bombesin/gastrin-releasing peptide (GRP) receptor antagonist [D-Tpi6, Leu13 psi(CH2NH)Leu14]BN(6-14)(RC-3095), an agonist of LH-RH [D-Lys6]-LH-RH and their combination were investigated in the androgen-dependent Dunning R-3327H rat prostate cancer model. Both analogs were administered by continuous subcutaneous infusion from osmotic minipumps for 7 weeks.

RESULTS

Tumor volumes and weights were significantly reduced by treatment with RC-3095, compared with those of controls. In rats that received [D-Lys6]-LH-RH, there was a greater decrease in tumor weight and volume than that produced by RC-3095, and the weights of testes, ventral prostate, and seminal vesicles also were reduced. The combination of RC-3095 and [D-Lys6]-LH-RH had the greatest inhibitory effect on tumor growth. Histologic parameters demonstrated a significant increase of the ratio of apoptotic to mitotic indices in the groups treated with [D-Lys6]-LH-RH or the combination. Serum LH and testosterone levels were greatly depressed by [D-Lys6]-LH-RH or the combination. Specific high-affinity binding sites for bombesin/GRP, epidermal growth factor (EGF), and insulin-like growth Factor I (IGF-I) were found on the tumor membranes. The concentration of receptors for EGF was significantly reduced by treatment with the bombesin/GRP antagonist RC-3095.

CONCLUSIONS

Combination therapy of LH-RH analogs with bombesin antagonists such as RC-3095 might be considered for improvement of hormonal therapy of prostate cancer.

Inhibition of 80 kDa protein phosphorylation by short-wavelength UV light in NIH 3T3 cells

The exposure of NIH 3T3 fibroblast cells to 254 nm UV radiation resulted in a temporary depression of DNA synthesis and inhibition of 80 kDa protein phosphorylation. This inhibition of protein phosphorylation was correlated with decreased protein kinase C activity in the membrane fractions of UV-damaged cells. The inositol triphosphate contents measured, by the competitive binding assay using bovine adrenal binding protein, showed 80% reduction in the fibroblasts treated with 15 J/m2 of UV light. The intracellular diacylglycerol concentration was also markedly reduced in UV-damaged cells. The results suggest that UV light causes acute reductions of inositol triphosphate and diacylglycerol contents in cells along with decreases in membrane protein kinase C activity, which leads to the inhibition of phosphorylation of an acidic protein of 80 kDa.

Differential induction of phosphatidylcholine hydrolysis, diacylglycerol formation and protein kinase C activation by epidermal growth factor and transforming growth factor-alpha in normal human skin fibroblasts and keratinocytes

We have investigated coupling between the epidermal growth factor (EGF) receptor and the phospholipase C (PLC)/protein kinase C (PKC) signal-transduction system in normal skin fibroblasts and keratinocytes, for which EGF and transforming growth factor alpha (TGF-alpha) are mitogenic. EGF and TGF-alpha induced a rapid increase in tyrosine phosphorylation of the EGF receptor, in both fibroblasts and keratinocytes, but failed to induce tyrosine phosphorylation of PLC-gamma 1 or detectable phosphoinositide hydrolysis, as measured by two sensitive assays. In fibroblasts, EGF induced phosphatidylcholine (PC) hydrolysis, resulting in increased diacylglycerol (DAG). In contrast, in keratinocytes, there was no detectable PC hydrolysis or elevation of DAG in response to EGF or TGF-alpha. EGF and TGF-alpha activated PKC in fibroblasts, as evidenced by increased phosphorylation of a specific cellular PKC substrate (myristoylated alanine-rich C-kinase substrate, 'MARCKS'). In keratinocytes, TGF-alpha and EGF induced only a modest increase in MARCKS protein phosphorylation. This apparent modest activation of PKC, in the absence of detectable DAG formation, may have been mediated by arachidonic acid, which was released from keratinocytes in response to TGF-alpha, and has been shown to stimulate PKC activity in vitro. These data demonstrate that (1) in dermal fibroblasts and keratinocytes, which express normal levels of EGF receptors, EGF receptor activation is not coupled to tyrosine phosphorylation of PLC-gamma 1 or PtdIns hydrolysis, suggesting that these events are not required for the mitogenic activity of EGF or TGF-alpha in these cells, (2) coupling of EGF receptor to PC hydrolysis is cell-type specific, and (3) in skin fibroblasts, DAG, formed through EGF-induced PC hydrolysis, is capable of activating PKC.

Homologous desensitization of bombesin-induced increases in intracellular Ca2+ in quiescent Swiss 3T3 cells involves a protein kinase C-independent mechanism

Addition of bombesin to Swiss 3T3 cells causes a rapid and transient increase in the intracellular concentration of Ca2+ ([Ca2+]i), which is followed by desensitization to a subsequent addition of the peptide. The concentrations of bombesin used to study this acute cellular desensitization (0.1-0.5 nM) did not deplete the intracellular pool of Ca2+ released by inositol(1,4,5)trisphosphate, as shown by addition of vasopressin after consecutive additions of bombesin. Two lines of evidence support the conclusion that activation of protein kinase C (PKC) does not mediate the acute homologous desensitization of Ca2+ responses induced by bombesin. First, long-term treatment (48 h) of Swiss 3T3 cells with phorbol 12,13-dibutyrate (PDB) to deplete PKC did not prevent homologous desensitization. The responses to second additions of bombesin at 0.1, 0.25, and 0.5 nM were 42%, 26% and 11% of the initial responses, respectively. Second, the PKC inhibitor GF 109203X did not alter homologous desensitization at concentrations that completely prevented the inhibition of Ca2+ mobilization induced by PDB and blocked PDB-mediated phosphorylation of the prominent PKC substrate 80K/MARCKS. We conclude that acute homologous desensitization of Ca2+ responses induced by bombesin occurs through a PKC-independent mechanism.

Cross talk among tyrosine kinase receptors in PC12 cells: desensitization of mitogenic epidermal growth factor receptors by the neurotrophic factors, nerve growth factor and basic fibroblast growth factor

We have studied the effects of nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) on epidermal growth factor (EGF) binding to PC12 cells. We show that NGF and bFGF rapidly induce a reduction in 125I-EGF binding to PC12 cells in a dose-dependent manner. This decrease amounts to 50% for NGF and 35% for bFGF. Both factors appear to act through a protein kinase C(PKC)-independent pathway, because their effect persists in PKC-downregulated PC12 cells. Scatchard analysis indicates that NGF and bFGF decrease the number of high affinity EGF binding sites. In addition to their effect on EGF binding, NGF and bFGF activate in intact PC12 cells one or several serine/threonine kinases leading to EGF receptor threonine phosphorylation. Using an in vitro phosphorylation system, we show that NGF- or bFGF-activated extracellular regulated kinase 1 (ERK1) is able to phosphorylate a kinase-deficient EGF receptor. Phosphoamino acid analysis indicates that this phosphorylation occurs mainly on threonine residues. Furthermore, two comparable phosphopeptides are observed in the EGF receptor, phosphorylated either in vivo after NGF treatment or in a cell-free system by NGF-activated ERK1. Finally, a good correlation was found between the time courses of ERK1 activation and 125I-EGF binding inhibition after NGF or bFGF treatment. In conclusion, in PC12 cells the NGF- and bFGF-stimulated ERK1 appears to be involved in the induction of the threonine phosphorylation of the EGF receptor and the decrease in the number of high affinity EGF binding sites.

Effect of bombesin, gastrin-releasing peptide (GRP)(14-27) and bombesin/GRP receptor antagonist RC-3095 on growth of nitrosamine-induced pancreatic cancers in hamsters

Female Syrian golden hamsters with N-nitroso-bis (2-oxopropyl) amine (BOP)-induced pancreatic cancers were treated for 2 months with bombesin/gastrin-releasing peptide (GRP) antagonist D-Tpi6,Leu13 psi(CH2NH)Leu14 bombesin(6-14) (RC-3095). Bombesin and GRP(14-27) were also administered alone and in combination with the antagonist RC-3095. RC-3095 exerted a dose-dependent inhibitory effect on growth of pancreatic cancers. The number of animals with pancreatic cancers was significantly lower in the group treated with 60 micrograms/day of RC-3095 and the weight of tumorous pancreata was reduced. Administration of bombesin or GRP alone did not stimulate the growth of pancreatic tumors and, in fact, had a slightly suppressive effect on cancers which was significant only in Experiment I. Bombesin and GRP (14-27) given together with RC-3095 did not nullify the inhibitory effect of the antagonist on pancreatic cancer growth. Actually, a greater inhibition of pancreatic tumors was observed after administration of RC-3095 together with bombesin or GRP, than with RC-3095 alone. The mechanism of action of bombesin, GRP, and bombesin antagonists on pancreatic cancers appears to be complex. The inhibitory effect of bombesin antagonists on pancreatic cancer growth was accompanied by a decrease in the binding capacity of EGF receptors in tumor membranes. Administration of bombesin also caused a down-regulation of EGF receptors and the greatest decrease in binding capacity of EGF receptors was observed after treatment with RC-3095 in combination with GRP. Inhibition of pancreatic cancer can thus be tentatively explained by some common pathways in the action of bombesin, GRP and their antagonists, that could be mediated by interference with EGF-receptor mechanisms.

Anti-bombesin monoclonal antibodies modulate fetal mouse lung growth and maturation in utero and in organ cultures

Fetal pulmonary neuroendocrine cells (PNECs) contain abundant gastrin-releasing peptide (GRP, mammalian bombesin-like peptide [BLP]). Previously, addition of bombesin resulted in increased fetal lung growth and maturation in utero and in organ cultures. A monoclonal antibody (mAb) to bombesin (2A11) blocked baseline automaturation of lung organ cultures in serum-free medium. In the present study, we analyze lung development following daily in utero administration of 2A11 from gestational days 15-18. Fetal lung treated with 2A11 and then harvested on day 18 demonstrated a dose-dependent decrease in surfactant phospholipid synthesis compared to controls treated with MOPC, an unreactive mAb. However, 2A11-treated fetal lung harvested on day 17 showed paradoxical increases in 3H-choline incorporation into saturated phosphatidylcholine, 3H-thymidine incorporation into DNA, and relative numbers of differentiated type II pneumocytes. In serum-containing day 17 lung organ cultures, 2A11 stimulated choline and thymidine incorporation. Since epidermal growth factor (EGF) is the only agent besides bombesin known to stimulate both fetal lung growth and maturation, we added EGF to serum-free cultures and reconstituted the stimulatory effects. A murine EGF receptor mAb (ERA) blocked 2A11-induced lung growth and maturation in serum-containing cultures, and this effect was overcome by adding EGF. In vivo, ERA also blocked stimulatory effects of 2A11 in fetal lung on day 17. These observations suggest that EGF receptor up-regulation may maintain lung growth and maturation if BLP levels are diminished on day 17. Nonetheless, BLPs appear to be involved in lung maturation on day 18, supporting a role for PNECs in normal lung development.

Phosphorylation and redistribution of the phosphatidylinositol-transfer protein in phorbol 12-myristate 13-acetate- and bombesin-stimulated Swiss mouse 3T3 fibroblasts

By immunofluorescence microscopy it was shown that the phosphatidylinositol-transfer protein (PI-TP) becomes associated with the Golgi membranes when confluent (quiescent) Swiss mouse 3T3 fibroblast cells are stimulated with phorbol 12-myristate 13-acetate (PMA) and bombesin. Dibutyryl cyclic AMP or dexamethasone had no effect on the intracellular redistribution of PI-TP. In exponentially growing cells and in serum-starved (semi-quiescent) cells, PI-TP is already associated with Golgi structures. Stimulation of semi-quiescent cells by PMA resulted in a rapid redistribution of PI-TP. A similar yet slower response was observed after stimulation with bombesin. Stimulation of semi-quiescent 3T3 cells by PMA significantly increased the phosphorylation of PI-TP, as shown by immunoprecipitation of PI-TP from pre-labelled cells. No significant increase in phosphorylation of PI-TP was observed after stimulation of these cells by bombesin. Purified PI-TP was shown to be a substrate for protein kinase C in vitro. The possibility that the phosphorylation of PI-TP after activation of protein kinase C is involved in the observed redistribution of PI-TP is discussed.

Extracellular ATP-induced regulation of epidermal growth factor signaling in cultured renal LLC-PK1 cells

We investigated the effect of extracellular ATP on the interaction of epidermal growth factor (EGF) with its receptor in cultured renal epithelial cells, LLC-PK1. Pretreatment with ATP, but not adenosine, inhibited the binding of 125I-labeled EGF. The inhibition demonstrated by ATP resulted from a decrease in the affinity of EGF receptors for its ligand, with no change in the number of EGF receptors. Incubation of phorbol 12-myristate 13-acetate (PMA) for 30 min mimicked the ATP-mediated inhibition. On the other hand, prolonged pretreatment with PMA, which leads to disappearance of protein kinase C activity, reversed the inhibition. In addition, pretreatment with the protein kinase C inhibitor 1-(5-isoquinoline sulfonyl)-2-methylpiperazine prevented the ATP-mediated inhibition. ATP triggered an increase in inositol 1,4,5-trisphosphate levels and translocation of protein kinase C from cytosol to membranes, consist with the stimulation of phospholipase C and the activation of protein kinase C. These results demonstrate that extracellular ATP attenuates the ligand binding affinity of EGF receptor via the stimulation of phospholipase C, leading to the activation of protein kinase C in the LLC-PK1 cells.