Biomedical subjects

D H Coy

Publications and source records attributed to D H Coy.

At least 163 records · Page 9Linked to original sources

PubMed1991

Human growth hormone-releasing hormone analogues with much improved in vitro growth hormone-releasing potencies in rat pituitary cells.

Enhancement of the amphiphilic alpha-helical properties of the central and C-terminal regions of growth hormone-releasing hormone (GRH) by substitution with helix-favouring amino acids, particularly Ala, can result in significant improvements in GH-releasing potencies using monolayer cultures of rat pituitary cells, a system which reflects analogue receptor affinity rather than effects of structural modifications on pharmacokinetic properties. For instance, previously reported, helix-enhanced [Ala15]GRH-(1-29)NH2 was presently 5 times more potent than [Gly15]GRH-(1-29)NH2 in this assay. The extent and importance of alpha-helical character further towards the N-terminus is less clear since Chou-Fasman probability calculations indicate also the possibility of beta-bend formation in the 6-10 region. However, replacement of Asn8 with Ala resulted in a 4-fold improvement in potency and when this was combined with Ala15 to give [Ala8,15]GRH-(1-29)NH2 a 15-fold increase in potency was achieved and combination of D-Ala2, Ala8 and Ala15 gave a 27-fold increase indicating that the effects of all of these modifications were additive. Computer analysis furthermore revealed that substitution of Ala for Ser in position 9 should also increase alpha-helix probability from 0.93 to 1.05. [D-Ala2,Ala8,9,15]GRH- (1-29)NH2 was 49 times more potent than GRH itself making it by far the most potent analogue thus far reported in an in vitro assay system. The Ala8 and Ala9 substitutions were also effective in improving the inhibitory potency of a GRH receptor antagonist, [D-Arg2,Leu27]GRH-(1-29)NH2.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1991

New reduced peptide bond substance P agonists and antagonists: effects on smooth muscle contraction.

Following the recent discovery of a new substance P (SP) competitive pancreatic acini cell receptor antagonist containing a reduced peptide bond in place of the C-terminal peptide bond, a new series of full chain and short chain (heptapeptide and hexapeptide) substance P analogues have been prepared in which one of the C-terminal-region peptide bonds has been replaced by CH2NH or CH2O groups. They were compared for their ability to recognize NK1 and/or NK2 tachykinin receptor binding sites on guinea pig ileum and rat duodenum smooth muscle preparations, respectively. It was found that all full sequence SP pseudopeptides were agonists with much reduced bioactivity in both tested systems and, in addition, [Gly9 psi(CH2NH)Leu10,Leu11]SP was found to be a relatively selective agonist for NK1 binding sites. Substitution of leucine at position 11 of SP heptapseudopeptides with phenylalanine generated a pseudopeptide with weak agonist activity when Gln at position 5 was replaced by D-Phe, or antagonists when this residue was replaced by D-Nal or D-Cpa. [Leu10 psi(CH2NH)Leu11]SP-(6-11) with Gln at position 6 substituted by D-Phe was a relatively stronger antagonist in both assay systems. These results suggest that, as with several other peptide systems of late, manipulation of the peptide bonds in SP can produce receptor antagonists which in some cases approach the potency of the classic spantide series and, furthermore, that the approach might be used to induce NK receptor specificity in both agonist and antagonist analogs.

Amino Acid Sequence↗

PubMed1991

Effect of substance P/bombesin antagonists on the release of growth hormone by GHRP and GHRH.

The substance P(SP)/bombesin (Bn) antagonists [DArg1DTrp7,9Leu11] SP(P-7482), [DArg1-DPro2DTrp7,9Leu11]SP (P-7483), [DArg1DPhe5DTrp7,9Leu11]SP(P-7492), and the growth hormone releasing hormone (GHRH) antagonist [DArg2Ala8,9,15]GHRH(1-29)(DC21-366) were tested for their in vitro effects on the release of growth hormone (GH) in the presence of GHRH and growth hormone releasing peptide, HisDTrpAlaTrpDPheLysNH2(GHRP). P-7492, P-7483, and P-7482 decreased, dose-dependently, the release of GH by GHRP (IC50 = 0.2 microM, 0.85 microM, and 6 microM, respectively). These antagonists had only a 10-15% inhibitory effect on the stimulated GH release of GHRH even at high dosage. DC21-366 decreased the stimulated release of GH by GHRH (IC50 = 0.16 microM) but not by GHRP. Neither SP nor Bn had GH releasing or inhibitory effects in this system.

Amino Acid Sequence↗

PubMed1991

Covalently cyclized agonist and antagonist analogues of bombesin and related peptides.

During a search for possible cyclization points in shortened, potent bombesin agonists and antagonists, it was found that the joining of amino acid residues in positions 6 and 14 by various means resulted in retention of significant binding affinity for rat pancreatic acini and murine Swiss 3T3 cells. In one series of analogues, Cys residues in these positions were used for bridging via a disulfide bond. (D)-C-Q-W-A-V-G-H-L-C-NH2 retained significant binding affinity for rat pancreatic acini cells and was a full amylase releasing agonist (EC50 187 nM). Potency was markedly increased by substituting D-Ala for Gly (EC50 67 nM compared to 10 nM for its linear counterpart) and was decreased by substituting L-Cys for D-Cys in this analogue (EC50 214 nM), thus strongly suggesting stabilization of peptide folding by the D residues. Elimination of the COOH-terminal amino acid produces competitive antagonists in the linear analogues; however, (D)-C-Q-W-A-V-G-H-C-NH2 was devoid of activity. Likewise, cyclization to position 13 with the 14 amino acids intact to give (D)-C-Q-W-A-V-G-H-C-L-NH2 resulted in an almost inactive peptide. On the other hand, as in the linear series, the reduced peptide bond analogue, (D)-C-Q-W-A-V-(D)-A-H-L-psi (CH2NH)-C-NH2, was a receptor antagonist (IC50 5.7 mM), albeit much weaker than the corresponding linear analogues, but with no residual agonist activity. Direct head-to-tail cyclization was also tried. Both cyclo[(D)-F-Q-W-A-V-G-H-L-L] (EC50 346 nM) and the shorter cyclo [Q-W-A-V-G-H-L-L] (EC50 1236 nM) were full agonists. Elimination of the COOH-terminal residue in cyclo[(D)-p-Cl-F-Q-W-A-V-(D)-A-H-L] produced an agonist (EC50 716 nM) rather than an antagonist. These results provide support for the proposal that both bombesin agonists and antagonists adopt a folded conformation at their receptor(s). Furthermore, the retention of appreciable potencies using several cyclization strategies and chain lengths suggests that further optimization of these structures both in terms of potency and ring size is possible. Since these peptides have increased conformational restriction, they should begin to serve as useful substrates for NMR and molecular modeling studies aimed at comparing the obviously subtle differences between agonist and antagonist structures.

Amino Acid Sequence↗

PubMed1991

Galanin inhibits pancreatic amylase secretion in the pentobarbital-anesthetized rat.

The potent inhibitory effect of galanin on basal and pentagastrin-stimulated gastric acid secretion in vivo, and the presence of galanin-containing nerves in gastrointestinal tract and pancreas, suggested that this peptide may regulate the exocrine secretion of the GI system. Male rats were anesthetized with pentobarbital and the dose-dependent inhibitory effects of galanin on basal and stimulated pancreatic protein and amylase secretions were investigated in separate experiments. Galanin was administered intravenously in the following doses: 3, 6, 10, 15 and 20 micrograms/kg/h (0.93, 1.86, 3.1, 4.65 and 6.2 nmol/kg/h), and pancreatic secretions measured. The maximal effective dose of galanin (3.1 nmol/kg/h) on basal pancreatic secretions was found, and was used for evaluating the inhibitory effect of galanin on pancreatic protein and amylase secretions stimulated by bombesin, secretin and cholecystokinin. Galanin potently inhibited basal, bombesin-, secretin- and cholecystokinin-stimulated pancreatic protein and amylase secretion. Inhibitory effect of galanin was dose-dependent and biphasic.

Amylases↗

PubMed1991

Distinguishing bombesin receptor subtypes using the oocyte assay.

Physiological responses to mammalian bombesin-like peptides were studied in Xenopus oocytes injected with mRNA isolated from Swiss 3T3 cells and rat esophagus in order to identify and characterize bombesin receptor subtypes. Both groups respond similarly to either gastrin releasing peptide or neuromedin B, but only the response to neuromedin B in oocytes expressing the esophagus mRNA is not blocked by a specific gastrin releasing peptide receptor antagonist, des-Met-[D-Phe6]Bn(6-13) ethyl ester. Complete desensitization of gastrin releasing peptide-evoked responses in oocytes expressing esophagus mRNA does not abolish neuromedin B-evoked responses. A single application of neuromedin B abolishes responses to subsequently applied gastrin releasing peptide in oocytes expressing esophagus, but not Swiss 3T3, mRNA. RNA blot hybridization studies using a Swiss 3T3 gastrin releasing peptide receptor cDNA probe show no detectable hybridization in esophagus mRNA samples. These data suggest that a gastrin releasing peptide receptor is expressed in the esophagus and that it is distinct from that expressed in Swiss 3T3 cells and may represent a third subtype of mammalian bombesin receptor.

Animals↗

PubMed1991

Reduced peptide bond pseudopeptide analogues of secretin. A new class of secretin receptor antagonists.

The ability to assess the importance of secretin in various physiological processes is limited by the lack of specific potent antagonists. Recently, reduced peptide bond (psi) analogues of bombesin or substance P in which the -CONH- bond is replaced by -CH2NH- are reported to be receptor antagonists. To attempt to develop a new class of secretin receptor antagonists, we have adopted a similar strategy with secretin and sequentially altered the eight NH2-terminal peptide bonds, the biological active portion of secretin. In guinea pig pancreatic acini, secretin caused a 75-fold increase in cyclic AMP (cAMP). Secretin inhibited 125I-secretin binding with a half-maximal effect at 7 nM. Each of the psi analogues inhibited 125I-secretin binding. [psi 4,5]Secretin was the most potent, causing the half-maximal inhibition at 4 microM, and was 2-fold more potent than the [psi 1,2]secretin; 7-fold more than [psi 3,4]secretin, [psi 5,6]secretin, and [psi 8,9]secretin; 9-fold more than [psi 7,8]secretin; 13-fold more potent [psi 6,7]secretin, and 17-fold more than [psi 2,3]secretin. Secretin caused a half-maximal increase in cAMP at 1 nM. At concentrations up to 10 microM, [psi 2,3]secretin, [psi 4,5]secretin, and [psi 8,9]secretin did not alter cAMP whereas [psi 1,2]secretin and [psi 6,7]secretin caused a detectable increase in cAMP at 10 nM, [psi 7,8]secretin at 300 nM, [psi 5,6]secretin at 1 microM, and [psi 3,4]secretin at 10 microM. The [psi 4,5], [psi 2,3], and [psi 8,9] analogues of secretin each inhibited 1 nM secretin-stimulated cAMP as well as [psi 3,4]secretin, which functioned as a partial agonist. [psi 4,5]Secretin was the most potent, causing half-maximal inhibition at 3 microM whereas [psi 8,9]secretin was 6-fold less potent, and [psi 2,3]secretin and [psi 3,4]secretin were 17-fold less potent. [psi 4,5]Secretin inhibited secretin-stimulated cAMP and binding of 125I-secretin in a competitive manner. [psi 4,5]Secretin did not interact with cholecystokinin, bombesin, calcitonin gene-related peptide, or cholinergic receptors but did interact with receptors for vasoactive intestinal peptide, causing half-maximal inhibition at 72 microM and thus had a 18-fold higher affinity for secretin than vasoactive intestinal peptide receptors. These results indicate that reduced peptide bond analogues of the NH2 terminus of secretin represent a new class of secretin receptor antagonists. It is likely that in the future even more potent members of this class can be developed which may be useful to investigate the role of secretin in various physiological processes.

Amylases↗

PubMed1991

Progress in the development of potent bombesin receptor antagonists.

Bombesin and the mammalian-related peptides gastrin-releasing peptide (GRP), GRP and neuromedin B have been shown to have numerous actions in the CNS, gastrointestinal tract and on growth. However, the role of the peptides in various physiological processes has remained unclear because of the lack of potent antagonists. Recent in vitro studies have described four different classes of bombesin receptor antagonist, some of which are active in the nanomolar range and in vivo. Robert Jensen and David Coy describe recent insights into peptide structural determinants of biological activity. Evidence from structure-function studies have resulted in identification of some analogues that function as potent antagonists in all systems examined. Furthermore, various subtypes of bombesin receptors can now be differentiated by these various classes of antagonist.

Amino Acid Sequence↗

PubMed1991

Regulation of acid secretion by bombesin/GRP neurons of the gastric fundus.

Intramural neurons in the fundus of the isolated mouse stomach were activated by 1,1-dimethyl-4-phenylpiperazinium (DMPP) or by electrical field stimulation and the participation of cholinergic and bombesin/gastrin-releasing peptide (GRP) neurons in the regulation of acid secretion evaluated with atropine and a selective bombesin/GRP antagonist, [Leu13-psi(CH2NH)-Leu14]bombesin. For both DMPP and field stimulation, atropine inhibited acid secretion and augmented somatostatin secretion. The bombesin/GRP antagonist had an opposite effect, augmenting acid secretion and inhibiting somatostatin secretion to below basal levels. The combination of the two antagonists restored DMPP- and field-stimulated acid and somatostatin secretion to basal levels. The results indicate that neurally stimulated acid secretion in the isolated mouse stomach is regulated by cholinergic neurons that mediate stimulation and bombesin/GRP neurons that mediate inhibition of acid secretion. Cholinergic neurons exert their stimulatory effect by acting directly on parietal cells and indirectly by eliminating the inhibitory influence of somatostatin. Bombesin/GRP neurons exert their inhibitory effect mainly by inducing release of somatostatin; an additional direct inhibitory effect of bombesin/GRP neurons on parietal cells is possible.

Animals↗

PubMed1991

Gastrin-releasing peptide is a transmitter mediating porcine gallbladder contraction.

We studied the role of gastrin-releasing peptide (GRP) for porcine gallbladder motility. Immunohistochemistry visualized nerve fibers containing GRP-like immunoreactivity in muscularis. GRP concentration dependently stimulated contractions of muscularis strips (ED50, 2.9 nM). Neuromedin B was less potent (ED50, 0.1 microM), suggesting existence of GRP-preferring receptors. GRP-induced contractions were unaffected by muscarinic antagonism (1 microM atropine), axonal blockade (1 microM tetrodotoxin), cholecystokinin (CCK) receptor antagonism (10 microM MK-329), or substance P desensitization (1 microM), supporting the existence of myogenic GRP receptors. The bombesin (BN) analogue D-Phe6-BN-(6-13)propylamide (PA) stimulated contractions (ED50, 3.3 nM) with low efficacy (29% of that of GRP). D-Phe6-BN-(6-13)PA (1 microM) shifted GRP concentration-response curves one log to the right. D-Phe6-BN-(6-13)PA interacted specifically with GRP receptors; while abolishing responses to GRP (1 nM), responses to substance P (0.1 microM) and CCK-8 (1 nM) were unchanged. Electrical stimulation (10 Hz, 0.5 ms, 10 V) caused a rapid onset-slow offset, tetrodotoxin-sensitive excitation. Atropine reduced the amplitude to 58% and caused a delayed, slow onset-slow decline response. D-Phe6-BN-(6-13)PA reduced the amplitude to 59% and caused a very rapid onset-rapid decline response. Atropine plus D-Phe6-BN-(6-13)PA abolished responses to nerve stimulation. Nerve stimulation caused significant release of GRP-like immunoreactivity. Thus two neural inputs were defined: a cholinergic rapid onset-rapid offset excitation and a delayed, slow onset-slow offset excitation caused by release and subsequent binding of GRP to GRP-preferring receptors.

Animals↗

PubMed1991

Different receptors mediate the action of bombesin-related peptides on gastric smooth muscle cells.

Recent studies suggest that different subtypes of receptors may mediate the action of various bombesin-related peptides in different tissues. In the present study the ability of bombesin and its structurally related peptides [litorin, gastrin-releasing peptide (GRP), GRP18-27, neuromedin B, [Leu8]litorin, and bombesin nonapeptide BN(6-14)] to interact with smooth muscle cells isolated from guinea pig stomach was investigated. Each peptide induced a specific contractile response with potencies (D50 in pM) of [Leu8]litorin (0.7) greater than bombesin (1.2) greater than litorin (3) greater than neuromedin B (3.5) = GRP (3.8) = GRP18-27 (3.9) greater than BN(6-14) (70.9). The specific bombesin receptor antagonist psi 13,14-bombesin differed in its potency for inhibiting equipotent concentrations of bombesin, GRP, or neuromedin B, was equipotent for bombesin or GRP (IC50 12.7 and 22.1 nM), and was 11 times less potent for neuromedin B (IC50 234.5 nM), suggesting the presence of subtypes of receptors mediating the action of bombesin-related peptides. To further investigate this possibility, a technique of receptor protection that enables selective preservation of one receptor type was used. GRP or bombesin protected completely the response to GRP or bombesin but abolished the subsequent contractile response to neuromedin B. Neuromedin B, instead, protected only the response to neuromedin B. These results demonstrate that gastric smooth muscle cells possess specific receptors that interact with bombesin-related peptides and that two receptor subtypes mediate the contractile response to these peptides: one subtype is selective for bombesin or GRP, the other for neuromedin B.

Amino Acid Sequence↗

PubMed1991

Tissue distribution of PACAP as determined by RIA: highly abundant in the rat brain and testes.

A heterologous RIA method for pituitary adenylate cyclase activating polypeptide with 38 residues (PACAP38) and a homologous RIA method for a shorter form of PACAP with 27 residues (PACAP27) were established to determine PACAP content in central and peripheral tissues in rats. The highest concentration of radioimmunoassayable PACAP38 was found in the hypothalamus, but other brain regions also contained considerable amounts of PACAP38. PACAP38 concentration in the posterior pituitary was comparable with that in the extrahypothalamic brain, but its concentration in the anterior pituitary was very low. Unexpectedly, the testis contained a high abundance of PACAP38, and the total amount of PACAP in both testes exceeded its content in the whole brain. Reverse phase HPLC suggested that the major testicular PACAP38 immunoreactivity represents PACAP38. Among peripheral tissues, adrenal gland contained the second highest concentration of PACAP. Smaller amounts of PACAP were widely distributed in the digestive tract and other peripheral tissues. The concentration of PACAP in stomach, duodenum and jejunum appeared to be greater than in other portions of the gut. In all tissues, PACAP27 represented only a minor portion of total PACAP immunoreactivity.

Animals↗

PubMed1991

Distribution of vasoactive intestinal polypeptide (VIP) binding in circular muscle and characterization of VIP binding in canine small intestinal mucosa.

The present study examined the localization and characterization of [125I]vasoactive intestinal polypeptide (VIP) binding to synaptosomes and enterocyte membranes using preparations made from homogenized canine intestinal mucosa and compared it to [3H]saxitoxin binding and VIP-immunoreactive content (markers for synaptosomes). The highest [125I]VIP binding was located in the P2 fraction and was correlated with the locations of maximal [3H]saxitoxin binding and VIP-immunoreactive content. This correlation indicates that VIP receptors are present on synaptosomes of canine small intestinal mucosa. A fraction enriched in synaptosomes contained a high density of saturable VIP receptors (352 +/- 26.40 fmol/mg) having high affinity (Kd, 0.23 nM) for [125I]VIP. Studies of association and dissociation of [125I]VIP to this site revealed that binding was fully reversible and yielded a Kd value similar to that from equilibrium binding. Competition binding experiments suggested the presence of two binding sites, a high and a low affinity binding site. The order of competition potency was VIP greater than peptide histidine isoleucine greater than secretin greater than peptide histidine methionine greater than or equal to [D-Ala4]VIP greater than or equal to [Phe1]VIP greater than VIP10-28 greater than [4-Cl-D-Phe6-Leu17]VIP. All these competitors displaced all specifically bound VIP. VIP, peptide histidine isoleucine and secretin interacted differentially with each of the two binding sites. Peptide histidine methionine, [D-Ala4]VIP, [Phe1]VIP, VIP10-28 and [4-Cl-D-Phe6-Leu17]VIP interacted with a single low affinity at all binding sites. Other VIP binding sites were sought in circular muscle and submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

des-Met carboxyl-terminally modified analogues of bombesin function as potent bombesin receptor antagonists, partial agonists, or agonists.

In the present study we examined the effect of carboxyl-terminal modifications of des-Met14-bombesin (Bn) on Bn receptor affinity in murine 3T3 cells, rat and guinea pig pancreatic acini, and the ability to initiate biologic responses by synthesizing 18 des-Met14-Bn(6-13) analogues. With guinea pig acini and 3T3 cells, affinity was affected by the chain length of the alkyl moiety (R) added to [D-Phe6]Bn(6-13)NH2R with relative potencies: propyl greater than ethyl greater than butyl = hexyl greater than heptyl greater than free amide, whereas in rat acini affinity was not increased by the chain length. In each cell system the affinity of the alkylamide was not increased by insertion of a phenyl group in the alkyl side chain, by making the analogue more neuromedin B-like or by addition of a reduced peptide bond. The affinity in each cell system was increased by additions of other electron releasing groups to the COOH-terminal carboxyl group such as [D-Phe6]Bn(6-13)ethyl or methyl ester, or hydrazide. In guinea pig pancreas and 3T3 cells, 12 analogues were antagonists, 1 a full and 5 partial agonists. In rat pancreas, 8 were antagonists, 5 full agonists, and 5 partial agonists. Potent antagonists in each cell system were the methyl and ethyl ester, hydrazide, and ethylamide analogues. In 3T3 cells or guinea pig pancreas, agonist activity of the alkylamide was critically dependent on the chain length, whereas with rat pancreatic Bn receptors any alkylamide longer than the ethylamide had agonist activity. In all three cell systems any alteration that made the alkylamide more neuromedin B-like caused agonist activity. These results demonstrate that the nature of the substitution on the carboxyl terminus of des-Met14-Bn analogues is critically important, not only for determining Bn receptor affinity, but also for determining the ability to initiate a biologic response. In contrast to previous studies, the present results demonstrate that the presence of the COOH-terminal amino acid in position 14 of Bn is not essential for initiating a biologic response. Several des-Met14-Bn analogues were potent partial agonists, whereas others such as the hydrazide or ethyl ester are very potent antagonists.

Amylases↗

PubMed1990

Response of human lung tumor xenografts to treatment with a somatostatin analogue (Somatuline).

Four human small cell lung carcinomas, NCI-H69, NCI-N417, NCI-H345, LX-1, and a non-small cell lung carcinoma, H-165, implanted s.c. as tumor xenografts in athymic nude mice, were treated with Somatuline (BIM-23014C), an endocrinologically potent octapeptide analogue of somatostatin. All tumors responded, although in varying degrees, with percentage of test/control values ranging from 3 to 88. Somatuline administered as a perilesional infusion effectively inhibited xenograft growth inducing prolonged remissions. When treatment was terminated, some tumors regrew, suggesting antimitogenic activity rather than cytocidal. Absence of observable systemic or local toxicity during prolonged treatment would support this conclusion and suggest the feasibility of long term maintenance therapy with a resultant extended survival.

Aged↗

PubMed1990

Treatment of R-3327 prostate tumors with a somatostatin analogue (somatuline) as adjuvant therapy following surgical castration.

This study addresses, in an animal tumor model, the clinical problem of "escape from castration inhibition." Somatuline (BIM-23014C), an octapeptide analogue of somatostatin with enhanced potency and longer duration of biological activity was administered as a therapeutic agent, over a period of 90 and 197 days, to male Copenhagen rats bearing syngeneic Dunning R-3327-H prostate tumors. Androgen sensitivity was confirmed by the response of tumors to castration and by the significant inhibition of tumor growth in intact animals by treatment with a luteinizing hormone-releasing hormone antagonist (BIM-21009). Inhibition of tumor growth resulting from castration persisted for 102 days, after which progressive regrowth occurred, indicating an escape from castration inhibition. When Somatuline treatment was initiated as an adjuvant therapy 5 days after castration, the rate of tumor regrowth during escape was significantly retarded. During the period of 197 days postcastration, tumors in the vehicle-treated, intact controls grew to an average diameter of 38.6 +/- 7.6 mm and tumors in vehicle-treated castrate controls grew to an average diameter of 23.3 +/- 4.1 mm (60% test/control). Treatment with the luteinizing hormone-releasing hormone antagonist induced no significant additional tumor inhibitory effects in castrated animals which developed tumors having an average diameter of 30.2 +/- 8.2 mm (78% test/control). Treatment of tumors in castrate animals with Somatuline, on the other hand, induced a significant (P less than 0.01) tumor-inhibitory effect that was greater than that produced by castration alone, developing an average tumor diameter of only 14.3 +/- 2.6 mm, (37% test/control). A growth inhibitory effect was also inducible in animals having tumors that had already escaped castration inhibition. The relative nontoxicity of a somatostatin analogue such as Somatuline suggests that chronic or maintenance therapy of slow-growing prostate cancers may be both feasible and acceptable in a clinical setting.

Animals↗

PubMed1990

Presence of highly selective receptors for PACAP (pituitary adenylate cyclase activating peptide) in membranes from the rat pancreatic acinar cell line AR 4-2J.

We characterized highly selective receptors for PACAP, the pituitary adenylate cyclase activating peptide, in the tumoral acinar cell line AR 4-2J derived from the rat pancreas. PACAP, a novel hypothalamic peptide related to vasoactive intestinal peptide (VIP), was tested as the full natural 38-residue peptide (PACAP-38) and as an N-terminal amidated 27-residue derivative (PACAP-27). The binding sites showed considerable affinity for [125I]PACAP-27 (Kd = 0.4 nM) and PACAP-38, while their affinity for VIP and the parent peptide helodermin was 1000-fold lower. These receptors were coupled to adenylate cyclase, the potency of PACAP-38 and PACAP-27 (Kact = 0.2 nM) being much higher than that of VIP (Kact = 100 nM) and helodermin (Kact = 30 nM). Chemical cross-linking of [125I]PACAP-27 followed by SDS-PAGE and autoradiography revealed a specifically cross-linked peptide with an Mr of 68,000 (including 3000 for one PACAP-27 molecule).

Adenylyl Cyclases↗

PubMed1990

Desmethionine alkylamide bombesin analogues: a new class of bombesin receptor antagonists with potent antisecretory activity in pancreatic acini and antimitotic activity in Swiss 3T3 cells.

Bombesin-related peptides have a large number of physiological functions as well as having an autocrine growth mechanism for the regulation of small cell lung cancer cells. In the present study we have synthesized 21 des-Met amide or alkylamide analogues of bombesin and compared their abilities to function as bombesin receptor antagonists in guinea pig pancreatic acini and Swiss 3T3 cells with those of the previously most potent antagonist described, [Leu13 psi(CH2NH)Leu14]bombesin (analogue I). All des-Met analogues functioned as antagonists. Bn(1-13)NH2 was approximately equipotent to I (Ki = 60-80 nM) whereas Bn(6-13)NH2 was 30-fold less potent (Ki = 1800 nM). Formation of an ethylamide, Bn(6-13)ethylamide, increased the potency 30-fold such that this octapeptide was equipotent to I. The addition of a D-Phe6 moiety to I did not change potency but caused a 30-fold increase in potency of Bn(6-13)NH2 and a 8-fold increase in the potency of Bn(6-13)ethylamide (Ki = 16 nM). Additional studies of both NH2- and COOH-terminal alterations in Bn(6-13)NH2 demonstrated that the most potent antagonist was [D-Phe6]Bn(6-13)propylamide (PA), having IC50's of 1.6 nM and 0.8 nM for bombesin-stimulated amylase release and Swiss 3T3 cell growth, respectively. Detailed studies of the most potent amide analogue, [D-Phe6]Bn(6-13)NH2, and alkylamide analogue, [D-Phe6]Bn(6-13)PA, demonstrated that these analogues functioned as competitive antagonists and that their action was selective for the bombesin receptor. These results demonstrate that, as with CCK- and gastrin-related peptides, the C-terminal amino acid is important for initiating a biologic response but not essential for determining receptor affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylases↗