Small cell lung cancer bombesin receptors are antagonized by reduced peptide bond analogues

The potency of 3 reduced peptide bond analogues of bombesin (BN) was investigated using small cell lung cancer (SCLC) cell lines. (Psi13,14, Leu14)BN, (Psi9,10, Leu14)BN and (Psi12,13, Leu14)BN inhibited specific binding of 125I-GRP with IC50 values of 15, 90, and 600 nM. (Psi13,14, Leu14)BN and (Psi9,10, Leu14)BN did not elevate cytosolic Ca2+ levels but antagonized the increase in cytosolic Ca2+ caused by BN. (Psi13,14, Leu14)BN antagonized the clonal growth of SCLC cells caused by BN. These data indicate that reduced peptide bond analogues may disrupt the autocrine growth cycle of SCLC cells by functioning as BN receptor antagonists.     

Substance P analogues function as bombesin receptor antagonists and inhibit small cell lung cancer clonal growth

Human small cell lung cancer (SCLC) produces and secretes BN/GRP (bombesin/gastrin releasing peptide). Because BN stimulates the growth of SCLC cells and these cells have receptors for BN-like peptides, it is important to define agents which disrupt this self-promoting autocrine growth cycle. Here, substance P analogues were evaluated as BN receptor antagonists using SCLC cell lines. (D-Arg¹, D-Pro², D-Trp^7,9, Leu¹¹) substance P [(APTTL)SP] was one of the more potent analogues tested in inhibiting BN-like peptide receptor binding with an IC₅₀ value of 1 μM. Micromolar concentrations of (APTTL)SP antagonized BN receptor mediated elevation of cytosolic Ca²⁺ levels and decreased the colony formation in soft agarose. These data suggest that SP analogues function as SCLC BN receptor antagonists and may be useful in disrupting the autocrine growth function of BN-like peptides.     

Des-Met14]bombesin analogues function as small cell lung cancer bombesin receptor antagonists.

A series of bombesin (BN) analogues lacking the C-terminal methionine at the 14 position were evaluated as BN receptor antagonists. [D-Phe6]BN(6-13)amide inhibited specific 125I-GRP binding to lung cancer cell line NCI-H720 with an IC50 value of 12 nM. In contrast, [D-Phe6]BN(6-13)propylamide, butylamide and methylester were more potent with IC50 values of 3, 5 and 5 nM whereas [D-Phe6,Sta13]BN(6-13)amide was less potent with an IC50 value of 180 nM. [D-Phe6]BN(6-13)propylamide antagonized the ability of BN to elevate cytosolic Ca2+, whereas [D-Phe6]BN(6-13)butylamide was a partial agonist. In a small cell lung cancer (SCLC) growth assay, [D-Phe6]BN(6-13)propylamide inhibited colony formation. In summary, BN analogues which lack a C-terminal methionine may function as useful SCLC BN receptor antagonists.     

BW1023U90: A new GRP receptor antagonist for small-cell lung cancer cells

Gastrin-releasing peptide (GRP) receptor antagonists were synthesized and their ability to interact with small-cell lung cancer (SCLC) cells determined. [¹²⁵I]BW1023U90, bound with high affinity (K_d = 2 nM) to a single class of sites (Bmax = 55 fmol/mg protein) using SCLC cell line NCI-H345. [¹²⁵I]BW1023U90 binding was time dependent and reversible even at 37°C as the ligand was minimally internalized. Specific [¹²⁵I]BW1023U90 binding was inhibited with high affinity by GRP as well as bombesin (BB) but not neuromedin B (NMB). BW1023U90 inhibited the ability of BB to elevate cytosolic Ca²⁺ and increase the growth of SCLC cells. A BW1023U90 analogue, BW2258U89 (10 μg/day, SC) slowed SCLC xenograft formation in nude mice and [¹²⁵I]BW1023U90 localized to SCLC tumors 1 h after injection into nude mice. BW2258U89 (4% by weight) was placed in microspheres and slowly released over a 3-week period in nude mice bearing SCLC xenografts. The microspheres containing BW2258U89 strongly inhibited SCLC growth in vivo. A radioimmunoassay was developed for the GRP receptor antagonists and the rabbit antiserum cross-reacted totally with BW2258U89 or BW1023U90. BW2258U89 immunoreactivity (5 nM) was detected in the plasma of nude mice containing the microspheres after 1 week. These data suggest that GRP receptor antagonists bind to receptors on SCLC tumors.     

Two bombesin analogues discriminate between neuromedin B- and bombesin-induced calcium flux in a lung cancer cell line

We examined the profile of two bombesin (BN) antagonists, (CH₃)₂CHCO-His-Trp-Ala-Val- -Ala-His-Leu-NHCH₃] (ICI 216140) and [ -Phe⁶,des-Met¹⁴]BN(6–14)ethylamide (DPDM-BN EA), against neuromedin B-induced Ca²⁺ mobilization in the small cell lung cancer (SCLC) line NCI-H345. Neuromedin B (NMB), a BN-like peptide sharing sequence homology with ranatensin, elicited a concentration-dependent Ca²⁺ release (in part) from intracellular stores. Sequential addition of NMB attenuated Ca²⁺ mobilization. Desensitization occurred between BN and NMB; depletion of intracellular Ca²⁺ is a likely mechanism because thapsigargin stimulated Ca²⁺ release after a maximally desensitizing dose of NMB. ICI 216140 and DPDM-BN EA competitively inhibited BN-induced Ca²⁺ transients. In contrast, these compounds antagonized NMB-stimulated Ca²⁺ transients in a noncompetitive manner. The pharmacological profiles obtained support receptor heterogeneity for BN-like peptides on this SCLC line, underscoring the need for thorough examination of dose-response relationships when investigating effects of BN analogues on intact cells.     

N-isobutyryl-His-Trp-Ala-Val-D-Ala-His-Leu-NHMe (ICI 216140) a potent in vivo antaconist analogue of bombesin/gastrin releasing peptide (BN/GRP) derived from the C-terminal sequence lacking the final methionine residue

The GRP receptor mediated growth response in Swiss 3T3 cells has been used to identify BN/GRP antagonists. Analysis of bombesin antagonism by substance P analogues and by truncated GRP analogues revealed that deletion of the C-terminal methionine residue was important for antagonism. Des-Met analogues showing potent antagonist activity in the in vitro 3T3 system (IC50 approximately 2nM) were synthesized. Further structural modification of these peptides led to the identification of (CH3)2CHCO-His-Trp-Ala-Val-D-Ala-His-Leu-NHCH3 (ICI 216140) which reduced bombesin-stimulated rat pancreatic amylase secretion to basal levels when administered subcutaneously at 2.0 mg per kg.     

The TIPP opioid peptide family: development of delta antagonists, delta agonists, and mixed mu agonist/delta antagonists

The discovery of the prototype delta opioid antagonists TIPP (H-Tyr-Tic-Phe-Phe-OH) and TIP (H-Tyr-Tic-Phe-OH) in 1992 was followed by extensive structure-activity relationship studies, leading to the development of analogues that are of interest as pharmacological tools or as potential therapeutic agents. Stable TIPP-derived delta opioid antagonists with subnanomolar delta receptor binding affinity and extraordinary delta receptor selectivity include TIPP[Psi] (H-Tyr-TicPsi[CH(2)NH]Phe-Phe-OH] and TICP[Psi] (H-Tyr-TicPsi[CH(2)NH]Cha-Phe-OH); Cha: cyclohexylalanine), which are widely used in opioid research. Theoretical conformational analyses in conjunction with the pharmacological characterization of conformationally constrained TIPP analogues led to a definitive model of the receptor-bound conformation of H-Tyr-Tic-(Phe-Phe)-OH-related delta opioid antagonists, which is characterized by all-trans peptide bonds. Further structure-activity studies revealed that the delta antagonist vs delta agonist behavior of TIP(P)-derived compounds depended on very subtle structural differences in diverse locations of the molecule and suggested a delta receptor model involving a number of different inactive receptor conformations. A further outcome of these studies was the identification of a new class of potent and very selective dipeptide delta agonists of the general formula H-Tyr-Tic-NH-X (X = arylalkyl), which are of interest for drug development because of their low molecular weight and lipophilic character. Most interestingly, TIPP analogues containing a C-terminal carboxamide group displayed a mixed mu agonist/delta antagonist profile, and thus were expected to be analgesics with a low propensity to produce tolerance and physical dependence. This turned out to be the case with the TIPP-derived mu agonist/delta antagonist DIPP-NH(2)[Psi] (H-Dmt-TicPsi[CH(2)NH]Phe-Phe-NH(2)); Dmt: 2',6'- dimethyltyrosine).     

Comparison of prolonged in vivo inhibitory activity of several potent bombesin (BN) antagonists on BN-stimulated amylase secretion in the rat.

New BN analogues designed to be competitive receptor antagonists at the BN/gastrin releasing peptide receptor(s) can exhibit diverse properties ranging from full antagonist, partial agonist or weak agonist activity, depending on the assay system and animal species employed. Here we evaluate the following 3 antagonists which have the most potent receptor affinities in several in vitro assay systems and are representative of 3 main classes of BN antagonists for their in vivo effects on pancreatic amylase secretion in the rat: [D-Cpa6,Phe14,psi 13-14]BN(6-14), [D-Phe6]BN(6-13) propylamide, and [D-Phe6]BN(6-13) methyl ester. After injection in the rat, the methyl ester was clearly the most potent antagonist and completely inhibited BN-stimulated amylase release at the 20 nmol/kg (IV bolus) for about 2 h. In contrast, the propylamide analogue at the 200 nmol/kg (IV bolus) dose produced incomplete inhibition of amylase release. Inhibition was transient and lasted for only about 1 h, possibly reflecting the significant agonist activity of this latter peptide in the rat pancreatic amylase secretion test in vitro. The psi-analogue, while being the longest acting analogue, was also incapable of lowering amylase to basal level at 50 times the BN dose, suggesting that it is a mixed agonist-antagonist in vivo as was also previously shown in vitro in the rat.     

High affinity receptors for bombesin/GRP-like peptides on human small cell lung cancer

The binding of a radiolabeled bombesin analogue to human small cell lung cancer (SCLC) cell lines was investigated. (125I-Tyr4)bombesin bound with high affinity (Kd = 0.5 nM) to a single class of sites (2,000/cell) using SCLC line NCI-H446. Binding was reversible, saturable and specific. The pharmacology of binding was investigated using NCI-H466 and SCLC line NCI-H345. Bombesin and structurally related peptides, such as gastrin releasing peptide (GRP), but not other peptides, such as substance P or vasopressin, inhibited high affinity (125I-Tyr4)BN binding activity. Finally, the putative receptor, a 78,000 dalton polypeptide, was identified by purifying radiolabeled cell lysates on bombesin or GRP affinity resins and then displaying the bound polypeptides on sodium dodecylsulfate polyacrylamide gels. Because SCLC both produces bombesin/GRP-like peptides and contains high affinity receptors for these peptides, they may function as important autocrine regulatory factors for human SCLC.     

Gastrin-releasing peptide and cancer

Over the past 20 years, abundant evidence has been collected to suggest that gastrin-releasing peptide (GRP) and its receptors play an important role in the development of a variety of cancers. In fact, the detection of GRP and the GRP receptor in small cell lung carcinoma (SCLC), and the demonstration that anti-GRP antibodies inhibited proliferation in SCLC cell lines, established GRP as the prototypical autocrine growth factor. All forms of GRP are generated by processing of a 125-amino acid prohormone; recent studies indicate that C-terminal amidation of GRP18-27 is not essential for bioactivity, and that peptides derived from residues 31 to 125 of the prohormone are present in normal tissue and in tumors. GRP receptors can be divided into four classes, all of which belong to the 7 transmembrane domain family and bind GRP and/or GRP analogues with affinities in the nM range. Over-expression of GRP and its receptors has been demonstrated at both the mRNA and protein level in many types of tumors including lung, prostate, breast, stomach, pancreas and colon. GRP has also been shown to act as a potent mitogen for cancer cells of diverse origin both in vitro and in animal models of carcinogenesis. Other actions of GRP relevant to carcinogenesis include effects on morphogenesis, angiogenesis, cell migration and cell adhesion. Future prospects for the use of radiolabelled and cytotoxic GRP analogues and antagonists for cancer diagnosis and therapy appear promising.     

Synthesis of peptide and pseudopeptide amides inhibiting the proliferation of small cell and epithelial types of lung carcinoma cells

Small cell lung cancer (SCLC) cell lines produce and secrete various peptide hormones, e.g. bombesin (BN)/gastrin releasing peptide (GRP) like peptides that are proposed to function as their autocrine growth factors. To inhibit the proliferative effect of these hormones we have synthesized short chain BN[7-14]-analogues replacing the C-terminal peptide bond by a methylene-amino (-CH₂NH-) unit and introducing d -Phe or d -Ser into position 12. As several substance P (SP) analogues were found to inhibit the growth of SCLC cells, some short chain SP-analogues have been synthesized. (Pseudo)octapeptides were synthesized in solution, by fragment condensation using the DCC/HOPfp method. Fragments and SP-analogues were synthesized stepwise using pentafluorophenyl esters. The resistance to hydrolysis of the reduced peptide bond made permitted exact quantification of the Leuψ(CH₂NH)Leu pseudopeptide in hydrolysates. The binding ability of both types of peptides to BN-receptors on Swiss 3T3 mouse fibroblast cells and their antiproliferative effect on NCI-H69 human SCLC cell line have been tested and compared with a short chain SP-antagonist pHOPA-d -Trp-Phe-d -Trp-Leu-Leu-NH₂ ( R ) previously described as a potent inhibitor of SCLC proliferation. While BN-analogues showed weak activity in inhibition of proliferation of SCLC cells, SP-analogues 6 : d -MePhe-d-T rp-Phe-d -Trp-Leuψ(CH₂NH)-Leu-NH₂ and 7 : d -MePhe-d -Trp-Phe-d -Trp-Leu-MPA, in spite of greatly diminished affinity towards the BN-receptor, inhibited SCLC proliferation more effectively than R ( 6 : IC₅₀=2 μm , 7 : IC₅₀=5 μm and R : IC₅₀=10 μm ). Moreover, 6 inhibited the respiratory activity of SK-MES 1 epithelial type of lung carcinoma cells in proliferating but not in the quiescent state, suggesting that the antiproliferative effect of these compounds is not due to simple cytotoxicity. These short chain analogues of SP might be promising candidates as therapeutic agents in the treatment of SCLC. © 1998 European Peptide Society and John Wiley & Sons, Ltd.     

A new high affinity technetium-99m-bombesin analogue with low abdominal accumulation

99mTc-labeled bombesin analogues have shown promise for noninvasive detection of many tumors that express bombesin (BN)/gastrin-releasing peptide (GRP) receptors. 99mTc-labeled peptides, however, have a tendency to accumulate in the liver and intestines due to hepatobiliary clearance as a result of the lipophilicity of the 99mTc chelates. This makes the imaging of lesions in the abdominal area difficult. In this study, we have synthesized a new high affinity 99mTc-labeled BN analogue, [DTPA1, Lys3(99mTc-Pm-DADT), Tyr4]BN, having a built-in pharmacokinetic modifier, DTPA, and labeled with 99mTc using a hydrophilic diaminedithiol chelator (Pm-DADT) to effect low hepatobiliary clearance. In vitro binding studies using human prostate cancer PC-3 cell membranes showed that the inhibition constant (Ki) for [DTPA1, Lys3(99Tc-Pm-DADT), Tyr4]BN was 4.1 +/- 1.4 nM. Biodistribution studies of [DTPA1, Lys3(99mTc-Pm-DADT), Tyr4]BN in normal mice showed very low accumulation of radioactivity in the liver and intestines (1.32 +/- 0.13 and 4.58 +/- 0.50% ID, 4 h postinjection, respectively). There was significant uptake (7.71 +/- 1.37% ID/g, 1 h postinjection) in the pancreas which expresses BN/GRP receptors. The uptake in the pancreas could be blocked by BN, partially blocked by neuromedin B, but not affected by somatostatin, indicating that the in vivo binding was BN/GRP receptor specific. Scintigraphic images showed specific, high contrast delineation of prostate cancer PC-3 xenografts in SCID mice. Thus, the new peptide has a great potential for imaging BN/GRP receptor-positive cancers located even in the abdomen.     

Internalization and degradation of peptides of the bombesin family in Swiss 3T3 cells occurs without ligand-induced receptor down-regulation.

The binding of [125I]gastrin releasing peptide ([125I]GRP) to Swiss 3T3 cells at 37 degrees C increases rapidly, reaching a maximum after 30 min and decreasing afterwards. The decrease in cell-associated radioactivity at this temperature is accompanied by extensive degradation of the labelled peptide. At 4 degrees C equilibrium binding is achieved after 6 h and [125I]GRP degradation is markedly inhibited. Extraction of surface-bound ligand at low pH demonstrates that the iodinated peptide is internalized within minutes after addition to 3T3 cells at 37 degrees C. The rate of internalization is strikingly temperature-dependent and is virtually abolished at 4 degrees C. In addition, lysomotropic agents including chloroquine increase the cell-associated radioactivity in cells incubated with [125I]GRP. The binding of [125I]GRP to Swiss 3T3 cells was not affected by pretreatment for up to 24 h with either GRP or bombesin at mitogenic concentrations. Furthermore, pretreatment with GRP did not reduce the affinity labelling of a Mr 75,000-85,000 surface protein recently identified as a putative receptor for bombesin-like peptides. These results demonstrate that while peptides of the bombesin family are rapidly internalized and degraded by Swiss 3T3 cells, the cell surface receptors for these molecules are not down-regulated.     

The bombesin/gastrin releasing peptide receptor antagonist RC-3095 blocks apomorphine but not MK-801-induced stereotypy in mice

Bombesin (BN)-like peptides might be involved in the pathogenesis of neuropsychiatric disorders such as schizophrenia. Stereotyped behaviors induced by the dopamine receptor agonist apomorphine or the N-methyl-D-aspartate glutamate receptor antagonist dizocilpine (MK-801) in rodents have been proposed as animal models of schizophrenic psychosis. In the present study we evaluated the effects of the BN/gastrin-releasing peptide receptor (GRP) antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) on apomorphine and MK-801-induced stereotyped behavior in mice. An intraperitoneal (i.p.) injection of RC-3095 (1.0, 10.0 or 100.0 mg/kg) blocked apomorphine-induced stereotypy. The inhibitory effect of RC-3095 on apomorhine-induced stereotypy was similar to that induced by haloperidol (0.5 mg/kg). RC-3095 did not affect stereotyped behavior induced by MK-801 (0.5 mg/kg). The results provide the first evidence that BN/GRP receptor antagonism blocks stereotyped behavior induced by a dopamine agonist. Together with previous evidence, the present study indicates that the BN/GRP receptor can be considered a drug target in the investigation of potential new agents for treating neuropsychiatric disorders.     

A structure function study of C-terminal extensions of bombesin.

Synthetic C-terminal extensions of BN were synthesized and the biological potency evaluated using Swiss 3T3 and small cell lung cancer cells. BN, which has an amidated C-terminal, inhibited specific [125I-Tyr4]BN binding activity to Swiss 3T3 cells with an IC50 value of 1 nM, whereas the IC50 of BN-OH, which has a free C-terminal, was 1800 nM. The IC50 values of BNG, BNGK and BNGKK were 1400, 4700 and 500 nM, respectively. Similar binding data were obtained using SCLC cell line NCI-H345 and the bombesin analogues functioned as agonists based on the ability to elevate cytosolic Ca2+ in Fura-2 AM loaded SCLC cells. Also, the bombesin analogues stimulated 3H-thymidine uptake in Swiss 3T3 cells and the ED50 values for BN, BNG, BNGK and BNGKK were 1, 1300, 3900 and 400 nM. These data suggest that an amidated C-terminal is essential for high affinity binding and potency of BN.     

The specific binding of the platelet-activating factor (PAF) receptor antagonist WEB 2086 and the benzodiazepine flunitrazepam to rat hepatocytes

Thieno-triazolodiazepines WEB 2086 and BN 50739 have been described as the potent PAF receptor antagonists. Binding of radiolabeled [³H]WEB 2086 has been widely employed to characterize PAF receptors in different cells. In a search for a PAF receptor in isolated rat hepatocytes, we discovered that the binding of [³H]WEB to rat hepatocytes was highly specific but had a relatively low affinity with a K_d of 113 nM and B_max of 0.65 pmol/10⁶ cells in freshly isolated cell suspension and K_d of 1.65 μM and B_max of 2.0 pmol/plate in cultured hepatocytes. No consistent specific binding of [³H]PAF itself was found in the same cell preparations. The binding of [³H]flunitrazepam in the presence of the peripheral type of benzodiazepine receptor antagonist Ro 5-4864 was saturated and exhibited a K_i of 3.8 nM and B_max of 3.5 pmol/plate. The central type of benzodiazepine receptor antagonist clonazepam also competed for the [³H]flunitrazepam binding, however with a much lower affinity. Various antagonists inhibited the binding of [³H]WEB 2086 with a rank order BN 50739⪢Ro 5-4864≥clonazepam. Interestingly, bicuculline, a specific antagonist of GABA(A) recognition sites, also significantly reduced the binding of [³H]WEB 2086. The binding of [³H]flunitrazepam was inhibited with a rank potency BN 50739⪢WEB 2086. Taken together, these findings suggest that the specific binding of PAF receptor antagonists WEB 2086 and BN 50739 in rat hepatocytes does not involve PAF receptors and occurs via peripheral benzodiazepine and, possibly GABA(A) receptor sites.     

Bombesin-like peptides and associated receptors within the brain: distribution and behavioral implications

As we commemorate the 25th anniversary of the journal Peptides, it is timely to review the functional significance of the bombesin (BB)-like peptides and receptors in the CNS. Over two decades ago we published an article in the journal Peptides demonstrating that BB-like peptides are present in high densities in certain rat brain regions (such as the paraventricular nucleus of the hypothalamus). Subsequently, one of the mammalian forms of BB, gastrin-releasing peptide (GRP) containing cell bodies were found in the suprachiasmatic nucleus of the hypothalamus and nucleus of the solitary tract of the hindbrain. Another related peptide, namely neuromedin (NM)B, was detected in the olfactory bulb and dentate gyrus. BB and GRP bind with high affinity to BB(2) receptors, whereas NMB binds with high affinity to BB(1) receptors. The actions of BB or GRP are blocked by BB(2) receptor antagonists such as (Psi(13,14)-Leu(14))BB whereas PD168368 is a BB(1) receptor antagonist. Exogenous administration of BB into the rat brain causes hypothermia, hyperglycemia, grooming and satiety. BB-like peptides activate the sympathetic nervous system and appear to modulate stress, fear and anxiety responses. GRP and NMB modulate distinct biological processes through discrete brain regions or circuits, and globally these peptidergic systems may serve in an integrative or homeostatic function.     

Modulation of bombesin-induced phosphatidylinositol hydrolysis in a small-cell lung-cancer cell line.

Bombesin is an amphibian tetradecapeptide whose mammalian homologue, gastrin-releasing peptide (GRP), is produced by many small-cell lung-cancer (SCLC) cells, and which can function in an autocrine growth-promoting manner in SCLC. Studies reported here show that [Tyr4]bombesin and its congeners increase inositol 1,4,5-trisphosphate within seconds in NCI-H345, a SCLC cell line that constitutively produces GRP. After 30 min in the presence of 0.01 M-Li+ and [Tyr4]bombesin, there is marked accumulation of inositol monophosphates and inositol tetrakisphosphate. Pretreatment with phorbol 12-myristate 13-acetate (PMA) for 20 min inhibited the ability of [Tyr4]bombesin to induce phosphatidylinositol (PtdIns) turnover and to increase intracellular free Ca2+ ([Ca2+]i). Pretreatment with PMA for 48 h attenuated the ability of subsequently added PMA to decrease the response to [Tyr4]bombesin. Pretreatment with pertussis toxin (PT; 1 microgram/ml for 18-24 h) decreased by less than 30% [Tyr4]bombesin-induced increases in [Ca2+]i and PtdIns metabolites. However, interpretation of this result is complicated by the inability of PT to ADP-ribosylate completely its substrates in intact NCI-H345 cells. In contrast, pretreatment with cholera toxin (1 microgram/ml for 18-24 h) lowered basal [Ca2+]i and basal inositol phosphate concentrations, attenuated the response of NCI-H345 to subsequently added [Tyr4]bombesin, and was not mimicked by treatments that increase cellular cyclic AMP. These data demonstrate the activation of phospholipase C in SCLC by bombesin congeners. In addition, the results suggest a regulatory role for protein kinase C, a cholera-toxin substrate, and perhaps a pertussis-toxin substrate in the response of SCLC to bombesin.     

Octapeptide analogues of somatostatin inhibit the clonal growth and vasoactive intestinal peptide-stimulated cyclic AMP formation in human small cell lung cancer cells.

Two endocrinologically active octapeptide analogues (BIM-23014 C and BIM-23034) of somatostatin (SRIF) containing either an N- or C-terminal 3-(2-naphthyl)-D-Ala residue were examined for their ability to inhibit the in vitro receptor binding, clonal growth, and vasoactive intestinal peptide (VIP)-stimulated cyclic AMP formation in human small cell lung cancer cell (SCLC) line NCI-H345. Both SRIF peptides inhibited [125I]SRIF(Tyr11)-14 binding with IC50 values in the low nM range. Colony formation in the in vitro SCLC growth assay was also inhibited in the same concentration range, as was VIP-stimulated cyclic AMP formation. Therefore, octapeptide analogues of SRIF function as SCLC SRIF receptor agonists.