New short-chain analogs of a substance-P antagonist inhibit proliferation of human small-cell lung-cancer cells in vitro and in vivo

Pentapeptides for the treatment of small cell lung cancer: Optimisation by Nind-alkyl modification of the tryptophan side chain

The pentapeptide, tert-Prenyl^4th-NH₂ (DMePhe-DTrp-Phe-DTrp(N-tert-prenyl)-Leu-NH₂), has recently been reported by our group to exhibit properties of substance P (SP) antagonist G against small cell lung cancer (SCLC). In this study, we undertook a systematic structure activity investigation to optimise this lead compound to improve its in vitro anti-tumour activity and biocompatibility. A series of d-tryptophan (D-Trp) derivatives were synthesised, with a range of aliphatic N-alkyl chains (methyl to pentyl) on the indole nitrogen (N^ind). These were incorporated into the pentapeptide sequence by substitution of the N^ind-tert-prenylated D-Trp 4th residue with the N^ind-alkylated D-Trp derivatives. These pentapeptides were significantly more potent than tert-Prenyl^4th-NH₂, with the N^ind-butyl modification generating the most cytotoxic peptides. Compared to tert-Prenyl^4th-NH₂, a single butyl modification on the 4th D-Trp residue (Butyl^4th-NH₂) showed a ∼3 fold enhancement in cytotoxicity in either the chemo-naive H69 or the DMS79 (originating from a patient treated with chemotherapeutics and radiation therapy) SCLC cell lines. In addition, the di-butylated sequence on the 2nd and 4th D-Trp residues (Butyl^2nd,4th-NH₂) gave ∼4.5 times higher cytotoxicity against the H69 cell line and a ∼2 fold increase against the DMS79 cell line, compared to tert-Prenyl^4th-NH₂. The favoured position for butyl modification was the 4th D-Trp residue, as the Butyl^2nd-NH₂ peptide gave lower cytotoxicity on both cell lines. Butylated peptide sequences, when exposed to neat mouse plasma for 24 h at 37 °C, were found to resist degradation with >80% remaining intact compared to ∼58% for tert-Prenyl^4th-NH₂. The degradation pathway in plasma occurs via de-amidation of the C-terminus, confirmed by mass spectrometry and RP-HPLC analysis. The butyl modification also conferred resistance to metabolism when tested using S9 liver fraction from mouse. The optimum analogue responsive against the DMS79 cell line was the Butyl^4th-NH₂ pentapeptide, which revealed a concentration dependent increase in apoptosis: the level of late apoptotic cells rose from ∼36% at 2 μM to ∼96% at 6 μM, as determined by flow cytometry, compared to the unmodified peptide that showed no such effect. Concluding, the butyl substitutions offered the best perspective for high cytotoxicity, induction of apoptosis and metabolic compatibility thereby comprising an improved broad spectrum SP antagonist candidate for treatment of SCLC.

N-tert-Prenylation of the indole ring improves the cytotoxicity of a short antagonist G analogue against small cell lung cancer

Natural prenylated indoles have been proposed as potential anticancer agents. To exploit this discovery for developing new peptide therapeutics, we report the first studies whereby incorporation of prenylated indoles into primary sequences has been achieved. We developed a route to synthesise Nα-Fmoc-protected tryptophan derivatives in which the prenyl group is linked to the N-indole core, using Pd(ii)-mediated C-H functionalisation of 2-methyl-2-butene. Based on the Substance P antagonist G (SPG), a well-known Small Cell Lung Cancer (SCLC) anticancer agent, we designed a new penta-peptide sequence to include a prenyl moiety on one of the tryptophan residues. The N-tert-prenylated tryptophan analogue was assembled into the pentameric peptide using standard solid phase peptide synthesis or liquid phase synthesis by fragment coupling. In vitro screening showed that the N-tert-prenylation of the indole ring on the tryptophan residue located near the C-terminal of the penta-peptide enhanced the cytotoxicity against H69 (IC50 = 2.84 ± 0.14 μM) and DMS79 (IC50 = 4.37 ± 0.44 μM) SCLC cell lines when compared with the unmodified penta-peptide (H69, IC50 = 30.74 ± 0.30 μM and DMS79, IC50 = 23.00 ± 2.07 μM) or the parent SPG sequence (IC50 > 30 μM, both cell lines). SCLC almost invariably relapses with therapy-resistant disease. The DMS79 cell line was established from a patient following treatment with a number of chemotherapeutics (cytoxan, vincristine and methotrexate) and radiation therapy. Treating DMS79 tumour-bearing nude mice provided a human xenograft model of drug resistance to test the efficacy of the prenylated peptide. A low dose (1.5 mg kg-1) of the prenylated peptide was found to reduce tumour growth by ∼30% (P < 0.05) at day 7, relative to the control group receiving vehicle only. We conclude that the availability of the Fmoc-Trp(N-tert-prenyl)-OH amino acid facilitates the synthesis of prenylated-tryptophan-containing peptides to explore their therapeutic potential.

Novel nontoxic heat shock protein 90 inhibitors having selective antiproliferative effect

Almost all heat shock protein 90 inhibitors reported so far, which are natural product derivatives, have problems mainly with toxic side effects, and with bioavailability and solubility. In our earlier studies, we compared the steric conformational structures of substance P[6-11] with our substance P antagonists in silico, and used the diverse biological effects of these compounds as tools in our modeling and design studies for discovering antiproliferative drugs. Here, we present a new synthesized short peptide-derivative compound family that inhibits only the function of the tumor cell's heat shock protein 90 and selectively kills in vitro more cancer cells than normal cells. During the lead generation, we observed that the difference between the most effective inhibitors was only one residue or group that caused diverse effects in vitro on the studied cell lines. According to our in vivo experiments on nude mice bearing lung cancer xenografts, the inhibitors restrained tumor growth, but not caused overt toxicity. We undertook NMR spectroscopy studies to analyze the 3D molecular structural differences of our inhibitors that control their binding to the target molecule. In conclusion, we demonstrated the efficacy of new selective and small molecule anticancerogen heat shock protein 90 inhibitors with peptide nature, without in vivo toxicity on nude mouse xenograft model. Our results also shed light on the mechanism of anticancerogen action of some substance P antagonists and their derivatives.

Role of NK-1 and NK-2 tachykinin receptor antagonism on the growth of human breast carcinoma cell line MDA-MB-231

We demonstrate that neurokinin A (NKA) and substance P (SP) play a role in the proliferation of the estrogen receptor-negative (ER-) cell line MDA-MB-231, a human breast carcinoma expressing both NK-1 and NK-2 receptors. In vitro experiments showed that the specific receptor antagonists MEN 11,467 (NK-1) and nepadutant (MEN 11,420; NK-2) inhibited tumor cell proliferation, and blocked the stimulatory effect of SP and NKA. Anti-tumoral activity of NK-1 and NK-2 receptor antagonists was demonstrated in nude mice, measuring growth inhibition of MDA-MB-231 tumor cells xenografted s.c. and by using the hollow-fiber assay. In both systems a significant inhibition was found when compounds were administered at 5 mg/kg i.v. every day for 2 weeks. Results obtained from both these models suggest that the in vivo activity of NK-1 and NK-2 antagonists may be a result of a cytostatic effect rather than a cytotoxic effect. Our results suggest that the control of breast carcinoma (ER-) growth by tachykinin receptor antagonists may become a new form of targeted therapy for these human tumors.

Comparative study of SP[6-11] and its analogs using simulated annealing

In this study we compared the steric structures of the bioactive part of substance P (SP[6-11]) and its analogs (NY3460 and pHOPA-SP5). The molecular dynamics-simulated annealing method was used to explore the conformational space, and the structural differences and similarities of these molecules were identified. For the three peptides, the conformational distributions were represented in Ramachandran density plots. The occurring secondary structural elements of the investigated molecules were identified, namely alpha-Helix, type III beta-Turn, gamma-Turn, and inverse gamma-Turn. For SP[6-11] and its two analogs, different intramolecular interactions (H-bonds between the main-chain atoms, aromatic-aromatic interactions, and amino-aromatic interactions) that can stabilize the various conformations of the three peptides were investigated. Detailed examination of these intramolecular interactions revealed that H-bonds between the main-chain atoms are relevant in the determination and stabilization of the conformer structures of the peptides, while the aromatic-aromatic interactions do not play an important stabilizing role. Furthermore, in the conformers of NY3460 and pHOPA-SP5, different types of amino-aromatic interactions were identified that contribute to the formation of the various structures of these peptides. For all three molecules, the orientations of the side chains were investigated and the rotamer populations were determined.

Substance-P-mediated immunomodulation of tumor growth in a murine model

BACKGROUND/OBJECTIVE

Substance P (SP) has been reported to have immunoregulatory properties including effects on many of the mediators involved in anti-tumor immunity. In this study, we investigated the effect of SP on tumor development in a murine model of melanoma. In addition, we examined the role of natural killer (NK) and T cells in SP-mediated modulation of tumor growth.

MATERIALS AND METHODS

Mice were implanted with mini-osmotic pumps that delivered a continuous infusion of either SP or PBS over a 14-day period. Five days following implantation, animals received K1735 melanoma cells and tumor growth was monitored. The role of NK and T cells in SP-mediated protection was examined by antibody depletion studies. To determine if cells from SP-treated animals could delay tumor growth in animals in the absence of exogenous SP infusion, splenocytes from mice treated with SP were adoptively transferred into SCID mice.

RESULTS

In vivoSP treatment led to a significant delay in tumor growth. When animals were depleted of NK or T cells, this protective effect was lost. Adoptive transfer of cells from SP-treated animals led to a significant protective effect on tumor growth in SCID mice.

CONCLUSION

Pretreatment of mice with SP provides protection against K1735 tumor growth, and this protection requires both T cells and NK cells. SP-mediated tumor protection can be transferred by the adoptive transfer of cells from SP-treated animals into animals that do not receive exogenous SP. These studies suggest a model in which in vivo SP treatment prior to tumor challenge primes immune mediators to prevent or delay tumor establishment.

Receptor Imaging in Oncology by Means of Nuclear Medicine: Current Status

To date, our understanding of the role of receptors and their cognate ligands in cancer is being successfully translated into the design and development of an arsenal of new, less toxic, and more specific anticancer drugs. Because most of these novel drugs are cytostatic, objective response as measured by morphologic imaging modalities (eg, computed tomography or magnetic resonance imaging) cannot be used as a surrogate marker for drug development or for clinical decision making. Positron emission tomography (PET) can be used to image and quantify the in vivo distribution of positron-emitting radioisotopes such as oxygen-15, carbon-11, and fluorine-18 that can be substituted or added into biologically relevant and specific receptor radioligands. Similarly, single-photon emission computed tomography (SPECT) can be used to image and quantify the in vivo distribution of receptor targeting compounds labeled with indium-111, technetium-99m, and iodine-123. By virtue of their whole-body imaging capacity and the absence of errors of sampling and tissue manipulation as well as preparation, both techniques have the potential to address locoregional receptor status noninvasively and repetitively. This article reviews available data on the in vivo evaluation of receptor systems by means of PET or SPECT for identifying and monitoring patients with sufficient receptor overexpression for tailored therapeutic interventions, and also for depicting tumor tissue and determining the currently largely unknown heterogeneity in receptor expression among different tumor lesions within and between patients.

Peptides with anticancer use or potential

This review is an attempt to illustrate the diversity of peptides reported for a potential or an established use in cancer therapy. With 612 references, this work aims at covering the patents and publications up to year 2000 with many inroads in years 2001-2002. The peptides are classed according to four categories of effective (or plausible) biological mechanisms of action: receptor-interacting compounds; inhibitors of protein-protein interaction; enzymes inhibitors; nucleic acid-interacting compounds. The fifth group is made of the peptides for which no mechanism of action has been found yet. Incidentally this work provides an overview of many of the modern targets of anticancer research.

Novel targets for lung cancer therapy: part I

Lung cancer is the second most common form of cancer in the United States, and although it accounts for 15% of all cancers, it is the most lethal, accounting for approximately 28% of cancer deaths. In 2002, it is estimated that 177,000 new cases of lung cancer will be diagnosed in the United States, and an estimated 160,000 men and women will die from the disease. This mortality rate is greater than that attributable to colorectal, breast, and prostate cancer combined. Systemic treatments for lung cancer with standard chemotherapy agents are still relatively ineffective. Agents targeting novel proliferative and survival pathways in lung cancer are needed to improve treatment outcomes. In recent years, numerous agents inhibiting aberrant processes in tumor cells have undergone clinical evaluation. This review is the first of a two-part series that summarizes pertinent preclinical and clinical information on novel drugs that target critical abnormalities in lung cancer. In this article, agents inhibiting growth factor receptors and various molecules downstream of activated signaling cascades, such as cytoplasmic second messengers, are described.

Therapeutic advances in small cell lung cancer

Small cell lung cancer (SCLC) is characterised by neuroendocrine differentiation, early metastatic potential and initial responsiveness to cytotoxic therapy. Unfortunately, despite recent therapeutic advances, most patients relapse and the overall five-year survival rate is only 5%. Standard treatment of SCLC consists of platinum-based combination chemotherapy, with thoracic irradiation added for patients with limited-stage disease. Several newer chemotherapeutic drugs have recently been shown to have significant activity in patients with untreated or relapsed SCLC. These agents include: the topoisomerase I inhibitors, topotecan and irinotecan; the taxanes, paclitaxel and docetaxel; the pyrimidine analogue, gemcitabine; and the vinca alkaloid, vinorelbine. Recent advances in our understanding of the molecular events involved in the pathogenesis and progression of SCLC have led to the identification of a variety of potential targets for novel therapeutic interventions. Strategies aimed at inhibiting the myriad of growth factor pathways that control the proliferation of SCLC cells, include: broad spectrum neuropeptide antagonists (e.g., substance P analogues); growth factor/receptor-specific inhibitors (e.g., anti-GRP monoclonal antibodies, bradykinin antagonist dimers); and a variety of selective protein kinase inhibitors. The importance of cell death pathways in carcinogenesis and treatment-resistance has led to several novel strategies targeting apoptotic mediators, such as bcl-2, that are frequently dysregulated in SCLC (e.g., bcl-2 antisense). Our current challenges are to further refine these promising therapeutic strategies, efficiently evaluate their activity in the clinical setting and integrate them into more effective treatment regimens to improve the overall prognosis of patients with SCLC.

Targeted cytotoxic analogue of bombesin/gastrin-releasing peptide inhibits the growth of H-69 human small-cell lung carcinoma in nude mice

Recently, we developed a powerful cytotoxic analogue of bombesin AN-215, in which the bombesin-like carrier peptide Gln-Trp-Ala-Val-Gly-His-Leu-psi(CH2-NH)-Leu-NH2 (RC-3094) is conjugated to a potent derivative of doxorubicin, 2-pyrrolinodoxorubicin (AN-201). Small-cell lung carcinomas (SCLCs) are known to express high levels of bombesin receptors. We evaluated whether these receptors could be used for targeting cytotoxic bombesin analogue to H-69 SCLC cells. H-69 cells were xenografted into male nude mice, which then received an intravenous injection of AN-215, cytotoxic radical AN-201, the carrier peptide RC-3094 alone or unconjugated mixture of RC-3094 and AN-201. The levels of mRNA for bombesin receptor subtypes were evaluated by reverse transcription-polymerase chain reaction. In vitro, both the analogue AN-215 and the radical AN-201 showed strong antiproliferative effects on H-69 cells, AN-215 requiring more time to exert its action at 10(-8) M concentration than AN-201. In vivo, the growth of H-69 SCLC tumours was significantly inhibited by the treatment with 200 nmol kg(-1) of AN-215, while equimolar doses of the cytotoxic radical AN-201 or the mixture of AN-201 and the carrier peptide were toxic and produced only a minor tumour inhibition as compared with control groups. mRNA for bombesin receptor subtypes 2 (BRS-2) and 3 (BRS-3) was detected in H-69 tumours. The mRNA levels for BRS-3, but not for BRS-2, were lower in the AN-215-treated tumours as compared with controls. Our results demonstrate that the cytotoxic bombesin analogue AN-215 could be considered for targeted therapy of tumours, such as SCLC, that express bombesin receptors.

Bradykinin antagonists: present progress and future prospects

Bradykinin (BK) antagonist peptides have been powerful tools for delineating roles of kinins in both normal and pathological physiology and offer promise of drug development for a variety of inflammatory conditions and cancers. At the present time, potent peptide antagonists are available that are either specific for BK B1 or B2 receptors, or are effective on both receptor classes. Non-peptide BK B2 antagonists are now being announced and are under investigation in several companies. The best peptide B1-B2 peptide antagonist is stable against all kininases, is orally available, and has a very long lifetime in vivo. Certain dimers of this antagonist, as well as several smaller molecules, are active against several cancers, both in vitro and in vivo.

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 Leupsi(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-Trp-Phe-D-Trp-Leu(psi)(CH2NH)-Leu-NH2 and 7: D-MePhe-DTrp-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 microM, 7: IC50 = 5 microM and R: IC50 = 10 microM). 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.

Induction of apoptosis by a short-chain neuropeptide analog in small cell lung cancer

Small cell lung cancer (SCLC) cells express a variety of neuropeptides which act as autocrine growth factors. Although several neuropeptide analogs have been reported to antagonize SCLC proliferation, the development of these compounds has been limited by their low potency and the cytostatic nature of their effects. In the present study we evaluated the cytotoxic activity of four short-chain substance P analogs (NY3460, NY3238[-pHOPA], NY3238[Phe1], NY3238[Lys5]) against a panel of five SCLC cell lines. NY3460 was the most potent compound in all five SCLC cell lines (IC50 = 2.8-3.7 microM) as assessed by a MTT growth inhibitory assay. NY3238[Phe1] was also relatively active in all cell lines (IC50 = 3.5-11.2 microM), while NY3238[Lys5] and NY3238[-pHOPA] were substantially less active. NY3460 was the only agent to induce an increase in the percentage of cells with subdiploid DNA content suggestive of apoptosis by flow cytometric DNA content analysis. The induction of apoptosis was confirmed by fluorescent microscopy in NCI-H69, NCI-H82, NCI-H446, and NCI-H510 cells after exposure to 5.0 microM NY3460 for 48 h. These findings suggest that NY3460 is a relatively potent cytotoxic inhibitor of SCLC growth, and that short-chain neuropeptide analogs deserve further evaluation as anti-SCLC agents.

Neuroligand-triggered calcium signalling in cultured human glioma cells

Cells from primary cultures of four glioblastomas (GB), three low-grade astrocytomas (A), and four low-grade oligodendrogliomas (O) were tested for the presence of neuroligand receptors linked to Ca2+ signalling by calcium imaging. Cells of days 3 to 21 in culture were incubated with 5 microM fluo-3-acetomethylester in a bath solution and stimulated with 0.1 mM ATP, 0.01 mM angiotensin II, bradykinin, histamine, norepinephrine, serotonin, and substance P for 15 s, with 0.01 mM glutamate and 50 mM K+ for 30 s. Changes in the Ca2+ concentration were measured with a confocal laser scanning microscope. In all glioma subtypes, the majority of cells showed Ca2+ responses after application of histamine (60% of cells tested in GB, 67% in A, 86% in O), bradykinin (66% in GB, 29% in A, 55% in O) and ATP (48% in GB, 70% in A, 47% in O). The other stimuli induced Ca2+ transients in a smaller proportion (between 33% and 2%) of the cells. Our study demonstrates that histamine, bradykinin and ATP are potent inducers of [Ca2+]i signals in gliomas.