Potentiation of the inhibitory effect of growth hormone-releasing hormone antagonists on PC-3 human prostate cancer by bombesin antagonists indicative of interference with both IGF and EGF pathways

Novel insight on GRP/GRPR axis in diseases

The gastrin-releasing peptide receptor (GRPR), a member of the G protein-coupled receptors (GPCRs), binds to ligands such as gastrin-releasing peptide (GRP) and plays a variety of biological roles. GRP/GRPR signalling is involved in the pathophysiological processes of many diseases, including inflammatory diseases, cardiovascular diseases, neurological diseases, and various cancers. In the immune system, the unique function of GRP/GRPR in neutrophil chemotaxis suggests that GRPR can be directly stimulated through GRP-mediated neutrophils to activate selective signalling pathways, such as PI3K, PKC, and MAPK, and participate in the occurrence and development of inflammation-related diseases. In the cardiovascular system, GRP increases intercellular adhesion molecule 1 (ICAM-1) and induces vascular cell adhesion molecule-1 (VCAM-1). GRP activates ERK1/2, MAPK, and AKT, leading to cardiovascular diseases, including myocardial infarction. Central nervous system signal transduction mediated by the GRP/GRPR axis plays a vital role in emotional responses, social interaction, and memory. The GRP/GRPR axis is elevated in various cancers, including lung, cervical, colorectal, renal cell, and head and neck squamous cell carcinomas. GRP is a mitogen in a variety of tumour cell lines. Its precursor, pro-gastrin-releasing peptide (ProGRP), may play an important role as an emerging tumour marker in early tumour diagnosis. GPCRs serve as therapeutic targets for drug development, but their function in each disease remains unclear, and their involvement in disease progression has not been well explored or summarised. This review lays out the above mentioned pathophysiological processes based on previous research conclusions. The GRP/GRPR axis may be a potential target for treating multiple diseases, and the study of this signalling axis is particularly important.

Bioorthogonal Chemistry Approach for the Theranostics of GRPR-Expressing Cancers

Several gastrin-releasing peptide receptor (GRPR) antagonists with improved in vivo behavior have been recently developed and tested in the clinic. However, despite the generally mild side effects of peptide receptor radionuclide therapy (PRRT), toxicity has been observed due to high doses delivered to nontarget tissues, especially in the kidneys and pancreas. Previous experiences with radiolabeled peptides opened a unique opportunity to explore GRPR pretargeting using clickable bombesin antagonists. Toward this goal, we used clickable DOTA-like radiocomplexes which have been previously evaluated by our group. We functionalized a potent GRPR antagonist with a clickable TCO moiety using two different linkers. These precursors were then studied to select the compound with the highest GRPR binding affinity and the best pharmacokinetics to finally explore the advantages of the devised pretargeting approach. Our results provided an important proof of concept toward the development of bioorthogonal approaches to GRPR-expressing cancers, which are worth investigating further to improve the in vivo results. Moreover, the use of clickable GRPR antagonists and DOTA/DOTAGA derivatives allows for fine-tuning of their pharmacokinetics and metabolic stability, leading to a versatile synthesis of new libraries of (radio)conjugates useful for the development of theranostic tools toward GRPR-expressing tumors.

Breast Cancer Takes up 99mTc Bombesin. A Preliminary Report

Background

Several tumors including lung, prostate, ovarian, colon, and exocrine pancreatic cancer show receptors for the amphibian neurotransmitter and growth factor bombesin (BN) and its mammalian counterparts gastrin-releasing peptide and neuromedin B. Also breast cancer has been reported to show such receptors: the presence of BN receptors in primary breast cancer has been demonstrated on cultured cells and by autoradiography on breast tissue samples. Authors who have studied BN receptors in breast cancer do not agree on their frequency in primary cancer, but indicate that 100% of metastatic breast cancers show such receptors.

Methods

We examined three primary breast cancer patients with 99mTc BN and 99mTc sestamibi one week before surgery. One of them showed axillary node invasion. The same acquisition technique was used for breast and chest imaging with both radiopharmaceuticals, whereas total body images were acquired only with 99mTc BN. Also the administered radioactivity was different: 20 mCi of 99mTc sestamibi and 5-8 mCi of 99mTc BN. Dynamic images were acquired for 20 mins after iv injection with the patient in ventral decubitus and the gamma camera positioned in lateral view, as is generally done in Khakhali's prone scintimammography. Anterior chest images were acquired for 30 mins. Prone scintimammography was performed one hour after administration of both tracers. ROIs were drawn on tumors and surrounding breast with the same technique in order to calculate the tumor to breast ratio (T/B). In addition, total body scan was performed one hour and three hours after 99mTc BN administration. All three patients underwent breast conserving surgery with lymphadenectomy. Postoperative pathologic assessment showed the following T and N stages in the three patients: T1bN0, T1cN0. and T1cN1.

Results

All three cancers were imaged with both tracers. The T/B of 99mTc BN was always higher than that of 99mTc sestamibi. Chest uptake was always much higher with 99mTc sestamibi than with 99mTc BN. Comparison between 99mTc BN and 99mTc sestamibi images gave other intriguing results: in the N1 patient both tracers clearly imaged the invaded node, but on the 99mTc BN image the primary tumor was larger than on the 99mTc sestamibi image and the node was smaller. It is known that 99mTc BN is not taken up by vessels and inflammatory tissue. The time activity curves of the two tracers were significantly different in all patients, with an increase in 99mTc BN uptake in the first three to five minutes, followed by a less sharp uprise of the curve, quite similar to a plateau.

Conclusions

Our first impression is that 99mTc BN is a useful breast cancer seeking agent and very promising for lymph node staging.

The gastrin-releasing peptide receptor as a marker of dysplastic alterations in cervical epithelial cells

BACKGROUND

Cervical cancer is a leading cancer in women worldwide. The Papanicolaou test (Pap test) remains the main screening tool; however, it produces high rates of false-negative and false-positive results. Gastrin-releasing peptide is a growth factor that has been implicated in many cancers, and its main receptor, the gastrin-releasing peptide receptor (GRPR), is nearly always expressed in cervical dysplasias and invasive carcinomas. The aim of this study was to evaluate the diagnostic potential of GRPR immunocytochemistry in detecting cervical dysplasia and invasive cancer.

METHODS

Cervical smears were collected from 66 women in Brazil and subjected to GRPR immunocytochemistry and the Pap test. GRPR and p16 immunohistochemistry were performed in biopsies if abnormalities were detected.

RESULTS

GRPR immunostaining sensitivity in detecting cervical lesions was 87.5% and its specificity was 76.7%. GRPR immunostaining showed 80% accuracy in identifying atypical squamous cells of undetermined significance (ASCUS), with 88% sensitivity and 71% specificity.

CONCLUSION

This is the first immunocytochemical evaluation of GRPR expression in cervical epithelial cells. This biomarker was strongly associated with cervical dysplasia and invasive cancers. GRPR immunosignaling showed high accuracy in detecting dysplasias in cells classified as ASCUS by Pap tests. Based on these results, immunocytochemistry for GRPR may be regarded as a valuable method for early detection of cervical intraepithelial neoplasia.

Regulation of bombesin-stimulated cyclooxygenase-2 expression in prostate cancer cells

Background

Cyclooxygenase-2 (COX-2) and the bombesin (BBS)-like peptide, gastrin-releasing peptide (GRP), have been implicated in the progression of hormone-refractory prostate cancer; however, a mechanistic link between the bioactive peptide and COX-2 expression in prostate cells has not been made.

Results

We report that BBS stimulates COX-2 mRNA and protein expression, and the release of prostaglandin E₂ from the GRP receptor (GRPR)-positive, androgen-insensitive prostate cancer cell line, PC-3. BBS-stimulated COX-2 expression is mediated, in part, by p38^MAPK and PI3 kinase (PI3K)/Akt pathways, and blocked by a GRPR antagonist. The PI3K/Akt pathway couples GRPR to the transcription factor, activator protein-1 (AP-1), and enhanced COX-2 promoter activity. Although BBS stimulates nuclear factor-kappaB (NF-κB) in PC-3, NF-κB does not regulate GRPR-mediated COX-2 expression. The p38^MAPK pathway increases BBS-stimulated COX-2 expression by slowing the degradation of COX-2 mRNA. Expression of recombinant GRPR in the androgen-sensitive cell line LNCaP is sufficient to confer BBS-stimulated COX-2 expression via the p38^MAPK and PI3K/Akt pathways.

Conclusions

Our study establishes a mechanistic link between GRPR activation and enhanced COX-2 expression in prostate cancer cell lines, and suggests that inhibiting GRPR may, in the future, provide an effective therapeutic alternative to non-steroidal anti-inflammatory drugs for inhibiting COX-2 in patients with recurrent prostate cancer.

Antiproliferative effect of growth hormone-releasing hormone (GHRH) antagonist on ovarian cancer cells through the EGFR-Akt pathway

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) are being developed for the treatment of various human cancers.

METHODS

MTT assay was used to test the proliferation of SKOV3 and CaOV3. The splice variant expression of GHRH receptors was examined by RT-PCR. The expression of protein in signal pathway was examined by Western blotting. siRNA was used to block the effect of EGFR.

RESULTS

In this study, we investigated the effects of a new GHRH antagonist JMR-132, in ovarian cancer cell lines SKOV3 and CaOV3 expressing splice variant (SV)1 of GHRH receptors. MTT assay showed that JMR-132 had strong antiproliferative effects on SKOV3 and CaOV3 cells in both a time-dependent and dose-dependent fashion. JMR-132 also induced the activation and increased cleaved caspase3 in a time- and dose-dependent manner in both cell lines. In addition, JMR-132 treatments decreased significantly the epidermal growth factor receptor (EGFR) level and the phosphorylation of Akt (p-Akt), suggesting that JMR-132 inhibits the EGFR-Akt pathway in ovarian cancer cells. More importantly, treatment of SKOV3 and CaOV3 cells with 100 nM JMR-132 attenuated proliferation and the antiapoptotic effect induced by EGF in both cell lines. After the knockdown of the expression of EGFR by siRNA, the antiproliferative effect of JMR-132 was abolished in SKOV3 and CaOV3 cells.

CONCLUSIONS

The present study demonstrates that the inhibitory effect of the GHRH antagonist JMR-132 on proliferation is due, in part, to an interference with the EGFR-Akt pathway in ovarian cancer cells.

Potential-dependent studies on the interaction between phenylalanine-substituted bombesin fragments and roughened Ag, Au, and Cu electrode surfaces

In this work, we report systematic surface-enhanced Raman spectroscopy (SERS) and generalized two-dimensional correlation analysis (G2DCA) studies of the structures of five specifically modified phenylalanine-substituted C-terminal bombesin 6-14 fragments (BN(6-14)). The fragments studied have all been tested as chemotherapeutic agents in cancer therapy, and they form amino acid sequences in bombesin: cyclo[d-Phe(6),His(7),Leu(14)]BN(6-14), [D-Phe(6),Leu-NHEt(13),des-Met(14)]BN(6-14), [D-Phe(6),Leu(13)-((R))-p-Cl-Phe(14)]BN(6-14), [D-Phe(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), and [D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14). We adsorbed these fragments onto roughened Ag, Au, and Cu electrode surfaces, using a potential range from -1.200 to 0.400 V, at physiological pH. We compared the adsorption mechanism of each fragment on these substrates, as well any changes observed with varying electrode potential, to determine the relationship between adsorption strength and geometry of each of the peptides wherever it was possible. For example, we showed that none of these fragments directly interact with the Ag, Au, and Cu surfaces via residues of Phe (phenylalanine) and Trp(8) (L-tryptophane at position 8 of the BN amino acid sequence) or by an amide bond, due to a very small shift in wavenumber of their characteristic vibrations. Specific interactions were recognized from the broadening, wavenumber shift, and increase in intensity of the W18 Trp(8) mode near 759 cm(-1) and decrease in nu(12) vibration frequency of the Phe residue. In general, more intense SERS bands were observed due to the Phe ring, compared with the Trp(8) ring, which suggested a preferential adsorption of phenylalanine over tryptophane. For [D-Tyr(6),beta-Ala(11),Phe(13),Nle(14)]BN(6-14), the data also suggest some interaction of a D-Tyr(6) residue (D-tyrosine at position 6). Finally, only slight rearrangements of these moieties on the substrates are observed with changes in electrode potential.

A standardised study to compare prostate cancer targeting efficacy of five radiolabelled bombesin analogues

Purpose

Prostate-specific antigen (PSA)-based screening for prostate cancer (PC) has dramatically increased early diagnosis. Current imaging techniques are not optimal to stage early PC adequately. A promising alternative to PC imaging is peptide-based scintigraphy using radiolabelled bombesin (BN) analogues that bind to gastrin-releasing peptide receptors (GRPR) being overexpressed in PC. When labelled to appropriate radionuclides BN targeting of GRPRs may also provide applications for peptide radionuclide receptor therapy (PRRT). Assessment studies under identical experimental conditions allowing a reliable comparison of the potential of such analogues are lacking. This study was performed to evaluate and directly compare five promising radiolabelled BN analogues for their targeting efficacy for PC under standardised conditions.

Methods

The BN agonists [¹¹¹In]DOTA-PESIN, [¹¹¹In]AMBA, [¹¹¹In]MP2346 and [¹¹¹In]MP2653 and one antagonist [^99mTc]Demobesin-1 were evaluated in GRPR-overexpressing human PC-3 tumour-bearing mice to determine peptide stability in vivo, biodistribution and GRPR targeting potential by animal SPECT/CT imaging and ex vivo autoradiography.

Results

HPLC analysis of blood showed intact Demobesin-1 at 5 and 15 min after injection (64.1 ± 1.6% and 41.0 ± 01%, respectively) being much less for the other compounds. AMBA, the second most stable analogue, showed 36.1 ± 2.7% and 9.8 ± 1.1% intact peptide after 5 and 15 min. PC-3 tumour uptake at 1 h was comparable for Demobesin-1, AMBA, PESIN and MP2346 (3.0 ± 0.4, 2.7 ± 0.5, 2.3 ± 0.5 and 2.1 ± 0.9%ID/g, respectively), but very low for MP2653 (0.9 ± 0.2%ID/g). In addition, MP2346 showed undesirably high uptake in the kidneys (7.9 ± 1.9%ID/g) being significantly less for the other analogues. AMBA, MP2346 and PESIN revealed favourable increases in tumour to blood ratios over time while changes in tumour to kidney and pancreas ratios for Demobesin-1 from 1 to 24 h after injection were significantly better than for the other analogues. All analogues visualised PC-3 tumours by SPECT/CT and autoradiography.

Conclusion

In the present study the BN antagonist Demobesin-1 was the best performing analogue showing superior in vivo stability, highest tumour uptake and retention while pancreatic and renal clearance were rapid. PESIN and AMBA were the best GRP agonists with sufficient in vivo stabilities as well as high tumour uptake and retention. Based on these results all three analogues deserve further evaluation for clinical use in PC patients.

Dose-dependent growth inhibition in vivo of PC-3 prostate cancer with a reduction in tumoral growth factors after therapy with GHRH antagonist MZ-J-7-138

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) inhibit the growth of various cancers and affect tumoral growth factors.

METHODS

We investigated the effect of a new GHRH antagonist MZ-J-7-138 at doses of 1.25, 2.5, 5 and 10 microg/day s.c. on the growth of PC-3 human androgen independent prostate cancers xenografted s.c. into nude mice. Binding assays were used to investigate GHRH receptors. The levels of IGF-II and VEGF in tumors were measured by radioimmunoassays.

RESULTS

Treatment with 2.5, 5, and 10 microg/day MZ-J-7-138 caused a significant dose-dependent growth reduction of PC-3 tumors. The greatest inhibition of 78% was obtained with 10 microg/day. The suppression of IGF-II protein levels in tumors was seen at all doses of MZ-J-7-138, but only 10 microg dose induced a significant inhibition. MZ-J-7-138 also reduced VEGF protein levels, the inhibition being significant at doses of 5 and 10 microg. Specific high affinity binding sites for GHRH were found on PC-3 tumors using (125)I-labeled GHRH antagonist JV-1-42. MZ-J-7-138 displaced radiolabeled JV-1-42 with an IC(50) of 0.32 nM indicating its high affinity to GHRH receptors. Real-time PCR analyses detected splice variant 1 (SV1) of GHRH receptor (GHRH-R) as well as pituitary type of GHRH-R and GHRH ligand.

CONCLUSION

Our results demonstrate the efficacy of GHRH antagonist MZ-J-7-138 in suppressing growth of PC-3 prostate cancer at doses lower than previous antagonists. The reduction of levels of growth factors such as VEGF and IGF-II in tumors by GHRH antagonist was correlated with the suppression of tumor growth.

Substituted hippurates and hippurate analogs as substrates and inhibitors of peptidylglycine alpha-hydroxylating monooxygenase (PHM)

Peptidyl alpha-hydroxylating monooxygenase (PHM) functions in vivo towards the biosynthesis of alpha-amidated peptide hormones in mammals and insects. PHM is a potential target for the development of inhibitors as drugs for the treatment of human disease and as insecticides for the management of insect pests. We show here that relatively simple ground state analogs of the PHM substrate hippuric acid (C(6)H(5)-CO-NH-CH(2)-COOH) inhibit the enzyme with K(i) values as low as 0.5microM. Substitution of sulfur atom(s) into the hippuric acid analog increases the affinity of PHM for the inhibitor. Replacement of the acetylglycine moiety, -CO-NH-CH(2)-COOH with an S-(thioacetyl)thioglycolic acid moiety, -CS-S-CH(2)-COOH, yields compounds with the highest PHM affinity. Both S-(2-phenylthioacetyl)thioglycolate and S-(4-ethylthiobenzoyl)thioglycolic acid inhibit the proliferation of cultured human prostate cancer cells at concentrations >100-fold excess of their respective K(i) values. Comparison of K(i) values between mammalian PHM and insect PHM shows differences in potency suggesting that a PHM-based insecticide with limited human toxicity can be developed.

Characterization of osteolytic, osteoblastic, and mixed lesions in a prostate cancer mouse model using 18F-FDG and 18F-fluoride PET/CT

The combination of small-animal PET/CT scans and conventional imaging methods may enhance the evaluation of in vivo biologic interactions of murine models in the study of prostate cancer metastasis to bone.

METHODS

Small-animal PET/CT scans using (18)F-fluoride ion and (18)F-FDG coregistered with high-resolution small-animal CT scans were used to longitudinally assess the formation of osteoblastic, osteolytic, and mixed lesions formed by human prostate cancer cell lines in a severe combined immunodeficient (SCID) mouse tibial injection model. These scans were correlated with plain radiographs, histomorphometry, and soft-tissue measurements.

RESULTS

Small-animal PET/CT scans were able to detect biologic activity of cells that induced an osteoblastic lesion 2 wk earlier than on plain radiographs. Furthermore, both the size and the activity of the lesions detected on PET/CT images significantly increased at each successive time point (P < 0.05). (18)F-FDG lesions strongly correlated with soft-tissue measurements, whereas (18)F-fluoride ion activity correlated with bone volume measured on histomorphometric analysis (P < 0.005). Osteolytic lesions were successfully quantified using small-animal CT, whereas lesion sizes measured on (18)F-FDG PET scans also strongly correlated with soft-tissue tumor burden (P < 0.05). In contrast, for mixed lesions, (18)F-fluoride ion and (18)F-FDG PET/CT scans detected only minimal activity.

CONCLUSION

(18)F-FDG and (18)F-fluoride ion PET/CT scans can be useful tools in characterizing pure osteolytic and osteoblastic lesions induced by human prostate cancer cell lines. The value of this technology needs further evaluation to determine whether these studies can be used effectively to detect more subtle responses to different treatment regimens in animal models.

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.

Gastrin-releasing peptide receptor as a molecular target in experimental anticancer therapy

Over the last two decades, several lines of experimental evidence have suggested that the gastrin-releasing peptide (GRP) may act as a growth factor in many types of cancer. For that reason, gastrin-releasing peptide receptor (GRPR) antagonists have been developed as anticancer candidate compounds, exhibiting impressive antitumoral activity both in vitro and in vivo in various murine and human tumors. In this article, the GRPR cell surface expression profile in human malignancies is reviewed aiming at the identification of potential tumor types for future clinical trials with GRP analogues and antagonists. In this review, we summarize the current literature regarding the GRPR status in human malignancies. Source data were obtained by searching all published material available through Medline, PubMed and relevant articles from 1971 to 2006. The data available demonstrated a high expression of GRPRs in a large spectrum of human cancers, demonstrating the potential relevance of this intracellular signaling pathway in various human tumor models. The GRPR may be an interesting target for therapeutic intervention in human malignancies, as carriers for cytotoxins, immunotoxins or radioactive compounds, being also a potential tool for tumor detection.

Clinical implications of neuroendocrine differentiation in prostate cancer

The cellular signaling pathways of the prostate play a central role in the induction, maintenance, and progression of prostate cancer (CaP). Neuroendocrine (NE) cells demonstrate attributes that suggest they are an integral part of these signaling cascades. We summarize what is known regarding NE cells in CaP focusing on NE cellular transdifferentiation. This significant event in CaP progression appears to be accelerated by androgen deprivation (AD) treatment. We examine biochemical pathways that may impact NE differentiation in a chronological manner focusing on AD therapy (ADT) as a central event in inducing androgen-independent CaP. Our analysis is limited to the common adenocarcinoma pattern of CaP and excludes small-cell and carcinoid prostatic variants. In conclusion, we speculate on the future of treatment and research in this area.

Insulin-Like Growth Factor (IGF) family and prostate cancer

There is abundant in vitro, animal and epidemiologic evidence to suggest that the Insulin-Like Growth Factor (IGF) family is a multi-component network of molecules which is involved in the regulation of both physiological and pathological growth processes in prostate. The IGF family plays a key role in cellular metabolism, differentiation, proliferation, transformation and apoptosis, during normal development and malignant growth. This family also seem essential in prostate cancer bone metastases, angiogenesis and androgen-independent progression. Therapeutic alternatives in men with progressive prostate cancer after androgen ablation are very limited. More effective therapies are needed for these patients. Pharmacologic interventions targeting the IGF family are being devised. Such strategies include reduction of IGF-I levels (growth hormone-releasing hormone antagonists, somatostatin analogs), reduction of functional IGF-I receptor levels (antisense oligonucleotides, small interfering RNA), inhibition of IGF-IR and its signalling (monoclonal antibodies, small-molecule tyrosine kinase inhibitors) and Insulin-Like Growth Factor Binding Proteins.

Bombesin regulates cyclin D1 expression through the early growth response protein Egr-1 in prostate cancer cells

Our previous studies indicate that the activation of mitogen-activated protein kinase (MAPK) pathway is involved in bombesin-induced cell proliferation in prostate cancer cells. Cyclin D1 is a critical regulator involved in cell cycle progression through the G1 phase into the S phase, thereby contributing to cell proliferation. Mostly, mitogen-stimulated expression of cyclin D1 is attributed to the extracellular signal-regulated kinase (ERK) activation. Here, we found that bombesin induced human cyclin D1 expression on both mRNA and protein levels in DU-145 prostate cancer cells. Mutational analyses showed that bombesin-enhanced cyclin D1 transcription required the binding of nuclear proteins to the -143 to -105 region of the human cyclin D1 promoter, which contains binding sites for transcription factors Sp-1 and early growth response protein (Egr-1). Do novo protein synthesis was requisite for bombesin-induced cyclin D1 expression. Further studies showed Egr-1 was induced upon bombesin stimulation. The induction of Egr-1 expression and its binding to the cyclin D1 promoter were essential for bombesin-enhanced cyclin D1 transcription. Inhibition of MAPK pathway with either the MEK1 inhibitor PD98059 or a dominant-negative Ras mutant, RasN17, abolished bombesin-induced cyclin D1 activation. Taken together, bombesin-induced cyclin D1 expression in prostate cancer cells is mediated by Egr-1 activation and the interaction of Egr-1 with the Egr-1/Sp1 motif of the cyclin D1 promoter through the activation of MAPK pathway. These findings represent a novel mechanism of bombesin-dependent stimulation of mitogenesis by regulating directly the cell cycle in prostate cancer.

Antagonists of growth hormone releasing hormone and bombesin inhibit the expression of EGF/HER receptor family in H-69 small cell lung carcinoma

Effects of in vivo treatment with antagonists of growth hormone-releasing hormone (GHRH), JV-1-65 and MZ-J-7-110, and bombesin/gastrin-releasing peptide antagonist RC-3940-II, on the EGF receptor (EGFR) family, were investigated in H-69 SCLC. Tumors were analyzed by RT-PCR, immunoblotting and binding assays. Treatment with these analogs reduced the binding capacity of EGFR by 18-64%, and inhibited the mRNA expression for EGFR, HER-2 and -3 by 27-75.4, 17-26.3, and 13.8-46.6%, respectively. The antagonists also decreased the protein levels for EGFR by 21-34%, HER-2 by 36-68% and HER-3 by 43-49%. This is the first demonstration that antiproliferative effects of GHRH antagonists are associated with a downregulation of EGF/HER receptors.

Antagonists of growth hormone releasing hormone (GHRH) and of bombesin/gastrin releasing peptide (BN/GRP) suppress the expression of VEGF, bFGF, and receptors of the EGF/HER family in PC-3 and DU-145 human androgen-independent prostate cancers

BACKGROUND

Antagonists of growth hormone releasing hormone (GHRH) as well as antagonists of bombesin/gastrin releasing peptide (BN/GRP) inhibit the growth of various malignancies (cancers) including prostate cancer.

METHODS

We investigated the effects of GHRH antagonists MZ-J-7-118 and RC-J-29-18, BN/GRP antagonists RC-3940-II and RC-3940-Et and the combination of MZ-J-7-118 and RC-3940-II on the growth of PC-3 and DU-145 human androgen independent prostate cancers xenografted s.c. into nude mice. To elucidate the mechanisms of action of these analogs, growth factors like IGF-II (insulin-like growth factor-II), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and epidermal growth factor receptor/human epidermal growth factor receptor (EGF-R/HER) family were measured in tumors as well as IGF-I in serum.

RESULTS

Antagonists of GHRH and BN/GRP alone or in combination significantly inhibited growth of PC-3 and DU-145 tumors, the greatest inhibition of tumor volume being achieved by combination of MZ-J-7-118 (5 microg/day) and RC-3940-II (10 microg/day). BN/GRP and GHRH antagonists and their combination also decreased the expression of VEGF significantly in PC-3 and non-significantly in DU-145, as measured by radioimmunoassay for VEGF protein and RT-PCR for mRNA levels of VEGF. GHRH and BN/GRP antagonists reduced bFGF concentrations and the maximal binding capacity of EGF receptors, and their mRNA levels in PC-3 and DU-145 tumors. mRNA levels for HER-2 and -3 were also diminished in PC-3 tumors by GHRH and BN/GRP antagonists. No changes in HER-4 were found after treatment. Serum IGF-I and tumoral IGF-II levels were not affected by the analogs.

CONCLUSIONS

BN/GRP and GHRH antagonists inhibit growth of PC-3 and DU-145 prostate cancers by suppressing the expression of tumoral growth factors such as VEGF and bFGF as well as the receptors for EGF and related HER-2 and -3. Additive effects on tumor inhibition (TI) in vivo, but not on VEGF, bFGF, or members of the EGF/HER receptor family, can be achieved by the joint administration of both classes of analogs.

Effective treatment of experimental human non-Hodgkin's lymphomas with antagonists of growth hormone-releasing hormone

Antagonists of growth hormone-releasing hormone (GHRH) were shown to inhibit the growth of various cancers. We investigated the antitumor activity and the mechanism of action of GHRH antagonists in human non-Hodgkin's lymphomas (NHL). Nude mice bearing xenografts of RL and HT human NHL were treated with GHRH antagonists MZ-5-156 and MZ-J-7-138 at a dose of 40 microg twice daily. The concentrations of serum IGF-1 and GHRH, bFGF, and VEGF in tumor tissue were measured by radioimmunoassays. Expression of GHRH and splice variant 1 of the GHRH receptor in both cell lines was examined by RT-PCR. The effects of MZ-5-156, MZ-J-7-138 and GHRH on cell proliferation were evaluated in vitro. Treatment with MZ-5-156 and MZ-J-7-138 significantly (P < 0.05) inhibited the growth of RL and HT tumors by 59.9-73.9%. High-affinity binding sites for GHRH and mRNA for GHRH and splice variant-1 of the GHRH receptors were found on RL and HT tumors. RL and HT cells contained GHRH peptide, and their growth in vitro was significantly inhibited by both antagonists. IGF-I levels in serum of mice were significantly decreased by antagonist MZ-5-156. Therapy with GHRH antagonists also significantly reduced tumoral bFGF, whereas VEGF levels were not suppressed. Our findings suggest that GHRH antagonists inhibit the growth of RL and HT lymphomas by direct effects mediated by tumoral receptors for GHRH. GHRH antagonists could offer a new therapeutic modality for the management of advanced NHL.

Extrapituitary Effects of the Growth Hormone-Releasing Hormone

Growth hormone-releasing hormone (GHRH) is a neuropeptide secreted by the hypothalamus that stimulates the synthesis and release of growth hormone (GH) in the pituitary. Accumulating evidence suggests that in addition to GHRH's neuroendocrine action, GHRH is present in several extrahypothalamic tissues and is involved in a variety of cellular processes. Its function is related to the regulation of cell proliferation and differentiation of various nonpituitary cell types. In certain cases, ectopic production of GHRH has also been implicated in carcinogenesis. The mechanisms by which GHRH affects the peripheral extrapituitary tissues remain poorly understood, but it is likely that classic neuroendocrine action as well as paracrine and autocrine pathways are involved. Some headway has been made in the identification of extrapituitary receptors for GHRH and cDNA as splice variants of these GHRH receptors found in various tumors. The fact that the nonpituitary GHRH receptors are not fully identified, however, remains the major obstacle in studying, at a more mechanistic level, the action of local GHRH. This review summarizes the information available regarding the role of GHRH in the extrapituitary tissues with emphasis on its potential therapeutic and diagnostic applications.

Inhibitory Effect of Antagonists of Bombesin and Growth Hormone-Releasing Hormone on Orthotopic and Intraosseous Growth and Invasiveness of PC-3 Human Prostate Cancer in Nude Mice

Purpose: To determine whether antagonists of growth hormone-releasing hormone (GHRH) and bombesin/gastrin-releasing peptide (BN/GRP) can inhibit the orthotopic and metastatic growth of PC-3 human androgen-independent prostate cancers.

Experimental Design: The effects of administration of GHRH antagonist MZ-J-7-118, BN/GRP antagonist RC-3940-II, and their combination on the growth and metastatic spread of PC-3 tumors implanted orthotopically into nude mice were evaluated. The efficacy of this treatment on PC-3 tumors implanted intratibially and s.c. was also determined.

Results: Treatment with MZ-J-7-118, RC-3940-II, or their combination significantly inhibited the growth of PC-3 tumors implanted orthotopically, intraosseously, and s.c. The combination of the two antagonists had the greatest effect, inhibiting orthotopic tumor growth by 77%, intratibially implanted tumors by 86%, and s.c. tumors by 86%. The therapy with BN/GRP and GHRH antagonists, especially in combination, also reduced the local tumor spread and distant metastases in animals bearing orthotopic tumors. Combination therapy was likewise the most effective in reducing the incidence and severity of tibial osteolytic lesions and pathologic fractures in intraosseously implanted tumors. High-affinity binding sites for BN/GRP and GHRH were found in s.c. and orthotopic PC-3 tumor samples. MZ-J-7-118, RC-3940-II, and the combination of both compounds inhibited in vitro growth of PC-3 cells.

Conclusions: Our findings show the efficacy of BN/GRP antagonists and GHRH antagonists for the treatment of advanced prostate cancer in preclinical metastatic models. As BN/GRP antagonists are already in clinical trials and GHRH antagonists are effective in androgen-independent prostate cancer models, these analogues could be considered for the management of advanced prostate carcinoma.

Gastrin-Releasing Peptide (GRP) Analogues for Cancer Imaging

Small neuropeptides, labeled with gamma- and/or beta-emitting radionuclides, are currently being investigated for their ability to bind to cell-surface receptors, overexpressed in a wide variety of malignant tissues being, thus, potentially useful for radionuclide detection and/or therapy for tumors. Particular attention has been focused on the amphibian peptide, bombesin (BN), and the molecularly related gastrin-releasing peptide (GRP). These peptides act as neurotransmitters and endocrine cancer cell-growth factors on normal tissues as well as on neoplastic cells of various origin. In recent investigations, modification of the native peptide structure has been attempted in order to obtain derivatives, which might easily be labeled with radionuclides. Thus, iodinated (I-125) BN derivatives, as well as Indium (In-111) labeled BN analogs are currently being investigated, presenting satisfactory tumor localization. Also, some new BN analogs containing a 6-carbon linker have been prepared and labeled with Rhenium-188, resulting in positive in vitro binding to prostate cancer cells. More recent studies refer to the Technetium-99m labeling of BN, performed either directly, after attaching proper technetium-chelating groups onto the BN sequence, or indirectly, by coupling BN to a preformed 99mTc-tagging ligand. Both types of conjugates were found to have a high in vitro affinity for cells with BN receptors, also presenting satisfactory in vivo uptake in experimental tumor models. Pilot clinical studies of a new BN-derived, 99mTc-labeled pentadecapeptide indicated significant uptake by breast cancer and invaded lymph nodes, as well as by prostate cancer, small-cell lung carcinoma, gastro-entero-pancreatic tumors, and others, Further studies of this new GRP derivative, as well as of other new BN-like peptides, are intensively performed internationally today.

Bombesin antagonists inhibit proangiogenic factors in human experimental breast cancers

The overexpression of angiogenic factors such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and insulin-like growth factors (IGFs) plays a role in the migration and proliferation of endothelial cells in many cancers. Consequently, we investigated the effects of bombesin/gastrin-releasing peptide (GRP) antagonists on the expression of these angiogenic factors, the activities of matrix metalloproteinases (MMPs)-2 and -9, as well as the vascular density in MDA-MB-435 human oestrogen-independent breast cancers. Nude mice bearing orthotopic xenografts of MDA-MB-435 breast cancers were treated with bombesin/GRP antagonists for 6 weeks. Daily administration of 20 μg of RC-3095 or 10 μg of RC-3940-II significantly decreased the weight of MDA-MB-435 cancers by 44 and 53%, respectively. The inhibition of tumour growth was associated with a substantial reduction in the expression of mRNA and protein levels of basic fibroblast growth factor (bFGF), IGF-II and VEGF-A in the tumours. Both bombesin/GRP antagonists significantly decreased the vessel density of the tumours by about 37%, as shown by immunohistochemical detection of vessels on tumour slides. Gelatinolytic activities, detected by zymography, revealed a 33–46% reduction in MMP-9 activity after the treatment with either antagonist. In vitro studies revealed that MDA-MB-435 cells secrete bFGF, IGF-II and VEGF-A, and the secretion of these factors is inhibited by RC-3095 and RC-3940-II. This study demonstrates the antiangiogenic effect of bombesin/GRP antagonists RC-3095 and RC-3940-II, and underscores their possible therapeutic application for treatment of breast cancers.

Antagonists of growth hormone-releasing hormone (GH-RH) enhance tumour growth inhibition induced by androgen deprivation in human MDA-Pca-2b prostate cancers

In the present study, we investigated whether the growth hormone-releasing hormone (GH-RH) antagonist JV-1-38 could enhance the effects of androgen deprivation produced by the anti-androgen Flutamide and luteinising hormone-releasing hormone (LH-RH) agonist Decapeptyl in an experimental model of human androgen-sensitive MDA PCa 2b prostate carcinoma implanted subcutaneously (s.c.) into nude mice. We also evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR) the effects of combined treatment on the mRNA expression for prostate-specific antigen (PSA) and measured serum PSA levels. In experiment 1, GH-RH antagonist JV-1-38 greatly inhibited tumour growth in combination with Decapeptyl, but was ineffective when given alone. Thus, combined therapy with JV-1-38 at 20 microg/day and Decapeptyl microcapsules releasing 12.5 microg/day for 29 days inhibited significantly (P<0.01) MDA PCa 2b tumour growth by 65%, compared with controls. Combined treatment also significantly (P<0.05) decreased serum PSA levels by 52% and reduced tumour weight by 54% vs. controls. In experiment 2, GH-RH antagonist JV-1-38 at 20 microg/day likewise showed powerful growth inhibitory effects when combined with Flutamide (25 mg/kg/day) for 21 days. Combined treatment with JV-1-38 and slow-release pellets of Flutamide significantly (P<0.001) inhibited tumour growth by 61% versus controls, and was significantly (P<0.05) more effective than Flutamide or JV-1-38 alone. Combination therapy also reduced significantly (P<0.001) tumour weight and serum PSA levels by 59 and 47%, respectively. The mRNA expression for PSA in MDA PCa 2b tumours was not changed by JV-1-38, Decapeptyl and Flutamide alone or in their respective combinations. Our findings suggest that GH-RH antagonists could enhance the tumour inhibitory effects of androgen deprivation for the primary therapy of patients with advanced prostate carcinoma.

Inhibition of mutant p53 expression and growth of DMS-153 small cell lung carcinoma by antagonists of growth hormone-releasing hormone and bombesin

We investigated the effects of growth hormone-releasing hormone (GHRH) antagonists, JV-1-65 and JV-1-63, and bombesin/gastrin-releasing peptide (BN/GRP) antagonist RC-3940-II on DMS-153 human small cell lung carcinoma xenografted into nude mice. Treatment with 10 microg/day JV-1-65 or RC-3940-II decreased tumor volume by 28% (P < 0.05) and 77% (P < 0.01), respectively, after 42 days compared with controls. Combination of JV-1-65 and RC-3940-II induced the greatest inhibition of tumor proliferation (95%; P < 0.01), suggesting a synergism. Western blotting showed that the antitumor effects of these antagonists were associated with inhibition of the expression of the mutant tumor suppressor protein p53 (Tp53). Mutation was detected by sequence analysis of the p53 gene at codon 155: ACC [Thr] --> CCC [Pro]. Combination of JV-1-65 and RC-3940-II decreased the levels of mutant p53 protein by 42% (P < 0.01) compared with controls. JV-1-65, JV-1-63, and RC-3940-II, given singly, reduced mutant p53 protein expression by 18-24% (P < 0.05). Serum insulin-like growth factor (IGF)-I levels were diminished in animals receiving GHRH antagonists. mRNA levels for IGF-II, IGF receptor-I, GRP receptor, and EGF receptor in tumors were significantly decreased by combined treatment with JV-1-65 and RC-3940-II. DMS-153 tumors expressed mRNAs for GHRH and GHRH receptor splice variants 1 and 2, suggesting that GHRH could be an autocrine growth factor. Proliferation of DMS-153 cells in vitro was stimulated by GRP and IGF-II and inhibited by JV-1-65. This study indicates that GHRH antagonists and BN/GRP antagonist inhibit the growth of DMS-153 small cell lung carcinoma concomitantly with the expression of mutant Tp53, which might uncouple the signal transduction pathways for cell growth stimulation.

Activation of extracellular signal-regulated kinase mediates bombesin-induced mitogenic responses in prostate cancer cells

Bombesin and its mammalian homologue gastrin-releasing peptide have been shown to be highly expressed and secreted by neuroendocrine cells in prostate cancer, and are thought to be related to the carcinogenesis and progression of this disease. We found, in this study, bombesin specifically induced mitogen-activated protein (MAP) kinase activation as shown by increased extracellular regulated kinase (ERK) phosphorylation and epidermal growth factor (EGF) receptor transactivation in prostate cancer cells, which express functional gastrin-releasing peptide receptor. The transactivation of EGF receptor was required for bombesin-induced ERK phosphorylation. Furthermore, non-receptor tyrosine kinase Src and cellular Ca2+ were shown to be involved in bombesin-induced EGF receptor transactivation and ERK phosphorylation. Inhibition of either EGF receptor transactivation or ERK activation blocked bombesin-induced DNA synthesis in these cells. Taken together, these data suggest bombesin may act as a mitogen in prostate cancer by activating MAP kinase pathway via EGFR transactivation.

Growth hormone-releasing hormone and extra-pituitary tumorigenesis: therapeutic and diagnostic applications of growth hormone-releasing hormone antagonists

Growth hormone-releasing hormone (GHRH) regulates growth hormone release from the pituitary. However, in addition to this neuroendocrine action, much evidence implies an additional role for GHRH in carcinogenesis in non-pituitary tissues. This role of GHRH in cancer development appears to be due to the operation of several mechanisms, which involve the regulation of the growth hormone-dependent hepatic insulin-like growth factor I (IGFI) production, tumoural IGF-I and IGF-II secretion and direct action of GHRH on tumour cells by autocrine and/or paracrine pathways. This review summarises the available information regarding the role of GHRH in tumorigenesis with special emphasis on the direct action of GHRH in primary and experimental cancers.

Immunohistochemical detection of gastrin releasing peptide in patients with prostate cancer

Gastrin releasing peptide (GRP) is a neuropeptide that has been suggested to play a role in the development of some malignancies. Our aim was: (1) to identify the expression of GRP in cancerous prostate glands, and (2) to correlate its expression to various pathological parameters and to the patient's clinical outcome. Using standard immunohistochemistry, we evaluated GRP expression in both biopsy and radical prostatectomy specimens from 30 patients with prostatic adenocarcinomas. GRP was expressed in 18 radical prostatectomy specimens (60%) and in 15 biopsies (50%). There was an association between positive immunoexpression of GRP, relapse ( P=0.029) and advanced tumor stages (i.e. pT3, pT4) ( P=0.049). In the respective biopsies, GRP immunostatus was similar to that observed in the subsequent radical prostatectomy specimens. GRP immunoexpression may be of some value as a diagnostic and prognostic marker. Patients whose pathology specimens demonstrate GRP immunopositivity should be closely monitored, since they appear to be at higher risk of disease progression and relapse.

Growth hormone-releasing hormone (GHRH) antagonists inhibit the proliferation of androgen-dependent and -independent prostate cancers

The antiproliferative effects of an antagonist of growth hormone-releasing hormone (GHRH) JV-1-38 were evaluated in nude mice bearing s.c. xenografts of LNCaP and MDA-PCa-2b human androgen-sensitive and DU-145 androgen-independent prostate cancers. In the androgen-sensitive models, JV-1-38 greatly potentiated the antitumor effect of androgen deprivation induced by surgical castration, but was ineffective when given alone. Thus, in castrated animals bearing MDA-PCa-2b cancers, the administration of JV-1-38 for 35 days virtually arrested tumor growth (94% inhibition vs. intact control, P < 0.01; and 75% vs. castrated control, P < 0.05). The growth of LNCaP tumors was also powerfully suppressed by JV-1-38 combined with castration (83% inhibition vs. intact control, P < 0.01; and 68% vs. castrated control, P < 0.05). However, in androgen-independent DU-145 cancers, JV-1-38 alone could inhibit tumor growth by 57% (P < 0.05) after 45 days. In animals bearing MDA-PCa-2b and LNCaP tumors, the reduction in serum prostate-specific antigen levels, after therapy with JV-1-38, paralleled the decrease in tumor volume. Inhibition of MDA-PCa-2b and DU-145 cancers was associated with the reduction in the expression of mRNA and protein levels of vascular endothelial growth factor. The mRNA expression for GHRH receptor splice variants was found in all these models of prostate cancer. Our results demonstrate that GHRH antagonists inhibit androgen-independent prostate cancers and, after combination with androgen deprivation, also androgen-sensitive tumors. Thus, the therapy with GHRH antagonist could be considered for the management of both androgen-dependent or -independent prostate cancers.

GRP receptor-mediated immediate early gene expression and transcription factor Elk-1 activation in prostate cancer cells

Bombesin (BN) and its mammalian homologue gastrin-releasing peptide (GRP) have been shown to play an important role in human cancer as autocrine and paracrine growth factors. Prostatic neuroendocrine cells are thought to secrete these regulatory peptides and they may therefore interact with their specific, aberrantly expressed GRP receptor (GRP-R) in prostate cancer. In this study, we investigated the effect of BN on immediate early gene expression in two androgen-independent prostate cancer cell lines DU-145 and PC-3 with functional GRP receptor. We found that BN induced c-fos mRNA expression in both cell lines in a time-dependent manner. In contrast, c-jun mRNA was only modestly induced in DU-145 cells but not at all in PC-3 cells. On the protein level, we detected BN-induced stimulation of the c-fos gene product but not of c-jun protein. Sustained increase of the c-myc gene product was detectable in PC-3 but not in DU-145 cells. Concurrently, we demonstrated BN-dependent activation of the transcription factor Elk-1 and significant increase of cell proliferation in both prostate cancer cell lines. Taken together, these data suggest that BN acts as a mitogen in prostate cancer and this might be associated with the activation of the transcription factor Elk-1 and the immediate early gene c-fos.

Inhibition of proliferation in human MNNG/HOS osteosarcoma and SK-ES-1 Ewing sarcoma cell lines in vitro and in vivo by antagonists of growth hormone-releasing hormone: effects on insulin-like growth factor II

BACKGROUND

Antagonists of growth hormone-releasing hormone (GH-RH) can inhibit the proliferation of various tumors either indirectly through the suppression of the pituitary growth hormone/hepatic insulin-like growth factor I (IGF-I) axis and the lowering of serum IGF-I concentration or directly by reducing the levels of IGF-I and IGF-II and their mRNA expression in tumors and blocking the effect of autocrine GH-RH. In this study, the authors investigated the effects of the GH-RH antagonist JV-1-38 on MNNG/HOS human osteosarcoma and SK-ES-1 human Ewing sarcoma cell lines.

METHODS

Male nude mice bearing subcutaneous xenografts of MNNG/HOS or SK-ES-1 tumors were treated subcutaneously with JV-1-38 at a dose of 20 microg twice daily for 4 weeks. The concentrations of IGF-I and IGF-II in serum and in tumor tissue were measured by radioimmunoassay. Tumor and liver levels of mRNA for IGF-I and IGF-II were determined by reverse transcriptase-polymerase chain reaction analysis. The effects of JV-1-38, IGF-I, and IGF-II on cell proliferation in vitro were evaluated.

RESULTS

GH-RH antagonist significantly (P < 0.05) inhibited the tumor volume and tumor weight of MNNG/HOS and SK-ES-1 tumors by > 50% after 4 weeks and increased tumor doubling time. JV-1-38 lowered the serum IGF-I level, decreased the expression of mRNA for IGF-I in the liver, and significantly (P < 0.05-0.01) reduced the concentration of IGF-II and mRNA levels for IGF-II in both sarcomas. The concentration of IGF-I was lowered only in SK-ES-1 tumors. In vitro, the proliferation of SK-ES-1 and MNNG/HOS cells was inhibited by JV-1-38 and by antisera to IGF-I and IGF-II.

CONCLUSIONS

The inhibition of MNNG/HOS osteosarcoma and SK-ES-1 Ewing sarcoma by GH-RH antagonists was linked to a suppression of IGF-II production in tumors. However, in SK-ES-1 tumors, the effects on IGF-I also may be involved.

The expression of growth hormone-releasing hormone (GHRH) and splice variants of its receptor in human gastroenteropancreatic carcinomas

Splice variants (SVs) of receptors for growth hormone-releasing hormone (GHRH) have been found in primary human prostate cancers and diverse human cancer cell lines. GHRH antagonists inhibit growth of various experimental human cancers, including pancreatic and colorectal, xenografted into nude mice or cultured in vitro, and their antiproliferative action could be mediated in part through SVs of GHRH receptors. In this study we examined the expression of mRNA for GHRH and for SVs of its receptors in tumors of human pancreatic, colorectal, and gastric cancer cell lines grown in nude mice. mRNA for both GHRH and SV(1) isoform of GHRH receptors was expressed in tumors of pancreatic (SW1990, PANC-1, MIA PaCa-2, Capan-1, Capan-2, and CFPAC1), colonic (COLO 320DM and HT-29), and gastric (NCI-N87, HS746T, and AGS) cancer cell lines; mRNA for SV(2) was also present in Capan-1, Capan-2, CFPAC1, HT-29, and NCI-N87 tumors. In proliferation studies in vitro, the growth of pancreatic, colonic, and gastric cancer cells was stimulated by GHRH(1-29)NH(2) and inhibited by GHRH antagonist JV-1-38. The stimulation of some gastroenteropancreatic cancer cells by GHRH was followed by an increase in cAMP production, and GHRH antagonist JV-1-38 competitively inhibited this effect. Our study indicates the presence of an autocrine/paracrine stimulatory loop based on GHRH and SV(1) of GHRH receptors in human pancreatic, colorectal, and gastric cancers. The finding of SV(1) receptor in human cancers provides an approach to an antitumor therapy based on the blockade of this receptor by specific GHRH antagonists.

Inhibition of proliferation of PC-3 human prostate cancer by antagonists of growth hormone-releasing hormone: lack of correlation with the levels of serum IGF-I and expression of tumoral IGF-II and vascular endothelial growth factor

BACKGROUND

Antagonists of growth hormone-releasing hormone (GHRH) such as JV-1-38 can inhibit androgen-independent prostate cancer directly by several mechanisms and/or indirectly by suppressing growth hormone/insulin-like growth factor-I (GH/IGF-I) axis. To shed more light on the mechanisms involved, the effects of JV-1-38 on PC-3 human prostate cancer were compared with those of somatostatin analog RC-160 in vivo and in vitro.

METHODS

Nude mice bearing PC-3 tumors received JV-1-38 (20 microg), RC-160 (50 microg) or a combination of JV-1-38 and RC-160. The concentration of IGF-I in serum and the expression of mRNA for IGF-II and vascular endothelial growth factor (VEGF) in tumor tissue were investigated.

RESULTS

In vivo, the final volume of PC-3 tumors treated with JV-1-38 was significantly lowered by 49% (P < 0.01), whereas RC-160 exerted only 30% inhibition (NS), compared with controls. Combined use of both compounds augmented tumor inhibition to 63% (P < 0.001). Serum IGF-I levels were decreased only in mice treated with RC-160. JV-1-38 suppressed mRNA for IGF-II in PC-3 tumors by 42%, whereas RC-160 alone or in combination with JV-1-38 caused a 65% reduction. JV-1-38 and RC-160 used as single drugs decreased the expression of VEGF by 50%, and their combination caused a 63% reduction. In vitro, JV-1-38 inhibited the proliferation of PC-3 cells by 39%. This effect could be partially reversed by addition of IGF-I to the serum-free medium. RC-160 alone did not affect the PC-3 cell growth in vitro, but in combination with JV-1-38 it augmented the antiproliferative effect of the GH-RH antagonist to 72%. Exposure to JV-1-38 in vitro reduced the expression of mRNA for IGF-II in PC-3 cells by 55% but did not change VEGF mRNA levels, whereas RC-160 had no effect.

CONCLUSIONS

The antiproliferative effect of JV-1-38 was not associated with the suppression of serum IGF-I and was only partially correlated with the expression of IGF-II and VEGF in PC-3 tumors, suggesting that other mechanisms play a role in the antitumor action of GHRH antagonists. Nevertheless, the stronger inhibition of tumor growth after combined treatment with JV-1-38 and RC-160 indicates that the interference with multiple local stimulatory factors leads to an enhanced inhibition of prostate cancer.

The metalloprotease Kuzbanian (ADAM10) mediates the transactivation of EGF receptor by G protein-coupled receptors

Communication between different signaling pathways enables cells to coordinate the responses to diverse environmental signals. Activation of the transmembrane growth factor precursors plays a critical role in this communication and often involves metalloprotease-mediated proteolysis. Stimulation of G protein-coupled receptors (GPCR) transactivates the EGF receptors (EGFRs), which occurs via a metalloprotease-dependent cleavage of heparin-binding EGF (HB-EGF). However, the metalloprotease mediating the transactivation remains elusive. We show that the integral membrane metalloprotease Kuzbanian (KUZ; ADAM10), which controls Notch signaling in Drosophila, stimulates GPCR transactivation of EGFR. Upon stimulation of the bombesin receptors, KUZ increases the docking and activation of adaptors Src homology 2 domain-containing protein and Gab1 on the EGFR, and activation of Ras and Erk. In contrast, transfection of a protease domain-deleted KUZ, or blocking endogenous KUZ by morpholino antisense oligonucleotides, suppresses the transactivation. The effect of KUZ on shedding of HB-EGF and consequent transactivation of the EGFR depends on its metalloprotease activity. GPCR activation enhances the association of KUZ and its substrate HB-EGF with tetraspanin CD9. Thus, KUZ regulates the relay between the GPCR and EGFR signaling pathways.

Technetium labeled bombesin-like peptide: preliminary report on breast cancer uptake in patients

Bombesin-like peptides are neurotransmitters and cancer growth factors. Several tumors, breast cancer among them, show one or more than one of the three known bombesin receptors. We have synthesized and labeled with technetium 99m a new pentadecapeptide, analogue to the leu13 amphibian bombesin (99mTc BN). Labeling yield was 83 +/- 4%. Prone Scintimammography was performed on five patients affected by breast cancers (T categorization: two T1b and three T1c), after injecting 0.7 mg, 185 to 296 MBq (5 to 8 mCi) of the peptide. Total body scan did not show free technetium biodistribution. No adverse reaction was observed. Prone Scintimammography with 99mTc Sestamibi (99mTc SM) was also performed few days later. 99mTc BN detected all 5 cancers, whereas 99mTc SM only four: all the T1c and one T1b cancer. Two of them showed axillary node invasion that was detected by both the radiotracers. A fibroadenoma present on contralateral breast to the one with cancer, was not detected neither by 99mTc SM nor by 99mTc BN. Tumor/breast normal tissue ratio (T/B) was constantly higher with 99mTc BN than with 99mTc SM. Maximal T/B was measured as 1.79 with 99mTc SM and 2.25 with 99mTc BN 5 min after fast i.v. administration. In conclusion our 99mTc BN is taken up by primary breast cancer showing higher T/B than 99mTc SM (p < 0.01). In our limited scale, 99mTc BN appears to be safe and, in our limited scale, even more accurate than 99mTc SM for detecting breast cancer.

Expression of growth hormone-releasing hormone (GHRH) and splice variants of GHRH receptors in human experimental prostate cancers

The expression of mRNA for GHRH and splice variants (SVs) of GHRH receptors in LNCaP, MDA-PCa-2b and PC-3 human prostate cancers grown in nude mice was investigated by RT-PCR. The expression of mRNA for GHRH was detected in LNCaP and PC-3, but not in MDA-PCa-2b prostatic carcinoma. RT-PCR analyses of mRNA isolated from LNCaP, MDA-PCa-2b and PC-3 cancers, revealed the presence of 720 and 566 bp products, corresponding to SV(1) and SV(2) isoforms of GHRH receptors. In PC-3 tumor membranes a radiolabeled GHRH antagonist [125I]-JV-1-42 was bound to one class of high-affinity binding sites (K(d)=1.81+/-0.47 nM) and maximum binding capacity of 332.7+/-27.8 fmol/mg membrane protein. The in vivo uptake of [125I]-JV-1-42 was observed in all xenografts of human prostate cancer, the tracer accumulation being the highest in PC-3 tumors. These results indicate that GHRH and SVs of its receptors, different from those found in the pituitary, are present in experimental human prostate cancers and may form a local mitogenic loop. The antiproliferative effects of GHRH antagonists on growth of prostate cancer could be exerted in part by an interference with this local GHRH system.

Elevated serum progastrin-releasing peptide (31-98) in metastatic and androgen-independent prostate cancer patients

BACKGROUND

Increases in neuroendocrine phenotype and secretory products are closely correlated with tumor progression and androgen independence in prostate cancer. In this study, we explored this correlation using serum progastrin-releasing peptide (ProGRP), a carboxy-terminal region common to three subtypes of precursors for gastrin-releasing peptide (GRP), which is released from the neuroendocrine phenotype to act as a growth factor.

METHODS

In 60 patients with benign prostatic hyperplasia (BPH) and 200 with prostate cancer, serum ProGRP levels were determined with an enzyme-linked immunosorbent assay (ELISA) kit and evaluated in relation to clinical stage, hormonal treatment, and prostate-specific antigen (PSA) values. Fourteen randomly selected patients were entered in the follow-up study. Additionally, expression of ProGRP as determined by immunohistochemical analysis was compared to that of chromogranin-A (CgA) in tissue samples from several subjects.

RESULTS

We found a positive correlation between PSA and ProGRP in patients with untreated prostate cancer; no correlation was found in the treated groups. The increases in the ProGRP value and in the percentage of patients with higher than normal values were significant (P < 0.0001), especially in the androgen-independent group (P < 0.0001). A longitudinal study showed that, in a subset of patients, the ProGRP values tended to increase transiently when the cancer became androgen independent, but remained unchanged or decreased at the androgen-dependent stage. Positive staining for ProGRP occurred in a different distribution in neuroendocrine tissues than that of staining for CgA.

CONCLUSIONS

The clinical results demonstrated the existence of a regulatory mechanism for GRP, which to date had only been observed in cell lines. These findings suggest that GRP is a growth factor potentially upregulated by androgen but that does not rely principally on androgen modulation. The large overlap in levels of ProGRP among the groups limits the use of this value as a monitoring tool. Measurement of ProGRP, however, does have potential as an independent parameter to evaluate androgen-independent progression and to facilitate a new therapeutic strategy that may compensate for current limitations of diagnosis based on PSA alone.

Inhibition of PC-3 human prostate cancers by analogs of growth hormone-releasing hormone (GH-RH) endowed with vasoactive intestinal peptide (VIP) antagonistic activity

Vasoactive intestinal peptide (VIP) stimulates the proliferation and invasiveness of malignant prostatic cells. Receptors for VIP and the closely related growth hormone-releasing hormone (GH-RH) show considerable homology and are found in prostatic and other carcinomas. Among various analogs of GH-RH synthesized, JV-1-52 is a non-selective VIP/GH-RH antagonist, whereas JV-1-53 is a VIP antagonist devoid of GH-RH antagonistic effect. In our study, nude mice bearing PC-3 human androgen-independent prostate carcinomas were treated with JV-1-52 or JV-1-53 (20 microg/day, s.c.) for 28 days. Both antagonists produced a similar reduction in tumor volume (62-67%, p < 0.01) and tumor weight (59-62%; p < 0.05) vs. controls and extended tumor doubling-time from 9.1 to about 16 days (p < 0.05). To investigate the mechanisms involved, in another study we compared the effects of JV-1-53 with those of somatostatin analog RC-160. VIP antagonist JV-1-53 reduced tumor weight by 67% (p < 0.01) and suppressed the expression of mRNA for c-fos and c-jun oncogenes by about 34% (p < 0.05), without affecting serum levels of insulin-like growth factor-I (IGF-I). In contrast, RC-160 (50 microg/day) reduced serum IGF-I by 19% (p < 0.05), but did not significantly decrease tumor weight. mRNA for VIP and high affinity receptors for VIP were detected on PC-3 tumors. Our results suggest that VIP/GH-RH antagonists can inhibit the growth of androgen-independent prostate cancer by abrogating the autocrine/paracrine mitogenic stimuli of VIP. The ability of GH-RH antagonists to block tumoral VIP receptors, in addition to GH-RH receptors, could be potentially beneficial for prostate cancer therapy.

Neuroendocrine pathogenesis in adenocarcinoma of the prostate

BACKGROUND

In the prostate, the importance of sex hormones for its normal development and function is well known. However, it has been proposed that various neuroendocrine (NE) hormones and growth factors may be involved in the pathogenesis of prostatic carcinoma (CaP). Neuroendocrine differentiation appears to be associated with tumour progression and the androgen-independent state, for which there is currently no successful therapy. Therefore, we need to improve our understanding of NE cells, their regulatory products and influence on the prostate gland. Finally, new therapeutic protocols need to be developed.

METHODS

Information is presented on prostatic NE cells and neuroendocrine differentiation (NED) in prostatic carcinoma. Neuroendocrine secretory products and interactions with epithelial prostate cells are investigated in order to understand their significance for the pathogenesis of the prostate gland, prognosis and therapy.

RESULTS

Recent research suggests that NE-secreted products. such as serotonin, somatostatin and bombesin, may influence growth, invasiveness, metastatic processes and angiogenesis in CaP. During recent years. new experimental models for NED have been developed to provide evidence that NE products may promote proliferation and confer antiapoptotic capabilities on non-neuroendocrine cells in close proximity to NE cells. Cancerous epithelial cells may become more responsive to NE factors by upregulation of receptors for neuropeptides, or may induce NE cells to upregulate the secretion and synthesis of NE factors. In the androgen independent state, neuropeptides and their intracellular signals may activate the androgen receptor. Furthermore, androgen ablation may lead to downregulation of neural endopeptidase 24.11 (a zinc-dependent metalloproteinase) and PSA, which would lead to increased levels of NE products becoming available. These studies confirm that NE cells and NED may have a significant impact on prostate cancer, especially in the androgen independent state.

CONCLUSIONS

Recent developments in molecular biology and pathophysiology of prostate cancer have increased our understanding of the NE regulatory mechanisms. Hopefully, this will lead to the development of entirely new therapeutic modalities. For example, somatostatin agonists may suppress angiogenesis and proliferation, and simultaneously promote apoptosis in prostate cancer cells. Somatostatin may thus have an important role in tumour biology, and in the future there may be a potential role for somatostatin analogues in the treatment of prostate cancer, but also for serotonin and bombesin receptor antagonists. However, a review of the accumulated knowledge in this field suggests that we still need to improve our understanding of NE cells and their regulatory products and influence on the prostate gland. and that clinical trials are needed, to test drugs based on neuroendocrine hormones and their agonists/antagonists.

Neuropeptides bombesin and calcitonin inhibit apoptosis-related elemental changes in prostate carcinoma cell lines

BACKGROUND

Etoposide-induced apoptosis in prostate carcinoma cells is associated with changes in the elemental content of the cells. The authors previously reported that calcitonin and bombesin inhibited etoposide-induced apoptosis in these cells. In the current study, the authors investigated whether these neuropeptides block the etoposide-induced changes in elemental content.

METHODS

Cells from the PC-3 and Du 145 prostate carcinoma cell lines were grown either on solid substrates or on thin plastic films on titanium electron microscopy grids, and they were exposed to etoposide for 48 hours in the absence or presence of calcitonin and bombesin. After the exposure, the cells were frozen and freeze dried, and their elemental content was analyzed by energy-dispersive X-ray microanalysis in both in the scanning electron microscope and the scanning transmission electron microscope.

RESULTS

Etoposide treatment consistently induced an increase in the cellular Na concentration and a decrease in the cellular K concentration, resulting in a marked increase of the Na/K ratio and also an increase in the phosphorus:sulphur (P/S) ratio. Both bombesin and calcitonin inhibited the etoposide-induced changes in the cellular Na/K ratio, and calcitonin, but not bombesin, inhibited the changes in the P/S ratio. No significant elemental changes were found with bombesin or calcitonin alone.

CONCLUSIONS

The neuropeptides bombesin and calcitonin, which inhibited etoposide-induced apoptosis, also inhibited the etoposide-induced elemental changes in prostate carcinoma cells. This important fact strengthens the link between apoptosis and changes in the intracellular elemental content. This correlation provides an objective basis for the study of neuropeptide target points and may be helpful for alternative therapeutic protocols using neuropeptide inhibitors in the treatment of patients with advanced prostatic carcinoma.

A potential autocrine pathway for growth hormone releasing hormone (GHRH) and its receptor in human prostate cancer cell lines

BACKGROUND

Recent studies have shown that GHRH antagonists inhibit prostate tumour growth and IGF-II production both in vivo and in vitro. The mechanism underlying these observations is unknown, but may involve an interaction with a prostatic GHRH receptor (GHRH-R), raising the possibility of an autocrine pathway for the GHRH axis in the prostate.

METHODS

GHRH and GHRH-R mRNA expression was examined by RT-PCR in human prostate cancer cell lines, and the authenticity of PCR products was confirmed by Southern analysis and cDNA sequencing. Immunohistochemical techniques were used to examine the expression of GHRH protein in prostate cancer cell lines.

RESULTS

GHRH-R (mRNA) and GHRH (mRNA and protein) are co-expressed in the ALVA-41, DU145, LNCaP and PC3 human prostate cancer cell lines.

CONCLUSIONS

These observations suggest the presence of an intact prostatic GHRH autocrine pathway which may stimulate prostate cell proliferation. This pathway may be disrupted by GHRH antagonists.

Peptide analogs in the therapy of prostate cancer

The use of peptide analogs in the therapy of prostate cancer is reviewed. The preferred primary treatment of advanced androgen-dependent prostate cancer is presently based on the use of depot preparations of LH-RH agonists. This treatment is likewise recommended in patients with rising PSA levels after surgery or radiotherapy. LH-RH agonists with or without antiandrogens can be also utilized prior to or following various local treatments in patients with clinically localized prostate cancer and at high risk for disease recurrence. LH-RH antagonists like Cetrorelix are in clinical trials. However, most patients with advanced prostatic carcinoma treated by any modality of androgen deprivation eventually relapse. Treatment of relapsed androgen-independent prostate cancer remains a major challenge, but new therapeutic modalities are being developed based on antagonists of growth hormone-releasing hormone (GH-RH) and bombesin, which inhibit growth factors or their receptors. Another approach consists of cytotoxic analogs of LH-RH, bombesin, and somatostatin containing doxorubicin or 2-pyrrolinodoxorubicin, which can be targeted to receptors for these peptides found in prostate cancers and their metastases. These cytotoxic analogs inhibit growth of experimental androgen-dependent or -independent prostate cancers and reduce the incidence of metastases. A rational therapy with peptide analogs could be selected on the basis of receptors present in biopsy samples. The approaches based on peptide analogs should result in a more effective treatment for prostate cancer.