Increased frequency of gastrin-releasing peptide receptor gene mutations during colon-adenocarcinoma progression

Identification of a novel immune signature for optimizing prognosis and treatment prediction in colorectal cancer

BACKGROUND

Globally, colorectal cancer (CRC) is one of the most lethal malignant diseases. However, the currently approved therapeutic options for CRC failed to acquire satisfactory treatment efficacy. Tailoring therapeutic strategies for CRC individuals can provide new insights into personalized prediction approaches and thus maximize clinical benefits.

METHODS

In this study, a multi-step process was used to construct an immune-related genes (IRGs) based signature leveraging the expression profiles and clinical characteristics of CRC from the Gene Expression Omnibus (GEO) database and the Cancer Genome Atlas (TCGA) database. An integrated immunogenomic analysis was performed to determine the association between IRGs with prognostic significance and cancer genotypes in the tumor immune microenvironment (TIME). Moreover, we performed a comprehensive in silico therapeutics screening to identify agents with subclass-specific efficacy.

RESULTS

The established signature was shown to be a promising biomarker for evaluating clinical outcomes in CRC. The immune risk score as calculated by this classifier was significantly correlated with over-riding malignant phenotypes and immunophenotypes. Further analyses demonstrated that CRCs with low immune risk scores achieved better therapeutic benefits from immunotherapy, while AZD4547, Cytochalasin B and S-crizotinib might have potential therapeutic implications in the immune risk score-high CRCs.

CONCLUSIONS

Overall, this IRGs-based signature not only afforded a useful tool for determining the prognosis and evaluating the TIME features of CRCs, but also shed new light on tailoring CRCs with precise treatment.

In Vivo Biodistribution and Efficacy Evaluation of NeoB, a Radiotracer Targeted to GRPR, in Mice Bearing Gastrointestinal Stromal Tumor

Simple Summary

NeoB is undergoing evaluation as a novel theragnostic agent—that is, that it can be employed either for the diagnosis of tumor expressing gastrin-releasing peptide receptor (GRPR) using nuclear imaging, or for the therapy of such GRPR positive tumors using internal radiotherapy. The switch from diagnosis to therapy simply rely on the choice of the radioisotope that is coupled to NeoB. The aim of our study was to investigate—for the first time—the potency of NeoB for tumor therapy once labeled with the beta- emitter Lu-177. This study has been conducted in mice bearing human Gastrointestinal Stromal Tumors (GIST). [¹⁷⁷Lu]Lu-NeoB was found to accumulate in the tumor, with only minimal retention in off-target organs. Consequently, mice treated with therapeutic doses of [¹⁷⁷Lu]Lu-NeoB (37MBq/week for three weeks) exhibited tumor regression and therefore long term survival in comparison to the control untreated mice.

Abstract

NeoB is a radiotracer targeting the gastrin-releasing peptide receptor (GRPR), a G-protein–coupled receptor expressed in various cancers. The aim of the present study was to evaluate the biodistribution and efficacy of this new therapeutic agent in Gastrointestinal Stromal Tumors (GIST). Eighty-two SCID mice bearing GIST-882 tumors were employed. [¹⁷⁷Lu]Lu-NeoB biodistribution was evaluated up to seven days by organ sampling (200 pmol/0.8 MBq, i.v.). For efficacy evaluation, mice received either saline, 400 pmol or 800 pmol of [¹⁷⁷Lu]Lu-NeoB (37MBq, 1/w, 3 w, i.v.). SPECT/CT imaging was performed at 24 h, and tumor volume was determined up to 100 days. Elevated and specific [¹⁷⁷Lu]Lu-NeoB uptake was found in the GIST tumor, as demonstrated by in vivo competition (19.1 ± 3.9 %ID/g vs. 0.3 ± 0.1 %ID/g at 4h). [¹⁷⁷Lu]Lu-NeoB tumor retention (half-life of 40.2 h) resulted in elevated tumor-to-background ratios. Tumor volumes were significantly reduced in both treated groups (p < 0.01), even leading to complete tumor regression at the 400 pmol dose. [¹⁷⁷Lu]Lu-NeoB exhibited excellent pharmacokinetics with elevated and prolonged tumor uptake and low uptake in non-target organs such as pancreas. The potential of this new theragnostic agent in different indications, including GIST, is under evaluation in the FIH [¹⁷⁷Lu]Lu-NeoB clinical trial.

Fluorescence imaging of bombesin and transferrin receptor expression is comparable to 18F-FDG PET in early detection of sorafenib-induced changes in tumor metabolism

Physical measurement of tumor volume reduction is the most commonly used approach to assess tumor progression and treatment efficacy in mouse tumor models. However, it is relatively insensitive, and often requires long treatment courses to achieve gross physical tumor destruction. As alternatives, several non-invasive imaging methods such as bioluminescence imaging (BLI), fluorescence imaging (FLI) and positron emission tomography (PET) have been developed for more accurate measurement. As tumors have elevated glucose metabolism, 18F-fludeoxyglucose (18F-FDG) has become a sensitive PET imaging tracer for cancer detection, diagnosis, and efficacy assessment by measuring alterations in glucose metabolism. In particular, the ability of 18F-FDG imaging to detect drug-induced effects on tumor metabolism at a very early phase has dramatically improved the speed of decision-making regarding treatment efficacy. Here we demonstrated an approach with FLI that offers not only comparable performance to PET imaging, but also provides additional benefits, including ease of use, imaging throughput, probe stability, and the potential for multiplex imaging. In this report, we used sorafenib, a tyrosine kinase inhibitor clinically approved for cancer therapy, for treatment of a mouse tumor xenograft model. The drug is known to block several key signaling pathways involved in tumor metabolism. We first identified an appropriate sorafenib dose, 40 mg/kg (daily on days 0-4 and 7-10), that retained ultimate therapeutic efficacy yet provided a 2-3 day window post-treatment for imaging early, subtle metabolic changes prior to gross tumor regression. We then used 18F-FDG PET as the gold standard for assessing the effects of sorafenib treatment on tumor metabolism and compared this to results obtained by measurement of tumor size, tumor BLI, and tumor FLI changes. PET imaging showed ~55-60% inhibition of tumor uptake of 18F-FDG as early as days 2 and 3 post-treatment, without noticeable changes in tumor size. For comparison, two FLI probes, BombesinRSense™ 680 (BRS-680) and Transferrin-Vivo™ 750 (TfV-750), were assessed for their potential in metabolic imaging. Metabolically active cancer cells are known to have elevated bombesin and transferrin receptor levels on the surface. In excellent agreement with PET imaging, the BRS-680 imaging showed 40% and 79% inhibition on days 2 and 3, respectively, and the TfV-750 imaging showed 65% inhibition on day 3. In both cases, no significant reduction in tumor volume or BLI signal was observed during the first 3 days of treatment. These results suggest that metabolic FLI has potential preclinical application as an additional method for detecting drug-induced metabolic changes in tumors.

Synthesis and structure-activity studies on novel analogs of human growth hormone releasing hormone (GHRH) with enhanced inhibitory activities on tumor growth

The syntheses and biological evaluations of new GHRH analogs of Miami (MIA) series with greatly increased anticancer activity are described. In the design and synthesis of these analogs, the following previous substitutions were conserved: D-Arg², Har⁹, Abu¹⁵, and Nle²⁷. Most new analogs had Ala at position 8. Since replacements of both Lys¹² and Lys²¹ with Orn increased resistance against enzymatic degradation, these modifications were kept. The substitutions of Arg at both positions 11 and 20 by His were also conserved. We kept D-Arg²⁸, Har²⁹ -NH₂ at the C-terminus or inserted Agm or 12-amino dodecanoic acid amide at position 30. We incorporated pentafluoro-Phe (Fpa₅), instead of Cpa, at position 6 and Tyr(Me) at position 10 and ω-amino acids at N-terminus of some analogs. These GHRH analogs were prepared by solid-phase methodology and purified by HPLC. The evaluation of the activity of the analogs on GH release was carried out in vitro on rat pituitaries and in vivo in male rats. Receptor binding affinities were measured in vitro by the competitive binding analysis. The inhibitory activity of the analogs on tumor proliferation in vitro was tested in several human cancer cell lines such as HEC-1A endometrial adenocarcinoma, HCT-15 colorectal adenocarcinoma, and LNCaP prostatic carcinoma. For in vivo tests, various cell lines including PC-3 prostate cancer, HEC-1A endometrial adenocarcinoma, HT diffuse mixed β cell lymphoma, and ACHN renal cell carcinoma cell lines were xenografted into nude mice and treated subcutaneously with GHRH antagonists at doses of 1-5μg/day. Analogs MIA-602, MIA-604, MIA-610, and MIA-640 showed the highest binding affinities, 30, 58, 48, and 73 times higher respectively, than GHRH (1-29) NH₂. Treatment of LNCaP and HCT-15 cells with 5μM MIA-602 or MIA-690 decreased proliferation by 40%-80%. In accord with previous tests in various human cancer lines, analog MIA-602 showed high inhibitory activity in vivo on growth of PC-3 prostate cancer, HT-mixed β cell lymphoma, HEC-1A endometrial adenocarcinoma and ACHN renal cell carcinoma. Thus, GHRH analogs of the Miami series powerfully suppress tumor growth, but have only a weak endocrine GH inhibitory activity. The suppression of tumor growth could be induced in part by the downregulation of GHRH receptors levels.

Preclinical therapy of benign prostatic hyperplasia with neuropeptide hormone antagonists

Benign prostatic hyperplasia (BPH) is a pathologic condition of the prostate described as a substantial increase in its number of epithelial and stromal cells. BPH may significantly reduce the quality of life due to the initiation of bladder outlet obstruction and lower urinary tract syndromes. Current medical therapies mostly consist of inhibitors of 5α-reductase or α₁-adrenergic blockers; their efficacy is often insufficient. Antagonistic analogs of neuropeptide hormones are novel candidates for the management of BPH. At first, antagonists of luteinizing hormone-releasing hormone (LHRH) have been introduced to the therapy aimed to reduce serum testosterone levels. However, they have also been found to produce an inhibitory activity on local LHRH receptors in the prostate as well as impotence and other related side effects. Since then, several preclinical and clinical studies reported the favorable effects of LHRH antagonists in BPH. In contrast, antagonists of growth hormone-releasing hormone (GHRH) and gastrin-releasing peptide (GRP) have been tested only in preclinical settings and produce significant reduction in prostate size in experimental models of BPH. They act at least in part, by blocking the action of respective ligands produced locally on prostates through their respective receptors in the prostate, and by inhibition of autocrine insulin-like growth factors-I/II and epidermal growth factor production. GHRH and LHRH antagonists were also tested in combination resulting in a cumulative effect that was greater than that of each alone. This article will review the numerous studies that demonstrate the beneficial effects of antagonistic analogs of LHRH, GHRH and GRP in BPH, as well as suggesting a potential role for somatostatin analogs in experimental therapies.

Targeted therapy in advanced metastatic colorectal cancer: Current concepts and perspectives

The introduction of new cytotoxic substances as well as agents that target vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) signaling has improved clinical outcome of patients with metastatic colorectal cancer (mCRC). In this review we summarize the most relevant clinical data on VEGF and EGFR targeting regimens in mCRC. The effects of available treatment strategies for mCRC are often temporary, with resistance and disease progression developing in most patients. Thus, new treatment strategies are urgently needed. Some GI peptides including gastrin and gastrin releasing peptide, certain growth factors such as insulin-like growth factor-I and II and neuropeptides such as growth hormone releasing hormone (GHRH) are implicated in the growth of CRC. Experimental investigations in CRC with antagonistic analogs of bombesin/gastrin-releasing peptide, GHRH, and with cytotoxic peptides that can be targeted to peptide receptors on tumors, are summarized in the second part of the review.

177Lu-labeled RGD-BBN heterodimeric peptide for targeting prostate carcinoma

INTRODUCTION

Radiolabeled Arg-Gly-Asp (RGD) and bombesin (BBN) heterodimers have been investigated for dual targeting of tumor integrin αvβ3 receptors and gastrin-releasing peptide receptors. The goal of this study was to evaluate the potential use of a Lu-labeled RGD-BBN heterodimer for targeted prostate cancer therapy.

MATERIALS AND METHODS

A 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-conjugated RGD-BBN peptide (DO3A-RGD-BBN) was radiolabeled with Lu and purified by high-performance liquid chromatography. The in-vivo biodistribution study of Lu-DO3A-RGD-BBN was carried out in mice bearing human prostate cancer PC3 xenografts. The receptor-targeting specificity of the radiolabeled peptide was assayed by injecting the tracer with the unlabeled RGD-BBN peptide. Radiation absorbed doses in adult male patients, based on biodistribution data from mice, were also calculated.

RESULTS

DO3A-RGD-BBN peptides were successfully labeled with Lu, and high radiochemical purity (>95%) could be achieved after high-performance liquid chromatography purification. In human PC3 xenograft-bearing mice, the tumor accumulation of Lu-DO3A-RGD-BBN was 5.88±1.12, 2.77±0.30, 2.04±0.19, and 1.18±0.19%ID/g at 0.5, 2, 24, and 48 h, respectively. With rapid clearance from normal tissues, the radiolabeled probe displayed high tumor-to-blood and tumor-to-muscle ratios. On calculating the radiation absorbed doses for Lu-DO3A-RGD-BBN, we found that the prostate tumor and the pancreas were the organs receiving the highest radiation absorbed doses.

CONCLUSION

Dual integrin αvβ3 and GPRP-targeted agent Lu-DO3A-RGD-BBN shows excellent prostate cancer-targeting ability, and it is worthy of further evaluation for prostate cancer-targeted therapy.

A new 18F-labeled BBN-RGD peptide heterodimer with a symmetric linker for prostate cancer imaging

A peptide heterodimer comprises two different receptor-targeting peptide ligands. Molecular imaging probes based on dual-receptor targeting peptide heterodimers exhibit improved tumor targeting efficacy for multi-receptor expressing tumors compared with their parent single-receptor targeting peptide monomers. Previously we have developed bombesin (BBN)-RGD (Arg-Gly-Asp) peptide heterodimers, in which BBN and RGD are covalently connected with an asymmetric glutamate linker (J Med Chem 52:425-432, 2009). Although (18)F-labeled heterodimers showed significantly better microPET imaging quality than (18)F-labeled RGD and BBN monomers in a PC-3 xenograft model which co-expresses gastrin-releasing peptide receptor (GRPR) and integrin αvβ3, tedious heterodimer synthesis due to the asymmetric nature of glutamate linker restricts their clinical applications. In this study, we report the use of a symmetric linker AEADP [AEADP = 3,3'-(2-aminoethylazanediyl)dipropanoic acid] for the synthesis of BBN-RGD peptide heterodimer. The (18)F-labeled heterodimer ((18)F-FB-AEADP-BBN-RGD) showed comparable microPET imaging results with glutamate linked BBN-RGD heterodimers, indicating that the replacement of glutamate linker with AEADP linker did not affect the biological activities of BBN-RGD heterodimer. The heterodimer synthesis is rather easy and straightforward. Because tumors often co-express multiple receptors, the use of a symmetric linker provides a general method of fast assembly of various peptide heterodimers for imaging multi-receptor expressing tumors.

In vitro binding evaluation of 177Lu-AMBA, a novel 177Lu-labeled GRP-R agonist for systemic radiotherapy in human tissues

Members of the gastrin-releasing peptide (GRP) family and its analogs bombesin (BBN) have been implicated in the biology of several human cancers including prostate, breast, colon and lung. To date, three mammalian GRP/BBN receptor subtypes have been cloned and characterized: the neuromedin B receptor (NMBR), the GRP receptor (GRPR) and the BBN-receptor subtype 3 (BB(3)). The fourth BBN receptor subtype, BB(4), has only been identified in amphibian and at present no mammalian equivalent of this receptor has been described. GRPR analogs have been used as carriers to deliver drugs, radionuclides and cytotoxins to target various cancer types that are GRPR positive. We investigated the in vitro binding properties of (177)Lu-AMBA, a novel radiolabelled BBN analog currently undergoing clinical trial as systemic radiotherapy for hormone refractory prostate cancer (HRPC) patients. Pharmacological analyses of the (177)Lu-AMBA was determined using in vitro binding studies using membrane target system containing specific receptor subtypes. We investigated the distribution of binding sites for (177)Lu-AMBA by receptor autoradiography on human neoplastic and non-neoplastic tissues. Pharmacological characterizations of (177)Lu-AMBA shows, high affinity towards NMB and GRP receptors, while little or no affinity towards BB(3) receptor. Among the 40 different types of non-neoplastic tissues tested seven of them showed limited but specific binding of (177)Lu-AMBA. Fourteen of 17 primary prostate cancers, six of 13 primary breast cancers expressed binding sites for (177)Lu-AMBA. Furthermore, no apparent differences in (177)Lu-AMBA-binding sites expression were observed between matched pairs (primary vs. secondary) of prostate and breast cancer tissues. These data represent the molecular basis for clinical applications of (177)Lu-AMBA for diagnosis and treatment of GRP-R and NMB-R positive tumors.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

18F-labeled BBN-RGD heterodimer for prostate cancer imaging

Both bombesin (BBN) analogs and cyclic RGD peptides have been suitably radiolabeled for prostate cancer imaging. However, the limited expression of gastrin-releasing peptide receptor (GRPR) and integrin alpha(v)beta(3) as well as unfavorable in vivo kinetics limited further applications of these imaging agents. We hypothesize that a peptide ligand recognizing both GRPR and integrin will be advantageous because of its dual-receptor-targeting ability.

METHODS

A BBN-RGD heterodimer was synthesized from bombesin(7-14) and c(RGDyK) through a glutamate linker and then labeled with (18)F via the N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) prosthetic group. The receptor-binding characteristics and tumor-targeting efficacy of (18)F-FB-BBN-RGD were tested in vitro and in vivo.

RESULTS

FB-BBN-RGD had comparable integrin alpha(v)beta(3)-binding affinity with c(RGDyK) and comparable GRPR-binding affinity with BBN(7-14). (18)F-FB-BBN-RGD had significantly higher tumor uptake compared with monomeric RGD and monomeric BBN peptide tracer analogs at all time points examined. The PC-3 tumor uptake of (18)F-FB-BBN-RGD was inhibited only partially in the presence of an excess amount of unlabeled BBN(7-14) or c(RGDyK) but was blocked completely in the presence of both BBN(7-14) and c(RGDyK). Compared with (18)F-FB-BBN and (18)F-FB-RGD, (18)F-FB-BBN-RGD also had improved pharmacokinetics, resulting in a significantly higher imaging quality.

CONCLUSION

Dual integrin alpha(v)beta(3) and GRPR recognition showed significantly improved tumor-targeting efficacy and pharmacokinetics compared with (18)F-labeled RGD and BBN analogs. The same heterodimeric ligand design may also be applicable to other receptor system combinations and other imaging modalities.

Phylogenetic analysis of the sequences of gastrin-releasing peptide and its receptors: Biological implications

The many biological activities of the hormone gastrin-releasing peptide (GRP), including stimulation of acid secretion and of tumour growth, are mediated by the gastrin-releasing peptide receptor (GRP-R). Here sequence comparisons are utilised to investigate the likely bioactive regions of the 125 amino acid GRP precursor and of GRP-R. Comparison of the sequences of the GRP precursor from 21 species revealed homology not only in the GRP region between amino acids 1 and 30, but also in C-terminal regions from amino acids 43 to 97. This observation is consistent with recent reports that peptides derived from the C-terminal region are biologically active. Comparison of the GRP-R sequence with the related receptors NMB-R and BRS-3 revealed that the family could be distinguished from other G-protein coupled receptors by the presence of the motif GVSVFTLTALS at the cytoplasmic end of transmembrane helix 3. Comparison of the sequences of the GRP-R from 21 species revealed that the most highly conserved regions occurred in transmembrane helices 2, 3, 5, 6 and 7, and in the third intracellular loop. These results will be important in guiding future structure-function studies of the GRP precursor and of GRP receptors.

CYP27A1 and CYP24 expression as a function of malignant transformation in the colon

Vitamin D deficiency is strongly associated with the risk of developing colorectal cancer (CRC). Because of the propensity of bioactive 1,25-dihydroxyvitamin D3 to cause toxic hypercalcemia, considerable effort has been directed to identifying safer drugs while retaining the efficacy of the parent compound. However, vitamin D precursors do not present toxicity concerns and may be sufficient for CRC chemoprevention or chemotherapy, providing the appropriate enzymes are present in colonic epithelia. We previously showed that CYP27B1 is present at equally high levels in the colon and CRC irrespective of differentiation but was not present in metastases. In this study we used quantitative immunohistochemistry to show that CYP27A1, converting D3 to 25-hydroxycholecalciferol, is present in increasing concentrations in the nuclei of normal colonic epithelia, aberrant crypt foci (ACF), and adenomatous polyps. Whereas total cellular CYP27A1 remains high in CRC and lymph node metastases, the amount of enzyme present in the nuclei decreases with tumor cell dedifferentiation while rising in the cytoplasm. Similarly, increasing amounts of the deactivating enzyme CYP24 are present in the nuclei of normal colonic epithelia, ACFs, and adenomatous polyps. Although the amount of total CYP24 decreases slightly in CRC as a function of tumor cell dedifferentiation and metastasis, location of this enzyme shifts almost entirely from the nuclear compartment to the cytoplasmic compartment. These data indicate that non-toxic vitamin D precursors should be sufficient for CRC chemoprevention, but that neither vitamin D nor its precursors may be sufficient for CRC chemotherapy.

Gastrin-releasing peptide mediates its morphogenic properties in human colon cancer by upregulating intracellular adhesion protein-1 (ICAM-1) via focal adhesion kinase

Gastrin-releasing peptide (GRP) and its receptor (GRPR) act as morphogens when expressed in colorectal cancer (CRC), promoting the assumption of a better differentiated phenotype by regulating cell motility in the context of remodeling and retarding tumor cell metastasis by enhancing cell-matrix attachment. Although we have shown that these processes are mediated by focal adhesion kinase (FAK), the downstream target(s) of GRP-induced FAK activation are not known. Since osteoblast differentiation is mediated by FAK-initiated upregulation of ICAM-1 (Nakayamada S, Okada Y, Saito K, Tamura M, Tanaka Y. J Biol Chem 278: 45368-45374, 2003), we determined whether GRP-induced activation of FAK alters ICAM-1 expression in CRC and, if so, determined the contribution of ICAM-1 to mediating GRP's morphogenic properties. Caco-2 and HT-29 cells variably express GRP/GRPR. These cells only express ICAM-1 when GRPR are present. In human CRC, GRPR and ICAM-1 are only expressed by better differentiated tumor cells, with ICAM-1 located at the basolateral membrane. ICAM-1 expression was only observed subsequent to GRPR signaling via FAK. To study the effect of ICAM-1 expression on tumor cell motility, CRC cells expressing GRP, GRPR, and ICAM-1 were cultured in the presence and absence of GRPR antagonist or monoclonal antibody to ICAM-1. CRC cells engaged in directed motility in the context of remodeling and were highly adherent to the extracellular matrix, only in the absence of antagonist or ICAM-1 antibody. These data indicate that GRP upregulation of ICAM-1 via FAK promotes tumor cell motility and attachment to the extracellular matrix.

Correlation between the expressions of gastrin, somatostatin and cyclin and cyclin-depend kinase in colorectal cancer

AIM

To explore the correlation between the expressions of gastrin (GAS), somatostatin (SS) and cyclin, cyclin-dependent kinase (CDK) in colorectal cancer, and to detect the specific regulatory sites where gastrointestinal hormone regulates cell proliferation.

METHODS

Seventy-nine resected large intestine carcinomatous specimens were randomly selected. Immunohistochemical staining for GAS, SS, cyclin D1, cyclin E, cyclin A, cyclin B1, CDK2 and CDK4 was performed according to the standard streptavidin-biotin-peroxidase (S-P) method. According to the semi-quantitative integral evaluation, SS and GAS were divided into high, middle and low groups. Cyclin D1, cyclin E, cyclin A, cyclin B1, CDK2, CDK4 expressions in the three GAS and SS groups were assessed.

RESULTS

The positive expression rate of cyclin D1 was significantly higher in high (78.6%, 11/14) and middle GAS groups (73.9%, 17/23) than in low GAS group (45.2%, 19/42) (P<0.05, c2(high vs low) = 4.691; P<0.05, c2(middle vs low) = 4.945). The positive expression rate of cyclin A was significantly higher in high (100%, 14/14) and middle GAS groups (82.6%, 19/23) than in low GAS group (54.8%, 23/42) (P<0.01, c2(high vs low) = 9.586; P<0.05, c2(middle vs low) = 5.040). The positive expression rate of CDK2 was significantly higher in high (92.9%, 13/14) and middle GAS groups (87.0%, 20/23) than in low GAS group (50.0%, 21/42) (P<0.01, c2(high vs low) = 8.086; P<0.01, c2(middle vs low) = 8.715). The positive expression rate of CDK4 was significantly higher in high (78.6%, 11/14) and middle GAS groups (78.3%, 18/23) than in low GAS group (42.9%, 18/42) (P<0.05, c2(high vs low) = 5.364; P<0.01, c2(middle vs low) = 7.539). The positive expression rate of cyclin E was prominently higher in low SS group (53.3%, 24/45) than in high (9.1%, 1/11) and middle (21.7%, 5/23) SS groups (P<0.05, c2(high vs low) = 5.325; P<0.05, c2(middle vs low) = 6.212). The positive expression rate of CDK2 was significantly higher in low SS group (77.8%, 35/45) than in high SS group (27.3%, 3/11) (P<0.01, c2(high vs low) = 8.151). There was a significant positive correlation between the integral ratio of GAS to SS and the semi-quantitative integral of cyclin D1, cyclin E, cyclin A, CDK2, CDK4 (P<0.05, (D1)r(s) = 0.252; P<0.01, (E)r(s) = 0.387; P<0.01, (A)r(s) = 0.466; P<0.01, (K2)r(s) = 0.519; P<0.01, (K4)r(s) = 0.434).

CONCLUSION

The regulation and control of gastrin, SS in colorectal cancer cell growth may be directly related to the abnormal expressions of cyclins D1, A, E, and CDK2, CDK4. The regulatory site of GAS in the cell cycle of colorectal carcinoma may be at the G(1), S and G(2) phases. The regulatory site of SS may be at the entrance of S phase.

Comparative in vitro and in vivo evaluation of two 64Cu-labeled bombesin analogs in a mouse model of human prostate adenocarcinoma

Bombesin (BBN), an analog of human gastrin-releasing peptide (GRP), binds to the GRP receptor (GRPR) with high affinity and specificity. Overexpression of GRPR has been discovered in mostly androgen-independent human prostate tissues and, thus, provides a potential target for prostate cancer diagnosis and therapy. We have previously demonstrated the feasibility of the positron emission tomography (PET) imaging using 64Cu-1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA)-[Lys3]BBN to detect GRPR-positive prostate cancer. In this study, we compared the receptor affinity, metabolic stability, tumor-targeting efficacy, and pharmacokinetics of a truncated BBN analog 64Cu-DOTA-Aca-BBN(7-14) with 64Cu-DOTA-[Lys3]BBN. Binding of each DOTA conjugate to GRPR on PC-3 and 22Rv1 prostate cancer cells was evaluated with competitive binding assay using 125I-[Tyr4]BBN as radioligand. In vivo pharmacokinetics was determined on male nude mice subcutaneously implanted with PC-3 cells. Dynamic microPET imaging was performed to evaluate the systemic distribution of the tracers. Metabolic stability of the tracers in blood, urine, tumor, liver and kidney was studied using high-performance liquid chromatography. The results showed that 125I-[Tyr4]BBN has a K(d) of 14.8+/-0.4 nM against PC-3 cells, and the receptor concentration on PC-3 cell surface is approximately 2.7+/-0.1 x 10(6) receptors per cell. The 50% inhibitory concentration value for DOTA-Aca-BBN(7-14) is 18.4 +/- 0.2 nM, and that for DOTA-[Lys3]BBN is 2.2 +/- 0.5 nM. DOTA-[Lys3]BBN shows a better tumor contrast and absolute tumor activity accumulation compared to DOTA-Aca-BBN(7-14). Studies on metabolic stability for both tracers on organ homogenates showed that 64Cu-DOTA-[Lys3]BBN is relatively stable. This study demonstrated that both tracers are suitable for targeted PET imaging to detect the expression of GRPR in prostate cancer, while 64Cu-DOTA-[Lys3]BBN may have a better potential for clinical translation.

Gastrin-releasing peptide and cancer

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

Expression of vitamin D receptor and 25-hydroxyvitamin D3-1{alpha}-hydroxylase in normal and malignant human colon

Considerable evidence exists to support the use of vitamin D to prevent and/or treat colorectal cancer. However, the routine use of bioactive vitamin D, 1,25-dihydroxyvitamin D3, is limited by the side effect of toxic hypercalcemia. Recent studies, however, suggest that colonic epithelial cells express 25-hydroxyvitamin D3-1alpha-hydroxylase, an enzyme that converts nontoxic pro-vitamin D, 25-hydroxycholecalciferol [25(OH)D3], to its bioactive form. Yet, nothing is known as to the cellular expression of 1alpha-hydroxylase and the vitamin D receptor (VDR) in the earliest histopathologic structures associated with malignant transformation such as aberrant crypt foci (ACF) and polyps [addressing the possibility of using nontoxic 25(OH)D3 for chemoprevention], nor is anything known as to the expression of these proteins in colorectal cancer as a function of tumor cell differentiation or metastasis [relevant to using 25(OH)D3 for chemotherapy]. In this study, we show that 1alpha-hydroxylase is present at equal high levels in normal colonic epithelium as in ACFs, polyps, and colorectal cancer irrespective of tumor cell differentiation. In contrast, VDR levels were low in normal colonic epithelial cells; were increased in ACFs, polyps, and well-differentiated tumor cells; and then declined as a function of tumor cell de-differentiation. Both 1alpha-hydroxylase and VDR levels were negligible in tumor cells metastasizing to regional lymph nodes. Overall, these data support using 25(OH)D3 for colorectal cancer chemoprevention but suggest that pro-vitamin D is less likely to be useful for colorectal cancer chemotherapy.

Allelic loss of the gene for the GPX1 selenium-containing protein is a common event in cancer

Selenium has been shown to reduce cancer incidence in animal models and more recent data indicate that it may be protective in humans as well. However, little is known about the mechanism by which selenium prevents cancer. Cytosolic glutathione peroxidase (GPX1), a selenium-containing antioxidant enzyme, has been implicated in the development of cancer of the head and neck, lung, and breast, in part because of allelic loss at the GPX1 locus. The study of allelic loss at the GPX1 locus in colon cancer was investigated by examining loss of heterozygosity (LOH) in DNA extracted from both tumor and adjacent histopathologically normal tissue obtained by laser capture microdissection. Tissue samples were obtained from 53 colon cancer patients. Two highly polymorphic markers, alanine codon repeats and a proline-leucine polymorphism (198P/L) present in the GPX1 gene, were used to examine LOH at this locus. Analysis of both polymorphisms identified LOH at GPX1 in a significant percentage of colorectal cancer (42%). These results indicated that LOH at the GPX1 locus is a common event in cancer development and that GPX1 or other tightly linked genes may be involved in the etiology of this disease.

Mitogenic effects of both amidated and glycine-extended gastrin-releasing peptide in defunctioned and azoxymethane-treated rat colon in vivo

Although there is abundant evidence that gastrin-releasing peptide acts as a mitogen in various carcinoma cell lines, the effect of administration of gastrin-releasing peptide on the colorectal mucosa in vivo has not been reported. The aims of this study were to determine whether continuous infusion of gastrin-releasing peptide stimulated proliferation or accelerated carcinogenesis in the rat gastrointestinal tract and other organs. The possible requirement for C-terminal amidation for mitogenic activity in vivo was also investigated. Proliferation was measured in the colon by metaphase index and by immunostaining for the proliferation marker Ki-67, and in other tissues by immunostaining alone. Acceleration of colorectal carcinogenesis was assessed by counting aberrant crypt foci after treatment with the carcinogen azoxymethane. Defunctioning of the rectum reduced both the proliferative index and the crypt height of the rectal mucosa of untreated rats. Treatment with amidated or glycine-extended gastrin-releasing peptide for 4 weeks using implanted mini-osmotic pumps resulted in a two- to three-fold increase in proliferation, and an increase in crypt height, in the defunctioned rectal mucosa (p<0.001), with smaller but significant increases in the caecum and distal colon. No changes in proliferation were detected in lung, pancreas or gastric mucosa. The numbers of aberrant crypt foci in the mid-colon, distal colon and rectum following treatment with azoxymethane were also significantly increased by infusion with amidated or glycine-extended gastrin-releasing peptide. We conclude that administration of gastrin-releasing peptide to mature rats stimulates proliferation and accelerates carcinogenesis in the colorectal mucosa, and that C-terminal amidation is not essential for either effect. Gastrin-releasing peptides could thus potentially act as promoters of colorectal carcinogenesis.

Correlation between expression of gastrin, somatostatin and cell apoptosis regulation gene bcl-2/bax in large intestine carcinoma

AIM: To explore the correlation between expression of somatostatin (SS), gastrin (GAS) and cell apoptosis regulation gene bcl-2/bax in large intestine carcinoma.

METHODS: Sixty-two large intestine cancer tissue samples were randomly and retrospectively selected from patients with large intestine carcinoma. Immunohistochemical staining for bcl-2, bax, GAS, SS was performed according to the standard streptavidin-biotin-peroxidase (S-P) method. According to the semi-quantitative integral evaluation, SS and GAS were divided into three groups as follows. Scores 1-3 were defined as the low expression group, 4-8 as the intermediate expression group, 9-16 as the high expression group. Bax and bcl-2 protein expressions in different GAS and SS expression groups of large intestine carcinoma were assessed.

RESULTS: The positive expression rate of bax had a prominent difference between SS and GAS high, intermediate and low expression groups (P<0.05, χ²_SS = 9.246; P<0.05, χ²_GAS = 6.981). The positive expression rate of bax in SS high (80.0%, 8/10) and intermediate (76.5%, 13/17) expression groups was higher than that in low expression group (40.0%, 14/35) (P<0.05, χ²_{high vs low} = 5.242; P<0.05,χ²_{middle vs low} = 6.097). The positive expression rate of bax in GAS high expression group (27.3%, 3/8) was lower than that in low expression group (69.4%, 25/36) (P<0.05, χ² = 4.594). However, bax expression in GAS intermediate expression group (46.7%, 7/15) was lower than that in low expression group, but not statistically significant. The positive expression rate of bcl-2 had a prominent difference between SS and GAS high, intermediate and low expression groups (P<0.05, χ²_SS = 7.178; P<0.05, χ²_GAS = 13.831). The positive expression rate of bcl-2 in GAS high (90.9%, 10/11) and intermediate (86.7%, 13/15) expression groups was higher than that in low expression group (44.4%, 16/36) (P<0.05, χ²_{high vs low} = 5.600; P<0.05, χ²_{middle vs low} = 7.695). However, the positive expression rate of bcl-2 in SS high (40.0%, 4/10) and intermediate (47.1%, 8/9) expression groups was lower than that in low expression group (77.1%, 27/35) (P<0.05, χ²_{high vs low} = 4.710; P<0.05, χ²_{middle vs low} = 4.706). There was a significant positive correlation between the integral ratio of GAS to SS and the integral of bcl-2 (P<0.01, r = 0.340). However, there was a negative correlation between the integral ratio of GAS to the SS and bax the integral of (P<0.05, r = -0.299).

CONCLUSION: The regulation and control of gastrin, somatostatin in cell apoptosis of large intestine carcinoma may be directly related to the abnormal expression of bcl-2, bax.

Differential expression of 37 selected genes in hormone‐refractory prostate cancer using quantitative taqman real‐time RT‐PCR

Progression of prostate cancer to androgen independence remains the primary obstacle to improved survival. The development of more effective treatments depends on our understanding of the molecular events associated with the hormone-refractory stage. We quantified, among 90 screened genes, the expression of 37 target genes, using real-time quantitative RT-PCR. Gene expression was studied in 13 samples of HPRC compared to 33 clinically localised cancers and normal prostate tissue. We identify 19 genes with significant differential expression in HRPC compared to localised prostate cancer. Genes with decreased expression included receptors for growth factors, MMR genes and the serine protease hepsin. Analysis of increased gene expression confirmed the importance of AR upregulation and highlighted genes not previously linked to HRPC, including enzymes involved in steroid synthesis and the antiapoptotic factor survivin. Progression of prostate cancer to the hormone-refractory state is associated with differential gene expression, which may prove useful for both understanding disease progression and the development of new therapeutic approaches.

Phosphorylation of focal adhesion kinase tyrosine 397 critically mediates gastrin-releasing peptide's morphogenic properties

We have proposed that gastrin-releasing peptide (GRP) and its receptor (GRP-R) are morphogens that when aberrantly re-expressed in colon cancer promote tumor cell differentiation and retard metastasis. Because circumstantial evidence suggested that these properties were mediated via focal adhesion kinase (FAK), the purpose of this study was to elucidate the role of GRP-induced activation of this enzyme on properties fundamental to metastasis including cell attachment, motility, and deformability. To do this, we studied 293 cells, a non-malignant epithelial cell line that we show expresses GRP and GRPR. To dissect out the role of FAK, 293 cells were modified to inducibly express the dominant negative enzyme FAK-related non-kinase (FRNK) under control of a Tet-On (i.e., doxycycline-sensitive) promoter. Under serum-free conditions, GRP acting in an autocrine manner caused FAK to be phosphorylated at Y397; and this could be completely inhibited either by incubating with the specific GRP-R antagonist D-Phe(6)(bombesin) methyl ester, or by upregulating FRNK using doxycycline. To measure cell attachment, we designed a cone-plate viscometer that recorded the shear stress required to detach cells from their underlying matrix. To assess motility, confluent cells were wounded and behavior assessed by time-lapse photography. To measure deformability, we recorded the ability of cells to be completely drawn into a micropipette <50% the size of the non-deformed cell. Control 293 cells adhered more avidly to their underlying matrix, rapidly remodeled wounded tissues without any increase in overall proliferation, and were less distensible than cells treated with antagonist or doxycycline. Thus, these findings suggest that expression of GRP/GRPR in cancer inhibits metastasis by enhancing cell attachment to the matrix, regulating motility in the context of remodeling, and decreasing deformability.