Bombesin related peptides/receptors and their promising therapeutic roles in cancer imaging,targeting and treatment

Introduction: Despite remarkable advances in tumor treatment, many patients still die from common tumors (breast, prostate, lung, CNS, colon, and pancreas), and thus, new approaches are needed. Many of these tumors synthesize bombesin (Bn)-related peptides and over-express their receptors (BnRs), hence functioning as autocrine-growth-factors. Recent studies support the conclusion that Bn-peptides/BnRs are well-positioned for numerous novel antitumor treatments, including interrupting autocrine-growth and the use of over-expressed receptors for imaging and targeting cytotoxic-compounds, either by direct-coupling or combined with nanoparticle-technology.

Areas covered: The unique ability of common neoplasms to synthesize, secrete, and show a growth/proliferative/differentiating response due to BnR over-expression, is reviewed, both in general and with regard to the most frequently investigated neoplasms (breast, prostate, lung, and CNS). Particular attention is paid to advances in the recent years. Also considered are the possible therapeutic approaches to the growth/differentiation effect of Bn-peptides, as well as the therapeutic implication of the frequent BnR over-expression for tumor-imaging and/or targeted-delivery.

Expert opinion: Given that Bn-related-peptides/BnRs are so frequently ectopically-expressed by common tumors, which are often malignant and become refractory to conventional treatments, therapeutic interventions using novel approaches to Bn-peptides and receptors are being explored. Of particular interest is the potential of reproducing with BnRs in common tumors the recent success of utilizing overexpression of somatostatin-receptors by neuroendocrine-tumors to provide the most sensitive imaging methods and targeted delivery of cytotoxic-compounds.     

Leptin and the treatment of obesity: its current status

Leptin, the protein product of the ob gene, is primarily an adipocyte-secreted hormone, whose functional significance is rapidly expanding. Although early research efforts were focused on defining leptin's role in reversing obesity in rodents, there is now substantial evidence indicating that its influence extends to several hypothalamic–pituitary–endocrine axes, including gonadal, adrenal, thyroid, growth hormone, and pancreatic islets. A role for leptin in hematopoiesis, angiogenesis, immune function, osteogenesis, and wound healing has also been documented. The results of recent clinical trials with recombinant human leptin indicated that its effectiveness in restoring energy balance and correcting obesity-related endocrinopathies in genetically obese rodent models extended only partially to the management of human obesity. New efforts in drug development have focused on leptin-related synthetic peptide agonists as potential anti-obesity pharmacophores.     

Anorectic action of bombesin requires receptor for corticotropin-releasing factor but not for oxytocin

The marked functional similarities between pharmacological effects of bombesin and of corticotropin-releasing factor (CRF), prompted the formulation and testing of our working hypothesis that BN may elicit its biological effects through the release of CRF. Central pretreatment with CRF receptor antagonists, -helical CRF-(9–41) (-CRF-(9–41)) or [

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-Phe¹², CMeLeu³⁷]CRF-(12–41) (CMeCRF), blocked the effects of centrally administered bombesin on food intake and related behaviors and partially attenuated the satiety effects of systemically administered bombesin. We also attempted to characterize the specificity of this interaction through the combined use of bombesin with the oxytocin antagonist, [d(CH₂)₅, Tyr(OMe)², Orn⁸]vasotocin (vasotocin). Central pretreatment with vasotocin failed to alter bombesin-induced behaviors, suggesting the absence of a pharmacological interaction between these two peptidergic systems. Finally, the CRF antagonist failed to reverse the oxytocin-induced suppression of food intake, indicating that CRF does not have a direct role in the mediation and/or modulation of the effects of oxytocin on food intake. Thus, the present experiments support the contention that bombesin partly mediates its feeding-suppressant effects through interactions with CRF. The specificity of this interaction is supported by the lack of interaction between bombesin and/or CRF with oxytocin.     

The role of melanocortins in body weight regulation: opportunities for the treatment of obesity

Five G-protein-coupled melanocortin receptors (MC₁–MC₅) are expressed in mammalian tissues. The melanocortin receptors support diverse physiological functions, including the regulation of hair color, adrenal function, energy homeostasis, feed efficiency, sebaceous gland lipid production and immune and sexual function. The melanocortins (adrenocorticotropic hormone (ACTH), -melanocyte-stimulating hormone (-MSH), β-MSH and γ-MSH) are agonist peptide ligands for the melanocortin receptors and these peptides are processed from the pre-prohormone proopiomelanocortin (POMC). Peptide antagonists for the melanocortin MC₁, MC₃ and MC₄ receptors include agouti-related protein (AgRP) and agouti. Diverse lines of evidence, including genetic and pharmacological data obtained in rodents and humans, support a role for the melanocortin MC₃ and MC₄ receptors in the regulation of energy homeostasis. Recent advances in the development of potent and selective peptide and non-peptide melanocortin receptor ligands are anticipated to help unravel the roles for the melanocortin receptors in humans and to accelerate the clinical use of small molecule melanocortin mimetics.     

The role of melanocortins in body weight regulation: opportunities for the treatment of obesity

Five G-protein-coupled melanocortin receptors (MC(1)-MC(5)) are expressed in mammalian tissues. The melanocortin receptors support diverse physiological functions, including the regulation of hair color, adrenal function, energy homeostasis, feed efficiency, sebaceous gland lipid production and immune and sexual function. The melanocortins (adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), beta-MSH and gamma-MSH) are agonist peptide ligands for the melanocortin receptors and these peptides are processed from the pre-prohormone proopiomelanocortin (POMC). Peptide antagonists for the melanocortin MC(1), MC(3) and MC(4) receptors include agouti-related protein (AgRP) and agouti. Diverse lines of evidence, including genetic and pharmacological data obtained in rodents and humans, support a role for the melanocortin MC(3) and MC(4) receptors in the regulation of energy homeostasis. Recent advances in the development of potent and selective peptide and non-peptide melanocortin receptor ligands are anticipated to help unravel the roles for the melanocortin receptors in humans and to accelerate the clinical use of small molecule melanocortin mimetics.     

Sibutramine sensitivity assay revealed a unique phenotype of bombesin BB3 receptor-deficient mice

Sibutramine sensitivity assay in genetically obese (bombesin BB3 receptor (BRS-3)-deficient mice, KK-Ay mice, db/db mice and Zucker obese rat) and wild-type animals was examined. The sensitivity of Sibutramine (10 mg/kg, p.o.) in BRS-3-deficient mice was retained as well as normal animals; however, it was decreased in KK-Ay, db/db mice and Zucker obese rat. The suppression values of food intake in BRS-3-deficient, KK-Ay, db/db mice and Zucker obese rat were 49.8+/-5.8%, 16.1+/-4.7%, 0.1+/-2.8% and -2.0+/-2.2% (mean +/- S.E.), respectively. Next, we found that the contribution of hyperphagia was small in the progress of obesity in BRS-3-deficient mice by calculating energy efficiency. Our results indicate that there is an inverse relationship between the sensitivity to Sibutramine and the contribution of hyperphagia to the progress of obesity in animals.     

Adipose targets for obesity drug development

The prevalence of obesity is increasing rapidly in most parts of the world and effective therapeutic drugs are urgently needed. The discovery of leptin in 1994 initiated a new understanding of adipose tissue function, and adipose tissue is now known to not only store and release fatty acids, but also to produce a wealth of factors that have an impact on the regulation of body weight and blood glucose homeostasis. Also, adipocytes express proteins that engage signalling pathways playing important roles in fuel substrate and energy metabolism. These proteins constitute a diverse array of adipose target candidates for the development of drugs to treat obesity. Some of these potential targets have been validated and are now in drug development stages, providing hope that the current obesity epidemic can be addressed by effective drug treatments in the near future.     

An evaluation of liraglutide including its efficacy and safety for the treatment of obesity

ABSTRACT

Introduction: The prevalence of obesity is increasing worldwide and associated conditions, particularly type 2 diabetes mellitus (T2DM), also show increasing prevalence. Lifestyle intervention should be the first line of management for obesity but additional pharmacotherapy is often required and bariatric surgery is appropriate in more severe cases. Drugs acting as glucagon-like peptide-1 receptor agonists (GLP-1RAs) developed for the management of T2DM reduce body weight and liraglutide is the first GLP-1RA to be approved for the treatment of obesity in patients with and without T2DM.

Areas covered: In this review of relevant published material, the authors summarize the pharmacokinetics, pharmacodynamics, clinical efficacy and safety of liraglutide for the treatment of obesity.

Expert opinion: Liraglutide effectively reduces body weight and body fat through mechanisms involving reduced appetite and lowered energy intake, independent of its glucose-lowering effects. Like most of the other medications currently available for obesity, liraglutide has some common adverse effects, although generally not serious ones. Liraglutide has additional benefits in reducing cardiovascular events in patients with T2DM but the cost and the need for daily injections may limit its use in obesity. Newer GLP-1RAs, such as semaglutide, or other drugs in development for obesity may have advantages over liraglutide.     

Novel peptides for the treatment of multiple sclerosis

Multiple sclerosis (MS) arises from T cell-mediated destruction of the myelin sheath. In MS patients who express the human leukocyte antigen (HLA)-DR2 haplotype (about two-thirds of MS patients), the major T cell response is directed to a region between residues 85 and 99 of myelin basic protein (MBP^{85 – 99}) presented on HLA-DR2. One approved medication for MS, amino acid copolymer-1 (Cop-1, Copaxone^TM, Teva) is thought to alter this anti-MBP^{85 – 99} response by interacting with HLA-DR2, but is only partially effective. Here, synthetic peptides were designed according to the binding motif of MBP^{85 – 99} and the binding pockets of HLA-DR2. It is claimed that some of these peptides, which bind to HLA-DR2 and inhibit activation of MBP-specific T cell lines better than Cop-1, might be more effective than the latter for MS therapy.     

Thyroid hormones in the pathogenesis and treatment of obesity

Thyroid hormones (TH) are potent modulators of adaptive thermogenesis and can potentially contribute to development of obesity. The decrease of T₃ in association with reduction of calorie intake is centrally regulated via decreases in leptin and melanocortin concentrations and peripherally via a decrease in deiodinase activity, all aimed at protein and energy sparing. The use of TH in the treatment of obesity is hardly justified except in cases of elevated thyrotropin (TSH) with low/normal T₃ and T₄ and/or a low T₃ or T′₃/T₄ or a high TSH/T₃ ratio. TH treatment with small doses of T₃ can also be exceptionally applied in obese patients resistant to dietary therapy who are taking β-adrenergic blockers or with obesity developed after cessation of cigarette smoking and with hyperlipidemia and a concomitant high thryrotropin/T₃ ratio. Supplementation with Se²⁺ and Zn²⁺ may be tried along with more severe calorie restriction to prevent decline of T₃.     

Glycation Methods for Bombesin Analogs Containing the (NαHis)Ac chelator for 99mTc(CO)3 Radiolabeling

The overexpression of peptide receptors in a variety of human carcinomas has generated considerable interest in peptide‐based radiopharmaceuticals for peptide receptor imaging and peptide receptor radiotherapy. The gastrin‐releasing peptide receptor is overexpressed in human prostate‐, breast‐, colon‐ and small cell lung carcinoma cells. We have developed metabolically stable ^99mTc‐radiolabeled bombesin ([Cha¹³, Nle¹⁴]BBS(7–14)) analogs, which bind with high affinity to the gastrin‐releasing peptide receptors. However, because of their lipophilicity, they showed unfavorable biodistribution with high hepatic accumulation and hepatobiliary excretion. We now report a study of different glycation methods for [Cha¹³, Nle¹⁴]BBS(7–14) analogs to improve their biodistribution profile. Whereas the glycation using the Maillard reaction was problematic, resulting in low yields, selective introduction of the glycomimetic shikimic acid to the side chain of a Lys residue was possible. A chemoselective ligation of α‐d ‐glucose to an amino‐oxyacetylated [Cha¹³, Nle¹⁴]BBS(7–14) analog could be achieved, but was complicated by the co‐elution of starting peptide and glycopeptide. The best procedure consisted of the [1,3]‐cycloaddition of N₃‐β‐d ‐glucose to a propargylglycine‐containing [Cha¹³, Nle¹⁴]BBS(7–14) analog, using a catalytic amount of Cu(I)I. All glycated [Cha¹³, Nle¹⁴]BBS(7–14) analogs showed high affinity for the gastrin‐releasing peptide receptor and rapid accumulation into PC‐3 tumor cells.     

Exenatide once weekly for the treatment of type 2 diabetes

Exenatide is the first glucagon-like peptide-1 (GLP-1) receptor agonist approved for the treatment of type 2 diabetes mellitus (T2DM). Exenatide lowers blood glucose through multiple mechanisms, including enhancement of glucose-dependent insulin secretion, suppression of excess glucagon secretion, reduction of food intake and slowing of gastric emptying. The current formulation of exenatide requires twice-daily dosing (exenatide BID), and an extended-release formulation of exenatide is now in development for use as a once-weekly injection (exenatide QW). The purpose of this report is to review the most current clinical data on the development of exenatide QW for the treatment of T2DM. In clinical trials, exenatide QW significantly improved glycemic control, resulted in patient weight loss, and was well tolerated in patients with T2DM. In a head-to-head clinical trial, exenatide QW caused greater improvements in glycemic control and was better tolerated than exenatide BID. Given the rapidly increasing prevalence of diabetes and obesity worldwide, exenatide QW is a promising development candidate for the treatment of T2DM.     

The potential role of estrogen receptors and the SRC family as targets for the treatment of breast cancer

Background: Breast cancer has a number of subtypes, the main ones are estrogen-receptor (ER)-positive, luminal type A and B. Treatment selection, with respect to hormonal therapy, is based upon ER expression. Whilst for ER-positive cancers, endocrine therapy is highly successful in the adjuvant setting, a significant proportion of cancers exhibit hormone resistance, often associated with altered growth factor receptor or ER signalling. Modulation of steroid receptor function by receptor co-activators or repressors is a potential mechanism of resistance. The p160 or SRC proto-oncogene family of co-activators are important in breast cancer response to endocrine therapy and can act as a paradigm of co-activator function. Objective/methods: This review focuses on the role of ER and ER co-activators in breast cancer and current approaches to targeting SRC co-factors for treatment of hormone-receptor-positive breast cancer. Results/conclusions: There is a drive to selectively apply aromatase inhibitors on the basis of either risk or biological evidence of resistance to tamoxifen treatment. Both strategies may yield improved treatment to benefit ratios.     

De novo design of DeltaF -containing heme-binding peptides

The structural characterization of de novo designed metalloproteins together with determination of chemical reactivity can provide a detailed understanding of the relationship between protein structure and functional properties. Toward this goal, using the basic scaffold of 1pbz (Rosenblatt et al. (2003) Proc Natl Acad Sci U S A;100:13140) we have designed cyclic DeltaF-containing heme-binding peptides. The alpha- and beta-bands in UV-Vis spectroscopy are indicative of bis-His-ligated heme complex. Most of our DeltaF-containing peptides have more affinity to cobalt(III)Coproporphyrinate-I than heme because cobalt(III)Coproporphyrinate-I contains two additional propionate groups which can have salt bridge interactions with the lysine residues in the peptide. Helicity induction in peptide by DeltaF and aromatic interaction of DeltaF with heme have increased the heme affinity of CP-6-12pbz (cyclic peptide with substitutions of Ala at positions 6 and 12 by DeltaF; 905/mm) compared with 1pbz (279/mm). The nuclear magnetic resonance spectra are indicative of overall helical structure for CP-6-12pbz and CP-6-12pbz in complex with cobalt (III)Coproporphyrinate-I. The descending order of heme affinity in peptides (CP-6-12pbz > CP-12pbz > CP-5-12pbz) indicates that DeltaF at i + 3 or i - 3 from the central H9 favors heme binding but disrupts the same when placed at i - 4.     

The discovery of taranabant, a selective cannabinoid-1 receptor inverse agonist for the treatment of obesity

The cannabinoid-1 receptor (CB1R) has emerged as one of the most important targets for the treatment of obesity. Pioneering studies with rimonabant helped to validate animal models of food intake reduction and weight loss and made the connection to weight loss in the clinic. A novel, acyclic amide was identified from a high throughput screen (HTS) of the Merck sample collection and found to be a potent and selective CB1R inhibitor. Further optimization led to more potent compounds that were orally active in reducing food intake and weight loss in diet-induced obese (DIO) rats. However, many of these analogues exhibited a high potential for bioactivation and the formation of reactive intermediates and covalent protein binding. Identification of the products of oxidative metabolism guided medicinal chemistry efforts to minimize the formation of these unwanted products. These efforts resulted in the identification of the CB1R inverse agonist, taranabant, which is currently in Phase-III clinical studies for the treatment of obesity. This mini-review will describe some of the medicinal chemistry strategies that were followed from the original high throughput screen hit to the discovery of taranabant.     

Stimulation of proliferation and migration of a colorectal cancer cell line by amidated and glycine-extended gastrin-releasing peptide via the same receptor

Although amidated forms of gastrin-releasing peptide (GRP) have been identified as autocrine growth factors in small cell lung cancer, their role in the development and progression of colorectal carcinoma is less clear. In addition, the biological activity of non-amidated gastrin-releasing peptide has not been investigated in colorectal carcinoma cells. We therefore investigated the effect of bombesin (a homologue of gastrin-releasing peptide) on proliferation, migration and inositol phosphate production in the human colorectal carcinoma cell line DLD-1, and determined the ability of gastrin-releasing peptide receptor antagonists to inhibit these effects. We also compared the biological activities of amidated and non-amidated GRP in the same assays. Treatment with either bombesin, or amidated or non-amidated GRP resulted in significant increase in proliferation, and in migration in a wound-healing assay. Both the mitogenic and migratory effects of amidated and non-amidated forms were inhibited by the GRP receptor antagonist [d-Phe⁶, Leu-NHet¹³, des-Met¹⁴]-bombesin(6-13). The presence of GRP receptor mRNA and GRP binding sites in three colorectal carcinoma cell lines was demonstrated by RT-PCR and by binding of radiolabelled bombesin, respectively. Transfection of DLD-1 cells with a dominant negative phosphatidylinositol 3-kinase did not affect bombesin-stimulated cell proliferation, but inhibited bombesin-stimulated cell migration. Bombesin and GRPgly activated phospholipase C, mitogen-activated protein kinase and focal adhesion kinase. We conclude that both amidated and non-amidated forms of gastrin-releasing peptide accelerate proliferation and migration of DLD-1 human colorectal carcinoma cells via the gastrin-releasing peptide receptor, but that phosphatidylinositol 3-kinase is only involved in the cell migration signalling pathway. Our results suggest a potential role for gastrin-releasing peptide receptor antagonists in the management of colorectal carcinoma.     

Lorcaserin: a novel serotonin 2C agonist for the treatment of obesity

Abstract

Background:

Obesity has become an epidemic in the United States and its prevalence continues to increase. Adjunctive treatment with pharmacotherapy is often reserved for individuals who fail to achieve their intended weight goals with diet and exercise alone. Current approved therapies for weight loss include phentermine, diethylpropion, orlistat, and phentermine/topiramate. The objective of this paper was to review the place of lorcaserin, a novel serotonin 2C agonist, which was FDA approved in July 2012. Unlike contemporary lipase inhibitors and sympathomimetic amines, lorcaserin is purported to reduce food consumption and increase satiety.     

Investigational therapies in the treatment of obesity

Obesity is a major public health concern and environmental factors are involved in its development. The hypothalamus is a primary site for the integration of signals for the regulation of energy homeostasis. Dysregulation of these pathways can lead to weight loss or gain. Some drugs in development can have favourable effects on body weight, acting on some of these pathways and leading to responses resulting in weight loss. Strategies for the management of weight reduction include exercise, diet, behavioural therapy, drug therapy and surgery. Investigational antiobesity medications can modulate energy homeostasis by stimulating catabolic or inhibiting anabolic pathways. Investigational drugs stimulating catabolic pathways consist of leptin, agonists of melanocortin receptor-4, 5-HT and dopamine; bupropion, growth hormone fragments, cholecystokinin subtype 1 receptor agonist, peptide YY_3-36, oxyntomodulin, ciliary neurotrophic factor analogue, β3-adrenergic receptor agonists, adiponectin derivatives and glucagon-like peptide-1. On the other hand, investigational drugs inhibiting anabolic pathways consist of the ghrelin receptor, neuropeptide Y receptor and melanin-concentrating hormone-1 antagonists; somatostatin analogues, peroxisome proliferator-activated receptor-γ and -β/δ antagonists, gastric emptying retardation agents, pancreatic lipase inhibitors, topiramate and cannabinoid-1 receptor antagonists. These differing approaches are reviewed and commented on in this article.     

Structural determinants for binding to CGRP receptors expressed by human SK-N-MC and Col 29 cells: studies with chimeric and other peptides

1. Structure-activity relationships for the binding of human α-calcitonin gene-related peptide 8–37 (hαCGRP_8–37) have been investigated at the CGRP receptors expressed by human SK-N-MC (neuroblastoma) and Col 29 (colonic epithelia) cells by radioligand binding assays and functional assays (hαCGRP stimulation of adenylate cyclase).
2. On SK-N-MC cells the potency order was hαCGRP_8–37>hαCGRP_19–37=AC187>rat amylin_8–37> hα[Tyr⁰]-CGRP_28–37 (apparent pKBs of 7.49±0.25, 5.89±0.20, 6.18±0.19, 5.85±0.19 and 5.25±0.07). The SK-N-MC receptor appeared CGRP₁-like.
3. On Col 29 cells, only hαCGRP_8–37 of the above compounds was able to antagonize the actions of hαCGRP (apparent pKB=6.48±0.28). Its receptor appeared CGRP₂-like.
4. hα[Ala^11,18]-CGRP_8–37, where the amphipathic nature of the N-terminal α-helix has been reduced, bound to SK-N-MC cells a 100 fold less strongly than hαCGRP_8–37.
5. On SK-N-MC cells, hαCGRP_8–18, _28–37 (M433) and mastoparan-hαCGRP_28–37 (M432) had apparent pKBs of 6.64±0.16 and 6.42±0.26, suggesting that residues 19–27 play a minor role in binding. The physico-chemical properties of residues 8–18 may be more important than any specific side-chain interactions.
6. M433 was almost as potent as hαCGRP_8–37 on Col 29 cells (apparent pKB=6.17±0.20). Other antagonists were inactive.

     

Cyclization of peptides on a solid support. Application to cyclic analogs of Substance P

The general conditions for cyclization of peptides on polymer matrix by disulfide bridge formation are reported. This procedure is based on attack of 3-nitro-2-pyridinesulfenyl group (Npys) by a thiol function. It has been used for synthesis of five cyclic analogs of Substance P.