Radiolabeled peptides and their expanding role in clinical imaging and targeted cancer therapy

There is an expanding body of evidence showing that synthetic peptides in combination with radioactive isotopes can be utilized for medical purposes. This area is of particular interest in oncology where applications in diagnosis and therapy are at different stages of development. We review the contributions in this area by the group originally founded by Carlo Pedone in Naples many years ago. We highlight the work of this group in the context of other developments in this area, focusing on three biologically relevant receptor systems: somatostatin, gastrin-releasing peptide, and cholecystokinin-2/gastrin receptors. We focus on key milestones, state of the art, and challenges in this area of research as well as the current and future outlook for expanding clinical applications.

Correction: Verdoliva et al. Zeolites as Acid/Basic Solid Catalysts: Recent Synthetic Developments. Catalysts 2019, 9, 248

The authors wish to make the following correction to this paper [...]

Bioactive Glass-Ceramic Scaffolds Coated with Hyaluronic Acid-Fatty Acid Conjugates: A Feasibility Study

Promoting bone healing is a key challenge in our society that can be tackled by developing new implantable biomaterials provided with regenerative properties. In this work, the coating of three-dimensional porous glass-derived scaffolds with hyaluronic acid (HA)-fatty acids was investigated for the first time. The starting scaffolds, based on bioactive silicate glass, were produced by foam replication followed by sintering; then, HA-palmitate and HA-oleate conjugate coatings were deposited on the scaffold struts through a dipping procedure. FT-IR analysis confirmed the successful deposition of the coatings on the surface and struts of the scaffolds, the foam-like architecture of which was maintained as assessed by SEM investigations. The in vitro bioactivity of the HA-fatty-acid-coated scaffolds was studied by immersion tests in simulated body fluid and the subsequent evaluation of hydroxyapatite formation. The deposition of the polymeric coating did not inhibit the apatite-forming ability of scaffolds, as revealed by the formation of nanostructured hydroxyapatite agglomerates 48 h from immersion. These promising results motivate further investigation of these novel bioactive systems, which are expected to combine the bone-bonding properties of the glass with the wound-healing promotion carried out by the polymeric conjugates.

Fluorescence Studies: A9 Peptide, Functionalized with a Fluorogenic Probe, Interacts with Its Receptor Model HER2-DIVMP

A recently developed synthetic protocol allowed for the functionalization of the active peptide A9 with a fluorogenic probe, which is useful for studying biomolecular interactions. Essentially, a nucleophilic attack on a halo-substituted benzofurazan is selectively performed by a cysteine sulfhydryl group. The process is assisted by the basic catalysis of activated zeolites (4 Å molecular sieves) and promoted by microwave irradiation. Fluorescence studies revealed that a donor-acceptor pair within the peptide sequence was introduced, thus allowing a deeper investigation on the interaction process between the peptide ligand and its receptor fragment. The obtained results allowed us to come full circle for all the currently understood structural determinants that were found to be involved in the binding process.

Microwave Heating Promotes the S-Alkylation of Aziridine Catalyzed by Molecular Sieves: A Post-Synthetic Approach to Lanthionine-Containing Peptides

Aziridine derivatives involved in nucleophilic ring-opening reactions have attracted great interest, since they allow the preparation of biologically active molecules. A chemoselective and mild procedure to convert a peptide cysteine residue into lanthionine via S-alkylation on aziridine substrates is presented in this paper. The procedure relies on a post-synthetic protocol promoted by molecular sieves to prepare lanthionine-containing peptides and is assisted by microwave irradiation. In addition, it represents a valuable alternative to the stepwise approach, in which the lanthionine precursor is incorporated into peptides as a building block.

Thio-conjugation of substituted benzofurazans to peptides: molecular sieves catalyze nucleophilic attack on unsaturated fused rings

An efficient procedure to selectively introduce benzofurazan moieties into peptides was developed. It employs zeolite to catalyze the S-conjugation reaction.

Peptide Ligands Specifically Targeting HER2 Receptor and the Role Played by a Synthetic Model System of the Receptor Extracellular Domain: Hypothesized Future Perspectives

A short (Fab)trastuzumab-derived peptide specific for HER2 receptor was identified. Its affinity for the model system HER2-DIVMP was found in a nanomolar range. The structural determinants responsible for the interaction between this ligand (A9) and HER2-DIVMP were investigated by both computational and NMR analysis. Next, the possibility of using A9 as HER2- specific probe for the nuclear medicine imaging was evaluated by conjugating A9 with the DTPA chelator and radiolabeling it with ¹¹¹In. The developed probe retained a nanomolar affinity to HER2-overexpressing cancer cells, however, some unspecific binding also occurred. The peptide internalization into cells by receptor-mediated endocytosis was also studied. Future perspectives are aimed at using A9 as a probe for molecular imaging diagnostics as well as active targeting of anticancer drugs. Lead structure optimization is needed to minimize the percentage of A9 unspecific binding and to increase the binding affinity to the receptor.

Diagnosis of benign paroxysmal positional vertigo in Emergency Department: Our experience

The Benign Paroxysmal Positional Vertigo (BPPV) represents the first cause of peripheral vertigo in populations and it is determined by a displacement of otoconial fragments within the semicircular canals. Following the patient’s head movements, these fragments, moving by inertia, incorrectly stimulate the canals generating vertigo. The BPPV is diagnosable by observing the nystagmus that is generated in the patient following the Dix-Hallpike maneuver used for BPPV diagnosis of vertical semi-circular canal, and, following the supine head yaw test used for lateral semi-circular canal. Correctly identifying the origin of this specific peripheral vertigo, would mean to obtain a faster diagnosis and an immediate resolution of the problem for the patient. In this context, this study aims to identify precise training activities, aimed at the application of specific diagnostic maneuverers for algorithm decisions in support of medical personnel. The evaluations reported in this study refer to the data collected in the Emergency Department of the Cardarelli Hospital of Naples. The results obtained, over a six-month observation period, highlighted the advantages of the proposed procedures in terms of costs, time and number of BPPV diagnoses.

Definition of miRNA Signatures of Nodal Metastasis in LCa: miR-449a Targets Notch Genes and Suppresses Cell Migration and Invasion

Laryngeal cancer (LCa), a neoplasm of the head and neck region, is a leading cause of death worldwide. Surgical intervention remains the mainstay of LCa treatment, but a crucial point is represented by the possible nodal involvement. Therefore, it is urgently needed to develop biomarkers and therapeutic tools able to drive treatment approaches for LCa. In this study, we investigated deregulated microRNAs (miRNAs) in tissues from LCa patients with either lymph node metastases (N+) or not (N−). miRNA expression profiling was performed by a comprehensive PCR array and subsequent validation by RT-qPCR. Results showed a significant decrease of miR-449a expression in N+ compared to N− patients, and miR-133b down-modulation in LCa tissues compared to paired normal ones. Receiver operating characteristic (ROC) curve analysis revealed the potential diagnostic power of miR-133b for LCa detection. According to the validation results, we selected miR-449a for further in vitro studies. Ectopic miR-449a expression in the LCa cell line Hep-2 inhibited invasion and motility in vitro, slowed cell proliferation, and induced the downregulation of Notch1 and Notch2 as direct targets of miR-449a. Collectively, this study provides new promising biomarkers for LCa diagnosis and a new opportunity to use miR-449a for the treatment of nodal metastases in LCa patients.

SPR and NMR characterization of the molecular interaction between A9 peptide and a model system of HER2 receptor: A fragment approach for selecting peptide structures specific for their target

The binding process of A9 peptide toward HER2-DIVMP, a synthetic model of the receptor domain IV, was studied by using the surface plasmon resonance (SPR) technique, with the aim of validating it as a fast and reliable screening method for selecting peptide ligands specifically targeting a domain of their target. To investigate the structural basis of A9 binding to the model of HER2-DIVMP, multiple ligand-based nuclear magnetic resonance (NMR) methods were applied. The use of saturation transfer difference (STD) and WaterLOGSY NMR experiments identified key residues in the peptide for the receptor binding. Moreover, the bound conformation of the A9 peptide was obtained using transferred nuclear Overhauser effect spectroscopy (trNOESY) experiments. The NMR data revealed an extended binding surface that confirms an in silico model previously reported. These structural findings could provide good starting points for future lead structures optimization specific for the receptor target.

Lanthionine Peptides by S-Alkylation with Substituted Cyclic Sulfamidates Promoted by Activated Molecular Sieves: Effects of the Sulfamidate Structure on the Yield

A green and efficient method for preparing lanthionine peptides by a highly chemoselective and stereochemically controlled procedure is presented. It involves an S-alkylation reaction, promoted by activated molecular sieves, on chiral cyclic sulfamidates, both N-protected and unprotected. Of note, the reaction yield was high also for cyclic sulfamidates bearing a free amine group, while other strategies failed to achieve a ring-opening nucleophilic reaction with N-unprotected substrates. To prove the feasibility of the procedure, the synthesis of a thioether ring B mimetic of the natural lantibiotic haloduracin β was performed.

Microwave heating in peptide side chain modification via cysteine alkylation

Microwave irradiation has been successfully applied to a selective synthetic procedure for introducing molecular substituents on peptides, providing a noticeable reduction of the reaction time and also an increased crude peptide purity for some compounds.

Eco-friendly microwave-assisted protocol to prepare hyaluronan-fatty acid conjugates and to induce their self-assembly process

An environmentally sustainable and energy-efficient synthetic process has been developed to prepare hyaluronan-based nano-sized material. It consists in a microwave-promoted acylation of the hydroxyl function of the polysaccharide with natural fatty acids, performed under solvent-free conditions. The efficient interaction of the solid reagents with the MW radiation accounts for the obtained high yielded products. The self-assembly process of the obtained compounds very fast occurred in an aqueous medium under MW-radiation, thus allowing the development of a green protocol for the nano-particles preparation.

HER2-mediated anticancer drug delivery: strategies to prepare targeting ligands highly specific for the receptor

HER2 receptor, for its involvement in tumorigenesis, has been largely studied as topic in cancer research. In particular, the employment of trastuzumab (Herceptin), a humanized anti-HER2 antibody, showed several clinical benefits in the therapy against the breast cancer. Moreover, for its accessible extracellular domain, this receptor is considered an ideal target to deliver anticancer drugs for the receptormediated anticancer therapy. By now, monoclonal antibody and its fragments, affibody, and some peptides have been employed as targeting agents in order to deliver various drugs to HER2 positive tumor cells. In particular, the ability to perform a fast and reliable screening of a large number of peptide molecules would make possible the selection of highly specific compounds to the receptor target. In this regard, the availability of preparing a simplified synthetic model which is a good mimetic of the receptor target and can be used in a reliable screening method of ligands would be of a strategic importance for the development of selective HER2-targeting peptide molecules. Herein, we illustrate the importance of HER2-targeted anticancer therapies. We also report on a synthetic and effective mimetic of the receptor, which revealed to be a useful tool for the selection of specific HER2 ligands.

Structural identification of an HER2 receptor model binding pocket to optimize lead compounds: a combined experimental and computational approach

In silico methods and experimental data obtained from fluorescence studies allowed the identification of a new binding pocket for the HER2-DIVMP receptor model.

Air oxidation method employed for the disulfide bond formation of natural and synthetic peptides

Among the available protocols, chemically driven approaches to oxidize cysteine may not be required for molecules that, under the native-like conditions, naturally fold in conformations ensuring an effective pairing of the right disulfide bridge pattern. In this contest, we successfully prepared the distinctin, a natural heterodimeric peptide, and some synthetic cyclic peptides that are inhibitors of the CXCR4 receptor. In the first case, the air oxidation reaction allowed to connect two peptide chains via disulfide bridge, while in the second case allowed the cyclization of rationally designed peptides by an intramolecular disulfide bridge. Computational approaches helped to either drive de-novo design or suggest structural modifications and optimal oxidization protocols for disulfide-containing molecules. They are able to both predict and to rationalize the propensity of molecules to spontaneously fold in suitable conformations to achieve the right disulfide bridges.

A biocompatible process to prepare hyaluronan-based material able to self-assemble into stable nano-particles

A microwave-assisted solvent-free process was employed to esterify palmitic, oleic and linoleic acids by hyaluronan alcoholic functions. The obtained HA derivatives were able to form stable spherical nano-sized aggregates, in a range of 63–266 nm.

Endothelial dysfunction: its clinical value and methods of assessment

Endothelial dysfunction (ED) is a systemic disorder characterized by reduced production of nitric oxide. This pathologic condition, which impairs vascular homeostasis, leads to the loss of protective properties of endothelial cells and is related to the pathogenesis of cardiovascular diseases. ED may affect every vascular bed, accounting for several clinical implications, particularly when the coronary bed is affected. Although the reliability of ED as a cardiovascular disease surrogate is still debated, many methods for its assessment have been proposed. In this review, we underline the clinical value of ED in the cardiovascular field and summarize the principal methods currently available for its assessment.

Reperfusion correlates and clinical outcomes of right ventricular dysfunction in patients with inferior ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention

We evaluated the relation between reperfusion indexes and right ventricular (RV) dysfunction in patients with inferior ST-segment elevation myocardial infarction (STEMI). We included patients with inferior STEMI undergoing percutaneous coronary intervention and right coronary artery as infarct-related artery. Myocardial reperfusion was evaluated by Thrombolysis In Myocardial Infarction (TIMI) flow, TIMI frame count, myocardial blush grade, and ST-segment resolution. RV dysfunction was defined as tricuspid annular plane systolic excursion≤16 mm in M-mode imaging. RV dysfunction was present in 58 of 141 patients (41.1%) and was more frequent in patients achieving suboptimal postprocedural TIMI flow grade (66.7% vs 36.7%, grades 0 to 2 vs 3, p=0.01), TIMI frame count (63.2% vs 37.7%, ≥40 vs <40 frames, p=0.04), and myocardial blush grade (33.3% vs 56.2%, grade 0 or 1 vs 2 or 3, p=0.001). RV dysfunction rates did not differ according to ST-segment resolution. Patients with RV dysfunction had increased rates of cardiac death (13.2% vs 2.6%, p=0.03), reinfarction (24.5% vs 10.3%, p=0.03), and stent thrombosis (22.6% vs 6.4%, p=0.01) at 2-year follow-up. Postprocedural TIMI flow grade 3 (odds ratio 0.25, 95% confidence interval 0.09 to 0.68, p=0.007) was the only reperfusion correlate of RV dysfunction at multivariate analysis. In an independent cohort of 84 patients with STEMI, postprocedural TIMI flow grade 3 had a limited sensitivity (52%), with a high specificity (74.5%) and negative predictive value (71%) for excluding RV dysfunction. In conclusion, in patients with inferior STEMI undergoing coronary revascularization, RV dysfunction is associated with a worse long-term prognosis. Postprocedural TIMI flow grade may be a useful tool to predict RV dysfunction.

Transradial versus transfemoral approach in patients undergoing percutaneous coronary intervention for acute coronary syndrome. A meta-analysis and trial sequential analysis of randomized controlled trials

Background

Transfemoral approach (TFA) remains the most common vascular access for percutaneous coronary intervention (PCI) in many countries. However, in the last years several randomized trials compared transradial approach (TRA) with TFA in patients with acute coronary syndrome (ACS), but only few studies were powered to estimate rare events. The aim of the current study was to clarify whether TRA is superior to TFA approach in patients with ACS undergoing percutaneous coronary intervention. A meta-analysis, meta-regression and trial sequential analysis of safety and efficacy of TRA in ACS setting was performed.

Methods and Results

Medline, the Cochrane Library, Scopus, scientific session abstracts and relevant websites were searched. Data concerning the study design, patient characteristics, risk of bias, and outcomes were extracted. The primary endpoint was death. Secondary endpoints were: major bleeding and vascular complications. Outcomes were assessed within 30 days. Eleven randomized trials involving 9,202 patients were included. Compared with TFA, TRA significantly reduced the risk of death (odds ratio [OR] 0.70; 95% confidence interval [CI], 0.53–0.94; p = 0.016), but this finding was not confirmed in trial sequential analysis, indicating that sufficient evidence had not been yet reached. Furthermore, TRA compared with TFA reduced the risk of major bleeding (OR 0.60; 95% CI, 0.41–0.88; p = 0.008) and vascular complications (OR 0.35; 95% CI, 0.28–0.46; p<0.001); these findings were supported by trial sequential analyses.

Conclusions

In patients with ACS undergoing PCI, a lower risk of death was observed with TRA. Nevertheless, the association between mortality and TRA in ACS setting should be interpreted with caution because it is based on insufficient evidence. However, because of the clinical relevance associated with major bleeding and vascular complications reduction, TRA should be recommended as first-choice vascular access in patients with ACS undergoing cardiac catheterization.

Effects of physical activity on endothelial progenitor cells (EPCs)

Physical activity has a therapeutic role in cardiovascular disease (CVD), through its beneficial effects on endothelial function and cardiovascular system. Circulating endothelial progenitor cells (EPCs) are bone marrow (BM) derived cells that represent a novel therapeutic target in CVD patients, because of their ability to home to sites of ischemic injury and repair the damaged vessels. Several studies show that physical activity results in a significant increase in circulating EPCs, and, in particular, there are some evidence of the beneficial exercise-induced effects on EPCs activity in CVD settings, including coronary artery disease (CAD), heart failure (HF), and peripheral artery disease (PAD). The aim of this paper is to review the current evidence about the beneficial effects of physical exercise on endothelial function and EPCs levels and activity in both healthy subjects and patients with CVD.

Chemical modifications of peptide sequences via S-alkylation reaction

A chemoselective, convenient, and mild synthetic strategy to modify peptides on a cysteine sulfhydryl group is described. It simply requires activated molecular sieves to selectively promote S-alkylation in the presence of peptide nucleophilic functionalities. The procedure is easy to perform, fast, and provides high yields even in the case of poor electrophilic groups. Moreover, the method allows an efficient one-pot poly alkylation, proving that the sulfhydryl reactivity does not rely on its specific position within the peptide sequence.

[Adipokines and coronary artery disease]

Adipose tissue, besides being an important energetic storage, is also a source of cytokines and hormones which act in a paracrine, autocrine and especially endocrine manner, influencing the cardiometabolic axis. Adipokines are a group of mediators with pleiotropic function, that are involved in many physiological processes, so that a disregulation in their secretion can lead to multiple pathological conditions. In this review our aim was to clarify the role of adipokines in the pathogenesis of atherosclerosis, especially in coronary artery disease, and based on current scientific evidence, to analyze the therapeutic and behavioral strategies that are so far available.

Abstract 4645: Preclinical development of RFF-1, a novel rational designed CXCL12 mimetic drug

The interaction between the chemokine receptor CXCR4 and its ligand, CXCL12, has been shown in pre-clinical models to facilitate tumour metastasis and to be involved in tissue repair and in recruitment of hematopoietic precursors. AMD3100, a potent CXCR4 antagonist, has been approved by FDA for stem cell mobilization in patients with multiple myeloma and non-Hodgkin lymphoma. Several other CXCR4 inhibitors are in clinical development (BTK140, CTCE-9908, MDX-1338 and POL6326), with the aim of inhibiting the development and progression of metastasis. In the rational design of CXCR4 inhibitors, a new class of cyclic peptide CXCL12-based CXCR4 inhibitors was discovered (IT Patent M12010A 000096; PCT WO2011/092575 A1) and validated for efficacy in in vitro and in vivo models. Among the tested peptides RFF-1 showed potent and specific inhibitory effects on CXCR4-mediated functions in multiple in vitro assays (P-ERK induction, migration and calcium mobilization CXCL12-induced and binding to CXCR4). C57/BL mice were injected with B16 melanoma cells transfected with human CXCR4. A 4,5 fold reduction in lung metastases was observed after 10 days treatment with 2 mg/kg intraperitoneally (i.p.) RFF-1 compared to the CXCR4 inhibitor AMD3100 (1.25mg/kg i.p), the powerful CXCR4 inhibitor not suitable for prolonged administration, that reduced lung metastases of about 4 fold. In another model of mouse osteosarcoma, K7M2 murine cells, were injected in Balb/C mice. A 3 fold reduction in lung metastases was observed after 15 days treatment with 10 mg/kg i.p. RFF-1 whereas AMD3100 treatment (2.5mg/kg i.p.) lead to 1.8 fold increase in lung metastases. Additionally, a 30% reduction in primary cell growth was achieved in a subcutaneous model of human renal cancer SN12C cells when i.p. treated with 2 mg/kg RFF-1. With the aim to evaluate RFF-1 efficacy in hematopoietic stem cell (HSC) mobilization DBA/2 healthy mice were injected with a single s.c. RFF-1 dose and peripheral blood HSC mobilization was evaluated by colony forming unit assay. Treatment with 30 mg/kg RFF-1 results in rapid, potent and durable mobilization of HSC reaching faster the peak compared to 20 mg/kg AMD3100. These results have prompted us to pursue the clinical development of peptide RFF-1. A first in human Phase I trial is planned to determine the maximal tolerated dose and recommended Phase 2 dose, toxicity profile, pharmacokinetics and antitumor activity of RFF-1 in patients with refractory solid tumors. The Phase I-II study of a novel CXCR4 antagonist provides the opportunity to develop settings in diseases where there is increasing evidence of a role for CXCR4 in the development and progression of metastases such as relapsed glioblastoma, neoadjuvant colorectal and breast cancer, and advanced prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4645. doi:1538-7445.AM2012-4645

Probing membrane topology of the antimicrobial peptide distinctin by solid-state NMR spectroscopy in zwitterionic and charged lipid bilayers

Distinctin is a 47-residue antimicrobial peptide, which interacts with negatively charged membranes and is active against Gram-positive and Gram-negative bacteria. Its primary sequence comprises two linear chains of 22 (chain 1) and 25 (chain 2) residues, linked by a disulfide bridge between Cys19 of chain 1 and Cys23 of chain 2. Unlike other antimicrobial peptides, distinctin in the absence of the lipid membrane has a well-defined three-dimensional structure, which protects it from protease degradation. Here, we used static solid-state NMR spectroscopy in mechanically aligned lipid bilayers (charged or zwitterionic) to study the topology of distinctin in lipid bilayers. We found that this heterodimeric peptide adopts an ordered conformation absorbed on the surface of the membrane, with the long helix (chain 2), approximately parallel to the lipid bilayer (~5° from the membrane plane) and the short helix (chain 1) forming a ~24° angle with respect to the bilayer plane. Since the peptide does not disrupt the macroscopic alignment of charged or zwitterionic lipid bilayers at lipid-to-protein molar ratio of 50:1, it is possible that higher peptide concentrations might be needed for pore formation, or alternatively, distinctin elicits its cell disruption action by another mechanism.

Abstract 2270: Design, synthesis, and functional characterization of new cycle-peptides inhibitors for C-X-C chemokine receptor-4 (CXCR4)

Modulation of the axis CXCR4/CXCL12 affected primary tumor growth and secondary lesions development. Moreover, CXCR4 inhibition increases hematopoietic stem cell mobility in patients undergoing autologous transplantation for myeloma and non-Hodgkin lymphoma. Although several CXCR4 inhibitors were described neither one reached satisfactory efficacy, bioavailability and acceptable toxicity. To develop new CXCR4 inhibitors through a rationale design approach, comparative studies were undertaken evaluating the N-terminal structure of the ligand CXCL12 and v-MIP II, an inhibitory chemokine like produced by the herpes virus 8-Kaposi associated. A common amino acidic motif (RFF) was identified in both structures although in inverted orientation. Having as a core this small domain, a new library (20 units) of cycle-peptide molecules was generated. 20 units of cycle-peptide molecules were synthesized that consists of 5 and 7 amino-acid residues cycled by a S-S bridge designed to interact with the receptor CXCR4. The peptides were characterized for functionally CXCR4 interaction through: 1. inhibition of CXCR4 binding; 2. inhibition of migration CXCL12-induced; 3. inhibition of calcium release CXCL12-induced; 4. Inhibition of P-Erk CXCL12-induced. Four peptides were identified as CXCR4 inhibitors. These four CXCR4 inhibitory peptides were further evaluated for the in vivo efficacy through inhibition of metastasis formation. B16 mouse melanoma cells transfected with CXCR4 were injected in the vein tail in C57 Bl mice and peptide treatment followed for 10 days. Dramatic reduction in number and size of lung metastases were registered in mice peptides-treated. Moreover, xenograft of human renal cancer cells SN12C-EGFP were subcutaneously injected and systemic peptides treatment followed for 10 days. Statistically significant decrease in tumor growth was showed in peptides treated mice. Taken together the data define four new CXCR4 inhibitory peptides, designed through innovative strategy, effective in “in vivo” systems deserving further development.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2270.

Imaging of alpha(v)beta(3) expression by a bifunctional chimeric RGD peptide not cross-reacting with alpha(v)beta(5)

PURPOSE

To test whether a novel bifunctional chimeric peptide comprising a cyclic Arg-Gly-Asp pentapeptide covalently bound to an echistatin domain can discriminate alpha(v)beta(3) from alpha(v)beta(5) integrin, thus allowing the in vivo selective visualization of alpha(v)beta(3) expression by single-photon and positron emission tomography (PET) imaging.

EXPERIMENTAL DESIGN

The chimeric peptide was preliminarily tested for inhibition of alpha(v)beta(3)-dependent cell adhesion and competition of 125I-echistatin binding to membrane of stably transfected K562 cells expressing alpha(v)beta(3) (Kalpha(v)beta(3)) or alpha(v)beta(5) (Kalpha(v)beta(5)) integrin. The chimeric peptide was then conjugated with diethylenetriaminepentaacetic acid and labeled with 111In for single-photon imaging, whereas a one-step procedure was used for labeling the full-length peptide and a truncated derivative, lacking the last five C-terminal amino acids, with 18F for PET imaging. Nude mice bearing tumors from Kalpha(v)beta(3), Kalpha(v)beta(5), U87MG human glioblastoma, and A431 human epidermoid cells were subjected to single-photon and PET imaging.

RESULTS

Adhesion and competitive binding assays showed that the novel chimeric peptide selectively binds to alpha(v)beta(3) integrin and does not cross-react with alpha(v)beta(5). In agreement with in vitro findings, single-photon and PET imaging studies showed that the radiolabeled chimeric peptide selectively localizes in tumor xenografts expressing alphavbeta3 and fails to accumulate in those expressing alpha(v)beta(5) integrin. When 18F-labeled truncated derivative was used for PET imaging, alphavbeta3- and alpha(v)beta(5)-expressing tumors were visualized, indicating that the five C-terminal amino acids are required to differentially bind the two integrins.

CONCLUSION

Our findings indicate that the novel chimeric Arg-Gly-Asp peptide, having no cross-reaction with alphavbeta5 integrin, allows highly selective alphavbeta3 expression imaging and monitoring.

Structural features of distinctin affecting peptide biological and biochemical properties

The antimicrobial peptide distinctin consists of two peptide chains linked by a disulfide bridge; it presents a peculiar fold in water resulting from noncovalent dimerization of two heterodimeric molecules. To investigate the contribution of each peptide chain and the S-S bond to distinctin biochemical properties, different monomeric and homodimeric peptide analogues were synthesized and comparatively evaluated with respect to the native molecule. Our experiments demonstrate that the simultaneous occurrence of both peptide chains and the disulfide bond is essential for the formation of the quaternary structure of distinctin in aqueous media, able to resist protease action. In contrast, distinctin and monomeric and homodimeric analogues exhibited comparable antimicrobial activities, suggesting only a partial contribution of the S-S bond to peptide killing effectiveness. Relative bactericidal properties paralleled liposome permeabilization results, definitively demonstrating that microbial membranes are the main target of distinctin activity. Various biophysical experiments performed in membrane-mimicking media, before and after peptide addition, provided information about peptide secondary structure, lipid bilayer organization, and lipid-peptide orientation with respect to membrane surface. These data were instrumental in the generation of putative models of peptide-lipid supramolecular pore complexes.

Synthesis and biological evaluation of cyclic and branched peptide analogues as ligands for cholecystokinin type 1 receptor

A library of cyclic CCK8 analogues, containing unnatural amino acids in the peptide sequence, is prepared using solid-phase synthesis. The structure of these cyclic peptides is based on a previously synthesised compound, cyclo-CCK8, selective for CCK(1) receptor. Structure-activity investigations are performed by evaluating the binding properties of the new analogues. In particular, the binding ability of the cyclic CCK8 analogues is tested by nuclear medicine studies on cell line transfected with CCK(1) receptor. Compounds named cyclo-A4-cyclo-A7 show binding constant in the range 6.0-8.0 microM, with an improved affinity over the previous described cyclo-CCK8, but almost comparable IC(50) values among new analogues towards CCK(1) were obtained.

Conformationally constrained CCK8 analogues obtained from a rationally designed peptide library as ligands for cholecystokinin type B receptor

A library of 14 cyclic peptide analogues derived from the octapeptide C-terminal sequence of the human cholecystokinin hormone (CCK(26-33), or CCK8) was designed, synthesized, and characterized. The 14 peptide analogues were rationally designed to specifically interact with the CCK type B receptor (CCK(B)-R) on the basis of the structure of the bimolecular complex between CCK8 and the third extracellular loop of CCK(B)-R, namely CCK(B)-R(352-379). The rational design of new ligands for CCK(B)-R has relied on stabilization by cyclic constraints of the structural motifs that bring the key residues of the ligand (especially Trp 30, Met 31, and Phe 33) in the proper spatial orientation for optimal interaction with the receptor. The binding affinity of the new ligands for CCK(B)-R was assessed by displacement experiments of (111)In-radiolabeled CCK8 in cells that overexpress the CCK(B) receptor. The new ligands generally showed binding affinities lower than that of parent CCK8, with the best compounds having IC50 values around 10 microM. Structure-activity relationship data show that preservation of the Trp 30-Met 31 motif is essential and that the Phe 33 side chain must be present. NMR conformational studies of the compound with maximal binding affinity (cyclo-B11, IC50=11 microM) in DPC micelles shows that this compound presents a turn-like conformation centered at the Trp 30-Met 31 segment, as planned by rational design. Such a conformation is stabilized by its interaction with the micelle rather than by the cyclic constraint.

Anthranilic Acid Based CCK1 Receptor Antagonists and CCK-8 Have a Common Step in Their “Receptor Desmodynamic Processes”

The interaction between the 1-47 N-terminus of the CCK(1)-R and the anthranilic acid based antagonists has been investigated by fluorescence spectroscopy. These antagonists interact with W39 of the N-terminal domain of the CCK(1)-R like that of the endogenous ligand CCK-8. This specific interaction was not found in other nonpeptide ligands of the CCK(1)-R. Conformational studies, using NMR and energy minimization procedures, have allowed formulation of a new hypothesis on the CCK(1)-R binding mode of the anthranilic antagonists.

Receptor fragment approach to the binding between CCK8 peptide and cholecystokinin receptors: A fluorescence study on type B receptor fragment CCKB-R (352-379)

Fluorescence titrations in a membrane mimetic solvent system allowed us to estimate that the dissociation constant of the bimolecular complex between CCK8 peptide and cholecystokinin type B receptor fragment CCK(B)-R (352-379) is in the micromolar range. When considered in the context of the full receptor/ligand model, these experiments demonstrate that the receptor fragment chosen on the basis of previous structural studies represents a reliable model system to monitor the ability of CCK8 or CCK8 analogs to bind the cholecystokinin receptor. Together with previous studies, this confirms that the receptor fragment approach adopted to define the binding mode of the CCK8 fragment of cholecystokinin with its two receptors, CCK(A) and CCK(B,) can be used to characterize the binding from the equilibrium standpoint. In this context, fluorescence spectroscopy proves to be the favored technique to measure dissociation constants in the nanomolar to micromolar range.

Synthesis and characterization of a sulfated and a non-sulfated cyclic CCK8 analogue functionalized with a chelating group for metal labelling

Two cyclic peptides, cyclo29,34[Dpr29, Lys34(DTPA-Glu)]-CCK8 (1) and cyclo29,34[Tyr27(SO3H), Dpr29, Lys34(DTPA-Glu)]-CCK8 (2), bearing the chelating moiety DTPA-Glu covalently bound to the Lys side chain have been synthesized by solid-phase methodology. The presence in compound 2 of many acidic functions characteristic of the chelating agent increases the lability of the sulfate group on the Tyr side chain. This finding suggests that prolonged acid treatments should be avoided during the preparation of such peptides. Sulfation of cyclo29,34[Dpr29, Lys34(DTPA-Glu)]-CCK8 was performed using a pyridine-SO3 complex as reagent. This reaction has been found to be the most suitable synthetic strategy for obtaining compound 2 in good yield. Cyclo29,34[Tyr27(SO3H), Dpr29, Lys34(DTPA-Glu)]-CCK8 is a new promising CCK8 analogue, able to coordinate radioactive isotopes of metal ions such as 111In(III), and to bind, in a selective way, the CCKA-R receptor.

In vitro and in vivo evaluation of 111In-DTPAGlu-G-CCK8 for cholecystokinin-B receptor imaging

Regulatory peptides and their analogs are being extensively investigated as radiopharmaceuticals for cancer imaging and therapy. Receptors of the cholecystokinin family have been shown to be overexpressed in different types of neuroendocrine tumors. The purposes of this study were to evaluate the cholecystokinin octapeptide amide (CCK8) peptide tagged with a diethylenetriaminepentaacetic acid derivative (DTPAGlu) and to test whether a (111)In-labeled conjugate ((111)In-DTPAGlu-G-CCK8, a derivative containing the chelating agent DTPAGlu bound through a glycine linker at the N-terminal end of the bioactive peptide CCK8) is suitable for cholecystokinin-B receptor (CCKBR) imaging.

METHODS

CCK8 was synthesized by solid-phase techniques and covalently coupled to DTPAGlu through a glycine linker at its amino terminus. The compound was labeled with (111)In. The radiochemical purity and stability of the compound were assessed by chromatographic methods. NIH-3T3 and A431 cells overexpressing CCKBR were used to characterize the in vitro properties of the compound. Nude mice bearing control and CCKBR-overexpressing A431 xenografts were used as an in vivo model.

RESULTS

DTPAGlu-G-CCK8 showed rapid and efficient labeling with (111)In. The radiolabeled conjugate showed specific binding to both cell lines overexpressing CCKBR. Binding was saturable, with a dissociation constant of approximately 20 nmol/L in both cell systems. Both cell lines showed internalization of the ligand after interaction with the receptor. Biodistribution studies showed rapid localization of (111)In-DTPAGlu-G-CCK8 on CCKBR-overexpressing A431 xenografts that was severalfold higher than that on control tumors at all time points tested. Unbound activity showed rapid clearance of over 80% through the kidneys by 30 min after injection. The labeled peptide conjugate was very stable in serum but showed a rapid breakdown after injection. Incubation with kidney homogenates suggested that most breakdown occurred in the kidneys, favoring the clearance of unbound activity.

CONCLUSION

Our findings indicate that the in vitro and in vivo characteristics of (111)In-DTPAGlu-G-CCK8 are favorable for CCKBR imaging, as the peptide shows high-affinity binding to the receptor, is internalized in CCKBR-expressing cells, and shows avid uptake in CCKBR-overexpressing xenografts, with rapid clearance of unbound radioactivity through the kidneys. Furthermore, the ease of synthesis, high labeling efficiency, and chemical stability of DTPAGlu make this chelating moiety an ideal candidate for widespread use in peptide radiolabeling for nuclear medicine applications.

A Cyclic CCK8 Analogue Selective for the Cholecystokinin Type A Receptor: Design, Synthesis, NMR Structure and Binding Measurements

A cyclic CCK8 analogue, cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 (Dpr=L-2,3-diaminopropionic acid), has been designed on the basis of the NMR structure of the bimolecular complex between the N-terminal fragment of the CCK(A) receptor and its natural ligand CCK8. The conformational features of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 have been determined by NMR spectroscopy in aqueous solution and in water containing DPC-d(38) micelles (DPC=dodecylphosphocholine). The structure of the cyclic peptide in aqueous solution is found to be in a relaxed conformation, with the backbone and Dpr29 side chain atoms making a planar ring and the N-terminal tripeptide extending approximately along the plane of this ring. In DPC/water, the cyclic peptide adopts a "boat-shaped" conformation, which is more compact than that found in aqueous solution. The cyclic constraint between the Dpr29 side chain and the CCK8 carboxyl terminus (Lys34) introduces a restriction in the backbone conformational freedom. However, the interaction of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 with the micelles still plays an important role in the stabilisation of the bioactive conformation. A careful comparison of the NMR structure of the cyclic peptide in a DPC micelle aqueous solution with the structure of the rationally designed model underlines that the turn-like conformation in the Trp30-Met31 region is preserved, such that the Trp30 and Met31 side chains can adopt the proper spatial orientation to interact with the CCK(A) receptor. The binding properties of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 to the N-terminal receptor fragment have been investigated by fluorescence spectroscopy in a micellar environment. Estimates of the apparent dissociation constant, K(d), were in the range of 70-150 nM, with a mean value of 120+/-27 nM. Preliminary nuclear medicine studies on cell lines transfected with the CCK(A) receptor indicate that the sulfated-Tyr derivative of cyclo(29,34)[Dpr(29),Lys(34)]-CCK8 displaces the natural ligand with an IC(50) value of 15 microM.