cNGR: A Novel Homing Sequence for CD13/APN Targeted Molecular Imaging of Murine Cardiac Angiogenesis In Vivo

A novel aminopeptidase N/CD13 inhibitor selectively targets an endothelial form of CD13 after coupling to proteins

Aminopeptidase N/CD13, a membrane-bound enzyme upregulated in tumor vasculature and involved in angiogenesis, can be used as a receptor for the targeted delivery of drugs to tumors through ligand-directed targeting approaches. We describe a novel peptide ligand (VGCARRYCS, called "G4") that recognizes CD13 with high affinity and selectivity. Enzymological and computational studies showed that G4 is a competitive inhibitor that binds to the catalytic pocket of CD13 through its N-terminal region. Fusing the peptide C-terminus to tumor necrosis factor-alpha (TNF) or coupling it to a biotin/avidin complex causes loss of binding and inhibitory activity against different forms of CD13, including natural or recombinant ectoenzyme and a membrane form expressed by HL60 promyelocytic leukemia cells (likely due to steric hindrance), but not binding to a membrane form of CD13 expressed by endothelial cells (ECs). Furthermore, G4-TNF systemically administered to tumor-bearing mice exerted anticancer effects through a CD13-targeting mechanism, indicating the presence of a CD13 form in tumor vessels with an accessible binding site. Biochemical studies showed that most CD13 molecules expressed on the surface of ECs are catalytically inactive. Other functional assays showed that these molecules can promote endothelial cell adhesion to plates coated with G4-avidin complexes, suggesting that the endothelial form of CD13 can exert catalytically independent biological functions. In conclusion, ECs express a catalytically inactive form of CD13 characterized by an accessible conformation that can be selectively targeted by G4-protein conjugates. This form of CD13 may represent a specific target receptor for ligand-directed targeted delivery of therapeutics to tumors.

Therapeutic Performance Evaluation of 213Bi-Labelled Aminopeptidase N (APN/CD13)-Affine NGR-Motif ([213Bi]Bi-DOTAGA-cKNGRE) in Experimental Tumour Model: A Treasured Tailor for Oncology

Since NGR-tripeptides (asparagine-glycine-arginine) selectively target neoangiogenesis-associated Aminopeptidase N (APN/CD13) on cancer cells, we aimed to evaluate the in vivo tumour targeting capability of radiolabelled, NGR-containing, ANP/CD13-selective [²¹³Bi]Bi-DOTAGA-cKNGRE in CD13pos. HT1080 fibrosarcoma-bearing severe combined immunodeficient CB17 mice. 10 ± 1 days after cancer cell inoculation, positron emission tomography (PET) was performed applying [⁶⁸Ga]Ga-DOTAGA-cKNGRE for tumour verification. On the 7th, 8th, 10th and 12th days the treated group of tumourous mice were intraperitoneally administered with 4.68 ± 0.10 MBq [²¹³Bi]Bi-DOTAGA-cKNGRE, while the untreated tumour-bearing animals received 150 μL saline solution. In addition to body weight (BW) and tumour volume measurements, ex vivo biodistribution studies were conducted 30 and 90 min postinjection (pi.). The following quantitative standardised uptake values (SUV) confirmed the detectability of the HT1080 tumours: SUV_mean and SUV_max: 0.37 ± 0.09 and 0.86 ± 0.14, respectively. Although no significant difference (p ≤ 0.05) was encountered between the BW of the treated and untreated mice, their tumour volumes measured on the 9th, 10th and 12th days differed significantly (p ≤ 0.01). Relatively higher [²¹³Bi]Bi-DOTAGA-cKNGRE accumulation of the HT1080 neoplasms (%ID/g: 0.80 ± 0.16) compared with the other organs at 90 min time point yields better tumour-to-background ratios. Therefore, the therapeutic application of APN/CD13-affine [²¹³Bi]Bi-DOTAGA- cKNGRE seems to be promising in receptor-positive fibrosarcoma treatment.

Targeting the Blood–Brain Tumor Barrier with Tumor Necrosis Factor-α

The blood–brain tumor barrier represents a major obstacle for anticancer drug delivery to brain tumors. Thus, novel strategies aimed at targeting and breaching this structure are of great experimental and clinical interest. This review is primarily focused on the development and use of a derivative of tumor necrosis factor-α (TNF) that can target and alter the blood–brain-tumor-barrier. This drug, called NGR-TNF, consists of a TNF molecule fused to the Cys-Asn-Gly-Arg-Cys-Gly (CNGRCG) peptide (called NGR), a ligand of aminopeptidase N (CD13)-positive tumor blood vessels. Results of preclinical studies suggest that this peptide-cytokine fusion product represents a valuable strategy for delivering TNF to tumor vessels in an amount sufficient to break the biological barriers that restrict drug penetration in cancer lesions. Moreover, clinical studies performed in patients with primary central nervous system lymphoma, have shown that an extremely low dose of NGR-TNF (0.8 µg/m²) is sufficient to promote selective blood–brain-tumor-barrier alteration, increase the efficacy of R-CHOP (a chemo-immunotherapy regimen) and improve patient survival. Besides reviewing these findings, we discuss the potential problems related to the instability and molecular heterogeneity of NGR-TNF and review the various approaches so far developed to obtain more robust and homogeneous TNF derivatives, as well as the pharmacological properties of other peptide/antibody-TNF fusion products, muteins and nanoparticles that are potentially useful for targeting the blood–brain tumor barrier. Compared to other TNF-related drugs, the administration of extremely low-doses of NGR-TNF or its derivatives appear as promising non-immunogenic approaches to overcome TNF counter-regulatory mechanism and systemic toxicity, thereby enabling safe breaking of the BBTB.

A comparison of the monomeric [68Ga]NODAGA-NGR and dimeric [68Ga]NOTA-(NGR)2 as aminopeptidase N ligand for positron emission tomography imaging in tumor-bearing mice

The aminopeptidase N (APN/CD13) is a key protein specifically expressed on activated endothelial cells and by various tumors, representing a promising target for molecular imaging and therapy of malignant diseases. It is known that the tripeptide NGR is a specific ligand for CD13, therefore radiolabeled NGR peptides are auspicious radiotracers for non-invasive imaging of CD13-positive tumors. From previous studies, it is known that the target affinity could be improved by molecules with multiple ligand sequences. Therefore, the aim of this study was to compare two NGR radioligands [⁶⁸Ga]NODAGA-NGR (NGR monomer) and [⁶⁸Ga]NOTA-(NGR)₂ (NGR dimer), the latter with two NGR ligand motifs, in vitro and in vivo. CD13 expression was determined by FACS in the human tumor cells A549, SKHep-1, and MDA-MB-231, followed by the investigation of the cell uptake of [⁶⁸Ga]NODAGA-NGR and [⁶⁸Ga]NOTA-(NGR)₂. For in vivo evaluation of [⁶⁸Ga]NODAGA-NGR and [⁶⁸Ga]NOTA-(NGR)₂, microPET and biodistribution were carried out in A549- and SKHep-1-bearing mice. After the final examination, tumors were cryo-conserved, cut, and stained against CD13 and CD31. A549 and SKHep-1 cells were identified as CD13 positive, whereas no CD13 expression was detected in MDA-MB-231 cells. The cell uptake study showed relatively low accumulation of both the NGR monomer and dimer in all tumor cell lines examined, with consistently higher cell uptake observed for the dimer than for the monomer. In vivo, [⁶⁸Ga]NODAGA-NGR and [⁶⁸Ga]NOTA-(NGR)₂ accumulated in the tumors, with slightly higher tumor-to-muscle ratio for the NGR dimer in A549 and SKHep-1. The tumor-to-liver ratio of the NGR dimer was diminished in comparison to the NGR monomer. This finding was confirmed by biodistribution, which revealed higher accumulation in liver and spleen for the NGR dimer. Immunohistochemical staining confirmed the CD13 expression in the tumors and tumor-associated vessels. In conclusion, both the [⁶⁸Ga]NODAGA-NGR and the [⁶⁸Ga]NOTA-(NGR)₂ were found to be suitable for PET imaging of CD13-positive tumors. Despite slight differences in tumor-to-background ratio and organ accumulation, both radiotracers can be considered comparable.

Nanotechnology Assisted Chemotherapy for Targeted Cancer Treatment: Recent Advances and Clinical Perspectives

Nanotechnology has recently provided exciting platforms in the field of anticancer research with promising potentials for improving drug delivery efficacy and treatment outcomes. Nanoparticles (NPs) possess different advantages over the micro and bulk therapeutic agents, including their capability to carry high payloads of drugs, with prolonged half-life, reduced toxicity of the drugs, and increased targeting efficiency. The wide variety of nanovectors, coupled with different conjugation and encapsulation methods available for different theranostic agents provide promising opportunities to fine-tune the pharmacological properties of these agents for more effective cancer treatment methods. This review discusses applications of NPs-assisted chemotherapy in preclinical and clinical settings and recent advances in design and synthesis of different nanocarriers for chemotherapeutic agents. Moreover, physicochemical properties of different nanocarriers, their impacts on different tumor targeting strategies and effective parameters for efficient targeted drug delivery are discussed. Finally, the current approved NPs-assisted chemotherapeutic agents for clinical applications and under different phases of clinical trials are discussed.

Research Progress of Radiolabeled Asn-Gly-Arg (NGR) Peptides for Imaging and Therapy

Asn-Gly-Arg (NGR) motifs have vasculature-homing properties via interactions with the aminopeptidase N (CD13) expressed on tumor neovasculature. Numerous NGR peptides with different molecular scaffolds have been exploited for targeted delivery of different compounds for imaging and therapy. When conjugated with NGR, complexes recognize the CD13 receptor expressed on the tumor vasculature, which improves the specificity to tumor and avoids systematic toxic reactions. Both preclinical and clinical studies performed with these products suggest that NGR-mediated vascular targeting is an effective strategy for delivering bioactive amounts of cytokines to tumor endothelial cells. For molecular imaging, radiolabeled peptides have been the most successful approach and have been translated into clinic. This review describes current data on radiolabeled tumor vasculature-homing NGR peptides for imaging and therapy.

Achievement in active agent structures as a power tools in tumor angiogenesis imaging

According to World Health Organization (WHO) cancer is the second most important cause of death globally. Because angiogenesis is considered as an essential process of growth, proliferation and tumor progression, within this review we decided to shade light on recent development of chemical compounds which play a significant role in its imaging and monitoring. Indeed, the review gives insight about the current achievements of active agents structures involved in imaging techniques such as: positron emission computed tomography (PET), magnetic resonance imaging (MRI) and single photon emission computed tomography (SPECT), as well as combination PET/MRI and PET/CT. The review aims to provide the journal audience with a comprehensive and in-deep understanding of chemistry policy in tumor angiogenesis imaging.

In vivo assessment of aminopeptidase N (APN/CD13) specificity of different 68Ga-labelled NGR derivatives using PET/MRI imaging

Aminopeptidase N (APN/CD13) plays an important role in neoangiogenic process in malignancies. Our previous studies have already shown that ⁶⁸Ga-labelled NOTA conjugated asparagine-glycine-arginine peptide (c[KNGRE]-NH₂) specifically bind to APN/CD13 expressing tumors. The aim of this study was to evaluate and compare the APN/CD13 specificity of newly synthesized ⁶⁸Ga-labelled NGR derivatives in vivo by PET/MRI imaging using hepatocellular carcinoma (He/De) and mesoblastic nephroma (Ne/De) tumor models. PET/MRI and ex vivo biodistribution studies were performed 11 ± 1 days after subcutaneous injection of tumor cells and 90 min after intravenous injection of ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR) (MG1) or ⁶⁸Ga-NODAGA-c(NGR) (MG2). The APN/CD13 selectivity was confirmed by blocking experiments and the APN/CD13 expression was verified by immunohistochemistry. ⁶⁸Ga-labelled c(NGR) derivatives were produced with high specific activity and radiochemical purity. In control animals, low radiotracer accumulation was found in abdominal and thoracic organs. Using tumor-bearing animals we found that the ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-NODAGA-c(NGR), and ⁶⁸Ga-NODAGA-c(NGR) (MG1) derivatives showed higher uptake in He/De and Ne/De tumors, than that of the accumulation of ⁶⁸Ga-NODAGA-c(NGR) (MG2). APN/CD13 is a very promising target in PET imaging, however, the selection of the appropriate ⁶⁸Ga-labelled NGR-based radiopharmaceutical is critical for the precise detection of tumor neo-angiogenesis and for monitoring the efficacy of anticancer therapy.

NGR-TNF Engineering with an N-Terminal Serine Reduces Degradation and Post-Translational Modifications and Improves Its Tumor-Targeting Activity

The therapeutic index of cytokines in cancer therapy can be increased by targeting strategies based on protein engineering with peptides containing the CNGRC (NGR) motif, a ligand that recognizes CD13-positive tumor vessels. We show here that the targeting domain of recombinant CNGRC-cytokine fusion proteins, such as NGR-TNF (a CNGRC-tumor necrosis factor-α (TNF) conjugate used in clinical studies) and NGR-EMAP-II, undergoes various post-translational modification and degradation reactions that lead to the formation of markedly heterogeneous products. These modifications include N-terminal cysteine acetylation or the formation of various asparagine degradation products, the latter owing to intramolecular interactions of the cysteine α-amino group with asparagine and/or its succinimide derivative. Blocking the cysteine α-amino group with a serine (SCNGRC) reduced both post-translational and degradation reactions. Furthermore, the serine residue reduced the asparagine deamidation rate to isoaspartate (another degradation product) and improved the affinity of NGR for CD13. Accordingly, genetic engineering of NGR-TNF with the N-terminal serine produced a more stable and homogeneous drug (called S-NGR-TNF) with improved antitumor activity in tumor-bearing mice, either when used alone or in combination with chemotherapy. In conclusion, the targeting domain of NGR-cytokine conjugates can undergo various untoward modification and degradation reactions, which can be markedly reduced by fusing a serine to the N-terminus. The SCNGRC peptide may represent a ligand for cytokine delivery to tumors more robust than conventional CNGRC. The S-NGR-TNF conjugate (more stable, homogeneous, and active than NGR-TNF) could be rapidly developed for clinical trials.

In Vivo Imaging of Hypoxia and Neoangiogenesis in Experimental Syngeneic Hepatocellular Carcinoma Tumor Model Using Positron Emission Tomography

Introduction

Hypoxia-induced α_νβ₃ integrin and aminopeptidase N (APN/CD13) receptor expression play an important role in tumor neoangiogenesis. APN/CD13-specific ⁶⁸Ga-NOTA-c(NGR), α_νβ₃ integrin-specific ⁶⁸Ga-NODAGA-[c(RGD)]₂, and hypoxia-specific ⁶⁸Ga-DOTA-nitroimidazole enable the in vivo detection of the neoangiogenic process and the hypoxic regions in the tumor mass using positron emission tomography (PET) imaging. The aim of this study was to evaluate whether ⁶⁸Ga-NOTA-c(NGR) and ⁶⁸Ga-DOTA-nitroimidazole allow the in vivo noninvasive detection of the temporal changes of APN/CD13 expression and hypoxia in experimental He/De tumors using positron emission tomography.

Materials and Methods

5 × 10⁶ hepatocellular carcinoma (He/De) cells were used for the induction of a subcutaneous tumor model in Fischer-344 rats. He/De tumor-bearing animals were anaesthetized, and 90 min after intravenous injection of 10.2 ± 1.1 MBq ⁶⁸Ga-NOTA-c(NGR) or ⁶⁸Ga-NODAGA-[c(RGD)]₂ (as angiogenesis tracers) or ⁶⁸Ga-DOTA-nitroimidazole (for hypoxia imaging), whole-body PET/MRI scans were performed.

Results

Hypoxic regions and angiogenic markers (α_vβ₃ integrin and APN/CD13) were determined using ⁶⁸Ga-NOTA-c(NGR), ⁶⁸Ga-DOTA-nitroimidazole, and ⁶⁸Ga-NODAGA-[c(RGD)]₂ in subcutaneously growing He/De tumors in rats. ⁶⁸Ga-NOTA-c(NGR) showed the strong APN/CD13 positivity of He/De tumors in vivo, by which observation was confirmed by western blot analysis. By the qualitative analysis of PET images, heterogenous accumulation was found inside He/De tumors using all radiotracers. Significantly (p ≤ 0.01) higher SUVmean and SUVmax values were found in the radiotracer avid regions of the tumors than those of the nonavid areas using hypoxia and angiogenesis-specific radiopharmaceuticals. Furthermore, a strong correlation was found between the presence of angiogenic markers, the appearance of hypoxic regions, and the tumor volume using noninvasive in vivo PET imaging.

Conclusion

⁶⁸Ga-DOTA-nitroimidazole and ⁶⁸Ga-NOTA-c(NGR) are suitable diagnostic radiotracers for the detection of the temporal changes of hypoxic areas and neoangiogenic molecule (CD13) expression, which vary during tumor growth in a hepatocellular carcinoma model.

Biomimetic nanovesicle design for cardiac tissue repair

Cardiovascular disease is a major cause of mortality and morbidity worldwide. Exosome therapies are promising for cardiac repair. Exosomes transfer cargo between cells, have high uptake by native cells and are ideal natural carriers for proteins and nucleic acids. Despite their proreparative potential, exosome production is dependent on parent cell state with typically low yields and cargo variability. Therefore, there is potential value in engineering exosomes to maximize their benefits by delivering customized, potent cargo for cardiovascular disease. Here, we outline several methods of exosome engineering focusing on three important aspects: optimizing cargo, homing to target tissue and minimizing clearance. Finally, we put these methods in context of the cardiac field and discuss the future potential of vesicle design.

In Vivo Tumor Growth Inhibition and Antiangiogenic Effect of Cyclic NGR Peptide-Daunorubicin Conjugates Developed for Targeted Drug Delivery

Among various homing devices, peptides containing the NGR tripeptide sequence represent a promising approach to selectively recognize CD13 receptor isoforms on the surface of tumor cells. They have been successfully used for the delivery of various chemotherapeutic drugs to tumor vessels. Here, we report on the murine plasma stability, in vitro and in vivo antitumor activity of our recently described bioconjugates containing daunorubicin as payload. Furthermore, CD13 expression of KS Kaposi’s Sarcoma cell line and HT-29 human colon carcinoma cell line was investigated. Flow cytometry studies confirm the fast cellular uptake resulting in the rapid delivery of the active metabolite Dau = Aoa-Gly-OH to tumor cells. The increased in vitro antitumor effect might be explained by the faster rearrangement from NGR to isoDGR in case of conjugate 2 (Dau = Aoa-GFLGK(c[NleNGRE]-GG)-NH₂) in comparison with conjugate 1 (Dau = Aoa-GFLGK(c[KNGRE]-GG)-NH₂). Nevertheless, results indicated that both conjugates showed significant effect on inhibition of proliferation in the primary tumor and also on blood vessel formation making them a potential candidate for targeting angiogenesis processes in tumors where CD13 and integrins are involved.

Mechanism of Action of the Tumor Vessel Targeting Agent NGR-hTNF: Role of Both NGR Peptide and hTNF in Cell Binding and Signaling

NGR-hTNF is a therapeutic agent for a solid tumor that specifically targets angiogenic tumor blood vessels, through the NGR motif. Its activity has been assessed in several clinical studies encompassing tumors of different histological types. The drug’s activity is based on an improved permeabilization of newly formed tumor vasculature, which favors intratumor penetration of chemotherapeutic agents and leukocyte trafficking. This work investigated the binding and the signaling properties of the NGR-hTNF, to elucidate its mechanism of action. The crystal structure of NGR-hTNF and modeling of its interaction with TNFR suggested that the NGR region is available for binding to a specific receptor. Using 2D TR-NOESY experiments, this study confirmed that the NGR-peptides binds to a specific CD13 isoform, whose expression is restricted to tumor vasculature cells, and to some tumor cell lines. The interaction between hTNF or NGR-hTNF with immobilized TNFRs showed similar kinetic parameters, whereas the competition experiments performed on the cells expressing both TNFR and CD13 showed that NGR-hTNF had a higher binding affinity than hTNF. The analysis of the NGR-hTNF-triggered signal transduction events showed a specific impairment in the activation of pro-survival pathways (Ras, Erk and Akt), compared to hTNF. Since a signaling pattern identical to NGR-hTNF was obtained with hTNF and NGR-sequence given as distinct molecules, the inhibition observed on the survival pathways was presumably due to a direct effect of the NGR-CD13 engagement on the TNFR signaling pathway. The reduced activation of the pro survival pathways induced by NGR-hTNF correlated with the increased caspases activation and reduced cell survival. This study demonstrates that the binding of the NGR-motif to CD13 determines not only the homing of NGR-hTNF to tumor vessels, but also the increase in its antiangiogenic activity.

Design, synthesis and biological evaluation of peptide-NSAID conjugates for targeted cancer therapy

Linear arginine-glycine-aspartic acid (RGD) and asparagine-glycine-arginine (NGR) peptide-nonsteroidal anti-inflammatory drug conjugates were synthesized to evaluate their anticancer effect. Two well-known targeting peptide sequences, RGD and NGR, were conjugated with naproxen and ibuprofen. It is expected that the RGD peptide selectively binds to α_v -integrin receptors, which are highly expressed in cancer cells, and that the NGR peptide selectively targets aminopeptidase N (APN/CD13, EC 3.4.11.2), which is overexpressed in blood vessels of tumors. To investigate the impact of possible steric hindrance due to the attachment of the drug to the peptide, a linear six-carbon linker (hexanoic acid) was also used as a spacer. Cytotoxic effects of the synthesized compounds were evaluated against several cancer cell lines, including MCF-7, A2780 (α_v β₃ positive), OVCAR3 (high α_v β₃ ), HT-1-80, and SKOV-3 cells (CD13 positive). The NGR conjugate forms of both ibuprofen and naproxen showed better activity against the SKOV-3 tumor cell line. The improved binding of these conjugates to their receptors was confirmed by docking studies.

CD13 tethers the IQGAP1-ARF6-EFA6 complex to the plasma membrane to promote ARF6 activation, β1 integrin recycling, and cell migration

Cell attachment to the extracellular matrix (ECM) requires a balance between integrin internalization and recycling to the surface that is mediated by numerous proteins, emphasizing the complexity of these processes. Upon ligand binding in various cells, the β1 integrin is internalized, traffics to early endosomes, and is returned to the plasma membrane through recycling endosomes. This trafficking process depends on the cyclical activation and inactivation of small guanosine triphosphatases (GTPases) by their specific guanine exchange factors (GEFs) and their GTPase-activating proteins (GAPs). In this study, we found that the cell surface antigen CD13, a multifunctional transmembrane molecule that regulates cell-cell adhesion and receptor-mediated endocytosis, also promoted cell migration and colocalized with β1 integrin at sites of cell adhesion and at the leading edge. A lack of CD13 resulted in aberrant trafficking of internalized β1 integrin to late endosomes and its ultimate degradation. Our data indicate that CD13 promoted ARF6 GTPase activity by positioning the ARF6-GEF EFA6 at the cell membrane. In migrating cells, a complex containing phosphorylated CD13, IQGAP1, GTP-bound (active) ARF6, and EFA6 at the leading edge promoted the ARF6 GTPase cycling and cell migration. Together, our findings uncover a role for CD13 in the fundamental cellular processes of receptor recycling, regulation of small GTPase activities, cell-ECM interactions, and cell migration.

Future perspectives of nanoparticle-based contrast agents for cardiac magnetic resonance in myocardial infarction

Cardiac Magnetic Resonance (CMR), thanks to high spatial resolution and absence of ionizing radiation, has been widely used in myocardial infarction (MI) assessment to evaluate cardiac structure, function, perfusion and viability. Nevertheless, it suffers from limitations in tissue and assessment of myocardial pathophysiological changes subsequent to MI. In this issue, nanoparticle-based contrast agents offer the possibility to track biological processes at cellular and molecular level underlying the various phases of MI, infarct healing and tissue repair. In this paper, first we examine the conventional CMR protocol and its findings in MI patients. Next, we looked at how nanoparticles can help in the imaging of MI and give an overview of the major approaches currently explored. Based on the presentation of successful nanoparticle applications as contrast agents (CAs) in preclinical and clinical models, we discuss promises and outstanding challenges facing the field of CMR in MI, their translational potential and clinical application.

Bioinformatics identification of potential candidate blood indicators for doxorubicin-induced heart failure

The care of individual patients requiring anthracyclines remains challenging as uncertainty persists on predictors of cardiotoxicity. The aim of the present study was to identify potential candidate blood indicators of doxorubicin-induced heart failure. The gene expression profiles of GSE40447 and GSE9128 microarray data were downloaded from the Gene Expression Omnibus database to identify differentially expressed genes (DEGs) using the R/Limma package or GEO2R. Functional and pathway enrichment analysis on DEGs were performed using DAVID database. The cardiovascular disease (CVD)-related DEGs were screen out based on the CardioGenBase database. The protein-protein interaction (PPI) network was constructed with STRING database and visualized by using Cytoscape. Then, the CVD-related DEGs were validated by intersection analysis with DEGs in GSE9128. The overlapping DEGs with a consistent expression pattern in GSE40447 and GSE9128 were identified as candidate indicators for doxorubicin-induced heart failure. A total of 516 DEGs potentially associated with doxorubicin-induced heart failure in GSE40447 were identified, which were mainly enriched in the gene ontology terms related to B cells, leukocytes, lymphocyte activation and B cell receptor signaling pathway. Of the DEGs, 42 were screened out as CVD-related DEGs by using CardioGenBase. Seven genes with high connectivity degree were presented in the PPI network. Finally, 5/6 CVD-related DEGs revealed by the intersection analysis were validated by GSE9128 and highlighted as candidate indicators of doxorubicin-induced heart failure: CD163, CD28, SLC25A20, ANPEP and TLR5. Several genes, including the 5 previously mentioned, were proposed as potential candidate blood indicators for doxorubicin-induced heart failure. Further experimental validations are greatly warranted for future clinical application.

Use of Cyclic Backbone NGR-Based SPECT to Increase Efficacy of Postmyocardial Infarction Angiogenesis Imaging

As CD13 is selectively expressed in angiogenesis, it can serve as a target for molecular imaging tracers to noninvasively visualize angiogenic processes in vivo. The CD13-targeting moiety NGR was synthesized and cyclized by native chemical ligation (NCL) instead of disulfide bridging, leading to a cyclic peptide backbone: cyclo(Cys-Asn-Gly-Arg-Gly) (coNGR). Beside this new monomeric coNGR, a tetrameric NGR peptide co(NGR)₄ was designed and synthesized. After radiolabeling, their in vitro and in vivo characteristics were determined. Both coNGR-based imaging agents displayed considerably higher standardized uptake values (SUVs) at infarcted areas compared to the previously reported disulfide-cyclized cNGR imaging agent. Uptake patterns of ¹¹¹In-coNGR and ¹¹¹In-co(NGR)₄ coincided with CD13 immunohistochemistry on excised hearts. Blood stability tests indicated better stability for both novel imaging agents after 50 min blood incubation compared to the disulfide-cyclized cNGR imaging agent. In mice, both coNGR peptides cleared rapidly from the blood mainly via the kidneys. In addition, co(NGR)₄ showed a significantly higher specific uptake in infarcted myocardium compared to coNGR and thus is a promising sensitive imaging agent for detection of angiogenesis in infarcted myocardium.

Nano-delivery system targeting to cancer stem cell cluster of differentiation biomarkers

Cancer stem cells (CSCs) are one of the most important origins of cancer progression and metastasis. CSCs have unique self-renewal properties and diverse cell membrane receptors that induced the resistance to the conventional chemotherapeutic agents. Therefore, the therapeutic removal of CSCs could result in the cancer cure with lack of recurrence and metastasis. In this regard, targeting CSCs in accordance to their specific biomarkers is a talented attitude in cancer therapy. Various CSCs surface biomarkers have been described, which some of them exhibited similarities on different cancer cell types, while the others are cancer specific and have just been reported on one or a few types of cancers. In this review, the importance of CSCs in cancer development and therapeutic response has been stated. Different CSCs cluster of differentiation (CD) biomarkers and their specific function and applications in the treatment of cancers have been discussed, Special attention has been made on targeted nano-delivery systems. In this regard, several examples have been illustrated concerning specific natural and artificial ligands against CSCs CD biomarkers that could be decorated on various nanoparticulated drug delivery systems to enhance therapeutic index of chemotherapeutic agents or anticancer gene therapy. The outlook of CSCs biomarkers discovery and therapeutic/diagnostic applications was discussed.

Vascular-homing peptides for cancer therapy

In the past 30 years, a variety of phage libraries have been extensively utilized to identify and develop tumor homing peptides (THPs). THPs specifically bind to tumor cells or elements of the tumor microenvironment while no or low affinity to normal cells. In this regard, the efficacy of therapeutic agents in cancer therapy can be enhanced by targeting strategies based on coupling with THPs that recognize receptors expressed by tumor cells or tumor vasculature. Especially, vascular-homing peptides, targeting tumor vasculature, have their receptors expressed on or around the blood vessel including pro-angiogenic factors, metalloproteinase, integrins, fibrin-fibronectin complexes, etc. This review briefly summarizes recent studies on identification and therapeutic applications of vascular-homing peptides targeting common angiogenic markers or with unknown vascular targets in some certain types of cancers. These newly discovered vascular-homing peptides are promising candidates which could provide novel strategies for cancer therapy.

iRGD as a tumor‑penetrating peptide for cancer therapy (Review)

As a tumor-targeting and ‑penetrating peptide, iRGD binds to αv integrins and neuropilin‑1 receptors, which are expressed at high levels on tumor cells and the surfaces of vasculature. Subsequently, iRGD penetrates deep into the tumor parenchyma with antitumor drugs, imaging agents, immune modulators and biological products. These substances are either chemically linked to the peptide or co‑injected with the peptide. The iRGD peptide can be readily synthesized, exhibits significantly improved penetration, compared with traditional peptides, and can effectively inhibit tumor metastasis. Therefore, the peptide is now used widely for the diagnosis and treatment of cancer. However, whether the peptide is able to promote the entry of drugs into non‑targeted cells remains to be fully elucidated. In this review, an overview of iRGD is presented, focusing on its identification, mechanism of action and previous studies on its roles in various types of cancer. Studies in previous years have demonstrated the potential of the iRGD protein for tumors diagnosis and targeted treatment, which warrants further investigation.

Systemic and tumor-targeted delivery of siRNA by cyclic NGR and isoDGR motif-containing peptides

The drug development of siRNA has been seriously hindered by the lack of an effective, safe and clinically applicable delivery system. The cyclic NGR motif and its isomerization product isoDGR recruit CD13 and integrin as their specific receptors, both of which are overexpressed by tumor and neovascular cells. In this study, a bi-functional peptide, named NGR-10R, was designed and tested for siRNA delivery in vitro and in vivo. Through the formation of peptide/siRNA nanoparticles, RNase resistance was greatly enhanced for the siRNAs. Both FACS and confocal assays revealed that the peptide/siRNA complexes were effectively internalized by MDA-MB-231 cells. Gene silencing assays indicated that anti-Lamin A/C siRNA delivered by NGR-10R robustly repressed gene expression in MDA-MB-231 and HUVEC (a CD13(+)/αvβ3(+) cell). Importantly, the siRNAs were efficiently delivered into tumor tissues and localized around the nuclei, as revealed by in vivo imaging and cryosection examination. In summary, NGR-10R not only efficiently delivered siRNAs into MDA-MB-231 cells in vitro but also delivered siRNAs into tumor cells in vivo, taking advantage of its specific binding to CD13 (neovascular) or αvβ3 (MDA-MB-231). Therefore, the NGR-10R peptide provides a promising siRNA delivery reagent that could be used for drug development, particularly for anti-tumor therapeutics.

Molecular Imaging of Angiogenesis in Cardiac Regeneration

PURPOSE OF REVIEW

Myocardial infarction (MI) leading to heart failure displays an important cause of death worldwide. Adequate restoration of blood flow to prevent this transition is a crucial factor to improve long-term morbidity and mortality. Novel regenerative therapies have been thoroughly investigated within the past decades.

RECENT FINDINGS

Increased angiogenesis in infarcted myocardium has shown beneficial effects on the prognosis of MI; therefore, the proangiogenic capacity of currently tested treatments is of specific interest. Molecular imaging to visualize formation of new blood vessels in vivo displays a promising option to monitor proangiogenic effects of regenerative substances.

SUMMARY

Based on encouraging results in preclinical models, molecular angiogenesis imaging has recently been applied in a small set of patients. This article reviews recent literature on noninvasive in vivo molecular imaging of angiogenesis after MI as an integral part of cardiac regeneration.

SPECT and PET imaging of angiogenesis and arteriogenesis in pre-clinical models of myocardial ischemia and peripheral vascular disease

Purpose

The extent of neovascularization determines the clinical outcome of coronary artery disease and other occlusive cardiovascular disorders. Monitoring of neovascularization is therefore highly important. This review article will elaborately discuss preclinical studies aimed at validating new nuclear angiogenesis and arteriogenesis tracers. Additionally, we will briefly address possible obstacles that should be considered when designing an arteriogenesis radiotracer.

Methods

A structured medline search was the base of this review, which gives an overview on different radiopharmaceuticals that have been evaluated in preclinical models.

Results

Neovascularization is a collective term used to indicate different processes such as angiogenesis and arteriogenesis. However, while it is assumed that sensitive detection through nuclear imaging will facilitate translation of successful therapeutic interventions in preclinical models to the bedside, we still lack specific tracers for neovascularization imaging. Most nuclear imaging research to date has focused on angiogenesis, leaving nuclear arteriogenesis imaging largely overlooked.

Conclusion

Although angiogenesis is the process which is best understood, there is no scarcity in theoretical targets for arteriogenesis imaging.

Selective subepicardial localization of monocyte subsets in response to progressive coronary artery constriction

Following myocardial infarction and atherosclerotic lesion development, monocytes contribute to myocardial protection and repair, while also partaking in myocardial ischemic injury. The balance of proinflammatory and reparative monocyte subsets is crucial in governing these therapeutic and pathological outcomes. Myocardial ischemic damage displays heterogeneity across the myocardium, whereby the subendocardium shows greatest vulnerability to ischemic damage. In this study we examined the transmural distribution of monocyte subsets in response to gradual coronary artery occlusion. CD14(+) monocytes were isolated from peripheral blood of New Zealand White rabbits and divided into two subgroups based on the expression of CD62L. We employed a rabbit model of progressive coronary artery obstruction to induce chronic myocardial ischemia and reinfused fluorescently labeled autologous monocytes. The distribution of fluorescently labeled autologous monocytes was examined with a high-resolution three-dimensional imaging cryomicrotome. The subepicardial layer contained the largest infiltration of both monocyte subgroups, with a significantly greater proportion of CD14(+)CD62L(+) monocytes at the time when the ischemic area was at a maximum. By targeting CD13(+) angiogenic vessels, we confirmed the presence of angiogenesis in epicardial and midmyocardial regions. These myocardial regions demonstrated the highest level of infiltration of both monocyte subsets. Furthermore, CD14(+)CD62L(+) monocytes showed significantly greater migration towards monocyte chemoattractant protein-1, greater adhesive capacity, and higher expression of C-C chemokine receptor type-2 relative to CD14(+)CD62L(-) monocytes. In conclusion, we note selective subepicardial distribution of monocyte subpopulations, with changes in proportion depending on the time after onset of coronary narrowing. Selective homing is supported by divergent migratory properties of each respective monocyte subgroup.

Molecular imaging of angiogenesis after myocardial infarction by (111)In-DTPA-cNGR and (99m)Tc-sestamibi dual-isotope myocardial SPECT

Background

CD13 is selectively upregulated in angiogenic active endothelium and can serve as a target for molecular imaging tracers to non-invasively visualise angiogenesis in vivo. Non-invasive determination of CD13 expression can potentially be used to monitor treatment response to pro-angiogenic drugs in ischemic heart disease. CD13 binds peptides and proteins through binding to tripeptide asparagine-glycine-arginine (NGR) amino acid residues.

Previous studies using in vivo fluorescence microscopy and magnetic resonance imaging indicated that cNGR tripeptide-based tracers specifically bind to CD13 in angiogenic vasculature at the border zone of the infarcted myocardium.

In this study, the CD13-binding characteristics of an ¹¹¹In-labelled cyclic NGR peptide (cNGR) were determined. To increase sensitivity, we visualised ¹¹¹In-DTPA-cNGR in combination with ^99mTc-sestamibi using dual-isotope SPECT to localise CD13 expression in perfusion-deficient regions.

Methods

Myocardial infarction (MI) was induced in Swiss mice by ligation of the left anterior descending coronary artery (LAD). ¹¹¹In-DTPA-cNGR and ^99mTc-sestamibi dual-isotope SPECT imaging was performed 7 days post-ligation in MI mice and in control mice. In addition, ex vivo SPECT imaging on excised hearts was performed, and biodistribution of ¹¹¹In-DTPA-cNGR was determined using gamma counting. Binding specificity of ¹¹¹In-DTPA-cNGR to angiogenic active endothelium was determined using the Matrigel model.

Results

Labelling yield of ¹¹¹In-DTPA-cNGR was 95% to 98% and did not require further purification. In vivo, ¹¹¹In-DTPA-cNGR imaging showed a rapid clearance from non-infarcted tissue and a urinary excretion of 82% of the injected dose (I.D.) 2 h after intravenous injection in the MI mice. Specific binding of ¹¹¹In-DTPA-cNGR was confirmed in the Matrigel model and, moreover, binding was demonstrated in the infarcted myocardium and infarct border zone.

Conclusions

Our newly designed and developed angiogenesis imaging probe ¹¹¹In-DTPA-cNGR allows simultaneous imaging of CD13 expression and perfusion in the infarcted myocardium and the infarct border zone by dual-isotope micro-SPECT imaging.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0081-7) contains supplementary material, which is available to authorized users.

In vivo imaging of Aminopeptidase N (CD13) receptors in experimental renal tumors using the novel radiotracer (68)Ga-NOTA-c(NGR)

PURPOSE

Aminopeptidase N (APN/CD13) plays an important role in tumor neoangiogenic process and the development of metastases. Furthermore, it may serve as a potential target for cancer diagnosis and therapy. Previous studies have already shown that asparagine-glycine-arginine (NGR) peptides specifically bind to APN/CD13. The aim of the study was to synthesize and investigate the APN/CD13 specificity of a novel (68)Ga-labeled NOTA-c(NGR) molecule in vivo using miniPET.

METHODS

c[KNGRE]-NH2 peptide was conjugated with p-SCN-Bn-NOTA and was labeled with Ga-68 ((68)Ga-NOTA-c(NGR)). Orthotopic and heterotopic transplanted mesoblastic nephroma (NeDe) bearing Fischer-344 rats were prepared, on which biodistribution studies and miniPET scans were performed for both (68)Ga-NOTA-c(NGR) and ανβ3 integrin selective (68)Ga-NODAGA-[c(RGD)]2 tracers. APN/CD13 receptor expression of NeDe tumors and metastases was analyzed by western blot.

RESULTS

(68)Ga-NOTA-c(NGR) was produced with high specific activity (5.13-5.92GBq/μmol) and with excellent radiochemical purity (95%<), at all cases. Biodistribution studies in normal rats showed that uptake of the (68)Ga-NOTA-c(NGR) was significantly (p⩽0.05) lower in abdominal organs in comparison with (68)Ga-NODAGA-[c(RGD)]2. Both radiotracers were mainly excreted from the kidney. In NeDe tumor bearing rats higher (68)Ga-NOTA-c(NGR) accumulation was found in the tumors than that of the (68)Ga-NODAGA-[c(RGD)]2. Using orthotopic transplantation, metastases were developed which showed specific (68)Ga-NOTA-c(NGR) uptake. Western blot analysis confirmed the presence of APN/CD13 expression in NeDe tumors and metastases.

CONCLUSION

Our novel radiotracer (68)Ga-NOTA-c(NGR) showed specific binding to the APN/CD13 expressed ortho- and heterotopic transplanted NeDe tumors. Therefore, (68)Ga-NOTA-c(NGR) is a suitable tracer for the detection of APN/CD13 positive tumors and metastases in vivo.

68Ga-labeled cyclic NGR peptide for microPET imaging of CD13 receptor expression

Peptides containing the asparagines-glycine-arginine (NGR) motif have been identified as specific ligands binding to CD13/aminopeptidase N (APN) receptor, a tumor neovascular biomarker. In this study, we synthesized a novel NGR-containing peptide (NOTA-G₃-NGR), and labeled NOTA-G₃-NGR with ⁶⁸Ga (t_1/2 = 67.7 min). The resulting ⁶⁸Ga-NOTA-G₃-NGR peptide was subject to in vitro and in vivo characterization. The microPET imaging results revealed that the ⁶⁸Ga-NOTA-G₃-NGR peptide exhibits rapid and specific tumor uptake, and high tumor-to-background contrast in a subcutaneous HT-1080 fibrosarcoma mouse model. We concluded that the ⁶⁸Ga-NOTA-G₃-NGR peptide has potential in the diagnosis of CD13-targeted tumor angiogenesis.

PET imaging of cardiac wound healing using a novel [68Ga]-labeled NGR probe in rat myocardial infarction

PURPOSE

Peptides containing the asparagine-glycine-arginine (NGR) motif bind to aminopeptidase N (CD13), which is expressed on inflammatory cells, endothelial cells, and fibroblasts. It is unclear whether radiolabeled NGR-containing tracers could be used for in vivo imaging of the early wound-healing phase after myocardial infarction (MI) using positron emission tomography (PET).

PROCEDURES

Uptake of novel tracer [(68)Ga]NGR was assessed together with [(68)Ga]arginine-glycine-aspartic acid ([(68)Ga]RGD) and 2-deoxy-2-[(18) F]fluoro-D-glucose after myocardial ischemia/reperfusion (MI/R) injury using μ-PET and autoradiography, and relative expressions of CD13 and integrin β3 were assessed in fibroblasts, inflammatory cells, and endothelial cells by immunohistochemistry.

RESULTS

In the infarcted myocardium, uptake of [(68)Ga]NGR was maximal from days 3 to 7 after MI/R, and correlated with fibroblast and inflammatory cell infiltration as well as [(68)Ga]RGD uptake.

CONCLUSIONS

[(68)Ga]NGR allows noninvasive and sequential determination of CD13 expression in fibroblasts and inflammatory cells by PET. This will facilitate monitoring of CD13 in the individual wound healing processes, allowing patient-specific therapies to improve outcome after MI.

68Ga-DOTA-NGR as a novel molecular probe for APN-positive tumor imaging using MicroPET

Aminopeptidase N (APN) is selectively expressed on many tumors and the endothelium of tumor neovasculature, and may serve as a promising target for cancer diagnosis and therapy. Asparagine-glycine-arginine (NGR) peptides have been shown to bind specifically to the APN receptor and have served as vehicles for the delivery of various therapeutic drugs in previous studies. The purpose of this study was to synthesize and evaluate the efficacy of a (68)Ga-labeled NGR peptide as a new molecular probe that binds to APN.

METHODS

NGR peptide was conjugated with 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) and labeled with (68)Ga at 95°C for 10 min. In vitro uptake and binding analysis was performed with A549 and MDA-MB231 cells. Biodistribution of (68)Ga-DOTA-NGR was determined in normal mice by dissection method. (68)Ga-DOTA-NGR PET was performed in A549 and MDA-MB231 xenografts, and included dynamic and static imaging. APN expression in tumors and new vasculatures was analyzed by immunohistochemistry.

RESULTS

The radiochemical purity of (68)Ga-DOTA-NGR was 98.0% ± 1.4% with a specific activity of about 17.49 MBq/nmol. The uptake of (68)Ga-DOTA-NGR in A549 cells increased with longer incubation times, and could be blocked by cold DOTA-NGR, while no specific uptake was found in MDA-MB231 cells. In vivo biodistribution studies showed that (68)Ga-DOTA-NGR was mainly excreted from the kidney, and rapidly cleared from blood and nonspecific organs. MicroPET imaging showed that high focal accumulation had occurred in the tumor site at 1 h post-injection (pi) in A549 tumor xenografts. A significant reduction of tumor uptake was observed following coinjection with a blocking dose of DOTA-NGR, whereas only mild uptake was found in MDA-MB231 tumor xenografts. Tumor uptake, measured as the tumor/lung ratio, increased with time peaking at 12.58 ± 1.26 at 1.5 h pi. Immunohistochemical staining confirmed that APN was overexpressed on A549 cells and neovasculature.

CONCLUSIONS

(68)Ga-DOTA-NGR was easily synthesized and showed favorable biodistribution and kinetics. (68)Ga-DOTA-NGR could also specifically bind to the APN receptor in vitro and in vivo, and might be a potential molecular probe for the noninvasive detection of APN-positive tumors and neovasculature.

Peptide-mediated targeting of cytokines to tumor vasculature: the NGR-hTNF example

A growing body of evidence suggests that the efficacy of cytokines in cancer therapy can be increased by targeting strategies based on conjugation with ligands that recognize receptors expressed by tumor cells or elements of the tumor microenvironment, including the tumor vasculature. The targeting approach is generally conceived to permit administration of low, yet pharmacologically active, doses of drugs, thereby avoiding toxic reactions. However, it is becoming clear that, in the case of cytokines, this strategy has another inherent advantage, i.e. the possibility of administering extremely low doses that do not activate systemic counter-regulatory mechanisms, which may limit their potential therapeutic effects. This review is focused on the use of tumor vasculature-homing peptides as vehicles for targeted delivery of cytokines to tumor blood vessel. In particular, we provide an overview of peptide-cytokine conjugates made with peptides containing the NGR, RGD, isoDGR or RGR sequences and describe, in more details, the biological and pharmacological properties of NGR-hTNF, a peptide-tumor necrosis factor-α conjugate that is currently being tested in phase II and III clinical studies. The results of preclinical and clinical studies performed with these products suggest that peptide-mediated vascular-targeting is indeed a viable strategy for delivering bioactive amounts of cytokines to tumor endothelial cells without causing the activation of counter-regulatory mechanisms and toxic reactions.

NGR-TNF, a novel vascular-targeting agent, does not induce cytokine recruitment of proangiogenic bone marrow-derived cells

Background:

Administration of certain chemotherapy drugs at the maximum tolerated dose, vascular-disrupting agents (VDAs) and irradiation can induce mobilisation and tumour homing of proangiogenic bone marrow-derived cells (BMDCs). Increases in cytokines and chemokines contribute to such mobilisation that eventually promotes tumour (re)growth. NGR-TNF is a vascular-targeting agent in advanced clinical development, coupling the CNGRCG angiogenic vessel-homing peptide with tumour necrosis factor-alpha (TNF). We investigated whether NGR-TNF mobilises host BMDCs and growth factors.

Methods:

Blood was obtained from Lewis lung carcinoma and 4T1 tumour-bearing mice at different time points following NGR-TNF, VDA or anti-VEGFR2/flk-1 antibody treatment. Levels of circulating growth factors were assessed by ELISAs. BMDCs were characterised by FACS. Circulating endothelial progenitor cells were defined as CD45⁻/CD13⁺/flk-1⁺/CD117⁺/7AAD⁻, Tie2-expressing monocytes as CD45⁺/CD11b⁺/Tie2⁺ and myeloid-derived suppressor cells as CD45⁺/CD11b⁺/Gr1⁺ cells.

Results:

NGR-TNF decreases tumour blood vessel density-inducing apoptosis of tumour and tumour endothelial cells. Unlike VDAs, or high-dose NGR-TNF, lower doses of NGR-TNF, comparable to those used in clinical trials, neither mobilise nor recruit to the tumour site proangiogenic BMDCs or induce host growth factors.

Conclusion:

Low-dose NGR-TNF exerts antitumour activity without inducing proangiogenic host responses, conceivably important for preventing/overcoming resistance and designing combination therapeutic strategies.

Synthesis and application of cNGR-containing imaging agents for detection of angiogenesis

Angiogenesis is a multi-step process regulated by pro- and anti-angiogenic factors. Inhibition of angiogenesis is a potential anti cancer treatment strategy that is now investigated clinically. In addition, advances in the understanding of the angiogenic process have led to the development of new angiogenesis therapies for ischemic heart disease. Currently, researchers search for objective measures that indicate pharmacological responses to pro- and anti-angiogenic drugs and therefore, there is a great interest in techniques to visualize angiogenesis noninvasively. As CD13 is selectively expressed in angiogenic blood vessels, it can serve as a target for molecular imaging tracers to noninvasively visualize angiogenic processes in animal models and patients. Here, an overview on the currently used CD13 targeted molecular imaging probes for noninvasive visualization of angiogenesis is given.

CD13 is essential for inflammatory trafficking and infarct healing following permanent coronary artery occlusion in mice

Aims

To determine the role of CD13 as an adhesion molecule in trafficking of inflammatory cells to the site of injury in vivo and its function in wound healing following myocardial infarction induced by permanent coronary artery occlusion.

Methods and results

Seven days post-permanent ligation, hearts from CD13 knockout (CD13^KO) mice showed significant reductions in cardiac function, suggesting impaired healing in the absence of CD13. Mechanistically, CD13^KO infarcts showed an increase in small, endothelial-lined luminal structures, but no increase in perfusion, arguing against an angiogenic defect in the absence of CD13. Cardiac myocytes of CD13^KO mice showed normal basal contractile function, eliminating myocyte dysfunction as a mechanism of adverse remodelling. Conversely, immunohistochemical and flow cytometric analysis of CD13^KO infarcts demonstrated a dramatic 65% reduction in infiltrating haematopoietic cells, including monocytes, macrophages, dendritic, and T cells, suggesting a critical role for CD13 adhesion in inflammatory trafficking. Accordingly, CD13^KO infarcts also contained fewer myofibroblasts, consistent with attenuation of fibroblast differentiation resulting from the reduced inflammation, leading to adverse remodelling.

Conclusion

In the ischaemic heart, while compensatory mechanisms apparently relieve potential angiogenic defects, CD13 is essential for proper trafficking of the inflammatory cells necessary to prime and sustain the reparative response, thus promoting optimal post-infarction healing.

Design and synthesis of small-molecule fluorescent photoprobes targeted to aminopeptdase N (APN/CD13) for optical imaging of angiogenesis

We report here the synthesis of a nonpeptide, small-molecule fluorescent imaging agent with high affinity to aminopeptidase N (APN/CD13), a key player in a variety of pathophysiological angiogenic processes. On the basis of a recently described lead structure, we synthesized three putative precursor compounds by introducing polyethylene glycol (PEG) spacers comprising amino groups for dye labeling. Different attachment sites resulted in substantial differences in target affinity, cell toxicity, and target imaging performance. In comparison to bestatin, a natural inhibitor of many aminopeptidases, two of our compounds (22, 23) exhibit comparable inhibition potency, while a third (21) does not show any inhibiting effect. Cell binding assays with APN-positive BT-549 and APN-negative BT-20 cells and the final fluorescent probes Cy 5.5-21 and Cy 5.5-23 confirm these findings. The favorable characteristics of Cy 5.5-23 will now be proven in in vivo experiments with murine models of high APN expression and may serve as a tool to better understand APN pathophysiology.

Plaque-Associated Vasa Vasorum in Aged Apolipoprotein E–Deficient Mice Exhibit Proatherogenic Functional Features In Vivo

Objective—

Neovascularization of human atherosclerotic plaques is implicated in plaque progression and destabilization, although its functional implications are yet unresolved. Here, we aimed to elucidate functional and morphological properties of plaque microvessels in mice in vivo.

Methods and Results—

Atherosclerotic carotid arteries from aged (>40 weeks) apolipoprotein E–deficient mice were imaged in vivo using multiphoton laser scanning microscopy. Two distinct groups of vasa vasorum microvessels were observed at sites of atherosclerosis development (median diameters of 18.5 and 5.9 μm, respectively), whereas microvessels within the plaque could only rarely be found. In vivo imaging showed ongoing angiogenic activity and injection of fluorescein isothiocyanate-dextran confirmed active perfusion. Plaque vasa vasorum showed increased microvascular leakage, combined with a loss of endothelial glycocalyx. Mean blood flow velocity in plaque-associated vasa vasorum was reduced by ±50% compared with diameter-matched control capillaries, whereas mean blood flow was reduced 8-fold. Leukocyte adhesion and extravasation were increased 6-fold in vasa vasorum versus control capillaries.

Conclusion—

Using a novel in vivo functional imaging strategy, we showed that plaque-associated vasa vasorum were angiogenically active and, albeit poorly, perfused. Moreover, plaque-associated vasa vasorum showed increased permeability, reduced blood flow, and increased leukocyte adhesion and extravasation (ie, characteristics that could contribute to plaque progression and destabilization).

The first ratiometric fluorescent probes for aminopeptidase N cell imaging

In the current paper, three activity-based colorimetric and ratiometric fluorescent probes based on a naphthalimide fluorophore were well designed and synthesized, which can be recognized and hydrolyzed by aminopeptidase N (APN) at both the enzymatic and cellular level by following the fluorescent emission wavelength change from blue to green light. As a result, these molecules were successfully identified as the first ratiometric fluorescent probes for APN cell imaging.

Peptides as targeting probes against tumor vasculature for diagnosis and drug delivery

Tumor vasculature expresses a distinct set of molecule signatures on the endothelial cell surface different from the resting blood vessels of other organs and tissues in the body. This makes them an attractive target for cancer therapy and molecular imaging. The current technology using the in vivo phage display biopanning allows us to quickly isolate and identify peptides potentially homing to various tumor blood vessels. Tumor-homing peptides in conjugation with chemotherapeutic drugs or imaging contrast have been extensively tested in various preclinical and clinical studies. These tumor-homing peptides have valuable potential as targeting probes for tumor molecular imaging and drug delivery. In this review, we summarize the recent advances about the applications of tumor-homing peptides selected by in vivo phage display library screening against tumor vasculature. We also introduce the characteristics of the latest discovered tumor-penetrating peptides in their potential clinical applications.

Contrast-enhanced MRI of murine myocardial infarction - part I

The use of contrast agents has added considerable value to the existing cardiac MRI toolbox that can be used to study murine myocardial infarction, as it enables detailed in vivo visualization of the molecular and cellular processes that occur in the infarcted and remote tissue. A variety of non-targeted and targeted contrast agents to study myocardial infarction are available and under development. Manganese, which acts as a calcium analogue, can be used to assess cell viability. Traditionally, low-molecular-weight Gd-containing contrast agents are employed to measure infarct size in a late gadolinium enhancement experiment. Gd-based blood-pool agents are used to study the vascular status of the myocardium. The use of targeted contrast agents facilitates more detailed imaging of pathophysiological processes in the acute and chronic infarct. Cell death was visualized by contrast agents functionalized with annexin A5 that binds specifically to phosphatidylserine accessible on dying cells and with an agent that binds to the exposed DNA of dead cells. Inflammation in the myocardium was depicted by contrast agents that target cell adhesion molecules expressed on activated endothelium, by contrast agents that are phagocytosed by inflammatory cells, and by using a probe that targets enzymes excreted by inflammatory cells. Cardiac remodeling processes were visualized with a contrast agent that binds to angiogenic vasculature and with an MR probe that specifically binds to collagen in the fibrotic myocardium. These recent advances in murine contrast-enhanced cardiac MRI have made a substantial contribution to the visualization of the pathophysiology of myocardial infarction, cardiac remodeling processes and the progression to heart failure, which helps to design new treatments. This review discusses the advances and challenges in the development and application of MRI contrast agents to study murine myocardial infarction.

In vivo tumor targeting by a NGR-decorated micelle of a recombinant diblock copolypeptide

Antivascular targeting is a promising strategy for tumor therapy. This strategy has the potential to overcome many of the transport barriers associated with targeting tumor cells in solid tumors, because the tumor vasculature is directly accessible to targeting vehicles in systemic circulation. We report a novel nanoscale delivery system consisting of multivalent polymer micelles to target receptors that are preferentially upregulated in the tumor vasculature and perivascular cells, specifically CD13. To this end we utilized amphiphilic block copolymers, composed of a genetically engineered elastin-like polypeptide (ELP) that self-assemble into monodisperse spherical micelles. These polymer micelles were functionalized by incorporating the NGR tripeptide ligand, which targets the CD13 receptor, on their corona. We examined the self-assembly and in vivo tumor targeting by these NGR-functionalized nanoparticles and show that multivalent presentation of NGR by micelle self-assembly selectively targets the tumor vasculature by targeting CD13. Furthermore, we show greater vascular retention and extravascular accumulation of nanoparticles in tumor tissue compared to normal tissue, although the enhancement is modest. These results suggest that enhanced delivery to solid tumors can be achieved by targeting upregulated receptors in the tumor vasculature with multivalent ligand-presenting nanoparticles, but additional work is required to optimize such systems for multivalent targeting.

Bioreducible polymers for gene delivery

Bioreducible polymers, which possess mainly disulfide linkages in the polymer structures, have appeared as ideal gene delivery carriers due to the high stability in extracellular physiological condition and bioreduction-triggered release of genetic materials, as well as decreased cytotoxicity because intracellular cytosol is a reducing environment containing high level of reducing molecules such as glutathione. This review will describe the initiation and recent advances in the development of bioreducible polymers for gene delivery, which includes reducibly cross-linked PEIs, polypeptides, polyion complex micelles, and poly(amido amine)s. There have been extensive researches performed to exhibit great gene delivery efficacy but still several important issues about pharmacokinetics or safety should be answered thoroughly for further rational design of bioreducible polymers having potentials in human gene delivery systems.

Nanotechnology-mediated targeting of tumor angiogenesis

Angiogenesis is disregulated in many diseased states, most notably in cancer. An emerging strategy for the development of therapies targeting tumor-associated angiogenesis is to harness the potential of nanotechnology to improve the pharmacology of chemotherapeutics, including anti-angiogenic agents. Nanoparticles confer several advantages over that of free drugs, including their capability to carry high payloads of therapeutic agents, confer increased half-life and reduced toxicity to the drugs, and provide means for selective targeting of the tumor tissue and vasculature. The plethora of nanovectors available, in addition to the various methods available to combine them with anti-angiogenic drugs, allows researchers to fine-tune the pharmacological profile of the drugs ad infinitum. Use of nanovectors has also opened up novel avenues for non-invasive imaging of tumor angiogenesis. Herein, we review the types of nanovector and therapeutic/diagnostic agent combinations used in targeting tumor angiogenesis.