Enhanced expression of CD13 in vessels of inflammatory and neoplastic tissues

CD13 expression affects glioma patient survival and influences key functions of human glioblastoma cell lines in vitro

CD13 (APN) is an Alanyl-Aminopeptidase with diverse functions. The role of CD13 for gliomas is still unknown. In this study, data of glioma patients obtained by TCGA and CGGA databases were used to evaluate the survival rate and prognostic value of CD13 expression level. Protein expression of CD13 was confirmed by immunofluorescence staining of fresh patient tissues. Eight human glioblastoma cell lines were studied by RT-PCR, Western Blot, immunofluorescence staining and flow cytometry to define CD13 expression. Cell lines with different CD13 expression status were treated with a CD13 inhibitor, bestatin, and examined by MTT, scratch and colony formation assaysas well as by apoptosis assay and Western Blots. Bioinformatics analysis indicated that patients with high expression of CD13 had poor survival and prognosis. Additionally, CD13 protein expression was positively associated with clinical malignant characteristics. Investigated glioblastoma cell lines showed distinct expression levels and subcellular localization of CD13 with intracellular enrichment. Bestatin treatment reduced proliferation, migration and colony formation of glioma cells in a CD13-dependent manner while apoptosis was increased. In summary, CD13 has an impact on glioma patient survival and is important for the main function of specific glioma cells.

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.

Cancer-specific glycosylation of CD13 impacts its detection and activity in preclinical cancer tissues

Harnessing the differences between cancer and non-cancer tissues presents new opportunities for selective targeting by anti-cancer drugs. CD13, a heavily glycosylated protein, is one example with significant unmet clinical potential in cancer drug discovery. Despite its high expression and activity in cancers, CD13 is also expressed in many normal tissues. Here, we report differential tissue glycosylation of CD13 across tissues and demonstrate for the first time that the nature and pattern of glycosylation of CD13 in preclinical cancer tissues are distinct compared to normal tissues. We identify cancer-specific O-glycosylation of CD13, which selectively blocks its detection in cancer models but not in normal tissues. In addition, the metabolism activity of cancer-expressed CD13 was observed to be critically dependent on its unique glycosylation. Thus, our data demonstrate the existence of discrete cancer-specific CD13 glycoforms and propose cancer-specific CD13 glycoforms as a clinically useful target for effective cancer-targeted therapy.

Identification of G4 motifs of various stem cell markers and their biophysical and biochemical characterization

Regulatory regions in the human genome, enriched in guanine-rich DNA sequences have a remarkable enrichment of G-rich sequences having a tendency to fold into G-quadruplex structures. To identify the G-quadruplex forming motifs in regulatory regions of stem cell markers, gene sequences of various stem cell markers were downloaded and analyzed to see the abundance of G-rich sequences. We observed the enrichment of G-rich sequences in stem cell markers (CD13, CD19, CD24 and CD38) which could possibly play a critical role in its regulation. We used Circular Dichroism (CD), UV-Thermal denaturation (UV-Tm) and polyacrylamide gel electrophoresis (PAGE) to demonstrate the formation of a G-quadruplex by G-rich sequences present in these stem cell markers. We observed that these G-rich sequences containing minimum consecutive G3 stretch separated by loop length ranging from one to three bases long adopt G-quadruplexes with different molecularity involving two-strands, three-strand and four-strand with parallel and antiparallel conformation. Interestingly, we proposed the formation of three-stranded G-quadruplex by CD13 in 100 mM Na+, CD19 in 100 mM K+, 100 mM K+ with 40 wt% PEG 200, and CD38 in 100 mM K+ + 40 wt% PEG 200. The formation of such diverse G-quadruplex structures in the regulatory regions leaves the fair possibility of recognition by regulatory factors to modulate the gene expression. First time, this study may give insight into the structural polymorphism of G4 forming motifs in different stem cell markers to design the best suitable ligand and to target them for therapeutic development.Communicated by Ramaswamy H. Sarma.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Challenges and advances for glioma therapy based on inorganic nanoparticles

Glioma is one of the most serious central nervous system diseases, with high mortality and poor prognosis. Despite the continuous development of existing treatment methods, the median survival time of glioma patients is still only 15 months. The main treatment difficulties are the invasive growth of glioma and the obstruction of the blood-brain barrier (BBB) to drugs. With rapid advancements in nanotechnology, inorganic nanoparticles (INPs) have shown favourable application prospects in the diagnosis and treatment of glioma. Due to their extraordinary intrinsic features, INPs can be easily fabricated, while doping with other elements and surface modification by biological ligands can be used to enhance BBB penetration, targeted delivery and biocompatibility. Guided glioma theranostics with INPs can improve and enhance the efficacy of traditional methods such as chemotherapy, radiotherapy and gene therapy. New strategies, such as immunotherapy, photothermal and photodynamic therapy, magnetic hyperthermia therapy, and multifunctional inorganic nanoplatforms, have also been facilitated by INPs. This review emphasizes the current state of research and clinical applications of INPs, including glioma targeting and BBB penetration enhancement methods, in vivo and in vitro biocompatibility, and diagnostic and treatment strategies. As such, it provides insights for the development of novel glioma treatment strategies.

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.

Is tumour-expressed aminopeptidase N (APN/CD13) structurally and functionally unique?

Aminopeptidase N (APN/CD13) is a multifunctional glycoprotein that acts as a peptidase, receptor, and signalling molecule in a tissue-dependent manner. The activities of APN have been implicated in the progression of many cancers, pointing toward significant therapeutic potential for cancer treatment. However, despite the tumour-specific functions of this protein that have been uncovered, the ubiquitous nature of its expression in normal tissues as generally reported remains a limitation to the potential utility of APN as a target for cancer therapeutics and drug discovery. With this in mind, we have extensively explored the literature, and present a comprehensive review that for the first-time provides evidence to support the suggestion that tumour-expressed APN may in fact be unique in structure, function, substrate specificity and activity, contrary to its nature in normal tissues. The review also focuses on the biology of APN, and its "moonlighting" functional roles in both normal physiology and cancer development. Several APN-targeting approaches that have been explored over recent decades as therapeutic strategies in cancer treatment, including APN-targeting agents reported both in preclinical and clinical studies, are also extensively discussed. This review concludes by posing critical questions about APN that remain unanswered and unexplored, hence providing opportunities for further research.

Retinoids Delivery Systems in Cancer: Liposomal Fenretinide for Neuroectodermal-Derived Tumors

Retinoids are a class of natural and synthetic compounds derived from vitamin A. They are involved in several biological processes like embryogenesis, reproduction, vision, growth, inflammation, differentiation, proliferation, and apoptosis. In light of their important functions, retinoids have been widely investigated for their therapeutic applications. Thus far, their use for the treatment of several types of cancer and skin disorders has been reported. However, these therapeutic agents present several limitations for their widespread clinical translatability, i.e., poor solubility and chemical instability in water, sensitivity to light, heat, and oxygen, and low bioavailability. These characteristics result in internalization into target cells and tissues only at low concentration and, consequently, at an unsatisfactory therapeutic dose. Furthermore, the administration of retinoids causes severe side-effects. Thus, in order to improve their pharmacological properties and circulating half-life, while minimizing their off-target uptake, various retinoids delivery systems have been recently developed. This review intends to provide examples of retinoids-loaded nano-delivery systems for cancer treatment. In particular, the use and the therapeutic results obtained by using fenretinide-loaded liposomes against neuroectodermal-derived tumors, such as melanoma, in adults, and neuroblastoma, the most common extra-cranial solid tumor of childhood, will be discussed.

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.

Breaching the Blood-Brain Tumor Barrier for Tumor Therapy

Tumors affecting the central nervous system (CNS), either primary or secondary, are highly prevalent and represent an unmet medical need. Prognosis of these tumors remains poor, mostly due to the low intrinsic chemo/radio-sensitivity of tumor cells, a meagerly known role of the microenvironment and the poor CNS bioavailability of most used anti-cancer agents. The BBTB is the main obstacle for anticancer drugs to achieve therapeutic concentrations in the tumor tissues. During the last decades, many efforts have been devoted to the identification of modalities allowing to increase drug delivery into brain tumors. Until recently, success has been modest, as few of these approaches reached clinical testing and even less gained regulatory approval. In recent years, the scenario has changed, as various conjugates and drug delivery technologies have advanced into clinical testing, with encouraging results and without being burdened by a heavy adverse event profile. In this article, we review the different approaches aimed at increasing drug delivery to brain tumors, with particular attention to new, promising approaches that increase the permeability of the BBTB or exploit physiological transport mechanisms.

Improving the antitumor activity of R-CHOP with NGR-hTNF in primary CNS lymphoma: final results of a phase 2 trial

Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) is the standard treatment of diffuse large B-cell lymphoma (DLBCL). Primary DLBCL of the central nervous system (CNS) (primary central nervous system lymphoma [PCNSL]) is an exception because of the low CNS bioavailability of related drugs. NGR-human tumor necrosis factor (NGR-hTNF) targets CD13+ vessels, enhances vascular permeability and CNS access of anticancer drugs, and provides the rationale for the treatment of PCNSL with R-CHOP. Herein, we report activity and safety of R-CHOP preceded by NGR-hTNF in patients with PCNSL relapsed/refractory to high-dose methotrexate-based chemotherapy enrolled in a phase 2 trial. Overall response rate (ORR) was the primary endpoint. A sample size of 28 patients was considered necessary to demonstrate improvement from 30% to 50% ORR. NGR-hTNF/R-CHOP would be declared active if ≥12 responses were recorded. Treatment was well tolerated; there were no cases of unexpected toxicities, dose reductions or interruptions. NGR-hTNF/R-CHOP was active, with confirmed tumor response in 21 patients (75%; 95% confidence interval, 59%-91%), which was complete in 11. Seventeen of the 21 patients with response to treatment received consolidation (ASCT, WBRT, and/or lenalidomide maintenance). At a median follow-up of 21 (range, 14-31) months, 5 patients remained relapse-free and 6 were alive. The activity of NGR-hTNF/R-CHOP is in line with the expression of CD13 in both pericytes and endothelial cells of tumor vessels. High plasma levels of chromogranin A, an NGR-hTNF inhibitor, were associated with proton pump inhibitor use and a lower remission rate, suggesting that these drugs should be avoided during TNF-based therapy. Further research on this innovative approach to CNS lymphomas is warranted. The trial was registered as EudraCT: 2014-001532-11.

Coronavirus Receptors as Immune Modulators

The Coronaviridae family includes the seven known human coronaviruses (CoV) that cause mild to moderate respiratory infections (HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1) as well as severe illness and death (MERS-CoV, SARS-CoV, SARS-CoV-2). Severe infections induce hyperinflammatory responses that are often intensified by host adaptive immune pathways to profoundly advance disease severity. Proinflammatory responses are triggered by CoV entry mediated by host cell surface receptors. Interestingly, five of the seven strains use three cell surface metallopeptidases (CD13, CD26, and ACE2) as receptors, whereas the others employ O-acetylated-sialic acid (a key feature of metallopeptidases) for entry. Why CoV evolved to use peptidases as their receptors is unknown, but the peptidase activities of the receptors are dispensable, suggesting the virus uses/benefits from other functions of these molecules. Indeed, these receptors participate in the immune modulatory pathways that contribute to the pathological hyperinflammatory response. This review will focus on the role of CoV receptors in modulating immune responses.

Increasing the activity of cell adherent cyclic NGR peptides by optimizing the peptide length and amino acid character

Cyclic peptides are an attractive modality for the development of therapeutics and the identification of functional cyclic peptides that contribute to novel drug development. The peptide array is one of the optimization methods for peptide sequences and also useful to understand sequence-function relationship of peptides. Cell adherent cyclic NGR peptide which selectively binds to the aminopeptidase N (APN or CD13) is known as an attractive tumor marker. In this study, we designed and screened a library of different length and an amino acid substitution library to identify stronger cell adhesion peptides and to reveal that the factor of higher binding between CD13 and optimized cyclic peptides. Additionally, we designed and evaluated 192 peptide libraries using eight representative amino acids to reduce the size of the library. Through these optimization steps of cyclic peptides, we identified 23 peptides that showed significantly higher cell adhesion activity than cKCNGRC, which was previously reported as a cell adhesion cyclic peptide. Among them, cCRHNGRARC showed the highest activity, that is, 1.65 times higher activity than cKCNGRC. An analysis of sequence and functional data showed that the rules which show higher cell adhesion activity for the three basic cyclic peptides (cCX₁ HNGRHX₂ C, cCX₁ HNGRAX₂ C, and cCX₁ ANGRHX₂ C) are related with the position of His residues and cationic amino acids.

Coronavirus Infections in Companion Animals: Virology, Epidemiology, Clinical and Pathologic Features

Coronaviruses are enveloped RNA viruses capable of causing respiratory, enteric, or systemic diseases in a variety of mammalian hosts that vary in clinical severity from subclinical to fatal. The host range and tissue tropism are largely determined by the coronaviral spike protein, which initiates cellular infection by promoting fusion of the viral and host cell membranes. Companion animal coronaviruses responsible for causing enteric infection include feline enteric coronavirus, ferret enteric coronavirus, canine enteric coronavirus, equine coronavirus, and alpaca enteric coronavirus, while canine respiratory coronavirus and alpaca respiratory coronavirus result in respiratory infection. Ferret systemic coronavirus and feline infectious peritonitis virus, a mutated feline enteric coronavirus, can lead to lethal immuno-inflammatory systemic disease. Recent human viral pandemics, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and most recently, COVID-19, all thought to originate from bat coronaviruses, demonstrate the zoonotic potential of coronaviruses and their potential to have devastating impacts. A better understanding of the coronaviruses of companion animals, their capacity for cross-species transmission, and the sharing of genetic information may facilitate improved prevention and control strategies for future emerging zoonotic coronaviruses. This article reviews the clinical, epidemiologic, virologic, and pathologic characteristics of nine important coronaviruses of companion animals.

Anchorage independence altered vasculogenic phenotype of melanoma cells through downregulation in aminopeptidase N /syndecan-1/integrin β4 axis

The detachment of tumor cells from extracellular matrix and survival under anchorage-independence were recognized as the initial step of tumor metastasis. Previously we had demonstrated that anchorage-independence altered gene expressions and showed characteristics of cell invasiveness loss, enhanced chemosensitivity, and enhanced subcutaneous tumor formation. However, whether it affected histological phenotypes in tumor tissues remained unclear. Melanoma metastases were generated in nude mice using adherent or suspended melanoma cells. Examination of melanoma metastases revealed histological features of extensive vascular structures in adherent cell-derived tumors, while not seen in suspended cell-derived tumors. Quantitative proteomic analysis at adherent, suspended, and re-attached melanoma cells suggested that aminopeptidase N was potentially downregulated upon cell suspension or reattachment. Downregulation of aminopeptidase N by gene-specific shRNAs showed reduced cell invasiveness and enhanced subcutaneous tumor formation that was consistent with previous observations. Experiments by suppression or overexpression of aminopeptidase N expression demonstrated that aminopeptidase N regulated syndecan-1 and integrin β4 expression through PKCδ pathway. Histological analysis at melanoma metastases further suggested that CD31⁺/aminopeptidase N⁺/syndecan-1⁺/integrin β4⁺ phenotypes were associated with vascular structures. In summary, we suggested the expression axis of aminopeptidase N/syndecan-1/integrin β4 in melanoma cells was suppressed by detachment stress, which diminished vascular phenotypes of melanoma metastases.

CD13 as a new tumor target for antibody-drug conjugates: validation with the conjugate MI130110

Background

In the search for novel antibody-drug conjugates (ADCs) with therapeutic potential, it is imperative to identify novel targets to direct the antibody moiety. CD13 seems an attractive ADC target as it shows a differential pattern of expression in a variety of tumors and cell lines and it is internalized upon engagement with a suitable monoclonal antibody. PM050489 is a marine cytotoxic compound tightly binding tubulin and impairing microtubule dynamics which is currently undergoing clinical trials for solid tumors.

Methods

Anti-CD13 monoclonal antibody (mAb) TEA1/8 has been used to prepare a novel ADC, MI130110, by conjugation to the marine compound PM050489. In vitro and in vivo experiments have been carried out to demonstrate the activity and specificity of MI130110.

Results

CD13 is readily internalized upon TEA1/8 mAb binding, and the conjugation with PM050489 did not have any effect on the binding or the internalization of the antibody. MI130110 showed remarkable activity and selectivity in vitro on CD13-expressing tumor cells causing the same effects than those described for PM050489, including cell cycle arrest at G2, mitosis with disarrayed and often multipolar spindles consistent with an arrest at metaphase, and induction of cell death. In contrast, none of these toxic effects were observed in CD13-null cell lines incubated with MI130110. Furthermore, in vivo studies showed that MI130110 exhibited excellent antitumor activity in a CD13-positive fibrosarcoma xenograft murine model, with total remissions in a significant number of the treated animals. Mitotic catastrophes, typical of the payload mechanism of action, were also observed in the tumor cells isolated from mice treated with MI130110. In contrast, MI130110 failed to show any activity in a xenograft mouse model of myeloma cells not expressing CD13, thereby corroborating the selectivity of the ADC to its target and its stability in circulation.

Conclusion

Our results show that MI130110 ADC combines the antitumor potential of the PM050489 payload with the selectivity of the TEA1/8 monoclonal anti-CD13 antibody and confirm the correct intracellular processing of the ADC. These results demonstrate the suitability of CD13 as a novel ADC target and the effectiveness of MI130110 as a promising antitumor therapeutic agent.

Dynamic transition of the blood-brain barrier in the development of non-small cell lung cancer brain metastases

Invasion of the brain by non-small cell lung cancer (NSCLC) results in a shift of the blood-brain barrier (BBB) to the insufficiently characterized blood-tumor barrier (BTB). Effective drug delivery through the BTB is one of the greatest therapeutic obstacles in treating brain metastases. Using an experimental model, we defined key changes within the BTB and the BBB in the brain around the tumor (BAT) region over time. Brain-seeking NSCLC cells were delivered into the circulation of athymic-nude mice via intracardiac injection and developing brain metastases were evaluated over six-weeks. Components of the BBB and BTB were analyzed using immunofluorescence microscopy and compared using a mixed model of regression. Our results demonstrate a dynamic time-dependent BTB phenotype. Capillaries of the BAT and BTB were dilated with increased CD31 expression compared to controls. Expression of collagen IV, a pan-basement membrane component, was significantly decreased in the BTB compared to the BBB. There was also a significant increase in the desmin-positive pericyte subpopulation in the BTB compared to the BBB. The most striking changes were identified in astrocyte water channels with a 12.18-fold (p < 0.001) decrease in aquaporin-4 in the BTB; the BAT was unchanged. Analysis of NSCLC brain metastases from patient samples similarly demonstrated dilated capillaries and loss of both collagen IV and aquaporin-4. These data provide a comprehensive analysis of the BTB in NSCLC brain metastasis. Astrocytic endfeet, pericytes, and the basement membrane are potential therapeutic targets to improve efficacy of chemotherapeutic delivery into NSCLC brain metastases.

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.

R-CHOP preceded by blood-brain barrier permeabilization with engineered tumor necrosis factor-α in primary CNS lymphoma

Patients with primary central nervous system lymphoma (PCNSL) are treated with high-dose methotrexate-based chemotherapy, which requires hospitalization and extensive expertise to manage related toxicity. The use of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) could overcome these difficulties, but blood-brain barrier (BBB) penetration of related drugs is poor. Tumor necrosis factor-α coupled with NGR (NGR-hTNF), a peptide targeting CD13⁺ vessels, induces endothelial permeabilization and improves tumor access of cytostatics. We tested the hypothesis that NGR-hTNF can break the BBB, thereby improving penetration and activity of R-CHOP in patients with relapsed/refractory PCNSL (NCT03536039). Patients received six R-CHOP21 courses, alone at the first course and preceded by NGR-hTNF (0.8 μg/m²) afterward. This trial included 2 phases: an "explorative phase" addressing the effect of NGR-hTNF on drug pharmacokinetic parameters and on vessel permeability, assessed by dynamic contrast-enhanced magnetic resonance imaging and ^99mTc-diethylene-triamine-pentacetic acid-single-photon emission computed tomography, and the expression of CD13 on tumor tissue; and an "expansion phase" with overall response rate as the primary end point, in which the 2-stage Simon Minimax design was used. At the first stage, if ≥4 responses were observed among 12 patients, the study accrual would have continued (sample size, 28). Herein, we report results of the explorative phase and the first-stage analysis (n = 12). CD13 was expressed in tumor vessels of all cases. NGR-hTNF selectively increased vascular permeability in tumoral/peritumoral areas, without interfering with drug plasma/cerebrospinal fluid concentrations. The NGR-hTNF/R-CHOP combination was well tolerated: there were only 2 serious adverse events, and grade 4 toxicity was almost exclusively hematological, which were resolved without dose reductions or interruptions. NGR-hTNF/R-CHOP was active, with 9 confirmed responses (75%; 95% confidence interval, 51-99), 8 of which were complete. In conclusion, NGR-hTNF/R-CHOP was safe in these heavily pretreated patients. NGR-hTNF enhanced vascular permeability specifically in tumoral/peritumoral areas, which resulted in fast and sustained responses.

Nanocomposites as biomolecules delivery agents in nanomedicine

Nanoparticles (NPs) are atomic clusters of crystalline or amorphous structure that possess unique physical and chemical properties associated with a size range of between 1 and 100 nm. Their nano-sized dimensions, which are in the same range as those of vital biomolecules, such as antibodies, membrane receptors, nucleic acids, and proteins, allow them to interact with different structures within living organisms. Because of these features, numerous nanoparticles are used in medicine as delivery agents for biomolecules. However, off-target drug delivery can cause serious side effects to normal tissues and organs. Considering this issue, it is essential to develop bioengineering strategies to significantly reduce systemic toxicity and improve therapeutic effect. In contrast to passive delivery, nanosystems enable to obtain enhanced therapeutic efficacy, decrease the possibility of drug resistance, and reduce side effects of "conventional" therapy in cancers. The present review provides an overview of the most recent (mostly last 3 years) achievements related to different biomolecules used to enable targeting capabilities of highly diverse nanoparticles. These include monoclonal antibodies, receptor-specific peptides or proteins, deoxyribonucleic acids, ribonucleic acids, [DNA/RNA] aptamers, and small molecules such as folates, and even vitamins or carbohydrates.

Core-matched nanoassemblies for targeted co-delivery of chemotherapy and photosensitizer to treat drug-resistant cancer

Emergence of drug resistance in tumors causes therapeutic failure or tumor relapse. Combination of chemotherapy and photodynamic therapy holds significant promise to treat drug-resistant tumors. However, stubborn hydrophobicity of photosensitizer (PS), low encapsulation efficiency and leaking problem of PS in organic carrier, and disparate physicochemical properties of PS and chemotherapeutics make the combination unachievable. Thus how to efficiently co-deliver the two functional agents to enable photo-chemotherapy seems to be one of the key challenges. Here, core-matched technology (CMT) was developed to realize efficient co-delivery of PS and chemotherapeutics, in which PS verteporfin (VP), tumor angiogenesis-targeting iNGR peptide and poly(lactic acid) (PLA) were respectively pre-modified with D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS), and the conjugates self-assembled into iNGR-modified and VP conjugated nanoassemblies (iNGR-VP-NA) with chemotherapeutic agent docetaxel (DTX) loaded in the hydrophobic core. The obtained iNGR-VP-NA-DTX was characterized by mean size of 166.0 ± 9.2 nm and morphology of uniformly spherical shape. In vitro, with the assistance of laser, iNGR-VP-NA-DTX exhibited higher cellular uptake, stronger cytotoxicity in HUVEC cells, drug-resistant HCT-15 tumor cells and more effective inhibition of tube formation than iNGR-VP-NA-DTX without laser or VP-NA-DTX with laser. After intravenously injected into mice, through the near-infrared light emitted by VP, iNGR-VP-NA exhibited improved accumulation compared to VP-NA in drug-resistant HCT-15 tumor. Besides, iNGR-VP-NA-DTX with laser enhanced inhibition of angiogenesis and induced severe apoptosis and necrosis in tumor tissues along with minimal impact to normal areas. These evidences demonstrated that iNGR-VP-NA-DTX was of great potential to treat drug-resistant tumors via efficient angiogenesis-targeted photo-chemotherapy. STATEMENT OF SIGNIFICANCE: Combination of chemotherapy and photodynamic therapy is thought to be a potential approach to treat drug-resistant cancer. However, it is difficult to realize optimized photo-chemotherapy in one nano-system. Here, iNGR-modified nanoassemblies is created based on core-matched nanotechnology to realize targeted photo-chemotherapy. In this study, the improved co-loading of chemotherapy and photosensitizer in the nanoassemblies exerted a synergistic anti-tumor effect and the decoration with iNGR enhanced tumor-targeting efficiency. In the presence of laser irradiation, the nanoassemblies exhibited enhanced and targeted anti-tumor efficacy in drug-resistant HCT-15 tumor both in vitro and in vivo.

Vitronectin from brain pericytes promotes adult forebrain neurogenesis by stimulating CNTF

Vitronectin (VTN) is a glycoprotein in the blood and affects hemostasis. VTN is also present in the extracellular matrix of various organs but little is known about its function in healthy adult tissues. We show, in adult mice, that VTN is uniquely expressed by approximately half of the pericytes of subventricular zone (SVZ) where neurogenesis continues throughout life. Intracerebral VTN antibody injection or VTN knockout reduced neurogenesis as well as expression of pro-neurogenic CNTF, and anti-neurogenic LIF and IL-6. Conversely, injections of VTN, or plasma from VTN+/+, but not VTN-/- mice, increased these cytokines. VTN promoted SVZ neurogenesis when LIF and IL-6 were suppressed by co-administration of a gp130 inhibitor. Unexpectedly, VTN inhibited FAK signaling and VTN-/- mice had increased FAK signaling in the SVZ. Further, an FAK inhibitor or VTN increased CNTF expression, but not in conditional astrocytic FAK knockout mice, suggesting that VTN increases CNTF through FAK inhibition in astrocytes. These results identify a novel role of pericyte-derived VTN in the brain, where it regulates SVZ neurogenesis through co-expression of CNTF, LIF and IL-6. VTN-integrin-FAK and gp130 signaling may provide novel targets to induce neurogenesis for cell replacement therapies.

Aminopeptidase N (CD13) targeted MR and NIRF dual-modal imaging of ovarian tumor xenograft

The development of tumor-specific imaging nanoprobes with the potential to improve the accuracy of cancer diagnosis has become an area of intense research. Aminopeptidase N (CD13) predominantly expresses on the surface of ovarian tumor cells and can be specifically recognized by Asn-Gly-Arg (NGR) peptide. The applicability of CD13 as a target for specific ovarian tumor imaging, however, remains unexploited so far. In this study, Cy5.5-labeled, NGR-conjugated iron oxide nanoparticles (Cy5.5-NGR-Fe₃O₄ NPs) were prepared as an ovarian tumor specific bimodal imaging nanoprobe. It is demonstrated that the conjugation of NGR targeting moiety leads to a higher cellular uptake toward ES-2 cells, the human ovarian carcinoma cells that highly express CD13. Moreover, magnetic resonance imaging of ovarian tumor xenograft reveals that the Fe₃O₄-Cy5.5-NGR NPs results in a significant T₂* signal reduction in the tumor. Meanwhile, near infrared fluorescence imaging indicates a higher accumulation of Fe₃O₄-Cy5.5-NGR NPs in the tumor xenograft. Therefore, CD13 could be applied as a novel and efficient target for constructing ovarian tumor specific nanoprobes with improved accuracy for ovarian tumor diagnosis.

Molecular Imaging of Aminopeptidase N in Cancer and Angiogenesis

This review focuses on recent advances in the molecular imaging of aminopeptidase N (APN, also known as CD13), a zinc metalloenzyme that cleaves N-terminal neutral amino acids. It is overexpressed in multiple cancer types and also on the surface of vasculature undergoing angiogenesis, making it a promising target for molecular imaging and targeted therapy. Molecular imaging probes for APN are divided into two large subgroups: reactive and nonreactive. The structures of the reactive probes (substrates) contain a reporter group that is cleaved and released by the APN enzyme. The nonreactive probes are not cleaved by the enzyme and contain an antibody, peptide, or nonpeptide for targeting the enzyme exterior or active site. Multivalent homotopic probes utilize multiple copies of the same targeting unit, whereas multivalent heterotopic molecular probes are equipped with different targeting units for different receptors. Several recent preclinical cancer imaging studies have shown that multivalent APN probes exhibit enhanced tumor specificity and accumulation compared to monovalent analogues. The few studies that have evaluated APN-specific probes for imaging angiogenesis have focused on cardiac regeneration. These promising results suggest that APN imaging can be expanded to detect and monitor other diseases that are associated with angiogenesis.

Vascular targeting of LIGHT normalizes blood vessels in primary brain cancer and induces intratumoural high endothelial venules

High-grade brain cancer such as glioblastoma (GBM) remains an incurable disease. A common feature of GBM is the angiogenic vasculature, which can be targeted with selected peptides for payload delivery. We assessed the ability of micelle-tagged, vascular homing peptides RGR, CGKRK and NGR to specifically bind to blood vessels in syngeneic orthotopic GBM models. By using the peptide CGKRK to deliver the tumour necrosis factor (TNF) superfamily member LIGHT (also known as TNF superfamily member 14; TNFSF14) to angiogenic tumour vessels, we have generated a reagent that normalizes the brain cancer vasculature by inducing pericyte contractility and re-establishing endothelial barrier integrity. LIGHT-mediated vascular remodelling also activates endothelia and induces intratumoural high endothelial venules (HEVs), which are specialized blood vessels for lymphocyte infiltration. Combining CGKRK-LIGHT with anti-vascular endothelial growth factor and checkpoint blockade amplified HEV frequency and T-cell accumulation in GBM, which is often sparsely infiltrated by immune effector cells, and reduced tumour burden. Furthermore, CGKRK and RGR peptides strongly bound to blood vessels in freshly resected human GBM, demonstrating shared peptide-binding activities in mouse and human primary brain tumour vessels. Thus, peptide-mediated LIGHT targeting is a highly translatable approach in primary brain cancer to reduce vascular leakiness and enhance immunotherapy. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Brain pericyte activation occurs early in Huntington's disease

Microvascular changes have recently been described for several neurodegenerative disorders, including Huntington's disease (HD). HD is characterized by a progressive neuronal cell loss due to a mutation in the Huntingtin gene. However, the temporal and spatial microvascular alterations in HD remain unclear. Also, knowledge on the implication of pericytes in HD pathology is still sparse and existing findings are contradictory. Here we examine alterations in brain pericytes in the R6/2 mouse model of HD and in human post mortem HD brain sections. To specifically track activated pericytes, we crossbred R6/2 mice with transgenic mice expressing the Green fluorescent protein gene under the Regulator of G-protein signaling 5 (Rgs5) promoter. We demonstrate an increase in activated pericytes in the R6/2 brain and in post mortem HD brain tissue. Importantly, pericyte changes are already detected before striatal neuronal cell loss, weight loss or behavioural deficits occur in R6/2 mice. This is associated with vascular alterations, whereby striatal changes precede cortical changes. Our findings suggest that pericyte activation may be one of the initial steps contributing to the observed vascular modifications in HD. Thus, pericytes may constitute an important target to address early microvascular changes contributing to disease progression in HD.

Interleukin-6 Trans-Signaling Pathway Promotes Immunosuppressive Myeloid-Derived Suppressor Cells via Suppression of Suppressor of Cytokine Signaling 3 in Breast Cancer

Interleukin-6 (IL-6) has been reported to stimulate myeloid-derived suppressor cells (MDSCs) in multiple cancers, but the molecular events involved in this process are not completely understood. We previously found that cancer-derived IL-6 induces T cell suppression of MDSCs in vitro via the activation of STAT3/IDO signaling pathway. In this study, we aimed to elucidate the underlying mechanisms. We found that in primary breast cancer tissues, cancer-derived IL-6 was positively correlated with infiltration of MDSCs in situ, which was accompanied by more aggressive tumor phenotypes and worse clinical outcomes. In vitro IL-6 stimulated the amplification of MDSCs and promoted their T cell suppression ability, which were fully inhibited by an IL-6-specific blocking antibody. Our results demonstrate that IL-6-dependent suppressor of cytokine signaling 3 (SOCS3) suppression in MDSCs induced phosphorylation of the JAK1, JAK2, TYK2, STAT1, and STAT3 proteins, which was correlated with T cell suppression of MDSCs in vitro. Therefore, dysfunction in the SOCS feedback loop promoted long-term activation of the JAK/STAT signaling pathway and predominantly contributed to IL-6-mediated effects on MDSCs. Furthermore, IL-6-induced inhibition of SOCS3 and activation of the JAK/STAT pathway was correlated with an elevated expression of IL-6 receptor α (CD126), in which the soluble CD126-mediated IL-6 trans-signaling pathway significantly regulated IL-6-mediated effects on MDSCs. Finally, IL-6-induced SOCS3 dysfunction and sustained activation of the JAK/STAT signaling pathway promoted the amplification and immunosuppressive function of breast cancer MDSCs in vitro and in vivo, and thus blocking the IL-6 signaling pathway is a promising therapeutic strategy for eliminating and inhibiting MDSCs to improve prognosis.

Proteomic analysis of the venom of the predatory ant Pachycondyla striata (Hymenoptera: Formicidae)

The ants use their venom for predation, defense, and communication. The venom of these insects is rich in peptides and proteins, and compared with other animal venoms, ant venoms remain poorly explored. The objective of this study was to evaluate the protein content of the venom in the Ponerinae ant Pachycondyla striata. Venom samples were collected by manual gland reservoir dissection, and samples were submitted to two-dimensional gel electrophoresis and separation by ion-exchange and reverse-phase high-performance liquid chromatography followed by mass spectrometry using tanden matrix-assisted laser desorption/ionization with time-of-flight (MALDI-TOF/TOF) mass spectrometry and electrospray ionization-quadrupole with time-of-flight (ESI-Q/TOF) mass spectrometry for obtaining amino acid sequence. Spectra obtained were searched against the NCBInr and SwissProt database. Additional analysis was performed using PEAKS Studio 7.0 (Sequencing de novo). The venom of P. striata has a complex mixture of proteins from which 43 were identified. Within the identified proteins are classical venom proteins (phospholipase A, hyaluronidase, and aminopeptidase N), allergenic proteins (different venom allergens), and bioactive peptides (U10-ctenitoxin Pn1a). Venom allergens are among the most expressed proteins, suggesting that P. striata venom has high allergenic potential. This study discusses the possible functions of the proteins identified in the venom of P. striata.

Glycine N-methylation in NGR-Tagged Nanocarriers Prevents Isoaspartate formation and Integrin Binding without Impairing CD13 Recognition and Tumor Homing

NGR (asparagine-glycine-arginine) is a tumor vasculature-homing peptide motif widely used for the functionalization of drugs, nanomaterials and imaging compounds for cancer treatment and diagnosis. Unfortunately, this motif has a strong propensity to undergo rapid deamidation. This reaction, which converts NGR into isoDGR, is associated with receptor switching from CD13 to integrins, with potentially important manufacturing, pharmacological and toxicological implications. It is found that glycine N-methylation of NGR-tagged nanocarriers completely prevents asparagine deamidation without impairing CD13 recognition. Studies in animal models have shown that the methylated NGR motif can be exploited for delivering radiolabeled compounds and nanocarriers, such as tumor necrosis factor-α (TNF)-bearing nanogold and liposomal doxorubicin, to tumors with improved selectivity. These findings suggest that this NGR derivative is a stable and efficient tumor-homing ligand that can be used for delivering functional nanomaterials to tumor vasculature.

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.

Surface Profiling of Extracellular Vesicles from Plasma or Ascites Fluid Using DotScan Antibody Microarrays

DotScan antibody microarrays were initially developed for the extensive surface profiling of live leukemia and lymphoma cells. DotScan's diagnostic capability was validated with an extensive clinical trial using mononuclear cells from the blood or bone marrow of leukemia or lymphoma patients. DotScan has also been used for the profiling of surface proteins on peripheral blood mononuclear cells (PBMC) from patients with HIV, liver disease, and stable and progressive B-cell chronic lymphocytic leukemia (CLL). Fluorescence multiplexing allowed the simultaneous profiling of cancer cells and leukocytes from disaggregated colorectal and melanoma tumor biopsies after capture on DotScan. In this chapter, we have used DotScan for the surface profiling of extracellular vesicles (EV) recovered from conditioned growth medium of cancer cell lines and the blood of patients with CLL. The detection of captured EV was performed by enhanced chemiluminescence (ECL) using biotinylated antibodies that recognized antigens expressed on the surface of the EV subset of interest. DotScan was also used to profile EV from the blood of healthy individuals and the ascites fluid of ovarian cancer patients. DotScan binding patterns of EV from human plasma and other body fluids may yield diagnostic or prognostic signatures for monitoring the incidence, treatment, and progression of cancers.

Efficacy of NGR peptide-modified PEGylated quantum dots for crossing the blood-brain barrier and targeted fluorescence imaging of glioma and tumor vasculature

Delivery of imaging agents to brain glioma is challenging because the blood-brain barrier (BBB) functions as a physiological checkpoint guarding the central nervous system from circulating large molecules. Moreover, the ability of existing probes to target glioma has been insufficient and needs to be improved. In present study, PEG-based long circulation, CdSe/ZnS quantum dots (QDs)-based nanoscale and fluorescence, asparagines-glycine-arginine peptides (NGR)-based specific CD13 recognition were integrated to design and synthesize a novel nanoprobe by conjugating biotinylated NGR peptides to avidin-PEG-coated QDs. Our data showed that the NGR-PEG-QDs were nanoscale with less than 100 nm and were stable in various pH (4.0~8.0). These nanomaterials with non-toxic concentrations could cross the BBB and target CD13-overexpressing glioma and tumor vasculature in vitro and in vivo, contributing to fluorescence imaging of this brain malignancy. These achievements allowed groundbreaking technological advances in targeted fluorescence imaging for the diagnosis and surgical removal of glioma, facilitating potential transformation toward clinical nanomedicine.

Platelet-derived growth factor-BB has neurorestorative effects and modulates the pericyte response in a partial 6-hydroxydopamine lesion mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease where the degeneration of the nigrostriatal pathway leads to specific motor deficits. There is an unmet medical need for regenerative treatments that stop or reverse disease progression. Several growth factors have been investigated in clinical trials to restore the dopaminergic nigrostriatal pathway damaged in PD. Platelet-derived growth factor-BB (PDGF-BB), a molecule that recruits pericytes to stabilize microvessels, was recently investigated in a phase-1 clinical trial, showing a dose-dependent increase in dopamine transporter binding in the putamen of PD patients. Interestingly, evidence is accumulating that PD is paralleled by microvascular changes, however, whether PDGF-BB modifies pericytes in PD is not known. Using a pericyte reporter mouse strain, we investigate the functional and restorative effect of PDGF-BB in a partial 6-hydroxydopamine medial forebrain bundle lesion mouse model of PD, and whether this restorative effect is accompanied by changes in pericyte features. We demonstrate that a 2-week treatment with PDGF-BB leads to behavioural recovery using several behavioural tests, and partially restores the nigrostriatal pathway. Interestingly, we find that pericytes are activated in the striatum of PD lesioned mice and that these changes are reversed by PDGF-BB treatment. The modulation of brain pericytes may contribute to the PDGF-BB-induced neurorestorative effects, PDGF-BB allowing for vascular stabilization in PD. Pericytes might be a new cell target of interest for future regenerative therapies.

NGR-tagged nano-gold: A new CD13-selective carrier for cytokine delivery to tumors

Colloidal gold (Au), a well-tolerated nanomaterial, is currently exploited for several applications in nanomedicine. We show that gold nanoparticles tagged with a novel tumor-homing peptide containing Asn-Gly-Arg (NGR), a ligand of CD13 expressed by the tumor neovasculature, can be exploited as carriers for cytokine delivery to tumors. Biochemical and functional studies showed that the NGR molecular scaffold/linker used for gold functionalization is critical for CD13 recognition. Using fibrosarcoma-bearing mice, NGR-tagged nanodrugs could deliver extremely low, yet pharmacologically active doses of tumor necrosis factor (TNF), an anticancer cytokine, to tumors with no evidence of toxicity. Mechanistic studies confirmed that CD13 targeting was a primary mechanism of drug delivery and excluded a major role of integrin targeting consequent to NGR deamidation, a degradation reaction that generates the isoAsp-Gly-Arg (isoDGR) integrin ligand. NGR-tagged gold nanoparticles can be used, in principle, as a novel platform for single- or multi-cytokine delivery to tumor endothelial cells for cancer therapy.

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.

Dendritic cells: In vitro culture in two- and three-dimensional collagen systems and expression of collagen receptors in tumors and atherosclerotic microenvironments

Dendritic cells (DCs) are immune cells found in the peripheral tissues where they sample the organism for infections or malignancies. There they take up antigens and migrate towards immunological organs to contact and activate T lymphocytes that specifically recognize the antigen presented by these antigen presenting cells. In the steady state there are several types of resident DCs present in various different organs. For example, in the mouse, splenic DC populations characterized by the co-expression of CD11c and CD8 surface markers are specialized in cross-presentation to CD8 T cells, while CD11c/SIRP-1α DCs seem to be dedicated to activating CD4 T cells. On the other hand, DCs have also been associated with the development of various diseases such as cancer, atherosclerosis, or inflammatory conditions. In such disease, DCs can participate by inducing angiogenesis or immunosuppression (tumors), promoting autoimmune responses, or exacerbating inflammation (atherosclerosis). This change in DC biology can be prompted by signals in the microenvironment. We have previously shown that the interaction of DCs with various extracellular matrix components modifies the immune properties and angiogenic potential of these cells. Building on those studies, herewith we analyzed the angiogenic profile of murine myeloid DCs upon interaction with 2D and 3D type-I collagen environments. As determined by PCR array technology and quantitative PCR analysis we observed that interaction with these collagen environments induced the expression of particular angiogenic molecules. In addition, DCs cultured on collagen environments specifically upregulated the expression of CXCL-1 and -2 chemokines. We were also able to establish DC cultures on type-IV collagen environments, a collagen type expressed in pathological conditions such as atherosclerosis. When we examined DC populations in atherosclerotic veins of Apolipoprotein E deficient mice we observed that they expressed adhesion molecules capable of interacting with collagen. Finally, to further investigate the interaction of DCs with collagen in other pathological conditions, we determined that both murine ovarian and breast cancer cells express several collagen molecules that can contribute to shape their particular tumor microenvironment. Consistently, tumor-associated DCs were shown to express adhesion molecules capable of interacting with collagen molecules as determined by flow cytometry analysis. Of particular relevance, tumor-associated DCs expressed high levels of CD305/LAIR-1, an immunosuppressive receptor. This suggests that signaling through this molecule upon interaction with collagen produced by tumor cells might help define the poorly immunogenic status of these cells in the tumor microenvironment. Overall, these studies demonstrate that through interaction with collagen proteins, DCs can be capable of modifying the microenvironments of inflammatory disease such as cancer or atherosclerosis.

Latent cytokines for targeted therapy of inflammatory disorders

INTRODUCTION

The use of cytokines as therapeutic agents is important, given their potent biological effects. However, this very potency, coupled with the pleiotropic nature and short half-life of these molecules, has limited their therapeutic use. Strategies to increase the half-life and to decrease toxicity are necessary to allow effective treatment with these molecules.

AREAS COVERED

A number of strategies are used to overcome the natural limitations of cytokines, including PEGylation, encapsulation in liposomes, fusion to targeting peptides or antibodies and latent cytokines. Latent cytokines are engineered using the latency-associated peptide of transforming growth factor-β to produce therapeutic cytokines/peptides that are released only at the site of disease by cleavage with disease-induced matrix metalloproteinases. The principles underlying the latent cytokine technology are described and are compared to other methods of cytokine delivery. The potential of this technology for developing novel therapeutic strategies for the treatment of diseases with an inflammatory-mediated component is discussed.

EXPERT OPINION

Methods of therapeutic cytokine delivery are addressed. The latent cytokine technology holds significant advantages over other methods of drug delivery by providing simultaneously increased half-life and localised drug delivery without systemic effects. Cytokines that failed clinical trials should be reassessed using this delivery system.

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.

Enhanced anti-tumor and anti-angiogenic efficacy of a novel liposomal fenretinide on human neuroblastoma

Neuroblastoma is an embryonal tumor originating from the simpatico-adrenal lineage of the neural crest. It approximately accounts for about 15% of all pediatric oncology deaths. Despite advances in multimodal therapy, metastatic neuroblastoma tumors at diagnosis remain a clinical challenge. Retinoids are a class of compounds known to induce both terminal differentiation and apoptosis/necrosis of neuroblastoma cells. Among them, fenretinide (HPR) has been considered one of the most promising anti-tumor agent but it is partially efficacious due to both poor aqueous solubility and rapid metabolism. Here, we have developed a novel HPR formulation, by which the drug was encapsulated into sterically stabilized nanoliposomes (NL[HPR]) according to the Reverse Phase Evaporation method. This procedure led to a higher structural integrity of liposomes in organic fluids for a longer period of time, in comparison with our previous liposomal formulation developed by the film method. Moreover, NL[HPR] were further coupled with NGR peptides for targeting the tumor endothelial cell marker, aminopeptidase N (NGR-NL[HPR]). Orthotopically xenografted neuroblastoma-bearing mice treated with NGR-NL[HPR] lived statistically longer than mice untreated or treated with free HPR (NGR-NL[HPR] vs both control and HPR: P<0.0001). Also, NL[HPR] resulted in a statistically improved survival (NL[HPR] vs both control and HPR: P<0.001) but to a less extent if compared with that obtained with NGR-NL[HPR] (NGR-NL[HPR] vs NL[HPR]: P<0.01). Staining of tumor sections with antibodies specific for neuroblastoma and for either pericytes or endothelial cells evidenced that HPR reduced neuroblastoma growth through both anti-tumor and anti-angiogenic effects, mainly when delivered by NGR-NL[HPR]. Indeed, in this group of mice a marked reduction of tumor progression, of intra-tumoral vessel counts and VEGF expression, together with a marked down-modulation of matrix metalloproteinases MMP2 and MMP9, was observed. In conclusion, the use of this novel targeted delivery system for the apoptotic and antiangiogenic drug, fenretinide, could be considered as an adjuvant tool in the future treatment of neuroblastoma patients.

Microarray analysis of the hypoxia-induced gene expression profile in malignant C6 glioma cells

Hypoxia is commonly featured during glioma growth and plays an important role in the processes underlying tumor progression to increasing malignancy. Here we compared the gene expression profiles of rat C6 malignant glioma cells under normoxic and hypoxic conditions by cDNA microarray analysis. Compared to normoxic culture conditions, 180 genes were up-regulated and 67 genes were down-regulated under hypoxia mimicked by CoCl2 treatment. These differentially expressed genes were involved in mutiple biological functions including development and differentiation, immune and stress response, metabolic process, and cellular physiological response. It was found that hypoxia significantly regulated genes involved in regulation of glycolysis and cell differentiation, as well as intracellular signalling pathways related to Notch and focal adhesion, which are closely associated with tumor malignant growth. These results should facilitate investigation of the role of hypoxia in the glioma development and exploration of therapeutic targets for inhibition of glioma growth.

Aminopeptidase N

The third edition of the Handbook of Proteolytic Enzymes aims to be a comprehensive reference work for the enzymes that cleave proteins and peptides, and contains over 850 chapters. Each chapter is organized into sections describing the name and history, activity and specificity, structural chemistry, preparation, biological aspects, and distinguishing features for a specific peptidase. The subject of Chapter 79 is Aminopeptidase N.

Keywords

Actinonin, amastatin, angiogenesis, angiotensin, bestatin, brush border, cancer, CD13, coronavirus, cysteinyl-glycinase, dipeptidyl peptidase IV, enkephalin, glutathione, neprilysin, puromycin, stem cells.

NGR peptide ligands for targeting CD13/APN identified through peptide array screening resemble fibronectin sequences

Peptides containing the Asn-Gly-Arg (NGR) motif are known to bind CD13 isoforms expressed in tumor vessels and have been widely used for tumor targeting. Residues flanking the NGR sequence play an important role in modulating the binding affinity and specificity of NGR for the CD13 receptor. Herein, we have used a rapid, easy, and reliable peptide array-whole cell binding assay for screening a library of NGR peptides with different flanking residues. A peptide array consisting of forty-five NGR containing peptides was synthesized on a cellulose membrane, followed by screening against CD13 positive (HUVEC and HT-1080) and CD13 negative cell lines (MDA-MB-435 and MDA-MB-231). The library screening led to the identification of five cyclic and acyclic NGR peptides that display higher binding (up to 5-fold) to CD13 positive cells with negligible binding to CD13 negative cell lines when compared to the lead sequence cyclic CVLNGRMEC. Peptides with high binding affinity for the CD13 positive cells also showed improved in vitro cellular uptake and specificity using flow cytometry and fluorescence microscopy. Interestingly, the identified peptides resemble the NGR sequences present in the human fibronectin protein. These NGR peptides are promising new ligands for developing tumor vasculature targeted drugs, delivery systems and imaging agents with reduced systemic toxicity.

Common chromosomal imbalances and stemness-related protein expression markers in endometriotic lesions from different anatomical sites: the potential role of stem cells

BACKGROUND

Endometriosis is a multifactorial gynecological disease characterized by the presence of functional endometrium-like tissue in ectopic sites. Several studies have focused on elucidating the immunological, endocrine, environmental and genetic factors involved in endometriosis. However, its pathogenesis is still unclear.

METHODS

High-resolution comparative genomic hybridization was applied to screen for genomic imbalances in laser microdissected stromal and epithelial cells from 20 endometriotic lesions and three samples of eutopic endometrium derived from eight patients. The expression of seven stemness-related markers (CD9, CD13, CD24, CD34, CD133, CD117/c-Kit and Oct-4) in endometrial tissue samples was evaluated by immunohistochemistry.

RESULTS

Samples of eutopic endometrium showed normal genomic profiles. In ectopic tissues, an average of 68 genomic imbalances was detected per sample. DNA losses were more frequently detected and involved mainly 3p, 5q, 7p, 9p, 11q, 16q, 18q and 19q. Many of the genomic imbalances detected were common to endometriotic stroma and epithelia and also among different endometriotic sites from the same patient. These findings suggested a clonal origin of the endometriotic cells and the putative involvement of stem cells. Positive immunostaining for CD9, CD34, c-Kit and Oct-4 markers was detected in isolated epithelial and/or stromal cells in eutopic and ectopic endometrium in the majority of cases.

CONCLUSIONS

The presence of shared genomic alterations in stromal and epithelial cells from different anatomical sites of the same patient and the expression of stemness-related markers suggested that endometriosis arises as a clonal proliferation with the putative involvement of stem cells.

Identification of glycoprotein markers for pancreatic cancer CD24+CD44+ stem-like cells using nano-LC-MS/MS and tissue microarray

Pancreatic adenocarcinoma is characterized by late diagnosis due to lack of early symptoms, extensive metastasis, and high resistance to chemo/radiation therapy. Recently, a subpopulation of cells within pancreatic cancers, termed cancer stem cells (CSCs), has been characterized and postulated to be the drivers for pancreatic cancer and responsible for metastatic spread. Further studies on pancreatic CSCs are therefore of particular importance to identify novel diagnosis markers and therapeutic targets for this dismal disease. Herein, the malignant phenotype of pancreatic cancer stem-like CD24+CD44+ cells was isolated from a human pancreatic carcinoma cell line (PANC-1) and demonstrated 4-fold increased invasion ability compared to CD24-CD44+ cells. Using lectin microarray and nano LC-MS/MS, we identified a differentially expressed set of glycoproteins between these two subpopulations. Lectin microarray analysis revealed that fucose- and galactose-specific lectins, UEA-1 and DBA, respectively, exhibit distinctly strong binding to CD24+CD44+ cells. The glycoproteins extracted by multilectin affinity chromatography were consequently analyzed by LC-MS/MS. Seventeen differentially expressed glycoproteins were identified, including up-regulated Cytokeratin 8/CK8, Integrin β1/CD29, ICAM1/CD54, and Ribophorin 2/RPN2 and down-regulated Aminopeptidase N/CD13. Immunohistochemical analysis of tissue microarrays showed that CD24 was significantly associated with late-stage pancreatic adenocarcinomas, and RPN2 was exclusively coexpressed with CD24 in a small population of CD24-positive cells. However, CD13 expression was dramatically decreased along with tumor progression, preferentially present on the apical membrane of ductal cells and vessels in early stage tumors. Our findings suggest that these glycoproteins may provide potential therapeutic targets and promising prognostic markers for pancreatic cancer.

Expression, immunogenicity, histopathology, and potency of a mosquito-based malaria transmission-blocking recombinant vaccine

Vaccines have been at the forefront of global research efforts to combat malaria, yet despite several vaccine candidates, this goal has yet to be realized. A potentially effective approach to disrupting the spread of malaria is the use of transmission-blocking vaccines (TBV), which prevent the development of malarial parasites within their mosquito vector, thereby abrogating the cascade of secondary infections in humans. Since malaria is transmitted to human hosts by the bite of an obligate insect vector, mosquito species in the genus Anopheles, targeting mosquito midgut antigens that serve as ligands for Plasmodium parasites represents a promising approach to breaking the transmission cycle. The midgut-specific anopheline alanyl aminopeptidase N (AnAPN1) is highly conserved across Anopheles vectors and is a putative ligand for Plasmodium ookinete invasion. We have developed a scalable, high-yield Escherichia coli expression and purification platform for the recombinant AnAPN1 TBV antigen and report on its marked vaccine potency and immunogenicity, its capacity for eliciting transmission-blocking antibodies, and its apparent lack of immunization-associated histopathologies in a small-animal model.

Cooperative effects of aminopeptidase N (CD13) expressed by nonmalignant and cancer cells within the tumor microenvironment

Processes that promote cancer progression such as angiogenesis require a functional interplay between malignant and nonmalignant cells in the tumor microenvironment. The metalloprotease aminopeptidase N (APN; CD13) is often overexpressed in tumor cells and has been implicated in angiogenesis and cancer progression. Our previous studies of APN-null mice revealed impaired neoangiogenesis in model systems without cancer cells and suggested the hypothesis that APN expressed by nonmalignant cells might promote tumor growth. We tested this hypothesis by comparing the effects of APN deficiency in allografted malignant (tumor) and nonmalignant (host) cells on tumor growth and metastasis in APN-null mice. In two independent tumor graft models, APN activity in both the tumors and the host cells cooperate to promote tumor vascularization and growth. Loss of APN expression by the host and/or the malignant cells also impaired lung metastasis in experimental mouse models. Thus, cooperation in APN expression by both cancer cells and nonmalignant stromal cells within the tumor microenvironment promotes angiogenesis, tumor growth, and metastasis.