Synergistic damage of tumor vessels with ultra low-dose endothelial-monocyte activating polypeptide-II and neovasculature-targeted tumor necrosis factor-alpha

Current and emerging therapies for primary central nervous system lymphoma

Primary central nervous system (CNS) lymphoma (PCNSL) is a rare type of extranodal lymphoma exclusively involving the CNS at the onset, with diffuse large B-cell lymphoma (DLBCL) as the most common histological subtype. As PCNSL is a malignancy arising in an immune-privileged site, suboptimal delivery of systemic agents into tumor tissues results in poorer outcomes in PCNSL than in non-CNS DLBCLs. Commonly used regimens for PCNSL include high-dose methotrexate-based chemotherapy with rituximab for induction therapy and intensive chemotherapy followed by autologous hematopoietic stem cell transplantation or whole-brain radiotherapy for consolidation therapy. Targeted agents against the B-cell receptor signaling pathway, microenvironment immunomodulation and blood-brain barrier (BBB) permeabilization appear to be promising in treating refractory/relapsed patients. Chimeric antigen receptor-T cells (CAR-T cells) have been shown to penetrate the BBB as a potential tool to manipulate this disease entity while controlling CAR-T cell-related encephalopathy syndrome. Future approaches may stratify patients according to age, performance status, molecular biomarkers and cellular bioinformation. This review summarizes the current therapies and emerging agents in clinical development for PCNSL treatment.

Endothelial transdifferentiation of human HGC-27 gastric cancer cells in vitro

Malignant tumor cells are able to transdifferentiate into other cell types in various tissues or organs. Recent studies have demonstrated the ability of cancer cells to transdifferentiate into functional endothelial cells (ECs). However, whether human gastric cancer (GC) cells are able to transdifferentiate into other cell types has remained largely elusive. Furthermore, whether HGC-27 cells are able to participate in GC angiogenesis remains to be clarified. In the present study, the HGC-27 cell line grown under hypoxic conditions for 4 days exhibited the typical ‘flagstone’ appearance, which is typical for cultured ECs. HGC-27 cells cultured on Matrigel under hypoxic conditions gradually formed net-like structures. Furthermore, the cultured HGC-27 cells expressed CD31, CD34 and von Willebrand factor, the molecular markers for ECs, under hypoxic conditions. These results indicated that HGC-27 cells, cultured under hypoxic conditions, are able to transdifferentiate into EC-like cells in vitro.

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.

Endothelial Monocyte-Activating Polypeptide-II Induces BNIP3-Mediated Mitophagy to Enhance Temozolomide Cytotoxicity of Glioma Stem Cells via Down-Regulating MiR-24-3p

Preliminary studies have shown that endothelial-monocyte-activating polypeptide-II (EMAP-II) and temozolomide (TMZ) alone can exert cytotoxic effects on glioma cells. This study explored whether EMAP-II can enhance the cytotoxic effects of TMZ on glioma stem cells (GSCs) and the possible mechanisms associated with Bcl-2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3)-mediated mitophagy facilitated by miR-24-3p regulation. The combination of TMZ and EMAP-II significantly inhibited GSCs viability, migration, and invasion, resulting in upregulation of the autophagy biomarker microtubule-associated protein one light chain 3 (LC3)-II/I but down-regulation of the proteins P62, TOMM 20 and CYPD, changes indicative of the occurrence of mitophagy. BNIP3 expression increased significantly in GSCs after treatment with the combination of TMZ and EMAP-II. BNIP3 overexpression strengthened the cytotoxic effects of EMAP-II and TMZ by inducing mitophagy. The combination of EMAP-II and TMZ decreased the expression of miR-24-3p, whose target gene was BNIP3. MiR-24-3p inhibited mitophagy and promoted proliferation, migration and invasion by down-regulating BNIP3 in GSCs. Furthermore, nude mice subjected to miR-24-3p silencing combined with EMAP-II and TMZ treatment displayed the smallest tumors and the longest survival rate. According to the above results, we concluded that EMAP-II enhanced the cytotoxic effects of TMZ on GSCs' proliferation, migration and invasion both in vitro and in vivo.

AIMp1 Potentiates TH1 Polarization and Is Critical for Effective Antitumor and Antiviral Immunity

Dendritic cells (DCs) must integrate a broad array of environmental cues to exact control over downstream immune responses including T_H polarization. The multienzyme aminoacyl-tRNA synthetase complex component AIMp1/p43 responds to cellular stress and exerts pro-inflammatory functions; however, a role for DC-expressed AIMp1 in T_H polarization has not previously been shown. Here, we demonstrate that the absence of AIMp1 in bone marrow-derived DC (BMDC) significantly impairs cytokine and costimulatory molecule expression, p38 MAPK signaling, and T_H1 polarization of cocultured T-cells while significantly dysregulating immune-related gene expression. These deficits resulted in significantly compromised BMDC vaccine-mediated protection against melanoma. AIMp1 within the host was also critical for innate and adaptive antiviral immunity against influenza virus infection in vivo. Cancer patients with AIMp1 expression levels in the highest tertiles exhibited a 70% survival advantage at 15-year postdiagnosis as determined by bioinformatics analysis of nearly 9,000 primary human tumor samples in The Cancer Genome Atlas database. These data establish the importance of AIMp1 for the effective governance of antitumor and antiviral immune responses.

NGR-peptide-drug conjugates with dual targeting properties

Peptides containing the asparagine-glycine-arginine (NGR) motif are recognized by CD13/aminopeptidase N (APN) receptor isoforms that are selectively overexpressed in tumor neovasculature. Spontaneous decomposition of NGR peptides can result in isoAsp derivatives, which are recognized by RGD-binding integrins that are essential for tumor metastasis. Peptides binding to CD13 and RGD-binding integrins provide tumor-homing, which can be exploited for dual targeted delivery of anticancer drugs. We synthesized small cyclic NGR peptide-daunomycin conjugates using NGR peptides of varying stability (c[KNGRE]-NH2, Ac-c[CNGRC]-NH2 and the thioether bond containing c[CH2-CO-NGRC]-NH2, c[CH2-CO-KNGRC]-NH2). The cytotoxic effect of the novel cyclic NGR peptide-Dau conjugates were examined in vitro on CD13 positive HT-1080 (human fibrosarcoma) and CD13 negative HT-29 (human colon adenocarcinoma) cell lines. Our results confirm the influence of structure on the antitumor activity and dual acting properties of the conjugates. Attachment of the drug through an enzyme-labile spacer to the C-terminus of cyclic NGR peptide resulted in higher antitumor activity on both CD13 positive and negative cells as compared to the branching versions.

Succinimide Formation from an NGR-Containing Cyclic Peptide: Computational Evidence for Catalytic Roles of Phosphate Buffer and the Arginine Side Chain

The Asn-Gly-Arg (NGR) motif and its deamidation product isoAsp-Gly-Arg (isoDGR) have recently attracted considerable attention as tumor-targeting ligands. Because an NGR-containing peptide and the corresponding isoDGR-containing peptide target different receptors, the spontaneous NGR deamidation can be used in dual targeting strategies. It is well known that the Asn deamidation proceeds via a succinimide derivative. In the present study, we computationally investigated the mechanism of succinimide formation from a cyclic peptide, c[CH₂CO-NGRC]-NH₂, which has recently been shown to undergo rapid deamidation in a phosphate buffer. An H₂PO₄⁻ ion was explicitly included in the calculations. We employed the density functional theory using the B3LYP functional. While geometry optimizations were performed in the gas phase, hydration Gibbs energies were calculated by the SM8 (solvation model 8) continuum model. We have found a pathway leading to the five-membered ring tetrahedral intermediate in which both the H₂PO₄⁻ ion and the Arg side chain act as catalyst. This intermediate, once protonated at the NH₂ group on the five-membered ring, was shown to easily undergo NH₃ elimination leading to the succinimide formation. This study is the first to propose a possible catalytic role for the Arg side chain in the NGR deamidation.

Self-targeting of TNF-releasing cancer cells in preclinical models of primary and metastatic tumors

Circulating cancer cells can putatively colonize distant organs to form metastases or to reinfiltrate primary tumors themselves through a process termed "tumor self-seeding." Here we exploit this biological attribute to deliver tumor necrosis factor alpha (TNF), a potent antitumor cytokine, directly to primary and metastatic tumors in a mechanism that we have defined as "tumor self-targeting." For this purpose, we genetically engineered mouse mammary adenocarcinoma (TSA), melanoma (B16-F10), and Lewis lung carcinoma cells to produce and release murine TNF. In a series of intervention trials, systemic administration of TNF-expressing tumor cells was associated with reduced growth of both primary tumors and metastatic colonies in immunocompetent mice. We show that these malignant cells home to tumors, locally release TNF, damage neovascular endothelium, and induce massive cancer cell apoptosis. We also demonstrate that such tumor-cell-mediated delivery avoids or minimizes common side effects often associated with TNF-based therapy, such as acute inflammation and weight loss. Our study provides proof of concept that genetically modified circulating tumor cells may serve as targeted vectors to deliver anticancer agents. In a clinical context, this unique paradigm represents a personalized approach to be translated into applications potentially using patient-derived circulating tumor cells as self-targeted vectors for drug delivery.

The tumor vessel targeting agent NGR-TNF controls the different stages of the tumorigenic process in transgenic mice by distinct mechanisms

NGR-TNF is a vascular targeting agent in advanced clinical development, coupling tumor necrosis factor-α (TNF) with the CNGRCG peptide, which targets a CD13 isoform specifically expressed by angiogenic vessels. Antitumor efficacy of NGR-TNF has been described in different transplantation tumor models. Nevertheless, the mechanism underlying its activity is not fully understood. In the wild type and in the immunodeficient (RAG^-/-) RIP1-Tag2 models of multistage pancreatic carcinogenesis, we demonstrate that CD13 is highly expressed on endothelial cells of hyperplastic and angiogenic islets, whereas its expression is down regulated in tumors where it partially colocalize with pericytes. In vivo CNGRCG peptides coupled to fluorescent nanoparticles (quantum dots) bind to CD13 and colocalize with anti-CD31, in pancreatic islets. At early stage, low doses of NGR-murine (m)TNF have a direct cytotoxic effect inducing endothelial cell apoptosis, reducing vessel density and eventually inhibiting the development of angiogenic islets. At a later stage, NGR-mTNF is able to reduce tumor growth inducing vascular normalization, exclusively when treatment is carried out in the immunocompetent mice. Interestingly, NGR-mTNF-treated tumors from these mice are characterized by CD8⁺ T cell infiltration. At molecular level, overexpression of genes involved in vessels normalization was detected only in NGR-mTNF-treated tumors from immunocompetent mice. These findings identified a new mechanism of action of NGR-mTNF, providing support for the development of new therapeutic strategies combining chemotherapy or active/adoptive immunotherapies to low dose NGR-TNF treatment.

Development of cyclic NGR peptides with thioether linkage: structure and dynamics determining deamidation and bioactivity

NGR peptides that recognize CD13 receptors in tumor neovasculature are of high interest, in particular due to their potential applications in drug targeting. Here we report the synthesis and structural analysis of novel thioether bond-linked cyclic NGR peptides. Our results show that their chemostability (resistance against spontaneous decomposition forming isoAsp and Asp derivatives) strongly depends on both sample handling conditions and structural properties. A significant correlation was found between chemostability and structural measures, such as NH(Gly)-CO(Asn-sc) distances. The side-chain orientation of Asn is a key determining factor; if it is turned away from HN(Gly), the chemostability increases. Structure stabilizing factors (e.g., H-bonds) lower their internal dynamics, and thus biomolecules become even more resistant against spontaneous decomposition. The effect of cyclic NGR peptides on cell adhesion was examined in A2058 melanoma cell lines. It was found that some of the investigated peptides gradually increased cell adhesion with long-term characteristics, indicating time-dependent formation of integrin binding isoAsp derivatives that are responsible for the adhesion-inducing effect.

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.

Evaluation of poly-mechanistic antiangiogenic combinations to enhance cytotoxic therapy response in pancreatic cancer

Gemcitabine (Gem) has limited clinical benefits in pancreatic ductal adenocarcinoma (PDAC). The present study investigated combinations of gemcitabine with antiangiogenic agents of various mechanisms for PDAC, including bevacizumab (Bev), sunitinib (Su) and EMAP II. Cell proliferation and protein expression were analyzed by WST-1 assay and Western blotting. In vivo experiments were performed via murine xenografts. Inhibition of in vitro proliferation of AsPC-1 PDAC cells by gemcitabine (10 µM), bevacizumab (1 mg/ml), sunitinib (10 µM) and EMAP (10 µM) was 35, 22, 81 and 6 percent; combination of gemcitabine with bevacizumab, sunitinib or EMAP had no additive effects. In endothelial HUVECs, gemcitabine, bevacizumab, sunitinib and EMAP caused 70, 41, 86 and 67 percent inhibition, while combination of gemcitabine with bevacizumab, sunitinib or EMAP had additive effects. In WI-38 fibroblasts, gemcitabine, bevacizumab, sunitinib and EMAP caused 79, 58, 80 and 29 percent inhibition, with additive effects in combination as well. Net in vivo tumor growth inhibition in gemcitabine, bevacizumab, sunitinib and EMAP monotherapy was 43, 38, 94 and 46 percent; dual combinations of Gem+Bev, Gem+Su and Gem+EMAP led to 69, 99 and 64 percent inhibition. Combinations of more than one antiangiogenic agent with gemcitabine were generally more effective but not superior to Gem+Su. Intratumoral proliferation, apoptosis and microvessel density findings correlated with tumor growth inhibition data. Median animal survival was increased by gemcitabine (26 days) but not by bevacizumab, sunitinib or EMAP monotherapy compared to controls (19 days). Gemcitabine combinations with bevacizumab, sunitinib or EMAP improved survival to similar extent (36 or 37 days). Combinations of gemcitabine with Bev+EMAP (43 days) or with Bev+Su+EMAP (46 days) led to the maximum survival benefit observed. Combination of antiangiogenic agents improves gemcitabine response, with sunitinib inducing the strongest effect. These findings demonstrate advantages of combining multi-targeting agents with standard gemcitabine therapy for PDAC.

Bacillus-derived poly-γ-glutamic acid attenuates allergic airway inflammation through a Toll-like receptor-4-dependent pathway in a murine model of asthma

BACKGROUND

Asthma is an inflammatory disease of the airways that is mediated by Th2 responses. Poly-γ-glutamic acid (γ-PGA) is an extracellular polymeric compound that is synthesized by Bacillus cells. Previously, we found that γ-PGA promoted Th1 cell development in a manner dependent on antigen-presenting cells, but inhibited Th2 cell development.

OBJECTIVE

To investigate the effect of γ-PGA on dendritic cells (DCs), and its potential for treating Th2-mediated allergic asthma.

METHODS

Wild-type, Toll-like receptor (TLR)-2 deficient, and TLR-4-defective mice were used. DCs derived from the bone marrow and extracted from the lung were stimulated with γ-PGA and assayed for the expression of signalling molecules, costimulatory molecules, and cytokines. Mice were sensitized and challenged with ovalbumin (OVA) to induce asthma. They were repeatedly injected intranasally with γ-PGA before and during the challenge period, and inflammation and structural remodelling of the airways were examined.

RESULTS

γ-PGA selectively signalled conventional DCs to activate NF-κB and mitogen-activated protein kinase, leading to the up-regulation of CD86, CD40, and IL-12, but not IL-10 and IL-6. These effects of γ-PGA were dependent on TLR-4 and independent of TLR-2. Importantly, the intranasal administration of γ-PGA to OVA-sensitized/challenged mice reduced the airway hyperresponsiveness and allergic inflammation such as leucocyte influx, goblet cell hyperplasia, eosinophilia, and Th2 cytokine production. In addition to lowered IgE titres, the treatment of mice with γ-PGA significantly reduced the multiplication and Th2 polarization of mediastinal lymph node T cells upon allergen-specific restimulation. These anti-asthmatic effects of γ-PGA were also abolished in TLR-4-defective mice.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data indicate that γ-PGA activates DCs to favour Th1 cell induction through a TLR-4-dependent pathway and alleviates pathologic symptoms in a Th2-biased asthmatic model. These findings highlight the potential of γ-PGA for the treatment of asthma and other allergic disease in which Th2 polarization plays an important role.

Enhancing cytotoxic agent activity in experimental pancreatic cancer through EMAP II combination therapy

PURPOSE

Gemcitabine has limited benefits as single agent or in combination for pancreatic ductal adenocarcinoma (PDAC). Endothelial monocyte-activating polypeptide II (EMAP) enhances gemcitabine effects in PDAC. We evaluated the combination effects of EMAP, doxorubicin, and docetaxel in experimental PDAC.

METHODS

Cell proliferation, protein expression, and apoptosis were analyzed by WST-1 assay, Western blotting, and FACS analysis. Tumor growth and survival experiments were performed in murine xenografts.

RESULTS

PDAC cell proliferation in vitro was not affected by EMAP, compared to a small inhibition through doxorubicin, docetaxel, and gemcitabine. EMAP addition to these agents did not increase the antiproliferative effects. In endothelial cells, EMAP, doxorubicin, docetaxel, and gemcitabine all had antiproliferative effects. Addition of EMAP to these cytotoxic agents had additive effects. In PDAC cells, no agent induced measurable apoptosis, whereas in endothelial cells, all agents either alone or in combination did. Doxorubicin, docetaxel, gemcitabine, and EMAP all decreased tumor growth. EMAP addition increased inhibitory effects of docetaxel and gemcitabine, but not of doxorubicin. However, compared to controls (median survival: 17 days), EMAP (14 days) had no survival benefit, while docetaxel (29 days), gemcitabine (25 days), and docetaxel followed by gemcitabine sequence (37 days) extended animal survival. Addition of EMAP to docetaxel (35 days), gemcitabine (28 days), and docetaxel gemcitabine sequence (41 days) extended the survival. Doxorubicin effects were not enhanced by EMAP.

CONCLUSIONS

The antiendothelial combination therapy benefit through EMAP is not limited to gemcitabine and may facilitate the development of more effective alternative cytotoxic therapy strategies against PDAC.

Role of ATP synthase alpha subunit in low-dose endothelial monocyte-activating polypeptide-II-induced opening of the blood-tumor barrier

This study was performed to determine whether the α subunit of ATP synthase (α-ATP synthase) on brain microvascular endothelial cells (BMECs) serves as the functional target for endothelial monocyte-activating polypeptide-II (EMAP-II)-induced increase in blood-tumor barrier (BTB) permeability. Using a rat C6 glioma model, we found that low-dose (80 ng/kg) EMAP-II significantly decreased the mRNA and protein expression levels of tight junction (TJ)-related proteins claudin-5, occludin, and ZO-1 on BMECs. Meantime, radioimmunity and Western blot assay showed a significant decrease in the expression levels of cAMP and catalytic subunit of protein kinase A (PKAcs) of tumor tissues. Also, pretreatment with specific α-ATP synthase antibody significantly blocked the effects of EMAP-II on TJ-related proteins, cAMP, and PKAcs. In addition, double immunofluorescence assay identified that EMAP-II was co-localized with α-ATP synthase on BMECs. This in vivo study demonstrated that α subunit of ATP synthase on BMECs serves as the functional target for EMAP-II selective opening of the BTB, and that cAMP/PKA signaling transduction pathway might be involved in the modulating process.

Endothelial-monocyte-activating polypeptide II increases blood-tumor barrier permeability by down-regulating the expression levels of tight junction associated proteins

This study was performed to determine whether endothelial-monocyte-activating polypeptide (EMAP) II increases the permeability of the blood-tumor barrier (BTB) in the rat model of C6 glioma, and whether EMAP II opens the BTB by affecting tight junction (TJ) associated proteins zonula occluden-1 (ZO-1), occludin and claudin-5. The rats were divided into eight groups randomly: control group, EMAPII 0h group, EMAPII 0.5h group, EMAPII 1h group, EMAPII 2h group, EMAPII 3h group, EMAPII 6h group and EMAPII 12h group. The BTB permeability was assessed by Evans blue extravasation. The mRNA and protein expressions of ZO-1, occludin, and claudin-5 were determined by reverse transcriptase-polymerase chain reaction, western blot, and immunohistochemistry assays. The BTB permeability significantly increased after EMAP II injection in different doses (40ng/kg, 80ng/kg and 160ng/kg). The BTB permeability started to increase from 0.5h, reached a peak at 1h, and finally returned to the level of EMAP II 0h group after EMAP II injection at dose of 80ng/kg. The mRNA and protein expression levels of ZO-1, occludin and claudin-5 were significantly decreased after EMAP II injection. This study demonstrates for the first time that EMAP II increases the permeability of BTB selectively, and the possible mechanism is associated with the down-regulation of ZO-1, occludin and claudin-5.

Innate immune cells induce hemorrhage in tumors during thrombocytopenia

Platelets are crucial regulators of tumor vascular homeostasis and continuously prevent tumor hemorrhage through secretion of their granules. However, the reason for tumor bleeding in the absence of platelets remains unknown. Tumors are associated with inflammation, a cause of hemorrhage in thrombocytopenia. Here, we investigated the role of the inflamed tumor microenvironment in the induction of tumor vessel injury in thrombocytopenic mice. Using s.c. injections of vascular endothelial growth factor or tumor necrosis factor-alpha combined with depletion of neutrophils, we demonstrate that enhancing the opening of endothelial cell junctions was not sufficient to cause bleeding in the absence of platelets; instead, induction of tissue hemorrhage in thrombocytopenia required recruitment of leukocytes. Immunohistology revealed that thrombocytopenia-induced tumor hemorrhage occurs at sites of macrophage and neutrophil accumulation. Mice deficient in beta2 or beta3 integrins, which have decreased neutrophil and/or macrophage infiltration in their tumor stroma, were protected from thrombocytopenia-induced tumor hemorrhage, indicating that, in the absence of platelets, stroma-infiltrating leukocytes induced tumor vessel injury. This injury was independent of reactive oxygen species generation and of complement activation, as suggested by the persistence of tumor hemorrhage in C3- and nicotinamide adenine dinucleotide phosphate oxidase-deficient thrombocytopenic mice. Our results show that platelets counteract tumor-associated inflammation and that the absence of this platelet function elicits vascular injuries by tumor-infiltrating innate immune cells.

Improving TNF as a cancer therapeutic: tailor-made TNF fusion proteins with conserved antitumor activity and reduced systemic side effects

Tumor necrosis factor (TNF) is highly pleiotropic cytokine regulating diverse cellular processes such as proliferation, cell migration, angiogenesis, differentiation, apoptosis, necrosis, but also survival. Because of its name-giving tumor necrosis-inducing capabilities, TNF has attracted attention very early for antitumor therapy. Although TNF is in clinical use for treatment of soft tissue sarcoma in isolated limb perfusion, its broad use in tumor therapy is prevented so far by its strong systemic proinflammatory effects. Nevertheless, over the past decade, a variety of tailor-made TNF variants have been developed with the aim to reduce TNFs systemic activity without losing its antitumoral effects. Here, we review the progress made toward improving the efficacy of TNF by genetic engineering, tumor targeting, and introduction of prodrug concepts.

Tumor vasculature-targeted delivery of tumor necrosis factor-alpha

BACKGROUND

Recently, considerable efforts have been directed toward antivascular therapy as a new modality to treat human cancers. However, targeting a therapeutic gene of interest to the tumor vasculature with minimal toxicity to other tissues remains the objective of antivascular gene therapy. Tumor necrosis factor-alpha (TNF-alpha) is a potent antivascular agent but has limited clinical utility because of significant systemic toxicity. At the maximum tolerated doses of systemic TNF-alpha, there is no meaningful antitumor activity. Hence, the objective of this study was to deliver TNF-alpha targeted to tumor vasculature by systemic delivery to examine its antitumor activity.

METHODS

A hybrid adeno-associated virus phage vector (AAVP) was used that targets tumor endothelium to express TNF-alpha (AAVP-TNF-alpha). The activity of AAVP-TNF-alpha was analyzed in various in vitro and in vivo settings using a human melanoma tumor model.

RESULTS

In vitro, AAVP-TNF-alpha infection of human melanoma cells resulted in high levels of TNF-alpha expression. Systemic administration of targeted AAVP-TNF-alpha to melanoma xenografts in mice produced the specific delivery of virus to tumor vasculature. In contrast, the nontargeted vector did not target to tumor vasculature. Targeted AAVP delivery resulted in expression of TNF-alpha, induction of apoptosis in tumor vessels, and significant inhibition of tumor growth. No systemic toxicity to normal organs was observed.

CONCLUSIONS

Targeted AAVP vectors can be used to deliver TNF-alpha specifically to tumor vasculature, potentially reducing its systemic toxicity. Because TNF-alpha is a promising antivascular agent that currently is limited by its toxicity, the current results suggest the potential for clinical translation of this strategy.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

The tumour microenvironment: a novel target for cancer therapy

Cancer therapy is in the midst of a major paradigm shift. Traditionally, cancer treatments have focused on tumour cells. However, studies over the past few decades have demonstrated that cancer is a vastly complex entity with multiple components affecting a tumour's growth, invasion and metastasis. These components, collectively termed the 'tumour microenvironment', include endothelial cells, pericytes, fibroblasts, inflammatory cells, leucocytes and elements of the extracellular matrix (ECM). Biological agents that target components of the tumour microenvironment may provide an interesting alternative to traditional tumour cell-directed therapy. Because of the complexity of the tumour milieu, the most beneficial therapy will likely involve the combination of one or more agents directed at this new target. This review highlights recent preclinical and clinical studies involving agents that target tumour vasculature, leucocytes, pericytes, cancer-associated fibroblasts and ECM components. We pay particular attention to combination therapies targeting multiple components of the tumour microenvironment, and aim to demonstrate that this strategy holds promise for the future of cancer treatment.

Targeted Cancer Therapy with Tumor Necrosis Factor-Alpha

Tumor necrosis factor-alpha (TNF-α), a member of the TNF superfamily, was the first cytokine to be evaluated for cancer biotherapy. However, the clinical use of TNF-α is severely limited by its toxicity. Currently, TNF-α is administered only through locoregional drug delivery systems such as isolated limb perfusion and isolated hepatic perfusion. To reduce the systemic toxicity of TNF-α, various strategies have been explored over the last several decades. This review summarizes current state-of-the-art targeted cancer therapy using TNF-α. Passive targeting, cell-based therapy, gene therapy with inducible or tissue-specific promoters, targeted polymer-DNA complexes, tumor pre-targeting, antibody-TNF-α conjugate, scFv/TNF-α fusion proteins, and peptide/TNF-α fusion proteins have all been investigated to combat cancer. Many of these agents are already in advanced clinical trials. Molecular imaging, which can significantly speed up the drug development process, and nanomedicine, which can integrate both imaging and therapeutic components, has the potential to revolutionize future cancer patient management. Cooperative efforts from scientists within multiple disciplines, as well as close partnerships among many organizations/entities, are needed to quickly translate novel TNF-α-based therapeutics into clinical investigation.

The moonlighting enzyme CD13: old and new functions to target

Aminopeptidase N (CD13) is a widely expressed ectoenzyme with functions that do not always depend on its enzymatic activity: an aspect that has been overlooked. Numerous CD13-targeting tools have been developed in the last few years. Several of them are already undergoing clinical trials, and there are promising reports on the effectiveness of others in animal models of disease. However, their efficacy might be obscured by their effects on unrecognized functions of CD13, resulting in unexpected complications. The purpose of this review is (i) to discuss the various functions ascribed to CD13 and the possible mechanisms behind them and (ii) to consider some of the questions that need to be answered to achieve a better understanding of the biological relevance of these functions, a more precise interpretation of the results obtained after their manipulation and a more rational design of CD13-targeting agents.