Seeding of intravascular stents with genetically engineered endothelial cells

The use of intravascular stents may be limited by both local thrombosis and restenosis due to intimal proliferation. In an effort to provide solutions to these problems, we seeded stents with genetically engineered endothelial cells in vitro. Using retroviral-mediated gene transfer, we inserted the gene for either bacterial beta-galactosidase or human tissue-type plasminogen activator (t-PA) into cultured sheep endothelial cells. The endothelial cells were seeded onto stainless steel stents and grown until the stents were covered. Expression of intracellular beta-galactosidase and high level secretion of t-PA were demonstrated both before and after the transduced cells were seeded onto the stents. Eight stents were expanded by in vitro balloon inflation, with observation of the seeded endothelial layer both prior to and after expansion. Most of the endothelial cells remained on the stents after balloon inflation. We conclude that intravascular stents can be coated with a layer of genetically engineered endothelial cells that can be either specifically labeled or made to secrete high levels of a therapeutic protein. Much of the layer of genetically engineered cells remains after the expansion of the stent in vitro. In vivo implantation of stents coated with genetically engineered endothelial cells may allow 1) introduction of genetically engineered endothelial cells directly into the vascular wall and 2) improvement of stent function through localized delivery of anticoagulant, thrombolytic, or antiproliferative molecules.     

Nestin:A novel angiogenesis marker and possible target for tumor angiogenesis

Abnormal vasculature,termed tumor vessels,is a hallmark of solid tumors.The degree of angiogenesis is associated with tumor aggressiveness and clinical outcome.Therefore,exact quantification of tumor vessels is useful to evaluate prognosis.Furthermore,selective detection of newly formed tumor vessels within cancer tissues using specific markers raises the possibility of molecular targeted therapy via the inhibition of tumor angiogenesis.Nestin,an intermediate filament protein,is reportedly expressed in repair processes,various neoplasms,and proliferating vascular endothelial cells.Nestin expression is detected in endothelial cells of embryonic capillaries,capillaries of the corpus luteum,which replenishes itself by angiogenesis,and proliferating endothelial progenitor cells,but not in mature endothelial cells.Therefore,expression of nestin is relatively limited to proliferating vascular endothelial cells and endothelial progenitor cells.Nestin expression is also reported in blood vessels within glioblastoma,prostate cancer,colorectal cancer,and pancreatic cancer,and its expression is more specific for newly formed blood vessels than other endothelial cell markers.Nestin-positive blood vessels form smaller vessels with high proliferation activity in tumors.Knockdown of nestin in vascular endothelial cells suppresses endothelial cell growth and tumor formation ability of pancreatic cancers in vivo.Using nestin to more accurately evaluate microvessel density in cancer specimens may be a novel prognostic indicator.Furthermore,nestin-targeted therapy may suppress tumor proliferation via inhibition of angiogenesis in numerous malignancies,including pancreatic cancer.In this review article,we focus on nestin as a novel angiogenesis marker and possible therapeutic target via inhibition of tumor angiogenesis.     

A mathematical model of the contribution of endothelial progenitor cells to angiogenesis in tumors: implications for antiangiogenic therapy

The traditional view of angiogenesis emphasizes proliferation and migration of vessel wall-associated endothelial cells. However, circulating endothelial progenitor cells have recently been shown to contribute to tumor angiogenesis. Here we quantify the relative contributions of endothelial and endothelial progenitor cells to angiogenesis using a mathematical model. The model predicts that during the early stages of tumor growth, endothelial progenitors have a significant impact on tumor growth and angiogenesis, mediated primarily by their localization in the tumor, not by their proliferation. The model also shows that, as the tumor grows, endothelial progenitors adhere preferentially near the tumor periphery, coincident with the location of highest vascular density, supporting their potential utility as vectors for targeted delivery of therapeutics. Model simulations of various antiangiogenic strategies show that those therapies that effectively target both endothelial and endothelial progenitor cells, either by restoring the balance between angiogenic stimulators and inhibitors or by targeting both types of cells directly, are most effective at delaying tumor growth. The combination of continuous low-dose chemotherapy and antiangiogenic therapy is predicted to have the most significant effect on therapeutic outcome. The model offers new insight into tumor angiogenesis with implications for the rational design of antiangiogenic therapy.     

Angiogenesis in hematologic malignancies

Angiogenesis, defined as the blood vessel generation from preexisting blood vessels, was found to play an important role in the progression of solid tumors. In addition, bone marrow-derived endothelial precursor cells may contribute to tumor angiogenesis. Recently angiogenesis induction was described in several hematologic neoplasms as leukemia, lymphoma, myelodysplastic syndrome and multiple myeloma (MM). Clinical angiogenesis research also termed as angiodiagnosis has established the prognostic relevance of markers of angiogenesis e.g., microvessel density and circulating levels of angiogenic peptides. Development of antiangiogenic treatment for hematologic neoplasms has recently been sparked by the success of Thalidomide (Thal) which has antiangiogenic properties in MM. Antiangiogenic treatment strategies are now being tested in clinical trials on several types of hematologic neoplasms.     

Suppression of glioblastoma angiogenicity and tumorigenicity by inhibition of endogenous expression of vascular endothelial growth factor.

The development of new capillary networks from the normal microvasculature of the host appears to be required for growth of solid tumors. Tumor cells influence this process by producing both inhibitors and positive effectors of angiogenesis. Among the latter, the vascular endothelial growth factor (VEGF) has assumed prime candidacy as a major positive physiological effector. Here, we have directly tested this hypothesis in the brain tumor, glioblastoma multiforme, one of the most highly vascularized human cancers. We introduced an antisense VEGF expression construct into glioblastoma cells and found that (i) VEGF mRNA and protein levels were markedly reduced, (ii) the modified cells did not secrete sufficient factors so as to be chemoattractive for primary human microvascular endothelial cells, (iii) the modified cells were not able to sustain tumor growth in immunodeficient animals, and (iv) the density of in vivo blood vessel formation was reduced in direct relation to the reduction of VEGF secretion and tumor formation. Moreover, revertant cells that recovered the ability to secrete VEGF regained each of these tumorigenic properties. These results suggest that VEGF plays a major angiogenic role in glioblastoma.     

Bone marrow-derived circulating endothelial precursors do not contribute to vascular endothelium and are not needed for tumor growth

The mechanisms by which bone marrow (BM)-derived stem cells might contribute to angiogenesis and the origin of neovascular endothelial cells (ECs) are controversial. Neovascular ECs have been proposed to originate from VEGF receptor 2-expressing (VEGFR-2+) stem cells mobilized from the BM by VEGF or tumors, and it is thought that angiogenesis and tumor growth may depend on such endothelial precursors or progenitors. We studied the mobilization of BM cells to circulation by inoculating mice with VEGF polypeptides, adenoviral vectors expressing VEGF, or tumors. We induced angiogenesis by syngeneic melanomas, APCmin adenomas, adenoviral VEGF delivery, or matrigel plugs in four different genetically tagged universal or endothelial cell-specific chimeric mouse models, and subsequently analyzed the contribution of BM-derived cells to endothelium in a wide range of time points. To study the existence of circulating ECs in a nonmyeloablative setting, pairs of genetically marked parabiotic mice with a shared anastomosed circulatory system were created. We did not observe specific mobilization of VEGFR-2+ cells to circulation by VEGF or tumors. During angiogenesis, abundant BM-derived perivascular cells were recruited close to blood vessel wall ECs but did not form part of the endothelium. No circulation-derived vascular ECs were observed in the parabiosis experiments. Our results show that no BM-derived VEGFR-2+ or other EC precursors contribute to vascular endothelium and that cancer growth does not require BM-derived endothelial progenitors. Endothelial differentiation is not a typical in vivo function of normal BM-derived stem cells in adults, and it has to be an extremely rare event if it occurs at all.     

Genetically engineered endothelial cells remain adherent and viable after stent deployment and exposure to flow in vitro.

Intravascular stents, currently in experimental human use for recurrent arterial stenosis, are plagued by subacute thrombosis. As a therapeutic approach to stent-related thrombosis, we and others have suggested coating stents with endothelial cells before implantation. In a previous study we demonstrated the feasibility of coating stents with endothelial cells that were genetically modified to secrete large amounts of human tissue plasminogen activator. In the present study we attempted both to develop a clinically applicable protocol for stent seeding and to test whether seeded cells would remain adherent to stents after exposure to pulsatile flow. Endothelial cells were harvested from the saphenous veins of sheep with survival of the donor animals. Harvested cells were transduced with a retroviral vector containing a marker gene and seeded onto catheter-mounted stents under sterile conditions. Scanning electron microscopy revealed complete coverage of the stent surfaces by seeded cells. Stents were expanded and exposed to pulsatile flow in vitro. Substantial cell retention was observed on the lateral stent surfaces by light microscopy and scanning electron microscopy; fewer cells were seen on the luminal and abluminal surfaces. Removal of seeded cells from flow-exposed stents by trypsin digestion resulted in the recovery of approximately 70% of the seeded cells. These cells were viable and healthy as judged by their ability to proliferate to confluence with the same kinetics as control (non-flow-exposed) cells. Autologous genetically modified endothelial cells can be seeded onto catheter-mounted stents in a sterile manner, and stent deployment under flow conditions results in substantial retention of viable cells.     

In vivo expression of insulin-like growth factor-binding protein-2 in human gliomas increases with the tumor grade

Human central nervous system tumors and glioma cell lines highly express the insulin-like growth factor-binding protein (IGFBP)-2. As IGFBP-2 can affect tumor growth, we studied the relationship between IGFBP-2 expression and the malignancy of brain tumors in vivo. To do so, we investigated by immunohistochemistry the accumulation of IGFBP-1, -2, and -3 in 50 human gliomas classified by the WHO Malignancy Scale. Double labeling using anti-CD68 (monocytes/macrophages), antiglial fibrillary acidic protein, and anti-CD3 (T cells) antibodies was performed to further characterize the IGFBP-1, -2, and -3(+) cells. The expression of IGFBP messenger RNAs (mRNAs) was tested by RT-PCR in tumor samples from nine gliomas of different grades and in eight cell lines representing the cellular composition of human glioma. As controls, the accumulation of IGFBP-2 was investigated in normal brain and in the rat C6 glioblastoma model. IGFBP-1 and -3 accumulated in endothelial and macrophage/microglial cells. IGFBP-2(+) macrophage/microglial and glioma cells clustered in the immediate vicinity of focal necrosis of the human gliomas as well as of the rat C6 glioblastoma. The labeling score of IGFBP-1 accumulation in endothelial cells correlated negatively (P: = 0.0229), and that of IGFBP-2 accumulation in glioma cells correlated positively (P: < 0.0006) with the tumor grade of the gliomas. In addition, RT-PCR analysis confirmed mRNA expression of IGFBP-1, -2, and -3 by the gliomas and glial cells. Small amounts of IGFBP-1 and -3 mRNA, but high amounts of IGFBP-2 mRNA, were detectable in macrophage-like and glioma cell lines. The results suggest cell type-specific accumulation of IGFBP-1, -2, and -3 in human glial tumors of the brain. The increase in IGFBP-2 expression with this malignancy suggests a role of IGFBP-2 in the biology of human gliomas.     

Possible angiogenic roles of insulin-like growth factor II and its receptors in uterine vascular adaptation to pregnancy

Adaptation of the maternal uterine vasculature is essential for normal fetal and placental development in which angiogenesis is considered one of the most critical adaptive changes during pregnancy. Highly expressed in cytotrophoblasts and maternal endothelial cells during pregnancy, IGF-II promotes cell migration and regulates fetal and placental growth. We hypothesized that IGF-II regulates uterine angiogenesis during pregnancy. Both uterine vasculature and isolated uterine microvascular endothelial cells expressed high levels of IGF-II and IGF-II/mannose-6 phosphate receptor mRNA as shown by in situ hybridization. Physiological concentrations of IGF-II significantly increased vessel formation, as shown by a three-dimensional angiogenesis assay in vitro or a chicken chorionallantoic membrane assay in vivo. The angiogenic response of IGF-II could be reversed by the addition of beta-galactosidase or rabbit-antihuman IGF-II/M6P receptor antiserum, whereas blocking antibodies against IGF-I receptor or insulin receptor influenced IGF-II-induced sprout formation. IGF-II promoted migration of endothelial cells (10-250 ng/ml) tested in a modified Boyden chamber, but no stimulating effect on proliferation was observed. The application of several intracellular signal transduction molecules and their inhibitors indicated that protein kinase C and G(i) protein might play a role in the IGF-II-induced angiogenesis. Our results suggest an important angiogenic role of IGF-II in the vascular adaptation to pregnancy.     

Inhibition of brain tumor growth by intravenous poly (β-L-malic acid) nanobioconjugate with pH-dependent drug release [corrected

Effective treatment of brain neurological disorders such as Alzheimer's disease, multiple sclerosis, or tumors should be possible with drug delivery through blood-brain barrier (BBB) or blood-brain tumor barrier (BTB) and targeting specific types of brain cells with drug release into the cell cytoplasm. A polymeric nanobioconjugate drug based on biodegradable, nontoxic, and nonimmunogenic polymalic acid as a universal delivery nanoplatform was used for design and synthesis of nanomedicine drug for i.v. treatment of brain tumors. The polymeric drug passes through the BTB and tumor cell membrane using tandem monoclonal antibodies targeting the BTB and tumor cells. The next step for polymeric drug action was inhibition of tumor angiogenesis by specifically blocking the synthesis of a tumor neovascular trimer protein, laminin-411, by attached antisense oligonucleotides (AONs). The AONs were released into the target cell cytoplasm via pH-activated trileucine, an endosomal escape moiety. Drug delivery to the brain tumor and the release mechanism were both studied for this nanobiopolymer. Introduction of a trileucine endosome escape unit resulted in significantly increased AON delivery to tumor cells, inhibition of laminin-411 synthesis in vitro and in vivo, specific accumulation in brain tumors, and suppression of intracranial glioma growth compared with pH-independent leucine ester. The availability of a systemically active polymeric drug delivery system that passes through the BTB, targets tumor cells, and inhibits glioma growth gives hope for a successful strategy of glioma treatment. This delivery system with drug release into the brain-specific cell type could be useful for treatment of various brain pathologies.     

Expansion of endothelial surface by an increase of vessel diameter during tumor angiogenesis in experimental and hepatocellular and pancreatic cancer

AIM: A low vessel density is a common feature of malignant tumors. We suggested that the expansion of vessel diameter might reconstitute the oxygen and nutritient‘s supply in this situation. The aim of the present study was to compare the number and diameter of blood vessels in pancreatic and liver carcinoma with normal tissue.METHODS: Tumor induction of pancreatic (DSL6A) or hepatocellular (Morris-hepatoma) carcinoma was performed in male Lewis (pancreatic cancer) and ACI (hepatoma) rats by an orthotopic inoculation of solid tumor fragments (pancreatic cancer) or tumor cells (hepatoma). Six weeks (pancreatic cancer) or 12 d (hepatoma) after tumor implantation, the tumor microvasculature as well as normal pancreatic or liver blood vessels were investigated by intravital microscopy. The number of perfused blood vessels in tumor and healthy tissue was assessed by computer-assisted image analysis.RESULTS: The vessel density in healthy pancreas (565&#177;89n/mm^2) was significantly higher compared to pancreatic cancer (116&#177;36 n/mm^2) (P&lt;0.001). Healthy liver showed also a significantly higher vessel density (689+36 n/ram2) compared to liver carcinoma (286+32 n/mm2) (P&lt;0.01). The comparison of diameter frequency showed a significant increase of vessel diameter in both malignant tumors compared to normal tissue (P&lt;0.05).CONCLUSION: The expansion of endothelial cells during tumor angiogenesis is accompanied to a large extent by an increase of vessel diameter rather than by formation of new blood vessels. This may be a possible adaptive mechanism by which experimental pancreatic and hepatocellular cancers expand their endothelial diffusion surface of endothelium to compensate for inadequate neoangiogenesis.     

A predictive microfluidic model of human glioblastoma to assess trafficking of blood–brain barrier-penetrant nanoparticles

The blood–brain barrier represents a significant challenge for the treatment of high-grade gliomas, and our understanding of drug transport across this critical biointerface remains limited. To advance preclinical therapeutic development for gliomas, there is an urgent need for predictive in vitro models with realistic blood–brain-barrier vasculature. Here, we report a vascularized human glioblastoma multiforme (GBM) model in a microfluidic device that accurately recapitulates brain tumor vasculature with self-assembled endothelial cells, astrocytes, and pericytes to investigate the transport of targeted nanotherapeutics across the blood–brain barrier and into GBM cells. Using modular layer-by-layer assembly, we functionalized the surface of nanoparticles with GBM-targeting motifs to improve trafficking to tumors. We directly compared nanoparticle transport in our in vitro platform with transport across mouse brain capillaries using intravital imaging, validating the ability of the platform to model in vivo blood–brain-barrier transport. We investigated the therapeutic potential of functionalized nanoparticles by encapsulating cisplatin and showed improved efficacy of these GBM-targeted nanoparticles both in vitro and in an in vivo orthotopic xenograft model. Our vascularized GBM model represents a significant biomaterials advance, enabling in-depth investigation of brain tumor vasculature and accelerating the development of targeted nanotherapeutics.

High-grade gliomas are the most common primary malignant brain tumors in adults (1). These include grade IV astrocytomas, commonly known as glioblastoma multiforme (GBM), which account for more than 50% of all primary brain cancers and have dismal prognoses, with a 5-y survival rate of less than 5% (2). Due to their infiltrative growth into the healthy brain tissue, surgery often fails to eradicate all tumor cells (3). While chemotherapy and radiation modestly improve median survival (4), most patients ultimately succumb to their tumors. This is primarily due to the presence of a highly selective and regulated endothelium between blood and brain parenchyma known as the blood–brain barrier (BBB) (5), which limits the entry of therapeutics into the brain tissue where tumors are located. The BBB, characterized by a unique cellular architecture of endothelial cells (ECs), pericytes (PCs), and astrocytes (ACs) (6, 7), displays up-regulated expression of junctional proteins and reduced paracellular and transcellular transports compared to other endothelia (8). While this barrier protects the brain from toxins and pathogens, it also severely restricts the transport of many therapeutics, as evidenced by the low cerebrospinal fluid (CSF)-to-plasma ratio of most chemotherapeutic agents (9). There is thus an important need to develop new delivery strategies to cross the BBB and target tumors, enabling sufficient drug exposure (10).Despite rigorous research efforts to develop effective therapies for high-grade gliomas, the majority of trialed therapeutics have failed to improve outcomes in the clinic, even though the agents in question are effective against tumor cells in preclinical models (11). This highlights the inability of current preclinical models to accurately predict the performance of therapeutics in human patients. To address these limitations, we developed an in vitro microfluidic model of vascularized GBM tumors embedded in a realistic human BBB vasculature. This BBB-GBM platform features brain microvascular networks (MVNs) in close contact with a GBM spheroid, recapitulating the infiltrative properties of gliomas observed in the clinic (12) and those of the brain tumor vasculature, with low permeability, small vessel diameter, and increased expression of relevant junctional and receptor proteins (7). This platform is well suited for quantifying vascular permeability of therapeutics and simultaneously investigating modes of transport across the BBB and into GBM tumor cells.There is strong rationale for developing therapeutic nanoparticles (NPs) for GBM and other brain tumors, as they can be used to deliver a diverse range of therapeutic agents and, with appropriate functionalization, can be designed to exploit active transport mechanisms across the BBB (13, 14). Liposomal NPs have been employed in the oncology clinic to improve drug half-life and decrease systemic toxicity (15), but, to date, no nanomedicines have been approved for therapeutic indications in brain tumors. We hypothesize that a realistic BBB-GBM model composed entirely of human cells can accelerate preclinical development of therapeutic NPs. Using our BBB-GBM model, we investigated the trafficking of layer-by-layer NPs (LbL-NPs) and ultimately designed a GBM-targeted NP. The LbL approach leverages electrostatic assembly to generate modular NP libraries with highly controlled architecture. We have used LbL-NPs to deliver a range of therapeutic cargos in preclinical tumor models (16, 17) and have recently demonstrated that liposomes functionalized with BBB-penetrating ligands improved drug delivery across the BBB to GBM tumors (18). Consistent with clinical data (19), we observed that the low-density lipoprotein receptor-related protein 1 (LRP1) was up-regulated in the vasculature near GBM spheroids in the BBB-GBM model and leveraged this information to design and iteratively test a library of NPs. We show that the incorporation of angiopep-2 (AP2) peptide moieties on the surface of LbL-NPs leads to increased BBB permeability near GBM tumors through LRP1-mediated transcytosis. With intravital imaging, we compared the vascular permeabilities of dextran and LbL-NPs in the BBB-GBM platform to those in mouse brain capillaries and validated the predictive potential of our in vitro model. Finally, we show the capability of the BBB-GBM platform to screen therapeutic NPs and predict in vivo efficacy, demonstrating improved efficacy of cisplatin (CDDP) when encapsulated in GBM-targeting LbL-NPs both in vitro and in vivo.     

Neural stem cells display extensive tropism for pathology in adult brain: evidence from intracranial gliomas

One of the impediments to the treatment of brain tumors (e.g., gliomas) has been the degree to which they expand, infiltrate surrounding tissue, and migrate widely into normal brain, usually rendering them "elusive" to effective resection, irradiation, chemotherapy, or gene therapy. We demonstrate that neural stem cells (NSCs), when implanted into experimental intracranial gliomas in vivo in adult rodents, distribute themselves quickly and extensively throughout the tumor bed and migrate uniquely in juxtaposition to widely expanding and aggressively advancing tumor cells, while continuing to stably express a foreign gene. The NSCs "surround" the invading tumor border while "chasing down" infiltrating tumor cells. When implanted intracranially at distant sites from the tumor (e.g., into normal tissue, into the contralateral hemisphere, or into the cerebral ventricles), the donor cells migrate through normal tissue targeting the tumor cells (including human glioblastomas). When implanted outside the CNS intravascularly, NSCs will target an intracranial tumor. NSCs can deliver a therapeutically relevant molecule-cytosine deaminase-such that quantifiable reduction in tumor burden results. These data suggest the adjunctive use of inherently migratory NSCs as a delivery vehicle for targeting therapeutic genes and vectors to refractory, migratory, invasive brain tumors. More broadly, they suggest that NSC migration can be extensive, even in the adult brain and along nonstereotypical routes, if pathology (as modeled here by tumor) is present.     

Survival and differentiation of adult neuronal progenitor cells transplanted to the adult brain.

The dentate gyrus of the hippocampus is one of the few areas of the adult brain that undergoes neurogenesis. In the present study, cells capable of proliferation and neurogenesis were isolated and cultured from the adult rat hippocampus. In defined medium containing basic fibroblast growth factor (FGF-2), cells can survive, proliferate, and express neuronal and glial markers. Cells have been maintained in culture for 1 year through multiple passages. These cultured adult cells were labeled in vitro with bromodeoxyuridine and adenovirus expressing beta-galactosidase and were transplanted to the adult rat hippocampus. Surviving cells were evident through 3 months postimplantation with no evidence of tumor formation. Within 2 months postgrafting, labeled cells were found in the dentate gyrus, where they differentiated into neurons only in the intact region of the granule cell layer. Our results indicate that FGF-2 responsive progenitors can be isolated from the adult hippocampus and that these cells retain the capacity to generate mature neurons when grafted into the adult rat brain.     

Tat-mediated delivery of heterologous proteins into cells.

The Tat protein of human immunodeficiency virus 1 (HIV-1) can enter cells efficiently when added exogenously in tissue culture. To assess if Tat can carry other molecules into cells, we chemically cross-linked Tat peptides (residues 1-72 or 37-72) to beta-galactosidase, horseradish peroxidase, RNase A, and domain III of Pseudomonas exotoxin A (PE) and monitored uptake colorimetrically or by cytotoxicity. The Tat chimeras were effective on all cell types tested, with staining showing uptake into all cells in each experiment. In mice, treatment with Tat-beta-galactosidase chimeras resulted in delivery to several tissues, with high levels in heart, liver, and spleen, low-to-moderate levels in lung and skeletal muscle, and little or no activity in kidney and brain. The primary target within these tissues was the cells surrounding the blood vessels, suggesting endothelial cells, Kupffer cells, and/or splenic macrophages. Tat-mediated uptake may allow the therapeutic delivery of macromolecules previously thought to be impermeable to living cells.     

Gene therapy for brain tumors: regression of experimental gliomas by adenovirus-mediated gene transfer in vivo.

The therapeutic efficacy of adenovirus-mediated herpes simplex virus thymidine kinase (HSV-tk) gene transduction of rat C6 glioma cells followed by ganciclovir (GCV) administration was studied in tumors generated in the brains of nude mice. C6 glioma cells were efficiently transduced in vitro by a replicative-defective recombinant adenovirus carrying the HSV-tk gene (ADV/RSV-tk) that rendered them sensitive to GCV in a dose-dependent manner. Tumors were generated by stereotaxic intracerebral injection of 1 x 10(4) C6 cells in nude mice. After 8 days of tumor growth, 3 x 10(8) ADV/RSV-tk viral particles were injected into the tumors and the mice subsequently were treated with GCV for 6 days. Tumor size in untreated and treated animals was compared 20 days after tumor implantation. The mean cross-sectional area of the tumors in the treated animals was 23-fold smaller than in control animals and the tumor volume was reduced by > 500-fold. These results demonstrate that the recombinant adenoviral vector can function as an efficient gene delivery vehicle for the treatment of gliomas by in vivo gene therapy.     

Antitumor activity of cytotoxic T lymphocytes engineered to target vascular endothelial growth factor receptors

The demonstration that angiogenesis is required for the growth of solid tumors has fueled an intense interest in the development of new therapeutic strategies that target the tumor vasculature. Here we report the development of an immune-based antiangiogenic strategy that is based on the generation of T lymphocytes that possess a killing specificity for cells expressing vascular endothelial growth factor receptors (VEGFRs). To target VEGFR-expressing cells, recombinant retroviral vectors were generated that encoded a chimeric T cell receptor comprised of VEGF sequences linked to intracellular signaling sequences derived from the zeta chain of the T cell receptor. After transduction of primary murine CD8 lymphocytes by such vectors, the transduced cells were shown to possess an efficient killing specificity for cells expressing the VEGF receptor, Flk-1, as measured by in vitro cytotoxicity assays. After adoptive transfer into tumor-bearing mice, the genetically modified cytotoxic T lymphocytes strongly inhibited the growth of a variety of syngeneic murine tumors and human tumor xenografts. An increased effect on in vivo tumor growth inhibition was seen when this therapy was combined with the systemic administration of TNP-470, a conventional angiogenesis inhibitor. The utilization of the immune system to target angiogenic markers expressed on tumor vasculature may prove to be a powerful means for controlling tumor growth.     

Expansion of endothelial surface by an increase of vessel diameter during tumor angiogenesis in experimental hepatocellular and pancreatic cancer

AIM: A low vessel density is a common feature of malignant tumors. We suggested that the expansion of vessel diameter might reconstitute the oxygen and nutritient’s supply in this situation. The aim of the present study was to compare the number and diameter of blood vessels in pancreatic and liver carcinoma with normal tissue. METHODS: Tumor induction of pancreatic (DSL6A) or hepatocellular (Morris-hepatoma) carcinoma was performed in male Lewis (pancreatic cancer) and ACI (hepatoma) rats by an orthotopic inoculation of solid tumor fragments (pancreatic cancer) or tumor cells (hepatoma). Six weeks (pancreatic cancer) or 12 d (hepatoma) after tumor implantation, the tumor microvasculature as well as normal pancreatic or liver blood vessels were investigated by intravital microscopy. The number of perfused blood vessels in tumor and healthy tissue was assessed by computer-assisted image analysis. RESULTS: The vessel density in healthy pancreas (565 ± 89 n/mm²) was significantly higher compared to pancreatic cancer (116 ± 36 n/mm²) (P < 0.001). Healthy liver showed also a significantly higher vessel density (689 ± 36 n/mm²) compared to liver carcinoma (286 ± 32 n/mm²) (P < 0.01). The comparison of diameter frequency showed a significant increase of vessel diameter in both malignant tumors compared to normal tissue (P < 0.05). CONCLUSION: The expansion of endothelial cells during tumor angiogenesis is accompanied to a large extent by an increase of vessel diameter rather than by formation of new blood vessels. This may be a possible adaptive mechanism by which experimental pancreatic and hepatocellular cancers expand their endothelial diffusion surface of endothelium to compensate for inadequate neoangiogenesis.     

IL-20 is an arteriogenic cytokine that remodels collateral networks and improves functions of ischemic hind limbs

Successful therapeutic angiogenesis for the treatment of ischemic disorders relies on selection of optimal proangiogenic or arteriogenic agents that are able to promote establishment of functional collateral networks. Here, we show that IL-20, a pleiotropic inflammatory cytokine, displays an imperative effect on vascular remodeling. Stimulation of both large and microvascular endothelial cells with IL-20 leads to activation of receptor-dependent multiple intracellular signaling components, including increased phosphorylation levels of JAK2/STAT5, Erk1/2, and Akt; activation of small GTP-binding proteins Rac and Rho; and intracellular release of calcium. Surprisingly, IL-20 significantly promotes endothelial cell tube formation without affecting their proliferation and motility. These findings suggest that the vascular function of IL-20 involves endothelial cell organization, vessel maturation, and remodeling. Consistent with this notion, delivery of IL-20 to the ischemic muscle tissue significantly improves arteriogenesis and blood perfusion in a rat hind-limb model. Our findings provide mechanistic insights on vascular functions of IL-20 and define therapeutic implication of this cytokine for the treatment of ischemic disorders.