Endothelial cell-based cytokine gene delivery inhibits 9L glioma growth in vivo

Tumor microenvironment tenascin-C promotes glioblastoma invasion and negatively regulates tumor proliferation

BACKGROUND

Glioblastoma (GBM) is the most frequent and aggressive primary brain tumor in adults. Recent research on cancer stroma indicates that the brain microenvironment plays a substantial role in tumor malignancy and treatment responses to current antitumor therapy. In this work, we have investigated the effect of alterations in brain tumor extracellular matrix tenascin-C (TNC) on brain tumor growth patterns including proliferation and invasion.

METHODS

Since intracranial xenografts from patient-derived GBM neurospheres form highly invasive tumors that recapitulate the invasive features demonstrated in human patients diagnosed with GBM, we studied TNC gain-of-function and loss-of function in these GBM neurospheres in vitro and in vivo.

RESULTS

TNC loss-of-function promoted GBM neurosphere cell adhesion and actin cytoskeleton organization. Yet, TNC loss-of-function or exogenous TNC had no effect on GBM neurosphere cell growth in vitro. In animal models, decreased TNC in the tumor microenvironment was accompanied by decreased tumor invasion and increased tumor proliferation, suggesting that TNC regulates the "go-or-grow" phenotypic switch of glioma in vivo. We demonstrated that decreased TNC in the tumor microenvironment modulated behaviors of stromal cells including endothelial cells and microglia, resulting in enlarged tumor blood vessels and activated microglia in tumors. We further demonstrated that tumor cells with decreased TNC expression are sensitive to anti-proliferative treatment in vitro.

CONCLUSION

Our findings suggest that detailed understanding of how TNC in the tumor microenvironment influences tumor behavior and the interactions between tumor cells and surrounding nontumor cells will benefit novel combinatory antitumor strategies to treat malignant brain tumors.

FasL gene knock-down therapy enhances the antiglioma immune response

Malignant glioma is a lethal form of brain cancer that is very difficult to treat. The aggressive behavior of these neoplasms and their limited responsiveness to therapy has been attributed in part to the ability of these tumors to evade the immune system. Gliomas, like many other solid tumors, express components of numerous immune escape mechanisms, including immunosuppressive proteins such as TGF-beta, IL-10, and FasL. Here, we show that FasL expression can support the growth of experimental intracranial glioma. We show that FasL is readily detected in human glioblastoma multiforme clinical specimens. FasL was found to be expressed by three well-characterized rat glioma cell lines (9L, F98, and C6) and glioma cell-derived FasL mediated the death of phytohemagglutinin-stimulated Jurkat T-lymphocytes when cocultured with glioma cells in vitro. We asked if inhibiting 9L-derived FasL altered the growth of experimental glioma. FasL expression knockdown using shRNA reduced the growth of subcutaneous and intracranial 9L gliomas by approximately 50% in immune competent Fisher 344 rats. In contrast, FasL expression knockdown had no affect on the growth of intracranial 9L glioma in T-cell deficient athymic rats. Intracranial tumors derived from FasL knockdown 9L glioma cells contained up to 3-fold more tumor infiltrating T-cells than tumors derived from control 9L cells. These results demonstrate that down-regulating FasL expression and/or function in glial malignancies can enhance T-cell tumor infiltration and inhibit tumor growth. The findings suggest that targeting endogenous FasL in glial malignancies could enhance the efficacy of emerging immune-based treatment strategies.

A glycosylated nitric oxide donor, beta-Gal-NONOate, and its site-specific antitumor activity

So far, nitric oxide (NO) donors have been applied to various aspects of antitumor therapy. To selectively sensitize tumor cells and avoid unwanted side effects, we recently synthesized a beta-galactosidase-activatable NO-releasing compound, beta-galactosyl-pyrrolidinyl diazeniumdiolate (beta-Gal-NONOate). In this study, we first verified its superiority over its parent diazeniumdiolate (NONOate) in terms of targeted intracellular NO-releasing and antitumor activity with 9L/LacZ cells (rat glioma cell line 9L with transformed LacZ gene) in vitro. beta-Gal-NONOate only released NO when hydrolyzed by induced beta-galactosidase in 9L/LacZ cells, which led to its more powerful cytotoxicity than that of NONOate. The results showed that beta-Gal-NONOate produced higher NO levels than NONOate in 9L/LacZ cells at equal concentration, and hence induced optimal NO levels for antitumor activity. However, in 9L cells, beta-Gal-NONOate showed less toxicity than NONOate. Therefore, it is demonstrated that beta-Gal-NONOate is a site-specific prodrug for targeting NO intracellularly as a beta-galactosidase-sensitive NO donor, and it is also expected to be a promising probe in numerous experimental settings and a potential therapeutic drug for antitumor treatment.

Endothelial cell transplantation for gene therapy in experimental gliomas

OBJECTIVE

Malignant gliomas are prominent targets for cancer gene therapy approaches because of their poor prognosis despite all available therapies. Endothelial cells (ECs) are considered attractive vehicles for cell-based gene therapy because of their tropism to the tumor vasculature. In this study, we investigated the potential of ECs to incorporate into glioma vessels after intra-arterial or local application to establish whether ECs can be used as cellular vectors for gene therapy in gliomas.

METHODS

Immortalized rat brain endothelial cells (BECs) were modified to express either beta-galactosidase or green fluorescent protein (GFP). The ability of transduced BECs to integrate into tumor vessels after interstitial implantation was evaluated in C6 and 9L glioma models. The fate of GFP-BECs was investigated after selective intracarotid injection into C6 tumor-bearing animals.

RESULTS

The interstitially grafted BECs organized themselves into vascular-like structures and integrated into the tumor vasculature. Transgene expression was limited to 10 days after injection. After selective intra-arterial injection, numerous GFP-BECs were adherent to the vascular lumen at least 7 days after injection. These cells were evenly distributed within small vessels and capillaries of the injected hemisphere and did not home selectively to the tumor vessels.

CONCLUSION

Cell-based therapy approaches to brain tumor treatment using BECs as cellular vectors might be hampered by the rapid downregulation of transgene expression and by the fact that these cells do not home specifically to tumor vessels after intra-arterial injection. Nevertheless, locoregional administration of BECs might be an interesting approach for delivering molecules to brain tumors when short-term expression of transgene in the perivascular space is desirable.

Cellular vehicles for cancer gene therapy: current status and future potential

Cancer is a difficult target for any therapeutic strategy; therefore, there is a continuous search for new therapeutic modalities, for application either alone or in combination. In this regard, gene-based therapy is a new approach that offers hope of improved control of tumors. Intensive research to apply gene therapy for cancer treatment has led to identification of the most important technical and theoretical barriers that need to be overcome for clinical success. One of the central unresolved challenges remains the issue of specific and efficient delivery of genes to target cells or tissues, emphasizing the importance of the gene carrier. Along with different viral and non-viral vector systems, mammalian cells have also been considered as vehicles for delivery of anti-cancer therapeutics. The cell-based delivery approach was introduced as the first attempt to apply gene therapy to cancer treatment, and in general, has followed most of the ups and downs of gene therapy applications, progressing alongside new knowledge gained in this field. As a result, significant progress has been made in some aspects of the cell-based approach, while the development of other essential issues is only just gaining speed. It appears that the initial phase of development of cell-based protocols - the achievement of efficient ex vivo cell loading with therapeutics - has largely been fulfilled. However, the desired efficacy of cell-based strategies in general has not yet been reached, and specificity of tumor homing needs to be improved considerably. There is hope that advances in related scientific fields will promote the utilization of cells as powerful and versatile vehicles for cancer gene therapy.

Development of an in vitro blood–brain barrier model—cytotoxicity of mercury and aluminum

In this study, in vitro blood-brain barrier (BBB) models composed of two different cell types were compared. The aim of our study was to find an alternative human cell line that could be used in BBB models. Inorganic and organic mercury and aluminum were studied as model chemicals in the testing of the system. BBB models were composed of endothelial RBE4 cell line or retinal pigment epithelial (RPE) cell line ARPE-19 and neuronal SH-SY5Y cells as target cells. Glial U-373 MG cells were included in part of the tests to induce the formation of a tighter barrier. Millicell CM filter inserts were coated with rat-tail collagen, and RBE4 or ARPE-19 cells were placed on the filters at the density of 3.5-4 x 10(5) cells/filter. During culture, the state of confluency was microscopically observed and confirmed by the measurement of electrical resistance caused by the developing cell layer. The target cells, SH-SY5Y neuroblastoma cells, were plated on the bottom of cell culture wells at the density of 100000 cells/cm(2). In part of the studies, glial U-373 MG cells were placed on the under side of the membrane filter. When confluent filters with ARPE-19 or RBE4 cells were placed on top of the SH-SY5Y cells, different concentrations of mercuric chloride, methyl mercury chloride, and aluminum chloride were added into the filter cups along with a fluorescent tracer. Exposure time was 24 h, after which the cytotoxicity in the SH-SY5Y cell layer, as well as in the ARPE-19 or RBE4 cell layer, was evaluated by the luminescent measurement of total ATP. The leakage of the fluorescent tracer was also monitored. The results showed that both barrier cell types were induced by glial cells. Inorganic and organic mercury caused a leakage of the dye and cytotoxicity in SH-SY5Y cells. Especially, methyl mercury chloride could exert an effect on target cells before any profound cytotoxicity in barrier cells could be seen. Aluminum did not cause any leakage in the barrier cell layer, and even the highest concentration (1 mM) of aluminum did not cause any cytotoxicity in the SH-SY5Y cells. In conclusion, BBB models composed of RBE4 and ARPE-19 cells were able to distinguish between different toxicities, and ARPE-19 cells are thus promising candidates for studies of drug penetration through the blood-brain barrier.

Characterization of 9L glioma model of the Wistar rat

The aim of our study was to develop and characterize solid brain tumors in Wistar rats, which could be used in investigations concerning the molecular mechanisms that lay beneath the genesis of the gliomas as well as in the testing of curative potentials of various therapeutics. The tumors were induced by intracerebral inoculation of 9L glioma cells and characterized by morphometrical, histological and immunohistochemical analysis after 7, 14 and 21 postimplantation days. Immunohistochemical characterization included detection of the nuclear antigene Ki-67 as the proliferative cell marker, GFAP as a tracer of reactive gliosis surrounding the tumor mass, and CD4/CD8 and ED1 antigens, as markers of the immunological response. Our results showed that after 7 days all experimental animals developed solid, well-circumcised tumors, which were clearly separated from the surrounding brain tissue. Tumors showed progressive growth from the 7th to the 21st day despite the observed immunological response starting after 14 days. Histologically tumors were hypercellular with neovascularization and necrosis. These results indicate that reproducible morphometric evaluation can be performed on 9L tumors growing in immunocompetent Wistar rats, enabling its use as an animal tumor model for the evaluation of various therapeutic approaches.

Gene transfer to induce angiogenesis in myocardial and limb ischaemia

Stimulation of angiogenesis/arteriogenesis by gene transfer methods offers hope for treating patients with myocardial and peripheral limb ischaemia who are not candidates for standard revascularisation procedures. Preclinical studies showed that adenoviral and plasmid vectors encoding various angiogenic cytokines were capable of inducing functionally significant angiogenesis in vitro and in animal models of chronic myocardial ischaemia. Early clinical studies using VEGF121-, FGF-4- and VEGF165-encoding vectors showed a reasonable safety profile with promising results. However, significant advances in vector technology including regulatable and longer-term expression, delivery strategies (local and organ/tissue specific), clinical trial design, and outcome measure development are needed before this investigational treatment becomes reality.

Evoked acetylcholine release by immortalized brain endothelial cells genetically modified to express choline acetyltransferase and/or the vesicular acetylcholine transporter

Immortalized rat brain endothelial RBE4 cells do not express choline acetyltransferase (ChAT), but they do express an endogenous machinery that enables them to release specifically acetylcholine (ACh) on calcium entry when they have been passively loaded with the neurotransmitter. Indeed, we have previously reported that these cells do not release glutamate or GABA after loading with these transmitters. The present study was set up to engineer stable cell lines producing ACh by transfecting them with an expression vector construct containing the rat ChAT. ChAT transfectants expressed a high level of ChAT activity and accumulated endogenous ACh. We examined evoked ACh release from RBE4 cells using two parallel approaches. First, Ca2+-dependent ACh release induced by a calcium ionophore was followed with a chemiluminescent procedure. We showed that ChAT-transfected cells released the transmitter they had synthesized and accumulated in the presence of an esterase inhibitor. Second, ACh released on an electrical depolarization was detected in real time by a whole-cell voltage-clamped Xenopus myocyte in contact with the cell. Whether cells synthesized ACh or whether they were passively loaded with ACh, electrical stimulation elicited the release of ACh quanta detected as inward synaptic-like currents in the myocyte. Repetitive stimulation elicited a continuous train of responses of decreasing amplitudes, with rare failures. Amplitude analysis showed that the currents peaked at preferential levels, as if they were multiples of an elementary component. Furthermore, we selected an RBE4 transgenic clone exhibiting a high level of ChAT activity to introduce the Torpedo vesicular ACh transporter (VAChT) gene. However, as the expression of ChAT was inactivated in stable VAChT transfectants, the potential influence of VAChT on evoked ACh release could only be studied on cells passively loaded with ACh. VAChT expression modified the pattern of ACh delivery on repetitive electrical stimulation. Stimulation trains evoked several groups of responses interrupted by many failures. The total amount of released ACh and the mean quantal size were not modified. As brain endothelial cells are known as suitable cellular vectors for delivering gene products to the brain, the present results suggest that RBE4 cells genetically modified to produce ACh and intrinsically able to support evoked ACh release may provide a useful tool for improving altered cholinergic function in the CNS.

Scatter factor/hepatocyte growth factor gene transfer increases rat blood-glioma barrier permeability

Malignant gliomas are associated with a dysfunctional blood-tumor barrier (BTB) that causes substantial morbidity. Scatter factor/hepatocyte growth factor (SF/HGF) is a multifunctional growth factor that correlates with glioma malignancy and has several biological properties that suggest a role in enhancing blood-glioma barrier permeability. In this study, we examined the effects of glioma cell SF/HGF expression on BTB permeability to horseradish peroxidase (HRP). Fischer 344 rats bearing intrastriatal 9L tumors engineered to secrete SF/HGF (9L-SF) and SF/HGF-negative control tumors (9L-neo) received intracardiac injections of HRP and were rapidly decapitated. Densitometric analysis of brain sections reacted with diaminobenzidine showed significantly greater extravascular HRP surrounding SF/HGF-secreting tumors than 9L-neo tumors of comparable size (p<0.05). HRP enzymatic activity associated with striata containing SF/HGF-expressing tumors was 1. 6-fold greater than that of striata containing control tumors (p<0. 05). Northern analysis showed that expression of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) did not differ between 9L-neo and 9L-SF tumors. These data demonstrate that SF/HGF expression by intracerebral glial tumors can enhance BTB permeability independent of changes in VEGF/VPF expression.

IL-10 gene transfer to intracranial 9L glioma: tumor inhibition and cooperation with IL-2

This study examines the effects of interleukin-10 (IL-10) and combination IL-10 + IL-2 gene transfer on experimental brain tumor growth in vivo. 9L gliosarcoma cells were engineered to stably express murine IL-10 (9L-IL-10 cells) and implanted subcutaneously or to the caudate/putamen of syngeneic rats. The growth of tumors expressing IL-10 was substantially reduced compared to that of control tumors (p < 0.05). Intracranial tumors expressing IL-10 and IL-2 were established by co-implanting 9L-IL-10 cells with endothelial cells engineered to express IL-2. At 14 days post-implantation, tumors expressing IL-10 + IL-2 were 99% smaller than control-transfected tumors (p < 0.0001). This extent of anti-tumor effect could not be achieved by expression of IL-10 or IL-2 alone within tumors. Neither IL-10 nor a combination of IL-10 + IL-2 gene delivery inhibited tumor growth in severe combined immunodeficient (SCID-Beige) mice (p > 0.05). Immunohistochemical analysis revealed that IL-10 + IL-2 gene delivery markedly increased T-cell infiltration within the striatum ipsilateral to tumor cell implantation. These findings establish that IL-10 expression, particularly in combination with IL-2 expression, can have significant immune-dependent anti-tumor actions within intracranial gliomas.

Rat brain tumor models in experimental neuro-oncology: the 9L, C6, T9, F98, RG2 (D74), RT-2 and CNS-1 gliomas

Rat brain tumor models have been widely used in experimental neuro-oncology for almost three decades. The present review, which will be selective rather than comprehensive, will focus entirely on seven rat brain tumor models and their utility in evaluating the efficacy of various therapeutic modalities. Although no currently available animal brain tumor model exactly simulates human high grade brain tumors, the rat models that are currently available have provided a wealth of information on in vitro and in vivo biochemical and biological properties of brain tumors and their in vivo responses to various therapeutic modalities. Ideally, valid brain tumor models should be derived from glial cells, grow in vitro and in vivo with predictable and reproducible growth patterns that simulate human gliomas, be weakly or non-immunogenic, and their response to therapy, or lack thereof, should resemble human brain tumors. The following tumors will be discussed. The 9L gliosarcoma, which was chemically induced in an inbred Fischer rat, has been one of the most widely used of all rat brain tumor models and has provided much useful information relating to brain tumor biology and therapy. The T9 glioma, although generally unrecognized, was and probably still is the same as the 9L. Both of these tumors can be immunogenic under the appropriate circumstances, and this must be taken into consideration when using either of them for studies of therapeutic efficacy, especially if survival is used as an endpoint. The C6 glioma, which was chemically induced in an outbred Wistar rat, has been extensively used for a variety of studies, but is not syngeneic to any inbred strain. Its potential to evoke an alloimmune response is a serious limitation, if it is being used in survival studies. The F98 and RG2 (D74) gliomas were both chemically induced tumors that appear to be either weakly or non-immunogenic. These tumors have been refractory to a variety of therapeutic modalities and their invasive pattern of growth and uniform lethality following an innoculum of as few as 10 tumor cells make them particularly attractive models to test new therapeutic modalities. The Avian Sarcoma Virus induced tumors and a continuous cell line derived from one of them, designated RT-2, have been useful for studies in which de novo tumor induction is an important requirement. These tumors, however, are immunogenic and this may limit their usefulness for survival studies. Finally, a new chemically induced tumor recently has been described, the CNS-1, and it appears to have a number of properties that should make it useful in experimental neuro-oncology. It is essential to recognize, however, the limitations of each of the models that have been described, and depending upon the nature of the study to be conducted, it is important that the appropriate model be selected.

Scatter factor/hepatocyte growth factor expression enhances human glioblastoma tumorigenicity and growth

We have shown previously that the multifunctional cytokine scatter factor/hepatocyte growth factor (SF/HGF) is elevated in human malignant gliomas. In this study we investigated how human SF/HGF expression affects the malignancy of the U373 human glioblastoma cell line in vivo and in vitro. Human SF/HGF gene transfer increased U373 glioblastoma tumorigenicity by > or = 20-fold and enhanced the growth rate of intracerebral U373 xenografts by 3- to 8-fold. SF/HGF expression had no effect on the proliferation of glioblastoma cell monolayers but increased their anchorage-independent colony formation in soft agar by 5- to 8-fold. These results are the first to show that SF/HGF expression by human glioblastoma cells enhances their growth dysregulation in vitro and malignancy in vivo.

Regulation of angiogenesis in malignant gliomas

Gliomas are highly resistant to conventional therapeutic measures, requiring the development of novel treatments. Since gliomas are particularly vascular tumors, one approach involves treatments directed at inhibiting angiogenic mechanisms. Although multiple factors contribute to the ultimate vascularization of any tumor, some are especially relevant to gliomas. Early experimental work directed at inhibiting angiogenic pathways has shown promise toward achieving control of tumor growth. This article focuses on the evidence that angiogenesis and related vascular cell responses play important roles in glioma biology, and reviews those biochemical pathways known through experimentation to be involved in the vascular response to gliomas. Finally, contemporary vessel-targeted approaches that have been used to inhibit glioma growth are discussed.