A self-guidance biological hybrid drug delivery system driven by anaerobes to inhibit the proliferation and metastasis of colon cancer

Colorectal cancer is often accompanied by multiple organ metastasis. Anaerobic Bifidobacterium Infantis (BI) bacterial can selectively grow in hypoxic colorectal tumor microenvironment (TME), to own the natural advantage of preferentially colorectal tumor targeting. Herein, a self-guidance biological hybrid drug delivery system (BI-ES-FeAlg/DOX) based on BI was constructed to inhibit the proliferation and metastasis of colon cancer. Results demonstrated that BI-ES-FeAlg/DOX could overcome physical barriers to target and accumulate in colon tumor tissues. Then DOX was released to kill tumor cells along with the phase transition (solid to liquid) of FeAlg hydrogel, due to Fe³⁺ was reduced to Fe²⁺by intracellular GSH. Meanwhile, BI-ES selectively colonized into tumors and expressed endostatin (ES) protein to down-regulate VEGF and bFGF expression, exerting anti-angiogenic effect. Moreover, FeAlg catalyzed H₂O₂ in the local tumor to generate cytotoxic ·OH, further enhancing the antitumor effect. The pharmacodynamic result in AOM/DSS model proved that BI-ES-FeAlg/DOX had the best therapeutic effect, with the final V/V₀ of 2.19 ± 0.57, which was significantly lower than the other groups. Meanwhile, on CT-26 tumor-bearing model, it also showed an outstanding anti-tumor effect with inhibition rate of 82.12% ± 3.08%. In addition, lung metastases decreased significantly in tumor metastasis model after BI-ES-FeAlg/DOX treatment.

Secreted Factors from Stem Cells of Human Exfoliated Deciduous Teeth Directly Activate Endothelial Cells to Promote All Processes of Angiogenesis

Diabetes is a major risk factor for atherosclerosis and ischemic vascular diseases. Recently, regenerative medicine is expected to be a novel therapy for ischemic diseases. Our previous studies have reported that transplantation of stem cells promoted therapeutic angiogenesis for diabetic neuropathy and ischemic vascular disease in a paracrine manner, but the precise mechanism is unclear. Therefore, we examined whether secreted factors from stem cells had direct beneficial effects on endothelial cells to promote angiogenesis. The soluble factors were collected as conditioned medium (CM) 48 h after culturing stem cells from human exfoliated deciduous teeth (SHED) in serum-free DMEM. SHED-CM significantly increased cell viability of human umbilical vein endothelial cells (HUVECs) in MTT assays and accelerated HUVECs migration in wound healing and Boyden chamber assays. In a Matrigel plug assay of mice, the migrated number of primary endothelial cells was markedly increased in the plug containing SHED-CM or SHED suspension. SHED-CM induced complex tubular structures of HUVECs in a tube formation assay. Furthermore, SHED-CM significantly increased neovascularization from the primary rat aorta, indicating that SHED-CM stimulated primary endothelial cells to promote comprehensive angiogenesis processes. The angiogenic effects of SHED-CM were the same or greater than the effective concentration of VEGF. In conclusion, SHED-CM directly stimulates vascular endothelial cells to promote angiogenesis and is promising for future clinical application.

Effect of LLLT on endothelial cells culture

Growth factors as vascular endothelial growth factor (VEGF), produced by the endothelial cells, take an essential part in pathological and physiological angiogenesis. The possibility of angiogenesis modulation by application of laser radiation may contribute to the improvement of its use in this process. Thus, the aim of the study was to investigate the influence of low-level laser therapy (LLLT) on the proliferation of endothelial cells, secretion of VEGF-A and presence of soluble VEGF receptors (sVEGFR-1 and sVEGFR-2) in the medium after in vitro culture. Isolated human umbilical vein endothelial cells (HUVECs) were irradiated using a diode laser at a wavelength of 635 nm and power density of 1,875 mW/cm². Depending on radiation energy density, the experiment was conducted in four groups: I 0 J/cm² (control group), II 2 J/cm², III 4 J/cm², and IV 8 J/cm². The use of laser radiation wavelength of 635 nm, was associated with a statistically significant increase in proliferation of endothelial cells (p = 0.0041). Moreover, at 635-nm wavelength, all doses of radiation significantly reduced the concentration of sVEGFR-1 (p = 0.0197).

Clinical significance of serum and tumor tissue endostatin evaluation in operable non-small cell lung cancer

Endostatin, as the most potential antiangiogenic factor, is a naturally occurring fragment of collagen XVIII in bloodstream capable of inhibiting tumor growth and metastasis. This study was conducted to explore the clinical value of endostatin in serum and tumor tissue in patients with operable non-small cell lung cancer (NSCLC). ELISA and immunohistochemistry were applied to detect the expression of endostatin in serum and tumor tissue in 105 patient-matched operable NSCLC patients. The serum level of endostatin was significantly higher in NSCLC patients than healthy individuals (P=0.0018). Cases with poorer differentiation showed a higher endostatin serum level (P=0.008). There was no significant correlation between tumor tissue expression and clinical parameters, such as TNM stage, differentiation degree, histological type and lymph node invasion status. A stronger expression of endostain in tumor tissue was associated with a higher serum level (r=0.223). The univariate and multivariate analyses with Cox proportional hazards model for overall survival showed that tumor stage and node status were independent prognostic factors, whereas neither endostatin levels in serum nor in tumor tissue showed potential in predicting the long-term survival of operable NSCLC patients. In conclusion, the results observed in the present study did not support the prediction of overall survival in operable NSCLC based on the expression levels of endostatin in serum and tumor tissue.

A review of RGD-functionalized nonviral gene delivery vectors for cancer therapy

The development of effective treatments that enable many patients suffering from cancer to be successfully cured is highly demanded. Angiogenesis, which is a process for the formation of new capillary blood vessels, has a crucial role in solid tumor progression and the development of metastasis. Antiangiogenic therapy designed to prevent tumor angiogenesis, thereby arresting the growth or spread of tumors, has emerged as a non-invasive and safe option for cancer treatment. Due to the fact that integrin receptors are overexpressed on the surface of angiogenic endothelial cells, various strategies have been made to develop targeted delivery systems for cancer gene therapy utilizing integrin-targeting peptides with an exposed arginine-glycine-aspartate (RGD) sequence. The aim of this review is to summarize the progress and prospect of RGD-functionalized nonviral vectors toward targeted delivery of genetic materials in order to achieve an efficient therapeutic outcome for cancer gene therapy, including antiangiogenic therapy.

Liposomal nanomedicine for breast cancer therapy

Liposomes are well-established nanocarriers for improving the therapeutic index of anticancer agents. A remarkable understanding in the pathophysiology of breast cancer progression has emerged with information on the involved specific biomolecules, which may serve as molecular targets for its therapy. Hormonal and nonhormonal receptors can both be exploited for targeting to breast cancer cells. Targeted delivery of cytotoxic drugs using liposomes is a novel approach for breast cancer therapy. In the present article, we summarize molecular targets present on the breast cancer cells. Recent developments in liposome-based delivery of bioactives for selective treatments of breast cancer are discussed. In addition, utilization of bioenvironmental conditions of tumor for liposome-based targeted delivery is also summed up.

AAV2-mediated in vivo immune gene therapy of solid tumours

Background

Many strategies have been adopted to unleash the potential of gene therapy for cancer, involving a wide range of therapeutic genes delivered by various methods. Immune therapy has become one of the major strategies adopted for cancer gene therapy and seeks to stimulate the immune system to target tumour antigens. In this study, the feasibility of AAV2 mediated immunotherapy of growing tumours was examined, in isolation and combined with anti-angiogenic therapy.

Methods

Immune-competent Balb/C or C57 mice bearing subcutaneous JBS fibrosarcoma or Lewis Lung Carcinoma (LLC) tumour xenografts respectively were treated by intra-tumoural administration of AAV2 vector encoding the immune up-regulating cytokine granulocyte macrophage-colony stimulating factor (GM-CSF) and the co-stimulatory molecule B7-1 to subcutaneous tumours, either alone or in combination with intra-muscular (IM) delivery of AAV2 vector encoding Nk4 14 days prior to tumour induction. Tumour growth and survival was monitored for all animals. Cured animals were re-challenged with tumourigenic doses of the original tumour type. In vivo cytotoxicity assays were used to investigate establishment of cell-mediated responses in treated animals.

Results

AAV2-mediated GM-CSF, B7-1 treatment resulted in a significant reduction in tumour growth and an increase in survival in both tumour models. Cured animals were resistant to re-challenge, and induction of T cell mediated anti-tumour responses were demonstrated. Adoptive transfer of splenocytes to naïve animals prevented tumour establishment. Systemic production of Nk4 induced by intra-muscular (IM) delivery of Nk4 significantly reduced subcutaneous tumour growth. However, combination of Nk4 treatment with GM-CSF, B7-1 therapy reduced the efficacy of the immune therapy.

Conclusions

Overall, this study demonstrates the potential for in vivo AAV2 mediated immune gene therapy, and provides data on the inter-relationship between tumour vasculature and immune cell recruitment.

The endogenous soluble VEGF receptor-2 isoform suppresses lymph node metastasis in a mouse immunocompetent mammary cancer model

BACKGROUND

Cancer metastasis contributes significantly to cancer mortality and is facilitated by lymphangiogenesis and angiogenesis. A new splicing variant, endogenous soluble vascular endothelial growth factor receptor-2 (esVEGFR-2) that we recently identified is an endogenous selective inhibitor of lymphangiogenesis. To evaluate the antimetastatic potential of esVEGFR-2, gene therapy with vector expressing esVEGFR-2 (pesVEGFR-2) or endostatin (pEndo) as a positive control was conducted on murine metastatic mammary cancer.

METHODS

Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of pesVEGFR-2, pEndo or pVec as control, once a week for six weeks. In vivo gene electrotransfer was performed on the tumors after each injection.

RESULTS

Deaths from metastasis were much lower in the pesVEGFR-2 and pEndo groups than in those of the pVec. Tumor volume was significantly lower in the pesVEGFR-2 and the pEndo groups throughout the study. Multiplicity of lymph node and lung metastatic nodules was significantly suppressed in the pesVEGFR-2 and pEndo groups. Moreover, the total number of overall metastasis including the other organs was also decreased in these groups. However, pesVEGFR-2 was not able to decrease the number of lungs, ovaries, kidneys and adrenals with metastasis as counted by unilateral or bilateral metastasis. The number of CD34+/Lyve-1⁻ blood microvessels was significantly decreased in the pEndo group, while the number of CD34⁻/Lyve-1+ lymphatic vessels was significantly decreased in the pesVEGFR-2 and pEndo groups. In addition, a significant reduction in the number of dilated lymphatic vessels containing intraluminal cancer cells was observed in the pesVEGFR-2 and pEndo groups. Levels of apoptosis were significantly increased in the pEndo group, whereas the rates of cell proliferation were significantly decreased in the pesVEGFR-2 and pEndo groups.

CONCLUSIONS

Our data demonstrate that esVEGFR-2 can inhibit mainly lymph node metastasis. The antimetastatic activity of esVEGFR-2 may be of high clinical significance in the treatment of metastatic breast cancer because lymph node involvement is a most important prognostic factor in cancer patients.

VEGF and TNF up-regulate, NSAID down-regulate SOX18 protein level in HUVEC

Angiogenesis, the process of generating new blood vessels, is essential to embryonic development, organ formation, tissue regeneration and remodeling, reproduction and wound healing. Also, it plays an important role in many pathological conditions, including chronic inflammation and cancer. Angiogenesis is regulated by a complex interplay of growth factors, inflammatory mediators, adhesion molecules, morphogens and guidance molecules. Transcription factor SOX18 is transiently expressed in nascent endothelial cells during embryonic development and postnatal angiogenesis, but little is known about signaling pathways controlling its expression. The aim of this study was to investigate whether pro-angiogenic molecules and pharmacological inhibitors of angiogenesis modulate SOX18 expression in endothelial cells. Therefore, we treated human umbilical vein endothelial cells (HUVEC) with angiogenic factors, extracellular matrix proteins, inflammatory cytokines and nonsteroidal anti-inflammatory drugs (NSAID) and monitored SOX18 expression. We have observed that the angiogenic factor VEGF and the inflammatory cytokine TNF increase, while the NSAID ibuprofen and NS398 decrease the SOX18 protein level. These results for the first time demonstrate that SOX18 expression is modulated by factors and drugs known to positively or negatively regulate angiogenesis. This opens the possibility of pharmacological manipulation of SOX18 gene expression in endothelial cells to stimulate or inhibit angiogenesis.

Gene therapy for prostate cancer

Cancer remains a leading cause of morbidity and mortality. Despite advances in understanding, detection, and treatment, it accounts for almost one-fourth of all deaths per year in Western countries. Prostate cancer is currently the most commonly diagnosed noncutaneous cancer in men in Europe and the United States, accounting for 15% of all cancers in men. As life expectancy of individuals increases, it is expected that there will also be an increase in the incidence and mortality of prostate cancer. Prostate cancer may be inoperable at initial presentation, unresponsive to chemotherapy and radiotherapy, or recur following appropriate treatment. At the time of presentation, patients may already have metastases in their tissues. Preventing tumor recurrence requires systemic therapy; however, current modalities are limited by toxicity or lack of efficacy. For patients with such metastatic cancers, the development of alternative therapies is essential. Gene therapy is a realistic prospect for the treatment of prostate and other cancers, and involves the delivery of genetic information to the patient to facilitate the production of therapeutic proteins. Therapeutics can act directly (eg, by inducing tumor cells to produce cytotoxic agents) or indirectly by upregulating the immune system to efficiently target tumor cells or by destroying the tumor's vasculature. However, technological difficulties must be addressed before an efficient and safe gene medicine is achieved (primarily by developing a means of delivering genes to the target cells or tissue safely and efficiently). A wealth of research has been carried out over the past 20 years, involving various strategies for the treatment of prostate cancer at preclinical and clinical trial levels. The therapeutic efficacy observed with many of these approaches in patients indicates that these treatment modalities will serve as an important component of urological malignancy treatment in the clinic, either in isolation or in combination with current approaches.

Tumour angiogenesis: its mechanism and therapeutic implications in malignant gliomas

Angiogenesis is a key event in the progression of malignant gliomas. The presence of microvascular proliferation leads to the histological diagnosis of glioblastoma multiforme. Tumour angiogenesis involves multiple cellular processes including endothelial cell proliferation, migration, reorganisation of extracellular matrix and tube formation. These processes are regulated by numerous pro-angiogenic and anti-angiogenic growth factors. Angiogenesis inhibitors have been developed to interrupt the angiogenic process at the growth factor, receptor tyrosine kinase and intracellular kinase levels. Other anti-angiogenic therapies alter the immune response and endogeneous angiogenesis inhibitor levels. Most anti-angiogenic therapies for malignant gliomas are in Phase I/II trials and only modest efficacies are reported for monotherapies. The greatest potential for angiogenesis inhibitors may lie in their ability to combine safely with chemotherapy and radiotherapy.

Effects of a cyclooxygenase-1-selective inhibitor in a mouse model of ovarian cancer, administered alone or in combination with ibuprofen, a nonselective cyclooxygenase inhibitor

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to be potent inhibitors of the cyclooxygenases. The present study was designed to investigate the effects of a cyclooxygenase (COX)-1 inhibitor, SC-560, administered alone or in combination with ibuprofen on the growth inhibition of s.c. human ovarian SKOV-3 carcinoma and on angiogenesis. The effects of SC-560 and ibuprofen on tumor growth inhibition have been examined in mouse ovarian cancer models. Angiogenesis of both COX inhibitors was measured by reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. Prostaglandin E(2) (PGE(2)) levels in tumor tissues of mice were also determined by ELISA. The inhibitory rates in SC-560 group alone and in combination with ibuprofen group were 21.21% and 41.55%, respectively. In combination therapy with SC-560 and ibuprofen, tumor volumes were significantly reduced compared with that of control group (P < 0.05). In treatment groups, both COX inhibitors significantly reduced intratumor PGE(2) levels (all P < 0.01). Microvessel density (MVD) in tumor tissues were significantly decreased from 80.90 +/- 5.14 in vehicle-treated to 40.70 +/- 10.45 and 38.90 +/- 8.41 in SC-560 group alone and combination ibuprofen therapy (all P < 0.01). Ibuprofen was similar to the cyclooxygenase-1-selective inhibitor SC-560 in its ability to suppress the values of MVD of tumor tissues. SC-560 administered alone or in combination with ibuprofen inhibited the COX-associated up-regulation of VEGF. These studies demonstrate synergism between two COX inhibitors and that antiangiogenic therapy can be used to inhibit ovarian cancer growth.

AAV-HGFK1 and Ad-p53 cocktail therapy prolongs survival of mice with colon cancer

This study tried to evaluate the application of a novel cancer gene therapy using recombinant adeno-associated virus (AAV) carrying the kringle 1 domain of human hepatocyte growth factor (AAV-HGFK1) in combination with recombinant adenovirus carrying p53 gene (Ad-p53). BALB/c and nude mice models of colon cancer were established and the mice were treated with AAV-HGFK1 alone or in combination with Ad-p53. Combination of AAV-HGFK1 and Ad-p53 significantly prolonged the survival of the mice and also significantly inhibited primary and secondary tumor growth. Histochemical examination of the tumors revealed that AAV-HGFK1+Ad-p53 combinatorial treatment not only induced necrosis and apoptosis in the tumors but also suppressed tumor angiogenesis. The antiangiogenesis effect could likely be attributed to the ability of AAV-HGFK1+Ad-p53 viral cocktail to inhibit endothelial cell migration and proliferation. AAV-HGFK1+Ad-p53 also inhibited tumor cell growth in vitro by inhibiting epidermal growth factor receptor phosphorylation. Therefore, AAV-HGFK1+Ad-p53 cocktail therapy has a significantly higher therapeutic effect than AAV-HGFK1 or Ad-p53 alone and is a novel promising gene therapy for colon cancer.

Tumor escape from endogenous, extracellular matrix-associated angiogenesis inhibitors by up-regulation of multiple proangiogenic factors

PURPOSE

Thrombospondin-1 (Tsp1), endostatin, and tumstatin are extracellular matrix-associated proteins that inhibit angiogenesis. We examined the mechanisms by which tumor cells may bypass the antiangiogenic effects of these endogenous regulators.

EXPERIMENTAL DESIGN

CT26 colon and RenCa renal carcinoma cells were stably transfected with Tsp1, endostatin, or tumstatin cDNA. Subcutaneous and metastatic tumor growth in syngeneic mice was analyzed. Expression of proangiogenic factors in resulting tumors was measured by quantitative real-time PCR. The combination of Tsp1 and vascular endothelial growth factor (VEGF) receptor-2 inhibition was also examined.

RESULTS

There was significant suppression of angiogenesis in flank tumors and liver metastases formed from cells overexpressing Tsp1, endostatin, or tumstatin. However, all tumors ultimately escaped angiogenesis inhibition. The combination of all three angiogenesis inhibitors had no additive effect beyond overexpression of a single inhibitor. Using quantitative real-time PCR, we found that VEGF and platelet-derived growth factor (PDGF)-A levels were routinely up-regulated at least 5-fold in all CT26 tumors overexpressing any antiangiogenic protein, and there were variable increases in angiopoietin 2 (Ang2), basic fibroblast growth factor, and PDGF-B. In contrast, RenCa tumors, which have high baseline levels of VEGF and PDGF-B, relied on basic fibroblast growth factor, Ang1, and PDGF-A up-regulation to counteract Tsp1 overexpression. Growth of CT26 cells with Tsp1 overexpression was suppressed when anti-VEGFR-2 treatment was added.

CONCLUSIONS

Cancer cells with overexpression of three different endogenous angiogenesis inhibitor eventually escape angiogenesis inhibition by up-regulation of various proangiogenic factors. Tsp1, endostatin, and tumstatin may be functionally redundant in this system. These endogenous angiogenesis inhibitors are likely best used in combination with the blockade of proangiogenic pathways or with traditional chemotherapy or radiation therapy.

Electrogene therapy using endostatin, with or without suicide gene therapy, suppresses murine mammary tumor growth and metastasis

Syngeneic inoculated metastatic mammary cancers received direct intratumoral injection of a plasmid vector containing either endostatin (pEndo) with or without a suicide gene (pHSVtk), pHSVtk alone or control vector once a week for 8 weeks. We applied electrogene transfer to the tumors after each injection and administered ganciclovir (GCV) to pHSVtk-transfected mice using an osmotic minipump. Anticancer efficacy was monitored using a variety of parameters, namely tumor volume, intratumoral microvessel density and DNA synthesis, number of mice with metastasis, and number of sites of metastasis per mouse. Tumor volume was significantly lower in all therapeutic groups, with the most effective growth suppression in the pEndo+pHSVtk/GCV group. Lymph node metastasis was significantly less frequent in all therapeutic groups, whereas the multiplicity of lung metastases was significantly lower only in the pEndo and pEndo+pHSVtk/GCV groups. All therapeutic groups showed significantly lower intratumor microvessel density and DNA synthesis. The pEndo and pEndo+pHSVtk/GCV groups also showed a significant reduction in the numbers of dilated lymphatic vessels containing intralumenal tumor cells. Our data suggest that endostatin electrogene therapy alone or in combination with pHSVtk/GCV suicide gene therapy is more beneficial than suicide gene therapy alone. The observed antimetastatic activity of endostatin may be of high clinical significance in the treatment of metastatic breast cancer.

Antitumor efficacy of AAV-mediated systemic delivery of interferon-beta

Type I interferons (alpha/beta) have significant antitumor activity although their short half-life and systemic side effects have limited their clinical utility. An alternative dosing schedule of continuous, low-level delivery, as is achieved by gene therapy, rather than intermittent, high concentration pulsed-dosing, might avoid the toxicity of interferon while maintaining its antitumor efficacy. We have tested a gene therapy approach in murine tumor models to treat malignancies that have shown responsiveness to interferon in clinical trials. The tumor cell lines used were moderately sensitive to the direct effects of human interferon-beta (hIFN-beta) in vitro. For in vivo testing, systemic delivery of hIFN-beta was generated following liver-targeted delivery of adeno-associated virus (AAV) vector carrying the hIFN-beta transgene. This prevented engraftment of subcutaneous human gliomas, and orthotopic, localized (intrarenal) and disseminated (primarily pulmonary) human renal cell carcinomas; and caused regression of established tumors at these sites. In a syngeneic, immunocompetent model of melanoma, AAV IFN-beta treatment limited subcutaneous tumor growth and prevented disseminated disease. A significant decrease in mean intratumoral vessel density was demonstrated in hIFN-beta-treated tumors, suggesting that in addition to a direct tumoricidal effect, the antitumor efficacy of AAV IFN-beta in this study was due to its ability to inhibit angiogenesis.

Suppression of tumor growth by intra-muscular transfer of naked DNA encoding adrenomedullin antagonist

We have recently reported that the intra-tumoral injection of adrenomedullin (AM) antagonist (AMA; AM (22-52)) peptides significantly reduced the in vivo growth of a pancreatic cancer cell line in severely combined immunodeficient (SCID) mice. In the present study, we examined the effects of intra-tumoral and intra-muscular transfers of naked DNA encoding AMA on the in vivo growth of cancer cell lines. We demonstrate that these treatments induce the regression of a pancreatic cancer cell line and a breast cancer cell line inoculated in SCID mice. Furthermore, CD31-positive cells disappear completely from tumor tissues, following treatment, indicating that neo-vascularization is entirely inhibited. These results suggest that the intra-tumoral or intra-muscular transfer of naked DNA encoding AMA might be a promising alternative modality for treating human cancers.

Angiostatin is directly cytotoxic to tumor cells at low extracellular pH: a mechanism dependent on cell surface-associated ATP synthase

Angiostatin, a proteolytic fragment of plasminogen, is a potent angiogenesis inhibitor able to suppress tumor growth and metastasis through inhibition of endothelial cell proliferation and migration. Previously, we showed that angiostatin binds and inhibits F(1)F(o) ATP synthase on the endothelial cell surface and that anti-ATP synthase antibodies reduce endothelial cell proliferation. ATP synthase also occurs on the extracellular surface of a variety of cancer cells, where its function is as yet unknown. Here, we report that ATP synthase is present and active on the tumor cell surface, and angiostatin, or antibody directed against the catalytic beta-subunit of ATP synthase, inhibits the activity of the synthase. We show that tumor cell surface ATP synthase is more active at low extracellular pH (pH(e)). Low pH(e) is a unique characteristic of the tumor microenvironment. Although the mechanism of action of angiostatin has not been fully elucidated, angiostatin treatment in combination with acidosis decreases the intracellular pH (pH(i)) of endothelial cells, leading to cell death. We also find that, at low pH(e), angiostatin and anti-beta-subunit antibody induce intracellular acidification of A549 cells, as well as a direct cytotoxicity that is absent in tumor cells with low levels of extracellular ATP synthase. These results establish angiostatin as an antitumorigenic and antiangiogenic agent through a mechanism implicating tumor cell surface ATP synthase. Furthermore, these data provide evidence that extracellular ATP synthase plays a role in regulating pH(i) in cells challenged by acidosis.

Angiogenic and antiangiogenic gene therapy

Gene therapy is thought to be a promising method for the treatment of various diseases. One gene therapy strategy involves the manipulations on a process of formation of new vessels, commonly defined as angiogenesis. Angiogenic and antiangiogenic gene therapy is a new therapeutic approach to the treatment of cardiovascular and cancer patients, respectively. So far, preclinical and clinical studies are successfully focused mainly on the treatment of coronary artery and peripheral artery diseases. Plasmid vectors are often used in preparations in angiogenic gene therapy trials. The naked plasmid DNA effectively transfects the skeletal muscles or heart and successfully expresses angiogenic genes that are the result of new vessel formation and the improvement of the clinical state of patients. The clinical preliminary data, although very encouraging, need to be well discussed and further study surely continued. It is really possible that further development of molecular biology methods and advances in gene delivery systems will cause therapeutic angiogenesis as well as antiangiogenic methods to become a supplemental or alternative option to the conventional methods of treatment of angiogenic diseases.

Tumor vascular targeting therapy with viral vectors

Tumor angiogenesis is crucial for the progression and metastasis of cancer. The vasculature of tumor tissue is different from normal vasculature. Therefore, tumor vascular targeting therapy could represent an effective therapeutic strategy with which to suppress both primary tumor growth and tumor metastasis. The use of viral vectors for tumor vascular targeting therapy is a promising strategy based on the unique properties of viral vectors. In order to circumvent the potential problems of antiviral neutralizing antibodies, poor access to extravascular tumor tissue, and toxicities to normal tissue, viral vectors need to be modified to target the tumor endothelial cells. Viral vectors that could be used for tumor vascular targeting therapy include adenoviral vectors, adeno-associated viral vectors, retroviral vectors, lentiviral vectors, measles virus, and herpes simplex viral vectors. In this review, we will summarize the strategies available for targeting viral vectors for tumor vascular targeting therapy.

Chronic gene delivery of interferon-inducible protein 10 through replication-competent retrovirus vectors suppresses tumor growth

Sustained maintenance of therapeutic levels of angiostatic proteins in tumor tissues continues to represent a major challenge to antiangiogenesis therapy of cancer. In this study, we tested the hypothesis of utilizing gene transfer via replication-competent retroviral (RCR) vectors for chronic protein delivery. We now show that bioactive human interferon-inducible protein-10 (IP10) can be secreted from a variety of mammalian cells upon transduction with RCR vectors carrying the human IP10 gene. The production of IP10 from RCR-transduced cells could be maintained for at least three months in culture. The level and duration of IP10 expression in vivo was sufficient to inhibit growth of subcutaneous (s.c.) tumors as well as metastatic lesions in mice. This tumor inhibition was correlated to a marked reduction in tumor vascularization and mitotic activity. By conducting immunohistological studies, we have been able to show that IP10 vector-affected tumors evidenced elevated levels of IL-12p35 mRNA, with no sign of changes in the local inflammatory response, however, as determined by macrophage infiltration and the expression of proinflammatory cytokines. We are addressing the feasibility of using RCR vector-based gene therapy as a more convenient alternative tool to chronically deliver antiangiogenic proteins for cancer therapy.

A reassessment of vascular endothelial growth factor in central nervous system pathology

✓ Overexpression of vascular endothelial growth factor (VEGF) is associated with several central nervous system (CNS) diseases and abnormalities, and is often postulated as a causative factor and promising therapeutic target in these settings. The authors' goal was to reassess the contribution of VEGF to the biology and pathology of the CNS.

The authors review the literature relating to the following aspects of VEGF: 1) the biology of VEGF in normal brain; 2) the involvement of VEGF in CNS disorders other than tumors (traumatic and ischemic injuries, arteriovenous malformations, inflammation); and 3) the role of VEGF in brain tumor biology (gliomas and the associated vasogenic edema, and hemangioblastomas).

The authors conclude the following: first, that VEGF overexpression contributes to the phenotype associated with many CNS disorders, but VEGF is a reactive rather than a causative factor in many cases; and second, that use of VEGF as a therapeutic agent or target is complicated by the effects of VEGF not only on the cerebral vasculature, but also on astrocytes, neurons, and inflammatory cells. In many cases, therapeutic interventions targeting the VEGF/VEGF receptor axis are likely to be ineffective or even detrimental. Clinical manipulation of VEGF levels in the CNS must be approached with caution.

Delivery of antiangiogenic agents for cancer gene therapy

The understanding that tumor growth and metastasis are angiogenesis dependent processes has led to interest in targeting tumor vasculature in anticancer therapy. Furthermore, recent insights into the molecular interactions that orchestrate physiologic and pathologic angiogenesis have resulted in a variety of antiangiogenic strategies. A gene therapy-mediated approach for the delivery of antiangiogenic agents has several advantages, including the potential for sustained expression. However, the choice of angiogenesis inhibitor, method of gene delivery, and target/site for transgene expression are important variables to be considered when designing this approach. Here we review the major alternatives within each of these categories and provide illustrative examples of their use in preclinical models.

Interferon-mediated anti-angiogenic therapy for neuroblastoma

Angiogenesis appears to be a fundamental requirement for tumor growth, invasion and metastasis. Evidence also exists to suggest that inhibition of tumor-associated angiogenesis can retard tumor growth and prevent tumor spread. Several naturally occurring angiogenesis inhibitors have been identified, including type I interferons (alpha/beta). These proteins are potent inhibitors of angiogenesis and may also have direct anti-tumor and immunomodulatory effects. Because anti-angiogenic therapy is likely cytostatic, long-term delivery of angiogenesis inhibitors may be required for the successful treatment of cancer. We have, therefore, explored the utility of a gene therapy-mediated approach for the delivery of interferon-beta and tested this approach, both alone and in combination with conventional chemotherapy, in murine models of neuroblastoma.

Careful decoy receptor titering is required to inhibit tumor angiogenesis while avoiding adversely altering VEGF bioavailability

To inhibit tumor-induced angiogenesis, the VEGF signaling pathway was targeted using AAV vectors encoding a VEGF decoy receptor, a truncated, soluble form of the murine VEGF receptor-2 (tsFlk-1). This approach initially had significant anti-neuroblastoma efficacy in murine xenograft models of local and metastatic disease, but when higher circulating levels of tsFlk-1 were established, tumor growth was more aggressive than even in control mice. Part of the mechanism for this apparent tumor resistance was increased human VEGF expression by the tumor cells. However, further investigation revealed that although a greater amount of VEGF could be bound by higher levels of tsFlk-1, more VEGF also existed in an unbound state and was, therefore, available to support angiogenesis. This novel, tumor-independent mechanism for resistance to antiangiogenic strategies suggests that careful titering of angiogenesis inhibitors may be required to achieve maximal antitumor efficacy and avoid therapy resistance mediated, in part, by ligand bioavailability. This has important implications for therapeutic strategies that use decoy receptors and other agents, such as antibodies, to bind angiogenic factors, in an attempt to inhibit tumor neovascularization.

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.

Expression of human apolipoprotein(a) kringles in colon cancer cells suppresses angiogenesis-dependent tumor growth and peritoneal dissemination

BACKGROUND

Anti-angiogenesis therapy has been regarded as a promising treatment of cancer based on the fact that most tumors and their metastasis are angiogenesis-dependent. Gene therapy can potentially expand the horizons of tumor angiogenesis therapy by virtue of its ability to produce high concentrations of therapeutic agents in a local area for a sustained period. The present study was performed to evaluate the therapeutic potential of gene therapy for the treatment of cancer and metastasis.

METHODS

The murine colon carcinoma cell line CT26 was manipulated ex vivo to express an anti-angiogenic molecule, LK68, consisting of human apolipoprotein(a) kringle domains, KIV(9)-KIV(10)-KV, using retrovirus-mediated gene transfer. Its effects on colon tumor growth and metastasis were evaluated in experimental animal models established by injecting LK68-expressing and control CT26 cells subcutaneously or into the peritoneal cavity of BALB/c mice, respectively.

RESULTS

Expression of LK68 significantly suppressed colon tumor growth in mice, but did not influence the growth of tumor cells in vitro. Immunohistochemical analysis of tumor tissues revealed a significant reduction in microvessel density in LK68-expressing tumors. Thus, the suppression of tumor growth appears to result mainly from inhibition of tumor angiogenesis. This decrease in vessel density is correlated with a notable increase in tumor cell apoptosis in vivo, but has no influence on proliferation. Moreover, expression of LK68 prevents peritoneal dissemination, and consequently improves overall host survival.

CONCLUSIONS

These results collectively indicate that a gene therapy strategy using LK68 cDNA is useful for the treatment for both colon tumor growth and peritoneal dissemination.

Suppression of Colorectal Cancer Liver Metastasis and Extension of Survival by Expression of Apolipoprotein(a) Kringles

The formation of hepatic metastases in colorectal cancer is the main cause of patient death. Current therapies directed at hepatic metastasis of colorectal cancer have had minimal impact on outcome. Therefore, alternative treatment strategies for liver metastasis require development. The present study was performed to evaluate the application of cDNA of LK68 encoding apolipoprotein(a) kringles IV-9, IV-10, and V as possible candidates for gene therapy treatment of this life-threatening disease. The murine colorectal cancer cell line CT26 was transduced ex vivo with LK68 cDNA via retroviral gene transfer, and an experimental model of hepatic metastasis was established by injecting LK68-expressing and control cells into the spleens of BALB/c mice. Expression of LK68 did not affect the growth characteristics and viability of transduced CT26 cells in vitro. LK68 produced from CT26 cells substantially inhibited the migration of endothelial cells in vitro. In vivo, substantial suppression of liver metastasis and prolonged survival were observed in mice bearing LK68-expressing CT26 cells, compared with controls. LK68-expressing liver metastases were restricted to smaller sizes and displayed decreased microvessel density and increased tumor cell apoptosis. Our data collectively indicate that LK68 suppresses angiogenesis-dependent progression of prevascular micrometastases to macroscopic tumors and their growth, which are clinically accessible and biologically relevant therapeutic targets. We propose that antiangiogenic gene therapy with LK68 is a promising strategy for the treatment of colorectal cancer liver metastasis.

Early genetic mechanisms underlying the inhibitory effects of endostatin and fumagillin on human endothelial cells

A tumor needs to initiate angiogenesis in order to develop its own blood supply, to grow, to invade, and to spread. Angiogenesis, under normal conditions, is a tightly regulated balance between endogenous pro- and antiangiogenic factors. In this study, we investigated, by microarray analysis, the effects of two known antiangiogenic agents (endostatin and fumagillin) on the gene expression profiles of human umbilical vein endothelial cells (HUVEC) in order to elucidate pathways common to the effects of these agents. We observed a majority of gene expression changes within 1 and 2 h of treatment. The genes demonstrating these early expression changes are involved in cell proliferation, gene transcription, and a number have unknown functions. We selected four genes (DOC1, KLF4, TC-1, ID1) from the microarray profile that showed a similar pattern of expression for both of the antiangiogenic agents we tested. We then used small interfering RNAs (siRNA) in an attempt to better understand the role of these selected genes in the inhibitory activity of these agents. Because the gene expression changes occurred within 1 and 2 h of treatment, these genes might be involved in the initial pathways of angiogenesis inhibition.

Parvovirus vectors for cancer gene therapy

Parvoviruses comprise a group of single-stranded DNA viruses with greater potential for gene therapy applications. Unique characteristics of paroviruses, such as non-pathogenicity, antioncogenicity and methods of efficient recombinant vector production, have drawn more attention towards utilising parvovirus-based vectors in cancer gene therapy. Although > 30 different parvoviruses have been identified so far, recombinant vectors derived from adeno-associated virus (AAV), minute virus of mice (MVM), LuIII and parvovirus H1 have been successfully tested in many preclinical models of human diseases, including cancer. The present article will focus on the potential of non-replicating and autonomously replicating parvoviral vectors in cancer gene therapy, including strategies that target tumour cells directly or indirectly.

Targeted molecular imaging

Molecular imaging aims to visualize the cellular and molecular processes occurring in living tissues, and for the imaging of specific molecules in vivo, the development of reporter probes and dedicated imaging equipment is most important. Reporter genes can be used to monitor the delivery and magnitude of therapeutic gene transfer, and the time variation involved. Imaging technologies such as micro-PET, SPECT, MRI and CT, as well as optical imaging systems, are able to non-invasively detect, measure, and report the simultaneous expression of multiple meaningful genes. It is believed that recent advances in reporter probes, imaging technologies and gene transfer strategies will enhance the effectiveness of gene therapy trials.

Endothelial progenitor cells’ ‘homing’ specificity to brain tumors

Current treatment of malignant glioma brain tumors is unsatisfactory. Gene therapy has much promise, but target-specific vectors are needed. Endothelial progenitor cells (EPCs) have in vivo homing specificity to angiogenic sites and are thus potential vehicles for site-specific gene therapy. However, reports of EPCs "homing" to intracranial solid tumors are lacking. We investigated EPCs' "homing" specificity using a murine intracranial glioma model. EPCs, derived from human cord blood, were labeled with a fluorogenic agent CFSE and intravenously injected into SCID mice bearing orthotopic gliomas. At 7-14 days after EPC injection, mouse brains and other vital organs were examined for distribution of transplanted EPCs. As controls, CFSE-labeled human umbilical vein endothelial cells (HUVECs) and EPCs were intravenously injected into matched glioma SCID mice (HUVEC control groups) and nontumor SCID mice (nontumor-bearing control groups), respectively. Fluorescence image analysis revealed that systemically transplanted EPCs 'homed' to brain tumors with significantly higher specificity as compared to other organs within the experimental group (P<0.001) and to anatomically matched brain sections from the control groups (P<0.001). Our study demonstrates EPCs' in vivo tropism for intracranial gliomas, with potential for cell delivery of brain tumor spatial-specific gene therapy.

Antiangiogenic therapy for the treatment of pediatric solid malignancies

Although the past 30 years have seen remarkable progress in the treatment of childhood malignancies, not all types of cancer have enjoyed this improvement in prognosis. Because of this, clinical trials are ongoing in which novel treatment approaches are being evaluated, including immunotherapy, radionuclide therapy, and the use of agents that induce tumor apoptosis or differentiation. Additional treatment strategies are needed, however. One such strategy involves the use of angiogenesis inhibitors. Angiogenesis is the biologic process of new blood vessel formation. In addition to occurring as part of several normal, physiologic processes, angiogenesis is an essential component of a number of pathologic conditions, including cancer. Compelling data suggest that inhibition of angiogenesis can not only prevent tumor-associated neovascularization but also affect tumor growth and spread. An anticancer approach in which the tumor-induced new blood vessels are targeted is particularly appealing for several reasons. First, despite the extreme molecular and phenotypic heterogeneity of human cancer, it is likely that most, if not all, tumor types require neovascularization to achieve their full malignant phenotype. Therefore, antiangiogenic therapy may have broad applicability for the treatment of human cancer, as well as the many other pathologic processes that depend on angiogenesis. Second, the endothelial cells, although rapidly proliferating, are inherently normal with a very low rate of mutation. They are, therefore, unlikely to evolve an angiogenesis inhibitor-insensitive phenotype. This is in distinction to the rapidly proliferating tumor cells that do undergo a high rate of spontaneous mutation and therefore can readily generate drug-resistant clones. This review discusses progress in the development of antiangiogenic therapy for the treatment of pediatric solid tumors.

Effect of Tinospora cordifolia on the cytokine profile of angiogenesis-induced animals

The antiangiogenic activity of Tinospora cordifolia was studied using in vivo as well as in vitro models. In vivo antiangiogenic activity was studied using B16F10 melanoma cell-induced capillary formation in animals. Intraperitoneal administration of the extract at a concentration of 20 mg/kg significantly inhibited the tumour directed capillary formation induced by melanoma cells. Analysis of the serum cytokine profile showed a drastic increase of proinflammatory cytokines such as IL-1beta, IL-6, TNF-alpha, granulocyte monocyte-colony stimulating factor (GM-CSF) and the direct endothelial cell proliferating agent vascular endothelial cell growth factor (VEGF) in the angiogenesis-induced control animals. Administration of Tinospora extract could differentially regulate these cytokine's elevation. The differential regulation is further evidenced by the increased production of antiangiogenic agents IL-2 and tissue inhibitor of metalloprotease-1 (TIMP-1) in the B16F10-injected, extract-treated animals. Moreover, using an in vitro rat aortic ring assay, it was observed that the extract at nontoxic concentrations inhibited the production of proangiogenic factors from B16F10 melanoma cells. Direct treatment of the extract also inhibits the microvessel outgrowth from the aortic ring. Hence, the observed antiangiogenic activity of the plant T. cordifolia is related, at least in part, to the regulation of the levels of these cytokines and growth factors in the blood of the angiogenesis-induced animal.

Single-chain antibody and its derivatives directed against vascular endothelial growth factor: application for antiangiogenic gene therapy

Single-chain antibodies (scFv) have an enormous potential for clinical application. However, rapid blood clearance and difficulties in large-scale production of active scFvs have limited the practical use of these antibody fragments. Recently, an anti-vascular endothelial growth factor (VEGF) scFv (scFv V65) was selected in our laboratory from a human antibody phage-display library. This antibody was able to reduce tumor growth in mice by approximately 50%. Here, we employ a gene therapy strategy for sustained in vivo expression of scFv V65 and its derivatives. scFv fusion proteins containing parts of the constant IgG1 region were generated (minibody and scFv V65-Fc) to increase the serum half-life of the scFv V65. Systemic administration of recombinant adenovirus encoding scFv V65 resulted in substantial tumor inhibition. This effect could be improved by multiple virus injections. We found that the efficacy of different scFv V65 formats was dependent on the mode of administration: whereas scFv V65-Fc was the most efficient when expressed locally, scFv V65 was superior when delivered systemically. Our results show that therapeutic levels of scFv V65 can be obtained by systemic injection of recombinant adenoviruses. Therefore, therapeutic gene delivery of scFv is a feasible strategy that overcomes several limitations of conventional antibody therapy.

Adenovirus-mediated gene therapy with an antiangiogenic fragment of thrombospondin-1 inhibits human leukemia xenograft growth in nude mice

Recent investigations support the idea that angiogenesis is involved in the pathophysiology of leukemia. Within a given microenvironment, the angiogenic response is regulated by a delicate balance of angiogenesis inducers and inhibitors. Thrombospondin-1 (TSP-1) is a multifunctional extracellular glycoprotein showing angiostatic properties in multiple in vitro and in vivo assays. Interestingly, there is also proangiogenic domain in this complex molecule. Development of TSP-1 as an antiangiogenic drug has been hindered by multiplicity of its functional effects, difficulties in its production and its poor pharmacokinetics. The aim of the present study was to establish a recombinant adenovirus (ADV.TSP-1(f)) expressing antiangiogenic fragment of TSP-1 (TSP-1(f)), and to determine the feasibility for use of the adenovirally expressed TSP-1(f) in leukemia gene therapy. The results of this investigation showed that TSP-1(f) was expressed efficiently in adenovirus-transduced human myelogenous leukemia K562 cells. Compared to the controls, although there was almost no effect on proliferation of K562 cells in vitro, adenovirus-mediated TSP-1(f) transduction inhibited the growth of K562 xenografts dramatically. Furthermore, the microvessel density (MVD) was much lower in the ADV.TSP-1(f)-treated tumors compared to the controls. These data support the use of in vivo gene delivery approach to produce antiangiogenic fragment of TSP-1 for leukemia therapy.

Antiangiogenic gene therapy for hepatocellular carcinoma using angiostatin gene

Recent studies have reported that antiangiogenic gene delivery into cancer cells inhibits growth of certain tumors in vivo. Hepatocellular carcinoma (HCC) is a hypervascular cancer, and antiangiogenic gene therapy might be suitable for HCC. In the present study, we investigated the antiangiogenic effects of angiostatin gene transduction into HCC both in vitro and in vivo. Angiostatin gene was cloned into a pSecTag2B mammalian expression vector to construct pSecTag2B-ANG. pSecTag2B or pSecTag2B-ANG were transfected into an HCC cell line, PLC/PRF/5, and then stable transfectants were obtained by Zeocin selection. pSecTag2B or pSecTag2B-ANG transfection did not alter the expression of vascular endothelial growth factor (VEGF), a potent angiogenic stimulator, or pigment epithelium-derived factor (PEDF), an angiogenic inhibitor, in PLC/PRF/5 cells. However, conditioned media (CM) derived from pSecTag2B-ANG-transfected PLC/PRF/5 cells (CM-ANG) suppressed the proliferation and migration of human umbilical vein endothelial cells (HUVEC) by 35% and 50%, respectively, relative to their effects on nontransfected cells. In in vivo experiments, pSecTag2B-ANG stable transfected (CM-Mock) and nontransfected cells (CM-N) were mixed at various proportions and the mixed cells were subcutaneously implanted into athymic mice. Suppression of tumor growth was noted in mice implanted with angiostatin gene-transfected cells, and such suppression was proportional with the percentage of transfected cells. Analysis of the vascular density in these tumors showed that the tumor growth suppression effect of angiostatin gene correlated with suppression of tumor vascularity. In conclusion, antiangiogenic gene therapy using angiostatin gene is potentially suitable for the treatment of patients with HCC.

Systemic administration of a recombinant adenovirus encoding a HSA-Angiostatin kringle 1-3 conjugate inhibits MDA-MB-231 tumor growth and metastasis in a transgenic model of spontaneous eye cancer

We previously reported that intratumoral injection of AdK3, a recombinant adenovirus encoding human angiostatin kringle (K) 1 to 3, inhibits tumor vascularization and tumor growth. To reduce the serum clearance of this factor, we constructed an adenovirus (AdK3-HSA) that carries a chimeric gene encoding a fusion protein between angiostatin K1-3 and human serum albumin (HSA). This conjugate inhibited endothelial cell proliferation as efficiently as K1-3. K3-HSA serum concentrations in immunodeficient mice systemically injected with AdK3-HSA were dramatically higher than in AdK3-injected mice. Furthermore, the growth of MDA-MB-231 tumors grafted into nude mice that had been injected intravenously with AdK3-HSA was inhibited by 79% (versus 17% with AdK3). In TRP-1/SV40 Tag transgenic mice, which spontaneously develop eye tumors with brain metastases, intravenous injections of AdK3-HSA in newborn mice blocked metastatic dissemination efficiently and significantly, and prolonged survival by 3 weeks. After 2 months, only 46% of AdK3-HSA-treated animals developed micrometastases, whereas 94% of the AdCO1-injected group displayed numerous macrometastases. Nevertheless, ocular tumor growth was not modified because of impaired diffusion of the conjugate in the eye compartment. Our results show that HSA genetic coupling is an efficient way to increase the pharmacokinetics of circulating angiogenic inhibitors and thus their antitumoral activity.

Armed therapeutic viruses: strategies and challenges to arming oncolytic viruses with therapeutic genes

Oncolytic viruses are attractive therapeutics for cancer because they selectively amplify, through replication and spread, the input dose of virus in the target tumor. To date, clinical trials have demonstrated marked safety but have not realized their theoretical efficacy potential. In this review, we consider the potential of armed therapeutic viruses, whose lytic potential is enhanced by genetically engineered therapeutic transgene expression from the virus, as potential vehicles to increase the potency of these agents. Several classes of therapeutic genes are outlined, and potential synergies and hurdles to their delivery from replicating viruses are discussed.

Prospective analysis of circulating endostatin levels in patients with renal cell carcinoma

BACKGROUND

The aim of the current study was to assess circulating levels of endogenous endostatin in patients with renal carcinoma and to determine the relationship of these levels to circulating levels of vascular endothelial growth factor (VEGF) and prognosis.

METHODS

The authors prospectively studied 66 patients (48 male, 18 female; mean age, 50 years) undergoing nephrectomy for renal carcinoma on clinical trials at the National Cancer Institute. Metastases were present in 51 of 66 patients (77%) at the time of nephrectomy. Preoperative and followup serum endostatin and VEGF levels were determined using competitive enzyme immunoassays and compared to a group of 32 age- and gender-matched healthy controls. Associations between circulating endostatin levels and clinicopathologic variables, including survival, were determined.

RESULTS

Preoperative endostatin levels were higher in renal carcinoma patients than in healthy controls (P = 0.05). There was a weak to moderate correlation between pretreatment serum endostatin levels and serum VEGF levels (r = 0.47; P = 0.001), and levels of both proteins increased significantly following nephrectomy (P < 0.0001 and P < 0.0001, respectively; n = 41). In addition, patients whose endostatin levels increased more than twofold after nephrectomy had significantly poorer prognoses than patients without such an increase (P = 0.018). This association was more pronounced when patients without metastases were excluded (P = 0.0037).

CONCLUSIONS

Circulating endostatin levels are elevated in patients with renal carcinoma and correlate with circulating VEGF levels. Endostatin levels increase after nephrectomy, and patients with the greatest increases experience shortened survival times. These findings suggest an association between tumor aggressiveness and the production of endogenous endostatin in patients with renal carcinoma.

Electrotransfer of gene encoding endostatin into normal and neoplastic mouse tissues: inhibition of primary tumor growth and metastatic spread

Electroporation-mediated gene transfer relies upon direct delivery of plasmids into cells permeabilized by electric fields, a method more efficient than transfer using nonviral vectors, although neither approaches the transfer efficiency of viral vectors. Here we studied electrotransfer of a gene encoding an angiogenesis inhibitor (endostatin) into primary tumors and muscle tissues, which would serve as a site of synthesis and secretion into the bloodstream of a therapeutic antimetastatic protein with systemic effects. Optimum electroporation conditions (voltage, number and duration of impulses, separation of caliper electrodes) were first established to maximize expression of a reporter gene transferred into murine Renca kidney carcinoma, B16(F10) melanoma, or skeletal muscle tissues. In neoplastic tissues, electrotransfer of plasmid DNA was far more efficient than electroporation with lipoplexes, but no differences between naked DNA and lipoplexes were found in case of electroporated muscles. We then studied the electrotransfer of plasmid DNA carrying the endostatin gene into pre-established experimental Renca tumors. A significant inhibition of tumor growth was observed in animals electroporated with this construct. Electrotransfer of the endostatin gene into muscle tissues resulted in reduced numbers of experimental B16(F10) metastases in the lungs. This study clearly shows that electroporation may be used to efficiently transfer antiangiogenic genes into both normal and neoplastic tissues.

Thromboembolic disease and cancer: possible new treatments

Hypoxia-induced endothelin (ET) and vascular endothelial growth or permeability factor (VEGF) play an important role in tumor biology by promoting angiogenesis. Angiogenesis alters hemostasis and promotes thromboembolic disease (TED). Therapeutic angiogenesis directed against ET and VEGF may reduce the incidence of TED in cancer patients.

Transcriptional targeting of conditionally replicating adenovirus to dividing endothelial cells

Conditionally replicating adenoviruses (CRADs) are a novel strategy in cancer treatment and clinical trials using CRADs targeted to tumor cells have been reported recently. We hypothesized that it would be possible to construct CRADs targeted to dividing endothelial cells, which are present in the tumor endothelium. We utilized the regulatory elements of Flk-1 and endoglin genes, which have been shown to be highly overexpressed in angiogenic endothelial cells, to construct two CRADs: Ad.Flk-1, which has adenoviral E1A gene under the control of the Flk-1 enhancer/promoter, and Ad.Flk-Endo, which harbors the same Flk-1 enhancer/promoter as Ad.Flk-1, plus it has the adenoviral E1B gene under control of the endoglin promoter. Viral titer measurements by plaque assay showed that in human umbilical vein endothelial cells (HUVECs), both CRADs replicated at levels comparable to that of wild-type adenovirus. In Flk-1 and endoglin negative Hep3B and A549 cells, however, the replication of Ad.Flk-1 and Ad.Flk-Endo was reduced by 30-fold and 600-fold, respectively. Cytotoxicity assays demonstrated that both CRADs killed HUVECs as effectively as wild-type adenovirus and their cytotoxicity in Hep3B and A549 cells was comparable to nonreplicating control adenovirus. Furthermore, there was a striking inhibition (83-91%) of capillary network formation in an in vitro angiogenesis assay when HUVECs were infected with Ad.Flk-1 or Ad.Flk-Endo as compared with the nonreplicating control virus. These results demonstrate that CRADs can be transcriptionally targeted to dividing endothelial cells with high specificity, and that the combined use of Flk-1 and endoglin regulatory elements has a synergistic effect on targeting specificity. This principle may be incorporated into novel therapeutic agents to develop anti-angiogenic treatment for cancer.

The X-ray crystallographic structure of the angiogenesis inhibitor angiostatin

Angiogenesis inhibitors have gained much public attention recently as anti-cancer agents and several are currently in clinical trials, including angiostatin (Phase I, Thomas Jefferson University Hospital, Philadelphia, PA). We report here the bowl-shaped structure of angiostatin kringles 1-3, the first multi-kringle structure to be determined. All three kringle lysine-binding sites contain a bound bicine molecule of crystallization while the former of kringle 2 and kringle 3 are cofacial. Moreover, the separation of the kringle 2 and kringle 3 lysiner binding sites is sufficient to accommodate the alpha-helix of the 30 residue peptide VEK-30 found in the kringle 2/VEK-30 complex. Together the three kringles produce a central cavity suggestive of a unique domain where they may function in concert.