Angiogenesis-regulating cytokines: activities and interactions

Mechanisms Involved in Apice Closure of Pulpless Teeth – Literature Review

Background:

Unfinished root formation has always offered challenges in endodontics due to technical difficulties and weakened teeth resistance during the lifetime of an individual. Pulp revascularization therapy appeared as a solution for apical closure and root maturation. The existence of oral stem cells involved in the process associated with traditional resident cells requires adequate blood supply given by induced controlled injury deliberately accomplished into the periapical zone.

Objective:

The aim of this work was to research, through literature review, the main mechanisms involved in the process of apical closure through the technique of pulp revascularization.

Conclusion:

Apice closure in pulpless teeth seems to happen as a result of professional intervention and biological activity. The success rate depends on the role of traditional local immune cells and stem cells associated with adequate blood supply to finish root formation.

Epigalloccatechin-3-gallate inhibits ocular neovascularization and vascular permeability in human retinal pigment epithelial and human retinal microvascular endothelial cells via suppression of MMP-9 and VEGF activation

Epigalloccatechin-3-gallate (EGCG) is the main polyphenol component of green tea (leaves of Camellia sinensis). EGCG is known for its antioxidant, anti-inflammatory, antiviral, and anti-carcinogenic properties. Here, we identify EGCG as a new inhibitor of ocular angiogenesis and its vascular permeability. Matrix metalloproteinases (MMPs) and vascular endothelial growth factor (VEGF) play a key role in the processes of extracellular matrix (ECM) remodeling and microvascular permeability during angiogenesis. We investigated the inhibitory effects of EGCG on ocular neovascularization and vascular permeability using the retina oriented cells and animal models induced by VEGF and alkaline burn. EGCG treatment significantly decreased mRNA and protein expression levels of MMP-9 in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA) and tumor necrosis factor alpha (TNF-α) in human retinal pigment epithelial cells (HRPECs). EGCG also effectively protected ARPE-19 cells from cell death and attenuated mRNA expressions of key angiogenic factors (MMP-9, VEGF, VEGF Receptor-2) by inhibiting generation of reactive oxygen species (ROS). EGCG significantly inhibited proliferation, vascular permeability, and tube formation in VEGF-induced human retinal microvascular endothelial cells (HRMECs). Furthermore, EGCG significantly reduced vascular leakage and permeability by blood-retinal barrier breakdown in VEGF-induced animal models. In addition, EGCG effectively limited upregulation of MMP-9 and platelet endothelial cell adhesion molecule (PECAM/CD31) on corneal neovascularization (CNV) induced by alkaline burn. Our data suggest that MMP-9 and VEGF are key therapeutic targets of EGCG for treatment and prevention of ocular angiogenic diseases such as age-related macular degeneration, diabetic retinopathy, and corneal neovascularization.

Angiogenesis in the course of enucleation-induced adrenal regeneration--expression of selected genes and proteins involved in development of capillaries

Enucleation-induced rapid proliferation of adrenocortical cells and restoration of adrenals structure requires formation of new blood vessels. The performed studies aimed to select from around 30,000 transcripts, identified by means of Affymetrix(®) Rat Gene 1.1 ST Array, the genes involved in angiogenesis in the course of enucleation-induced adrenal regeneration and to characterize their expression levels in regenerating gland between days 1 and 15 after surgery. At day 1 of regeneration almost 2000 genes showed more than 2-fold up/down-regulation. At days 1-3 after surgery the highest expression demonstrated genes involved in the development of inflammation and blood clot formation. From around 2000 genes we selected genes involved in angiogenesis. During the regeneration 62 genes involved in angiogenesis were identified as up- or down-regulated. Some data were also validated by QPCR. Levels of Vegfa and Kdr (Vegfr-2) mRNAs were very low at day 1 of regeneration and remained unchanged thereafter. The highest expression of Figf gene was found at day 5 while that of Vwf gene at days 1 and 2 after surgery. Levels of Thy1 mRNA increased notably between days 2 and 5 of the experiment. In comparison to control rats, Mc2r (ACTH receptor) expression was lowered at day 1 of the experiment and remained unchanged thereafter. This suggests that enucleation-induced adrenal neoangiogenesis does not require elevated expression of ACTH receptor. Results of our studies strongly suggest that enucleation-induced adrenal regeneration is an angiogenesis-dependent process. Moreover, immunohistochemistry suggests that regenerating adrenal parenchymal cells release numerous angiogenic factors which paracrinally may regulate formation of new vessels.

Influence of sera from interstitial lung disease patients on angiogenic activity of mononuclear cells

Chronic inflammation stimulates of neovascularization. The aim of this study was to evaluate the effect of sera from interstitial lung diseases (ILD) patients on angiogenic capabilities of different subsets of mononuclear cells. Serum samples were obtained from 22 patients with sarcoidosis, 20 with hypersensitivity pneumonitis, 20 with idiopathic pulmonary fibrosis, 9 with systemic sclerosis, 6 with pulmonary Langerhans cells histiocytosis, and from 20 healthy volunteers. Animal model of leukocyte induced angiogenesis assay was used as an angiogenic test. The pattern of angiogenic reaction was different in different diseases. Sera from systemic sclerosis and pulmonary Langerhans cells histiocytosis patients exerted inhibitory effects on angiogenesis, but sera from sarcoidosis, hypersensitivity pneumonitis, and idiopathic pulmonary fibrosis patients stimulated angiogenesis. Sera from sarcoidosis and pulmonary Langerhans cells histiocytosis primed monocytes for the production of angiogenic factors. The number of microvessels created after incubation of mononuclear cells depleted of monocytes with sera from systemic sclerosis patients significantly decreased. We conclude that the role of monocytes in the modulation of angiogenesis varies depending on the type of ILD. Sera from sarcoidosis stimulate and from pulmonary Langerhans cells histiocytosis patients inhibit neovascularization induced by monocyte mediators. Sera from systemic sclerosis inhibit angiogenesis induced by lymphocyte products.

Effects of dilution and prolonged storage with preservative in a polyethylene container on Bevacizumab (Avastin™) for topical delivery as a nasal spray in anti-hereditary hemorrhagic telangiectasia and related therapies

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular dysplasia and severe, recurrent epistaxis is a common clinical phenotype associated with HHT. An intranasal treatment regime of diluted Avastin™ (Bevacizumab; recombinant humanized anti-vascular epithelial growth factor immunoglobin G1) using apulsatile nasal irrigator has proven efficacious in clinical practice. However, concerns regarding the stability of Avastin™ following dilution and prolonged storage in standard containers used for drug delivery, such as polyethylene bottles, have so far prevented a more widespread clinical use. Compatibility with the preservative benzalkonium chloride was also unknown.

OBJECTIVE

This study aimed at determining, whether dilution, prolonged refrigerated storage and the presence of the preservative benzalkonium chloride - as required for novel Avastin™ formulations - affected the biochemical and electrochemical properties of the drug.

METHODS

We performed a detailed biochemical and electrochemical analysis of Avastin™, including native and sodium dodecyl sulfate polyacrylamide gel electrophoresis, enzyme-linked immunosorbent assay and isoelectric focusing.

RESULTS

We did not detect any evidence of degeneration or aggregation following dilution and prolonged, refrigerated storage or from the presence of benzalkonium chloride. All biochemical and electrochemical properties of Avastin™ after dilution and prolonged, refrigerated storage were undistinguishable from control.

CONCLUSIONS

Our data provide important insight into the stability of Avastin™ and allow the consideration of novel Avastin™ formulations, including its use in a metered-dose nasal spray for the treatment of HHT and other applications.

Targeting activin receptor-like kinase 1 inhibits angiogenesis and tumorigenesis through a mechanism of action complementary to anti-VEGF therapies

Genetic and molecular studies suggest that activin receptor-like kinase 1 (ALK1) plays an important role in vascular development, remodeling, and pathologic angiogenesis. Here we investigated the role of ALK1 in angiogenesis in the context of common proangiogenic factors [PAF; VEGF-A and basic fibroblast growth factor (bFGF)]. We observed that PAFs stimulated ALK1-mediated signaling, including Smad1/5/8 phosphorylation, nuclear translocation and Id-1 expression, cell spreading, and tubulogenesis of endothelial cells (EC). An antibody specifically targeting ALK1 (anti-ALK1) markedly inhibited these events. In mice, anti-ALK1 suppressed Matrigel angiogenesis stimulated by PAFs and inhibited xenograft tumor growth by attenuating both blood and lymphatic vessel angiogenesis. In a human melanoma model with acquired resistance to a VEGF receptor kinase inhibitor, anti-ALK1 also delayed tumor growth and disturbed vascular normalization associated with VEGF receptor inhibition. In a human/mouse chimera tumor model, targeting human ALK1 decreased human vessel density and improved antitumor efficacy when combined with bevacizumab (anti-VEGF). Antiangiogenesis and antitumor efficacy were associated with disrupted co-localization of ECs with desmin(+) perivascular cells, and reduction of blood flow primarily in large/mature vessels as assessed by contrast-enhanced ultrasonography. Thus, ALK1 may play a role in stabilizing angiogenic vessels and contribute to resistance to anti-VEGF therapies. Given our observation of its expression in the vasculature of many human tumor types and in circulating ECs from patients with advanced cancers, ALK1 blockade may represent an effective therapeutic opportunity complementary to the current antiangiogenic modalities in the clinic.

Role of unc5b in retinal neovascularization in mice with oxygen-induced retinopathy

AIM

To explore the role of unc5b in retinal neovascularization in murine oxygen-induced retinopathy (OIR).

METHODS

On postnatal 7(P7), C57BL/6J mice were exposed to 75%±2% oxygen for 5 days. On postnatal 12(P12), the mice were brought back to the room air (21% oxygen) to induce retinal neovascularization. Western blot analysis was performed to examine the temporal expression of unc5b in murine retinas. Double staining for unc5b and isolectin B4 were employed to determine the location of unc5b in murine retinas. The effect of unc5b on retinal neovascularization was evaluated by intravitreal injection of unc5b-FC in mice with OIR. Retinal neovascularization was measured by counting neovascular cell nuclei above the internal limiting membrane and by angiography of flat-mounted retinas perfused with fluorescein dextran.

RESULTS

Compared to age-matched normal mice, the expression of unc5b was significantly increased in retinas of OIR mice on P17 and P21. Unc5b was apparently expressed in retinal vessels of OIR while being negative in normal retinal vessels. Retinal neovascularization in eyes injected with unc5b-FC was significantly reduced.

CONCLUSION

Unc5b-FC can effectively inhibit retinal neovascularization induced by OIR. It may serve as a powerful and novel therapy for ischemia-induced retinal disease.

Callusmassage. A new treatment modality for non-unions of the irradiated mandible

Recent reports on orthopaedic surgery focus on mechanical stimulation of the regenerate during distraction therapy of non-unions in long-bone-surgery. In the field of maxillofacial surgery, callus stimulating techniques are rarely reported. The case of a 65-year-old man with a radiogenic mandibular non-union after ablative tumour therapy and pre-operative radiation therapy presented with a non-union. Vertical distraction in combination with subsequent repeated, stepwise compression and distraction (=massage) had a positive effect on the consolidation of the regenerate.

Laminin-5-enriched extracellular matrix accelerates angiogenesis and neovascularization in association with ePTFE

The performance of biomedical implant devices is often limited by inappropriate tissue responses associated with synthetic materials used in device construction. Adverse healing responses, in particular the lack of an extensive vascular supply in the peri-implant tissue, are believed to lead to the ultimate failure of many of these medical devices. Accelerated formation of new blood vessels in the peri-implant tissue and within porous polymeric implants is hypothesized to improve the performance of such biomedical implant devices. The current study evaluated the use of cell-mediated, extracellular matrix modification of expanded polytetrafluoroethylene (ePTFE) to increase vessel growth in peri-implant tissue and within the pores of the implants. Discs of ePTFE were modified through cell-mediated matrix deposition using epithelial and endothelial cell lines with variable deposition of collagen types, fibronectin, and laminin types. Cell matrix-modified discs, Matrigel-coated discs, and nonmodified discs were implanted in both the adipose and subcutaneous tissues of the rat. Following a 5-week implant period, samples were removed and evaluated histologically and morphometrically for the presence of blood vessels in the peri-implant tissue and within the pores of the polymer as well as for the presence of activated macrophages and monocytes. A significantly increased presence of activated macrophages and monocytes was associated only with the samples modified with the matrix from a human microvessel endothelial cell line. Increased vessel density was identified in association with those ePTFE samples modified with either the 804-G, HaCaT, or II-4 cell matrices, all of which have extracellular matrices enriched in the protein laminin-5.

Induction of a potential paracrine angiogenic loop between human THP-1 macrophages and human microvascular endothelial cells during Bartonella henselae infection

Bartonella henselae is responsible for various disease syndromes that loosely correlate with the immune status of the host. In the immunocompromised individual, B. henselae-induced angiogenesis, or bacillary angiomatosis, is characterized by vascular proliferative lesions similar to those in Kaposi's sarcoma. We hypothesize that B. henselae-mediated interaction with immune cells, namely, macrophages, induces potential angiogenic growth factors and cytokines which contribute in a paracrine manner to the proliferation of endothelial cells. Vascular endothelial growth factor (VEGF), a direct inducer of angiogenesis, and interleukin-1beta (IL-1beta), a potentiator of VEGF, were detected within 12 and 6 h, respectively, in supernatants from phorbol 12-myristate 13-acetate-differentiated human THP-1 macrophages exposed to live B. henselae. Pretreatment of macrophages with cytochalasin D, a phagocytosis inhibitor, yielded comparable results, suggesting that bacterium-cell attachment is sufficient for VEGF and IL-1beta induction. IL-8, an angiogenic cytokine with chemotactic properties, was induced in human microvascular endothelial cells (HMEC-1) within 6 h of infection, whereas no IL-8 induction was observed in infected THP-1 cells. In addition, conditioned medium from infected macrophages induced the proliferation of HMEC-1, thus demonstrating angiogenic potential. These data suggest that Bartonella modulation of host or target cell cytokines and growth factors, rather than a direct role of the bacterium as an endothelial cell mitogen, is the predominant mechanism responsible for angiogenesis. B. henselae induction of VEGF, IL-1beta, and IL-8 outlines a broader potential paracrine angiogenic loop whereby macrophages play the predominant role as the effector cell and endothelial cells are the final target cell, resulting in their proliferation.

Inhibitory effect on expression of angiogenic factors by antiangiogenic agents in renal cell carcinoma

Since it has been widely recognised that renal cell carcinoma is refractory to standard therapies such as chemotherapy and radiotherapy, a new modality of treatment is needed. One of the potential alternative therapies for renal cell carcinoma may be inhibition of angiogenesis. In this study, we analysed the inhibitory effects of several potential agents on expression of angiogenic factors such as vascular endothelial growth factor and basic fibroblast growth factor, which are the main mediators in angiogenesis of renal cell carcinoma. We used medroxyprogesterone acetate, interferon-alpha, interferon-gamma, minocycline hydrochrolide and genistein, which are known to be antiangiogeneic. Northern blot analyses revealed that, among the five agents examined, genistein had a strong inhibitory effect on expression of vascular endothelial growth factor mRNA and basic fibroblast growth factor mRNA. Medroxyprogesterone acetate and interferon-alpha did not significantly decrease the level of either vascular endothelial growth factor mRNA or basic fibroblast growth factor mRNA. Interferon-gamma and minocycline had mild inhibitory effects on vascular endothelial growth factor mRNA and basic fibroblast growth factor mRNA expression. Genistein also inhibited both vascular endothelial growth factor mRNA and basic fibroblast growth factor mRNA expression after treatment with epidermal growth factor and hypoxia. These findings suggest that one of the mechanisms of the inhibition of angiogenesis by genistein is suppression of the expression of the angiogenic factors vascular endothelial growth factor and basic fibroblast growth factor in renal cell carcinoma.

Anti-angiogenic effects of the thienopyridine SR 25989 in vitro and in vivo in a murine pulmonary metastasis model

Neovascularisation is a key step in tumour growth and establishment of distant metastases. We have recently demonstrated that the thienopyridine SR 25989 an enantiomer of the anti-aggregant clopidogrel (Plavix) lacking anti-aggregant activity, inhibits endothelial cell proliferation in vitro by increasing the expression of endogenous thrombospondin-1, a natural potent inhibitor of angiogenesis. The anti-angiogenic effect of SR 25989 was further assessed in vitro in a quantitative assay of angiogenesis comprising a fragment of rat aorta embedded in a fibrin gel and in vivo in a pulmonary metastatic model using C57BL/6 mice inoculated in the foot pad with the highly metastatic melanoma cell line B16 F10. SR 25989 induced a dose dependent inhibition of spontaneous microvessel development in vitro reaching half maximal inhibition at around less than 50 microM and caused platelet derived growth factor induced angiogenesis to regress as a function of thienopyridine concentration. In vivo, SR 25989 did not alter significantly the growth rate of the primary tumour in the foot pad and did not inhibit development of inguinal nodes which appeared after amputation. However, the number and size of lung metastases were reduced in treated animals when examined at the time of sacrifice. In addition, the few metastases over 1 mm3 did not show any neovascularisation, as confirmed by negative von Willebrand immunostaining and in contrast to intense vascularisation seen in metastases developed by control mice. These results confirm that SR 25989 possesses potent anti-angiogenic properties and is able to inhibit metastatic dissemination and growth. The lack of effect on the primary tumour and inguinal nodes illustrates the complexity of the mechanisms involved in tumoural neo-angiogenesis and points out the possibility for distinct processes leading to neovascularisation in primary tumour as opposed to metastases.

Histone deacetylases inhibitors as anti-angiogenic agents altering vascular endothelial growth factor signaling

Angiogenesis is a complex biological process involving the coordinated modulation of many genes. Histone deacetylases (HDAC) are a growing family of enzymes that mediate the availability of chromatin to the transcriptional machinery. Trichostatin-A (TSA) and suberoylanilide hydroxamic acid (SAHA), two HDAC inhibitors known to relieve gene silencing, were evaluated as potential antiangiogenic agents. TSA and SAHA were shown to prevent vascular endothelial growth factor (VEGF)-stimulated human umbilical cord endothelial cells (HUVEC) from invading a type I collagen gel and forming capillary-like structures. SAHA and TSA inhibited the VEGF-induced formation of a CD31-positive capillary-like network in embryoid bodies and inhibited the VEGF-induced angiogenesis in the CAM assay. TSA also prevented, in a dose-response relationship, the sprouting of capillaries from rat aortic rings. TSA inhibited in a dose-dependent and reversible fashion the VEGF-induced expression of VEGF receptors, VEGFR1, VEGFR2, and neuropilin-1. TSA and SAHA upregulated the expression by HUVEC of semaphorin III, a recently described VEGF competitor, at both mRNA and protein levels. This effect was specific to endothelial cells and was not observed in human fibroblasts neither in vascular smooth muscle cells. These observations provide a conspicuous demonstration that HDAC inhibitors are potent anti-angiogenic factors altering VEGF signaling.

Breast cancer in the clinic: treatments past, treatments future

Therapeutic options for the patient with systemic breast cancer were long limited to either chemotherapy and hormonal therapy. While these therapies provide palliation for many patients with advanced disease, and occasionally cure the patient with micrometastatic disease, they are not optimal either with regard to toxicity or efficacy. This paper reviews the past of systemic therapy (chemotherapy and hormonal therapy), then discusses developing treatment strategies. These strategies include the recently introduced anti-HER-2 antibody trastuzumab, novel agents targeting other aspects of tumor growth mechanisms, as well as agents blocking angiogenesis.

Cutting edge: systemic inhibition of angiogenesis underlies resistance to tumors during acute toxoplasmosis

The ability of various infections to suppress neoplastic growth has been well documented. This phenomenon has been traditionally attributed to infection-induced concomitant, cell-mediated antitumor immunity. We found that infection with Toxoplasma gondii effectively blocked neoplastic growth of a nonimmunogenic B16.F10 melanoma. Moreover, this effect was independent of cytotoxic T or NK cells, production of NO by macrophages, or the function of the cytokines IL-12 and TNF-alpha. These findings suggested that antitumor cytotoxicity was not the primary mechanism of resistance. However, infection was accompanied by strong, systemic suppression of angiogenesis, both in a model system and inside the nascent tumor. This suppression resulted in severe hypoxia and avascular necrosis that are incompatible with progressive neoplastic growth. Our results identify the suppression of tumor neovascularization as a novel mechanism critical for infection-induced resistance to tumors.

Redefining the target: chemotherapeutics as antiangiogenics

Angiogenesis, or new blood vessel formation, is now known to play an important role in both growth and metastasis of many cancers. The central importance of angiogenesis and the understanding of how new blood vessels are formed, has led to novel therapies designed to interrupt this process. Though specific antiangiogenic compounds have only recently entered the clinic, they herald a new era, one in which biology is the basis for therapy. The intense interest in angiogenesis has also lead to a re-examination of the activity of many established cytotoxic agents. Claims of antiangiogenic activity abound, unfortunately, with no common criteria and often little evidence of clinical relevance. What are we to think? Have oncologists unknowingly been administering antiangiogenic therapy all these years? If chemotherapeutics are really antiangiogenics in disguise, why have they failed to cure most solid tumors? Might the hard-learned lessons of chemotherapy resistance pertain to the novel antiangiogenics as well? Though we can offer no certain answers to these important questions, we do offer a framework on which to order the rapidly burgeoning literature. We suggest criteria by which a cytotoxic agent might reasonably be considered to have meaningful antiangiogenic activity. Finally, we describe potential mechanisms of resistance to antiangiogenic chemotherapies-some of which may apply to the pure antiangiogenics currently in development.

Impaired angiogenic balance and suppression of tumorigenicity in HeLa cells chronically exposed to interferon-alpha

We have previously reported that IFNalpha-chronic treatment for 41 days induced a partial phenotype reversion on HeLa cells along with a down-regulation of HPV18 mRNA levels. However, tumorigenicity of these cells in nude mice was unchanged. Interestingly, after 1 year of IFNalpha-chronic exposition, HeLa cells failed to induce s.c. tumors when injected into nude mice. In such experimental conditions both HPV18 DNA integration pattern and viral DNA copy number present in HeLa cells remained intact in the nontumorigenic phenotype cells. As result of the treatment with IFNalpha, HeLa cells rendered more resistant to lysis mediated by activated natural killer cells in vitro. Furthermore, IFNalpha-chronic treatment was able to induce VEGF and decrease bFGF mRNA expression, suggesting a potential effect on the angiogenic behavior of these tumoral cells. Thus, long-term treatment of HeLa cells with IFNalpha can accomplish a reversion of the malignant phenotype by a sequential multistep mechanism, in which the antiangiogenic effect of IFNalpha could be one of the contributing events.

Hypoxia-inducible angiopoietin-2 expression is mimicked by iodonium compounds and occurs in the rat brain and skin in response to systemic hypoxia and tissue ischemia

Angiopoietins are ligands for the endothelial cell tyrosine kinase receptor Tie-2. Ang-1, the major physiological activator of Tie-2, promotes blood vessel maturation and stability. Ang-2 counteracts this effect by competitively inhibiting the binding of Ang-1 to Tie-2. Using a combined RNase protection/semiquantitative reverse transcriptase-polymerase chain reaction approach, we demonstrate that hypoxia up-regulates Ang-2 mRNA levels by up to 3.3-fold in two human endothelial cell lines. In bovine microvascular endothelial (BME) cells, the flavoprotein oxidoreductase inhibitor diphenylene iodonium (DPI) and the related compound iodonium diphenyl mimic induction of Ang-2 but not vascular endothelial growth factor (VEGF) by hypoxia; in combination with hypoxia, DPI further increases Ang-2 expression but has no effect on the induction of VEGF by hypoxia. Neither Ang-2 or VEGF was increased by cyanide or rotenone, suggesting that failure in mitochondrial electron transport is not involved in the oxygen-sensing system that controls their expression. In ischemic rat dorsal skin flaps or in the brain of rats maintained for 12 hours under conditions of hypoxia, Ang-2 mRNA was up-regulated 7.5- or 17.6- fold, respectively. VEGF was concomitantly increased, whereas expression of Ang-1, Tie-2, and the related receptor Tie-1 was unaltered. In situ hybridization localized Ang-2 mRNA to endothelial cells in hypoxic skin. These findings 1) show that up-regulation of Ang-2 by hypoxia occurs widely in endothelial cells in vitro and in vivo; 2) suggest that induction of Ang-2, but not VEGF, by hypoxia in BME cells is controlled by a flavoprotein oxidoreductase that is sensitive to iodonium compounds; and 3) point to Ang-2 and VEGF as independently regulated and selective effectors of hypoxia-induced vascular sprouting.

Toward checkmate: biology and breast cancer therapy for the new millennium

A better understanding of the biology of breast cancer should lead to the rational development of new treatments and the ability to customize therapy for individual patients. Though promising in theory, translating advances in biological knowledge to the clinic has been difficult. Recently several areas of research have produced treatments which have entered clinical trials: three will be reviewed here. The growth of breast cancer is regulated by growth factors and their receptors; amplification or overexpression is associated with poor prognosis. As such inhibition of growth factors and/or growth factor receptors may provide an ideal therapeutic target. Herceptin binds to c-erbB-2, a member of the epidermal growth factor receptor family. Significant responses were seen in patients with c-erbB-2 overexpressing breast cancer with Herceptin administered as a single agent or in combination with chemotherapy. Herceptin was approved by the Food and Drug Administration in late 1998. Breast cancer invasion and metastasis requires degradation of the surrounding basement membrane by matrix metalloproteinases and other proteolytic enzymes. Synthetic inhibitors of these enzymes are now in clinical trials. Breast cancers must stimulate angiogenesis, the growth of new blood vessels, in order to grow beyond a few millimeters in diameter. This nascent vascular network provides another opportunity for therapy. Preclinical models support the critical role of angiogenesis and the therapeutic benefit of angiogenesis inhibition; clinical trials are underway.

Human three-dimensional fibroblast cultures express angiogenic activity

Human neonatal fibroblasts were cultured on a lactate-glycollate copolymer scaffold for 12-16 days to form a three-dimensional dermal equivalent tissue. The cellular content of vascular endothelial growth factor (VEGF) mRNA in these three-dimensional cultures was 22-fold greater than that observed in the same fibroblasts grown as monolayers. No induction was shown by hepatocyte growth factor (HGF) or angiopoietin 1 indicating that the effect was specific to VEGF. The predominant VEGF splice variant, detected by RT-PCR corresponded to the 121 amino acid form, with less of the 165 amino acid form. The cell-associated forms (189 and 206 amino acids) comprised less than 1% of the total VEGF mRNA. VEGF and HGF proteins, determined by ELISA, were secreted in physiologically significant amounts, 0.5-4 ng per 24 h/10(6) cells. Conditioned medium from the three-dimensional cultures stimulated proliferation of endothelial cells in a dose-dependent manner and induced cellular expression of integrin alpha(v)beta(3). Conditioned medium from the same dermal fibroblasts cultured in monolayer showed little angiogenic activity in any of these assays. Using the chorioallantoic membrane (CAM) angiogenesis assay, the cultures stimulated blood vessel production 2.8-fold over scaffold alone. VEGF-neutralizing antibody reduced the vessel development in the CAM to the level in the scaffold control. Anti-HGF antibody had no significant effect. In conclusion, three-dimensional cultures of dermal equivalent tissue express angiogenic activity to a greater extent than monolayer cultures, some of which can be assigned to VEGF.

Regulation of angiopoietin-2 mRNA levels in bovine microvascular endothelial cells by cytokines and hypoxia

Angiopoietin-2 (Ang2) is a ligand for the endothelial cell tyrosine kinase receptor Tie2 and counteracts blood vessel maturation/stability mediated by angiopoietin-1 (Ang1), the other known ligand of Tie2. Using degenerate oligonucleotides and reverse transcriptase-polymerase chain reaction, we have screened bovine microvascular endothelial (BME), aortic, lymphatic, pulmonary artery, and transformed fetal aortic endothelial cells, as well as rat smooth muscle cells for Ang1 and Ang2 expression. Except for high Ang2 mRNA levels found in BME cells, none of the endothelial cell types studied expressed appreciable levels of Ang1 or Ang2 mRNAs, whereas smooth muscle cells expressed both Ang1 and Ang2. BME cell Ang2 mRNA levels were increased by vascular endothelial growth factor (1.9- to 2.9-fold), basic fibroblast growth factor (1.6- to 2-fold), both cytokines in combination (2.9- to 4-fold), and hypoxia (3.1- to 5.6-fold) and were decreased by Ang1 (31% to 70%) or transforming growth factor-ss1 (64% to 81%). Ang2 also decreased (60% to 82%) BME cell Ang2 mRNA. mRNA levels for the Tie1 or Tie2 receptors were only slightly modulated under the conditions described above. These findings suggest that the angiogenic effect of a number of regulators may be achieved in part through the regulation of an autocrine loop of Ang2 activity in microvascular endothelial cells.

Upregulation of interleukin 8 by oxygen-deprived cells in glioblastoma suggests a role in leukocyte activation, chemotaxis, and angiogenesis

Leukocyte infiltration and necrosis are two biological phenomena associated with the development of neovascularization during the malignant progression of human astrocytoma. Here, we demonstrate expression of interleukin (IL)-8, a cytokine with chemotactic and angiogenic properties, and of IL-8-binding receptors in astrocytoma. IL-8 expression is first observed in low grade astrocytoma in perivascular tumor areas expressing inflammatory cytokines. In glioblastoma, it further localizes to oxygen-deprived cells surrounding necrosis. Hypoxic/anoxic insults on glioblastoma cells in vitro using anaerobic chamber systems or within spheroids developing central necrosis induced an increase in IL-8 messenger RNA (mRNA) and protein expression. mRNA for IL-8-binding chemokine receptors CXCR1, CXCR2, and the Duffy antigen receptor for chemokines (DARC) were found in all astrocytoma grades by reverse transcription/PCR analysis. In situ hybridization and immunohistochemistry localized DARC expression on normal brain and tumor microvascular cells and CXCR1 and CXCR2 expression to infiltrating leukocytes. These results support a model where IL-8 expression is initiated early in astrocytoma development through induction by inflammatory stimuli and later in tumor progression increases due to reduced microenvironmental oxygen pressure. Augmented IL-8 would directly and/or indirectly promote angiogenesis by binding to DARC and by inducing leukocyte infiltration and activation by binding to CXCR1 and CXCR2.