Epidermal growth factor stimulates vascular endothelial growth factor production by human malignant glioma cells: a model of glioblastoma multiforme pathophysiology

Rational bases for the development of EGFR inhibitors for cancer treatment

Growth factor receptors and their ligands not only regulate normal cell processes but have been also identified as key regulators of human cancer formation. The epidermal growth factor receptor (EGFR/ErbB1/HER1) belongs to the ErbB/HER-family of tyrosine kinase receptors (RTKs). These trans-membrane proteins are activated following binding with peptide growth factors of the EGF-family of proteins. Several evidences suggest that cooperation of multiple ErbB receptors and ligands is required for the induction of cell transformation. In this respect, EGFR, upon activation, sustains a complex and redundant network of signal transduction pathways with the contribution of other trans-membrane receptors. EGFR has been found to be expressed and altered in a variety of malignancies and clearly it plays a significant role in tumor development and progression, including cell proliferation, regulation of apoptotic cell death, angiogenesis and metastatic spread. Moreover, amplification of the EGFR gene and mutations in the EGFR tyrosine kinase domain have been recently reported in human carcinomas. As a result, investigators have developed approaches to inhibit the effects of EGFR activation, with the aim of blocking tumor growth and invasion. A number of agents targeting EGFR, including specific antibodies directed against its ligand-binding domain and small molecules inhibiting its tyrosine kinase activity are either in clinical trials or are already approved for clinical treatment. This article reviews the EGFR role in carcinogenesis and tumor progression as rational bases for the development of specific therapeutic inhibitors.

Overcoming resistance to molecularly targeted anticancer therapies: Rational drug combinations based on EGFR and MAPK inhibition for solid tumours and haematologic malignancies

Accumulating evidence suggests that cancer can be envisioned as a "signaling disease", in which alterations in the cellular genome affect the expression and/or function of oncogenes and tumour suppressor genes. This ultimately disrupts the physiologic transmission of biochemical signals that normally regulate cell growth, differentiation and programmed cell death (apoptosis). From a clinical standpoint, signal transduction inhibition as a therapeutic strategy for human malignancies has recently achieved remarkable success. However, as additional drugs move forward into the clinical arena, intrinsic and acquired resistance to "targeted" agents becomes an issue for their clinical utility. One way to overcome resistance to targeted agents is to identify genetic and epigenetic aberrations underlying sensitivity/resistance, thus enabling the selection of patients that will most likely benefit from a specific therapy. Since resistance often ensues as a result of the concomitant activation of multiple, often overlapping, signaling pathways, another possibility is to interfere with multiple, cross-talking pathways involved in growth and survival control in a rational, mechanism-based, fashion. These concepts may be usefully applied, among others, to agents that target two major signal transduction pathways: the one initiated by epidermal growth factor receptor (EGFR) signaling and the one converging on mitogen-activated protein kinase (MAPK) activation. Here, we review the molecular mechanisms of sensitivity/resistance to EGFR inhibitors, as well as the rationale for combining them with other targeted agents, in an attempt to overcome resistance. In the second part of the paper, we review MAPK-targeted agents, focusing on their therapeutic potential in haematologic malignancies, and examine the prospects for combinations of MAPK inhibitors with cytotoxic agents or other signal transduction-targeted agents to obtain synergistic anti-tumour effects.

Cellular responses to EGFR inhibitors and their relevance to cancer therapy

EGFR is a trans-membrane receptor tyrosine kinase that belongs to the HER family of receptors. The EGFR family plays an essential role in normal organ development by mediating morphogenesis and differentiation. Unlike normal cells that have tight regulatory mechanisms controlling EGFR pathways, tumor cells often have dysregulated EGFR signaling through receptor overexpression and/or mutation. This leads to proliferation under adverse conditions, invasion of surrounding tissues, and increased angiogenesis as well as resistance to radiation and chemotherapy. Therefore, EGFR is a legitimate therapeutic target. Numerous EGFR inhibitors are under development, but to date only four of them are FDA-approved, including two that inhibit the receptor's intracellular tyrosine kinase activity (gefitinib and erlotinib) and two that block extracellular ligand binding (cetuximab, and most recently panitumumab). In this review, we focus on how these different inhibitors affect EGFR signaling and the mechanisms by which they potentiate the effects of chemotherapy and radiation therapy. Numerous clinical trials have been conducted with these agents either as monotherapy, in combination with chemotherapy, or concurrently with radiation. Unfortunately, many of the clinical trials reported so far have shown at best limited gains; therefore, understanding the actions of these agents is essential to improving their efficacy in the treatment of cancers.

Vascular endothelial growth factor (VEGF) signaling in tumor progression

Vascular endothelial cells are ordinarily quiescent in adult humans and divide less than once per decade. When tumors reach a size of about 0.2-2.0mm in diameter, they become hypoxic and limited in size in the absence of angiogenesis. There are about 30 endogenous pro-angiogenic factors and about 30 endogenous anti-angiogenic factors. In order to increase in size, tumors undergo an angiogenic switch where the action of pro-angiogenic factors predominates, resulting in angiogenesis and tumor progression. One mechanism for driving angiogenesis results from the increased production of vascular endothelial growth factor (VEGF) following up-regulation of the hypoxia-inducible transcription factor. The human VEGF family consists of VEGF (VEGF-A), VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PlGF). The VEGF family of receptors consists of three protein-tyrosine kinases and two non-protein kinase receptors (neuropilin-1 and -2). Owing to the importance of angiogenesis in tumor progression, inhibition of VEGF signaling represents an attractive cancer treatment.

High EGFR expression predicts poor prognosis in patients with squamous cell carcinoma of the oral cavity and oropharynx: A TMA-based immunohistochemical analysis

This retrospective study was designed to investigate the prognostic significance of EGFR overexpression in human oral squamous cell carcinoma on a long-term follow-up. EGFR expression was examined immunohistochemically on a tissue microarray (TMA) of paraffin embedded tissue specimens from 109 patients who underwent surgical treatment for squamous cell carcinoma of the oral cavity and oropharynx in the period between 1980 and 1997. High EGFR expression was found in 80 (73.42%) of the tumour samples. Kaplan-Meier curves showed that EGFR overexpression was significantly related to decreased overall survival (p=0.05). Multivariate analysis showed that EGFR overexpression is an independent prognostic marker in these patients (p=0.02, RR 3.6). These results confirm that EGFR overexpression is an independent prognostic marker in patients with squamous cell carcinoma of the oral cavity and oropharynx. The EGFR antigen represents an attractive target for targeted therapies with monoclonal antibodies or specific tyrosine-kinase inhibitors in these patients.

Serum EGFR and serum HER-2/neu are useful predictive and prognostic markers in metastatic breast cancer patients treated with metronomic chemotherapy

BACKGROUND

Metronomic chemotherapy has been demonstrated to be of value in patients with advanced breast cancer. No reliable markers of response are available. In breast tumor, HER-2/neu is a prognostic factor, whereas no definite data exist for EGFR. The aim of the study was to evaluate the prognostic and predictive role of serum HER-2/neu and serum EGFR in breast cancer patients treated with low-dose chemotherapy.

METHODS

Serum levels of HER-2/neu (n = 135) and of EGFR (n = 113) were prospectively determined before the start of chemotherapy, after 2 months of treatment, and when progressive disease was diagnosed.

RESULTS

Elevated (>15 ng/mL) serum HER-2/neu before the start of chemotherapy was not associated with response rate, whereas elevated serum HER-2/neu at 2 months was significantly associated with reduced long-term clinical benefit (24 weeks) (P < .001), as well as changes in HER-2/neu levels between baseline and 2 months (P < .0001). Multivariate analysis identified a >or=20% increase of serum HER-2/neu as an independent factor for progression-free survival (PFS). Kinetics of serum HER-2/neu were significantly associated with PFS (P < .0001) and overall survival (OS) (P = .015). Low baseline serum levels of EGFR (<45 ng/mL) were predictive of reduced response rate both at 2 months (P = .031) and after 24 weeks (P = .022). Moreover, they were significantly associated with reduced PFS (P = .016) and OS (P = .015).

CONCLUSIONS

Serum HER-2/neu and EGFR may represent useful markers for early prediction of probability of response, PFS, and OS in patients with advanced breast cancer treated with metronomic chemotherapy.

Reactive oxygen species regulate epidermal growth factor-induced vascular endothelial growth factor and hypoxia-inducible factor-1alpha expression through activation of AKT and P70S6K1 in human ovarian cancer cells

The epidermal growth factor (EGF) and EGF receptor (EGFR) family are often overexpressed in various human cancers including ovarian cancer. While it is generally believed that reactive oxygen species (ROS) are involved in the intracellular signaling events, the role of ROS in EGF-induced angiogenesis and carcinogenesis remains to be elucidated. The present study investigated the role of ROS in the regulation of AKT, p70S6K1, vascular endothelial growth factor (VEGF), and hypoxia-inducible factor 1 (HIF-1) in ovarian cancer cells. In this study, OVCAR-3 cells were treated with EGF and catalase, an H2O2 scavenger. EGF treatment increases H2O2 production, leading to activation of the AKT/p70S6K1 pathway, resulting in increased VEGF expression at the transcriptional level. The inhibition of H(2)O(2) production by catalase abolished EGF-induced AKT and p70S6K1 activation, and VEGF expression through HIF-1alpha expression. Forced expression of p70S6K1 and HIF-1alpha reversed catalase- and rapamycin-inhibited VEGF transcriptional activation. We also showed that rapamycin, p70S6K1 inhibitor and catalase overexpression inhibited tumor angiogenesis. This study demonstrates a novel mechanism of EGF-induced VEGF and HIF-1alpha expression through production of H2O2 and activation of AKT and p70S6K1 in human ovarian cancer cells. This study also indicates that p70S6K1 and H2O2 are important in tumor angiogenesis. The results of the study could have an important implication in ovarian cancer therapy.

Synergistic up-regulation of vascular endothelial growth factor (VEGF) expression in macrophages by adenosine A2A receptor agonists and endotoxin involves transcriptional regulation via the hypoxia response element in the VEGF promoter

Macrophages are an important source of vascular endothelial growth factor (VEGF). Adenosine A2A receptor (A2AR) agonists with Toll-like receptor (TLR) 2, 4, 7, and 9 agonists synergistically induce macrophage VEGF expression. We show here using VEGF promoter-luciferase reporter constructs that the TLR4 agonist Escherichia coli lipopolysaccharide (LPS) and the A2AR agonists NECA and CGS21680 synergistically augment VEGF transcription in macrophages and that the HRE in the VEGF promoter is essential for this transcription. We examined whether LPS and/or NECA induce HIF-1alpha expression. HIF-1alpha mRNA levels were increased in LPS-treated macrophages in an NF-kappaB-dependent manner; NECA strongly increased these levels in an A2AR-dependent manner. LPS induced luciferase expression from a HIF-1alpha promoter-luciferase construct in an A2AR-independent manner. Further stimulation with NECA did not increase HIF-1alpha promoter activity, indicating that the A2AR-dependent increase in HIF-1alpha mRNA is post-transcriptional. LPS/NECA treatment also increased HIF-1alpha protein and DNA binding levels. Deletion of putative NF-kappaB-binding sites from the VEGF promoter did not affect LPS/NECA-induced VEGF promoter activity, suggesting that NF-kappaB is not directly involved in VEGF transcription. Taken together, these data indicate that LPS/NECA-induced VEGF expression involves transcriptional regulation of the VEGF promoter by HIF-1alpha through the HRE. HIF-1alpha is transcriptionally induced by LPS and post-transcriptionally up-regulated in an A2AR-dependent manner.

Regulation of angiogenesis and tumor growth by p110 alpha and AKT1 via VEGF expression

Recent studies demonstrate that PI3K activation and PTEN mutation are frequently found in many human cancer cells and tissues. However, the mechanism of PI3K signaling in human cancer tumorigenesis remains to be elucidated. In this study we specifically downregulated p110alpha expression in ovarian cancer cells using siRNA interference. We found that p110alpha downregulation greatly decreased ovarian tumor growth and angiogenesis, and that p110alpha siRNA inhibited VEGF expression through decreasing hypoxia-inducible factor 1alpha expression in both ovarian cancer cells and tumor tissues. To determine the downstream targets of PI3K in regulating tumor growth and angiogenesis, we find that AKT1 is a major downstream mediator for regulating tumor growth, angiogenesis, and VEGF expression. These data show that p110alpha and AKT1 play an important role in tumor growth by inducing angiogenesis and by increasing HIF-1alpha and VEGF expression. This work provides a better understanding of the molecular mechanism of human cancer induced by the activation of PI3K signaling.

Gene-linked shift in ganglioside distribution influences growth and vascularity in a mouse astrocytoma

Brain tumor growth and progression is dependent upon vascularity, and is associated with altered ganglioside composition and distribution. In this study, we examined the influence of gangliosides on growth and vascularity in a malignant mouse astrocytoma, CT-2A. Ganglioside distribution was altered in CT-2A tumor cells using an antisense construct to beta-1,4-N-acetylgalactosaminyltransferase (GalNAc-T), a key enzyme that uses the simple ganglioside GM3 as a substrate for the synthesis of the more complex gangliosides, GM2, GM1 and GD1a. GalNAc-T gene expression was significantly lower in CT-2A cells stably transfected with the antisense GalNAc-T plasmid, pcDNA3.1/TNG (CT-2A/TNG) than in either non-transfected CT-2A or mock-transfected (CT-2A/V) control tumor cells. GM3 was elevated from 16% to 58% of the total ganglioside distribution, whereas GM1 and GD1a were reduced from 17% and 49% to 10% and 17%, respectively, in CT-2A/TNG tumor cells. Growth, vascularity (blood vessel density and Matrigel assay) and vascular endothelial growth factor (VEGF) expression was significantly less in CT-2A/TNG tumors than in control CT-2A brain tumors. In addition, the expression of VEGF, hypoxia-inducible factor 1alpha (HIF-1alpha) and neuropilin-1 (NP-1) was significantly lower in CT-2A/TNG tumor cells than in control CT-2A tumor cells. These data suggest that gene-linked changes in ganglioside composition influence the growth and angiogenic properties of the CT-2A astrocytoma.

New molecular targeted therapies in thyroid cancer

Carcinoma of the thyroid gland is the most common malignancy of the endocrine system. Differentiated tumors are often curable with surgical resection and radioactive iodine. A small percentage of such patients, however, do not undergo remission and need new therapeutic approaches. Both anaplastic and medullary thyroid carcinomas exhibit aggressive behavior and are usually resistant to current therapeutic modalities. Thyroid carcinoma represents a fascinating model and a particularly promising paradigm for targeted therapy because some of the key oncogenic events are activating mutations of genes coding for tyrosine kinases, and these occur early in cancer development. A prototype is the RET proto-oncogene, a receptor tyrosine kinase, which is a key regulator of development and a 'hotspot' for oncogenic mutations. Mutations in the RET proto-oncogene have been identified as causative for papillary carcinoma and familial medullary thyroid carcinoma, making it an attractive target for selective inhibition in these subtypes. ZD 6474 has shown promising activity in preclinical models against RET kinase, and its contemporary inhibition of vascular endothelial growth factor and epidermal growth factor pathways renders it a very attractive drug for clinical trials in thyroid cancer. Activating point mutation of B-RAF can occur early in the development of papillary carcinoma. Moreover, papillary carcinomas with these mutations have more aggressive properties and are diagnosed more often at an advanced stage. Clinical evaluation of B-RAF-targeting drugs is undergoing and trials in thyroid cancer are planned. Agents that restore radioiodine uptake, such as histone deacetylase inhibitors and retinoids, represent another exciting field in new drug development in thyroid cancer.

Chenodeoxycholic acid stimulates the progression of human esophageal cancer cells: A possible mechanism of angiogenesis in patients with esophageal cancer

Bile acids are known to promote the growth of gastrointestinal cancer. However, the underlying mechanism remains unclear. We examined whether bile acids induce tumor growth via the cyclooxygenase (COX)-2 angiogenic pathway. In vitro, esophageal squamous cell carcinoma (ESCC) cells and esophageal adenocarcinoma cells were studied. Production of prostaglandin E2 (PGE2) and vascular endothelial growth factor (VEGF) in response to treatment with chenodeoxycholic acid (CDCA) was assessed by enzyme-linked immunosorbent assay (ELISA). COX-2 protein and VEGF protein were measured by immunoblot analysis, and COX-2 activity was measured by ELISA. In vivo, CDCA was administered to ESCC cell-bearing mice. Tumor tissues were analyzed immunohistochemically, and microvessel density was evaluated. Clinically, 134 patients with ESCC who underwent esophagectomy were studied. In vitro, CDCA induced the production of PGE2 and VEGF in dose- and time-dependent manners, and these effects were attenuated by a selective COX-2 inhibitor, mitogen-activated protein kinases inhibitor, or epidermal growth factor receptor inhibitor. CDCA-induced COX-2 in the cell lysate increased the secretion of VEGF into the culture medium. In vivo, CDCA markedly enhanced tumor growth and increased vascularization. Clinically, patients whose tumors expressed both COX-2 and VEGF had poor outcomes. Our results suggest that bile acids, important constituents of duodenal fluid, stimulate the development of human esophageal cancer by promoting angiogenesis via the COX-2 pathway.

Expression of vascular endothelial growth factor and basic fibroblast growth factor in gastric carcinoma and their significances

AIM: To investigate the expression of vascular endothelial growth factor (VEGF), basic fibro-blast growth factor (bFGF) in serum and tissues of gastric cancer patients and the clinical charac-teristics of gastric cancer.

METHODS: Avidin-biotin system enzyme-linked immunosorbent assay (ABC-ELISA) was used to examine the serum expression of VEGF and bFGF in preoperative gastric cancer patients (n = 73) and healthy individuals (n = 20). Meanwhile, immunohistochemistry was used to detect the expression of VEGF and bFGF in the cancer and cancer-adjacent tissues.

RESULTS: The serum expression of VEGF and bFGF in gastric cancer patients were significantly higher than those in the healthy controls (VEGF: 101.8 ± 53.3 ng/L vs 16.1 ± 22.5 ng/L, P < 0.05; bFGF: 152.9 ± 42.7 ng/L vs 25.0 ± 11.4 ng/L, P < 0.05). The serum expression of VEGF and bFGF were significantly correlated with the depth of invasion, TNM staging, lymph node metastasis and distant metastasis, but not with the age, sex of patients, and pathological types (P < 0.05). The positive rates of VEGF and bFGF expression in gastric cancer tissues were significantly higher than those in the cancer-adjacent tissues (χ² = 32.1, P < 0.05; χ² = 17.7, P < 0.05). The tissue expression of VEGF and bFGF were also correlated with the depth of invasion, TNM staging, lymph node metastasis and distant metastasis (P < 0.05), but not with the age, sex of patients, and pathological types. There existed positive correlations between serum and tissue expression of VEGF and bFGF (in serum: r = 0.439, P < 0.01; in tissue: r = 0.391, P < 0.01). The correlation between serum and tissue expression was also significantly positive (VEGF: r = 0.346, P < 0.01; bFGF: r = 0.304, P < 0.01).

CONCLUSION: VEGF and bFGF play important roles in the oncogenesis, progression, metastasis and prognosis of gastric cancer, which may become new tumor markers for preoperative diagnosis, postoperative following-up, metastasis or recurrence monitoring, assessment of anti-angiogenesis drugs.

Novel Combinations Based on Epidermal Growth Factor Receptor Inhibition: Fig. 1

In spite of recent advances in molecular biology leading to the introduction of clinically active novel agents, such as imatinib, erlotinib, and bevacizumab, therapy of the most common epithelial tumors, such as lung cancer, remains unsuccessful. The diversity of molecular abnormalities in these tumors is felt to partly contribute to their resistance to therapy. It is, therefore, widely accepted that one approach to improving the efficacy of cancer therapy is the development of rational, hypothesis-based combinations of anticancer agents that may exhibit synergistic cytotoxic interactions. A number of empirical combination studies with the epidermal growth factor receptor and classic cytotoxic agents were undertaken in clinical trials, with disappointing results. It is, therefore, felt that preclinical combinations of epidermal growth factor receptor inhibitors and other novel agents, based on sound knowledge of complementary signaling pathways whose concerted inhibition would be hypothesized to inhibit growth, is the reasonable approach in the future. A brief overview of some of these pathways (mammalian target of rapamycin, vascular endothelial growth factor receptor, and ras/mitogen-activated protein kinase signaling) is provided in this review.

Gemcitabine in combination with EGF-Receptor antibody (Cetuximab) as a treatment of cholangiocarcinoma: a case report

Background

Extensive disease of cholangiocarcinoma (CC) determines the overall outcome and limits curative resection. Despite chemotherapy, which has been introduced to improve the outcome of biliary tract malignancies, the benefit in survival is still marginal.

Case presentation

We report a 69-year-old patient with non-resectable CC showing hepatic metastasis and peritoneal carcinomatosis. Diagnosis was based on computed tomography, mini-laparoscopy and bioptic specimens. Histology revealed an adenocarcinoma of the biliary tract with expression of epithelial growth factor receptor. After informed consent the patient received experimental gemcitabine (1000 mg/m²) every other week and cetuximab (250 mg/m²) weekly for palliative chemotherapy. During the reported follow up (since time of first presentation) 20 cycles of chemotherapy were administered. Relevant chemotherapy-related toxicity was limited on gemcitabine-associated side effects. Predominantly, haematological toxicity (CTC, grade 3) and neutropenic fever (CTC, grade 3) promoted by catheter-related sepsis were observed. Cetuximab caused only mild skin toxicity (CTC, grade 1).

Chemotherapy led to a partial response (> 30% reduction, according to RECIST) of the target lesions and disappearance of the peritoneal carcinomatosis as shown by computed tomography. Partial response occurred after 17 weeks of treatment and remained stable during the entire course of chemotherapy for 9.7 months. In parallel, Ca 19-9 serum levels, which were elevated 5-fold at time of diagnosis, returned to normal after 16 weeks of treatment. The performance status stabilized and intravenous alimentation could be discontinued.

Conclusion

Our experience from one patient with CC suggests, that a combination of cytotoxic chemotherapy together with cetuximab may show promising efficacy in respect to survival and quality of life. Therefore cetuximab, as a component of palliative chemotherapy in biliary tract cancer, needs further evaluation in prospective randomized trials.

Molecular biology of epidermal growth factor receptor inhibition for cancer therapy

Understanding the role of the epidermal growth factor receptor (EGFR) in cellular signalling processes underlying malignancy has enabled the development of rationally designed EGFR-targeted therapeutics. Strategies have been devised to interfere with the EGFR signalling at three different levels: at the extracellular level, competing with ligand binding; at the intracellular level, inhibiting the activation of the tyrosine kinase; or at the mRNA level, modulating the expression of the EGFR protein. Each of these strategies has proven to have an antitumour effect mediated by events such as inhibition of cell proliferation, induction of apoptosis, decrease of cellular invasion and migration; and/or inhibition of angiogenesis. Furthermore, the combination of these strategies with traditional chemotherapy or radiotherapy has generally resulted in enhanced antitumour effects. Likewise, the benefit of interfering simultaneously with different signalling pathways has been documented to improve tumour growth inhibition. These preclinical results have encouraged clinical studies that led to the FDA approval of three drugs. However, finding the perfect strategy for each individual patient appears to be a limiting factor, demanding further research to be able to generate relevant molecular expression profiles on a case-to-case basis. Taken together, a successful EGFR inhibition will require a better understanding of signalling pathways in combination with the development of rationally designed effective molecules.

EGFR tyrosine kinase inhibitors decrease VEGF expression by both hypoxia-inducible factor (HIF)-1-independent and HIF-1-dependent mechanisms

Epidermal growth factor receptor (EGFR) inhibitors can decrease vascular endothelial growth factor (VEGF) expression and tumor angiogenesis. In the current study, we investigate the molecular pathways by which this occurs using two drugs that have been used in the clinic, gefitinib (Iressa) and erlotinib (Tarceva). The decrease in VEGF expression by gefitinib in SQ20B squamous cell carcinoma cells was opposed by adenoviral expression of Akt in these cells. The hypoxia-inducible factor-1 (HIF-1) binding site located at approximately -1 kbp in the VEGF promoter was not required for down-regulation of promoter activity by gefitinib under normoxia. Furthermore, the drug decreased activity of a reporter containing the -88/+54 region. In a gel shift assay, gefitinib led to decreased retardation of a labeled DNA oligonucleotide probe corresponding to the -88/-66 region of the VEGF promoter, which contains Sp1 binding sites. These effects of gefitinib on VEGF promoter activity and DNA binding were both reversed by Akt expression. Phosphorylation of Sp1 was decreased in the presence of gefitinib. Gefitinib also decreases VEGF expression by decreasing HIF-1alpha expression. This occurs due to decreased protein translation without any change in the level of HIF-1alpha mRNA. Together, these results suggest that gefitinib decreases VEGF expression both by decreasing Sp1 binding to the proximal core VEGF promoter and by down-regulating HIF-1alpha expression. Similar results were obtained with erlotinib in SQ20B and gefitinib in HSC3 squamous carcinoma cells. These results indicate that there are at least two separate mechanisms by which EGFR inhibitors decrease VEGF expression.

The Molecular Biology of Pulmonary Metastasis

Curing cancer requires the treatment of metastatic disease. Whether this is a patient with advanced disease and clinically apparent metastases, or if the patient with localized disease is at risk for development of dissemination, failure to control metastasis will result in a poor outcome. Here, we have presented a molecular guide to our current understanding of the processes underlying metastasis. Experimental clinical trials designed to further the understanding of metastasis are often limited by selection of patients with advanced disease. Therefore, our understanding of the processes involved in the metastatic cascade is limited by the availability of comprehensive experimental model systems. The study of metastasis relies most heavily on xenografts, tumors using human cell lines, or tumor tissue that can grow in mice. These models present a limited recapitulation of the patients. Xenograft models require some degree of immunosuppression on the part of the host, because mice with native immune systems will reject transplanted human tumors, preventing their growth. As a result, mice with immune defects ranging from depleted T cells (nude mice) to absent T, B, and NK cells (SCID-Beige) are used as hosts. As the evasion of the immune system is a key function demonstrated by the metastatic cancer cell, xenograft models, by necessity, subvert this step. Furthermore, recent studies have established that angiogenesis in transplanted tumors is different than in native tumors, further highlighting the limitations of these models. With these limitations, studies of metastasis may require development of models of autochthonous tumors, that is, tumors originating in the study animals. A number of cell lines of autochthonous murine tumors have been established that generate metastatic disease after implantation into mice. Moreover, some transgenic animals spontaneously develop metastatic tumors that, although occurring in genetically engineered animals, may represent the most complete model from early development to late effects. Finally, a very promising field of autochthonous tumor studies lies in work with companion animals (pets). Some dogs will have cancer, often with striking similarities to those of their human counterparts. These pets may represent an important study group, because they have autochthonous tumors, occurring spontaneously, in an outbred population. In all of these cases, the tumor, new vasculature, and the immune system are syngeneic with the host. In addition to the advances in model systems, advances in technology will further our understanding and ability to combat metastatic disease. As demonstrated, genomics is proving to be a powerful tool in identifying those at risk for metastasis. From these genetic signatures, molecular targets may be deduced from the genes altered in patients with poor prognoses. Furthermore, other molecular tools such as proteomic analysis may provide further information. Clearly, therefore, a synthesis of different technologies and complimentary information will be required to target metastases and improve the outcome for patients affected by them.

Laminin alpha2 chain-positive vessels and epidermal growth factor in lung neuroendocrine carcinoma: a model of a novel cooperative role of laminin-2 and epidermal growth factor in vessel neoplastic invasion and metastasis

Capillaries expressing the laminin alpha2 chain in basement membranes may be considered early developing vessels in normal and neoplastic human tissues. Therefore, we investigated whether up-regulation of this extracellular matrix protein favors transendothelial migration of neoplastic cells and then metastasis. In lung small and large cell neuroendocrine carcinomas, which exhibit a stronger metastatic tendency among carcinomas, laminin alpha2 chain-positive vessels were more numerous than in carcinoid tumors and supraglottis, breast, and lung non-small cell carcinomas, suggesting a direct relationship between these vessels and metastasis. In vitro studies showed that epidermal growth factor (EGF) induced a more efficient migration of the AE-2 lung neuroendocrine carcinoma cell line through the purified laminin alpha2 chain rather than through the laminin beta1 chain and fibronectin. AE-2 cells constitutively expressed all EGF receptors and the alpha6beta1 integrin, which is one of the laminin alpha2 chain receptors. EGF up-regulated alpha6beta1 expression in several tumors. In this regard, we show that EGF increased the chemo-kinetic migration of AE-2 cells through EAHY endothelial monolayers, which was inhibited by the anti-alpha6 integrin chain monoclonal antibody. These data indicate that laminin alpha2 chain and alpha6beta1 may be mutually involved in EGF-dependent migration of AE-2 cells and that laminin alpha2 chain-positive vessels may favor metastasis of EGF-dependent tumors.

Mechanisms of angiogenesis in gliomas

Gliomas are the most frequent primary tumors of the central nervous system in adults. Glioblastoma multiforme, the most aggressive form of astrocytic tumors, displays a rapid progression that is accompanied by particular poor prognosis of patients. Intense angiogenesis is a distinguishing pathologic characteristic of these tumors and in fact, glioblastomas are of the most highly vascularized malignant tumors. For this reason, research and therapy strategies have focused on understanding the mechanisms leading to the origin of tumor angiogenic blood vessels in order to develop new approaches that effectively block angiogenesis and cause tumor regression. We discuss here some important features of glioma angiogenesis and we present molecules and factors and their possible functions and interactions that play a role in neovascularization. In spite of the great progress that molecular biology has achieved on investigating tumor angiogenesis, many aspects remain obscure and the complexity of the angiogenic process stands for an obstacle in identifying the exact and complete molecular pathways orchestrating new blood vessels formation, which are necessary for the survival and expansion of these tumors.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Anti-tumor activity of the combination of cetuximab, an anti-EGFR blocking monoclonal antibody and ZD6474, an inhibitor of VEGFR and EGFR tyrosine kinases

PURPOSE

The epidermal growth factor receptor (EGFR) autocrine pathway plays an important role in cancer cell growth. Vascular endothelial growth factor A (VEGF-A) is a key regulator of tumor-induced endothelial cell proliferation and vascular permeability. ZD6474 is an orally available, small molecule inhibitor of VEGF receptor-2 (VEGFR-2), EGFR and RET tyrosine kinase activity. We investigated the activity of ZD6474 in combination with cetuximab, an anti-EGFR blocking monoclonal antibody, to determine the anti-tumor activity of EGFR blockade through the combined use of two agents targeting the receptor at different molecular sites in cancer cells and of VEGFR-2 blockade in endothelial cells.

EXPERIMENTAL DESIGN

The anti-tumor activity in vitro and in vivo of ZD6474 and/or cetuximab was tested in human cancer cell lines with a functional EGFR autocrine pathway.

RESULTS

The combination of ZD6474 and cetuximab determined synergistic growth inhibition in all cancer cell lines tested as assessed by the Chou and Talalay method. In nude mice bearing established human colon carcinoma (GEO) or lung adenocarcinoma (A549) xenografts and treated with ZD6474 and/or cetuximab for 4 weeks, a reversible tumor growth inhibition was caused by each drug. In contrast, a more significant tumor growth delay resulted from the combination of the two agents with an approximately 100-110 days increase in mice median overall survival as compared to single agent treatment.

CONCLUSIONS

This study provides a rationale for evaluating in a clinical setting the double blockade of EGFR in combination with inhibition of VEGFR-2 signaling as cancer therapy.

Targeting multiple signal transduction pathways in lung cancer

Growth factor signals are propagated from the cell surface to intracellular processes that control critical functions such as growth, differentiation, angiogenesis, and inhibition of apoptosis via sequential kinase signaling. These kinases are receptor kinases, which are transmembrane proteins such as epidermal growth factor receptor or cytoplasmic kinases such as Src kinase. In malignancies, these signaling pathways are often exploited to optimize tumor growth and metastasis. Thus, they represent attractive targets for cancer therapy. This review will summarize current knowledge of the small-molecule multiple-kinase inhibitors in lung cancer therapy. These inhibitors generally hinder the phosphorylation of several protein kinases of membrane receptors, such as vascular endothelial growth factor receptors, platelet-derived growth factor receptors, the human epidermal growth factor receptor family, and cytoplasmic receptors such as c-Kit, Raf kinase, and FLT3. These inhibitors include ZD6474, SU11248, AEE 788, sorafenib, vatalanib, and AG-013736.

Mechanisms of disease: Radiosensitization by epidermal growth factor receptor inhibitors

The epidermal growth factor receptor (EGFR) inhibitors are among the most intensely studied new molecular therapeutic agents. Although response rates have been somewhat disappointing when EGFR inhibitors are used as single-agent therapy for advanced disease, these inhibitors may be more effective as chemo- and radiosensitizers. The first phase III randomized trial evaluating EGFR inhibitors as radiosensitizers in patients with locally advanced head and neck cancer was strongly positive, indicating significant potential of this class of agents to improve outcome with radiotherapy. However, optimal implementation of EGFR inhibitors as radiosensitizers depends, in part, on a better understanding of the mechanisms of radiosensitization. Preclinical studies provide important observations with regard to potential mechanisms. The phenotypic cellular changes associated with EGFR inhibition are impressively consistent between different model systems, with almost all studies showing that EGFR inhibitors affect proliferation, angiogenesis, and cell survival. Whether EGFR inhibitors influence response to radiation directly, or whether the improved response is a result of additive effects of the two modalities, remains unclear. However, cell-cycle arrest, endothelial cell sensitivity, and apoptotic potential are all important factors in radiation response of epithelial tumors. Furthermore, less-studied effects of EGFR inhibitors on DNA repair suggest that modulation of DNA damage response to cytotoxic injury might result in radio- or chemosensitization. This review will explore potential mechanisms of radiosensitization by EGFR inhibitors.

Targeted molecular therapy of anaplastic thyroid carcinoma with AEE788

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive human malignancies with a mean survival of only 6 months. The poor prognosis of patients with ATC reflects the current lack of curative therapeutic options and the need for development of novel therapeutic strategies. In this study, we report the results of a preclinical study of AEE788, a dual inhibitor of epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) tyrosine kinases, against ATC. AEE788 was able to inhibit the proliferation and induce apoptosis of ATC cell lines in vitro. Administration of AEE788, alone and in combination with paclitaxel, to athymic nude mice bearing s.c. ATC xenografts inhibited the growth of ATC xenografts by 44% and 69%, respectively, compared with the control group. Furthermore, tumors from mice treated with AEE788, alone and in combination with paclitaxel, showed increase in apoptosis of tumor cells by approximately 6- and 8-fold, respectively, compared with the control group. The microvessel density within the ATC xenografts was decreased by >80% in the mice treated with AEE788 alone and in combination with paclitaxel compared with the control group. Lastly, immunofluorescence microscopy showed the inhibition of EGFR autophosphorylation on the tumor cells as well as the inhibition of VEGFR-2 autophosphorylation on tumor endothelium. Considering the fact that curative options seldom exist for patients with ATC, concurrent inhibition of EGFR and VEGFR tyrosine kinases seems to be a valid and promising anticancer strategy for these patients.

Epidermal growth factor receptor directed therapy in head and neck cancer

Squamous cell head and neck cancer (SCCHN) is the seventh most common cause of cancer death worldwide and its incidence is rising rapidly in developing countries. Despite recent advances in managing locally advanced SCCHN, patients with recurrent and metastatic SCCHN have a poor prognosis and little progress has been made its management. Epidermal growth factor receptor (EGFR) has been implicated in the pathogenesis of SCCHN and is a marker of poor prognosis. Recent advances in targeted therapeutics against EGFR are being investigated clinically. In this article, we review the different modalities utilized to inhibit EGFR signaling in SCCHN, including small molecule tyrosine kinase inhibitors, monoclonal antibodies, anti-sense therapy and immunotoxin conjugates. Monotherapy with EGFR inhibitors has demonstrated response rates between 5 and 15% in advanced SCCHN. However, combining EGFR inhibitors with cytotoxic chemotherapy or radiation therapy appears to augment response rates and survival. With the foundation for the use of EGFR inhibitors laid in these studies, future studies will need to optimize the delivery of these agents in combination with conventional therapies.

Resistance to epidermal growth factor receptor-targeted therapy

The epidermal growth factor receptor (EGFR) has been a major target of molecular anticancer therapy. Two approaches have been developed, involving monoclonal antibodies and receptor tyrosine kinase inhibitors, and both have demonstrated benefit in clinical trials. However, evidence of resistance to these drugs has been described. Cellular levels of EGFR do not always correlate with response to the EGFR tyrosine kinase inhibitors, indicating acquired resistance to these drugs. Since EGFR antagonists interfere with the activation of several intracellular pathways that control cell proliferation, survival, apoptosis, angiogenesis, invasion and metastasis, acquired resistance can occur as a result of several different molecular mechanisms: autocrine/paracrine production of ligand, receptor mutation, constitutive activation of the downstream pathway and activation of alternative pathways. We will describe here potential mechanisms that can cause resistance to EGFR-targeted drugs. Combinations of EGFR antagonists with inhibitors targeting different signaling mechanism(s) - such as insulin-like growth factor receptor and vascular endothelial growth factor receptor - that share the same downstream mediator (e.g., phosphatidylinositol 3-kinase/Akt, mitogen-activated protein kinase), may circumvent or delay the development of resistance to EGFR antagonists resulting in enhanced antitumor activities.

The role of the extracellular matrix in angiogenesis in malignant glioma tumors

Angiogenesis is a promising target for the development of effective strategies for the treatment of malignant brain tumors in that it has the potential to starve large tumors and prevent the regrowth of residual margins. Two critical steps in angiogenesis, the proliferation of activated endothelial cells and their migration into the perivascular space (sprouting), require adherence of the endothelial cells to the extracellular matrix (ECM). Thus, the availability of the appropriate ligands within the ECM contributes to the regulation of angiogenesis. In addition, several components of the ECM can act through other mechanisms to further promote angiogenesis or inhibit it. Current evidence suggests that the regulation of angiogenesis is a dynamic process in which the endothelial cells can promote angiogenesis by secreting proteases that remodel the ECM, tumor cells can further promote angiogenesis by secreting ECM components and actively remodeling their environment, and stromal cells may respond to angiogenesis associated with tumors and inflammatory reactions by secreting inhibitory molecules. Here, we provide a critical review of the protein and proteoglycan components of the ECM that have been implicated in angiogenesis with an emphasis on their role in promoting or inhibiting angiogenesis in brain tumors.

Imatinib and hydroxyurea in pretreated progressive glioblastoma multiforme: a patient series

BACKGROUND

Grade IV malignancies of the brain, such as glioblastoma multiforme (GBM), are associated with a dismal prognosis. Autocrine and paracrine loops of platelet-derived growth factor (PDGF) signaling, as well as other signal transduction pathways, have been postulated to play a role in glioblastoma transformation, and molecules involved in these pathways can potentially serve as targets for therapeutic inhibitory agents. Imatinib, an inhibitor of PDGF receptors alpha and beta, as well as other selected tyrosine kinases, is indicated for treatment of chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor (GIST). Unfortunately, imatinib, as with many conventional chemotherapeutic agents, has limited efficacy as monotherapy in GBM. In preclinical studies, the chemotherapeutic agent hydroxyurea is demonstrated to have cytotoxic effects additive with imatinib.

PATIENTS AND METHODS

We tested the combination of hydroxyurea and imatinib in 30 grade IV progressive GBM patients refractory to chemo- and radiotherapy. All 30 patients were evaluable after a median 19 weeks observation time.

RESULTS

Combination therapy with imatinib and hydroxyurea resulted in a 20% response rate, including complete and partial responses. Patients experiencing response or stable disease yielded a combined clinical benefit rate of 57%. Median time to progression was 10 weeks and median overall survival was 19 weeks. Three patients continue to survive on combination therapy, with the shortest duration being 106 weeks. Six-month and 2-year progression-free survival rates were 32% and 16%, respectively.

CONCLUSION

The efficacy results, combined with findings that imatinib and hydroxyurea were well tolerated, suggest that this combination shows promise as therapy for GBM.

The antitumor and antiangiogenic activity of vascular endothelial growth factor receptor inhibition is potentiated by ErbB1 blockade

PURPOSE

Receptor tyrosine kinases of the ErbB family play important roles in the control of tumor growth. Vascular endothelial growth factor (VEGF) stimulates endothelial cell proliferation, enhances vascular permeability, and plays an important role in tumor vascularization. We evaluated the effects of selective VEGF receptor (VEGFR; PTK787/ZK222584) and ErbB (PKI166 and ZD1839) inhibitors on tumor growth and angiogenesis and asked whether additional therapeutic benefit was conferred by combination treatment.

EXPERIMENTAL DESIGN

The antitumor activity of each inhibitor alone or in combination was assessed in human cancer models in immunocompromised mice. ErbB receptor expression and activation of downstream signaling pathway was evaluated in both tumor and endothelial cells.

RESULTS

Both ErbB inhibitors significantly enhanced the antitumor activity of PTK787/ZK222584. In vitro, ErbB1 inhibition blocked VEGF release by tumor cells and proliferation of both tumor and endothelial cells. In an in vitro angiogenesis assay, epidermal growth factor (EGF) stimulated the release of VEGF by smooth muscle cells resulting in increased angiogenesis, a response blocked by administration of PTK787/ZK222584. Under basal condition, both ZD1839 and PTK787/ZK222584 blocked sprouting, likely via inhibition of an autocrine ErbB1 loop and VEGFR signaling, respectively, in endothelial cells. In conditions of limiting VEGF, EGF plays an important role in endothelial cell proliferation, survival, and sprouting.

CONCLUSION

We have shown that activation of ErbB1 triggers a plethora of effects, including direct effects on tumor and endothelial cells and indirect effects mediated via induction of VEGF release. Simultaneous blockade of ErbB1 and VEGFR pathways results in a cooperative antitumor effect, indicating that this combination may represent a valid therapeutic strategy.

Cooperative Antitumor Effect of Multitargeted Kinase Inhibitor ZD6474 and Ionizing Radiation in Glioblastoma

PURPOSE

Glioblastoma multiforme is an aggressive disease in which vascular endothelial growth factor (VEGF) and the EGF receptor (EGFR) are implicated in tumor growth, relapse, and resistance to radiotherapy and chemotherapy. The VEGF receptors VEGFR-1 (flt-1) and VEGFR-2 (KDR), typically present on endothelial cells, have also been identified in human glioblastoma tissues and cell lines. In addition, EGFR is dysregulated in the majority of human glioblastomas and EGFR overexpression correlates with shorter survival. We have investigated the antitumor and antiangiogenic effect of ZD6474, an inhibitor of both VEGFR and EGFR signaling as a single agent and in combination with ionizing radiation.

EXPERIMENTAL DESIGN

We have used ZD6474 and/or ionizing radiation in human glioblastoma cell lines D54 and U251 in vitro and in nude mice bearing established xenografts. The effects of treatment on tumor blood vessels and protein expression were evaluated by Western blot and immunohistochemistry.

RESULTS

As single agents, ionizing radiation and ZD6474 caused a dose-dependent inhibition of soft agar growth in D54 and U251 cell lines, whereas a cooperative effect was obtained in combination. Treatment of mice bearing D54 xenografts with either ZD6474 or radiotherapy alone caused tumor growth inhibition that was reversible upon treatment cessation. A cooperative and long-lasting inhibition of tumor growth was obtained with ZD6474 in combination with concomitant radiotherapy. The antiproliferative effect was accompanied by inhibition of VEGF protein expression and inhibition of angiogenesis as measured by vessel counting.

CONCLUSION

This study shows the antitumor activity of ZD6474 in combination with ionizing radiation in glioblastoma both in vitro and in vivo, and provides a scientific rationale to evaluate ZD6474 alone or in combination with radiotherapy in patients affected by this disease.

Angiogenesis and lung cancer: prognostic and therapeutic implications

Lung cancer is the most common cause of cancer death worldwide, with most patients dying with metastatic disease. The prognosis for the majority of patients remains poor. It is evident that advances in the treatment of this and other tumor types will require new approaches, and recent research has focused on molecular-targeted therapies. A key therapeutic strategy is inhibition of specific processes essential for tumor vascular development (a concept known to be beneficial in colorectal cancer) and a range of such antiangiogenic agents are currently in development. The most promising of these target the proangiogenic vascular endothelial growth factor (VEGF), either by preventing VEGF-receptor binding or inhibiting downstream receptor signaling. However, other more direct approaches against tumor vasculature are also in development. Since antiangiogenic agents often exert an indirect, cytostatic effect, many are being evaluated in combination with conventional chemotherapies in order to optimize the anticancer effects of both strategies. Additionally, the combination of several antiangiogenic agents is also being explored. This has become possible given the large number of agents currently available. As part of this evaluation process, the assessment of surrogate markers of target inhibition and treatment effect is ongoing in the hope of identifying reliable surrogate markers to aid the development of this new generation of anticancer agents.

The effect of epidermal growth factor on production of vascular endothelial growth factor by amnion-derived (WISH) cells

Our objective was to clarify the physiological role of vascular endothelial growth factor (VEGF) by amnion-derived (WISH) cells. WISH cells were cultured, and the effect of epidermal growth factor (EGF), mitogen-activated protein (MAP) kinase kinase or extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors (U0126) or phosphatidylinositol (PI) 3-kinase on the production of VEGF was examined. VEGF was assayed by ELISA. The activation of MAP kinase and akt, which is phosphorylated by PI 3-kinase, were detected by Western blot analysis using anti-phosphorylated MAP kinase antibody and anti-phosphorylated akt antibody. In the time course of VEGF production following EGF treatment, VEGF production showed a significant increase only after 16 (p < 0.01)-32h (p < 0.01). EGF increased the production of VEGF by WISH cells in a dose-dependent manner. The MAP kinase and akt activity were determined by treatment with EGF. VEGF production was significantly decreased following pretreatment with U0126 or wortmannin for two hours before treatment with EGF (p < 0.01, p < 0.01). WISH cells appeared to produce VEGF via a mechanism involving tyrosine kinase activation of EGF receptor and MAP kinase or PI 3-kinase. It is suggested that VEGF may contribute to the neovascularization and proliferation of the placenta and gestational tissue, and EGF may play an important role in regulation of VEGF production in the placenta.

ZD6474--a novel inhibitor of VEGFR and EGFR tyrosine kinase activity

Angiogenesis is crucial for maintaining the supply of oxygen and nutrients required to support solid tumour growth. Inhibitors of tumour blood vessel formation are therefore being sought, in particular, inhibitors of vascular endothelial growth factor-A (VEGF)-signalling, which has a pivotal role in stimulating neovascular growth and survival. ZD6474 is an orally bioavailable inhibitor of VEGF receptor-2 tyrosine kinase activity that in preclinical studies has been shown to inhibit both VEGF-induced signalling in endothelial cells and tumour-induced angiogenesis. Consistent with inhibition of angiogenesis, once-daily oral dosing of ZD6474 produced significant broad-spectrum antitumour activity in a panel of histologically diverse human tumour xenografts. In addition to its antiangiogenic properties, ZD6474 also has activity against the epidermal growth factor receptor (EGFR) tyrosine kinase, which could impart a direct inhibitory effect on tumour cell growth and survival. This may be particularly relevant in tumours with a dependency upon EGFR signalling, for example in certain tumours harbouring activating mutations in EGFR. RET kinase has also been identified as a third target for ZD6474. This review summarises preclinical studies with this unique agent and considers its future direction in cancer treatment.

Endogenous inhibitors of angiogenesis in malignant gliomas: nature's antiangiogenic therapy

Angiogenesis is necessary for tumor growth beyond a volume of approximately 2 mm(3). This observation, along with the accessibility of tumor vessels to therapeutic targeting, has resulted in a research focus on inhibitors of angiogenesis. A number of endogenous inhibitors of angiogenesis are found in the body. Some of these are synthesized by specific cells in different organs, and others are created by extracellular proteolytic cleavage of plasma-derived or extracellular matrix-localized proteins. In this review, we focus on angiostatin, endostatin, PEX, pigment epithelial-derived factor, and thrombospondin (TSP)-1 and -2, either because these molecules are expressed in malignant glioma biopsies or because animal studies in malignant glioma models have suggested that their therapeutic administration could be efficacious. We review the known mechanisms of action, potential receptors, expression in glioma biopsy samples, and studies testing their potential therapeutic efficacy in animal models of malignant glioma. Two conclusions can be made regarding the mechanisms of action of these inhibitors: (1) Several of these inhibitors appear to mediate their antiangiogenic effect through multiple protein-protein interactions that inhibit the function of proangiogenic molecules rather than through a specific receptor-mediated signaling event, and (2) TSP-1 and TSP-2 appear to mediate their antiangiogenic effect, at least in part, through a specific receptor, CD36, which initiates the antiangiogenic signal. Although not proven in gliomas, evidence suggests that expression of specific endogenous inhibitors of angiogenesis in certain organs may be part of a host antitumor response. The studies reviewed here suggest that new antiangiogenic therapies for malignant gliomas offer exciting promise as nontoxic, growth-inhibitory agents.

Prolactin-induced expression of vascular endothelial growth factor via Egr-1

Angiogenesis is a dynamic process regulated by both local and systemic factors. Among these is vascular endothelial growth factor (VEGF), a potent effector of angiogenesis and vascular permeability. Previously we showed that VEGF is temporally and spatially regulated in the mouse mammary gland during development and lactation. Given the functions of prolactin (PRL) during these stages and the supporting role of the vasculature, we investigated the regulation of VEGF by PRL. Treatment of HC11 mouse mammary epithelial and Nb2 rat lymphoma cells with PRL induced VEGF expression. Deletion and mutation analysis identified a GC-rich region in the proximal region of the VEGF promoter that constitutively bound Sp1 and PRL-induced Egr-1. These sites conferred PRL-responsiveness leading to increased VEGF transcription. The induction of VEGF by PRL was PRL receptor-, Jak2- and MAP kinase kinase-dependent. Our results indicate that PRL induces VEGF expression through Egr-1, and implicates VEGF as an intermediary of PRL-regulated angiogenesis.

Interleukin-6 increases vascular endothelial growth factor and angiogenesis in gastric carcinoma

Interleukin-6 (IL-6) is a proinflammatory cytokine associated with the disease status of gastric carcinoma (GC). Vascular endothelial growth factor (VEGF) is a potent tumor angiogenic factor in GC. In this study, we attempted to clarify whether IL-6 can regulate VEGF and angiogenesis in GC. GC samples from 54 surgical specimens were subjected to immunohistochemical examination of IL-6, VEGF, and tumor microvessels, and results showed that IL-6 was positively correlated with VEGF expression and tumor vasculature. We determined VEGF expression in four GC cell lines by ELISA, revealing that GC cells can produce significant amount of VEGF with increasing dose and duration of IL-6 stimulation. Next, a luciferase reporter gene assay was employed to determine the signaling pathway driving the VEGF promoter by IL-6, which showed that the JAK/STAT pathway is involved in the stimulation of VEGF gene expression. The effects of IL-6 on angiogenesis in vitro and in vivo were evaluated by HUVEC studies and the Matrigel plug assay, respectively. Results showed that IL-6 effectively promoted HUVEC proliferation and tube formation in vitro and Matrigel plug vascularization in vivo, primarily by inducing VEGF in GC. This study provides evidence that the multifunctional cytokine, IL-6, may induce VEGF expression which increases angiogenesis in gastric carcinogenesis.

AEE788, a Dual Tyrosine Kinase Receptor Inhibitor, Induces Endothelial Cell Apoptosis in Human Cutaneous Squamous Cell Carcinoma Xenografts in Nude Mice

PURPOSE

We investigated whether concomitant blockade of the epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) signaling pathways by AEE788, a dual inhibitor of EGFR and VEGFR tyrosine kinases, would inhibit the growth of cutaneous squamous cell carcinoma (SCC) cells and human cutaneous cancer xenografts in nude mice.

EXPERIMENTAL DESIGN

We examined the effects of AEE788 on the phosphorylation of EGFR and VEGFR-2 in cutaneous SCC cells expressing EGFR and VEGFR-2 and cutaneous SCC cell growth and apoptosis. We assessed the in vivo antitumor effects of AEE788 in a xenograft model in nude mice. AEE788 (50 mg/kg) was given orally thrice weekly to mice that had been s.c. injected with Colo16 tumor cells. Mechanisms of in vivo AEE788 activity were determined by immunohistochemical analysis.

RESULTS

Treatment of cutaneous SCC cells with AEE788 led to dose-dependent inhibition of EGFR and VEGFR-2 phosphorylation, growth inhibition, and induction of apoptosis. In mice treated with AEE788, tumor growth was inhibited by 54% at 21 days after the start of treatment compared with control mice (P < 0.01). Immunohistochemical analysis revealed that AEE788 inhibited phosphorylation of EGFR and VEGFR and induced apoptosis of tumor cells and tumor-associated endothelial cells.

CONCLUSIONS

In addition to inhibiting cutaneous cancer cell growth by blocking EGFR and VEGFR signaling pathways in vitro, AEE788 inhibited in vivo tumor growth by inducing tumor and endothelial cell apoptosis.

Integrated Array-Comparative Genomic Hybridization and Expression Array Profiles Identify Clinically Relevant Molecular Subtypes of Glioblastoma

Glioblastoma, the most aggressive primary brain tumor in humans, exhibits a large degree of molecular heterogeneity. Understanding the molecular pathology of a tumor and its linkage to behavior is an important foundation for developing and evaluating approaches to clinical management. Here we integrate array-comparative genomic hybridization and array-based gene expression profiles to identify relationships between DNA copy number aberrations, gene expression alterations, and survival in 34 patients with glioblastoma. Unsupervised clustering on either profile resulted in similar groups of patients, and groups defined by either method were associated with survival. The high concordance between these separate molecular classifications suggested a strong association between alterations on the DNA and RNA levels. We therefore investigated relationships between DNA copy number and gene expression changes. Loss of chromosome 10, a predominant genetic change, was associated not only with changes in the expression of genes located on chromosome 10 but also with genome-wide differences in gene expression. We found that CHI3L1/YKL-40 was significantly associated with both chromosome 10 copy number loss and poorer survival. Immortalized human astrocytes stably transfected with CHI3L1/YKL-40 exhibited changes in gene expression similar to patterns observed in human tumors and conferred radioresistance and increased invasion in vitro. Taken together, the results indicate that integrating DNA and mRNA-based tumor profiles offers the potential for a clinically relevant classification more robust than either method alone and provides a basis for identifying genes important in glioma pathogenesis.

Genetic and hypoxic regulation of angiogenesis in gliomas

Infiltrative astrocytic neoplasms are by far the most common malignant brain tumors in adults. Clinically, they are highly problematic due to their widely invasive nature which makes a complete resection almost impossible. Biologic progression of these tumors is inevitable and adjuvant therapies are only moderately effective in prolonging survival. Glioblastoma multiforme (GBM; WHO grade IV), the most malignant form of infiltrating astrocytoma, can evolve from a lower grade precursor tumor (secondary GBM) or can present as high grade lesion from the outset, so-called de novo GBM. Molecular genetic investigations suggest that GBMs are comprised of multiple molecular genetic subsets. Notwithstanding the diversity of genetic alterations leading to the GBM phenotype, the vascular changes that evolve in this disease, presumably favoring further growth, are remarkably similar. Underlying genetic alterations in GBM may tilt the balance in favor of an angiogenic phenotype by upregulation of pro-angiogenic factors and down-regulation of angiogenesis inhibitors. Increased vascularity and endothelial cell proliferation in GBMs are also driven by hypoxia-induced expression of pro-angiogenic cytokines, such vascular endothelial growth factor (VEGF). Understanding the contribution of genetic alterations and hypoxia in angiogenic dysregulation in astrocytic neoplasms will lead to the development of better anti-angiogenic therapies for this disease. This review will summarize the properties of angiogenic dysregulation that lead to the highly vascularized nature of these tumors.

Simultaneously targeting epidermal growth factor receptor tyrosine kinase and cyclooxygenase-2, an efficient approach to inhibition of squamous cell carcinoma of the head and neck

PURPOSE

Epidermal growth factor receptor (EGFR) and cyclooxygenase-2 (Cox-2) contribute to development of squamous cell carcinoma of the head and neck (SCCHN). Simultaneously blocking both EGFR and Cox-2-mediated pathways may be an efficient means of inhibiting cancer cell growth in SCCHN.

EXPERIMENTAL DESIGN

A combination of EGFR-selective tyrosine kinase inhibitors (TKIs) AG1478 or ZD1839 (Iressa or gefitinib) with a Cox-2 inhibitor (Cox-2I) celecoxib (Celebrex) was studied for its effects on cell growth, cell cycle progression, and apoptosis in SCCHN cell lines by cell growth assay, clonogenic assay, flow cytometric analysis, and terminal deoxynucleotidyl transferase-mediated nick end labeling assay. A potential effect of EGFR TKIs and Cox-2I on angiogenesis was examined by endothelial capillary tube formation assay. Primary and secondary targets of EGFR TKIs and Cox-2I were also examined using immunoblotting and immunoprecipitation after the combined treatment.

RESULTS

The combination of AG1478 or ZD1839 with celecoxib either additively or synergistically inhibited growth of the five SCCHN cell lines examined, significantly induced G(1) arrest and apoptosis, and suppressed capillary formation of endothelium. Furthermore, the combination showed strong reductions of p-EGFR, p-extracellular signal-regulated kinase 1/2, and p-Akt in SCCHN cells as compared with the single agents. Both AG1478 and ZD1839 inhibited expression of Cox-2 protein, whereas celecoxib mainly blocked the production of prostaglandin E(2).

CONCLUSIONS

These results suggest that cell growth inhibition induced by a combination of EGFR TKIs and Cox-2I is mediated through simultaneously blocking EGFR and Cox-2 pathways. This combination holds a great potential for the treatment and/or prevention of SCCHN.

Antitumor Activity of ZD6474, a Vascular Endothelial Growth Factor-2 and Epidermal Growth Factor Receptor Small Molecule Tyrosine Kinase Inhibitor, in Combination with SC-236, a Cyclooxygenase-2 Inhibitor

Purpose: The epidermal growth factor receptor (EGFR) autocrine pathway plays an important role in cancer cell growth. Vascular endothelial growth factor (VEGF) is a key regulator of tumor-induced endothelial cell proliferation and vascular permeability. Enhanced cyclooxygenase-2 (COX-2) expression has been linked to cancer cell proliferation, EGFR activation, VEGF secretion, and tumor-induced angiogenesis. ZD6474 is an orally available, small molecule, dual VEGF receptor-2 (VEGFR-2) and EGFR tyrosine kinase inhibitor. We investigated the activity of ZD6474 in combination with SC-236, a selective COX-2 inhibitor, to determine the antitumor activity of the simultaneous blockade of EGFR, COX-2, and VEGF functions.

Experimental Design: The antitumor activity in vitro and in vivo of ZD6474 and/or SC-236 was tested in human cancer cell lines with a functional EGFR autocrine pathway.

Results: The combination of ZD6474 and SC-236 determined supra-additive growth inhibition in all cancer cell lines tested. In nude mice bearing established human colon (GEO) or lung adenocarcinoma (A549) cancer xenografts and treated with ZD6474 and/or SC-236 for 3 weeks, a reversible tumor growth inhibition was seen with each agent, whereas a more prolonged growth inhibition that lasted for 3 to 5 weeks following the end of treatment resulted from the combination of the two agents. A long-term, 10-week treatment with ZD6474 plus SC-236 resulted in sustained tumor growth inhibition in all mice with tumor eradication in 3 of 10 GEO tumor–bearing mice and in 4 of 10 A549 tumor–bearing mice.

Conclusions: This study provides a rationale for evaluating the simultaneous blockade of EGFR, COX-2, and VEGF signaling as cancer therapy in a clinical setting.

Targeting vascular endothelial growth factor and angiogenesis for the treatment of colorectal cancer

Angiogenesis, the development and proliferation of new blood vessels, is critical for the growth of tumors. The process of new blood vessel formation is under complex control from a variety of pro- and anti-angiogenesis factors. By identifying and understanding these factors, new therapies have been developed to inhibit tumor growth and survival by blocking tumor-related angiogenesis. Recent success with the monoclonal antibody against vascular endothelial growth factor (VEGF; bevacizumab) in a large, randomized, phase III study has provided a critical proof of principle for this therapeutic area. This review will outline the biology of angiogenesis in colorectal cancer and discuss the current status of angiogenesis inhibition in its treatment.

ErbB2 overexpression in mammary cells upregulates VEGF through the core promoter

The angiogenic molecule, vascular endothelial growth factor (VEGF), is a critical regulator of normal and pathologic angiogenesis. ErbB2, an epidermal growth factor receptor family member whose overexpression in mammary tumors is correlated with poor patient prognosis, has been implicated as a positive modulator of VEGF expression. Mammary tumor cells overexpressing ErbB2 (NAFA cells) and a normal mouse mammary cell line (HC11) transfected with ErbB2 expression vectors were used to study the effects of ErbB2 overexpression on VEGF regulation. We found that ErbB2 overexpression led to an increase in endogenous VEGF mRNA as well as ErbB3 protein levels in HC11 cells. Additionally, we determined that ErbB2 overexpression-mediated upregulation of VEGF involves at least two distinct promoter elements, one previously identified as the hypoxia responsive element and the other the core promoter region (-161 to -51bp), which is specifically controlled via two adjacent SP1 binding sites (-80 to -60bp).