The establishment of a vascular supply is required for organ development and differentiation as well as for tissue repair and reproductive functions in the adult1 Neovascularization (angiogenesis) is also implicated in the pathogenesis of a number of disorders These include: proliferative retinopathies, age-related macular degeneration, tumors, rheumatoid arthritis, and psoriasis1,2 A strong correlation has been noted between density of microvessels in primary breast cancers and their nodal metastases and patient survival3 Similarly, a correlation has been reported between vascularity and invasive behavior in several other tumors4–6

The biology of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen in vitro and an angiogenic inducer in a variety of in vivo models. Hypoxia has been shown to be a major inducer of VEGF gene transcription. The tyrosine kinases Flt-1 (VEGFR-1) and Flk-1/KDR (VEGFR-2) are high-affinity VEGF receptors. The role of VEGF in developmental angiogenesis is emphasized by the finding that loss of a single VEGF allele results in defective vascularization and early embryonic lethality. VEGF is critical also for reproductive and bone angiogenesis. Substantial evidence also implicates VEGF as a mediator of pathological angiogenesis. In situ hybridization studies demonstrate expression of VEGF mRNA in the majority of human tumors. Anti-VEGF monoclonal antibodies and other VEGF inhibitors block the growth of several tumor cell lines in nude mice. Clinical trials with various VEGF inhibitors in a variety of malignancies are ongoing. Very recently, an anti-VEGF monoclonal antibody (bevacizumab; Avastin) has been approved by the Food and Drug Administration as a first-line treatment for metastatic colorectal cancer in combination with chemotherapy. Furthermore, VEGF is implicated in intraocular neovascularization associated with diabetic retinopathy and age-related macular degeneration.

/pdf/vascular-endothelial-growth-factor-basic-science-and-17gyy6h97s.pdf

Vascular endothelial growth factor: basic science and clinical progress.

Nonsteroidal anti-inflammatory drugs (NSAIDs) represent one of the most highly utilized classes of pharmaceutical agents in medicine. All NSAIDs act through inhibiting prostaglandin synthesis, a catalytic activity possessed by two distinct cyclooxygenase (COX) isozymes encoded by separate genes. The discovery of COX-2 launched a new era in NSAID pharmacology, resulting in the synthesis, marketing, and widespread use of COX-2 selective drugs. These pharmaceutical agents have quickly become established as important therapeutic medications with potentially fewer side effects than traditional NSAIDs. Additionally, characterization of the two COX isozymes is allowing the discrimination of the roles each play in physiological processes such as homeostatic maintenance of the gastrointestinal tract, renal function, blood clotting, embryonic implantation, parturition, pain, and fever. Of particular importance has been the investigation of COX-1 and -2 isozymic functions in cancer, dysregulation of inflammation, and Alzheimer's disease. More recently, additional heterogeneity in COX-related proteins has been described, with the finding of variants of COX-1 and COX-2 enzymes. These variants may function in tissue-specific physiological and pathophysiological processes and may represent important new targets for drug therapy.

Cyclooxygenase Isozymes: The Biology of Prostaglandin Synthesis and Inhibition

Vascular endothelial growth factor (VEGF) is a fundamental regulator of normal and abnormal angiogenesis. Recent evidence indicates that VEGF is essential for embryonic vasculogenesis and angiogenesis. Furthermore, VEGF is required for the cyclical blood vessel proliferation in the female reproductive tract and for longitudinal bone growth and endochondral bone formation. Substantial experimental evidence also implicates VEGF in pathological angiogenesis. Anti-VEGF monoclonal antibodies or other VEGF inhibitors block the growth of many tumor cell lines in nude mice. Furthermore, the concentrations of VEGF are elevated in the aqueous and vitreous humors of patients with proliferative retinopathies such as the diabetic retinopathy. In addition, VEGF-induced angiogenesis results in a therapeutic benefit in several animal models of myocardial or limb ischemia. Currently, both therapeutic angiogenesis using recombinant VEGF or VEGF gene transfer and inhibition of VEGF-mediated pathological angiogenesis are being pursued.

Molecular and biological properties of vascular endothelial growth factor.

BACKGROUND

The cyclooxygenase (COX) enzyme catalyzes the formation of prostaglandins, which can affect cell proliferation and alter the response of the immune system to malignant cells. The inducible form of COX, COX-2, has been shown to be important in carcinogenesis.



METHODS

The authors studied COX-1 and -2 expression in 20 tumors of the lung, colon, and breast (60 total) by using commercially available monoclonal and polyclonal antibodies on formalin fixed, paraffin embedded tissue. Our evaluation also included seven carcinoma-associated colonic adenomas and 10 mammary ductal carcinomas in situ (DCIS). Quantitation of immunoreactivity was accomplished using an immunohistochemical scoring system that approximates the use of image analysis-based systems.



RESULTS

Ninety percent of lung tumors (squamous cell carcinomas and adenocarcinomas), 71% of colon adenocarcinomas and 56% of breast tumors (DCIS and infiltrating ductal and lobular carcinomas) expressed COX-2 at a moderate to strong level, which was significantly different from the negligible expression in distant nonneoplastic epithelium (controls; P < 0.0001). Poorly differentiated histologic features were correlated with low COX-2 expression overall, especially in colon carcinomas. Among breast carcinomas, DCIS was more likely to express COX-2 than invasive carcinomas. Adenomatous colonic epithelium showed moderate COX-2 expression, as did adjacent nonneoplastic epithelium. COX-1 immunoreactivity was essentially weak to moderate in all tissues evaluated.



CONCLUSIONS

COX-2 expression is upregulated in well and moderately differentiated carcinomas of the lung, colon, and breast whereas COX-1 appears to be constitutively expressed at low levels. A possible COX-2 paracrine effect is suggested by moderate immunoreactivity in adjacent nonneoplastic epithelium. Cancer 2000;89:2637–45. © 2000 American Cancer Society.

COX-2 is expressed in human pulmonary, colonic, and mammary tumors.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2895%2900956-A

Induction of vascular endothelial growth factor expression in synovial fibroblasts by prostaglandin E and interleukin‐1: a potential mechanism for inflammatory angiogenesis

The effects of non-steroidal antiinflammatory drugs (NSAIDs) on non-small cell lung cancer (NSCLC) were investigated. Arachidonic acid (AA) was metabolized to prostaglandin E2 (PGE2) in NSCLC cells. NSAIDs such as aspirin or indomethacin reduced PGE2 levels in NCI-H157 and H1264 cells, and the decrease caused by PGE2 was reversed by epidermal growth factor (EGF). By RT-PCR, both cyclooxygenase (COX)-1 and COX-2 mRNAs are detected in NCI-H157 and H1264 cells. By Northern analysis, COX-2 mRNA was induced by EGF and phorbol ester. By immunocytochemistry, COX-1 and COX-2 enzymes were localized to NSCLC tumors. Aspirin, indomethacin and ibuprofen decreased NSCLC growth in vitro. Aspirin and indomethacin inhibited proliferation of NSCLC xenografts in nude mice. These data suggest that COX enzymes may be important regulatory components of NSCLC.

Non-small cell lung cancer cycloxygenase activity and proliferation are inhibited by non-steroidal antiinflammatory drugs

Dissociation of Basal Turnover and Cytokine-Induced Transcript Stabilization of the Human Cyclooxygenase-2 mRNA by Mutagenesis of the 3′-Untranslated Region☆☆☆

Prostaglandin E2 and vasoactive intestinal peptide increase vascular endothelial cell growth factor mRNAs in lung cancer cells.

Cyclooxygenase (Cox)-2 is a recently-identified isoform of prostaglandin synthase, a rate-limiting enzyme in prostaglandin (PG) biosynthesis. PGs are short-lived mediators that regulate a variety of biological processes in the vasculature including angiogenesis. While PGE2 is a potent inducer of angiogenesis, the mechanisms involved are not well-understood. We have cloned the Cox-2 gene as a differentiation-induced early response gene from human umbilical vein endothelial cells (HUVEC). The expression of the Cox-2 gene is induced in a sustained manner by the inflammatory mediator interleukin-1 (IL-1) and is suppressed by the anti-inflammatory glucocorticoid dexamethasone (dex). Post-transcriptional regulation of Cox-2 mRNA stability is a major mechanism that regulates the expression of the Cox-2 gene. IL-1 stabilizes the Cox-2 transcript turn-over and thereby achieve a sustained induction of the Cox-2-dependent PG synthesis. In contrast to the Cox-1 enzyme, the expression of the Cox-2 enzyme is low in normal quiescent tissues; however, in acute inflammation, Cox-2 in induced transiently and is suppressed as the inflammatory response subsides. In chronic inflammatory diseases such as rheumatoid arthritis (RA), however, the Cox-2 gene is chronically expressed in an exaggerated manner. High levels of Cox-2 expression is correlated with the highly angiogenic state of the RA synovium. Because PGE2 is a major prostanoid produced and PGE2 also induces angiogenesis, the mechanisms of Cox-2–dependent angiogenesis was further investigated. While PGE2 does not directly induce angiogenic behavior in endothelial cells in vitro, PGE2-treated RA synovial fibroblasts expressed high levels of vascular endothelial cell growth factor (VEGF) mRNA. The induction appears to utilize the EP2 subtype of the PGE receptor which signals via the Gs/ cAMP/ protein kinase A pathway. These data suggest that Cox-2-derived PGE2 may be an indirect angiogenic factor in RA. In addition to RA, Cox-2 expression is also upregulated in the colorectal cancer. That Cox-2-derived PG may play a causative role in colorectal cancer development is suggested by epidemiological data which demonstrated that Cox inhibitors reduced the incidence of and death from colon cancer. It is not known how high-levels of Cox-2 expression contributes to the development of the malignant disease. However, the ability of Cox enzymes to activate mutagens as well as the property of prostanoids to induce cell proliferation, angiogenesis and immunosuppression may be involved. These data suggest that the dysregulated expression of the early response gene Cox-2 is an important component of many proliferative diseases and that induction of angiogenesis may be a critical component. Better understanding of the mechanisms involved in Cox-2 expression and function may yield novel therapeutic approaches for the control of proliferative and angiogenic diseases such as RA and colon cancer.

Pazit Ben-Av

Papers

Induction of vascular endothelial growth factor expression in synovial fibroblasts by prostaglandin E and interleukin‐1: a potential mechanism for inflammatory angiogenesis

Non-small cell lung cancer cycloxygenase activity and proliferation are inhibited by non-steroidal antiinflammatory drugs

Dissociation of Basal Turnover and Cytokine-Induced Transcript Stabilization of the Human Cyclooxygenase-2 mRNA by Mutagenesis of the 3′-Untranslated Region☆☆☆

Prostaglandin E2 and vasoactive intestinal peptide increase vascular endothelial cell growth factor mRNAs in lung cancer cells.

Role of the Early Response Gene Cyclooxygenase (Cox)-2 in Angiogenesis