|Year : 2018 | Volume
| Issue : 5 | Page : 211-215
Angiogenesis in head and neck cancer: An overview
Roopan Prakash1, Vishnu Mohan2, Pillai Arun Gopinathan1, Manoj S Nair1, J T Ramani Bai3
1 Department of Oral Pathology, Sri Sankara Dental College, Trivandrun, Kerala, India
2 Department of Periodontics, Kannur Dental College, Anjarakandy, Kerala, India
3 Department of Microbiology, S R Medical College, Trivandrun, Kerala, India
|Date of Web Publication||24-Oct-2018|
Dr. Roopan Prakash
Department of Oral Pathology, Sri Sankara Dental College, Trivandrun, Kerala
Source of Support: None, Conflict of Interest: None
Angiogenesis is a critical player in many pathologic processes, especially in neoplasms. Unregulated angiogenesis is thought to be indispensable in tumor growth and metastasis. Angiogenesis is the growth of new blood vessels from preexisting vasculature. The growing tumor mass requires an adequate amount of oxygen and nutrients which are supplied by complex network of tumor blood microvessels. The identification of molecules involved in the regulation of angiogenesis may provide new possibilities for the development of drugs suitable for inhibition of angiogenesis.
Keywords: Angiogenesis, metastasis, microvessel, neoplasm
|How to cite this article:|
Prakash R, Mohan V, Gopinathan PA, Nair MS, Bai J T. Angiogenesis in head and neck cancer: An overview. J Int Oral Health 2018;10:211-5
|How to cite this URL:|
Prakash R, Mohan V, Gopinathan PA, Nair MS, Bai J T. Angiogenesis in head and neck cancer: An overview. J Int Oral Health [serial online] 2018 [cited 2019 Jul 21];10:211-5. Available from: http://www.jioh.org/text.asp?2018/10/5/211/243859
| Introduction|| |
Oral squamous cell carcinoma (OSCC) is the most common malignancy of the oral cavity. Oral carcinogenesis is a two-step process characterized by an initial precancerous lesion that will develop into cancer. The most common potentially malignant lesion is leukoplakia which is characterized by the appearance of white patches in oral mucosa. The malignant potential of leukoplakia is 5%; and currently, there are no prognostic markers that suggest those that progress and not. The histopathological examination of biopsied specimens of leukoplakia shows mainly hyperkeratosis, and nonspecific hyperplasia and only about 50% of the lesions show evidence of dysplasia.,
The progression of oral dysplastic lesions into OSCC is characterized by an increase in “Angiogenic switch” which is characterized by an increase in neovascularization, which can be considered as an indicator of malignant transformation.,
Angiogenesis is the process of new capillary blood vessel formation from preexisting vasculature. It is an important physiologic process during growth, tissue injury, repair, and wound healing., It is believed that tumor mass cannot exist in volume >1 mm3 without proper vascular supply, which indicates angiogenesis is critical in neoplastic growth. Head and neck squamous cell carcinoma (HNSCC) is also believed to arise through a multistep process that involves the activation of oncogenes as well as the inactivation of tumor suppressor genes. These genetic changes generate concomitant phenotypic changes in the tumor cells that allow them to continue to survive and expand until they become a large and clinically detectable tumor mass. The development of cell immortality, ability to invade tissue and metastasize, as well as acquiring the ability to induce angiogenesis, is some of these phenotypic changes. The expression of the angiogenic phenotype in the tumor microenvironment is an extremely complex process involving the interaction of many different cell types. Like all solid tumors, HNSCCs must develop direct and indirect ways to induce the production of new blood vessels to continue to expand and metastasize.,,
In this review, we will discuss in detail on angiogenesis and the differences in microvessel density (MVD) in oral dysplastic lesions and OSCC.
| Vasculogenesis|| |
The cells of tissues and organ system in the body are nourished with nutrients and oxygen by the blood vascular system, providing for circulation of fluids and various signaling molecules. The emergence of the blood vascular system (vasculogenesis) is one of the earliest events in embryogenesis. It denotes assembly of blood vessels during embryonic development. In embryo, the precursor cells called hemangioblasts will develop from mesoderm from which the primitive blood vessels will develop. Hemangioblasts is a dual precursor cell. It gives rise to hematopoietic stem cells and angioblasts. Hematopoietic stem cells give rise to hematopoietic cells, and angioblasts are the precursor of endothelial cells which gives rise to the blood vessels.,
Types of angiogenesis
- Sprouting angiogenesis
- Intussusceptive angiogenesis.
Angiogenesis is triggered by hypoxic tissue. Hypoxic cell acts as angiogenic center. Angiogenic center is basically anything that releases proangiogenic molecules.
There are many proangiogenic molecules,, [Table 1].
Vascular endothelial growth factor (VEGF) is a factor regulating vascular permeability. VEGF-A is the most important proangiogenic molecule. Sprouting angiogenesis is mainly associated with capillaries. Capillaries are made of endothelial cells lining a basement membrane consisting of extracellular matrix proteins mainly collagen. Pericytes are contractile cells that lines capillaries and venules. Extracellular matrix proteins are secreted by fibroblasts. Sprouting angiogenesis involves two capillaries which produces two sprouts toward each other which migrate to the angiogenic center. The walls of arteries and veins are formed by several layers of smooth muscle cells. Pericytes are cells of mesenchymal origin, which lines capillaries and fine vessels. They comprise a heterogeneous population of cells capable of differentiation to different types of mesenchymal cells such as smooth muscle cells, fibroblasts, and osteoblasts.
Tip cell selection
The first step in angiogenesis is a process known as tip cell selection. Tip cells are the endothelial cell in the sprout that is specialized to guide the sprout toward the angiogenic center. These tip cells receive the maximum amount of VEGF-A. These endothelial cells have receptors known as VEGF receptor 2 (VEGFR-2).,,,
Notch signaling pathway
These tip cells produce long processes called filopodia toward the angiogenic center. When VEGFA binds to the VEGFR2 on the surface of the tip cells, it releases Delta-like ligand 4 (DLL4). The endothelial cells adjacent to the tip cells have receptors that will bind to DLL4; this inactivates VEGFR2 on the adjacent endothelial cells. The receptors that bind to DLL4 are called Notch receptors.
The proteolytic enzymes secreted by the filopodia on tip cells will break down the basement membrane. As the tip cells move toward the angiogenic center the adjacent stalk cells will proliferate and stalk elongation occurs.
The proliferating stalk cells will have vacuoles which then forms tubes (Tubulogenesis). The sprouts from two capillaries will fuse together. Angiogenic center will receive oxygenated blood flowing through these tubes. The angiogenic center will stop producing VEGF-A. The basement membrane is laid down around the newly formed capillaries. Pericyte stabilization occurs, and new blood vessels are completely formed, [Figure 1].
Intussusceptive/spitting angiogenesis (1986)
Intussusceptive angiogenesis can occur in larger blood vessels like arteries and veins in addition to capillaries. The endothelial cells lining blood vessels will curve or protrude into the lumen. The basement membrane follows the path of endothelial cells. These endothelial cells form two separate capillaries. Fibroblasts secrete collagen between the two newly formed capillaries. VEGF-A is responsible for intussusceptive angiogenesis, The complex signaling mechanisms are not clearly understood, and research is still going on to explain the mechanisms of intussusceptive angiogenesis.
| Vascular Endothelial Growth Factor|| |
VEGF is a potent angiogenic cytokine discovered and cloned by Napoleone Ferrara in 1989. It is also known as vascular permeability factor because of its ability to induce vascular leakage. VEGF family includes VEGF-A, VEGF-B, VEGF-C, VEGF-D, and VEGF-E and the placental growth factor. VEGF-A is mainly involved in angiogenesis, whereas VEGF-C and VEGF-D are involved in lymphangiogenesis.,,,,,
The VEGF family and their receptors (VEGFR) are grabbing more attention in the field of cancer research. VEGF is a powerful angiogenic agent in neoplastic tissues, as well as in normal tissues. Under the influence of certain cytokines and other growth factors, the VEGF family appears in cancerous tissue and the adjacent stroma and plays an important role in neovascularization.,,,,,,
Hypoxia induces the expression of VEGF and its receptor through hypoxia-inducible factor-1α. VEGF is secreted by the tumor cells to feed on the new blood vessels produced by angiogenesis. The major receptors to which the VEGF family of cytokines bind (VEGF receptors (VEGFRs) belong to a subfamily of Class III transmembrane receptor tyrosine kinases (TKs and RTKs) that are expressed at high levels in cells of the endothelial lineage.,,,,
| How Benign Hyperkeratotic Lesions Transform to Carcinoma|| |
There are several factors to consider. The epithelial changes in mild dysplasia may be subtle or focal and may be attributed to epithelial changes secondary to reaction to injury or inflammation, often termed “reactive epithelial atypia.” Leukoplakic areas that show keratosis or hyperkeratosis histopathologically and have little evidence of cytologic abnormality may, in fact, represent the very earliest changes in carcinogenesis. High-throughput molecular technologies are currently being used in an effort to further depict the molecular pathways of cancer.
It is well known that tumor growth depends on angiogenesis and that the ingrowth of new capillaries increases the opportunity for tumor cells to enter the circulation, then metastasize to a distant site. Metastatic tumor growth depends on neovascularization in at least two steps:First, malignant cells must exit from a primary tumor into the blood circulation after the tumor becomes neovascularized. Second, after arrival at distant organs, metastatic cells must again induce angiogenesis for a tumor to expand to a detectable size. Several studies have indicated that angiogenic activators play an important part in the growth and spread of tumors. The changes in the connective tissue have been evident by the occurrence of an inflammatory component as well as an increase in vascularity.,,,,
| Endothelial Markers|| |
Platelet endothelial cell adhesion molecule-1 (CD31)
The distinct markers for angiogenesis include CD31 and VEGF. CD31 is a member of immunoglobulin superfamily platelet endothelial cell adhesion molecule-1 (PECAM-1). CD31 is expressed on the surface of the endothelial cells and is frequently used for monitoring the MVD in malignant lesions.,,,,,,
Staining of microvessels
The specimens from the paraffin-embedded blocks are cut into 3-μm sections. Standard immunohistochemistry staining is performed. Monoclonal Rabbit anti-human CD31-antibody (Pathnsitu) can be used for detection of endothelial cells [Figure 2] and [Figure 3].
|Figure 2: Photomicrograph: Immunohistochemical staining of CD31 in oral squamous cell carcinoma as seen under low power (×10)|
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|Figure 3: Immunohistochemical staining of CD31 in Oral SCC as seen under high power (×40)|
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Briefly, the sections should be placed on silane coated slides and deparaffinized and dehydrated, then the slides are treated with distilled water for 5 min.
Counting of microvessels (microvessel density)
Neoangiogenesis is an important step in tumor progression. An important predictor for tumor behavior is intratumor MVD. Any brown staining endothelial cell or endothelial cell cluster that was clearly separate from adjacent microvessels, tumor cells, and other connective tissue elements were considered a single, countable microvessel. To determine the MVD, tissue sections were initially screened at low power (×10) to identify areas of highest vascularization (hot spots). The sections were fixed with ×10 and ×40 magnification objectives fitted with 1 cm2 ocular grid employing Binocular compound microscope and Research Microscope for photomicrograph. Microvessel counts were performed in ten fields at ×10 magnification with the use of ocular grid subdivided into 100 areas in ten fields of vision, and for each field, the hotspot MVD was noted.
| Role of Mast Cells in Angiogenesis|| |
Mast cells can stimulate angiogenesis thus inducing tumor progression and metastasis. The products secreted by mast cells such as tryptase, heparin, basic fibroblast growth factor either directly promote tumor angiogenesis by stimulating the migration and/or proliferation of endothelial cells or indirectly through degradation of extracellular matrix. Tryptase and chymase can activate matrix metalloproteinases (MMP). MMP-9 plays a vital role in angiogenesis, tumor invasion, and metastasis because of its ability to cleave type IV collagen in the basement membrane.,
Cell surface markers for the various types of mast cells include: CD2 (early T-cell marker), CD23 (low-affinity receptor for immunoglobulin E), CD25 (cutaneous mast cells), CD68 (mast cells, macrophages, and melanomas), CD88 (mast cells, neutrophils, monocytes, macrophages, and hepatocytes), CD117 (c-kit mutation found in systemic mastocytosis), and CD203c (mast cells and basophils, and their precursors). In addition, immunohistochemical for tryptase and chymase can be used.,,,
| Antiangiogenic Therapy|| |
The presence of angiogenic factors is not enough to initiate the new vascular growth. Proangiogenic factors are counterbalanced by a number of natural antiangiogenic molecules.,,
In addition to the anti-angiogenic agents such as angiostatin, thrombospondin-1, and numerous drugs inhibiting angiogenesis are available listed in [Table 2].
Lenvatinib is the most potent anti-angiogenic drug because it inhibits both VEGFR and also Fibroblast growth factor receptor (FGFR) signalling pathways. Lenvatinib provides not only anti-angiogenic effects but also cause direct antitumor effects through inhibition of FGFR signalling pathway in cancer cells.,,
| Discussion|| |
OSCC encompasses all malignancies originating in the oral cavity. Oral cancer ranks sixth in the most common cancer in the world and third in the developing countries. Five-year survival rates for all oral cancers cases are 79% for those with localized disease, 42% for regional disease and 19% for disease with distant metastases.,,,
Leukoplakia is essentially an asymptomatic lesion; outcomes must be considered in terms of recurrence of disease or transformation to OSCC at a similar or distant site. Unfortunately, a variable proportion of leukoplakia undergoes malignant transformation. Although it is believed that oral potentially malignant lesions and epithelial dysplasia are more likely to progress to cancer, various studies indicate that it is not inevitable that a dysplastic lesion will progress to cancer.,,,,
Mohtasham et al. observed an increase in MVD during the transformation from normal oral mucosa, through dysplasia, to carcinoma in situ and infiltrating carcinoma indicating the role of angiogenesis in the progression of cancer. The higher values for MVD found in OSCC, and dysplastic oral mucosa in comparison with normal oral mucosa suggests that it is a factor for indicating oral tumor progression.,,,,
Iamaroon et al. found a significant correlation between the mast cell density and microvascular density in OSCC. Their findings suggest that mast cells may upregulate angiogenesis in OSCC, perhaps through the release of MC tryptase.
Kalra et al. conducted a study to validate topographic distribution of MVD found that there was a significant correlation between MVD and disease progression and number of blood vessels increased from well to poorly differentiated OSCC.,
| Conclusion|| |
The elaborate knowledge on angiogenesis and antiangiogenic therapy has made a possible new approach for the treatment of HNSCC. Targeted therapy with reduced toxicity can be developed with the identification of gene expression profiles of angiogenic phenotype in head and neck cancer. The understanding of the mode of action of antiangiogenic drugs in head and neck cancer can be improved with surrogate markers, including noninvasive molecular imaging techniques. Recent research suggests that treating patients with anti-angiogenic drugs will stop the mechanisms by which tumors can directly and indirectly induce blood vessel growth. If such a protocol could be developed, it should provide us with the ability to prevent the development of HNSCC and perhaps other malignancies as well.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]