Info

"Modified from Leedy et al., Otol. Head Neck Surg. 111(4), 417^*22 (1994).

"Adapted from Williams et al., Am. J. Surg. 168(5), 373-380 (1994).

"Modified from Leedy et al., Otol. Head Neck Surg. 111(4), 417^*22 (1994).

Tissue

FIGURE 7.4 Changes in vascularity with disease progression. Vascularity was measured as microvascular volume (MVV). Adapted from Pazouki et al., J. Pathol. 183, 39^3 (1997).

Tissue

FIGURE 7.4 Changes in vascularity with disease progression. Vascularity was measured as microvascular volume (MVV). Adapted from Pazouki et al., J. Pathol. 183, 39^3 (1997).

The application of experimental procedures, such as proliferation and chemotaxis assays of endothelial cells, allowed several groups of researchers to identify an increasing number of proangiogenic factors [49], which have been shown to modulate angiogenesis in vivo and in vitro. Among these, FGFs and VEGF are the most potent inducers of angiogenesis [87-92], The angiogenic factors responsible for the progression of the squamous cell carcinoma of the head and neck have not been as well described as for other types of cancer [93], Although an increasing number of reports have confirmed the correlation of angiogenesis with HNSCC development [65,72,74,76,80,81], how the angiogenic factors regulate the distinct steps of the angiogenic

FIGURE 7.5 Microvessel count and clinical outcome in the tumor and in the tissue peripheral to the tumor. Adapted from Albo et al., Ann. Plast. Surg. 32, 588-594 (1994).

Peritumoral area

Tumor process in this type of cancer is not fully understood [93-95],

Several proangiogenic factors and cytokines have been shown to be secreted by HNSCC cell lines, such as bFGF, insulin-like growth factor II (IGF-II), platelet-derived endothelial cell growth factor (PD-ECGF), transforming growth factor (TGF)-a [96,97], prostaglandin 2 (PGE2), transforming growth factor (TGF)-|3, and VEGF [95], As a consequence, it has been demonstrated that supernatants from HNSCC cultured cell lines displayed stimulatory effects on endothelial cell growth into microvessel-like structures and on their motility in various in vitro models [94,95] (Fig. 7.6).

1. Basic Fibroblast Growth Factor

Basic fibroblast growth factor (bFGF or FGF-2) is one of 20 distinct members of the FGF family widely expressed in normal [98,99] and malignant [100-104] tissues, including squamous cell carcinoma of the head and neck [105]. bFGF is an 18-kDa protein shown to have biological effects in different cells and organ systems, including tumorigenesis and angiogenesis [106-108]. The biological response to bFGF is modulated by interaction with low-affinity cell surface and extracellular matrix heparan sulfate proteoglycans (HSPGs), which enable the growth factor to bind and activate its high-affinity tyrosine kinase receptors (FGFR1 and FGFR2), thereby forming a trimolecular active complex [109-112]. bFGF lacks the classic leader sequence, which targets intracellular proteins for secretion to the extracellular environment. Several reports indicate that bFGF release occurs via ER- and Golgi-independent passive processes, such as cell death, wounding, and chemical injury [87,113,114]. Nevertheless, other secretory mechanisms that account for bFGF release might exist. Digestion of HSPGs by hepari-nases or by glycosaminoglycan-degrading enzymes is an additional established mechanism for the solubilization of bFGF from the extracellular matrix [115-117]. It has been

6 13 25 50

Concentration (%)

FIGURE 7.6 Head and neck squamous cell carcinoma-induced endothelial cell proliferation: dose response. TMB assay of endothelial cell proliferation in response to increasing concentrations of tumor supernatants. Adapted from Petruzzelli et al., Head Neck 19, 57682 (1997).

FIGURE 7.5 Microvessel count and clinical outcome in the tumor and in the tissue peripheral to the tumor. Adapted from Albo et al., Ann. Plast. Surg. 32, 588-594 (1994).

6 13 25 50

Concentration (%)

FIGURE 7.6 Head and neck squamous cell carcinoma-induced endothelial cell proliferation: dose response. TMB assay of endothelial cell proliferation in response to increasing concentrations of tumor supernatants. Adapted from Petruzzelli et al., Head Neck 19, 57682 (1997).

proposed that the binding of bFGF to a secreted bFGF-binding protein, designated FGF-BP1 [118], might represent a novel mechanism for bFGF release from the extracellular matrix

[119.120], FGF-BPI has been shown to be upregulated in adult skin during early stages of carcinogenesis, as well as in some colon carcinoma and squamous cell carcinoma cell lines

[120.121], Moreover, the depletion of FGF-BP mRNA levels in ribozyme-targeted squamous cell carcinoma (SCC) and colon adenocarcinoma cell lines resulted in a significant reduction of tumor growth and angiogenic rate, thereby suggesting the role of FGF-BP as an angiogenic switch molecule in human tumors [121. Further studies will be needed to elucidate the role of FGF-BPI in the progression of HNSCC. The release of bFGF in vivo may influence solid tumor growth and neovascularization by an autocrine [122-126] and paracrine [127] mode of action. Accordingly, neutralizing anti-bFGF antibodies affect tumor growth under defined experimental conditions [121].

bFGF has been shown to exert motogenic and mitogenic effects in fibroblasts and endothelial cells, and also to be a powerful inducer of angiogenesis in vivo [128,129]. The binding of bFGF to the cell surface receptor induces receptor tyrosine-kinase dimerization and autophosphorylation [130], The phosphorylated FGFRs associate and subsequently activate SH2 domain-containing downstream signaling molecules, such as PLCy [131,132] and Src [133,134], Moreover, on ligand-dependent receptor autophosphorylation, adaptor proteins, such as Grb2 and She, link the FGFRs to the Ras/MAP kinase signaling cascade [135], Grb2 and She form a complex with the GDP/GTP exchange factor Son of Sevenless (Sos) that results in the translocation of Ras to the plasma membrane and its further activation by the exchange of GDP for GTP by Sos. Thus, activated Ras leads to the consecutive activation of a cascade of protein kinases involving Raf, MEK, and p44/42MAPK, also known as extracellular signal-regulated kinase 1 and 2 (ERK-1 and ERK-2) [135]. Furthermore, bFGF-dependent phosphorylation of FRS-2 (FGF receptor substrate 2), a membrane associated protein, has been shown to link FGFR to p44/42MAPK [136],

The bFGF-dependent upregulation of p44/42MAPK is likely to be the molecular mechanism by which the growth factor is likely to induce the mitogenesis of endothelial cells in the angiogenic process. However, whether the induction of endothelial cell migration occurs on the activation of the same or different signal transduction pathway(s) is still controversial [137].

To date, a handful of investigators have been attempting to correlate the overexpression of bFGF with the angiogenic phenotype of HNSCC. bFGF was found to be strongly expressed in very actively proliferating and highly oxygenated regions of murine SCCs [138,139], whereas it was not detected in tumor areas bordering on necrosis, which are poorly vascularized and hypoxic [140]. Shultze-Hector and Haghayegh [105] further confirmed these findings by demonstrating a correlation between bFGF production by tumor cells and vascular endothelial cell growth rate in murine HNSCC cell lines. Moreover, the staining of human HNSCC cell lines with polyclonal antibodies against bFGF revealed a highly heterogeneous distribution of the growth factor within the tumor that was associated with the inhomogeneous tumor cell proliferation throughout the viable tumor tissue [105] (Fig. 7.7). Dellacono et al. [141] showed in 45 HNSCC specimens that in the majority of samples, cells presented an intense positive staining for bFGF. In addition, in samples from patients affected by an early stage disease, bFGF expression was more elevated than in those with late stage HNSCC. These results also correlated with the expression of FGFR1 and FGFR2 in the same specimens, thus suggesting that tumor cells may upregulate FGFR expression in response to augmented bFGF levels in the surrounding tissues.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment