Both in vivo and in vitro studies have shown that extracts and compounds isolated from berries show anti-cancer activities in several types of tumors, such as esophageal tumors, colon cancer, prostate cancer, and breast cancer. However, the molecular mechanisms responsible for such anti-cancer activities remain ambiguous.
Cell signaling is a complex net system that governs basic cellular activities and coordinates cell actions. After activated, cell signaling pathway components regulate their target proteins such as transcription factors, which further modulate the expression of different target genes. Thus, these pathways play fundamental roles in modulating various biological processes, including cell cycle, cell proliferation, differentiation, and survival.
The abnormal activation of several signaling pathways has been linked to the development of various cancers and the inhibition of these pathways has also been considered as a strategy for cancer prevention and therapy. A series of in vitro studies have been carried out to elucidate the inhibition of cellular signaling pathways leading to anti-cancer effects of berry extracts. Several pathways, such as receptor tyrosine kinases (RTKs), phosphatidylinositol-3-kinase/Akt (PI3K/Akt), and mitogen-activated protein kinases (MAPKs), have been reported to participate in the chemopreventive effects of berry extracts.
As a result, several transcription factors and their downstream target genes, such as nuclear factor KB (NFKB), activator protein-1 (AP-1), cyclooxygenase-2 (COX-2), and vascular endothelial growth factor (VEGF), have also been connected to the chemopreventive effects of berry extracts.
Various growth factors, such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF), transduce their mitogenic signals through the activation of receptor tyrosine kinases (RTKs)
RTKs are transmembrane proteins that have multiple functional domains, including an extracellular ligand-binding domain, a transmembrane segment, and intracellular domains, which contain the juxtamembrane segment, the tyrosine kinase catalytic domain, and a carboxy-terminal tail. Upon growth factor binding to its specific receptor, mutual transphosphorylation of tyrosine residues within active RTK dimers recruits intracellular proteins endowed with phosphotyrosine-binding domains. Proximal targets of RTKs invoke PI3K/AKT and MAPKs pathways, which leads to further diverse biological responses.
RTKs have been shown to be involved in malignant transformation and tumor proliferation. It is well known that the aberrant signaling by RTKs is critically involved in human cancers and other hyper-proliferative diseases. Constitutive activation of RTKs, which has been shown to be important for malignant transformation and tumor proliferation, can occur by several mechanisms. In most cases, gene amplification, overexpression, and mutations, are responsible for the acquired transforming potential of oncogenic RTKs.
Oncogenic mutations disrupt normal regulatory mechanisms and lead to the constitutive activation of the kinases. Point mutations or rearrangements in the extracellular domain mimic ligand-binding, thereby causing constitutive dimerization. Vascular endothelial growth factor receptor (VEGFR) is a key modulator of angiogenesis. Highly expressed in a variety of human malignancies, epidermal growth factor receptor (EGFR) is correlated with poor tumor differentiation, fast tumor growth, and high metastatic rate.
EGFR binding with its ligand activates multiple signaling pathways, including the PI3K/AKT pathway. Approximately 10–15% of patients with nonsmall cell lung cancer have tumors that depend on the activation of EGFR. Abnormal expression and function of human EGFR have also been found to be responsible for the development and progression of prostate cancer. Deregulation of fibroblast growth factor receptor (FGFR) signaling, another important member of RTKs, by either mutations or ligand/receptor overexpression could make it constitutively active, leading to cancer development. Overexpression of other growth factor receptors, including insulin-like growth factor receptor (IGFR), platelet-derived growth factor receptor (PDGFR), and EGFR, has also been considered to be associated with poor prognosis in breast cancer.
The inhibition of RTKs has been considered as a strategy for chemoprevention of cancers. Targeted agents inhibit receptor tyrosine kinase signaling by binding the extracellular component of a growth receptor, the soluble ligand that triggers the receptor, or intracellular sites that interfere with downstream signaling events. Due to its universal expression in head and neck squamous cell carcinoma (HNSCC), EGFR has long been a target for the treatment of HNSCC. Gefitinib is an orally-active EGFR inhibitor that blocks EGFR signaling in vitro. It thereby inhibits the growth, proliferation, and survival of many solid tumors.
Clinical trial data show that gefitinib mono-therapy is generally well tolerated in patients with a wide range of tumor types. Targeted therapies against ErbB family have shown some promise in the treatment of hormone-refractory prostate cancer. RTK inhibitors against the receptors for different growth factors manifest significant antiangiogenic activities. These compounds can also enhance tumor radiation response by attacking tumor microvasculature.
Our website is not responsible for the information contained by this article. Articleinput.com is a free articles resource thus practically any visitor can submit an article. However if you notice any copyrighted material, please contact us and we will remove the article(s) in discussion right away.
Note: This article was sent to us by: Ian H. Markus at 01132011
1. Observations of in vitro hormonal studies
All articles are property of their respective authors. Please read our Privacy Policy!
© 2009 ArticleInput.com.
Partners: Damenmode