No abstract

Insulin-like growth factors and their principal receptor, IGF-I receptor (IGF-IR), are frequently expressed in human colon cancers and play a role in preventing apoptosis, enhancing cell proliferation, and inducing expression of vascular endothelial growth factor (VEGF). The role of IGF-IR in regulating angiogenesis and metastases of human colon cancer has not been elucidated. To determine the in vitro and in vivo effects of IGF-IR in human colon cancer growth and angiogenesis, human KM12L4 colon cancer cells were transfected with a truncated dominant-negative form of IGF-IR (IGF-IR dom-neg). IGF-IR dom-neg-transfected cells demonstrated markedly decreased constitutive expression of VEGF mRNA and protein. Subcutaneous injections of IGF-IR dom-neg-transfected cells in nude mice led to significantly decreased tumor growth (p Ͻ 0.05) that was associated with decreased tumor cell proliferation, VEGF expression, and vessel count and with increased tumor cell apoptosis (p Ͻ 0.05 for all parameters compared with controls). In addition, pericyte coverage of endothelial cells was significantly decreased in tumors from IGF-IR dom-neg-transfected cells. Following this observation, we demonstrated in vitro that vascular smooth muscle cells migrated significantly less in conditioned medium derived from IGF-IR dom-neg-transfected cells compared with medium from control cells. After splenic injections, IGF-IR dom-neg transfectants failed to produce liver metastases, in contrast to parental cells and mock transfectants (p Ͻ 0.05). In addition, IGF-IR dom-neg-transfected cells failed to form liver tumors after direct injection into the liver. These studies demonstrate that the IGF-IR plays an important role in multiple mechanisms that mediate the growth, angiogenesis, and metastasis of human colon cancer. IGF-IR is a valid target for the therapy of human colon cancer.

Catechins are key components of teas that have antiproliferative properties. We investigated the effects of green tea catechins on intracellular signalling and VEGF induction in vitro in serum-deprived HT29 human colon cancer cells and in vivo on the growth of HT29 cells in nude mice. In the in vitro studies, (-)-epigallocatechin gallate (EGCG), the most abundant catechin in green tea extract, inhibited Erk-1 and Erk-2 activation in a dose-dependent manner. However, other tea catechins such as (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epicatechin (EC) did not affect Erk-1 or 2 activation at a concentration of 30 μM. EGCG also inhibited the increase of VEGF expression and promoter activity induced by serum starvation. In the in vivo studies, athymic BALB/c nude mice were inoculated subcutaneously with HT29 cells and treated with daily intraperitoneal injections of EC (negative control) or EGCG at 1.5 mg day −1 mouse −1 starting 2 days after tumour cell inoculation. Treatment with EGCG inhibited tumour growth (58%), microvessel density (30%), and tumour cell proliferation (27%) and increased tumour cell apoptosis (1.9-fold) and endothelial cell apoptosis (3-fold) relative to the control condition ( P < 0.05 for all comparisons). EGCG may exert at least part of its anticancer effect by inhibiting angiogenesis through blocking the induction of VEGF. © 2001 Cancer Research Campaign http://www.bjcancer.com

Vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) regulate colon cancer growth and metastasis. Previous studies utilizing antibodies against the VEGF receptor (DC101) or EGF receptor (C225) have demonstrated independently that these agents can inhibit tumour growth and induce apoptosis in colon cancer in in vivo and in vitro systems. We hypothesized that simultaneous blockade of the VEGF and EGF receptors would enhance the therapy of colon cancer in a mouse model of peritoneal carcinomatosis. Nude mice were given intraperitoneal injection of KM12L4 human colon cancer cells to generate peritoneal metastases. Mice were then randomized into one of four treatment groups: control, anti-VEGFR (DC101), anti-EGFR (C225), or DC101 and C225. Relative to the control group, treatment with DC101 or with DC101+C225 decreased tumour vascularity, growth, proliferation, formation of ascites and increased apoptosis of both tumour cells and endothelial cells. Although C225 therapy did not change any of the above parameters, C225 combined with DC101 led to a significant decrease in tumour vascularity and increases in tumour cell and endothelial cell apoptosis (vs the DC101 group). These findings suggest that DC101 inhibits angiogenesis, endothelial cell survival, and VEGF-mediated ascites formation in a murine model of colon cancer carcinomatosis. The addition of C225 to DC101 appears to lead to a further decrease in angiogenesis and ascites formation. Combination anti-VEGF and anti-EGFR therapy may represent a novel therapeutic strategy for the management of colon peritoneal carcinomatosis. © 2001 Cancer Research Campaign http://www.bjcancer.com

Small tumor vessels are composed of endothelial cells (ECs) surrounded by pericytes. Pericytes are believed to be an EC survival factor, but their mechanism of action is unknown. One possible mediator, VEGF, promotes angiogenesis, EC proliferation, and EC permeability, and it protects ECs from apoptosis. We hypothesized that PDGF (platelet‐derived growth factor)‐BB, a cytokine released from tumor and ECs, mediates pericyte function by inducing VEGF, which in turn may affect EC survival. Using two pericyte‐like cell lines, 10T1/2 cells (murine pericyte cell line) and human vascular smooth muscle cells (hVSMCs), we showed that PDGF‐BB increased VEGF mRNA transcription. Although PDGF‐BB activated both the mitogen‐activated protein kinase and phosphatidylinositol 3‐kinase (PI3‐K) pathways, activation of the PI3‐K pathway was the most important pathway for VEGF induction. Conditioned medium derived from colon cancer cells also induced VEGF in pericyte‐like cells via the PI3‐K pathway, which was blocked by SU6668, a tyrosine kinase inhibitor that blocks the receptors for PDGF, VEGF, and basic fibroblast growth factor. Conditioned medium from hVSMCs pretreated with PDGF‐BB prevented apoptosis of ECs, and this effect was partially abrogated by neutralizing antibodies to VEGF. These studies suggest that pericytes may protect ECs from apoptosis, in part, by cytokine signaling that increases VEGF.

No abstract

Summary. Epidemiological studies have suggested that consumption of green tea may decrease cancer risk. In addition, abundant pre-clinical data from several laboratories have provided convincing evidence that polyphenols present in green tea afford protection against cancer in both in vivo and in vitro studies. Recently, epigallocatechin gallate (EGCG), a putative chemopreventive agent and a major component of green tea, was reported to inhibit tumour invasion and angiogenesis, processes that are essential for tumour growth and metastasis. Understanding the basic principles by which EGCG inhibits tumour invasion and angiogenesis may lead to the development of new therapeutic strategies, in addition to supporting the role of green tea as a cancer chemopreventive agent.

Recent studies have suggested that the expression of interleukin-8 (IL-8) directly correlates with the vascularity of human gastric carcinomas. In this study, the effect of IL-1b on IL-8 expression in human gastric cancer TMK-1 cells and the underlying signal transduction pathways were investigated. IL-1b induced the IL-8 expression in a time-and concentration-dependent manner. IL-1b induced the activation of extracellular signalregulated kinases-1/2 and P38 mitogen-activated protein kinase (MAPK), but not the activation of c-jun aminoterminal kinse and Akt. Specific inhibitors of MEK-1 (PD980590) and P38 MAPK (SB203580) were found to suppress the IL-8 expression and the IL-8 promoter activity. Expression of vectors encoding a mutated-type MEK-1 and P38 MAPK resulted in decrease in the IL-8 promoter activity. IL-1b also induced the production of reactive oxygen species (ROS). N-acetyl cysteine (NAC) prevented the IL-1b-induced ROS production and IL-8 expression. In addition, exogenous H 2 O 2 could induce the IL-8 expression. Deletional and site-directed mutagenesis studies on the IL-8 promoter revealed that activator protein-1 (AP-1) and nuclear factor (NF)-jB sites were required for the IL-1b-induced IL-8 transcription. Electrophoretic mobility shift assay confirmed that IL-1b increased the DNA-binding activity of AP-1 and NF-jB. Inhibitor (PD980590, SB203580) and ROS scavenger (NAC) studies revealed that the upstream signalings for the transcription factors AP-1 and NF-jB were MAPK and ROS, respectively. Conditioned media from the TMK-1 cells pretreated with IL-1b could remarkably stimulate the in vitro growth of HUVEC and this effect was partially abrogated by IL-8-neutralizing antibodies. The above results suggest that MAPK-AP-1 and ROS-NF-jB signaling pathways are involved in the IL-1b-induced IL-8 expression and that these paracrine signaling pathways induce endothelial cell proliferation.