Biomedical subjects

Oliver Stoeltzing

Publications and source records attributed to Oliver Stoeltzing.

30 records · Page 2Linked to original sources

PubMed2003

Biology of angiogenesis in tumors of the gastrointestinal tract.

The realization that the growth and spread of tumors are dependent on angiogenesis has created new avenues of research designed to help us to better understand cancer biology and to facilitate the development of new therapeutic strategies. However, the process of angiogenesis consists of multiple, sequential, and interdependent steps with a myriad of positive and negative regulators of angiogenesis being involved. The survival of tumors and thus their metastases are dependent upon the balance of endogenous angiogenic and anti-angiogenic factors such that the outcome favors increased angiogenesis. Several growth factors have been identified that regulate angiogenesis in cancers of the gastrointestinal tract. These include pro-angiogenic factors like vascular endothelial growth factor (VEGF) and anti-angiogenic factors, i.e., thrombospondin. The following review provides a brief overview about the most important factors that are involved in the angiogenic process in tumors derived from colon, stomach, and pancreas. A thorough understanding of the role these factors play in the angiogenic process may lead to the development of novel therapeutic antineoplastic strategies.

Angiogenesis Inhibitors↗

PubMed2003

Regulation of hypoxia-inducible factor-1alpha, vascular endothelial growth factor, and angiogenesis by an insulin-like growth factor-I receptor autocrine loop in human pancreatic cancer.

Activation of the insulin-like growth factor-I receptor (IGF-IR) was recently shown to modulate angiogenesis by up-regulating the expression of vascular endothelial growth factor (VEGF). We hypothesized that inhibiting IGF-IR function would inhibit angiogenesis and growth of pancreatic cancer in vivo and sought to identify major signaling pathways regulated by IGF-IR in pancreatic cancer cells. Human pancreatic cancer cells (L3.6pl) were stably transfected with a dominant-negative form of IGF-IR (IGF-IR DN) or an empty vector (pcDNA). In vitro, IGF-IR DN cells exhibited a decrease in both constitutive and inducible phosphorylation of IGF-IR and Erk1/2. Constitutive expression of nuclear hypoxia-inducible factor-1alpha and secreted VEGF (P < 0.01) protein levels also were significantly lower in IGF-IR DN cells than in pcDNA cells. In vivo, IGF-IR inhibition led to decreases in pancreatic tumor volume and weight, vessel density, and tumor cell proliferation (P < 0.01 for all) and increases in tumor cell apoptosis (P < 0.02). Our results suggest that autocrine activation of the IGF-IR system significantly affects VEGF expression and angiogenesis in human pancreatic cancer. Thus, IGF-IR may be a valid target in the treatment of pancreatic cancer.

Adenocarcinoma↗

PubMed2003

Promises and pitfalls of anti-angiogenic therapy in clinical trials.

A significant body of research has implicated the process of angiogenesis in the growth and spread of tumors. Elucidation of the mechanisms of tumor angiogenesis has led to the development of multiple anti-angiogenic agents. However, the perceived differences between the results of preclinical studies and those of early phases of clinical trials have led to questions being asked regarding the efficacy of these agents. There are many reasons for this discrepancy, including difficulties in the appropriate interpretation of preclinical data and clinical trial design. Further insights into the complex process of angiogenesis are essential for the development of effective anti-angiogenic regimens.

Angiogenesis Inhibitors↗

PubMed2003

Angiogenesis and antiangiogenic therapy of colon cancer liver metastasis.

The fact that tumor growth and metastatic spread relies on angiogenesis has been widely proven and accepted. The understanding of cancer biology and metastasis formation has led to the development of new therapeutic approaches that target tumor biology. The survival and establishment of metastatic lesions depend on a shift in the normal balance of proangiogenic and antiangiogenic factors that favor angiogenesis. Colorectal cancer is one of the leading cancer deaths worldwide. Angiogenesis has been associated with colon cancer progression and metastatic spread, thereby significantly affecting patient survival. New experimental approaches that inhibit angiogenic processes have demonstrated promising antineoplastic effects on metastatic colorectal cancer and are partially being investigated in clinical trials. This review focuses on angiogenesis in colorectal cancer metastasis formation as a target for antiangiogenic therapy, describing the experience from experimental studies and current clinical trials.

Angiogenesis Inhibitors↗

PubMed2002

Role of P38 MAPK, AP-1, and NF-kappaB in interleukin-1beta-induced IL-8 expression in human vascular smooth muscle cells.

Interleukin (IL)-1 modulates the expression of various genes in normal and tumor cells. We investigated the molecular mechanisms underlying IL-1beta-induced expression of IL-8 mRNA and protein in human vascular smooth muscle cells (hVSMCs). P38 mitogen-activated protein kinase (MAPK) was activated after 5min of IL-1beta treatment, whereas the extracellular signal-regulated kinases, the c-jun amino-terminal kinases, and protein kinase B/Akt were not activated by IL-1beta. IL-1beta induced activation of a full-length IL-8 promoter-reporter construct. Deletional mutagenesis localized the IL-1beta-responsive domains to two regions (-133 to -98 and -85 to -50) that contain consensus binding sites for activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB), respectively. Site-directed mutagenesis of the 133-bp minimal promoter confirmed that these sites were required for promoter activity. Electrophoretic mobility shift assays confirmed that IL-1beta increased AP-1 and NF-kappaB DNA-binding activities in a time-dependent manner. SB203580, a specific P38 MAPK inhibitor, partially blocked IL-1beta induction of IL-8 mRNA, IL-8 promoter activity, and AP-1 nuclear extract binding but not NF-kappaB DNA binding. Our data demonstrate that AP-1 and NF-kappaB are essential transcription factors for IL-1beta-induced IL-8 gene expression in hVSMCs. P38 MAPK is involved in inducing IL-8 gene transcription via AP-1 activation in hVSMCs.

Binding Sites↗

PubMed2002

The role of the microenvironment and intercellular cross-talk in tumor angiogenesis.

The expression of angiogenic factors in tumors is controlled by intrinsic factors in the tumor and by the host microenvironment. Endothelial cells within particular tumor microenvironments interact not only with tumor cells but also with immune cells, fibroblasts, pericytes, and the extracellular matrix (ECM). The relationship and cross-talk among these cells determine gene expression, phenotypic distinction, and ultimately whether endothelial cells survive, proliferate, or undergo apoptosis. The diversity of angiogenic factor expression in tumors at different sites, combined with the fact that endothelial cells in different organs and tumors are phenotypically distinct, constitutes a formidable challenge for the development of effective anti-angiogenic therapies.

Angiogenesis Inhibitors↗

PubMed2002

Role of angiogenesis in the development and growth of liver metastasis.

Cancer metastasis is a highly complex process that involves aberrations in gene expression by cancer cells leading to transformation, growth, angiogenesis, invasion, dissemination, survival in the circulation, and subsequent attachment and growth in the organ of metastasis. Angiogenesis facilitates metastasis formation by providing a mechanism to (1) increase the likelihood of tumor cells entering the blood circulation and (2) provide nutrients and oxygen for growth at the metastatic site. The formation and establishment of metastatic lesions depend on the activation of multiple angiogenic pathways at both primary and metastatic sites. A variety of factors involved in the angiogenesis of liver metastasis have been identified and may serve as prognostic markers and targets for therapy. Vascular endothelial growth factor, interleukin-8, and platelet-derived endothelial cell growth factor are all proangiogenic factors that have been associated with liver metastasis from various primary tumor types. Inhibition of the activity of these factors is a promising therapeutic approach for patients with liver metastases. In addition, inhibition of integrins that mediate endothelial cell survival may also serve as a component of therapeutic regimens for liver metastases. This review focuses on the biology of angiogenesis in liver metastasis formation and growth. Because colorectal carcinoma is the most common tumor to metastasize to the liver, this disease will serve as a paradigm for the study of angiogenesis in liver metastases.

Endothelial Growth Factors↗

PubMed2002

Antiangiogenic therapy targeting factors that enhance endothelial cell survival.

The process of angiogenesis involves the formation of new blood vessels from established vasculature and the maintenance of the fragile neovascular network. Recent studies have shown that several angiogenic factors not only induce angiogenesis but also act as endothelial cell (EC) survival factors. Vascular endothelial growth factor, a potent angiogenic factor, is also an EC survival factor via activation of EC-specific tyrosine kinase receptors. Angiopoietin-1 has recently been shown to stabilize EC networks by binding to the EC-specific tyrosine kinase receptor Tie-2; in contrast, angiopoietin-2 is antagonistic to angiopoietin-1 and destabilizes EC networks. Integrins may function as EC survival factors by preventing apoptosis by numerous mechanisms mediated by binding to the extracellular matrix. Integrins may also function in concert with vascular endothelial growth factor to promote EC survival. Lastly, pericytes contribute to EC stabilization by cell-cell contact and/or secretion of survival factors, such as vascular endothelial growth factor. Targeting EC survival factors may provide a novel antineoplastic strategy for cancer.

Angiogenesis Inhibitors↗

PubMed2002

Impact of insulin-like growth factor receptor-I function on angiogenesis, growth, and metastasis of colon cancer.

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 < 0.05) that was associated with decreased tumor cell proliferation, VEGF expression, and vessel count and with increased tumor cell apoptosis (p < 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 < 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.

Cell Division↗

PubMed2002

Angiopoietins and their role in colon cancer angiogenesis.

Tumor angiogenesis is a complicated process that is regulated by numerous factors simultaneously and in a coordinated fashion. Angiogenic factors drive the process of neovascularization, but the initiation of angiogenesis involves priming of endothelial cells so that they will respond to mitogenic stimuli. The angiopoietins (Ang) -1 and -2 mediate endothelial cell stability through binding to their endothelial cell-specific receptor, Tie-2. Ang-1 leads to endothelial cell stability, and, in vivo, to an actual decrease in angiogenesis. This is likely due to its ability to enhance adhesion to the perivascular tissues. In contrast, Ang-2 leads to endothelial cell instability and may be an initiating factor in angiogenesis, priming endothelial cells for mitogenic signals. Thus, a novel antiangiogenic strategy may be one that leads to enhanced endothelial cell stability, thereby protecting endothelial cells from standard angiogenic stimuli. This may ultimately lead to tumor dormancy by transforming a rapidly growing tumor into an indolent tumor.

Angiopoietin-1↗

PubMed2002

Synopsis of angiogenesis inhibitors in oncology.

Angiogenesis is a dynamic process essential for primary tumor growth and metastases. New insights into the basic understanding of the biologic processes responsible for angiogenesis have led to the characterization of potential therapeutic targets. Several strategies for the development of antiangiogenic therapeutic modalities have been employed, including agents that (1) decrease the activity of specific angiogenic factors, (2) decrease th$ activity of endothelial survival factors, (3) increase the activity of naturally occurring antiangiogenic agents, or (4) indirectly downregulate angiogenic and survivalfactor activity. Because antiangiogenic therapy is unlikely to induce tumor regression, the criteria for efficacy must be evaluated by means other than the standard response criteria used to evaluate cytotoxic chemotherapy. Further, the redundancy of molecules responsible for the angiogenic process suggests it is unlikely that a single antiangiogenic agent will provide prolonged inhibition of angiogenesis. Nevertheless, the understanding of the basic principles that drive tumor angiogenesis will lead to the development of therapies that will likely prolong survival without the toxicity associated with standard chemotherapy.

Angiogenesis Inhibitors↗

PubMed2002

Blockade of insulin-like growth factor I receptor function inhibits growth and angiogenesis of colon cancer.

PURPOSE AND EXPERIMENTAL DESIGN: Insulin-like growth factors (IGFs) I and II and their principle 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). To elucidate the in vitro and in vivo effects of IGF-IR in human colon cancer growth and angiogenesis, HT29 cells were transfected with a truncated dominant-negative (DN) form of IGF-IR or vector alone. RESULTS: IGF-I increased VEGF expression in parental and vector-transfected cells, whereas IGF-I induction of VEGF mRNA and protein was abrogated in IGF-IR DN cells. The IGF-IR DN cells demonstrated inhibited growth in both monolayer culture and soft agar (P < 0.05). s.c. injections of IGF-IR DN cells in nude mice led to significantly decreased tumor growth (P < 0.05). Immunohistochemical analyses revealed that IGF-I DN tumors demonstrated decreased tumor cell proliferation, VEGF expression, and vessel count and increased tumor cell apoptosis (P < 0.05 for all parameters compared with controls). Furthermore, IGF-IR DN-transfected cells yielded significantly decreased tumorigenicity and growth in the liver. CONCLUSIONS: These studies demonstrate that the IGF ligand-receptor system plays an important role in multiple mechanisms that mediate human colon cancer growth including regulation of VEGF and angiogenesis.

Animals↗