Biomedical subjects

P Kunkel

Publications and source records attributed to P Kunkel.

16 recordsLinked to original sources

PubMed2003

Invasion as limitation to anti-angiogenic glioma therapy.

The inhibition of tumor angiogenesis could be an efficient therapeutic strategy for the treatment of malignant gliomas. Prominent neovascularization is induced by these tumors, and microvascular proliferation is a malignancy grading criterion. However, glioma cells can also invade the brain diffusely over long distances without necessarily requiring angiogenesis. Experimentally, it was shown that especially during early stages of growth in rodent brain, glioma cells can coopt the preexistent host vasculature to recruit their blood supply in the absence of neovascularization. This phenomenon was only observed in orthotopic models in which the tumor cells were implanted into the brain which is a densely vascularized environment, but not in subcutaneous models in which tumor cells are implanted into a virtual space. Using an orthotopic mouse model, we analyzed whether systemic anti-angiogenic therapy with an antibody against the vascular endothelial growth factor receptor-2 (VEGFR-2) could inhibit intracerebral growth of xenografted human glioblastoma cells and what effect this treatment had on tumor morphology and invasiveness. We found that anti-angiogenic therapy inhibited tumor growth by 80% compared to buffer-treated controls. The intratumoral microvessel density was reduced by at least 40% in treated animals compared to controls. However, in mice treated with the anti-VEGFR-2 antibody, we noticed a striking increase in the number and total area of small satellite tumors clustered around the primary mass. These satellites usually contained central vessel cores, and tumor cells often had migrated along blood vessels over long distances to eventually reach the surface and spread in the subarachnoid space. Systemic anti-angiogenic therapy can thus apparently increase the invasiveness of gliomas in the orthotopic model. Tumor cell invasion was tightly associated with preexistent blood vessels, suggesting that increased cooption of the host vasculature could represent a compensatory mechanism that is selected for by inhibiting adequate tumor vascularization.

Angiogenesis Inhibitors↗

PubMed2001

Inhibition of glioma angiogenesis and growth in vivo by systemic treatment with a monoclonal antibody against vascular endothelial growth factor receptor-2.

Using an orthotopic intracerebral model, we investigated whether systemic treatment with DC101, a monoclonal antibody against vascular endothelial growth factor receptor (VEGFR)-2, could inhibit angiogenesis and the growth of human glioblastoma cells in severe combined immunodeficient mice. Intraperitoneal treatment with DC101, control IgG, or PBS was initiated either on day 0 or, in another series, on day 6 after tumor cell implantation, and animals were killed approximately 2 weeks after tumor cell injection. Tumor volumes in animals treated with DC101 were reduced by 59 and 81% compared with IgG and PBS controls, respectively (P < 0.001), when treatment was initiated immediately, and similar results were obtained when treatment started on day 6. Microvessel density in tumors of DC101-treated animals was reduced by at least 40% compared with animals treated with control IgG or PBS (P < 0.01). We observed a reduction in tumor cell proliferation and an increase in apoptosis in DC101-treated animals (P < 0.001). However, in mice treated with DC101, we also noticed a striking increase in the number and total area of small satellite tumors clustered around, but distinct from, the primary. These satellites usually contained central vessel cores, and tumor cells often had migrated over long distances along the host vasculature to eventually reach the surface and spread leptomeningeally. We conclude that systemic antagonization of VEGFR-2 can inhibit glioblastoma neovascularization and growth but can lead to increased cooption of preexistent cerebral blood vessels. Therefore, a combination of different treatment modalities which also include anti-invasive therapy may be needed for an effective therapy against glioblastoma, and the use of an antibody against VEGFR-2 may be one effective component.

Animals↗

PubMed2001

An FGF-binding protein (FGF-BP) exerts its biological function by parallel paracrine stimulation of tumor cell and endothelial cell proliferation through FGF-2 release.

Fibroblast growth factors FGF-1 (aFGF) and FGF-2 (bFGF) are found in most embryonic and adult normal and tumor tissues, where they are immobilized in the extracellular matrix (ECM). Mobilization of these FGFs is part of a tightly controlled process resulting in the activation of high-affinity FGF receptors. Recently, we have shown that a secreted FGF-binding protein (FGF-BP) binds non-covalently to FGF-2 and is able to release it from the ECM. This process of growth factor bioactivation seems to play a pivotal role in the growth of squamous cell carcinomas, especially through induction of tumor angiogenesis. Since previous studies provided only indirect evidence for the proposed mechanism of FGF-BP-mediated FGF-2 release, we decided to use recombinant purified FGF-BP to study further the underlying mechanism of FGF-BP action. Here we show that FGF-BP is able to bind directly to FGF-2 without additional cofactors and to exhibit bioactivity. The purified recombinant FGF-BP stimulates tumor cell growth as well as endothelial cell growth and chemotaxis, indicating a dual growth-supporting role of FGF-BP in tumors. We show that this paracrine FGF-BP effect is dependent on endogenously expressed FGF-2, since it can be completely blocked by anti-FGF-2 antibodies. In tumor xenografts and in tumor cells, we detected a pattern of specific FGF-BP-immunoreactive high molecular weight forms, which presumably represent stable covalent complexes of FGF-BP and show marked differences in their occurrence in different tumors and in their heparin binding affinity. By providing further insight into the mechanism of FGF-BP action, our results emphasize the relevance of FGF-BP and of FGF-2 in tumor growth.

Adrenal Gland Neoplasms↗

PubMed2001

Expression and localization of scatter factor/hepatocyte growth factor in human astrocytomas.

Scatter factor/hepatocyte growth factor (SF/HGF) is a pleiotropic cytokine that has been implicated in glioma invasion and angiogenesis. The SF/HGF receptor, MET, has been found to be expressed in neoplastic astrocytes as well as in endothelial cells of the tumor vasculature. Both SF/HGF and MET expression have also been described to correlate with the malignancy grade of human gliomas. However, most glioblastoma cell lines lack SF/HGF expression, raising the question of the cellular origin of SF/HGF in vivo. Using in situ hybridization, we analyzed glioblastomas, anaplastic astrocytomas, diffuse astrocytomas, pilocytic astrocytomas, and normal brain for the expression of SF/HGF mRNA. We detected strong SF/HGF expression by the majority of the tumor cells and by vascular endothelial cells in all glioblastoma specimens analyzed. Combined use of in situ hybridization with fluorescence immunohistochemistry confirmed the astrocytic origin of the SF/HGF-expressiong cells. In contrast, CD68-immunoreactive microglia/macrophages, as well as vascular smooth muscle cells reactive to alpha-smooth muscle actin, lacked SF/HGF expression. In anaplastic, diffuse, and pilocytic astrocytomas, SF/HGF expression was confined to a subset of tumor cells, and signals were less intense than in glioblastomas. In addition, we detected SF/HGF mRNA in cortical neurons. SF/HGF expression was not up regulated around necroses or at tumor margins. MET immunoreactivity was observed in GFAP-expressing astrocytic tumor cells and endothelial cells as well as in a subset of microglia/macrophages. We conclude that in vivo, both autocrine and paracrine stimulation of tumor cells and endothelium through the SF/HGF-MET system are likely to contribute to tumor invasion and angiogenesis. Lack of SF/HGF expression by most cultured glioblastoma cells is not representative of the in vivo situation and most likely represents a culture artifact.

Astrocytoma↗

PubMed1999

Tauroursodeoxycholate ameliorates reperfusion injury after pig liver transplantation.

Reperfusion injury is a serious problem after clinical liver transplantation, often leading to dys- or even non-function of grafts. The present study was designed to determine whether the hydrophilic bile salt tauroursodeoxycholate (TUDC), known to be hepatoprotective in cholestatic liver disease, mitigates reperfusion injury in an in vivo pig liver transplantation model. Liver transplantation was performed in 12 pigs after a preservation time of 8 h. TUDC was administered to donor and recipient animals, and saline to controls. Blood was drawn at different time points for determination of liver enzymes. Bile samples were collected, and bile flow (BF), and bile salt secretion rate (BSSR) determined. Samples of liver tissue and bile ducts were taken for assessment by light and electron microscopy. Liver enzymes were significantly lower in the TUDC group. BF and BSSR were significantly higher. Microscopy revealed better preservation of bile duct architecture of the TUDC-infused animals. We can conclude that infusions of TUDC in pig livers ameliorate reperfusion injury in vivo. The molecular basis for this finding may be the membrane stabilizing effect of TUDC. Further studies are warranted to clarify its effect.

Animals↗

PubMed1985