Purpose: In the brain, tumors may grow without inducing angiogenesis, via co-option of the dense pre-existent capillary bed. The purpose of this study was to investigate how this phenomenon influences the outcome of antiangiogenic therapy.Experimental Design: Mice carrying brain metastases of the human, highly angiogenic melanoma cell line Mel57-VEGF-A were either or not treated with different dosages of ZD6474, a vascular endothelial growth factor (VEGF) receptor 2 tyrosine kinase inhibitor with additional activity against epidermal growth factor receptor. Effect of treatment was evaluated using contrast-enhanced magnetic resonance imaging (CE-MRI) and (immuno)morphologic analysis.Results: Placebo-treated Mel57-VEGF-A brain metastases evoked an angiogenic response and were highlighted in CE-MRI. After treatment with ZD6474 (100 mg/kg), CE-MRI failed to detect tumors in either prevention or therapeutic treatment regimens. However, (immuno)histologic analysis revealed the presence of numerous, small, nonangiogenic lesions. Treatment with 25 mg/kg ZD6474 also resulted in efficient blockade of vessel formation, but it did not fully inhibit vascular leakage, thereby still allowing visualization in CE-MRI scans.Conclusions: Our data show that, although angiogenesis can be effectively blocked by ZD6474, in vessel-dense organs this may result in sustained tumor progression via co-option, rather than in tumor dormancy. Importantly, blocking VEGF-A may result in undetectability of tumors in CE-MRI scans, leading to erroneous conclusions about therapeutic efficacy during magnetic resonance imaging followup. The maintenance of VEGF-A-induced vessel leakage in the absence of neovascularization at lower ZD6474 doses may be exploited to improve delivery of chemotherapeutic agents in combined treatment regimens of antiangiogenic and chemotherapeutic compounds.

Recently it has become evident that obesity is associated with low-grade chronic inflammation. The transcription factor peroxisome proliferator-activated receptor ␣ (PPAR␣) has been shown to have a strong antiinflammatory action in liver. However, the role of PPAR␣ in obesity-induced inflammation is much less clear. Therefore, the aim of our study was to determine whether PPAR␣ plays a role in obesity-induced hepatic inflammation. To induce obesity, wild-type sv129 and PPAR␣ ؊/؊ mice were exposed to a chronic high-fat diet (HFD), using a low-fat diet (LFD) as control. In wild-type mice, HFD significantly increased the hepatic and adipose expression of numerous genes involved in inflammation. Importantly, this effect was amplified in PPAR␣ ؊/؊ mice, suggesting an antiinflammatory role of PPAR␣ in liver and adipose tissue. Further analysis identified specific chemokines and macrophage markers, including monocyte chemotactic protein 1 and F4/ 80؉ , that were elevated in liver and adipose tissue of PPAR␣ ؊/؊ mice, indicating increased inflammatory cell recruitment in the knockout animals. When all groups of mice were analyzed together, a significant correlation between hepatic triglycerides and expression of inflammatory markers was observed. Many inflammatory genes that were up-regulated in PPAR␣ ؊/؊ livers by HFD were down-regulated by treatment with the PPAR␣ ligand Wy-14643 under normal nonsteatotic conditions, either in vivo or in vitro, suggesting an antiinflammatory effect of PPAR␣ that is independent of reduction in liver triglycerides. In conclusion, our results suggest that PPAR␣ protects against obesity-induced chronic inflammation in liver by reducing hepatic steatosis, by direct down-regulation of inflammatory genes, and by attenuating inflammation in adipose tissue. (Endocrinology 148: [2753][2754][2755][2756][2757][2758][2759][2760][2761][2762][2763] 2007)

Glioblastomas are highly aggressive primary brain tumors. Curative treatment by surgery and radiotherapy is generally impossible due to the presence of diffusely infiltrating tumor cells. Furthermore, the blood-brain barrier (BBB) in infiltrative tumor areas is largely intact, and this hampers chemotherapy as well. The occurrence of angiogenesis in these tumors makes these tumors attractive candidates for antiangiogenic therapies.

Proper delineation of gliomas using contrast-enhanced magnetic resonance imaging (CE-MRI) poses a problem in neuro-oncology. The blood brain barrier (BBB) in areas of diffuse-infiltrative growth may be intact, precluding extravasation and subsequent MR-based detection of the contrast agent gadolinium diethylenetriaminepenta-acetic acid (Gd-DTPA). Treatment with antiangiogenic compounds may further complicate tumor detection as such compounds can restore the BBB in angiogenic regions. The increasing number of clinical trials with antiangiogenic compounds for treatment of gliomas calls for the development of alternative imaging modalities. Here we investigated whether CE-MRI using ultrasmall particles of iron oxide (USPIO, Sinerem 1 ) as blood pool contrast agent has additional value for detection of glioma in the brain of nude mice. We compared conventional T1-weighted Gd-DTPA-enhanced MRI to T2*-weighted USPIOenhanced MRI in mice carrying orthotopic U87 glioma, which were either or not treated with the antiangiogenic compound vandetanib (ZD6474, ZACTIMA TM ). In untreated animals, vessel leakage within the tumor and a relatively high tumor blood volume resulted in good MRI visibility with Gd-DTPA-and USPIOenhanced MRI, respectively. Consistent with previous findings, vandetanib treatment restored the BBB in the tumor vasculature, resulting in loss of tumor detectability in Gd-DTPA MRI. However, due to decreased blood volume, treated tumors could be readily detected in USPIO-enhanced MRI scans. Our findings suggest that Gd-DTPA MRI results in overestimation of the effect of antiangiogenic therapy of glioma and that USPIO-MRI provides an important complementary diagnostic tool to evaluate response to antiangiogenic therapy of these tumors. ' 2007 Wiley-Liss, Inc.

Tumour metastasis is the result of a complex sequence of events, including migration of tumour cells through stroma, proteolytic degradation of stromal and vessel wall elements, intravasation, transport through the circulation, extravasation and outgrowth at compatible sites in the body (the 'seed and soil' hypothesis). However, the high incidence of metastasis from various tumour types in liver and lung may be explained by a stochastic process as well, based on the anatomical relationship of the primary tumour with the circulation and mechanical entrapment of metastatic tumour cells in capillary beds. We previously reported that constitutive VEGF-A expression in tumour xenografts facilitates this type of metastatic seeding by promoting shedding of multicellular tumour tissue fragments, surrounded by vessel wall elements, into the circulation. After transport through the vena cava, such fragments may be trapped in pulmonary arteries, allowing them to expand to symptomatic lesions. Here we tested whether this process has clinical relevance for clear cell renal cell carcinoma (ccRCC), a prototype tumour in the sense of high constitutive VEGF-A expression. To this end we collected and analysed outflow samples from the renal vein, directly after tumour nephrectomy, in 42 patients diagnosed with ccRCC. Tumour fragments in venous outflow were observed in 33% of ccRCC patients and correlated with the synchronous presence or metachronous development of pulmonary metastases (p < 0.001, Fisher's exact test). In patients with tumours that, in retrospect, were not of the VEGF-A-expressing clear cell type, tumour fragments were never observed in the renal outflow. These data suggest that, in ccRCC, a VEGF-A-induced phenotype promotes a release of tumour cell clusters into the circulation that may contribute to pulmonary metastasis.