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Selective occlusion of tumor vasculature was tested as a therapy for solid tumors in a mouse model. The formation of blood clots (thrombosis) within the tumor vessels was initiated by targeting the cell surface domain of human tissue factor, by means of a bispecific antibody, to an experimentally induced marker on tumor vascular endothelial cells. This truncated form of tissue factor (tTF) had limited ability to initiate thrombosis when free in the circulation, but became an effective and selective thrombogen when targeted to tumor endothelial cells. Intravenous administration of the antibody-tTF complex to mice with large neuroblastomas resulted in complete tumor regressions in 38 percent of the mice.

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Pegylated paramagnetic and fluorescent immunoliposomes were designed to enable the parallel detection of the induced expression of molecular markers on endothelial cells with magnetic resonance imaging (MRI) and fluorescence microscopy. MRI is capable of three-dimensional noninvasive imaging of opaque tissues at near cellular resolution, while fluorescence microscopy can be used to investigate processes at the subcellular level. As a model for the expression of a molecular marker, human umbilical vein endothelial cells (HUVEC) were treated with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) to upregulate the expression of the adhesion molecule E-selectin/CD62E. E-selectin-expressing HUVEC were incubated with pegylated paramagnetic fluorescently labeled liposomes carrying anti-E-selectin monoclonal antibody as a targeting ligand. Both MRI and fluorescence microscopy revealed the specific association of the liposomal MR contrast agent with stimulated HUVEC. This study suggests that this newly developed system may serve as a useful diagnostic tool to investigate pathological processes in vivo with MRI.

The hallmark of liver fibrosis is an increased extracellular matrix deposition, caused by an activation of hepatic stellate cells (HSC). Therefore, this cell type is an important target for pharmacotherapeutic intervention. Antifibrotic drugs are not efficiently taken up by HSC or may produce unwanted side-effects outside the liver. Cell-specific delivery can provide a solution to these problems, but a specific drug carrier for HSC has not been described until now. The mannose 6-phosphate/insulin-like growth factor II (M6P/ IGF-II) receptor, which is expressed in particular upon HSC during fibrosis, may serve as a target-receptor for a potential carrier. The aim of the present study was to examine if human serum albumin (HSA) modified with mannose 6-phosphate (M6P) is taken up by HSC in fibrotic livers. A series of M6P x -modified albumins were synthetized: x ‫؍‬ 2, 4, 10, and 28. Organ distribution studies were performed to determine total liver uptake. The hepatic uptake of M6P x -HSA increased with increasing M6P density. M6P x -HSA with a low degree of sugar loading (x ‫؍‬ 2-10) remained in the plasma and accumulated for 9% ؎ 0.5% or less in fibrotic rat livers. An increase in the molar ratio of M6P: HSA to 28:1 caused an increased liver accumulation to 59% ؎ 9% of the administered dose. Furthermore, we determined quantitatively the in vivo intrahepatic distribution of M6P x -HSA using double-immunostaining techniques. An increased substitution of M6P was associated with an increased accumulation in HSC; 70% ؎ 11% of the intrahepatic staining for M6P 28

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OBJECTIVE-The mechanism underlying pericyte loss during incipient diabetic retinopathy remains controversial. Hyperglycemia induces angiopoietin-2 (Ang-2) transcription, which modulates capillary pericyte coverage. In this study, we assessed loss of pericyte subgroups and the contribution of Ang-2 to pericyte migration.RESEARCH DESIGN AND METHODS-Numbers of total pericytes and their subgroups were quantified in retinal digest preparations of spontaneous diabetic XLacZ mice. Pericytes were divided into subgroups according to their localization, their position relative to adjacent endothelial cells, and the expression of LacZ. The contribution of Ang-2 to pericyte migration was assessed in Ang-2 overexpressing (mOpsinhAng2) and deficient (Ang2LacZ) mice.RESULTS-Pericyte numbers were reduced by 16% (P Ͻ 0.01) in XLacZ mice after 6 months of diabetes. Reduction of pericytes was restricted to pericytes on straight capillaries (relative reduction 27%, P Ͻ 0.05) and was predominantly observed in LacZpositive pericytes (Ϫ20%, P Ͻ 0.01). Hyperglycemia increased the numbers of migrating pericytes (69%; P Ͻ 0.05), of which the relative increase due to diabetes was exclusively in LacZ-negative pericytes, indicating reduced adherence to the capillaries (176%; P Ͻ 0.01). Overexpression of Ang-2 in nondiabetic retinas mimicked diabetic pericyte migration of wild-type animals (78%; P Ͻ 0.01). Ang-2 deficient mice completely lacked hyperglycemia-induced increase in pericyte migration compared with wildtype littermates.CONCLUSIONS-Diabetic pericyte loss is the result of pericyte migration, and this process is modulated by the Ang-Tie system.