Vessel fractions in tumor xenografts depicted by flow- or contrast-sensitive three-dimensional high-frequency Doppler ultrasound respond differently to antiangiogenic treatment.

High-frequency volumetric Power Doppler ultrasound (HF-VPDU) captures flow-dependent signals in blood vessels and can be used to assess antiangiogenic therapy effects in rodent tumors. However, the sensitivity is limited to vessels larger than capillaries. Contrast-enhanced HF-VPDU reveals all perfused vessels by assessing stimulated acoustic emissions from disintegrating microbubbles. Thus, we investigated whether flow-sensitive and contrast-enhanced HF-VPDU can depict different vessel fractions and assess their early response to antiangiogenic therapy. Mice with A431 tumors were scanned before and after administration of polybutylcyanoacrylate microbubbles by HF-VPDU. Animals received either antiangiogenic treatment (SU11248) or a control substance and were imaged repeatedly over 9 days. At each time point, tumors were removed for immunohistochemical analysis. During growth of untreated tumors, vascularization decreased correspondingly on flow-sensitive and contrast-enhanced scans. Treated tumors showed a significantly (P < 0.05) stronger decline in vascularization than controls, which was more pronounced in contrast-enhanced scans. Surprisingly, whereas vascularization remained low in contrast-enhanced scans, flow-sensitive ultrasound indicated a reincrease after day 6 with a higher vascularization than the controls at day 9. Histologic evaluation indicated that immature vessels degraded markedly on therapy, whereas large mature vessels on the tumor periphery were more therapy resistant and drew closer due to tumor shrinkage. In conclusion, contrast-enhanced HF-VPDU and flow-sensitive HF-VPDU are both capable of assessing the effects of antiangiogenic therapy. Because contrast-sensitive ultrasound is more sensitive for small immature vessels and flow-sensitive ultrasound mostly captures large vessels at the tumor periphery, the combination of both methods can provide evidence of vascular maturity in tumors.

Pharmacodynamics of streptavidin-coated cyanoacrylate microbubbles designed for molecular ultrasound imaging.

OBJECTIVES: To assess the pharmacodynamic behavior of cyanoacrylate, streptavidin-coated microbubbles (MBs) and to investigate their suitability for molecular ultrasound imaging. MATERIALS AND METHODS: Biodistribution of MBs was analyzed in tumor-bearing mice using gamma-counting, immunohistochemistry, flow cytometry, and ultrasound. Further, vascular endothelial growth factor receptor 2-antibody coupled MBs were used to image tumor neovasculature. RESULTS: After 1 minute >90% of MBs were cleared from the blood and pooled in the lungs, liver, and spleen. Subsequently, within 1 hour a decent reincrease of MB-concentration was observed in the blood. The remaining MBs were removed by liver and spleen macrophages. About 30% of the phagocytosed MBs were intact after 48 hours. Shell fragments were found in the kidneys only. No relevant MB-accumulation was observed in tumors. In contrast, vascular endothelial growth factor receptor 2-specific MBs accumulated significantly within the tumor vasculature (P < 0.05). CONCLUSIONS: The pharmacokinetic behavior of streptavidin-coated cyanoacrylate MBs has been studied. In this context, the low amount of MBs in tumors after >5 minutes is beneficial for specific targeting of angiogenesis.

Molecular profiling of angiogenesis with targeted ultrasound imaging: early assessment of antiangiogenic therapy effects.

Molecular ultrasound is capable of elucidating the expression of angiogenic markers in vivo. However, the capability of the method for volumetric "multitarget quantification" and for the assessment of antiangiogenic therapy response has rather been investigated. Therefore, we generated cyanoacrylate microbubbles linked to vascular endothelial growth factor receptor 2 (VEGFR2) and alphavbeta3 integrin binding ligands and quantified their accumulation in squamous cell carcinoma xenografts (HaCaT-ras-A-5RT3) in mice with the quantitative volumetric ultrasound scanning technique, sensitive particle acoustic quantification. Specificity of VEGFR2 and alphavbeta3 integrin binding microbubbles was shown, and changes in marker expression during matrix metalloproteinase inhibitor treatment were investigated. In tumors, accumulation of targeted microbubbles was significantly higher compared with nonspecific ones and could be inhibited competitively by addition of the free ligand in excess. Also, multimarker imaging could successfully be done during the same imaging session. Molecular ultrasound further indicated a significant increase of VEGFR2 and alphavbeta3 integrin expression during tumor growth and a considerable decrease in both marker densities after matrix metalloproteinase inhibitor treatment. Histologic data suggested that the increasing VEGFR2 and alphavbeta3 integrin concentrations in tumors during growth are related to an up-regulation of its expression by the endothelial cells, whereas its decrease under therapy is more related to the decreasing relative vessel density. In conclusion, targeted ultrasound appears feasible for the longitudinal molecular profiling of tumor angiogenesis and for the sensitive assessment of therapy effects in vivo.

Acute liver failure after a late TIPSS revision.

We report a rare case of late transjugular intrahepatic portosystemic stent shunt (TIPSS) occlusion due to progressive stent protrusion into the periportal liver parenchyma, which was a result of delayed liver shrinkage 2 years after TIPSS. The initial TIPSS procedure had been carried out in a 52-year-old man as a bridge for liver transplantation because of post-alcoholic liver cirrhosis. We describe the applied TIPSS recanalization and revision technique. Immediately after TIPSS revision acute liver failure developed, which required emergency liver transplantation.