Endothelial vascular cell adhesion molecule 1 is a marker for high-risk carotid plaques and target for ultrasound molecular imaging.

BACKGROUND: Molecular imaging of carotid plaque vulnerability to atheroembolic events is likely to lead to improvements in selection of patients for carotid endarterectomy (CEA). The aims of this study were to assess the relative value of endothelial inflammatory markers for this application and to develop molecular ultrasound contrast agents for their imaging. METHODS: Human CEA specimens were obtained prospectively from asymptomatic (30) and symptomatic (30) patients. Plaques were assessed by semiquantitative immunohistochemistry for vascular cell adhesion molecule 1 (VCAM-1), lectin-like oxidized low-density lipoprotein receptor 1, P-selectin, and von Willebrand factor. Established small peptide ligands to each of these targets were then synthesized and covalently conjugated to the surface of lipid-shelled microbubble ultrasound contrast agents, which were then evaluated in a flow chamber for binding kinetics to activated human aortic endothelial cells under variable shear conditions. RESULTS: Expression of VCAM-1 on the endothelium of CEA specimens from symptomatic patients was 2.4-fold greater than that from asymptomatic patients (P < .01). Expression was not significantly different between groups for P-selectin (P = .43), von Willebrand factor (P = .59), or lectin-like oxidized low-density lipoprotein receptor 1 (P = .99). Although most plaques from asymptomatic patients displayed low VCAM-1 expression, approximately one in five expressed high VCAM-1 similar to plaques from symptomatic patients. In vitro flow chamber experiments demonstrated that VCAM-1-targeted microbubbles bind cells that express VCAM-1, even under high-shear conditions that approximate those found in human carotid arteries, whereas binding efficiency was lower for the other agents. CONCLUSIONS: VCAM-1 displays significantly higher expression on high-risk (symptomatic) vs low-risk (asymptomatic) carotid plaques. Ultrasound contrast agents bearing ligands for VCAM-1 can sustain high-shear attachment and may be useful for identifying patients in whom more aggressive treatment is warranted.

Optimization of Phase-Change Contrast Agents for Targeting MDA-MB-231 Breast Cancer Cells.

Breast cancer remains a leading cause of death for women throughout the world. Recent advances in medical imaging technologies and tumor targeting agents signify vast potential for progress toward improved management of this global problem. Phase-change contrast agents (PCCAs) are dynamic imaging agents with practical applications in both the research and clinical settings. PCCAs possess characteristics that allow for cellular uptake where they can be converted from liquid-phase PCCAs to gaseous microbubbles via ultrasound energy. Previously, we reported successful internalization of folate-targeted PCCAs in MDA-MB-231 breast cancer cells followed by ultrasound-mediated activation to produce internalized microbubbles. This study examines the binding, internalization and activation of folate-receptor targeted PCCAs in MDA-MB-231 breast cancer cells as a function of gaseous core compositions, incubation time and ultrasound exposure period. In vitro results indicate that internalization and ultrasound-mediated activation of PCCAs were significantly greater using a 50:50 mixture of decafluorobutane:dodecafluoropentane compared with other core compositions: 50:50 octafluoropropane:decafluorobutane (p < 0.0001), decafluorobutane (p < 0.04) and dodecafluoropentane (p < 0.0001). Furthermore, it was found that PCCAs composed of perfluorocarbons with higher boiling points responded with greater activation efficiency when exposed to 12 s of ultrasound exposure as opposed to 4 s of ultrasound exposure. When evaluating different incubation times, it was found that incubating the PCCAs with breast cancer cells for 60 min did not produce significantly greater internalization and activation compared with incubation for 10 min; this was concluded after comparing the number of microbubbles present per cell before ultrasound versus post-ultrasound, and finding a ratio of intracellular microbubbles post-ultrasound/pre-ultrasound, 3.46 versus 3.14, respectively. The data collected in this study helps illustrate further optimization of folate-receptor targeted PCCAs for breast cancer targeting and imaging.