Journal Article

in vivo imaging; human embryonic stem cells; hESCs; endothelial cells; ECs; AngioSense

Background: Differentiation of human embryonic stem cells into endothelial cells (hESC-ECs) has the potential to provide an unlimited source of cells for novel transplantation therapies of ischemic diseases by supporting angiogenesis and vasculogenesis. However, the endothelial differentiation efficiency of the conventional embryoid body (EB) method is low while the 2-dimensional method of co-culturing with mouse embryonic fibroblasts (MEFs) require animal product, both of which can limit the future clinical application of hESC-ECs. Moreover, to fully understand the beneficial effects of stem cell therapy, investigators must be able to track the functional biology and physiology of transplanted cells in living subjects over time.

Methodology: In this study, we developed an extracellular matrix (ECM) culture system for increasing endothelial differentiation and free from contaminating animal cells. We investigated the transcriptional changes that occur during endothelial differentiation of hESCs using whole genome microarray, and compared to human umbilical vein endothelial cells (HUVECs). We also showed functional vascular formation by hESC-ECs in a mouse dorsal window model. Moreover, our study is the first so far to transplant hESC-ECs in a myocardial infarction model and monitor cell fate using molecular imaging methods.

Conclusion: Taken together, we report a more efficient method for derivation of hESC-ECs that express appropriate patterns of endothelial genes, form functional vessels in vivo, and improve cardiac function. These studies suggest that hESC-ECs may provide a novel therapy for ischemic heart disease in the future.

Journal Article

ProSense; AngioSense; in vivo imaging

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Journal Article

Apoptosis; Phosphatidylserine; Annexin A5; Molecular Imaging; Targeted Drug Delivery; in vivo imaging; FMT; fluorescence molecular tomography; Annexin-Vivo

Cells are able to execute apoptosis by activating series of specific biochemical reactions. One of the most prominent characteristics of cell death is the externalization of phosphatidylserine (PS), which in healthy cells resides predominantly in the inner leaflet of the plasma membrane. These features have made PS-externalization a well-explored phenomenon to image cell death for diagnostic purposes. In addition, it was demonstrated that under certain conditions viable cells express PS at their surface such as endothelial cells of tumor blood vessels, stressed tumor cells and hypoxic cardiomyocytes. Hence, PS has become a potential target for therapeutic strategies aiming at Targeted Drug Delivery. In this review we highlight the biomarker PS and various PS-binding compounds that have been employed to target PS for diagnostic purposes. We emphasize the 35 kD human protein annexin A5, that has been developed as a Molecular Imaging agent to measure cell death in vitro, and non-invasively in vivo in animal models and in patients with cardiovascular diseases and cancer. Recently focus has shifted from diagnostic towards therapeutic applications employing annexin A5 in strategies to deliver drugs to cells that express PS at their surface.

Journal Article

monocytes; atherosclerosis; in vivo imaging; VivoTag; nano-sensors

N/A

Journal Article

FMT-CT; molecular imaging; atherosclerosis; protease activity; inflammation; in vivo imaging; fluorescence molecular tomography; ProSense

Objective: Proteases are emerging biomarkers of inflammatory diseases. In atherosclerosis, these enzymes are often secreted by inflammatory macrophages, digest the extracellular matrix of the fibrous cap and destabilize atheromata. Protease function can be monitored with protease activatable imaging probes and quantitated in vivo by fluorescence molecular tomography (FMT). To address two major constraints currently associated with imaging of murine atherosclerosis (lack of highly sensitive probes and absence of anatomical information), we compared protease sensors (PS) of variable size and pharmacokinetics and co-registered FMT datasets with computed tomography (FMT-CT).

Methods and results: Co-registration of FMT and CT was achieved with a multimodal imaging cartridge containing fiducial markers detectable by both modalities. A high-resolution CT angiography protocol accurately localized fluorescence to the aortic root of atherosclerotic apoE-/- mice. To identify suitable sensors, we first modeled signal kinetics in-silico and then compared three probes with identical oligo-L-lysine cleavage sequences: PS-5, 5nm in diameter containing 2 fluorochromes , PS-25, a 25nm version with an elongated lysine chain and PS-40, a polymeric nanoparticle. Serial FMT-CT showed fastest kinetics for PS-5 but, surprisingly, highest fluorescence in lesions of the aortic root for PS-40. PS-40 robustly reported therapeutic effects of atorvastatin, corroborated by ex vivo imaging and qPCR for the model protease cathepsin B.

Conclusions: FMT-CT is a robust and observer-independent tool for non-invasive assessment of inflammatory murine atherosclerosis. Reporter-containing nanomaterials may have unique advantages over small molecule agents for in vivo imaging.