FMN-coated fluorescent iron oxide nanoparticles for RCP-mediated targeting and labeling of metabolically active cancer and endothelial cells.

Riboflavin is an essential vitamin for cellular metabolism and is highly upregulated in metabolically active cells. Consequently, targeting the riboflavin carrier protein (RCP) may be a promising strategy for labeling cancer and activated endothelial cells. Therefore, Ultrasmall SuperParamagnetic Iron Oxide nanoparticles (USPIO) were adsorptively coated with the endogenous RCP ligand flavin mononucleotide (FMN), which renders them target-specific and fluorescent. The core diameter, surface morphology and surface coverage of the resulting FMN-coated USPIO (FLUSPIO) were evaluated using a variety of physico-chemical characterization techniques (TEM, DLS, MRI and fluorescence spectroscopy). The biocompatibility of FLUSPIO was confirmed using three different cell viability assays (Trypan blue staining, 7-AAD staining and TUNEL). In vitro evaluation of FLUSPIO using MRI and fluorescence microscopy demonstrated high labeling efficiency of cancer cells (PC-3, DU-145, LnCap) and activated endothelial cells (HUVEC). Competition experiments (using MRI and ICP-MS) with a 10- and 100-fold excess of free FMN confirmed RCP-specific uptake of the FLUSPIO by PC-3 cells and HUVEC. Hence, RCP-targeting via FMN may be an elegant way to render nanoparticles fluorescent and to increase the labeling efficacy of cancer and activated endothelial cells. This was shown for FLUSPIO, which due to their high T(2)-relaxivity, are favorably suited for MR cell tracking experiments and cancer detection in vivo.

Application of molecular ultrasound for imaging integrin expression.

Stabilized microbubbles with a size between 1-5 µm are used as ultrasound contrast agents in the clinical routine. They have shown convincing results for the vascular characterization of tissues as well as in echocardiography. Due to their size, microbubbles strictly remain intravascular where they can be detected with high sensitivity and specificity. This qualifies them for intravascular molecular imaging. Many studies have been published reporting on the successful use of microbubbles conjugated to specific ligands for target identification in vivo. Among them, there are several promising examples on how to use molecular ultrasound for the imaging of integrin expression. This review provides an overview on the composition of ultrasound contrast agents that can be used for molecular imaging and their detection by ultrasound using destructive and non destructive methods. Furthermore, concrete examples are given on the use of molecular ultrasound to characterize integrin expression on vessels. These cover oncological applications where integrin targeted microbubbles were used to identify and characterize tumor angiogenesis and to assess tumor response to antiangiogenic drugs as well as to radiotherapy. In addition, increased accumulation of integrin targeted microbubbles was found during vascular reformation in ischemic tissues as well as in vulnerable atherosclerotic plaques. In summary, there is clear evidence from preclinical studies that integrin targeted ultrasound imaging is a valuable tool for the characterization of a broad spectrum of diseases. Thus, more efforts should be put into translating this promising technology into the clinics.

Comparison of conventional time-intensity curves vs. maximum intensity over time for post-processing of dynamic contrast-enhanced ultrasound.

Our aim was to prospectively compare two post-processing techniques for dynamic contrast-enhanced ultrasound and to evaluate their impact for monitoring antiangiogenic therapy. Thus, mice with epidermoid carcinoma xenografts were examined during administration of polybutylcyanoacrylate-microbubbles using a small animal ultrasound system (40 MHz). Cine loops were acquired and analyzed using time-intensity (TI) and maximum intensity over time (MIOT) curves. Influences of fast (50 microl/2s) vs. slow (50 microl/10s) injection of microbubbles on both types of curves were investigated. Sensitivities of both methods for assessing effects of antiangiogenic treatment (SU11248) were examined. Correlative histological analysis was performed for vessel-density. Mann-Whitney test was used for statistical analysis. Microbubble injection rates significantly influenced upslope, time-to-peak and peak enhancement of conventional TI curves (p<0.05) but had almost no impact on maximum enhancement of MIOT curves (representing relative blood volume). Additionally, maximum enhancement of MIOT curves captured antiangiogenic therapy effects more reliably and earlier (already after 1 day of therapy; p<0.05) than peak enhancement of TI curves. Immunohistochemistry validated the significantly (p<0.01) lower vessel densities in treated tumors and high correlation (R(2)=0.95) between vessel-density and maximum enhancement of MIOT curves was observed. In conclusion, MIOT is less susceptible to variations of the injection's speed. It enables to assess changes of the relative blood volume earlier and with lower standard deviations than conventional TI curves. It can easily be translated into clinical practice and thus may provide a promising tool for cancer therapy monitoring.