Omniparticle Contrast Agent for Multimodal Imaging: Synthesis and Characterization in an Animal Model.

PURPOSE: Individual imaging modalities have certain advantages, but each suffers from drawbacks that other modalities may overcome. The goal of this study was to create a novel contrast agent suitable for various imaging modalities that after a single administration can bridge and strengthen the collaboration between the research fields as well as enrich the information obtained from any one modality. PROCEDURES: The contrast agent platform is based on dextran-coated iron oxide nanoparticles (for MRI and MPI) and synthesized using a modified co-precipitation method, followed by a series of conjugation steps with a fluorophore (for fluorescence and photoacoustic imaging), thyroxine (for CT imaging), and chelators for radioisotope labeling (for PET imaging). The fully conjugated agent was then tested in vitro in cell uptake, viability, and phantom studies and in vivo in a model of intraductal injection and in a tumor model. RESULTS: The agent was synthesized, characterized, and tested in vitro where it showed the ability to produce a signal on MRI/MPI/FL/PA/CT and PET images. Studies in cells showed the expected concentration-dependent uptake of the agent without noticeable toxicity. In vivo studies demonstrated localization of the agent to the ductal tree in mice after intraductal injection with different degrees of resolution, with CT being the best for this particular application. In a model of injected labeled tumor cells, the agent produced a signal with all modalities and showed persistence in tumor cells confirmed by histology. CONCLUSIONS: A fully functional omniparticle contrast agent was synthesized and tested in vitro and in vivo in two animal models. Results shown here point to the generation of a potent signal in all modalities tested without detrimental toxicity. Future use of this agent includes its exploration in various models of human disease including image-guided diagnostic and therapeutic applications.

Dual-modality, fluorescent, PLGA encapsulated bismuth nanoparticles for molecular and cellular fluorescence imaging and computed tomography.

Reports of molecular and cellular imaging using computed tomography (CT) are rapidly increasing. Many of these reports use gold nanoparticles. Bismuth has similar CT contrast properties to gold while being approximately 1000-fold less expensive. Herein we report the design, fabrication, characterization, and CT and fluorescence imaging properties of a novel, dual modality, fluorescent, polymer encapsulated bismuth nanoparticle construct for computed tomography and fluorescence imaging. We also report on cellular internalization and preliminary in vitro and in vivo toxicity effects of these constructs. 40 nm bismuth(0) nanocrystals were synthesized and encapsulated within 120 nm Poly(dl-lactic-co-glycolic acid) (PLGA) nanoparticles by oil-in-water emulsion methodologies. Coumarin-6 was co-encapsulated to impart fluorescence. High encapsulation efficiency was achieved ∼70% bismuth w/w. Particles were shown to internalize within cells following incubation in culture. Bismuth nanocrystals and PLGA encapsulated bismuth nanoparticles exhibited >90% and >70% degradation, respectively, within 24 hours in acidic, lysosomal environment mimicking media and both remained nearly 100% stable in cytosolic/extracellular fluid mimicking media. µCT and clinical CT imaging was performed at multiple X-ray tube voltages to measure concentration dependent attenuation rates as well as to establish the ability to detect the nanoparticles in an ex vivo biological sample. Dual fluorescence and CT imaging is demonstrated as well. In vivo toxicity studies in rats revealed neither clinically apparent side effects nor major alterations in serum chemistry and hematology parameters. Calculations on minimal detection requirements for in vivo targeted imaging using these nanoparticles are presented. Indeed, our results indicate that these nanoparticles may serve as a platform for sensitive and specific targeted molecular CT and fluorescence imaging.

Cellular MRI as a suitable, sensitive non-invasive modality for correlating in vivo migratory efficiencies of different dendritic cell populations with subsequent immunological outcomes.

The clinical application of dendritic cells (DC) as adjuvants in immunotherapies such as the cell-based cancer vaccine continues to gain interest. The overall efficacy of this emerging immunotherapy, however, remains low. Studies suggest the stage of maturation and activation of ex vivo-prepared DC immediately prior to patient administration is critical to subsequent DC migration in vivo, which ultimately affects overall vaccine efficacy. While it is possible to generate mature and activated DC ex vivo using various stimulatory cocktails, in the case of cancer patients, the qualitative and quantitative assessment of which DC stimulatory cocktail works most effectively to enhance subsequent DC migration in vivo is difficult. Thus, a non-invasive imaging modality capable of monitoring the real-time migration of DC in long-term studies is required. In this paper, we address whether cellular magnetic resonance imaging (MRI) is sufficiently sensitive to quantitatively detect differences in the migratory abilities of two different DC preparations: untreated (resting) versus ex vivo matured in a mouse model. In order to distinguish our ex vivo-generated DC of interest from surrounding tissues in magnetic resonance (MR) images, DC were labeled in vitro with the superparamagnetic iron oxide (SPIO) nanoparticle FeREX®. Characterization of DC phenotype and function following addition of a cytokine maturation cocktail and the toll-like receptor ligand CpG, both in the presence and in the absence of SPIO, were also carried out. Conventional histological techniques were used to verify the quantitative data obtained from MR images. This study provides important information relevant to tracking the in vivo migration of ex vivo-prepared and stimulated DC.