Liquid Perfluorocarbon Nanoparticles Research Articles

Polypyrrole-coated phase-change liquid perfluorocarbon nanoparticles for the visualized photothermal-chemotherapy of breast cancer

A theranostic nanoplatform (DTX/PFH@PPy-FA) for multi-modal imaging-guided photothermal-chemotherapy has been constructed. Lipid-perfluorohexane (PFH) nanodroplet loaded with docetaxel (DTX) was coated with a polypyrrole (PPy) shell. Then the folic acid (FA) molecule with active tumor-targeting function was modified on the surface of PPy shell. Due to the good photothermal conversion performance, PPy shell can raise the temperature under the near infrared laser irradiation, which not only produces photothermal effect to kill tumor cells, but also promotes liquid-gas phase change of PFH, and produces ultrasound imaging effect. The results of photothermal experiment and imaging experiment confirmed that the obtained DTX/PFH@PPy-FA possessed good photothermal, photoacoustic imaging and ultrasound imaging effects in vitro and in vivo. The results of in vitro cell experiments showed that DTX/PFH@PPy-FA had a active targeting ability to tumor cells, and its photothermal-chemotherapy synergistically inhibited the proliferation of tumor cells. In vivo study on 4T1-bearing BALB/c mice indicated that the photothermal-chemotherapy of DTX/PFH@PPy-FA not only effectively inhibited the growth of 4T1 breast cancer, but also inhibited lung metastasis. This multifunctional nanoparticle is expected to become a new nanoplatform for the visualized photothermal-chemotherapy of cancer. Statement of SignificanceIn this work, we presented a multi-modal imaging-guided photothermal-chemotherapy theranostic nanoplatform (DTX/PFH@PPy-FA) for visualized treatment of breast cancer. The docetaxel (DTX) loaded perfluorohexane (PFH) nanodroplets (DTX/PFH@SPC) were firstly prepared and then coated with polypyrrole shell (PPy). Then, PEGylated folic acid was covalently modified to obtain the folate-targeted multifunctional nanoparticle (DTX/PFH@PPy-FA). Due to the good photothermal conversion performance, PPy shell can raise the temperature under the near infrared laser irradiation, which not only produces photothermal effect to kill tumor cells, but also promotes liquid-gas phase change of PFH, and produces good ultrasound imaging effect. The PPy shell also imparts photoacoustic imaging characteristics to the nanoparticles. Experimental results show that our prepared DTX/PFH@PPy-FA possesses folic acid-mediated tumor targeting ability, ultrasound and photoacoustic imaging, and photothermal-chemotherapy synergistic effect. This multi-functional nanoparticle is expected to become a new platform for the visualized photothermal-chemotherapy of breast cancer.

Selective intracellular delivery of perfluorocarbon nanodroplets for cytotoxicity threshold reduction on ultrasound-induced vaporization.

Phase-change nanodroplets (PCNDs), which are liquid perfluorocarbon nanoparticles, have garnered much attention as ultrasound-responsive nanomedicines. The vaporization phenomenon has been employed to treat tumors mechanically. However, the ultrasound pressure applied to induce vaporization must be low to avoid damage to nontarget tissues. Here, we report that the pressure threshold for vaporization to induce cytotoxicity can be significantly reduced by selective intracellular delivery of PCNDs into targeted tumors. In vitro experiments revealed that selective intracellular delivery of PCNDs induced PCND aggregation specifically inside the targeted cells. This close-packed configuration decreased the pressure threshold for vaporization to induce cytotoxicity. Moreover, following ultrasound exposure, significant decrease was observed in the viability of cells that incorporated PCNDs (35%) but not in the viability of cells that did not incorporate PCNDs (88%). Intracellular delivery of PCNDs reduced ultrasound pressure applied for vaporization to induce cytotoxicity. Confocal laser scanning microscopy and flow cytometry revealed that prolonged PCND-cell incubation increased PCND uptake and aggregation. This aggregation effect might have contributed to the cytotoxicity threshold reduction effect.

Hyaluronic acid and polydopamine functionalized phase change nanoparticles for ultrasound imaging-guided photothermal-chemotherapy.

In this study, we successfully prepared polydopamine (PD) and hyaluronic acid (HA) coated liquid perfluorocarbon nanoparticles, which integrated the good photothermal conversion effect of PD, the ultrasound imaging properties of the liquid fluorocarbon and active tumor-targeting of HA. Liquid perfluorocarbon nanodroplets significantly improved in terms of their physical stability after being coated with PD and HA as the shell. Photothermal and ultrasound imaging experiments showed that PD could effectively convert near-infrared (NIR) laser energy into heat for photothermal therapy, which could induce a phase change of the liquid perfluorocarbon, thereby generating microbubbles, enhancing ultrasound imaging signals and promoting drug release. In vitro cellular experiments showed that HA on the surface of the nanoparticles could actively target 4T1 breast cancer cells by CD44 receptor-mediated endocytosis. Furthermore, the novel nanosystem has shown effective inhibition of tumor growth by synergistic photothermal-chemotherapy in tumor-bearing mice. In conclusion, the novel nanosystem we prepared in this study is expected to provide a new strategy for the diagnosis and treatment of cancer.

Selective intracellular vaporisation of antibody-conjugated phase-change nano-droplets in vitro

While chemotherapy is a major mode of cancer therapeutics, its efficacy is limited by systemic toxicities and drug resistance. Recent advances in nanomedicine provide the opportunity to reduce systemic toxicities. However, drug resistance remains a major challenge in cancer treatment research. Here we developed a nanomedicine composed of a phase-change nano-droplet (PCND) and an anti-cancer antibody (9E5), proposing the concept of ultrasound cancer therapy with intracellular vaporisation. PCND is a liquid perfluorocarbon nanoparticle with a liquid–gas phase that is transformable upon exposure to ultrasound. 9E5 is a monoclonal antibody targeting epiregulin (EREG). We found that 9E5-conjugated PCNDs are selectively internalised into targeted cancer cells and kill the cells dynamically by ultrasound-induced intracellular vaporisation. In vitro experiments show that 9E5-conjugated PCND targets 97.8% of high-EREG-expressing cancer cells and kills 57% of those targeted upon exposure to ultrasound. Furthermore, direct observation of the intracellular vaporisation process revealed the significant morphological alterations of cells and the release of intracellular contents.

Perfluorocarbon Nanoemulsions for Quantitative Molecular Imaging and Targeted Therapeutics

A broad array of nanomaterials is available for use as contrast agents for molecular imaging and drug delivery. Due to the lack of endogenous background signal in vivo and the high NMR sensitivity of the (19)F atom, liquid perfluorocarbon nanoemulsions make ideal agents for cellular and magnetic resonance molecular imaging. The perfluorocarbon core material is surrounded by a lipid monolayer which can be functionalized with a variety of agents including targeting ligands, imaging agents and drugs either individually or in combination. Multiple copies of targeting ligands (approximately 20-40 monoclonal antibodies or 200-400 small molecule ligands) serve to enhance avidity through multivalent interactions while the composition of the particle's perfluorocarbon core results in high local concentrations of (19)F. Additionally, lipophilic drugs contained within molecularly targeted nanoemulsions can result in contact facilitated drug delivery to target cells. Ultimately, the dual use of perfluorocarbon nanoparticles for both site targeted drug delivery and molecular imaging may provide both imaging of disease states as well as conclusive evidence that drug delivery is localized to the area of interest. This review will focus on liquid perfluorocarbon nanoparticles as (19)F molecular imaging agents and for targeted drug delivery in cancer and cardiovascular disease.

Nanoparticle pharmacokinetic profiling in vivo using magnetic resonance imaging

Contrast agents targeted to molecular markers of disease are currently being developed with the goal of identifying disease early and evaluating treatment effectiveness using noninvasive imaging modalities such as MRI. Pharmacokinetic profiling of the binding of targeted contrast agents, while theoretically possible with MRI, has thus far only been demonstrated with more sensitive imaging techniques. Paramagnetic liquid perfluorocarbon nanoparticles were formulated to target alpha(v)beta(3)-integrins associated with early atherosclerosis in cholesterol-fed rabbits to produce a measurable signal increase on magnetic resonance images after binding. In this work, we combine quantitative information of the in vivo binding of this agent over time obtained by means of MRI with blood sampling to derive pharmacokinetic parameters using simultaneous and individual fitting of the data to a three compartment model. A doubling of tissue exposure (or area under the curve) is obtained with targeted as compared to control nanoparticles, and key parameter differences are discovered that may aid in development of models for targeted drug delivery.

Effective Method of Characterizing Specific Liquid Fluorocarbon Interactions Using Ultrasound

Several studies have used the analytical results available for structure factor, osmotic pressure, vapor pressure, and suspension viscosity to characterize nanoparticle interactions. In this work a novel attempt has been made to characterize seven different types of liquid per fluorocarbon nanoparticles (LPFC-np) by estimating packing factor, segment diameter, chemical potential, Rao's constant, and adiabatic and isothermal compressibilities using experimental ultrasonic velocity as input. The segment diameter has also been examined by using experimental surface tension and viscosity for comparison. The calculations were extended for different temperatures involving four different equations of state. We have tested the sensitivity of all these parameters to a very small change in the heat capacity ratio. This extensive calculation helps to make a reasonable description about the interactions among the LPFC-np. Also a better correlation could be determined between the interaction of ultrasound with LPFC-np (as a facilitator) and the pure absorption (propagation) of ultrasound by the entire system.

Synthetic nanoparticle vehicles deliver siRNA to vascular endothelial cells for VCAM‐1 knockdown

The therapeutic promise of siRNA relies on its ability to knock down genes with minimal side effects. Upregulation of inflammatory genes such as vascular cell adhesion molecule‐1 (VCAM‐1) in atherosclerosis suggests that targeted delivery of siRNA as an antiatherosclerotic therapy might modify disease progression. We have shown previously that liquid perfluorocarbon nanoparticle emulsions (PFC‐NP) can serve as molecularly targeted vehicles for imaging and drug delivery in vivo. In this study, we sought to utilize PFC NP as carriers of siRNA to endothelial cells. Cationic PFC‐NP emulsions were produced with 1,2‐Dioleoyl‐3‐Trimethylammonium‐Propane (DOTAP). siRNA to VCAM‐1 was complexed to the emulsions and incubated with mouse 2F‐2B endothelial cells. We observed that fluorescently labeled siRNA in cells 24 h after transfection as determined by confocal microscopy. Optimized transfection conditions (10 pM PFC‐NP with 5 nM siRNA) produce a 52% decrease in VCAM‐1 mRNA levels after 48h. Corresponding viability data measured 24 h after transfection using flow cytometry indicated 80–90% viability in 2F‐2B cells under similar transfection conditions. Accordingly, these particles offer an efficient method for siRNA delivery to endothelial cells and they can simultaneously serve as a vehicle for molecular imaging to confirm siRNA delivery. This work was supported by NIH grant #HL073646

Fibrin-Targeted Perfluorocarbon Nanoparticles for Targeted Thrombolysis

Reperfusion of the ischemic brain is the most effective therapy for acute stroke, restoring blood flow to threatened tissues. Thrombolytics, such as recombinant tissue plasminogen activator, administered within 3 h of symptom onset can improve neurologic outcome, although the potential for adverse hemorrhagic events limits its use to less than 3% of acute ischemic stroke patients. Targeting of clot-dissolving therapeutics has the potential to decrease the frequency of complications while simultaneously increasing treatment effectiveness, by concentrating the available drug at the desired site and permitting a lower systemic dose. We aimed to develop a fibrin-specific, liquid perfluorocarbon nanoparticle that is surface modified to deliver the plasminogen activator streptokinase. We also aimed to evaluate its effectiveness for targeted thrombolysis in vitro using quantitative acoustic microscopy. Human plasma clots were formed in vitro and targeted with streptokinase-loaded nanoparticles, control nanoparticles or a mixture of both. Depending on the treatment group, clots were then exposed to either phosphate-buffered saline (PBS), PBS with plasminogen or PBS with plasminogen and free streptokinase. Spatially registered ultrasound scans were performed at 15-min intervals for 1 h to quantify changes in clot morphology and backscatter. Nanoparticles bound to the clot significantly increased the acoustic contrast of the targeted clot surface, permitting volumetric estimates. Profile plots of detected clot surfaces demonstrated that streptokinase-loaded, fibrin-targeted perfluoro-octylbromide nanoparticles in the presence of plasminogen induced rapid fibrinolysis (<60 min) without concurrent microbubble production and cavitation. Streptokinase-loaded or fibrin-targeted control nanoparticles insonified in PBS did not induce clot lysis. Morphologic changes in the treated group were accompanied by temporal and spatial changes in backscatter. Ultrasound exposure had no effect on the digestion process. Effective concentrations of targeted streptokinase were orders of magnitude lower than equivalently efficacious levels of free drug. Moreover, increasing competitive inhibition of fibrin-bound streptokinase nanoparticles reduced clot lysis in a monotonic fashion. As little as 1% surface targeting of streptokinase nanoparticles produced significant decreases in clot volumes (approximately 30%) in 1 h. This new nanoparticle-based thrombolytic agent provides specific and rapid fibrinolysis in vitro and may have a clinical role in early reperfusion during acute ischemic stroke.

Fluorine Cardiovascular Magnetic Resonance Angiography In Vivo at 1.5 T with Perfluorocarbon Nanoparticle Contrast Agents

While the current gold standard for coronary imaging is X-ray angiography, evidence is accumulating that it may not be the most sensitive technique for detecting unstable plaque. Other imaging modalities, such as cardiovascular magnetic resonance (CMR), can be used for plaque characterization, but suffer from long scan and reconstruction times for determining regions of stenosis. We have developed an intravascular fluorinated contrast agent that can be used for angiography with cardiovascular magnetic resosnace at clinical field strengths (1.5 T). This liquid perfluorocarbon nanoparticle contains a high concentration of fluorine atoms that can be used to generate contrast on 19F MR images without any competing background signal from surrounding tissues. By using a perfluorocarbon with 20 equivalent fluorine molecules, custom-built RF coils, a modified clinical scanner, and an efficient steady-state free procession sequence, we demonstrate the use of this agent for angiography of small vessels in vitro, ex vivo, and in vivo. The surprisingly high signal generated with very short scan times and low doses of perfluorocarbon indicates that this technique may be useful in clinical settings when coupled with advanced imaging strategies.

Molecular Imaging With Targeted Perfluorocarbon Nanoparticles: Quantification of the Concentration Dependence of Contrast Enhancement for Binding to Sparse Cellular Epitopes

Targeted, liquid perfluorocarbon nanoparticles are effective agents for acoustic contrast enhancement of abundant cellular epitopes ( e.g., fibrin in thrombi) and for lower prevalence binding sites, such as integrins associated with tumor neovasculature. In this study, we sought to delineate the quantitative relationship between the extent of contrast enhancement of targeted surfaces and the density (and concentration) of bound perfluorocarbon (PFC) nanoparticles. Two dramatically different substrates were utilized for targeting. In one set of experiments, the surfaces of smooth, flat, avidin-coated agar disks were exposed to biotinylated nanoparticles to yield a thin layer of targeted contrast. For the second set of measurements, we targeted PFC nanoparticles applied in thicker layers to cultured smooth muscle cells expressing the transmembrane glycoprotein “tissue factor” at the cell surface. An acoustic microscope was used to characterize reflectivity for all samples as a function of bound PFC (determined via gas chromatography). We utilized a formulation of low-scattering nanoparticles having oil-based cores to compete against high-scattering PFC nanoparticles for binding, to elucidate the dependence of contrast enhancement on PFC concentration. The relationship between reflectivity enhancement and bound PFC content varied in a curvilinear fashion and exhibited an apparent asymptote (approximately 16 dB and 9 dB enhancement for agar and cell samples, respectively) at the maximum concentrations (∼150 μg and ∼ 1000 μg PFOB for agar and cell samples, respectively). Samples targeted with only oil-based nanoparticles exhibited mean backscatter values that were nearly identical to untreated samples (<1 dB difference), confirming the oil particles’ low-scattering behavior. The results of this study indicate that substantial contrast enhancement with liquid perfluorocarbon nanoparticles can be realized even in cases of partial surface coverage (as might be encountered when targeting sparsely populated epitopes) or when targeting surfaces with locally irregular topography. Furthermore, it may be possible to assess the quantity of bound cellular epitopes through acoustic means. (E-mail: jnm@cvu.wustl.edu)

19 F magnetic resonance imaging for stem/progenitor cell tracking with multiple unique perfluorocarbon nanobeacons

MRI has been employed to elucidate the migratory behavior of stem/progenitor cells noninvasively in vivo with traditional proton (1H) imaging of iron oxide nanoparticle-labeled cells. Alternatively, we demonstrate that fluorine (19F) MRI of cells labeled with different types of liquid perfluorocarbon (PFC) nanoparticles produces unique and sensitive cell markers distinct from any tissue background signal. To define the utility for cell tracking, mononuclear cells harvested from human umbilical cord blood were grown under proendothelial conditions and labeled with nanoparticles composed of two distinct PFC cores (perfluorooctylbromide and perfluoro-15-crown-5 ether). The sensitivity for detecting and imaging labeled cells was defined on 11.7T (research) and 1.5T (clinical) scanners. Stem/progenitor cells (CD34+ CD133+ CD31+) readily internalized PFC nanoparticles without aid of adjunctive labeling techniques, and cells remained functional in vivo. PFC-labeled cells exhibited distinct 19F signals and were readily detected after both local and intravenous injection. PFC nanoparticles provide an unequivocal and unique signature for stem/progenitor cells, enable spatial cell localization with 19F MRI, and permit quantification and detection of multiple fluorine signatures via 19F MR spectroscopy. This method should facilitate longitudinal investigation of cellular events in vivo for multiple cell types simultaneously.

Acoustic Activation of Targeted Liquid Perfluorocarbon Nanoparticles Does Not Compromise Endothelial Integrity

Perfluorocarbon nanoparticles consisting essentially of liquid perfluoro-octyl bromide (PFOB) core surrounded by a lipid monolayer can serve as highly specific site-targeted contrast and therapeutic agents after binding to cellular biomarkers. Based on previous findings that ultrasound applied at 2 MHz and 1.9 mechanical index (MI) for a 5-min duration dramatically enhances the cellular interaction of targeted PFOB nanoparticles with melanoma cells in vitro without inducing apoptosis or other harmful effects to cells that are targeted, we sought to define mechanisms of interaction and the safety profile of ultrasound used in conjunction with liquid perfluorocarbon nanoparticles for targeted drug delivery, as compared with conventional microbubble ultrasound contrast agents under identical insonification conditions. Cell-culture inserts were used to grow a confluent monolayer of human umbilical vein endothelial cells. Definity in conjunction with continuous wave ultrasound (2.25 MHz for 1 and 5 min) increased the permeability of monolayer by four to six times above the normal, decreased transendothelial electrical resistance (a sign of reduced membrane integrity), and decreased cell viability by approximately 50%. Histological evaluation demonstrated extensive disruptions of cell monolayers. Nanoparticles (both nontargeted and targeted) elicited no changes in these different measures under similar insonification conditions and did not disrupt cell monolayers. We hypothesize that ultrasound facilitates drug transport from the perfluorocarbon nanoparticles not by cavitation-induced effects on cell membrane but rather by direct interaction with the nanoparticles that stimulate lipid exchange and drug delivery.

Unique perfluorocarbon nanobeacons improve stem/progenitor cell tracking with MRI

Conventional 1H Magnetic Resonance Imaging (MRI) has been employed to define the migratory behavior of stem/progenitor cells noninvasively in vivo. In contrast, we propose fluorine (19F) MRI of liquid perfluorocarbon nanoparticles (PFC NP: 200 nm) comprising a phospholipid/surfactant monolayer surrounding a PFC core could provide a unique and sensitive cell marker distinct from tissue background signal. To determine the utility for cell tracking, stem/progenitor cells were harvested by density gradient centrifugation from human umbilical cord blood, grown under proendothelial conditions, and labeled with fluorescent PFC NP. Internalization of NP alone, without aid of any additional agents, was confirmed with confocal microscopy showing abundant NP uptake and distribution throughout the cytosol. Flow cytometry indicated ≥68% of cells contained NP and stained positive for CD34, CD133, and CD31 markers. Labeled cells were readily imaged using the 19F nuclear NP signal at 1.5T in vitro; and at 12T after injection of 106 cells into mouse skeletal muscle in situ. PFC NP provide an unequivocal signal for stem/progenitor cells, do not require adjunctive procedures to achieve cellular uptake, enable spatial cell localization with 19F MR imaging, and provide opportunity for quantification via 19F MR spectroscopy. This molecular imaging and tracking approach should facilitate longitudinal investigation of cellular events in vivo such as stem/progenitor cell localization, implantation, and differentiation.

Sonic activation of molecularly-targeted nanoparticles accelerates transmembrane lipid delivery to cancer cells through contact-mediated mechanisms: Implications for enhanced local drug delivery

Liquid perfluorocarbon nanoparticles serve as sensitive and specific targeted contrast and drug delivery vehicles by binding to specific cell surface markers. We hypothesized that application of acoustic energy at diagnostic power levels could promote nanoparticle-associated drug delivery by stimulating increased interaction between the nanoparticle's lipid layer and the targeted cell's plasma membrane. Ultrasound (mechanical index = 1.9) applied with a conventional ultrasound imaging system to nanoparticles targeted to alpha(v)beta3-integrins on C32 melanoma cancer cells in vitro produced no untoward effects. Within 5 min, lipid delivery from nanoparticles into cell cytoplasm was dramatically augmented. We also demonstrate the operation of a potential physical mechanism for this effect, the acoustic radiation force on the nanoparticles, which may contribute to the enhanced lipid delivery. Accordingly, we propose that local delivery of lipophilic substances (e.g., drugs) from targeted nanoparticles directly into cell cytoplasm can be augmented rapidly and safely with conventional ultrasound imaging devices through nondestructive mechanisms.

Augmented and selective delivery of liquid perfluorocarbon nanoparticles to melanoma cells with ultrasound

Previous work has demonstrated the ability of liquid perfluorocarbon (PFC) nanoparticles to deliver therapeutic agents to cells selectively by binding to specific cellular epitopes, and confirmed the ability to simultaneously image these targeted nanoparticles with ultrasound. In this study, enhanced delivery of targeted PFC nanoparticles to cells expressing the integrin avb3 using clinical levels of ultrasound energy were studied. Nanoparticles complexed with ligands targeted to avb3 were incubated with cells (C32 melanoma) that expressed avb3 in culture. Control nanoparticles were produced that carried no ligand targeted to avb3. A custom specimen holder permitted simultaneous microscopic visualization of cell interactions during exposure to calibrated levels of ultrasound energy. After nanoparticle binding to cells and application of ultrasound, a roughly 2-fold increase in PFC content of the cells was observed. For control (nonbinding) nanoparticles, ultrasound exposure also increased PFC deposition, but the overall level was substantially less. Videodensitometric data show that nanoparticles were not destroyed by ultrasound exposure. Moreover, the alignment of nanoparticles relative to incident acoustic field demonstrate conclusively that acoustic radiation forces influence the nanoparticles and implicate these forces as participates in the enhanced delivery.

Characterization and biodistribution of a novel MRI molecular imaging agent by neutron activation analysis

Angiogenesis is integral to the development and progression of atherosclerotic disease and solid tumor growth. New microvessels form in atherosclerotic plaque and the presence of new vessels has been associated with carotid plaque instability. Likewise, solid tumor growth depends upon angiogenesis to provide tumor cells with oxygen and nutrients. Recently, Lanza et al. have demonstrated molecular imaging of angiogenesis both in human melanoma xenografts in nude mice and atherosclerotic rabbits by magnetic resonance imaging (MRI) with clinical magnet strengths using ανβ3-targeted nanoparticles developed in their lab. ανβ3-integrin is a selective molecular epitope expressed by angiogenic endothelium and the MRI contrast agent consists of a lipid-encapsulated, liquid perfluorocarbon nanoparticle directly coupled to a selective ανβ3 ligand. The nanoparticle also contains the paramagnetic contrast agent gadolinium linked to the nanoparticle as Gd-DTPA-bis-oleate. In this work we report on the use of neutron activation analysis to confirm the Gd content of the nanoparticle formulations and determine the biodistribution of Gd post injection.

Quantitative “magnetic resonance immunohistochemistry” with ligand‐targeted 19F nanoparticles

Unstable atherosclerotic plaques exhibit microdeposits of fibrin that may indicate the potential for a future rupture. However, current methods for evaluating the stage of an atherosclerotic lesion only involve characterizing the level of vessel stenosis, without delineating which lesions are beginning to rupture. Previous work has shown that fibrin-targeted, liquid perfluorocarbon nanoparticles, which carry a high payload of gadolinium, have a high sensitivity and specificity for detecting fibrin with clinical (1)H MRI. In this work, the perfluorocarbon content of the targeted nanoparticles is exploited for the purposes of (19)F imaging and spectroscopy to demonstrate a method for quantifiable molecular imaging of fibrin in vitro at 4.7 T. Additionally, the quantity of bound nanoparticles formulated with different perfluorocarbon species was calculated using spectroscopy. Results indicate that the high degree of nanoparticle binding to fibrin clots and the lack of background (19)F signal allow accurate quantification using spectroscopy at 4.7 T, as corroborated with proton relaxation rate measurements at 1.5 T and trace element (gadolinium) analysis. Finally, the extension of these techniques to a clinically relevant application, the evaluation of the fibrin burden within an ex vivo human carotid endarterectomy sample, demonstrates the potential use of these particles for uniquely identifying unstable atherosclerotic lesions in vivo.

Targeted nanoparticles for quantitative imaging of sparse molecular epitopes with MRI.

Before molecular imaging with MRI can be applied clinically, certain problems, such as the potential sparseness of molecular epitopes on targeted cell surfaces, and the relative weakness of conventional targeted MR contrast agents, must be overcome. Accordingly, the conditions for diagnostic conspicuity that apply to any paramagnetic MRI contrast agent with known intrinsic relaxivity were examined in this study. A highly potent paramagnetic liquid perfluorocarbon nanoparticle contrast agent ( approximately 250 nm diameter, >90,000 Gd3+/particle) was imaged at 1.5 T and used to successfully predict a range of sparse concentrations in experimental phantoms with the use of standard MR signal models. Additionally, we cultured and targeted the smooth muscle cell (SMC) monolayers that express "tissue factor," a glycoprotein of crucial significance to hemostasis and response to vascular injury, by conjugating an anti-tissue factor antibody fragment to the nanoparticles to effect specific binding. Quantification of the signal from cell monolayers imaged at 1.5 T demonstrated, as predicted via modeling, that only picomolar concentrations of paramagnetic perfluorocarbon nanoparticles were required for the detection and quantification of tissue factor at clinical field strengths. Thus, for targeted paramagnetic agents carrying high payloads of gadolinium, it is possible to quantify molecular epitopes present in picomolar concentrations in single cells with routine MRI.

First experience with noncavitational ultrasound enhancement of selective cellular delivery of liquid perfluorocarbon nanoparticles to Angiogenic sites

First experience with noncavitational ultrasound enhancement of selective cellular delivery of liquid perfluorocarbon nanoparticles to Angiogenic sites