Conroy Sun

Magnetic Nanoparticles in MR Imaging and Drug Delivery

Magnetic nanoparticles (MNPs) possess unique magnetic properties and the ability to function at the cellular and molecular level of biological interactions making them an attractive platform as contrast agents for magnetic resonance imaging (MRI) and as carriers for drug delivery. Recent advances in nanotechnology have improved the ability to specifically tailor the features and properties of MNPs for these biomedical applications. To better address specific clinical needs, MNPs with higher magnetic moments, non-fouling surfaces, and increased functionalities are now being developed for applications in the detection, diagnosis, and treatment of malignant tumors, cardiovascular disease, and neurological disease. Through the incorporation of highly specific targeting agents and other functional ligands, such as fluorophores and permeation enhancers, the applicability and efficacy of these MNPs have greatly increased. This review provides a background on applications of MNPs as MR imaging contrast agents and as carriers for drug delivery and an overview of the recent developments in this area of research.

Specific targeting of brain tumors with an optical/magnetic resonance imaging nanoprobe across the blood-brain barrier.

Nanoparticle-based platforms have drawn considerable attention for their potential effect on oncology and other biomedical fields. However, their in vivo application is challenged by insufficient accumulation and retention within tumors due to limited specificity to the target, and an inability to traverse biological barriers. Here, we present a nanoprobe that shows an ability to cross the blood-brain barrier and specifically target brain tumors in a genetically engineered mouse model, as established through in vivo magnetic resonance and biophotonic imaging, and histologic and biodistribution analyses. The nanoprobe is comprised of an iron oxide nanoparticle coated with biocompatible polyethylene glycol-grafted chitosan copolymer, to which a tumor-targeting agent, chlorotoxin, and a near-IR fluorophore are conjugated. The nanoprobe shows an innocuous toxicity profile and sustained retention in tumors. With the versatile affinity of the targeting ligand and the flexible conjugation chemistry for alternative diagnostic and therapeutic agents, this nanoparticle platform can be potentially used for the diagnosis and treatment of a variety of tumor types.

In vivo MRI detection of gliomas by chlorotoxin-conjugated superparamagnetic nanoprobes.

Converging advances in the development of nanoparticle-based imaging probes and improved understanding of the molecular biology of brain tumors offer the potential to provide physicians with new tools for the diagnosis and treatment of these deadly diseases. However, the effectiveness of promising nanoparticle technologies is currently limited by insufficient accumulation of these contrast agents within tumors. Here a biocompatible nanoprobe composed of a poly(ethylene glycol) (PEG) coated iron oxide nanoparticle that is capable of specifically targeting glioma tumors via the surface-bound targeting peptide, chlorotoxin (CTX), is presented. The preferential accumulation of the nanoprobe within gliomas and subsequent magnetic resonance imaging (MRI) contrast enhancement are demonstrated in vitro in 9L cells and in vivo in tumors of a xenograft mouse model. TEM imaging reveals that the nanoprobes are internalized into the cytoplasm of 9L cells and histological analysis of selected tissues indicates that there are no acute toxic effects of these nanoprobes. High targeting specificity and benign biological response establish this nanoprobe as a potential platform to aid in the diagnosis and treatment of gliomas and other tumors of neuroectodermal origin.

PEG-mediated synthesis of highly dispersive multifunctional superparamagnetic nanoparticles: their physicochemical properties and function in vivo.

Multifunctional superparamagnetic nanoparticles have been developed for a wide range of applications in nanomedicine, such as serving as tumor-targeted drug carriers and molecular imaging agents. To function in vivo, the development of these novel materials must overcome several challenging requirements including biocompatibility, stability in physiological solutions, nontoxicity, and the ability to traverse biological barriers. Here we report a PEG-mediated synthesis process to produce well-dispersed, ultrafine, and highly stable iron oxide nanoparticles for in vivo applications. Utilizing a biocompatible PEG coating bearing amine functional groups, the produced nanoparticles serve as an effective platform with the ability to incorporate a variety of targeting, therapeutic, or imaging ligands. In this study, we demonstrated tumor-specific accumulation of these nanoparticles through both magnetic resonance and optical imaging after conjugation with chlorotoxin, a peptide with high affinity toward tumors of the neuroectodermal origin, and Cy5.5, a near-infrared fluorescent dye. Furthermore, we performed preliminary biodistribution and toxicity assessments of these nanoparticles in wild-type mice through histological analysis of clearance organs and hematology assay, and the results demonstrated the relative biocompatibility of these nanoparticles.

Functionalized Nanoparticles with Long-Term Stability in Biological Media†

Nanoparticles have been extensively studied in recent years due to their unique optical, magnetic, or chemical properties.[1-4] While many synthetic methods have been investigated, an effective way to produce ultrafine and monodisperse nanoparticles with controllable sizes is thermal decomposition of precursors in organic solvents at high temperature.[5,6] In this approach, nanoparticles are stabilized by hydrophobic coatings and as a result, the as-synthesized nanoparticles can not be dispersed in aqueous solutions. In biomedical applications, nanoparticles have to be hydrophilic and maintain a superior stability in biological media. For advanced biomedical applications of nanoparticles (e.g., in vivo diagnostics and therapy), additional requirements such as minimization of non-specific uptake by reticulo-endothelial systems (RES) must be imposed in order to achieve long blood circulation time and high diagnostic or therapeutic efficiency.[7] In addition, the surface of the nanoparticle should possess functional groups for further conjugation of targeting ligand or therapeutic agents. Commonly used modification strategies for coating hydrophobic nanoparticles with hydrophilic polymers include ligand exchange,[8] micelle encapsulation,[9] and covalent bonding.[10] [11] Particularly, hydrophilic poly(ethylene glycol) (PEG) have been the focus of research as an effective coating materials for nanoparticles[2,12-15] due to its ability to resist protein fouling and provide steric hindrance preventing nanoparticle from aggregation.[12,16,17] Typical examples include coating PEG on hydrophobic nanoparticles via ligand exchange in which dopamine linked PEG replaces oleylamine & oleic acid on the particle[18] and coating PEG on iron oxide nanoparticles in situ via covalent bonding during the aqueous co-precipitation process.[10] Despite the advances made with those methods, the challenge remains in producing a highly stable polymeric coating on nanoparticles and retaining the long-term stability of functionalized nanoparticles in biological-relevant media.

Inhibition of tumor-cell invasion with chlorotoxin-bound superparamagnetic nanoparticles

Nanoparticles have been investigated as drug delivery vehicles, contrast agents, and multifunctional devices for patient care. Current nanoparticle-based therapeutic strategies for cancer treatment are mainly based on delivery of chemotherapeutic agents to induce apoptosis or DNA/siRNA to regulate oncogene expression. Here, a nanoparticle system that demonstrates an alternative approach to the treatment of cancers through the inhibition of cell invasion, while serving as a magnetic resonance and optical imaging contrast agent, is presented. The nanoparticle comprises an iron oxide nanoparticle core conjugated with an amine-functionalized poly(ethylene glycol) silane and a small peptide, chlorotoxin (CTX), which enables the tumor cell-specific binding of the nanoparticle. It is shown that the nanoparticle exhibits substantially enhanced cellular uptake and an invasion inhibition rate of approximately 98% compared to unbound CTX ( approximately 45%). Significantly, the investigation from flow cytometry analysis, transmission electron microscopy, and fluorescent imaging reveals that the CTX-enabled nanoparticles deactivated the membrane-bound matrix metalloproteinase 2 (MMP-2) and induced increased internalization of lipid rafts that contain surface-expressed MMP-2 and volume-regulating ion channels through receptor-mediated endocytosis, leading to enhanced prohibitory effects. Since upregulation and activity of MMP-2 have been observed in tumors of neuroectodermal origin, and in cancers of the breast, colon, skin, lung, prostate, ovaries, and a host of others, this nanoparticle system can be potentially used for non-invasive diagnosis and treatment of a variety of cancer types.

Tumor-targeted drug delivery and MRI contrast enhancement by chlorotoxin-conjugated iron oxide nanoparticles

AIMS This study examines the capabilities of an actively targeting superparamagnetic nanoparticle to specifically deliver therapeutic and MRI contrast agents to cancer cells. MATERIALS & METHODS Iron oxide nanoparticles were synthesized and conjugated to both a chemotherapeutic agent, methotrexate, and a targeting ligand, chlorotoxin, through a poly(ethylene glycol) linker. Cytotoxicity of this nanoparticle conjugate was evaluated by Alamar Blue cell viability assays, while tumor-cell specificity was examined in vitro and in vivo by MRI. RESULTS & DISCUSSION Characterization of these multifunctional nanoparticles confirms the successful attachment of both drug and targeting ligands. The targeting nanoparticle demonstrated preferential accumulation and increased cytotoxicity in tumor cells. Furthermore, prolonged retention of these nanoparticles was observed within tumors in vivo. CONCLUSION The improved specificity, extended particle retention and increased cytotoxicity toward tumor cells demonstrated by this multifunctional nanoparticle system suggest that it possesses potential for applications in cancer diagnosis and treatment.

Self-assembled coatings on individual monodisperse magnetite nanoparticles for efficient intracellular uptake.

Monodispersed iron oxide superparamagnetic nanoparticles were prepared using a novel circulating system. A simple dialysis method was developed to immobilize nanoparticles with functional biopolymers and targeting agents, which avoids the use of the normal centrifugation process that may cause particle agglomeration during the coating process. To enhance the specific targeting capability of the nanoparticles, a new chemical scheme was introduced, in which folic acid (FA) was chosen as the targeting agent combined with PEG serving to improve biocompatibility of nanoparticles. The AFM characterization showed that the nanoparticles produced are well dispersed with a narrow size distribution. The FTIR and XPS spectrum analyses indicated that PEG and FA-PEG have been chemically/covalently bonded to nanoparticles using synthetic approach introduced in this study. Our biological study showed that coating nanoparticles with PEG-FA significantly enhanced the intracellular uptake of nanoparticles by target cells.

X-Ray Luminescence Computed Tomography via Selective Excitation: A Feasibility Study

X-ray luminescence computed tomography (XLCT) is proposed as a new molecular imaging modality based on the selective excitation and optical detection of X-ray-excitable phosphor nanoparticles. These nano-sized particles can be fabricated to emit near-infrared (NIR) light when excited with X-rays, and, because because both X-rays and NIR photons propagate long distances in tissue, they are particularly well suited for in vivo biomedical imaging. In XLCT, tomographic images are generated by irradiating the subject using a sequence of programmed X-ray beams, while sensitive photo-detectors measure the light diffusing out of the subject. By restricting the X-ray excitation to a single, narrow beam of radiation, the origin of the optical photons can be inferred regardless of where these photons were detected, and how many times they scattered in tissue. This study presents computer simulations exploring the feasibility of imaging small objects with XLCT, such as research animals. The accumulation of 50 nm phosphor nanoparticles in a 2-mm-diameter target can be detected and quantified with subpicomolar sensitivity using less than 1 cGy of radiation dose. Provided sufficient signal-to-noise ratio, the spatial resolution of the system can be made as high as needed by narrowing the beam aperture. In particular, 1 mm spatial resolution was achieved for a 1-mm-wide X-ray beam. By including an X-ray detector in the system, anatomical imaging is performed simultaneously with molecular imaging via standard X-ray computed tomography (CT). The molecular and anatomical images are spatially and temporally co-registered, and, if a single-pixel X-ray detector is used, they have matching spatial resolution.

Synthesis and Radioluminescence of PEGylated Eu3+-doped Nanophosphors as Bioimaging Probes

Lanthanide-doped nanophosphors have received significant attention for use in biological sensing and imaging due to their unique optical properties. Much like semiconductor quantum dots (QDs), these luminescent nanocrystals offer several advantages over conventional organic fluorophores, including high photochemical stability, large Stokes shift, and tunable fluorescence emission. [1] Up-conversion nanophosphors, which are capable of absorbing two or more low-energy photons to emit a higher-energy photon, also exhibit favorable characteristics such as long fluorescence lifetimes, no photoblinking, and reduced autofluorescence. [2] The recent development of lanthanide-doped nanophosphors that function in the near-infrared (NIR) spectral range optimal for optical transmission through biological tissues (650–900 nm) has attracted great interest towards in vivo bioim-aging probes. [3–5] Alternatively, high-energy radiation, currently employed in medical imaging modalities, such as X-ray computed tomography (CT) or positron emission tomo graphy (PET), may also be used to excite NIR-emitting radioluminescent nanophosphors (RLNPs) for bioimaging.