MR lymphography: evidence of extravasation of superparamagnetic nanoparticles into the lymph

Lymph node staging using dedicated magnetic resonance contrast agents--the accumulation mechanism revisited

When diagnosing cancer, assessing the nodal stage is tremendously important in determining the patient's prognosis. Computed tomography (CT) and magnetic resonance (MR) imaging (MRI) assessments of the regional lymph node (LN) size and shape are currently used for the initial nodal staging in clinical settings, although this approach has a rather low sensitivity, and biopsy often leads to restaging of the LNs. Acknowledging the great medical need to accurately stage LNs, scientists and clinicians have been working since the late 1980s on MR contrast agents that provide more reliable staging results. Different types of molecules (i.e., iron oxide nanoparticles and Gd-based contrast agent) have shown promising LN accumulation and imaging results, but no clinically approved, dedicated LN staging contrast agent is currently available. The literature describes a mechanism of contrast agent accumulation in the LNs that considers some but not all published experimental evidence. However, confidence in the mechanism of LN accumulation is a prerequisite for the directed synthesis of compounds for accurate and sensitive LN staging. To improve our understanding of the LN contrast agent accumulation mechanism, we reviewed the published data on the enrichment of colloidal MR contrast agent candidates in LNs, and we suggest an extended mechanism for contrast agent enrichment in LNs. For further clarification, physiology and results from drug targeting studies are considered where applicable.

Cell uptake and in vitro toxicity of magnetic nanoparticles suitable for drug delivery

Magnetic targeting is useful for intravascular or intracavitary drug delivery, including tumor chemotherapy or intraocular antiangiogenic therapy. For all such in vivo applications, the magnetic drug carrier must be biocompatible and nontoxic. In this work, we investigated the toxic properties of magnetic nanoparticles coated with polyethylenoxide (PEO) triblock copolymers. Such coatings prevent the aggregation of magnetic nanoparticles and guarantee consistent magnetic and nonmagnetic flow properties. It was found that the PEO tail block length inversely correlates with toxicity. The nanoparticles with the shortest 0.75 kDa PEO tails were the most toxic, while particles coated with the 15 kDa PEO tail block copolymers were the least toxic. Toxicity responses of the tested prostate cancer cell lines (PC3 and C4-2), human umbilical vein endothelial cells (HUVECs), and human retinal pigment epithelial cells (HRPEs) were similar. Furthermore, all cell types took up the coated magnetic nanoparticles. It is concluded that magnetite nanoparticles coated with triblock copolymers containing PEO tail lengths of above 2 kDa are biocompatible and appropriate for in vivo application.

Cell-adhesive star polymers prepared by ATRP

This study presents the synthesis and evaluation of cell adhesive poly(ethylene oxide) (PEO) star polymers for potential biomedical applications. Star polymers with a size of approximately 20 nm and with relatively low polydispersities (M(w)/M(n) ≤ 1.6), containing GRGDS (Gly-Arg-Gly-Asp-Ser) segments, were prepared by atom transfer radical copolymerization of PEO methyl ether methacrylate macromonomer (MM), telechelic GRGDS-PEO-acrylate MM, and ethylene glycol dimethacrylate (EGDMA). Results from (1)H NMR spectroscopy confirmed the covalent incorporation of the peptide into the star periphery. In vitro cytotoxicity experiments showed star polymers to be cytocompatible (≥95% cell viability) and GRGDS-star hybrid hydrogels supported the attachment of MC3T3.E1 (subclone 4) cells. Hybrid hydrogels were prepared by free radical photopolymerization based on 10% (wt/v) PEO dimethacrylates M(n) = 4000 g/mol with 1% (wt/v) GRGDS-star polymers having different peptide content. Cell adhesiveness was also determined from thin film coatings prepared with GRGDS-containing star polymers on nonadherent plastic plates. After 24 h incubation, phase contrast microscopy and scanning electron microscopy (SEM) images showed uniform cell adhesion and distribution over the film containing cell-adhesive star polymers. These results confirm that incorporation of RGD ligand-binding motifs into PEO-based star polymers is required to influence substrate-cell interactions.

Imaging the lymphatic system: possibilities and clinical applications

The lymphatic system is anatomically complex and difficult to image. Lymph ducts are responsible for the drainage of part of the body's interstitial fluid. Lymph nodes account for the enrichment of lymph fluid, and can be involved in a large variety of diseases, especially cancer. For a long time, lymphatic imaging was limited to the sole use of conventional lymphography involving invasive procedures and patient discomfort. New contrast agents and techniques in ultrasound, nuclear medicine, and MR imaging are now available for imaging of both the lymphatic vessels and the lymph nodes. The objective of this review is to discuss the different imaging modalities of the lymphatic system, with a special focus on the new possibilities of lymphatic imaging including enhanced MR lymphography, sentinel node and positron emission tomography imaging, and contrast-enhanced ultrasound.

Nanosized cationic hydrogels for drug delivery: preparation, properties and interactions with cells

A new family of nanoscale materials on the basis of dispersed networks of cross-linked ionic and nonionic hydrophilic polymers is being developed. One example is the nanosized cationic network of cross-linked poly(ethylene oxide) (PEO) and polyethyleneimine (PEI), PEO-cl-PEI nanogel. Interaction of anionic amphiphilic molecules or oligonucleotides with PEO-cl-PEI results in formation of nanocomposite materials in which the hydrophobic regions from polyion-complexes are joined by the hydrophilic PEO chains. Formation of polyion-complexes leads to the collapse of the dispersed gel particles. However, the complexes form stable aqueous dispersions due to the stabilizing effect of the PEO chain. These systems allow for immobilization of negatively charged biologically active compounds such as retinoic acid, indomethacin and oligonucleotides (bound to polycation chains) or hydrophobic molecules (incorporated into nonpolar regions of polyion-surfactant complexes). The nanogel particles carrying biological active compounds have been modified with polypeptide ligands to enhance receptor-mediated delivery. Efficient cellular uptake and intracellular release of oligonucleotides immobilized in PEO-cl-PEI nanogel have been demonstrated. Antisense activity of an oligonucleotide in a cell model was elevated as a result of formulation of oligonucleotide with the nanogel. This delivery system has a potential of enhancing oral and brain bioavailability of oligonucleotides as demonstrated using polarized epithelial and brain microvessel endothelial cell monolayers.