Magnetic microspheres: a vehicle for selective targeting of drugs

Magnetic nanoparticles and nanocomposites for remote controlled therapies

This review highlights the state-of-the-art in the application of magnetic nanoparticles (MNPs) and their composites for remote controlled therapies. Novel macro- to nano-scale systems that utilize remote controlled drug release due to actuation of MNPs by static or alternating magnetic fields and magnetic field guidance of MNPs for drug delivery applications are summarized. Recent advances in controlled energy release for thermal therapy and nanoscale energy therapy are addressed as well. Additionally, studies that utilize MNP-based thermal therapy in combination with other treatments such as chemotherapy or radiation to enhance the efficacy of the conventional treatment are discussed.

The emerging applications of magnetic nanovectors in nanomedicine

The scientific disciplines that encompass medical therapy and diagnostics, in a continuing transition to personalized medicine, have found a valuable tool in the emerging field of nanotechnology. New nanotools are now enabling discoveries and advancements that form the foundation of what has become known collectively as nanomedicine. The global impact of these advancements are being seen in areas of advanced/improved early stage diagnostics, targeted drug delivery systems and imaging methods, all leading to more effective diagnostic/therapeutic strategies and outcomes. This review focuses on recent patent advancements in this transition with emphasis on the emerging role of magnetic nanovectors as enabling tools for the enhanced effectiveness of cancer diagnostics and therapeutics, considering its historical progression and future impact.

Physical methods for gene transfer

The key impediment to the successful application of gene therapy in clinics is not the paucity of therapeutic genes. It is rather the lack of nontoxic and efficient strategies to transfer therapeutic genes into target cells. Over the past few decades, considerable progress has been made in gene transfer technologies, and thus far, three different delivery systems have been developed with merits and demerits characterizing each system. Viral and chemical methods of gene transfer utilize specialized carrier to overcome membrane barrier and facilitate gene transfer into cells. Physical methods, on the other hand, utilize various forms of mechanical forces to enforce gene entry into cells. Starting in 1980s, physical methods have been introduced as alternatives to viral and chemical methods to overcome various extra- and intracellular barriers that limit the amount of DNA reaching the intended cells. Accumulating evidence suggests that it is quite feasible to directly translocate genes into cytoplasm or even nuclei of target cells by means of mechanical force, bypassing endocytosis, a common pathway for viral and nonviral vectors. Indeed, several methods have been developed, and the majority of them share the same underlying mechanism of gene transfer, i.e., physically created transient pores in cell membrane through which genes get into cells. Here, we provide an overview of the current status and future research directions in the field of physical methods of gene transfer.

Magnetic nanoparticles in magnetic resonance imaging and diagnostics

Magnetic nanoparticles are useful as contrast agents for magnetic resonance imaging (MRI). Paramagnetic contrast agents have been used for a long time, but more recently superparamagnetic iron oxide nanoparticles (SPIOs) have been discovered to influence MRI contrast as well. In contrast to paramagnetic contrast agents, SPIOs can be functionalized and size-tailored in order to adapt to various kinds of soft tissues. Although both types of contrast agents have a inducible magnetization, their mechanisms of influence on spin-spin and spin-lattice relaxation of protons are different. A special emphasis on the basic magnetism of nanoparticles and their structures as well as on the principle of nuclear magnetic resonance is made. Examples of different contrast-enhanced magnetic resonance images are given. The potential use of magnetic nanoparticles as diagnostic tracers is explored. Additionally, SPIOs can be used in diagnostic magnetic resonance, since the spin relaxation time of water protons differs, whether magnetic nanoparticles are bound to a target or not.

Magnetic nanoparticle drug carriers and their study by quadrupole magnetic field-flow fractionation

Magnetic nanoparticle drug carriers continue to attract considerable interest for drug targeting in the treatment of cancers and other pathological conditions. The efficient delivery of therapeutic levels of drug to a target site while limiting nonspecific, systemic toxicity requires optimization of the drug delivery materials, the applied magnetic field, and the treatment protocol. The history and current state of magnetic drug targeting is reviewed. While initial studies involved micrometer-sized and larger carriers, and work with these microcarriers continues, it is the sub-micrometer carriers or nanocarriers that are of increasing interest. An aspect of magnetic drug targeting using nanoparticle carriers that has not been considered is then addressed. This aspect involves the variation in the magnetic properties of the nanocarriers. Quadrupole magnetic field-flow fractionation (QMgFFF) is a relatively new technique for characterizing magnetic nanoparticles. It is unique in its capability of determining the distribution in magnetic properties of a nanoparticle sample in suspension. The development and current state of this technique is also reviewed. Magnetic nanoparticle drug carriers have been found by QMgFFF analysis to be highly polydisperse in their magnetic properties, and the strength of response of the particles to magnetic field gradients is predicted to vary by orders of magnitude. It is expected that the least magnetic fraction of a formulation will contribute the most to systemic toxicity, and the depletion of this fraction will result in a more effective drug carrying material. A material that has a reduced systemic toxicity will allow higher doses of cytotoxic drugs to be delivered to the tumor with reduced side effects. Preliminary experiments involving a novel method of refining a magnetic nanoparticle drug carrier to achieve this result are described. QMgFFF is used to characterize the refined and unrefined material.

Challenges in the development of magnetic particles for therapeutic applications

Certain iron-based particle formulations have useful magnetic properties that, when combined with low toxicity and desirable pharmacokinetics, encourage their development for therapeutic applications. This mini-review begins with background information on magnetic particle use as MRI contrast agents and the influence of material size on pharmacokinetics and tissue penetration. Therapeutic investigations, including (1) the loading of bioactive materials, (2) the use of stationary, high-gradient (HG) magnetic fields to concentrate magnetic particles in tissues or to separate material bound to the particles from the body, and (3) the application of high power alternating magnetic fields (AMF) to generate heat in magnetic particles for hyperthermic therapeutic applications are then surveyed. Attention is directed mainly to cancer treatment, as selective distribution to tumors is well-suited to particulate approaches and has been a focus of most development efforts. While magnetic particles have been explored for several decades, their use in therapeutic products remains minimal; a discussion of future directions and potential ways to better leverage magnetic properties and to integrate their use into therapeutic regimens is discussed.

Radical Crosslinked Albumin Microspheres as Potential Drug Delivery Systems: Preparation and In Vitro Studies

This article reports on the preparation of acryloylated bovine serum albumin microspheres and the evaluation of their employment in drug delivery areas. The influence of preparation parameters on albumin microspheres and the chemicophysical properties of loaded drugs were investigated. In particular, we focussed on acylation albumin degree and the amount of acryloylated albumin against comonomer in the polymerization step. Finally the release profile took into consideration the interaction drug-matrix, the fuctionalization degree of albumin, and the water affinity of matrix.

Surface modified superparamagnetic iron oxide nanoparticles: as a new carrier for bio-magnetically targeted therapy

Amino-functionalized superparamagnetic iron oxide nanoparticles (SPION) were synthesized by coprecipitation method. The particles were characterized by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron micrographs (SEM), transmission electron micrographs (TEM) and atomic force micrographs (AFM). The size of the modified particles varied in the range 10-15 nm and did not change significantly after modification. Hepama-1, an excellent humanized monoclonal antibody directed against liver cancer, was conjugated to the SPION to prepare immuno-magnetic nanoparticles (IMN). A direct labeling method was employed to radiolabel IMN with rhenium-188. The radiolabeling efficiency was about 90% with good in vitro stability. (188)Re labeled IMN could markedly kill SMMC-7721 liver cancer cells. Such SPION might be very useful for bio-magnetically targeted radiotherapy in liver cancer treatment.

Radical cross-linked albumin microspheres as potential drug delivery systems: preparation and in vitro studies

The aim of this research is the preparation of acryloylated bovine serum albumin microspheres and the evaluation of their employment in drug delivery. The influence of preparation parameters on albumin microspheres and the chemicophysical properties of loaded drugs were investigated. In particular, we focused our attention on acylation albumin degree, amount of acryloylated albumin against comonomer in the polymerization step, and finally the release profile. We considered on the interaction drug-matrix, the fuctionalization degree of albumin, and the water affinity of matrix.

Investigation of the magnetic properties of iron oxide nanoparticles used as contrast agent for MRI

Superparamagnetic iron oxide particles, a new class of contrast agents for MRI, are extremely good enhancers of proton relaxation. However, the development of such particle systems has resulted in a wide range of preparations whose physico-chemical properties differ greatly. We have conducted a set of physical experiments: X ray diffraction analysis, relaxivity measurements, susceptibility determinations, and thermomagnetic cycling on different preparations of superparamagnetic particles. Our results demonstrate a good correlation between susceptibilities measured in liquid samples at room temperature and the R2/R1 ratio. Susceptibility measurements between liquid nitrogen temperature and room temperature show three different types of behavior dependent on the size of iron oxide crystals. Comparison of heating and cooling curves from strong field thermomagnetic cycles provides information about the maghemite/magnetite crystal content. The information on magnetic properties reported in this study may help to characterize and to select these materials for use as MRI contrast agents.

In vitro release profile of mitomycin C from albumin microspheres: extrapolation from macrospheres to microspheres

To analyze the in vitro release profiles of mitomycin C from albumin microspheres prepared by chemical denaturation in a multiparticulate system, a method to calculate the total cumulative amount of mitomycin C released from a batch of microspheres was developed. Mitomycin C-loaded albumin macrospheres (diameter in mm range) were prepared, and the in vitro release kinetics of mitomycin C from individual macrospheres were determined. Then the relationship between the kinetic parameters and the physical parameters (e.g., diameter, weight) was investigated under the assumption that macrospheres and microspheres behave identically. Further, the size distribution of microspheres was measured, and the total cumulative amount of mitomycin C released from albumin microspheres was calculated. The release profiles of mitomycin C from individual macrospheres fitted first-order release kinetics better than spherical matrix kinetics. The calculated initial mitomycin C contents and first-order release rate constants for individual macrospheres were correlated with the weight and reciprocal of surface area of the macrospheres, respectively. The observed in vitro release profile for the microspheres agreed with the calculated values. These results suggest that this method is valid for calculating drug release from albumin microspheres.

Albumin microspheres as vehicles for the sustained and controlled release of doxorubicin

Biodegradable albumin microspheres have been prepared with the intention of targeting doxorubicin preferentially to tumour tissue. A high-yielding microsphere manufacturing process has been developed that involved the denaturation of an aqueous protein emulsion by chemical and/or thermal crosslinking methods. Microspheres can be closely sized to a diameter of 25.3 +/- 2.6 microns with the aid of micro-sieves. The in-vitro release of doxorubicin from albumin microspheres was measured using a continuous flow system. Doxorubicin release can be sustained for up to 10 days and the rate of release could be controlled by manipulating protein denaturation conditions between the temperatures 110-135 degrees C in the presence of 0-2% glutaraldehyde. Release of doxorubicin was significantly faster in human plasma compared with isotonic saline.

Effect of carrier dose on the multiple tissue disposition of doxorubicin hydrochloride administered via magnetic albumin microspheres in rats

The effect of carrier dose on the multiple tissue disposition of doxorubicin hydrochloride has been investigated in rats. The drug was encapsulated in submicron magnetic albumin microspheres using a heat-denaturation technique. The rat tail was used as a target organ. Two groups of animals were administered 2.0 or 0.04 mg/kg of microsphere-entrapped drug via the ventral caudal artery, and the predefined tail target site was exposed to a 8000-G magnetic field for 30 min after dosing. In each group, the animals were sacrificed in triplicate over a 48-h period, and their various tissues were analyzed for drug concentration using reversed-phase ion-pair HPLC. The reduction in carrier dose was found to increase drug distribution as well as the targeting efficiency for the target tissue. The drug delivery to heart and liver was reduced. The significance of carrier dose in the targeted delivery of drugs is discussed.

Magnetically controlled targeted micro-carrier systems

Magnetically controlled targeted drug delivery systems are aimed at concentrating drugs at a defined target site, with the aid of a magnetic field. This technique has been developed specifically for directing drugs away from the reticuloendothelial system (RES). Literature on this topic suggests that these delivery systems are capable of altering the distribution of chemotherapeutic agents in the body. Hence these delivery devices offer the possibility of improving the therapeutic efficacy of the associated drugs. This paper reviews the work done to date towards the development and evaluation of biodegradable and non-biodegradable magnetic targeted drug delivery systems and outlines their future prospects and limitations in cancer chemotherapy.

Trapping of chemical carcinogens with magnetic polyethyleneimine microcapsules: I. Microcapsule preparation and in vitro reactivity of encapsulated nucleophiles

In this paper we describe the synthesis and characterization of magnetic microcapsules, intended for use in vivo, and which contain polyethyleneimine nucleophilic targets capable of trapping electrophilic carcinogens. The microcapsules, 15-50 microns in diameter, consist of a semipermeable cross-linked nylon membrane surrounding core polyethyleneimine and magnetite. These microcapsules can be readily manipulated and extracted from aqueous suspensions by magnetic fields. Core polyethyleneimine was released after membrane rupture by sonication. Magnetic hemoglobin microcapsules were also prepared but were unsuitable due to precipitation of hemoglobin within the core. Treatment by proteolytic enzymes that are present in the gastrointestinal tract caused microcapsule damage resulting in protein release, whereas polyethyleneimine microcapsules remained unaffected. After incubation with N-[methyl-14C]-N-nitrosourea, (1) the microcapsules retained covalently bound radiolabel, both in core polyethyleneimine and the microcapsule membrane. The efficiency of the binding of 1 was investigated by varying the polymer concentration during microcapsule manufacture. These type of microcapsules appear to have the desired properties for investigating carcinogen exposure in the mammalian gastrointestinal tract. They can be prepared easily and reproducibly, contain sufficient magnetite to allow their facile recovery from aqueous suspensions, are easily broken to release soluble core polyethyleneimine, and are stable to hydrolytic enzymes (trypsin) in vitro.

Magnetic albumin/protein A immunomicrospheres. I. Preparation, antibody binding capacity and chemical stability

We describe a method of preparing small magnetic microspheres of albumin/protein A, uniform in size, at 200, 300 or 500 nm. It is shown that, independent of size, the microspheres always carry iron peripherally in their matrix and are thus magnetically responsive. A quantitative antibody binding capacity of 82 micrograms/mg microspheres was established for the 500 nm microspheres. The microspheres are stable in most commonly used buffers over a pH range of 2.5-9.2, but are appreciably unstable in such concentrated denaturing agents as 3 M TCN-, 6 M guanidine, or 8 M urea (loss of antibody binding capacity, 30% for TCN- and 70% for urea).