With the improvement of nanotechnology, many advanced research paths have been opened up in different fields, and one of the most promising applications is drug delivery systems (DDSs) for cancer treatment. In the past few decades, a variety of different types of nanoparticles encompassing various of routes of administration have been designed to achieve “precision treatment” of drugs, and the magnetic beads (MBs)-based carriers are one of them.
Structures of Magnetic Carriers
The carriers based on functionalized MBs usually have two types of structures:
- Magnetic particle core (usually magnetite,Fe3O4, or maghemite, γ -Fe2O3) coated with biocompatible polymer.
- Porous biocompatible polymer in whichmagnetic nanoparticles are precipitated inside the pores.
Recent developmental work on carriers has paid more attention to new polymeric or inorganic coatings on magnetite/maghemite nanoparticles, while noble metal coatings such as gold are also being considered.
Drug Release Mechanism
In general, there are three main mechanisms for releasing drug molecules from the functionalized magnetic beads (MBs) into blood vessels or tissues.
When drug molecules dissolve around or within the beads and migrate out of the beads, they will diffuse in body fluids.
When the polymer chains are hydrolyzed into lower molecular weight substances, degradation occurs, thereby effectively releasing the drug molecules trapped by the chains.
- Swelling Followed by Diffusion
As for the swelling controlled release systems, they are initially dry. However, when they are placed in the body, they swell, enabling the drug molecules to diffuse from the swollen network.
How it works?
In magnetic drug delivery system, cytotoxic drugs are usually attached to biocompatible magnetic bead carriers. These drug-carrier complexes are usually injected into the patient via the circulatory system. When the complexes enteres the bloodstream, an external high-gradient magnetic field will be used to concentrate the complexes on a specific target site in the body, such as tumor cells or diseased tissues. Once the drug-carrier complexes aggregates at the target site, the loaded drugs can be released either via enzymatic activity or changes in physiological conditions such as pH, osmolality, or temperature, and then be taken up by tumor cells. This kind of magnetic targeted drug delivery approach indeed has major advantages over the normal, non-targeted chemotherapies.
Fig. 1 Schematic illustration for magnetic drug delivery system in cross-section. (Applied Physics 2003, 36 (13), R167-R181)
Merits & Limitations
Drug delivery system employing magnetic beads as carriers is a promising cancer treatment because it can realize a precise targeted delivery pattern. On the one hand, it can reduce the amount of systemic distribution of the cytotoxic drugs, thus reducing the associated side-effects. On the other hand, it can reduce the required dosage through more efficient, locally targeted drugs.
However, the magnetic drug delivery system based on MBs is very promising, even if there are still some limitations and problems that need to be overcome.
- The possibility ofembolization of the blood vessels in the target region due to accumulation of the magnetic carriers
- Difficulties in scalingup from animal models due to the large distance between the target site and the magnet
- Drugs are nolonger attracted by the magnetic field once they are released
- Toxic responsesto the magnetic carriers are not sure.
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