Magnetic hyperthermia

Magnetic hyperthermia also known as magnetic nanoparticle mediated intracellular hyperthermia, is a thermotherapy which involves targeting of a tumor with the help of magnetic nanoparticles in the presence of external alternating magnetic field that causes production of heat through Néel-relaxationloss of magnetic nanoparticles. Heat generation through Néel-relaxation is due to rapid changes in the direction of magnetic moments, hindered by anisotropy energy that tends to turn the magnetic domain of the magnetic nanoparticle in a given direction according to their crystal lattice structure.

As a result temperature of tumor cells is increased within range of hyperthermia temperature (41 – 46oC). Tumor cells are more sensitive to heat as compared to normal cells due to poor vascularization, so the survival rate of tumor cells decrease drastically by increasing temperature and at one stage the tumor cells burst. This thermotherapy specifically destroys the tumor cells without destruction of neighbouring healthy cells.

There are various magnetic nanoparticles which have hyperthermia potential. In first category magnetite (Fe3O4) and maghemite (Fe2O3) are included. There is another category which is based on ferrites for example cobalt ferrites (CoFe2O4), manganese ferrite (MnFe2O4), nickel ferrite (NiFe2O4) and lithium ferrite (Li0.5Fe2.5O4).Another category which is based on metallic nanoparticles such as Ni,Co, Mn, Zn, etc.

Among all these magnetic nanoparticles, magnetite (Fe3O4) nanoparticlesarethe most promising for magnetic hyperthermia because magnetite has all those characteristics which are required for biomedical applications such as biocompatibility, non-toxicity, superparamagnetism, water-dispersible, ability to leave reticuloendothelial system (RES) and easy preparation. Magnetite can be stabilized by using different capping ligands, for example, dextran, carboxylic acid, polyvinyl alcohol and liposomes etc. Magnetic nanoparticles can be synthesized by different procedure such as co-precipitation, microemulsion, thermal-decomposition andflame spray synthesis, etc. The easiest method to synthesized iron oxide nanoparticle is co-precipitation.

There are three hyperthermia treatments 1) Local hyperthermia treatment is used to treat the small portion of body such as tumor to heat and it requires very high temperature to treat the tumor. 2) Regional hyperthermia is used to treat the large area of body such as an organ, body cavity.

Various methods are used to perform regional hyperthermia such as regional perfusion and in this technique nottoo much high temperature is required. 3) Whole body hyperthermia is used to treat metastatic cancer i.e. cancer which has spread within whole body. General mechanism of magnetic hyperthermia consists of two steps 1) preparation of magnetic nanoparticles 2) injection of magnetic fluid carrying magnetic nanoparticlesinto tumor site. There are various ways through which magnetic fluid can be injected to tumor.

Arterial injection is that way in which magnetic fluid is injected through artery supply of tumor. Direct injection is that way in which magnetic fluid is directly injected inside the tumor. The magnetic nanoparticles can also be strategically surface functionalize to target the tumor cells. Active targeting is very complicated way to inject magnetic fluid inside the tumor. This way is related to antibody targeting so for antibody targeting magnetic nanoparticles are coated with antibody of the desired tumor. The efficiency of this thermotherapy is determined by the ability of magnetic nanoparticles to be collected inside the desired area of body.

Once the magnetic nanoparticles are entered into the cancer cells through endocytosis they are heated with the help of an external localized and alternating magnetic field. An alternating external magnetic field causes the magnetic nanoparticles within the tumor tissue to vibrate and this vibrational energy is ultimately converted into heat causing the increase of local temperature of cancerous tissue leading to its destruction.

Magnetic hyperthermia is most promising technique as compared to other therapies because of these advantages; 1) a single administration in tumor is sufficient, 2) higher efficiency for low heating temperature due to intracellular heating, 3) possibility to target the tumor cells selectively and 4) magnetic hyperthermia can also be used in combination with radiotherapy and chemotherapy. Magnetic hyperthermia is most favorable technique to enhance quality of cancer treatment. Methods for injection of nanoparticles and active targeting of the tumor cells, development of different more efficient heat-producing nanoparticles, and monitoring of heat distribution are the essential parts of the upcoming research in this direction.

The authors are from the Department of Chemistry, University of Agriculture Faisalabad, Punjab, Pakistan.

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