Hyperthermia

Within oncology therapeutics, hyperthermia is a general term for the rise of temperature above the physiologic level (in the 42-46°C temperature range) within a targeted tumor without damaging the surrounding healthy tissue.  The rationale of this therapy is based on solid evidence from preclinical data that the antitumor cytotoxicity of radiation can be enhanced by previous temperature increase of cells or tumor tissues. It is accepted that at the cellular level hyperthermia provokes morphological and physiological changes, such as the loss of integrins from the cell surface, which is thought to be a perturbing effect on metabolic pathways preceding cell death. The actual mechanisms active during hyperthermia treatments seem to be similar to those of radiation regarding cell cycle sensitivity and hypoxia. The most extended method for reaching temperatures above the systemic values (i.e., 37•5°C) is based on the application of microwaves, although therapies involving laser or ionizing radiation have also been successfully applied to heat up malignant tissues. All these strategies are capable of easily rise the intracellular temperature to the degree needed for thermoablation, but also they all have undesired collateral effects such as ionization of genetic material (radiation) or lack of selectiveness (microwaves) that affect the surrounding healthy tissues.

Both effects add up: so the lost energy is converted into HEAT.

The technique that uses the above mechanism to induce heating of living tissues is often called

Magnetic Fluid Hyperthermia.

 The Magnetic Fluid Hyperthermia (MFH) is one among many techniques used in oncology, based on heating tissues for therapeutic purposes. MFH is usually used as a additive therapy  with standard treatments (radiotherapy, for example), and some preliminar studies have showed that the combination of radiation plus hyperthermia lead to increased results regarding tumoral regression.

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 There are many techniques involving laser, ionizing radiation, and microwaves as tools to heat up body (malignant) tissues. Although these techniques are capable of rise the intracellular temperature up to the cellular death, they may have unwanted collateral effects such as ionization of genetic material (radiation) or lack of selectiveness (microwaves) that affect the surrounding healthy tissues. 

A different approach, developed mostly along the last decade, is the selective thermo-cytolysis based on the process of magnetic losses. This strategy, called magneto-thermo-cytolysis or magneto-thermoablation, is a promising technique thanks to the development of precise methods for synthesizing functionalized magnetic nanoparticles (FMNPs). 

Magnetic nanoparticles with functionalized surfaces (so to attach with high specificity to a given tissue) are used for hyperthermia treatments seeking their  accumulation only in tumor tissue. Depending on the success in solving this biochemical and physiological specificity-problem, cancer-specific hyperthermia protocols could be developed.

Magnetic hyperthermia consists of increasing the temperature of the intracellular medium using magnetic nanoparticles, which dissipate heat when excited by a time varying magnetic field. The underlying physical mechanisms of MFH are related to the energy dissipation when a ferromagnetic material is placed on an external alternating magnetic field. When magnetic nanoparticles are associated to a target cell, the stress caused when heat is dissipated can kill the target cells with minimal damage to the non-targeted ones. This method showed promising results when explored for in vitro and in vivo applications for cancer treatment. This novel technique has been recently approved as a medical protocol that uses magnetic nanoparticles to heat areas of the body using the application of magnetic fields.

The physical mechanisms underlying energy absorption by MNPs are related to the existence of the magnetic relaxation of single domains by Arrhenius-Néel processes, and also the energy loss from mechanical rotation of the particles, acting against viscous forces of the liquid medium (Brown losses).  

Magnetic Fluid Hyperthermia

Hyperthermia in detail

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