Combining magnetism and light to fight cancer

Masson’s trichrome staining: the cell nuclei are blue-black, the cytoplasms (cell bodies) are mauve and the collagen fibers are green.
Credit: Riccardo Di Corato – laboratoire MSC (CNRS/Université Paris Diderot)

By combining, in a liposome, magnetic nanoparticles and photosensitizers that are simultaneously and remotely activated by external physical stimuli (a magnetic field and light), scientists obtained total tumor regression in mice.

Non-toxic when they are not activated, such therapies can also achieve a reduction in adverse effects. These results demonstrate the importance of multiple treatments.

One of the strategies employed to limit the adverse effects of cancer therapies is the development of nanocarrier systems that can convey active ingredients to target tumor cells. These are referred to as “physical” therapies when the active substances, molecules or nanoparticles, can be remotely activated by external physical stimuli — in this case by light or a magnetic field. In this context, the study team developed a new type of carrier that combines photosensitivity and magnetism. To achieve this, they first encapsulated magnetic nanoparticles in the inner compartment of a liposome in sufficient quantities to render it ultra-magnetic, before incorporating photosensitizers into its lipid bilayer, while preserving an optimum size for circulation in the blood.

These liposomes, containing magnetic nanoparticles and photosensitizers, were injected directly into the tumor in the mouse model. The scientists thus combined two techniques to achieve complete destruction of cancer cells. The first one, magnetic hyperthermia, consists in exciting the nanoparticles with a magnetic field to raise the temperature of the tumor and destroy it.. The second method, photodynamic therapy, is made possible by the photosensitizers, which, when activated, release reactive oxygen species that are toxic to tumor cells. These two physical therapies act in synergy on the activity of the proteins involved in apoptosis, or programmed cell death. Their combination thus induces total regression of the tumor, while a single therapy is not able to stop its growth.

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