International audienceChains of magnetosomes extracted from magnetotactic bacteria are shown to be highly efficient for alternative magnetic field cancer therapy. The viability of MDA-MB-231 breast cancer cells is relatively unaffected by the presence of less than ∼ 1 mg of chains of magnetosomes. When these cells are exposed to an oscillating magnetic field of frequency 183 kHz and field strengths of 20 to 60 mT, up to 100 % of them are destroyed. We show that it is possible to fully eradicate a tumor xeno-greffed on a mouse by administering a suspension containing ∼ 1 mg of chains of magnetosomes within the tumor and by exposing the mouse to three heat cycles of 20 minutes, during which the tumor temperature is raised to ∼ 43°C. We demonstrate the higher efficiency of the chains of magnetosomes compared with various other materials, i. e. whole inactive magnetotactic bacteria, individual magnetosomes not organized in chains and two different types of chemically synthesized nanoparticles currently tested for alternative magnetic field cancer therapy. The efficiency of the chains of magnetosomes is attributed to three factors, (i), a high magnetosome specific absorption rate (SAR), (ii), a homogenous distribution of the chains of magnetosomes within the tumor yielding uniform heating and (iii), the faculty of the chains of magnetosomes to penetrate within the cancer cells following the application of the alternative magnetic field, which enables intra-cellular heating. Biodistribution studies reveal that chains of magnetosomes administered directly within xeno-greffed breast tumors progressively leave the tumors during the 14 days following their administration and are then eliminated in the feces
In this work, we examine the mechanisms of heat production by whole intact cells of magnetotactic bacteria, Magnetospirillum magneticum strain AMB-1, as well as by their extracted chains of magnetosomes or extracted individual magnetosomes when they are exposed to an oscillating magnetic field of frequency 108 kHz and field amplitudes varied between 23 mT and 88 mT. For intact bacterial cells that contain chains of magnetosomes, heat is generated through hysteresis losses yielding specific absorption rates (SAR) of 110 W/gFe at 23 mT and 860 W/gFe at 88 mT. When the chains of magnetosomes are extracted from the bacterial cells and exposed to the same magnetic field, the heatproducing mechanism includes an additional contribution, one that is due to their rotation in the magnetic field. This results in the production of higher SAR of 860 W/gFe at 23 mT and 1240 W/gFe at 88 mT. Lower SAR values of 540 W/gFe at 23 mT and 970 W/gFe at 88 mT are obtained with the individual magnetosomes. This appears to be due to aggregation of the individual magnetosomes in the liquid, which prevents them from rotating as efficiently as the chains of magnetosomes.
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