Mikio Kishimoto

Ferromagnetic nanoparticles for magnetic hyperthermia and thermoablation therapy

The use of ferromagnetic nanoparticles for hyperthermia and thermoablation therapies has shown great promise in the field of nanobiomedicine. Even local hyperthermia offers numerous advantages as a novel cancer therapy; however, it requires a remarkably high heating power of more than 1u2009kWu2009g−1 for heat agents. As a candidate for high heat generation, we focus on ferromagnetic nanoparticles and compare their physical properties with those of superparamagnetic substances. Numerical simulations for ideal single-domain ferromagnetic nanoparticles with cubic and uniaxial magnetic symmetries were carried out and MH curves together with minor loops were obtained. From the simulation, the efficient use of an alternating magnetic field (AMF) having a limited amplitude was discussed. Co-ferrite nanoparticles with various magnitudes of coercive force were produced by co-precipitation and a hydrothermal process. A maximum specific loss power of 420u2009Wu2009g−1 was obtained using an AMF at 117u2009kHz with H0 = 51.4u2009kAu2009m−1 (640u2009Oe). The relaxation behaviour in the ferromagnetic state below the superparamagnetic blocking temperature was examined by Mossbauer spectroscopy.

Heating characteristics of ferromagnetic iron oxide nanoparticles for magnetic hyperthermia

Heating characteristics of Fe oxide nanoparticles designed for hyperthermia were examined. Samples with coercive forces from 50 to 280 Oe(codoped magnetite) were produced with a coprecipitation technique following by hydrothermal reaction. The maximum specific loss powers (SLPs) of 420 W/g was obtained at 117 kHz (640 Oe) for a dispersant sample with coercive force of 280 Oe (ATH9D). SLPs measured on dry powder samples at 17 kHz and measured at 117 kHz on dispersant samples were compared. The measured SLP amplitudes are lower for 17 kHz and higher for 117 kHz than those expected from ferromagnetic dc minor loops. For the 117 kHz case, friction of particles in a carrier fluid (similar mechanism to Brown relaxation in superparamagnetic dispersant samples) is considered to contribute to the heating mechanism.

Preparation of highly dispersible and tumor-accumulative, iron oxide nanoparticles: Multi-point anchoring of PEG-b-poly(4-vinylbenzylphosphonate) improves performance significantly

This paper describes the preparation of iron oxide nanoparticles, surface of which was coated with extremely high immobilization stability and relatively higher density of poly(ethylene glycol) (PEG), which are referred to as PEG protected iron oxide nanoparticles (PEG-PIONs). The PEG-PIONs were obtained through alkali coprecipitation of iron salts in the presence of the PEG-poly(4-vinylbenzylphosphonate) block copolymer (PEG-b-PVBP). In this system, PEG-b-PVBP served as a surface coating that was bound to the iron oxide surface via multipoint anchoring of the phosphonate groups in the PVBP segment of PEG-b-PVBP. The binding of PEG-b-PVBP onto the iron oxide nanoparticle surface and the subsequent formation of a PEG brush layer were proved by FT-IR, zeta potential, and thermogravimetric measurements. The surface PEG-chain density of the PEG-PIONs varied depending on the [PEG-b-PVBP]/[iron salts] feed-weight ratio in the coprecipitation reaction. PEG-PIONs prepared at an optimal feed-weight ratio in this study showed a high surface PEG-chain surface density (≈0.8 chainsnm(-2)) and small hydrodynamic diameter (<50 nm). Furthermore, these PEG-PIONs could be dispersed in phosphate-buffered saline (PBS) that contains 10% serum without any change in their hydrodynamic diameters over a period of one week, indicating that PEG-PIONs would provide high dispersion stability under in vivo physiological conditions as well as excellent anti-biofouling properties. In fact we have confirmed the prolong blood circulation time and facilitate tumor accumulation (more than 15% IDg(-1) tumor) of PEG-PIONs without the aid of any target ligand in mouse tumor models. The majority of the PEG-PIONs accumulated in the tumor by 96 h after administration, whereas those in normal tissues were smoothly eliminated by 96 h, proving the enhancement of tumor selectivity in the PEG-PION localization. The results obtained here strongly suggest that originally synthesized PEG-b-PVBP, having multipoint anchoring character by the phosphonate groups, is rational design for improvement in nanoparticle as in vivo application. Two major points, viz., extremely stable anchoring character and dense PEG chains tethered on the nanoparticle surface, worked simultaneously to become PEG-PIONs as an ideal biomedical devices intact for prolonged periods in harsh biological environments.

Hysteresis Power-Loss Heating of Ferromagnetic Nanoparticles Designed for Magnetic Thermoablation

We have fabricated ferromagnetic Fe-oxide nanoparticles as a candidate of hysteresis-loss heating materials used for hyperthermia and thermoablation and examined heating abilities. The coercivities were controlled in a range between 50 Oe and 240 Oe. The temperature-rising characteristics were examined for randomly oriented solid nanoparticles by applying a 17-kHz ac magnetic field with an amplitude up to 550 Oe. A temperature rising rate DeltaT/Deltat was proportional to the square of the peak magnetic field H 0 in the lower H 0 region; however, the relation dose not hold at higher H 0. The maximum loss power was obtained to be 4 W/g, which is smaller than the value expected from the minor loop experiment (13.7 W/g). The reason for small heating capability is discussed.

Minimally required heat doses for various tumour sizes in induction heating cancer therapy determined by computer simulation using experimental data

Purpose: Although induction heating cancer therapy (IHCT) using magnetic nanoparticles can be a promising approach to treatment-less multi-nodular cancers, the objective requirement for successful clinical application has not clearly been elucidated. We intended to define objective heat doses suitable for IHCT, especially focusing on the sizes of liver cancer nodules. Materials and methods: Alternating magnetic fields were applied to three human pancreatic cancer cell lines, the intercellular space of those cell pellets were filled with magnetic nanoparticles, and confirmed the cytotoxic effect of IHCT. Subsequently, the temperatures of liver cancer nodules in IHCT were simulated using a computer software program and the required heat dose for various sized tumours were determined. Results: Heating the cancer cells up to 50°C for 10 min was sufficient for complete cell killing and the heat dose of 1.7 W/gtumour is required for 10 mm tumour. Larger tumours require a smaller heat dose, e.g. 20 mm and 40 mm tumours require 0.7 W/gtumour and 0.6 W/gtumour, respectively, whereas smaller tumours require large amounts of heat, e.g. 5 mm and 1 mm tumours require 5.1 W/gtumour and 105 W/gtumour, respectively. Conclusions: Integrating the presently available technologies, including high-quality magnetic nanoparticles (1000 W/gmaterial) and effective drug delivery systems (1–2 mgmaterial/gtumour), treatment of a 10 mm tumour seems possible. Since treatment of smaller tumours less than 5 mm require substantial heat dose, researchers involved in IHCT should target cancer nodules of 10 mm or more, and develop a heat delivery system providing a minimum of 1.7 W/gtumour.

Dependences of Specific Loss Power on Magnetic Field and Frequency in Elongated Platelet

Elongated platelet γ-Fe2O3 particles with particle sizes of about 30 to 100 nm were prepared for magnetic thermoablation using hysteresis-loss heating of the ferromagnetic particles. The coercive force was based on the shape anisotropy of the elongated shape. The dependences of specific loss power (SLP) on the magnetic field strength and frequency were examined for particles in the range of 133 to 640 Oe and 117 to 429 kHz, respectively. The dependence of SLP on the magnetic field was similar to that of areas in minor hysteresis loops and showed that the heat generation in the particles was almost entirely based on hysteresis loss. To realize effective hysteresis-loss heating a magnetic field about four times stronger than the coercive force of particles was necessary. The SLP increased linearly with increasing frequency. Particles with a coercive force of 153 Oe showed an SLP of 1670 W/g under a magnetic field of 500 Oe and at a frequency of 429 kHz.

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Even with current promising antitumor antibodies, their antitumor effects on stroma‐rich solid cancers have been insufficient. We used mild hyperthermia with the intent of improving drug delivery by breaking the stromal barrier. Here, we provide preclinical evidence of cetuximab + mild hyperthermia therapy. We used four in vivo pancreatic cancer xenograft mouse models with different stroma amounts (scarce, MIAPaCa‐2; moderate, BxPC‐3; and abundant, Capan‐1 and Ope‐xeno). Cetuximab (1 mg/kg) was given systemically, and the mouse leg tumors were concurrently heated using a water bath method for 30 min at three different temperatures, 25°C (control), 37°C (intra‐abdominal organ level), or 41°C (mild hyperthermia) (n = 4, each group). The evaluated variables were the antitumor effects, represented by tumor volume, and in vivo cetuximab accumulation, indirectly quantified by the immunohistochemical fluorescence intensity value/cell using antibodies against human IgG Fc. At 25°C, the antitumor effects were sufficient, with a cetuximab accumulation value (florescence intensity/cell) of 1632, in the MIAPaCa‐2 model, moderate (1063) in the BxPC‐3 model, and negative in the Capan‐1 and Ope‐xeno models (760, 461). By applying 37°C or 41°C heat, antitumor effects were enhanced shown in decreased tumor volumes. These enhanced effects were accompanied by boosted cetuximab accumulation, which increased by 2.8‐fold (2980, 3015) in the BxPC‐3 model, 2.5‐ or 4.8‐fold (1881, 3615) in the Capan‐1 model, and 3.2‐ or 4.2‐fold (1469, 1922) in the Ope‐xeno model, respectively. Cetuximab was effective in treating even stroma‐rich and k‐ras mutant pancreatic cancer mouse models when the drug delivery was improved by combination with mild hyperthermia.

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We investigated the effect of copper substitution on the magnetic and physical properties of Fe₃O₄ prepared by coprecipitation and flux methods. The coprecipitation compositions were chosen according to the formula (Cu_x²⁺Fe_1-x²⁺) Fe₂³⁺O₄, where x varied between 0 and 1. We found that the flux treatment method is ideal for growing large particles of sub-micrometer size. The size of the final particles obtained was in the range of 200-1500 nm, and the size decreased with increasing copper content. Cubic spinel structured Cu_xFe_3-xO₄ particles were obtained by conducting hydrogen gas reduction process at 380 °C-530 °C for 1-2 h after flux treatment. From x-ray diffraction patterns, all particles were determined to be cubic spinel without any sign of the tetragonal structure expected from the Jahn-Teller effect. For these cubic spinel particles, saturation magnetization was controlled at 25-86 Am²/kg, and the value decreased linearly with increasing copper content. The coercive force remained almost constant at 13.7-19.1 kA/m, independent of the copper content.

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This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe3O4 particles with the size of 30-50 nm and a saturation magnetization of ~80

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Am2/kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe3O4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe3O4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe3O4 particles accumulated in primary tissues were ~38 -40 and 40-44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies.