Biocompatible and stable magnetosome minerals coated with poly-l-lysine, citric acid, oleic acid, and carboxy-methyl-dextran for application in the magnetic hyperthermia treatment of tumors

Set-up of a pharmaceutical cell bank of Magnetospirillum gryphiswaldense MSR1 magnetotactic bacteria producing highly pure magnetosomes

We report the successful fabrication of a pharmaceutical cellular bank (PCB) containing magnetotactic bacteria (MTB), which belong to the Magnetospirillum gryphiswaldense MSR1 species. To produce such PCB, we amplified MTB in a minimal growth medium essentially devoid of other heavy metals than iron and of CMR (Carcinogenic, mutagenic and reprotoxic) products. The PCB enabled to acclimate MTB to such minimal growth conditions and then to produce highly pure magnetosomes composed of more than 99.9% of iron. The qualification of the bank as a PCB relies first on a preserved identity of the MTB compared with the original strain, second on genetic bacterial stability observed over 100 generations or under cryo-preservation for 16 months, third on a high level of purity highlighted by an absence of contaminating microorganisms in the PCB. Furthermore, the PCB was prepared under high-cell load conditions (9.108 cells/mL), allowing large-scale bacterial amplification and magnetosome production. In the future, the PCB could therefore be considered for commercial as well as research orientated applications in nanomedicine. We describe for the first-time conditions for setting-up an effective pharmaceutical cellular bank preserving over time the ability of certain specific cells, i.e. Magnetospirillum gryphiswaldense MSR1 MTB, to produce nano-minerals, i.e. magnetosomes, within a pharmaceutical setting.

Non-pyrogenic highly pure magnetosomes for efficient hyperthermia treatment of prostate cancer

We report the fabrication of highly pure magnetosomes that are synthesized by magnetotactic bacteria (MTB) using pharmaceutically compatible growth media, i.e., without compounds of animal origin (yeast extracts), carcinogenic, mutagenic, or toxic for reproduction (CMR) products, and other heavy metals than iron. To enable magnetosome medical applications, these growth media are reduced and amended compared with media commonly used to grow these bacteria. Furthermore, magnetosomes are made non-pyrogenic by being extracted from these micro-organisms and heated above 400 °C to remove and denature bacterial organic material and produce inorganic magnetosome minerals. To be stabilized, these minerals are further coated with citric acid to yield M-CA, leading to fully reconstructed chains of magnetosomes. The heating properties and anti-tumor activity of highly pure M-CA are then studied by bringing M-CA into contact with PC3-Luc tumor cells and by exposing such assembly to an alternating magnetic field (AMF) of 42 mT and 195 kHz during 30 min. While in the absence of AMF, M-CA are observed to be non-cytotoxic, they result in a 35% decrease in cell viability following AMF application. The treatment efficacy can be associated with a specific absorption rate (SAR) value of M-CA, which is relatively high in cellular environment, i.e., SAR_cell = 253 ± 11 W/g_Fe, while being lower than the M-CA SAR value measured in water, i.e., SAR_water = 1025 ± 194 W/g_Fe, highlighting that a reduction in the Brownian contribution to the SAR value in cellular environment does not prevent efficient tumor cell destruction with these nanoparticles. KEY POINTS : • Highly pure magnetosomes were produced in pharmaceutically compatible growth media • Non-pyrogenic and stable magnetosomes were prepared for human injection • Magnetosomes efficiently destroyed prostate tumor cells in magnetic hyperthermia.

Large-Scale Cultivation of Magnetotactic Bacteria and the Optimism for Sustainable and Cheap Approaches in Nanotechnology

Magnetotactic bacteria (MTB), a diverse group of marine and freshwater microorganisms, have attracted the scientific community's attention since their discovery. These bacteria biomineralize ferrimagnetic nanocrystals, the magnetosomes, or biological magnetic nanoparticles (BMNs), in a single or multiple chain(s) within the cell. As a result, cells experience an optimized magnetic dipolar moment responsible for a passive alignment along the lines of the geomagnetic field. Advances in MTB cultivation and BMN isolation have contributed to the expansion of the biotechnological potential of MTB in recent decades. Several studies with mass-cultured MTB expanded the possibilities of using purified nanocrystals and whole cells in nano- and biotechnology. Freshwater MTB were primarily investigated in scaling up processes for the production of BMNs. However, marine MTB have the potential to overcome freshwater species applications due to the putative high efficiency of their BMNs in capturing molecules. Regarding the use of MTB or BMNs in different approaches, the application of BMNs in biomedicine remains the focus of most studies, but their application is not restricted to this field. In recent years, environment monitoring and recovery, engineering applications, wastewater treatment, and industrial processes have benefited from MTB-based biotechnologies. This review explores the advances in MTB large-scale cultivation and the consequent development of innovative tools or processes.

Biomineralization and biotechnological applications of bacterial magnetosomes

Magnetosomes intracellularly biomineralized by Magnetotactic bacteria (MTB) are membrane-enveloped nanoparticles of the magnetic minerals magnetite (Fe₃O₄) or greigite (Fe₃S₄). MTB thrive in oxic-anoxic interface and exhibit magnetotaxis due to the presence of magnetosomes. Because of the unique characteristic and bionavigation inspiration of magnetosomes, MTB has been a subject of study focused on by biologists, medical pharmacologists, geologists, and physicists since the discovery. We herein first briefly review the features of MTB and magnetosomes. The recent insights into the process and mechanism for magnetosome biomineralization including iron uptake, magnetosome membrane invagination, iron mineralization and magnetosome chain assembly are summarized in detail. Additionally, the current research progress in biotechnological applications of magnetosomes is also elucidated, such as drug delivery, MRI image contrast, magnetic hyperthermia, wastewater treatment, and cell separation. This review would expand our understanding of biomineralization and biotechnological applications of bacterial magnetosomes.

90Y-CA/SPIONs for dual magnetic hyperthermia-radionuclide nanobrachytherapy of solid tumours

Radiolabelled superparamagnetic iron oxide nanoparticles (SPIONs) are a promising nanomaterial for the development of dual radiation/hyperthermia cancer therapy. To that purpose, flower-shaped SPIONs with an exceptional heating capability were synthesised and coated with citrate, dextran or (3-aminopropyl)triethoxysilane. Both non-coated and coated SPIONs were nontoxic to CT-26 mouse colon cancer cells up to 1.0 mg ml^-1in vitro. In an oscillating magnetic field, citrate-coated SPIONs (CA/SPIONs) displayed the highest heating rate (SAR ∼ 253 W g^-1) and the strongest hyperthermia effects against CT-26 cells. Labelling of the CA/SPIONs by the⁹⁰Y radionuclide, emitting β^-radiation with an average/maximum energy of 0.94/2.23 MeV, and deep tissue penetration generated⁹⁰Y-CA/SPIONs intended for the therapy of solid tumours. However, intravenous injection of⁹⁰Y-CA/SPIONs in CT-26 xenograft-bearing mice resulted in low tumour accumulation. On the contrary, intratumoural injection resulted in long-term retention at the injection site. A single intratumoural injection of 0.25 mg CA/SPIONs followed by 30-min courses of magnetic hyperthermia for four consecutive days caused a moderate antitumour effect against CT-26 and 4T1 mouse tumour xenografts. Intratumoural application of 1.85 MBq/0.25 mg⁹⁰Y-CA/SPIONs, alone or combined with hyperthermia, caused a significant (P ≤ 0.01) antitumour effect without signs of systemic toxicity. The results confirm the suitability of⁹⁰Y-CA/SPIONs for monotherapy or dual magnetic hyperthermia-radionuclide nanobrachytherapy (NBT) of solid tumours.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Core-Shell Fe3O4@Au Nanorod-Loaded Gels for Tunable and Anisotropic Magneto- and Photothermia

Hyperthermia therapeutic treatments require improved multifunctional materials with tunable synergetic properties. Here, we report on the synthesis of Fe₃O₄@Au core-shell nanorods and their subsequent incorporation into an agarose hydrogel to obtain anisotropic magnetic and optical properties for magneto- and photothermal anisotropic transductions. Highly monodisperse ferrimagnetic Fe₃O₄ nanorods with tunable size were synthesized using a solvothermal method by varying the amount of hexadecylamine capping ligands. A gold shell was coated onto Fe₃O₄ nanorods by the intermediate formation of core-satellite structures and a subsequent controlled growth process, leading to an optical response variation from the visible to the near-infrared (NIR) region. The nanorods were oriented within an agarose hydrogel to fabricate free-standing anisotropic materials, providing a proof-of-concept for the applicability of these materials for anisotropic magneto- and photothermia applications. The strong gelling behavior upon cooling and shear-thinning behavior of agarose enable the fabrication of magnetically active continuous hydrogel filaments upon injection. These developed multifunctional nanohybrid materials represent a base for advanced sensing, biomedical, or actuator applications with an anisotropic response.

A review of recent advances in magnetic nanoparticle-based theranostics of glioblastoma

Rapid vascular growth, infiltrative cells and high tumor heterogenicity are some glioblastoma multiforme (GBM) characteristics, making it the most lethal form of brain cancer. Low efficacy of the conventional treatment modalities leads to rampant disease progression and a median survival of 15 months. Magnetic nanoparticles (MNPs), due to their unique physical features/inherent abilities, have emerged as a suitable theranostic platform for targeted GBM treatment. Thus, new strategies are being designed to enhance the efficiency of existing therapeutic techniques such as chemotherapy, radiotherapy, and so on, using MNPs. Herein, the limitations of the current therapeutic strategies, the role of MNPs in mitigating those inadequacies, recent advances in the MNP-based theranostics of GBM and possible future directions are discussed.

Immunogenic Cell Death Induced by Chemoradiotherapy of Novel pH-Sensitive Cargo-Loaded Polymersomes in Glioblastoma

Background

Inducing the immunogenic cell death of tumour cells can mediate the occurrence of antitumour immune responses and make the therapeutic effect more significant. Therefore, the development of treatments that can induce ICD to destroy tumour cells most effectively is promising. Previously, a new type of pH-sensitive polymersome was designed for the treatment of glioblastoma which represents a promising nanoplatform for future translational research in glioblastoma therapy. In this study, the aim of this work was to analyse whether chemoradiotherapy of the novel pH-sensitive cargo-loaded polymersomes can induce ICD.

Methods

Cell death in U87-MG and G422 cells was induced by Au-DOX@PO-ANG, and cell death was analysed by CCK-8 and flow cytometry. The release of CRT was determined by using laser scanning confocal microscopy and flow cytometry. ELISA kits were used to detect the release of HMGB1 and ATP. The dying cancer cells treated with different treatments were cocultured with bone-marrow-derived dendritic cells (BMDCs), and then flow cytometry was used to determine the maturation rate of BMDCs (CD11c+CD86+CD80+) to analyse the in vitro immunogenicity. Tumour vaccination experiments were used to evaluate the ability of Au-DOX@PO-ANG to induce ICD in vivo.

Results

We determined the optimal treatment strategy to evaluate the ability of chemotherapy combined with radiotherapy to induce ICD and dying cancer cells induced by Au-DOX@PO-ANG+RT could induce calreticulin eversion to the cell membrane, promote the release of HMGB1 and ATP, and induce the maturation of BMDCs. Using dying cancer cells induced by Au-DOX@PO-ANG+RT, we demonstrate the efficient vaccination potential of ICD in vivo.

Conclusion

These results identify Au-DOX@PO-ANG as a novel immunogenic cell death inducer in vitro and in vivo that could be effectively combined with RT in cancer therapy.

Stable Iron Oxide Nanoflowers with Exceptional Magnetic Heating Efficiency: Simple and Fast Polyol Synthesis

Magnetically induced hyperthermia has reached a milestone in medical nanoscience and in phase III clinical trials for cancer treatment. As it relies on the heat generated by magnetic nanoparticles (NPs) when exposed to an external alternating magnetic field, the heating ability of these NPs is of paramount importance, so is their synthesis. We present a simple and fast method to produce iron oxide nanostructures with excellent heating ability that are colloidally stable in water. A polyol process yielded biocompatible single core nanoparticles and nanoflowers. The effect of parameters such as the precursor concentration, polyol molecular weight as well as reaction time was studied, aiming to produce NPs with the highest possible heating rates. Polyacrylic acid facilitated the formation of excellent nanoheating agents iron oxide nanoflowers (IONFs) within 30 min. The progressive increase of the size of the NFs through applying a seeded growth approach resulted in outstanding enhancement of their heating efficiency with intrinsic loss parameter up to 8.49 nH m² kg_Fe^-1. The colloidal stability of the NFs was maintained when transferring to an aqueous solution via a simple ligand exchange protocol, replacing polyol ligands with biocompatible sodium tripolyphosphate to secure the IONPs long-term colloidal stabilization.

A comprehensive assessment of the biocompatibility of Magnetospirillum gryphiswaldense MSR-1 bacterial magnetosomes in vitro and in vivo

Bacterial magnetosomes (BMs) are iron oxide nanoparticles synthesized naturally by magnetotactic bacteria, made up of nano-sized inorganic crystals enclosed by a lipid bilayer membrane. Due to several superior characteristics, such as the narrow size distribution, uniform morphology, high purity and crystallinity, single magnetic domain as well as easy surface modification, increasing biomedical and biotechnological applications of BMs have been developed. The attracted wide attentions raise the urge for the evaluation of safety and toxicity. In this work, we performed a rather comprehensive and systematic assessment of in vitro and in vivo toxicity of BMs from MSR-1, including the cytotoxicity, mice bodyweights, blood test, organ coefficients, inflammation, and hemocompatibility study. We found that BMs have good biocompatibility except for influences on the immune response as demonstrated by enhanced activation of the complement system and inhibition of lymphocyte proliferation when used with an excessive concentration. BMs induced the production of reactive oxygen species (ROS) in macrophages at a dose-dependent manner but did not cause cell membrane damage and cell cycle arrest until the concentration is approximately 40 times the clinical dosage. We anticipate our work will guide modifications of BMs and expand their future applications.

Why Does Not Nanotechnology Go Green? Bioprocess Simulation and Economics for Bacterial-Origin Magnetite Nanoparticles

Nanotechnological developments, including fabrication and use of magnetic nanomaterials, are growing at a fast pace. Magnetic nanoparticles are exciting tools for use in healthcare, biological sensors, and environmental remediation. Due to better control over final-product characteristics and cleaner production, biogenic nanomagnets are preferable over synthetic ones for technological use. In this sense, the technical requirements and economic factors for setting up industrial production of magnetotactic bacteria (MTB)-derived nanomagnets were studied in the present work. Magnetite fabrication costs in a single-stage fed-batch and a semicontinuous process were US$ 10,372 and US$ 11,169 per kilogram, respectively. Depending on the variations of the production process, the minimum selling price for biogenic nanomagnets ranged between US$ 21 and US$ 120 per gram. Because these prices are consistently below commercial values for synthetic nanoparticles, we suggest that microbial production is competitive and constitutes an attractive alternative for a greener manufacturing of magnetic nanoparticles nanotools with versatile applicability.

Magnetic Testis Targeting and Magnetic Hyperthermia for Noninvasive, Controllable Male Contraception via Intravenous Administration

Mild testicular hyperthermia by the photothermal effect of gold nanorods could realize controllable male contraception. However, associated limitations, such as testicular administration and infrared laser inflicting severe pain, and the nondegradability of nanoparticles potentially causing toxicity, have restricted further clinical application. Inspired by the excellent physicochemical properties of iron oxide nanoparticles (IONPs), and the finding that testicular injection of PEG-coated IONPs with a diameter of 50 nm (PEG@Fe₃O₄-50) following an alternating magnetic field (AMF) could achieve controllable male contraception; here we propose a noninvasive, targeting approach for male contraception via intravenous administration. The magnetic properties and testes targeting of IONPs were proven to be greatly affected by their surface chemistry and particle size. After systemic administration, citric acid stabilized IONPs with size of 100 nm (CA@Fe₃O₄-100) were found to be the best ideal thermoagent for realizing the noninvasive contraception. This study offers new strategies for male contraception.

Enhancement of T2* Weighted MRI Imaging Sensitivity of U87MG Glioblastoma Cells Using γ-Ray Irradiated Low Molecular Weight Hyaluronic Acid-Conjugated Iron Nanoparticles

INTRODUCTION

It has been reported that low-molecular-weight hyaluronic acid (LMWHA) exhibits a potentially beneficial effect on cancer therapy through targeting of CD44 receptors on tumor cell surfaces. However, its applicability towards tumor detection is still unclear. In this regard, LMWHA-conjugated iron (Fe3O4) nanoparticles (LMWHA-IONPs) were prepared in order to evaluate its application for enhancing the T2* weighted MRI imaging sensitivity for tumor detection.

METHODS

LMWHA and Fe3O4 NPs were produced using γ-ray irradiation and chemical co-precipitation methods, respectively. First, LMWHA-conjugated FITC was prepared to confirm the ability of LMWHA to target U87MG cells using fluorescence microscopy. The hydrodynamic size distribution and dispersion of the IONPs and prepared LMWHA-IONPs were analyzed using dynamic light scattering (DLS). In addition, cell viability assays were performed to examine the biocompatibility of LMWHA and LMWHA-IONPs toward U87MG human glioblastoma and NIH3T3 fibroblast cell lines. The ability of LMWHA-IONPs to target tumor cells was confirmed by detecting iron (Fe) ion content using the thiocyanate method. Finally, time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging and in vitro magnetic resonance imaging (MRI) were performed to confirm the contrast enhancement effect of LMWHA-IONPs.

RESULTS

Florescence analysis results showed that LMWHA-FITC successfully targeted the surfaces of both tested cell types. The ability of LMWHA to target U87MG cells was higher than for NIH3T3 cells. Cell viability experiments showed that the fabricated LMWHA-IONPs possessed good biocompatibility for both cell lines. After co-culturing test cells with the LMWHA-IONPs, detected Fe ion content in the U87MG cells was much higher than that of the NIH3T3 cells in both thiocyanate assays and TOF-SIMs images. Finally, the addition of LMWHA-IONPs to the U87MG cells resulted in an obvious improvement in T2* weighted MR image contrast compared to control NIH3T3 cells.

DISCUSSION

Overall, the present results suggest that LMWHA-IONPs fabricated in this study provide an effective MRI contrast agent for improving the diagnosis of early stage glioblastoma in MRI examinations.

Genetic changes and growth promotion of glioblastoma by magnetic nanoparticles and a magnetic field

Aim: To confirm the biological effects of manganese ferrite magnetic nanoparticles (MFMNPs) and an external magnetic field on glioblastoma cells. Methods: U-87MG glioblastoma cells were prepared, into which the uptake of MFMNPs was high. The cells were then exposed to an external magnetic field using a neodymium magnet in vitro and in vivo. Results: LRP6 and TCF7 mRNA levels involved in the Wnt/β-catenin signaling pathway were elevated by the influence of MFMNPs and the external magnetic field. MFMNPs and the external magnetic field also accelerated tumor growth by approximately 7 days and decreased survival rates in animal experiments. Conclusion: When MFMNPs and an external magnetic field are applied for a long time on glioblastoma cells, mRNA expression related to Wnt/β-catenin signaling is increased and tumor growth is promoted.

Light-Interacting iron-based nanomaterials for localized cancer detection and treatment

To improve the prognosis of cancer patients, methods of local cancer detection and treatment could be implemented. For that, iron-based nanomaterials (IBN) are particularly well-suited due to their biocompatibility and the various ways in which they can specifically target a tumor, i.e. through passive, active or magnetic targeting. Furthermore, when it is needed, IBN can be associated with well-known fluorescent compounds, such as dyes, clinically approved ICG, fluorescent proteins, or quantum dots. They may also be excited and detected using well-established optical methods, relying on scattering or fluorescent mechanisms, depending on whether IBN are associated with a fluorescent compound or not. Systems combining IBN with optical methods are diverse, thus enabling tumor detection in various ways. In addition, these systems provide a wealth of information, which is inaccessible with more standard diagnostic tools, such as single tumor cell detection, in particular by combining IBN with near-field scanning optical microscopy, dark-field microscopy, confocal microscopy or super-resolution microscopy, or the highlighting of certain dynamic phenomena such as the diffusion of a fluorescent compound in an organism, e.g. using fluorescence lifetime imaging, fluorescence resonance energy transfer, fluorescence anisotropy, or fluorescence tomography. Furthermore, they can in some cases be complemented by a therapeutic approach to destroy tumors, e.g. when the fluorescent compound is a drug, or when a technique such as photo-thermal or photodynamic therapy is employed. This review brings forward the idea that iron-based nanomaterials may be associated with various optical techniques to form a commercially available toolbox, which can serve to locally detect or treat cancer with a better efficacy than more standard medical approaches. STATEMENT OF SIGNIFICANCE: New tools should be developed to improve cancer treatment outcome. For that, two closely-related aspects deserve to be considered, i.e. early tumor detection and local tumor treatment. Here, I present various types of iron-based nanomaterials, which can achieve this double objective when they interact with a beam of light under specific and accurately chosen conditions. Indeed, these materials are biocompatible and can be used/combined with most standard microscopic/optical methods. Thus, these systems enable on the one hand tumor cell detection with a high sensitivity, i.e. down to single tumor cell level, and on the other hand tumor destruction through various mechanisms in a controlled and localized manner by deciding whether or not to apply a beam of light and by having these nanomaterials specifically target tumor cells.

Biomimetic keratin gold nanoparticle-mediated in vitro photothermal therapy on glioblastoma multiforme

Aim: To realize and characterize a new generation of keratin-coated gold nanoparticles (Ker-AuNPs) as highly efficient photosensitive nanosized therapeutics for plasmonic photothermal (PPT) therapy. Materials & methods: The chemical, physical, morphological and photothermal properties of Ker-AuNPs are investigated using dynamic light scattering, ζ-potential, UV-Visible, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy and high-resolution thermography. In vitro experiments are performed on a human glioblastoma cell line (i.e., U87-MG), using viability assays, transmission electron microscopy, fluorescence microscopy, cytometric analyses and PPT experiments. Results: Experiments confirm the excellent biocompatibility of Ker-AuNPs, their efficient cellular uptake and localized photothermal heating capabilities. Conclusion: The reported structural and functional properties pointed out these Ker-AuNPs as a promising new tool in the field of biocompatible photothermal agents for PPT treatments against cancer-related diseases.

Improved methods for mass production of magnetosomes and applications: a review

Magnetotactic bacteria have the unique ability to synthesize magnetosomes (nano-sized magnetite or greigite crystals arranged in chain-like structures) in a variety of shapes and sizes. The chain alignment of magnetosomes enables magnetotactic bacteria to sense and orient themselves along geomagnetic fields. There is steadily increasing demand for magnetosomes in the areas of biotechnology, biomedicine, and environmental protection. Practical difficulties in cultivating magnetotactic bacteria and achieving consistent, high-yield magnetosome production under artificial environmental conditions have presented an obstacle to successful development of magnetosome applications in commercial areas. Here, we review information on magnetosome biosynthesis and strategies for enhancement of bacterial cell growth and magnetosome formation, and implications for improvement of magnetosome yield on a laboratory scale and mass-production (commercial or industrial) scale.

Application of Magnetosomes in Magnetic Hyperthermia

Nanoparticles, specifically magnetosomes, synthesized in nature by magnetotactic bacteria, are very promising to be usedin magnetic hyperthermia in cancer treatment. In this work, using the solution of the stochastic Landau–Lifshitz equation, we calculate the specific absorption rate (SAR) in an alternating (AC) magnetic field of assemblies of magnetosome chains depending on the particle size D, the distance between particles in a chain a, and the angle of the applied magnetic field with respect to the chain axis. The dependence of SAR on the a/D ratio is shown to have a bell-shaped form with a pronounced maximum. For a dilute oriented chain assembly with optimally chosen a/D ratio, a strong magneto-dipole interaction between the chain particles leads to an almost rectangular hysteresis loop, and to large SAR values in the order of 400–450 W/g at moderate frequencies f = 300 kHz and small magnetic field amplitudes H₀ = 50–100 Oe. The maximum SAR value only weakly depends on the diameter of the nanoparticles and the length of the chain. However, a significant decrease in SAR occurs in a dense chain assembly due to the strong magneto-dipole interaction of nanoparticles of different chains.

Bio-synthesized iron oxide nanoparticles for cancer treatment

Various living organisms, such as bacteria, plants, and animals can synthesize iron oxide nanoparticles (IONP). The mechanism of nanoparticle (NP) formation is usually described as relying on the reduction of ferric/ferrous iron ions into crystallized nanoparticulate iron that is surrounded by an organic stabilizing layer. The properties of these NP are characterized by a composition made of different types of iron oxide whose most stable and purest one appears to be maghemite, by a size predominantly comprised between 5 and 380 nm, by a crystalline core, by a surface charge which depends on the nature of the material coating the iron oxide, and by certain other properties such as a sterility, stability, production in mass, absence of aggregation, that have apparently only been studied in details for IONP synthesized by magnetotactic bacteria, called magnetosomes. In the majority of studies, bio-synthesized IONP are described as being biocompatible and as not inducing cytotoxicity towards healthy cells. Anti-tumor activity of bio-synthesized IONP has mainly been demonstrated in vitro, where this type of NP displayed cytotoxicity towards certain tumor cells, e.g. through the anti-tumor activity of IONP coating or through IONP anti-oxidizing property. Concerning in vivo anti-tumor activity, it was essentially highlighted for magnetosomes administered in different types of glioblastoma tumors (U87-Luc and GL-261), which were exposed to a series of alternating magnetic field applications, resulting in mild hyperthermia treatments at typical temperatures of 41-45 °C, leading to the full disappearance of these tumors without any observable side effects.

Natural Metallic Nanoparticles for Application in Nano-Oncology

Here, the various types of naturally synthesized metallic nanoparticles, which are essentially composed of Ce, Ag, Au, Pt, Pd, Cu, Ni, Se, Fe, or their oxides, are presented, based on a literature analysis. The synthesis methods used to obtain them most often involve the reduction of metallic ions by biological materials or organisms, i.e., essentially plant extracts, yeasts, fungus, and bacteria. The anti-tumor activity of these nanoparticles has been demonstrated on different cancer lines. They rely on various mechanisms of action, such as the release of chemotherapeutic drugs under a pH variation, nanoparticle excitation by radiation, or apoptotic tumor cell death. Among these natural metallic nanoparticles, one type, which consists of iron oxide nanoparticles produced by magnetotactic bacteria called magnetosomes, has been purified to remove endotoxins and abide by pharmacological regulations. It has been tested in vivo for anti-tumor efficacy. For that, purified and stabilized magnetosomes were injected in intracranial mouse glioblastoma tumors and repeatedly heated under the application of an alternating magnetic field, leading to the full disappearance of these tumors. As a whole, the results presented in the literature form a strong basis for pursuing the efforts towards the use of natural metallic nanoparticles for cancer treatment first pre-clinically and then clinically.

Applications of magnetotactic bacteria and magnetosome for cancer treatment: A review emphasizing on practical and mechanistic aspects

Magnetotactic bacteria (MTB) synthesize iron oxide (Fe₃O₄) nanoparticles (NPs), called magnetosomes, with large sizes leading to a ferrimagnetic behavior and a stable magnetic moment at physiological temperature, a chain structure that prevents NP aggregation and promotes uniform NP distribution, and a mineral core of magnetite/maghemite composition, which can be stabilized by an organic coating. Such properties can favor magnetosome administration to humans under certain optimized non-toxic conditions of fabrication. In this review, I describe the fabrication methods, physico-chemical properties, and the anti-tumor activity of different types of MTB/magnetosome preparations, highlighting the bio-compatibility and excellent anti-tumor activity of purified non-pyrogenic magnetosome minerals stabilized by a synthetic chemical compound.

Magnetotactic Bacteria and Magnetosomes as Smart Drug Delivery Systems: A New Weapon on the Battlefield with Cancer?

An important direction of research in increasing the effectiveness of cancer therapies is the design of effective drug distribution systems in the body. The development of the new strategies is primarily aimed at improving the stability of the drug after administration and increasing the precision of drug delivery to the destination. Due to the characteristic features of cancer cells, distributing chemotherapeutics exactly to the microenvironment of the tumor while sparing the healthy tissues is an important issue here. One of the promising solutions that would meet the above requirements is the use of Magnetotactic bacteria (MTBs) and their organelles, called magnetosomes (BMs). MTBs are commonly found in water reservoirs, and BMs that contain ferromagnetic crystals condition the magnetotaxis of these microorganisms. The presented work is a review of the current state of knowledge on the potential use of MTBs and BMs as nanocarriers in the therapy of cancer. The growing amount of literature data indicates that MTBs and BMs may be used as natural nanocarriers for chemotherapeutics, such as classic anti-cancer drugs, antibodies, vaccine DNA, and siRNA. Their use as transporters increases the stability of chemotherapeutics and allows the transfer of individual ligands or their combinations precisely to cancerous tumors, which, in turn, enables the drugs to reach molecular targets more effectively.

A Method for Producing Highly Pure Magnetosomes in Large Quantity for Medical Applications Using Magnetospirillum gryphiswaldense MSR-1 Magnetotactic Bacteria Amplified in Minimal Growth Media

We report the synthesis in large quantity of highly pure magnetosomes for medical applications. For that, magnetosomes are produced by MSR-1 Magnetospirillum gryphiswaldense magnetotactic bacteria using minimal growth media devoid of uncharacterized and toxic products prohibited by pharmaceutical regulation, i.e., yeast extract, heavy metals different from iron, and carcinogenic, mutagenic and reprotoxic agents. This method follows two steps, during which bacteria are first pre-amplified without producing magnetosomes and are then fed with an iron source to synthesize magnetosomes, yielding, after 50 h of growth, an equivalent OD₅₆₅ of ~8 and 10 mg of magnetosomes in iron per liter of growth media. Compared with magnetosomes produced in non-minimal growth media, those particles have lower concentrations in metals other than iron. Very significant reduction or disappearance in magnetosome composition of zinc, manganese, barium, and aluminum are observed. This new synthesis method paves the way towards the production of magnetosomes for medical applications.

Nano-Therapies for Glioblastoma Treatment

Traditional anti-cancer treatments are inefficient against glioblastoma, which remains one of the deadliest and most aggressive cancers. Nano-drugs could help to improve this situation by enabling: (i) an increase of anti-glioblastoma multiforme (GBM) activity of chemo/gene therapeutic drugs, notably by an improved diffusion of these drugs through the blood brain barrier (BBB), (ii) the sensibilization of radio-resistant GBM tumor cells to radiotherapy, (iii) the removal by surgery of infiltrating GBM tumor cells, (iv) the restoration of an apoptotic mechanism of GBM cellular death, (v) the destruction of angiogenic blood vessels, (vi) the stimulation of anti-tumor immune cells, e.g., T cells, NK cells, and the neutralization of pro-tumoral immune cells, e.g., Treg cells, (vii) the local production of heat or radical oxygen species (ROS), and (viii) the controlled release/activation of anti-GBM drugs following the application of a stimulus. This review covers these different aspects.

Enhanced hyperthermic properties of biocompatible zinc ferrite nanoparticles with a charged polysaccharide coating

Zinc doping of superparamagnetic iron oxide nanoparticles coated with an ionic derivative of chitosan significantly improves their properties for magnetic hyperthermia.