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., SARcell = 253 ± 11 W/gFe, while being lower than the M-CA SAR value measured in water, i.e., SARwater = 1025 ± 194 W/gFe, 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.

Biodegraded magnetosomes with reduced size and heating power maintain a persistent activity against intracranial U87-Luc mouse GBM tumors.

BACKGROUND: An important but rarely addressed question in nano-therapy is to know whether bio-degraded nanoparticles with reduced sizes and weakened heating power are able to maintain sufficient anti-tumor activity to fully eradicate a tumor, hence preventing tumor re-growth. To answer it, we studied magnetosomes, which are nanoparticles synthesized by magnetotactic bacteria with sufficiently large sizes (~ 30 nm on average) to enable a follow-up of nanoparticle sizes/heating power variations under two different altering conditions that do not prevent anti-tumor activity, i.e. in vitro cellular internalization and in vivo intra-tumor stay for more than 30 days. RESULTS: When magnetosomes are internalized in U87-Luc cells by being incubated with these cells during 24 h in vitro, the dominant magnetosome sizes within the magnetosome size distribution (DMS) and specific absorption rate (SAR) strongly decrease from DMS ~ 40 nm and SAR ~ 1234 W/gFe before internalization to DMS ~ 11 nm and SAR ~ 57 W/gFe after internalization, a behavior that does not prevent internalized magnetosomes to efficiently destroy U87-Luc cell, i.e. the percentage of U87-Luc living cells incubated with magnetosomes decreases by 25% between before and after alternating magnetic field (AMF) application. When 2 µl of a suspension containing 40 µg of magnetosomes are administered to intracranial U87-Luc tumors of 2 mm3 and exposed (or not) to 15 magnetic sessions (MS), each one consisting in 30 min application of an AMF of 27 mT and 198 kHz, DMS and SAR decrease between before and after the 15 MS from ~ 40 nm and ~ 4 W/gFe down to ~ 29 nm and ~ 0 W/gFe. Although the magnetosome heating power is weakened in vivo, i.e. no measurable tumor temperature increase is observed after the sixth MS, anti-tumor activity remains persistent up to the 15th MS, resulting in full tumor disappearance among 50% of treated mice. CONCLUSION: Here, we report sustained magnetosome anti-tumor activity under conditions of significant magnetosome size reduction and complete loss of magnetosome heating power.

Fluorescent magnetosomes for controlled and repetitive drug release under the application of an alternating magnetic field under conditions of limited temperature increase (<2.5 °C).

Therapeutic substances bound to nanoparticles have been shown to dissociate following excitation by various external sources of energies or chemical disturbance, resulting in controllable and efficient antitumor activity. Bioconjugation is used to produce magnetosomes associated with Rhodamine B (RhB), whose fluorescence is partially quenched by the presence of iron oxide and becomes strongly enhanced when RhB dissociates from the magnetosomes under the application of an alternating magnetic field. This novel approach enables the release of a RhB model molecule while monitoring the mechanism by fluorescence. The dissociation mechanism of RhB is highlighted by exposing a suspension of fluorescent magnetosomes to an alternating magnetic field, by magnetically isolating the supernatant of this suspension, and by showing fluorescence enhancement of the supernatant. Furthermore, to approach in vivo conditions, fluorescent magnetosomes are mixed with tissue or introduced in the mouse brain and exposed to the alternating magnetic field. Most interestingly, the percentages of RhB dissociation measured at the beginning of magnetic excitation (ΔR/δt) or 600 seconds afterwards (R600 s) are ΔR/δt ∼ 0.13% and R600 s ∼ 50% under conditions of limited temperature increases (<2.5 °C), larger values than those of ΔR/δt ∼ 0.02-0.11% and R600 s ∼ 13%, estimated for temperature increase larger than 2.5 °C. Furthermore, when magnetic excitations are repeated two to five times, the temperature increase becomes undetectable, but RhB dissociation continues to occur up to the fifth magnetic excitation. Since high heating temperatures may be damaging for tissues, this study paves the way towards the development of a safe theranostic dissociating nano-probe operating under conditions of limited temperature increase.

Magnetic-field induced rotation of magnetosome chains in silicified magnetotactic bacteria.

Understanding the biological processes enabling magnetotactic bacteria to maintain oriented chains of magnetic iron-bearing nanoparticles called magnetosomes is a major challenge. The study aimed to constrain the role of an external applied magnetic field on the alignment of magnetosome chains in Magnetospirillum magneticum AMB-1 magnetotactic bacteria immobilized within a hydrated silica matrix. A deviation of the chain orientation was evidenced, without significant impact on cell viability, which was preserved after the field was turned-off. Transmission electron microscopy showed that the crystallographic orientation of the nanoparticles within the chains were preserved. Off-axis electron holography evidenced that the change in magnetosome orientation was accompanied by a shift from parallel to anti-parallel interactions between individual nanocrystals. The field-induced destructuration of the chain occurs according to two possible mechanisms: (i) each magnetosome responds individually and reorients in the magnetic field direction and/or (ii) short magnetosome chains deviate in the magnetic field direction. This work enlightens the strong dynamic character of the magnetosome assembly and widens the potentialities of magnetotactic bacteria in bionanotechnology.

Enhanced antitumor efficacy of biocompatible magnetosomes for the magnetic hyperthermia treatment of glioblastoma.

In this study, biologically synthesized iron oxide nanoparticles, called magnetosomes, are made fully biocompatible by removing potentially toxic organic bacterial residues such as endotoxins at magnetosome mineral core surfaces and by coating such surface with poly-L-lysine, leading to magnetosomes-poly-L-lysine (M-PLL). M-PLL antitumor efficacy is compared with that of chemically synthesized iron oxide nanoparticles (IONPs) currently used for magnetic hyperthermia. M-PLL and IONPs are tested for the treatment of glioblastoma, a dreadful cancer, in which intratumor nanoparticle administration is clinically relevant, using a mouse allograft model of murine glioma (GL-261 cell line). A magnetic hyperthermia treatment protocol is proposed, in which 25 µg in iron of nanoparticles per mm3 of tumor are administered and exposed to 11 to 15 magnetic sessions during which an alternating magnetic field of 198 kHz and 11 to 31 mT is applied for 30 minutes to attempt reaching temperatures of 43-46 °C. M-PLL are characterized by a larger specific absorption rate (SAR of 40 W/gFe compared to 26 W/gFe for IONPs as measured during the first magnetic session), a lower strength of the applied magnetic field required for reaching a target temperature of 43-46 °C (11 to 27 mT compared with 22 to 31 mT for IONPs), a lower number of mice re-administered (4 compared to 6 for IONPs), a longer residence time within tumours (5 days compared to 1 day for IONPs), and a less scattered distribution in the tumour. M-PLL lead to higher antitumor efficacy with full tumor disappearances achieved in 50% of mice compared to 20% for IONPs. This is ascribed to better ability of M-PLL, at equal iron concentrations, to maintain tumor temperatures at 43-46°C over a longer period of times.

Biocompatible coated magnetosome minerals with various organization and cellular interaction properties induce cytotoxicity towards RG-2 and GL-261 glioma cells in the presence of an alternating magnetic field.

BACKGROUND: Biologics magnetics nanoparticles, magnetosomes, attract attention because of their magnetic characteristics and potential applications. The aim of the present study was to develop and characterize novel magnetosomes, which were extracted from magnetotactic bacteria, purified to produce apyrogen magnetosome minerals, and then coated with Chitosan, Neridronate, or Polyethyleneimine. It yielded stable magnetosomes designated as M-Chi, M-Neri, and M-PEI, respectively. Nanoparticle biocompatibility was evaluated on mouse fibroblast cells (3T3), mouse glioblastoma cells (GL-261) and rat glioblastoma cells (RG-2). We also tested these nanoparticles for magnetic hyperthermia treatment of tumor in vitro on two tumor cell lines GL-261 and RG-2 under the application of an alternating magnetic field. Heating, efficacy and internalization properties were then evaluated. RESULTS: Nanoparticles coated with chitosan, polyethyleneimine and neridronate are apyrogen, biocompatible and stable in aqueous suspension. The presence of a thin coating in M-Chi and M-PEI favors an arrangement in chains of the magnetosomes, similar to that observed in magnetosomes directly extracted from magnetotactic bacteria, while the thick matrix embedding M-Neri leads to structures with an average thickness of 3.5 µm2 per magnetosome mineral. In the presence of GL-261 cells and upon the application of an alternating magnetic field, M-PEI and M-Chi lead to the highest specific absorption rates of 120-125 W/gFe. Furthermore, while M-Chi lead to rather low rates of cellular internalization, M-PEI strongly associate to cells, a property modulated by the application of an alternating magnetic field. CONCLUSIONS: Coating of purified magnetosome minerals can therefore be chosen to control the interactions of nanoparticles with cells, organization of the minerals, as well as heating and cytotoxicity properties, which are important parameters to be considered in the design of a magnetic hyperthermia treatment of tumor.

Nanoprobe Synthesized by Magnetotactic Bacteria, Detecting Fluorescence Variations under Dissociation of Rhodamine B from Magnetosomes following Temperature, pH Changes, or the Application of Radiation.

We report a method of fabrication of fluorescent magnetosomes, designated as MCR400, in which 400 µM of rhodamine B are introduced in the growth medium of AMB-1 magnetotactic bacteria and fluorescent magnetosomes are then extracted from these bacteria. These fluorescent magnetosomes behave differently from most fluorescent nanoprobes, which often lead to fluorescence losses over time due to photobleaching. Indeed, when MCR400 are heated to 30-90 °C, brought to an acidic pH, or exposed to radiations, we observed that their fluorescence intensity increased. We attributed this behavior to the dissociation of rhodamine B from the magnetosomes. Interestingly, enhanced fluorescence was also observed in vitro when MCR400 were mixed with either primary macrophages or tumor cells (TC1-GFP or RG2-Cells) or in vivo when MCR400 were introduced in rat glioblastoma. We showed that MCR400 internalize in tumor and immune cells (macrophages) leading to enhanced fluorescence, suggesting that fluorescent magnetosomes could be used during cancer treatments such as magnetic hyperthermia to image cells of interest such as immune or tumor cells.

Development of non-pyrogenic magnetosome minerals coated with poly-l-lysine leading to full disappearance of intracranial U87-Luc glioblastoma in 100% of treated mice using magnetic hyperthermia.

Magnetic hyperthermia was reported to increase the survival of patients with recurrent glioblastoma by 7 months. This promising result may potentially be further improved by using iron oxide nanoparticles, called magnetosomes, which are synthesized by magnetotactic bacteria, extracted from these bacteria, purified to remove most endotoxins and organic material, and then coated with poly-l-lysine to yield a stable and non-pyrogenic nanoparticle suspension. Due to their ferrimagnetic behavior, high crystallinity and chain arrangement, these magnetosomes coated with poly-l-lysine (M-PLL) are characterized by a higher heating power than their chemically synthesized counterparts currently used in clinical trials. M-PLL-enhanced antitumor efficacy was demonstrated by administering 500-700 µg in iron of M-PLL to intracranial U87-Luc tumors of 1.5 mm3 and by exposing mice to 27 magnetic sessions each lasting 30 min, during which an alternating magnetic field of 202 kHz and 27 mT was applied. Treatment conditions were adjusted to reach a typical hyperthermia temperature of 42 °C during the first magnetic session. In 100% of treated mice, bioluminescence due to living glioblastoma cells fully disappeared 68 days following tumor cell implantation (D68). These mice were all still alive at D350. Histological analysis of their brain tissues revealed an absence of tumor cells, suggesting that they were fully cured. In comparison, antitumor efficacy was less pronounced in mice treated by the administration of IONP followed by 23 magnetic sessions, leading to full tumor bioluminescence disappearance in only 20% of the treated mice.

Chains of magnetosomes with controlled endotoxin release and partial tumor occupation induce full destruction of intracranial U87-Luc glioma in mice under the application of an alternating magnetic field.

Previous studies showed that magnetic hyperthermia could efficiently destroy tumors both preclinically and clinically, especially glioma. However, antitumor efficacy remained suboptimal and therefore required further improvements. Here, we introduce a new type of nanoparticles synthesized by magnetotactic bacteria, called magnetosomes, with improved properties compared with commonly used chemically synthesized nanoparticles. Indeed, mice bearing intracranial U87-Luc glioma tumors injected with 13µg of nanoparticles per mm3 of tumor followed by 12 to 15 of 30min alternating magnetic field applications displayed either full tumor disappearance in 40% of mice or no tumor regression using magnetosomes or chemically synthesized nanoparticles, respectively. Magnetosome superior antitumor activity could be explained both by a larger production of heat and by endotoxins release under alternating magnetic field application. Most interestingly, this behavior was observed when magnetosomes occupied only 10% of the whole tumor volume, which suggests that an indirect mechanism, such as an immune reaction, takes part in tumor regression. This is desired for the treatment of infiltrating tumors, such as glioma, for which whole tumor coverage by nanoparticles can hardly be achieved.

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.

Magnetic hyperthermia, in which magnetic nanoparticles are introduced into tumors and exposed to an alternating magnetic field (AMF), appears to be promising since it can lead to increased life expectancy in patients. Its efficacy can be further improved by using biocompatible iron oxide magnetosome minerals with better crystallinity and magnetic properties compared with chemically synthesized nanoparticles (IONP - Iron Oxide Nanoparticles). To fabricate such minerals, magnetosomes are first isolated from MSR-1 magnetotactic bacteria, purified to remove potentially toxic organic bacterial residues and stabilized with poly-l-lysine (N-PLL), citric acid (N-CA), oleic acid (N-OA), or carboxy-methyl-dextran (N-CMD). The different coated nanoparticles appear to be composed of a cubo-octahedral mineral core surrounded by a coating of different thickness, composition, and charge, and to be organized in chains of various lengths. The in vitro anti-tumor and heating efficacies of these nanoparticles were examined by bringing them into contact with GL-261 glioblastoma cells and by applying an AMF. This led to a specific absorption rate of 89-196 W gFe -1, measured using an AMF of 198 kHz and 34-47 mT, and to percentages of tumor cell destruction due to the exposure of the nanoparticles to the AMF of 10 ± 3% to 43 ± 3% depending on the coating agent. These results show the potential of this protocol for the tumor treatment by magnetic hyperthermia.

Mass-dependent and -independent signature of Fe isotopes in magnetotactic bacteria.

Magnetotactic bacteria perform biomineralization of intracellular magnetite (Fe3O4) nanoparticles. Although they may be among the earliest microorganisms capable of biomineralization on Earth, identifying their activity in ancient sedimentary rocks remains challenging because of the lack of a reliable biosignature. We determined Fe isotope fractionations by the magnetotactic bacterium Magnetospirillum magneticum AMB-1. The AMB-1 strain produced magnetite strongly depleted in heavy Fe isotopes, by 1.5 to 2.5 per mil relative to the initial growth medium. Moreover, we observed mass-independent isotope fractionations in (57)Fe during magnetite biomineralization but not in even Fe isotopes ((54)Fe, (56)Fe, and (58)Fe), highlighting a magnetic isotope effect. This Fe isotope anomaly provides a potential biosignature for the identification of magnetite produced by magnetotactic bacteria in the geological record.

Chemical signature of magnetotactic bacteria.

There are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite. On Earth, magnetotactic bacteria perform biomineralization of intracellular magnetite nanoparticles under a controlled pathway. These bacteria are ubiquitous in modern natural environments. However, their identification in ancient geological material remains challenging. Together with physical and mineralogical properties, the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification, but this had never been explored quantitatively and systematically for many trace elements. Here, we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1. We show that, in biomagnetite, most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion. Furthermore, we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record.

Synthesis and biological evaluation of new bisphosphonate-dextran conjugates targeting breast primary tumor.

Bisphosphonates (BPs) have interesting antitumor effects as well in vitro as in vivo, despite their poor bioavailability in the organism after oral ingestion. To overcome this problem and reduce drug doses and secondary effects, we report the chemical synthesis of new bioconjugates. They were built with a nitrogen-containing BP as the drug covalently coupled to the carboxymethyldextran. This polysaccharide was used as a carrier, in order to increase BP lifetime in bloodstream and to target tumor cells which have a strong affinity with dextran. The efficiency of our vectorization system was biologically proved in vitro and in vivo on mammalian carcinoma models in mice.

Use of bacterial magnetosomes in the magnetic hyperthermia treatment of tumours: a review.

We review the most recent and significant results published in the field of magnetotactic bacteria (MTB), in particular data relating to the use of bacterial magnetosomes in magnetic hyperthermia for the treatment of tumours. We review different methods for cultivating MTB and preparing suspensions of bacterial magnetosomes. As well as the production of magnetosomes, we also review key data on the toxicity of the magnetosomes as well as their heating and anti-tumour efficiencies. The toxicity and efficiency of magnetosomes needs to be understood and the risk-benefit ratio with which to evaluate their use in the magnetic hyperthermia treatment of tumours needs to be measured.

Preparation of chains of magnetosomes, isolated from Magnetospirillum magneticum strain AMB-1 magnetotactic bacteria, yielding efficient treatment of tumors using magnetic hyperthermia.

Chains of magnetosomes isolated from Magnetospirillum magneticum strain AMB-1 magnetotactic bacteria by sonication at 30 W during 2 h are tested for magnetic hyperthermia treatment of tumors. These chains are composed of magnetosomes, which are bound to each other by a filament made of proteins. When they are incubated in the presence of cancer cells and exposed to an alternating magnetic field of frequency 198 kHz and average magnetic field strength of 20 or 30 mT, they produce efficient inhibition of cancer cell proliferation. This behavior is explained by a high cellular internalization, a good stability in solution and a homogenous distribution of the magnetosome chains, which enables efficient heating. When the chains are heated during 5 h at 90°C in the presence of 1% SDS, the filament binding the magnetosomes together is denatured and individual magnetosomes are obtained. By contrast to the chains of magnetosomes, the individual magnetosomes are prone to aggregation, are not stable in solution and do not produce efficient inhibition of cancer cell proliferation under application of an alternating magnetic field.

The effect of iron-chelating agents on Magnetospirillum magneticum strain AMB-1: stimulated growth and magnetosome production and improved magnetosome heating properties.

The introduction of various iron-chelating agents to the Magnetospirillum magneticum strain AMB-1 bacterial growth medium stimulated the growth of M. magneticum strain AMB-1 magnetotactic bacteria and enhanced the production of magnetosomes. After 7 days of growth, the number of bacteria and the production of magnetosomes were increased in the presence of iron-chelating agents by factors of up to ∼2 and ∼6, respectively. The presence of iron-chelating agents also produced an increase in magnetosome size and chain length and yielded improved magnetosome heating properties. The specific absorption rate of suspensions of magnetosome chains isolated from M. magneticum strain AMB-1 magnetotactic bacteria, measured under the application of an alternating magnetic field of average field strength ∼20 mT and frequency 198 kHz, increased from ∼222 W/g(Fe) in the absence of iron-chelating agent up to ∼444 W/g(Fe) in the presence of 4 µM rhodamine B and to ∼723 W/g(Fe) in the presence of 4 µM EDTA. These observations were made at an iron concentration of 20 µM and iron-chelating agent concentrations below 40 µM.

Chains of magnetosomes extracted from AMB-1 magnetotactic bacteria for application in alternative magnetic field cancer therapy.

Chains of magnetosomes extracted from AMB-1 magnetotactic bacteria are shown to be highly efficient for cancer therapy when they are exposed to an alternative magnetic field. When a suspension containing MDA-MB-231 breast cancer cells was incubated in the presence of various amounts of extracted chains of magnetosomes, the viability of these cells remained high in the absence of an alternative magnetic field. By contrast, when this suspension was exposed to an alternative magnetic field of frequency 183 kHz and field strengths of 20, 40, or 60 mT, up to 100% of these cells were destroyed. The antitumoral activity of the extracted chains of magnetosomes is demonstrated further by showing that they can be used to fully eradicate a tumor xenografted under the skin of a mouse. For that, a suspension containing ∼1 mg of extracted chains of magnetosomes was administered within the tumor and the mouse was exposed to three heat cycles of 20 min, during which the tumor temperature was raised to ∼43 °C. We also demonstrate the higher efficiency of the extracted 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 superparamagnetic iron oxide nanoparticles currently tested for alternative magnetic field cancer therapy. The higher efficiency of the extracted chains of magnetosomes compared with that of the other nanoparticles is attributed to three factors: (i) a specific absorption rate higher for the magnetosomes than for the chemically synthesized superparamagnetic iron oxide nanoparticles, (ii) a more uniform heating for the chains of magnetosomes than for the individual magnetosomes and (iii) the ability of the chains of magnetosomes to penetrate within the cancer cells or bind at the cell membrane following the application of the alternative magnetic field, which enables efficient cell destruction. Biodistribution studies revealed that extracted chains of magnetosomes administered directly within xenografted breast tumors progressively left the tumors during the 14 days following their administration and were then eliminated in large proportion in the feces.

A multimodal magnetic resonance imaging nanoplatform for cancer theranostics.

We describe an innovative multimodal system, which combines magnetic targeting of therapeutic agents with both magnetic resonance and fluorescence imaging into one system. This new magnetic nanoplatform consists of superparamagnetic γFe(2)O(3) nanoparticles, used clinically as an MRI contrast agent, conjugated to therapeutic molecules of the hydroxylmethylene bisphosphonate family (HMBPs): alendronate with an amine function as the terminal group. In vitro tests with breast cancer cells show that the γFe(2)O(3)@alendronate hybrid nanomaterial reduces cell viability and acts as a drug delivery system. We also investigated the anti-tumoural properties in vivo in nude mice xenografted with MDA-MB-231 tumours. We show that the presence of both γFe(2)O(3)@alendronate and a magnetic field significantly reduced the development of tumours. The amine functionalities can be used as precursor groups for the covalent coupling of peptides or monoclonal antibodies for specific biological targeting. The feasibility of this process was demonstrated by coupling rhodamine B, a fluorescence marker, to the γFe(2)O(3)@alendronate nanohybrid. The system showed fluorescent properties and high affinity for cells. Flow cytometry and fluorescence microscopy were used to study the kinetics of γFe(2)O(3)@alendronate uptake by cells. The magnetic and fluorescent nanoparticles are potential candidates for smart drug-delivery systems. Also, the superparamagnetic behaviour of such nanoparticles may be exploited as MRI contrast agents to improve therapeutic diagnostics.