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

Stable pharmaceutical composition of cryo-protected non-pyrogenic isotonic chains of magnetosomes for efficient tumor cell destruction at 45 ± 1 °C under alternating magnetic field or ultrasound application

We report a method to prepare biocompatible, stable, and highly pure iron oxide nano-minerals by following the steps consisting of: (i) amplifying magnetotactic bacteria in non-toxic minimal growth media; (ii) extracting magnetosomes from magnetotactic bacteria under alkaline lysis; (iii) heating magnetosomes above 400 °C to yield sterile magnetosome minerals, M-uncoated, devoid of active non-denatured bacterial organic material; (iv) coating M-uncoated with biocompatible carboxymethyl-dextran (CMD) compounds to yield stable M-CMD; (v) adding 5% sorbitol to M-CMD; and (vi) lyophilizing these mixtures, resulting in formulated nano-minerals in powder forms, designated as (M-CMD)F. The long-term stability of the final products is demonstrated by re-suspending (M-CMD)F in water after 12 months of storage, and by showing that these formulated magnetosomes have preserved their stability in suspension, chain arrangement, carbon content, surface charge, and surface composition. Furthermore, the formulation is optimized to yield an isotonic magnetosome suspension with an osmolality of between 275 and 290 mOsm kg-1 H2O upon reconstitution. On one hand, these formulated magnetosomes are fully biocompatible, i.e. sterile, non-pyrogenic, and non-cytotoxic towards 3T3, L929, and V79 healthy cells up to 1 mg mL-1 NP concentration iron. On the other hand, when they are brought into the presence of PC3-Luc prostate tumor cells and heated moderately at ∼41-46 °C for 20-30 minutes under low-intensity ultrasound or alternating magnetic field conditions, they efficiently destroy these tumor cells.

A Versatile Magnetic Nanoplatform for Plug-and-Play Functionalization: Genetically Programmable Cargo Loading to Bacterial Magnetosomes by SpyCatcher "Click Biology"

Bacterial magnetosomes ("MAGs") represent a promising class of magnetic iron oxide nanoparticles with exceptional material characteristics and high application potential in the biomedical and biotechnological field. For the surface functionalization of MAGs with different protein cargos, their enveloping membrane can be addressed by genetic means. However, the expression of foreign polypeptides as translational fusion to magnetosome membrane proteins is still laborious and lacks versatility as the generated particles are monospecific and thus restricted to predetermined functions. Utilizing the SpyTag-SpyCatcher (ST-SC) bioconjugate system, we here establish a flexible platform for the targeted nanoassembly of multifunctional MAGs that combines the rapidity of chemical coupling (e.g., by cross-linking reactions) and the unmatched selectivity and controllability of in vivo functionalization. MAGs genetically engineered to display either SC- or ST-connectors are shown to efficiently bind a variety of complementary tagged (protein) cargo. Specifically, we cover a broad spectrum of representative functional moieties and foreign cargo (such as enzymes, antibodies, fluorophores, and silica beads) with relevance in biotechnology and biomedicine and demonstrate the interchangeability of the MAGs-adapted ST-SC system. For the controlled generation of artificial shells surrounding the particles, SC-MAGs are effectively coated by protein-corona proteins. The potential of the here-provided toolkit is even more enhanced by using SC-MAGs as an affinity tool for selective protein pulldown in vitro and in vivo. Overall, this innovative technology turns bacterial MAGs into a flexible magnetic nanoscaffold for the targeted plug-and-play display of virtually unlimited additional functionalities, thereby generating a multitude of magnetic hybrid materials that can be used in many applications.

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.

Cell-Membrane-Coated and Cell-Penetrating Peptide-Conjugated Trimagnetic Nanoparticles for Targeted Magnetic Hyperthermia of Prostate Cancer Cells

Prostate malignancy represents the second leading cause of cancer-specific death among the male population worldwide. Herein, enhanced intracellular magnetic fluid hyperthermia is applied in vitro to treat prostate cancer (PCa) cells with minimum invasiveness and toxicity and highly specific targeting. We designed and optimized novel shape-anisotropic magnetic core-shell-shell nanoparticles (i.e., trimagnetic nanoparticles - TMNPs) with significant magnetothermal conversion following an exchange coupling effect to an external alternating magnetic field (AMF). The functional properties of the best candidate in terms of heating efficiency (i.e., Fe₃O₄@Mn_0.5Zn_0.5Fe₂O₄@CoFe₂O₄) were exploited following surface decoration with PCa cell membranes (CM) and/or LN1 cell-penetrating peptide (CPP). We demonstrated that the combination of biomimetic dual CM-CPP targeting and AMF responsiveness significantly induces caspase 9-mediated apoptosis of PCa cells. Furthermore, a downregulation of the cell cycle progression markers and a decrease of the migration rate in surviving cells were observed in response to the TMNP-assisted magnetic hyperthermia, suggesting a reduction in cancer cell aggressiveness.