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.