Silica@zirconia@poly(malic acid) nanoparticles: promising nanocarriers for theranostic applications

Silica@zirconia@poly(malic acid) nanocarriers of 110 nm mean diameter were designed, synthesized and characterized for the targeted delivery of diagnostic and therapeutic 99mTc to folate-overexpressing tumors. An important achievement was that a multifunctional L-(−)-malic-acid-based copolymer was formed in situ at the surface of the inorganic cores in a single synthetic step incorporating L-(−)-malic acid, β-cyclodextrin rings, folic acid moieties, and polyethylene glycol chains. Morphological and in-depth structural analysis of the particles proved their core@shell structure. Stability experiments in aqueous media evidenced that stable suspensions can be obtained from the lyophilized powder in 10 mM phosphate buffer at pH 7.4. During 14-day degradation experiments, the nanoparticles were found to be slowly dissolving (including inorganic core) in saline and also in total cell medium. An in vitro toxicity assay on hepatocytes showed a concentration-dependent decrease of cell viability down to 63 ± 1% at the highest applied concentration (0.5 mg ml−1). Proof of concept experiments of technetium-99m radiolabelling and in vivo labelling stability are presented.