PEGylated Anionic Magnetofluorescent Nanoassemblies: Impact of Their Interface Structure on Magnetic Resonance Imaging Contrast and Cellular Uptake

Abstract

Controlling the interactions of functional nanostructures with water and biological media represents high challenges in the field of bioimaging applications. Large contrast at low doses, high colloidal stability in physiological conditions, the absence of cell cytotoxicity, and efficient cell internalization represent strong additional needs. To achieve such requirements, we report on high-payload magnetofluorescent architectures made of a shell of superparamagnetic iron oxide nanoparticles tightly anchored around fluorescent organic nanoparticles. Their external coating is simply modulated using anionic polyelectrolytes in a final step to provide efficient magnetic resonance imaging (MRI) and fluorescence imaging of live cells. Various structures of PEGylated polyelectrolytes have been synthesized and investigated, differing from their iron oxide complexing units (carboxylic vs phosphonic acid), their structure (block- or comblike), their hydrophobicity, and their fabrication process [conventional or reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization] while keeping the central magnetofluorescent platforms the same. Combined photophysical, magnetic, NMRD, and structural investigations proved the superiority of RAFT polymer coatings containing carboxylate units and a hydrophobic tail to impart the magnetic nanoassemblies (NAs) with enhanced-MRI negative contrast, characterized by a high r/r ratio and a transverse relaxation r equal to 21 and 125 s mmol L, respectively, at 60 MHz clinical frequency (∼1.5 T). Thanks to their dual modality, cell internalization of the NAs in mesothelioma cancer cells could be evidenced by both confocal fluorescence microscopy and magnetophoresis. A 72 h follow-up showed efficient uptake after 24 h with no notable cell mortality. These studies again pointed out the distinct behavior of RAFT polyelectrolyte-coated bimodal NAs that internalize at a slower rate with no adverse cytotoxicity. Extension to multicellular tumor cell spheroids that mimic solid tumors revealed the successful internalization of the NAs in the periphery cells, which provides efficient deep-imaging labels thanks to their induced T* contrast, large emission Stokes shift, and bright dotlike signal, popping out of the strong spheroid autofluorescence.

Coating Effect on the 1H—NMR Relaxation Properties of Iron Oxide Magnetic Nanoparticles

“…We used four different MNP polyelectrolyte coatings: (i) Poly(acrylic acid), named PAA-A (average M n = 1800 g·mol −1 ), purchased from Sigma–Aldrich (St. Louis, MO, USA) and used as received; (ii) a copolymer issued from the random esterification of poly(methacrylic acid) (PMAA) chains with polyethylene glycol (PEG 2000 ), PMAA- g -PEG 2000 , named PEG-B (M n = 5.86 × 10 4 g·mol −1 ); (iii) and (iv), two comb-like polymers fabricated by reversible addition-fragmentation chain transfer (RAFT) based on PMMA and poly(ethylene glycol) methyl ether methacrylate (MAPEG 2000 ) with two different chain transfer agents, P(MAA- stat -MAPEG 2000 ), named respectively PEG-C for the hydrophobic transfer agent (M n = 3.99 × 10 4 g·mol −1 ) and PEG-D for the hydrophilic transfer agent (M n = 2.87 × 10 4 g·mol −1 ) [ 32 , 33 ].…”

The Biology of Malignant Mesothelioma and the Relevance of Preclinical Models

“…Indeed, some pathways involved in resistance to cell death are differentially regulated in monolayer and MCTS, and thus these models better mimic resistance to treatment compared with monolayer cells (64,(102)(103)(104)(105)(106). These models also reproduce the diffusion constraint of therapeutic molecules, such as antibodies or nanovectors (106)(107)(108)(109). The 3D structures also share common features with tumors from patients (101).…”

Luminophore and Magnetic Multicore Nanoassemblies for Dual-Mode MRI and Fluorescence Imaging

“…The use of magneto-fluorescent nanoassemblies provides generally biodegradable systems that advantageously avoid bioaccumulation. In this context, several molecular matrices are envisaged composed of polymers [151][152][153][154][155][156][157][158][159], lipids [160][161][162][163], PDots [164][165][166][167] or organic molecule [168][169][170][171][172] ( Figure 6). In this type of organization we will distinguish the assemblies with inert matrices of those composed of active units.…”

“…Moreover, for these systems, important brightness and photostability under irradiation of the fluorophores have been demonstrated during in cellulo fluorescence microscopy [167]. The use of small hydrophobic molecules with iron oxide nanoparticles chelating functions is another effective approach to obtain magnetofluorescent systems [168][169][170][171][172]. In these systems, the fluorescent core composed of 10 5 dyes is surrounded by magnetic nanoparticles shell [168].…”

“…The use of polyacrylic acid allows a very cohesive architecture, when the stabilization by citrate ions allows a dissociation [170]. These systems have been functionalized with polyethylene glycol-based copolymers to increase their circulation time [172]. Moreover, it has been shown that the presence of a hydrophobic tail in the copolymer increases the r 2 /r 1 two times compared to those which are without one [172].…”