(473d) Theranostic Nanocarriers Combining High Drug Loading, Heat Release, and Magnetic Particle Imaging

Introduction: Here we report formulation and characterization of theranostic nanocarriers that combine high and tunable loading of the chemotherapeutic drug doxorubicin with iron oxide nanoparticles that enable heat release in response to alternating magnetic field and unambiguous, quantitative, tomographic imaging in vivo through Magnetic Particle Imaging (MPI). The nanocarriers are obtained by Flash NanoPrecipitation (FNP), which enables scalable production. The doxorubicin and iron oxide loading can be easily tuned through the inlet stream concentrations and overall particle size can be tuned through the concentration of an outer amphiphilic block copolymer corona. We demonstrate high (up to 50% w/w) doxorubicin loading, pH tunable release, significant heat release in response to applied alternating magnetic fields (AMF), and ability to image through MPI.

Materials and Methods: To facilitate doxorubicin loading through FNP, we synthesized a doxorubicin prodrug (proDox) consisting of a doxorubicin-imine conjugate. The hydrolysis of proDox to the parent drug doxorubicin was evaluated via NMR as a function of temperature and water content. Flash Nanoprecipitation (FNP) with PEG-PLA block-copolymers, iron oxide nanoparticles, and proDox was used to create the nanocarriers. Magnetic filtration was used for purification after FNP, which is rapid and scalable. Nanocarriers were prepared under a variety of FNP conditions, including variation of proDox concentration, nature of outer block copolymer corona, and presence of a hydrophobic homopolymer. The concentration of drug in the nanocarriers was evaluated spectrophotometrically. Release tests were done at 37°C in a shaking incubator with aqueous media at pH values of 4, 6, and 7.4 to represent lysosomal, intratumoral, and vasculature pH conditions, respectively. Toxicity to cancer cells was assessed by seeding MDA-MB-231 cells at 5,000 cells/well onto a 96-well plate, letting the cells grow for 48 hours, exposing cells to free doxorubicin or doxorubicin-loaded MCNCs for 48 hours, and then performing a metabolic assay to quantify relative viability. Heat release from the nanocarriers was evaluated using a D5 Series Driver (nanoscale Biomagnetics) equipped with calorimetry coil. MPI scans were done with a Momentumâ„¢ Magnetic Particle Imaging scanner (Magnetic Insight).

Results and Discussion: Drug loading was found to be highly tunable via changing the concentration of proDox in the FNP inlet streams. All 5 conditions resulted in statistically significant differences in loading, with the loading increasing as the concentration of proDox increases. The loading ranged from 5 to 50 % w/w doxorubicin. Release studies showed that the release rate is fast and highly dependent on pH. The release rate was insensitive to the nature and molecular weight of the block copolymer corona used to cap the nanocarriers. This suggests that hydrolysis of the proDox is the rate limiting step for release. The nanocarriers were toxic to cancer cells in vitro, with an IC50 value of 1,100 nM, compared to 200 nM for free doxorubicin. The heating rate of the nanocarriers was tunable through the amplitude and frequency of the applied AMF. MPI scans showed that the nanocarriers can be imaged, which suggests further studies of pharmacokinetics and biodistribution using MPI, which provides for unambiguous, quantitative, tomographic, and longitudinal imaging of iron oxide nanoparticle biodistribution.

Conclusions: This study shows that magnetic nanoparticles can be combined with hydrophobic prodrugs to form nanocarriers that combine high drug loading, ability to release heat in response to alternating magnetic fields, and quantitative imaging through MPI.

Acknowledgements: We acknowledge funding from NSF HRD-1345156.