Synergistic Theranostics of Magnetic Resonance Imaging and Photothermal Therapy of Breast Cancer Based on the Janus Nanostructures Fe3O4-Aushell-PEG

Abstract

Background: Satisfactory prognosis of breast cancer (BC) is limited by difficulty in early diagnosis and insufficient treatment. The combination of molecular imaging and photothermal therapy (PTT) may provide a solution.

Methods: Fe₃O₄-Au_shell nanoparticles (NPs) were prepared by thermal decomposition, seeded growth and galvanic replacement and were comprehensively characterized. After conjugated to PEG, NPs were used as MRI and PTT agents in vitro and in vivo.

Results: Fe₃O₄-Au_shell NPs which had uniform Janus-like morphology were successfully synthesized. The Fe₃O₄ had a size of 18 ± 2.2 nm, and the Au_shell had an outer diameter of 25 ± 3.3 nm and an inner diameter of 20 ± 2.9 nm. The NPs showed superparamagnetism, a saturation magnetization of 36 emu/g, and an optical absorption plateau from 700 to 808 nm. The Fe₃O₄-Au_shell NPs were determined to possess good biocompatibility. After PEG coating, the zeta potential of NPs was changed from -23.75 ± 1.37 mV to -13.93 ± 0.55 mV, and the FTIR showed the characteristic C-O stretching vibration at 1113 cm^-1. The NPs' MR imaging implied that the T₂ can be shortened by Fe₃O₄-Au_shell NPs in a concentration-dependent manner, and the Fe₃O₄-Au_shell NPs coated with PEG at the molar ratio of 160 (PEG: NPs) showed the highest transverse relaxivity (r ₂) of 216 mM^-1s^-1. After irradiation at 0.65 W/cm² for 5 min, all cells incubated with the Fe₃O₄-Au_shell-PEG160 NPs (Fe: 30 ppm, Au: 70 ppm) died. After administrated intratumorally, Fe₃O₄-Au_shell-PEG160 notably decreased the signal intensity of tumor in T₂WI images. Under the same irradiation, the temperature of tumors injected with Fe₃O₄-Au_shell-PEG160 quickly rose to 54.6°C, and the tumors shrank rapidly and were ablated in 6 days.

Conclusion: Fe₃O₄-Au_shell-PEG NPs show good r ₂ and PTT performance and are promising synergistic theranostic agents of MRI and PTT for BC.

Keywords: early breast cancer theranostics; gold nanoshells; magnetic resonance imaging; nanoparticle; photothermal therapy.

Figure 1

(A, B, D and E) TEM of Fe₃O₄, Fe₃O₄-Ag_seed, Fe₃O₄-Ag, Fe₃O₄-Au_shell NPs, scale bar: 200 nm. (C) Absorbance of Fe₃O₄, Fe₃O₄-Ag, Fe₃O₄-Au_shell NPs. (F) EDS mapping of Fe₃O₄-Au_shell NP, scale bar: 20 nm.

Figure 2

(A) Relative cell viability of 4T1 cells incubated with different concentrations of Fe₃O₄-Au_shell for 24 h. (B) Hemolysis rate of RBC incubated with Fe₃O₄-Au_shell dispersions in PBS of various concentrations.

Figure 3

(A) Hysteresis loop of Fe₃O₄-Au_shell nanoparticles. (B) MRI T₂WI images of Fe₃O₄-Au_shell NPs with different PEG coating. (C) Linear regression of relaxation rate over different Fe concentrations of Fe₃O₄-Au_shell NPs with different PEG coating. (D) Calculated r₂ of Fe₃O₄-Au_shell NPs with different PEG coating. (E, F) Zeta potential and FTIR spectrum of NPs measured before and after PEG coating.

Figure 4

(A) Photothermal curves of Fe₃O₄-Au_shell NPs irradiated under 808 nm laser of 0.65 W/cm², 1.2 W/cm², 2.0 W/cm². (B) Photothermal curves of H₂O, Fe₃O₄, Fe₃O₄-Au_shell (Au: 70 ppm) and Fe₃O₄-Au_shell (Au: 23 ppm) under irradiation 1.2 W/cm² 808 nm laser. (C) Relative cell viability of 4T1 cells from different groups. Fluorescence microscope images of Calcein-AM/PI stained cells from groups of (D) untreated, (E) Fe₃O₄-Au_shell-PEG160, (F) laser and (G) Fe₃O₄-Au_shell-PEG160+laser. Green means live cells and red indicate dead cells, scale bar: 100 μm.

Figure 5

T₂WI images of tumor before (A) and after (C) Fe₃O₄-Au_shell injection, signal intensity rapidly decreased from 1487 ± 249 to 586 ± 233. Pseudo color was added by ImageJ (B and D).

Figure 6

(A) Mice weight, (C) mice tumor volume and (H) tumor photograph at different time points after treatment. Mice tumor’s thermal images (D) and temperature change (B) under 0.65 W/cm² laser irradiation for 5 min. (E–G) H&E staining of tumor from laser, NPs and untreated groups (scale bar: 50 μm). (I) H&E staining of vital organs harvested from different group mice at 14th day after treatment (scale bar: 50 μm).