Preloading of Hydrophobic Anticancer Drug into Multifunctional Nanocarrier for Multimodal Imaging, NIR-Responsive Drug Release, and Synergistic Therapy

Abstract

Applications of hydrophobic drug-based nanocarriers (NCs) remain largely limited because of their low loading capacity. Here, development of a multifunctional hybrid NC made of a magnetic Fe3O4 core and a mesoporous silica shell embedded with carbon dots (CDs) and paclitaxel (PTX), and covered by another layer of silica is reported. The NC is prepared via a one-pot process under mild condition. The PTX loading method introduced in this study simplifies drug loading process and demonstrates a high loading capacity due to mesoporous silica dual-shell structure, supramolecular π-stacking between conjugated rings of PTX molecules, and aromatic rings of the CDs in the hybrid NC. The CDs serve as both confocal and two-photon fluorescence imaging probes, while the Fe3O4 core serves as a magnetic resonance imaging contrast agent. Significantly, NC releases PTX in response to near infrared irradiation as a result of local heating of the embedded CDs and the heating of CDs also provides an additional therapeutic effect by thermally killing cancer cells in tumor in addition to the chemotherapeutic effect of released PTX. Both in vitro and in vivo results show that NC demonstrates high therapeutic efficacy through a synergistic effect from the combined chemo-photothermal treatments.

Keywords: hydrophobic drugs; mesoporous silica; multifunctional imaging; preloading; synergistic effects.

Figure 1

Synthesis and structure of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (a) Schematic illustration of formation of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. Step I: surface coating and encapsulation of Fe₃O₄ and CDs; step II: preloading of PTX and surface coating of Fe₃O₄@CDs@mSiO₂ with mesoporous silica. (b, c and d) TEM images of Fe₃O₄ core, Fe₃O₄@CDs@mSiO₂ NCs and Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. The insets in c and d are TEM images of a single Fe₃O₄@CDs@mSiO₂ NC and Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NC, respectively at a higher magnification.

Figure 2

Optical properties and size distribution of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (a) UV-vis absorption spectra of free PTX, Fe₃O₄@CDs@mSiO₂@mSiO₂ NCs and Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (b) Hydrodynamic size distributions of Fe₃O₄, Fe₃O₄@CDs@mSiO₂ NCs and Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs in distilled water at 25°C.

Figure 3

Optical property of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. Laser scanning confocal microscopy images of SF-763 cells incubated with Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs for 2 h under different excitation wavelengths: (a) 405 nm, (b) 488 nm, (c) 546 nm. (d) DAPI nuclear stain, (e) two-photon fluorescence, and (f) overlaid images of SF-763 cells incubated with Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. Excitation laser wavelength is 900 nm.

Figure 4

Magnetic properties and MRI of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (a) The hysteresis behavior of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs measured at room temperature. (b) R₂ (1/T₂) as a function of the concentration of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (c) T₂-weighted MR images and R₂ maps of MRI phantoms of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs at different NC concentrations.

Figure 5

Porous structure and drug release behavior of the hybrid NCs. (a) N₂ adsorption-desorption isotherm and (b) pore diameter distribution of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (c) HPLC analysis of initial PTX solution and residual PTX solution from the preparation of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs. (d) Release profiles of PTX from Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs in PBS at 37°C, with or without of irradiation of NIR light. NIR was irradiated at 1.5 W cm⁻² for 5 min each at predefined time points (6, 22, and 32 h). The inset in (d) is a schematic illustration of the release of PTX from Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs.

Figure 6

In vitro chemotherapy and phototherapy using hybrid NCs. (a) In vitro cytotoxicity of Fe₃O₄@CDs@mSiO₂@mSiO₂ NCs and Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs without and with NIR irradiation at 1.5 W cm⁻² for 5 min, as measured in terms of cell viability. (b) Therapeutic efficiencies of Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ NCs as a drug carrier and photothermal therapy agent for chemo, photothermal, and their combined treatments. The t-test was used to compare the therapeutic efficiencies of combined treatment with the additive efficiencies of chemo and photothermal treatments alone. All p-values are smaller than 0.01.

Figure 7

H&E stained tissue sections of mouse heart, kidney, liver, lung and spleen obtained from noninjected animals, and those injected with Fe₃O₄@CDs@mSiO₂@mSiO₂ (NO PTX NCs) or with Fe₃O₄@CDs@mSiO₂@PTX@mSiO₂ (PTX NCs) at a concentration of 0.05 mg mL⁻¹. The scale bar 100 µm.