In Vivo Integrity and Biological Fate of Chelator-Free Zirconium-89-Labeled Mesoporous Silica Nanoparticles

Abstract

Traditional chelator-based radio-labeled nanoparticles and positron emission tomography (PET) imaging are playing vital roles in the field of nano-oncology. However, their long-term in vivo integrity and potential mismatch of the biodistribution patterns between nanoparticles and radio-isotopes are two major concerns for this approach. Here, we present a chelator-free zirconium-89 ((89)Zr, t1/2 = 78.4 h) labeling of mesoporous silica nanoparticle (MSN) with significantly enhanced in vivo long-term (>20 days) stability. Successful radio-labeling and in vivo stability are demonstrated to be highly dependent on both the concentration and location of deprotonated silanol groups (-Si-O(-)) from two types of silica nanoparticles investigated. This work reports (89)Zr-labeled MSN with a detailed labeling mechanism investigation and long-term stability study. With its attractive radio-stability and the simplicity of chelator-free radio-labeling, (89)Zr-MSN offers a novel, simple, and accurate way for studying the in vivo long-term fate and PET image-guided drug delivery of MSN in the near future.

Keywords: chelator-free radio-labeling; mesoporous silica nanoparticle; positron emission tomography; zirconium-89.

Figure 1

Chelator-free ⁸⁹Zr labeling of MSN. (a) TEM image of MSN with an average particle size of ∼150 nm. (b) Nitrogen adsorption–desorption isotherms and the corresponding pore size distributions of MSN. (c) Schematic illustration showing the labeling of ⁸⁹Zr⁴⁺ to the deprotonated silanol groups (−Si–O^–) from the outer surface and inner meso-channels of MSN. (d) Time-dependent ⁸⁹Zr labeling yield in HEPES buffer solution (pH 7–8) with varied MSN concentrations (from 2 mg/mL to 2 × 10^–4 mg/mL).

Figure 2

Chelator-free ⁸⁹Zr labeling of dSiO₂. (a) Schematic illustration showing the labeling of ⁸⁹Zr⁴⁺ to the deprotonated silanol groups (−Si–O^–) from the outer surface of dSiO₂. (b) TEM image of dSiO₂ with an average particle size of ∼90 nm. (c) Time-dependent ⁸⁹Zr labeling yield in HEPES buffer solution (pH 7–8) with varied dSiO₂ concentrations (from 2 mg/mL to 2 × 10^–4 mg/mL).

Figure 3

In vitro stability of ⁸⁹Zr-labeled silica nanoparticles. Stability of (a) ⁸⁹Zr-MSN and (b) ⁸⁹Zr-dSiO₂ when challenged with DFO of varied concentrations from 0.05 to 5 mM at 37 °C for 48 h. (c) Stability of ⁸⁹Zr-MSN (red line) and ⁸⁹Zr-dSiO₂ (blue line) in whole mouse serum at 37 °C for 48 h. (d) Stability study of ⁸⁹Zr-MSN when challenged with EDTA (1 mM) at 37 °C for 1 week.

Figure 4

(a) TEM image of MSN with an average particle size of ∼90 nm. (b) Nitrogen adsorption–desorption isotherms and the corresponding pore size distributions of MSN. BET surface area was estimated to be 710.7 m²/g, and the average pore size was about 9–10 nm.

Figure 5

In vivo radiostability and ex vivo biodistribution studies. (a) Schematic illustration of ⁸⁹Zr-dSiO₂. (b) Biodistribution study of ⁸⁹Zr-dSiO₂ on day 21 p.i. (c) TEM image of ⁸⁹Zr-dSiO₂. (d) In vivo serial coronal maximum intensity projection PET images of mice at different time points after i.v. injection of ⁸⁹Zr-dSiO₂. (e) TEM image of ⁸⁹Zr-MSN. (f) In vivo serial coronal maximum intensity projection PET images of mice at different time points after i.v. injection of ⁸⁹Zr-MSN. (g) Schematic illustration of ⁸⁹Zr-MSN. (h) Biodistribution study of ⁸⁹Zr-MSN on day 21 p.i.

Figure 6

Quantitative region of interest analysis of the dynamic uptake change of ⁸⁹Zr in bone and liver. Time–activity curves of bone (a) and liver (c) upon i.v. injection of ⁸⁹Zr-dSiO₂ or ⁸⁹Zr-MSN into BALB/c mice over 21 days. Linear fitting of ⁸⁹Zr in (b) bone during stage 1 and (d) liver during stage 2.