Site-Specific 111In-Radiolabeling of Dual-PEGylated Porous Silicon Nanoparticles and Their In Vivo Evaluation in Murine 4T1 Breast Cancer Model

Abstract

Polyethylene glycol (PEG) has been successfully used for improving circulation time of several nanomaterials but prolonging the circulation of porous silicon nanoparticles (PSi NPs) has remained challenging. Here, we report a site specific radiolabeling of dual-PEGylated thermally oxidized porous silicon (DPEG-TOPSi) NPs and investigation of influence of the PEGylation on blood circulation time of TOPSi NPs. Trans-cyclooctene conjugated DPEG-TOPSi NPs were radiolabeled through a click reaction with [¹¹¹In]In-DOTA-PEG₄-tetrazine (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and the particle behavior was evaluated in vivo in Balb/c mice bearing 4T1 murine breast cancer allografts. The dual-PEGylation significantly prolonged circulation of [¹¹¹In]In-DPEG-TOPSi particles when compared to non-PEGylated control particles, yielding 10.8 ± 1.7% of the injected activity/g in blood at 15 min for [¹¹¹In]In-DPEG-TOPSi NPs. The improved circulation time will be beneficial for the accumulation of targeted DPEG-TOPSi to tumors.

Keywords: IEDDA; SPECT; click chemistry; indium-111; porous silicon.

Figure 1

Characterization of the nanoparticles: (A–C) TEM images of TOPSi, DPEG-TOPSi, and DPEG-TOPSi-NH₂ NPs, (D–F) FT-IR spectra, TGA, and N₂ ad/desorption curves (TOPSi (Blue), DPEG-TOPSi (Red) and DPEG-TOPSi-NH₂ (Green)), (G) Colloidal stability of the nanoparticles in PBS at 37 °C at different time points, and (H) Viability of macrophages when incubated with different nanoparticles.

Scheme 1

¹¹¹In-radiolabeling of DPEG-TOPSi particles with approaches A and B.

Scheme 2

Synthesis and radiolabeling of [¹¹¹In]In-DOTA-PEG₄-Tz ([¹¹¹In]1).

Figure 2

In vitro stability of [¹¹¹In]In-DPEG-TOPSi and [¹¹¹In]In-TOPSi particles in 10% and 50% human plasma and 1 × PBS (n = 3). Comparison of radiolabel stability after radiolabeling the NPs with two different methods; either by using the one-step approach A in which the NPs were incubated with [¹¹¹In]InCl₃ or by the two-step approach B, in which the TCO-functionalized DPEG-PSi NPs were radiolabeled by using a presynthesized [¹¹¹In]In-DOTA-PEG₄-Tz ([¹¹¹In]1). The radiolabel stability in plasma is decreasing significantly for approach A radiolabeled [¹¹¹In]In-DPEG-TOPSi NPs already after 1 h.

Figure 3

Biodistribution of (A) [¹¹¹In]In-DPEG-TOPSi and [¹¹¹In]In-TOPSi and (B) [¹¹¹In]In-DOTA-PEG₄-Tz ([¹¹¹In]1) at 1h in Balb/c mice (n = 4). Statistical analysis was made by using a t-test analysis, significant differences were found in liver, kidney, lung, spleen, and bone (thibia).

Figure 4

Quantification of resident time in blood for [¹¹¹In]In-DPEG-TOPSi, [¹¹¹In]In-TOPSi and [¹¹¹In]1 in Balb/c mice (n = 4) at 5 min, 15 min 30 min and 1 h after intravenous administration. Unpaired t-test was used to assess the statistical significance of the difference in the of the two particle types in blood, ** p > 0.0021.

Figure 5

Representative SPECT/CT images (coronal and transversal) from 30 min, 5 h and 24 h time points for [¹¹¹In]In-DPEG-TOPSi particles at 4T1 bearing mice. Location of the tumor is indicated by a cursor. Highest radioactivity levels were observed in liver and spleen.

Figure 6

Histological and autoradiography image from 4T1 tumor slice collected at 4 h after [¹¹¹In]In-DPEG-TOPSi administration.