Development of Small HN Linked Radionuclide Iodine-125 for Nanocarrier Image Tracing in Mouse Model

Abstract

Background: Radionuclides have important roles in clinical tumor radiotherapy as they are used to kill tumor cells or as imaging agents for drug tracing. The application of radionuclides has been developing as an increasing number of nanomaterials are used to deliver radionuclides to tumor areas to kill tumor cells. However, promoting the efficient combination of radionuclides and nanocarriers (NCs), enhancing radionuclide loading efficiency, and avoiding environmental pollution caused by radionuclide overuse are important challenges that hinder their further development.

Methods: In the present study, a new small molecule compound (3-[[(2S)-2-hydroxy-3-(4-hydroxyphenyl)-1-carbonyl] amino]-alanine, abbreviation: HN, molecular formula: C₁₂H₁₆N₂O₅) was synthesized as a linker between radionuclide iodine-125 (¹²⁵I) and NCs to enable a more efficient binding between NCs and radionuclides.

Results: In vitro evidence indicated that the linker was able to bind ¹²⁵I with higher efficiency (labeling efficiency >80%) than that of tyrosine, as well as various NCs, such as cellulose nanofibers, metal oxide NCs, and graphene oxide. Single-photon emission computed tomography/computed tomography imaging demonstrated the biological distribution of ¹²⁵I-labeled NCs in different organs/tissues after administration in mice.

Conclusion: These results showed an improvement in radionuclide labeling efficiency for nanocarriers and provided an approach for nanocarrier image tracing.

Keywords: SPECT/CT imaging; nanocarriers; radionuclide 125i; radionuclide labeling.

Figure 1

Schematic Diagram of HN Synthesis.

Figure 2

HN Synthesis HN synthesis procedure steps. i) Acetylation of compound 1 with Ac₂O in the presence of Py in DCM gave compound 2; ii) Reaction with compound 3 gave compound 4; iii) Deacetylation of compound 4 with NaOH gave compound 5 with 27.7% yield in MeOH; and iv) Boc-deprotection of compound 5 with TFA gave compound 6 with 94.1% yield in DCM.

Figure 3

Structure Analysis of HN Using 1H NMR Spectrum and LC-MS/MS (A)¹H NMR analysis of HN; (B) LC-MS/MS analysis of HN. Reaction product HN was detected using LC-MS/MS in positive ion mode to obtain its molecular weight.

Figure 4

Schematic Illustration and Verification of Iodogen Labeling for HN (A) Schematic illustration of iodogen labeling for HN. When one hydrogen atom in the ortho-position of benzene hydroxyl group is replaced with iodogen, a single iodine-labeled HN is formed, and when two hydrogen atoms are substituted, double iodine-labeled HN is formed; (B) Verification of iodogen labeling for HN. Reaction products containing HN, single iodine-labeled HN, and double iodine-labeled HN were detected using LC-MS/MS in positive ion mode to obtain their molecular weight.

Figure 5

The Electron Microscopy for NC Morphologies. (A) TEM and (B) AFM images of NCs. A drop of NC suspension (50 μg/mL) was placed on a grid or mica plate and then dried at room temperature for TEM or AFM observations.

Figure 6

SPECT/CT Images of ¹²⁵I-NCs in Different Nano–Bio Interfaces in Mice. (A)–(C) Distribution and retention of ¹²⁵I-NCs in mice were visualized using SPECT/CT imaging after different administration of ¹²⁵I-NCs 1 and 5 days post-injection; (D)–(F) Tissue distribution of ¹²⁵I-NCs determined using radioactivity assay.