Radiolabeled Silicon-Rhodamines as Bimodal PET/SPECT-NIR Imaging Agents

Area of Science:

• Biomedical Imaging
• Organic Chemistry
• Radiochemistry

Background:

• Radiolabeled fluorescent dyes are crucial for bimodal imaging, combining nuclear and optical techniques.
• Silicon-rhodamines (SiRs) offer desirable near-infrared (NIR) optical properties, including high quantum yields, extinction coefficients, and photostability.

Purpose of the Study:

• To synthesize, characterize, and radiolabel novel NIR-emitting silicon-rhodamine (SiR) fluorophores.
• To evaluate their potential as multimodal imaging agents for optical imaging (OI) combined with positron emission tomography (PET) or single photon emission computed tomography (SPECT).

Main Methods:

• Synthesis and characterization of novel SiR dyes using NMR, UV-Vis-NIR spectroscopy, and mass spectrometry.
• Optimization of radiolabeling conditions for fluorine-18 and iodine-123 incorporation.
• In vitro stability assessment of radiofluorinated SiRs in human serum.

Main Results:

• Optimized radiofluorination achieved radiochemical conversions (RCC) up to 70% and radiochemical yields (RCY) up to 54% (molar activity > 70 GBq/µmol).
• Radioiodination yielded RCCs over 92% and isolated 123I-labeled SiRs in 54% RCY (molar activity > 7.6 TBq/µmol).
• Radiofluorinated SiRs demonstrated in vitro stability exceeding 70% after 2 hours in human serum.

Conclusions:

• The developed radiolabeled SiRs are the first of their kind for multimodal PET/SPECT-NIR imaging.
• These novel agents represent a significant advancement for imaging-guided oncological surgery planning and execution.