A simple approach to a new T₈-POSS based MRI contrast agent

Area of Science:

• Materials Science
• Nanotechnology
• Radiology

Background:

• Polyhedral oligosilsesquioxanes (POSS) are explored as carriers for contrast agents.
• T8-silsesquioxane cages can be susceptible to hydrolysis, affecting agent stability.
• Developing stable and effective MRI contrast agents is crucial for medical diagnostics.

Purpose of the Study:

• To synthesize a novel T8-silsesquioxane based contrast agent for MRI.
• To evaluate the relaxivity and stability of the new agent under physiological conditions.
• To compare the new agent with clinically used contrast agents.

Main Methods:

• Synthesis of a C2-thiol-functionalized T8-silsesquioxane carrier.
• Preparation of a DOTA-based gadolinium(III) complex with allyl linkers.
• UV-light catalyzed thiol-ene click reaction for agent conjugation.
• Relaxivity measurements (r1) at 3 T and pH-dependent stability studies.
• Spectroscopic (NMR) and mass spectrometry for characterization.

Main Results:

• A new T8-silsesquioxane-based MRI contrast agent (13) was synthesized in 80% yield via a rapid thiol-ene click reaction.
• Compound 13 exhibited significantly enhanced longitudinal relaxivity (r1 = 9.5 ± 0.9 mM-1 s-1) compared to Dotarem™.
• The T8-cage of agent 13 demonstrated improved stability in neutral pH buffered solutions (t1/2 = 2.4 days) versus Gadoxane G, but accelerated decomposition under basic conditions.

Conclusions:

• A facile and efficient method for creating T8-silsesquioxane-based MRI contrast agents was established.
• The novel agent shows promising relaxivity and enhanced stability at physiological pH.
• Further investigation into the pH-dependent stability is warranted for clinical translation.