Side-Chain Effects on the MRI and Optical Properties of Bimodal Imaging Agents

In the management of cancer distinguishing tumor margins is an ongoing issue that can lead to insufficient removal of cancerous cells or excision of healthy tissue. To overcome this, bimodal imaging agents can be used for preoperative MR imaging to localize the bulk of a tumor, while intraoperative fluorescence imaging illuminates tumor margins for more accurate removal of diseased tissue. Lanthanide ions such as Tb(III) and Eu(III) display luminescent capabilities with long-lived luminescence lifetimes, and when chelated with a chromophore containing ligand, these compounds have the potential to act as both MR and optical imaging probes. The goal of this study is to evaluate the effect of varying ligand side-chains on the MRI and optical properties of europium and terbium complexes. To this end, three pyridine-containing ligands have been synthesized and characterized. Their respective Ln(III) complexes have been prepared, and the luminescent properties have been evaluated. We have found that the intensity of the emission is affected by ligand side-chain identity while the excitation and absorption properties are unaffected. Using phosphorescence lifetime measurements, each compound was estimated to have one bound water molecule, a necessary attribute to produce MRI contrast. Future work will include investigation of the MRI properties of these metal complexes.