Combination of transfection agents and magnetic resonance contrast agents for cellular imaging: relationship between relaxivities, electrostatic forces, and chemical composition.

The purpose of this study was to investigate the changes in electrostatic and magnetic resonance (MR) properties observed when MR contrast agents (CAs) (Feridex, MION-46L, or G5-dendrimer-DOTA-Gd) are combined with transfection agents (TAs) under various conditions for use as a CA-TA complex basis for cellular labeling and MRI. CAs were incubated with various classes of TAs for 0-48 hr in solutions of varying concentrations and pH values. NMR relaxation rates (1/T(1), 1/T(2)), MRI and zeta potential (ZP) of CA-TA solutions were measured. TAs decreased the 1/T(1) and 1/T(2) of G5-DOTA-Gd, Feridex, and MION-46L by 0-95%. Altering the pH of G5-DOTA-Gd-TA decreased the T(1)-weighted signal intensity (SI) on MRI from 0 to 78%. Measured ZP values for G5-DOTA-Gd, Feridex, and MION-46L were -51, -41, and -2.0 mV, respectively. The TA LV had a negative ZP, while the other TAs had ZPs ranging from +20 to +65 mV. The alteration of the ZP and NMR relaxivities of the MR CAs, Feridex, MION-46L, and G5-DOTA-Gd by TAs has been demonstrated. These results enhance our understanding of the relationship between electrostatic and MR properties.