MRI detection of tumor cells by targeting LDL receptors with Gd-loaded LDL particles

Gd-DO3A-diph and Gd-AAZTA-C17 are lipophilic Magnetic Resonance Imaging (MRI) agents that display high affinity for LDL particles. However, upon binding to LDL, Gd-DO3A-diph shows a decreased hydration that results in a lower enhancement of water proton relaxation rate. Conversely, Gd-AAZTA-C17 displays a strong relaxation enhancement at the imaging fields. Each LDL particle can load up to 100 and 400 units of Gd-DO3A-diph and Gd-AAZTA-C17 respectively. Their LDL adducts are uptaken by HepG2 and B16 tumor cells when added to the incubation medium. T1-measurements of the labeled cells indicate that Gd-AAZTA-C17 is significantly more efficient than Gd-DO3A-diph. Furthermore, it has been found that HepG2 hepatoma cells can internalize higher amounts of Gd-AAZTA-C17 than B16 cells and the involvement of LDL receptors (LDLRs) has been demonstrated in competition assays with free LDL. Gd-AAZTA-C17/LDL adduct proved to be an efficient probe in the MR-visualization of subcutaneous tumors in animal models obtained by injecting B16 melanoma cells into the right flank of mice. Finally, confocal microscopy validation of the distribution of LDL-based probes in the tumor has been obtained by doping the Gd-AAZTA-C17/LDL adduct with a fluorescent phospholipid moiety.