Magnetic resonance imaging visualization of targeted cells by the internalization of supramolecular adducts formed between avidin and biotinylated Gd3+ chelates

Abstract

The high binding affinity between avidin and biotin has been exploited to develop a procedure for magnetic resonance imaging (MRI) visualization of target cells. SHIN3 and PANC1 tumor cell lines have been used as target cells because they possess on their membranes galactosyl receptors able to bind avidin molecules. Avidin-Gd chelate adducts have been built by using two Gd complexes containing one (Gd-I) and two (Gd-II) biotin residues, respectively. The relaxivities of such supramolecular adducts are significantly higher than those shown by free Gd-I and Gd-II. There is evidence of the occurrence of multilayered adducts in which the bis-biotinylated Gd(3+) complex acts as a bridge between adjacent avidin molecules. MRI differentiation of labeled versus unlabeled cells has been attained when approximately 6 x 10(8) Gd units were internalized in each cell. Furthermore, there is a marked decrease in the measured intracellular T(1) relaxivity as the number of internalized Gd complexes increases, probably owing to too short relaxation times of endosomic water protons with respect to their diffusion lifetime.

An iron-based T 1 contrast agent made of iron-phosphate complexes: In vitro and in vivo studies

“…Gd 3+ complexes have received most attention as contrast agents for MRI applications due to their large magnetic moment and a suitable long electronic relaxation time. However, there is no natural human biochemistry for Gd 3+ that can be exploited when designing its contrast agents derivates (3)(4)(5)(6). On the other hand, agents based on Mn 2+ , Fe 3+ , and Cu 2+ ions are attractive alternatives (7)(8)(9) because these metals are already present in tissues and there is extensive information available about their human biochemistry, including transport, storage, compartmentalization and excretion mechanisms.…”

“…The complex [(tacn) 6 Fe 8 (µ 3 -O) 2 (µ 2 -OH) 12 ]Br 8 · 9H 2 O, where tacn = 1,4,6-triazacyclononane, and hereafter referred to as Fe 8 , was chosen by us in order to study its potential as contrast agent (13). Due to the size of Fe 8 molecules, the distribution and residence time in the tissues should be different and produce complementary information to that given by Gd-based chelates and iron oxide nanoparticles.…”

Harnessing Competing Endocytic Pathways for Overcoming the Tumor-Blood Barrier: Magnetic Resonance Imaging and Near-Infrared Imaging of Bifunctional Contrast Media

“…Subsequent in vitro studies showed that biotin-BSA-GdDTPA was effectively internalized by fibroblasts using caveolae mediated uptake, which could be suppressed by treatment with nystatin(9), (11). Upon internalization, the material is sequestered within small intracellular vacuoles leading to suppressed MRI relaxivity, which is regained only after the material is redistributed in the cells with cell division (12) (9). The contrast material did not extravasate into the interstitial space within the tumor nodules (9).…”

Target Visualization by MRI Using the Avidin/Biotin Amplification Route: Synthesis and Testing of a Biotin–Gd‐DOTA Monoamide Trimer

“…[9] Moreover, in the case of well-spaced bisbiotinylated compounds the formation of long chain polymers is, in part, hampered by the occurrence of intramolecular linkages, as previously shown in the case of biotin-DTPA dimers. [10] Therefore, molecules with three biotin moieties have to be designed to allow the formation of polymeric chains. Furthermore, we have to take into account not only that two of the three biotin moieties in tribiotinylated compounds would bind to the same protein molecule, but also the space needed for the insertion of three Gd III -DOTAMA complexes.…”

“…[10] Gd-DTPA-like complexes (DPTA = diethylenetriamine pentaacetic acid) containing one and two biotin residues were synthesized and their adducts with avidin were tested in vitro. Evidence for the occurrence of multilayered adducts in which the bisbiotinylated Gd III complex bridged adjacent avidin molecules was obtained.…”