TAMRA-IL-13-Conjugated functionalized gadolinium metallofullerene (Gd3N@C80(OH)-26(CH2CH2COOH)-16)


Leung K.

Publication Details



In vitro Rodents



Magnetic resonance imaging (MRI) maps information about tissues spatially and functionally (1). Protons (hydrogen nuclei) are widely used to create images because of their abundance in water molecules, which comprise >80% of most soft tissues. The contrast of proton MRI images depends mainly on the nuclear density (proton spins), the relaxation times of the nuclear magnetization (T1, longitudinal; T2, transverse), the magnetic environment of the tissues, and the blood flow to the tissues. However, insufficient contrast between normal and diseased tissues requires the use of contrast agents. Most contrast agents affect the T1 and T2 relaxation times of the surrounding nuclei, mainly the protons of water. T2* is the spin–spin relaxation time composed of variations from molecular interactions and intrinsic magnetic heterogeneities of tissues in the magnetic field. Cross-linked iron oxide nanoparticles and other iron oxide formulations affect T2 primarily and lead to a decreased signal (2). On the other hand, paramagnetic T1 agents, such as gadolinium (Gd3+) and manganese (Mn2+), accelerate T1 relaxation and lead to brighter contrast images.

Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor, with a median survival of ~1 year for GBM patients (3). The GBM tumor is highly invasive and resistant to treatment with radiation and chemotherapy. GBM tissues (~50%) have been reported to overexpress the interleukin-13 receptor α2 subunit (IL-13Rα2) relative to normal brain tissues (4). Debinski et al. (5) identified residues of IL-13 that bind specifically to IL-13Rα2. Fillmore et al. (6) designed a peptide (VDKLLLHLKKLFREGQFNRNFESIIICRDRT-OH, denoted as the IL-13 peptide) based on these residues, then attached a TAMRA fluorescent label and conjugated the IL-13 peptide to a functionalized (carboxylated/hydroxylated) Gd-metallofullerene carbon cage (TAMRA-IL-13-f-Gd3N@C80). TAMRA-IL-13-f-Gd3N@C80 has been studied for MRI of IL-13Rα2 expression on glioma tumors in mice.



Synthesis of Gd3N@C80(OH)-26(CH2CH2COOH)-16 (f-Gd3N@C80) was reported by Shu et al. (7). There were 3 Gd3+, 26 hydroxyl, and 16 carboxyl moieties per metallofullerene. f-Gd3N@C80 exhibited a hydrodynamic diameter of ~78 nm. The r1 and r2 relaxivity values (2.4 T) of f-Gd3N@C80 in phosphate-buffered saline (PBS, pH 7.4) at room temperature were 35 mM−1s−1 and 62 mM−1s−1, respectively. Fillmore et al. (6) prepared TAMRA-IL-13-f-Gd3N@C80 by conjugation of 7.5 nmol TAMRA-IL-13 peptide (4 kDa, obtained from New England Peptide, MA) to f-Gd3N@C80 (6.5 nmol) in the presence of N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide and N-hydroxysuccinimide in PBS for 18 h at room temperature. Polyacrylamide electrophoresis of TAMRA-IL-13-f-Gd3N@C80 showed the UV (550 nm excitation) visualization of TAMRA-IL-13 peptide attachment to f-Gd3N@C80. There were three to four TAMRA-IL-13 peptides per metallofullerene. The hydrodynamic diameter, zeta potential, and in vitro MRI characterization of TAMRA-IL-13-f-Gd3N@C80 were not reported.

In Vitro Studies: Testing in Cells and Tissues


Fillmore et al. (6) performed cellular uptake studies of TAMRA-IL-13-f-Gd3N@C80 (1.2 µM) and f-Gd3N@C80 (1.2 µM) in human glioma U87MG cells. U87MG cells treated with TAMRA-IL-13-f-Gd3N@C80 accumulated more Gd (882.3 pmol of Gd/105 cells) at 3 h after incubation than did U87MG cells treated with f-Gd3N@C80 (13.6 pmol of GD/105 cells) at the same time point. The cell viability was not affected by either agent at 3 h and 6 h after incubation. No blocking or in vitro MRI experiments were performed.

Animal Studies



Fillmore et al. (6) performed MRI (2.4 T) in nude mice (number of mice not reported) bearing an orthotopic U87MG xenograft. TAMRA-IL-13-f-Gd3N@C80 (amount administered not reported) was infused intratumorally by convection-enhanced delivery (CED) at 10 d after injection of tumor cells into the brain. There was a bright contrast at the infusion site immediately with T1-weighted MRI, compared to that at 12 h prior to CED infusion. At 24 h after infusion, MRI showed a visible contrast area (2.5 mm in diameter) at the tumor infusion site. Confocal microscopy images of the TAMRA fluorescent signal were co-localized with the tumor lesions. The investigators concluded that further studies are needed to assess the specificity of TAMRA-IL-13-f-Gd3N@C80 binding to IL-13Rα2.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

NIH Support

1R01-CA119371 R01 CA119371, 5P30 NS047463


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