Magnetic resonance tumor targeting imaging using gadolinium labeled human telomerase reverse transcriptase antisense probes

Abstract

To develop a molecular probe for MRI detection of human tumor telomerase reverse transcriptase (hTERT) mRNA expression. Uniformly phosphorothioate‐modified hTERT antisense oligonucleotide (ASON) homing hTERT mRNA was labeled with gadolinium (Gd) through the bifunctional chelator 1,4,7, 10‐tetraazacyclododecane‐N, N', N'', N'''‐tetraacetic acid (DOTA) stirred within 45 minutes at 60°C. The Gd labeled probes were characterized in vitro. The cellular uptake rate and biodistribution of 99mTc‐DOTA‐ASON was measured instead of that of Gd‐DOTA‐ASON. A549 lung adenocarcinoma model was established in BALB/c nude mice and Gd‐DOTA‐ASON was injected intraperitoneally and MR images were acquired using 7.0T Micro‐MRI (Bruker Biospec, Ettlingen, Germany) at different time points. Immunohistochemical analysis of telomerase activity of each xenograft was operated two days after in vivo imaging. The binding efficiency of Gd‐DOTA‐ASON reached as high as 71.7 ± 4.5% (n = 6). Gd‐DOTA‐ASON displayed perfect stability in fresh human serum at 37°C for 24 h. Compared with normal lung cells, A549 cells showed an obviously higher uptake of 99mTc‐DOTA‐ASON than that of lung cells (10.5 ± 2.7% vs. 4.8 ± 2.6%, P < 0.05). The signal intensity of A549 xenografts can be enhanced by Gd‐DOTA‐ASON and the signal to noise ratio (SNR) of tumor to muscle reached 2.37 and maintained a relatively high level within 6 h after injection. The activity of hTERT in A549 tumors can be suppressed by Gd‐DOTA‐ASON in pathological slices. The results of this study show that Gd‐DOTA‐ASON can be a promising intracellular MR contrast probe for targeting telomerase‐positive carcinomas. (Cancer Sci, doi: 10.1111/j.1349‐7006.2012.02316.x, 2012)

Advance of Molecular Imaging Technology and Targeted Imaging Agent in Imaging and Therapy

“…Tumors (arrows) all showed different enhancement level at 0.5 h, but in Gd-DOTA-ASON (upper line), the enhancement remained at 6 h, while Gd-DTPA (middle line) decreased obviously from 2 h (repetition time, 561 ms, echo time, 14 ms, and field of view, 4 cm); Gd-DOTA-SON (lower line) showed a similar trend to that of Gd-DOTA-ASON but with lower enhancement (adopted from Ren et al [61]).…”

“…18 F-FDG is the most widely used imaging agent based on small molecules, which is clinically applied for cancer imaging [ 60 ]. Ren et al [ 61 ] reported the use of gadolinium (Gd) to label uniformly phosphorothioate-modified human tumor telomerase reverse transcriptase (hTERT) antisense oligonucleotide (ASON) targeting hTERT mRNA and conducted a study in BALB/c nude mice with 7.0T Micro-MRI, showing that Gd-DOTA-ASON was a potential intracellular MR contrast probe for detection of telomerase-positive carcinomas ( Figure 6 ).…”

Radiolabeling of functional oligonucleotides for molecular imaging

“…In 2012, Ren et al reported the 99m Tc radiolabeling of human tumor telomerase reverse transcriptase hTERT antisense oligonucleotide through a bifunctional chelator DOTA. In this approach, the ASO sequence was conjugated with DOTA-NHS at the 3′-end amine with more than 85% radiochemical purity ( Ren et al, 2012 ).…”

Radiolabeling of Nucleic Acid Aptamers for Highly Sensitive Disease-Specific Molecular Imaging

“…In 2012, Ren et al reported the 99m Tc radiolabeling of hTERT (human tumor telomerase reverse transcriptase) antisense oligonucleotide (ASON) through the bifunctional chelator DOTA. The ASON sequence, 5′-TAG AGA CGT GGC TCT TGA-3′, was conjugated with DOTA–NHS via the amine-functionalization of the oligonucleotides at the 3′-end [51]. DOTA–NHS–ester was prepared using the published procedure [52,53].…”

“…Then, the semistable amino-reactive intermediate DOTA–NHS–ester was added to ASON and radiolabeled by 99m TcO 4 − with SnCl 2 at room temperature (Figure 7). The reported radiochemical purity was 85% [51]. Calzada et al successfully linked both 99m Tc and 67 Ga to an aptamer (Sgc8) through the HYNIC and DOTA chelators, which showed desirable biodistribution and pharmacokinetic properties [47].…”