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 (99m) Tc-
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 (99m) Tc-
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.