Molecular imaging and pharmacokinetics of ^99mTc‐hTERT antisense oligonucleotide as a potential tumor imaging probe

Abstract

Targeting and visualization of human telomerase reverse transcriptase (hTERT) represents a promising approach for providing diagnostic value. The uptake kinetics and imaging results of (99m) Tc-hTERT antisense oligonucleotides (ASON) in hTERT-expressing cells were examined in vitro and in vivo. The pharmacokinetics and acute toxicity studies of (99m) Tc-hTERT ASON were also performed. The labeling efficiencies of radiolabeled oligonucleotide reached 76 ± 5%, the specific activity was up to 1850 kBq/µg, and the radiochemical purity was above 96%. Radioactivity accumulated to a higher concentration in hTERT-expressing cells with antisense probe than with sense control (p < 0.05). Lipid carrier incorporation significantly increased the transmembrane delivery of radiolabeled probes (p < 0.05). hTERT-expressing xenografts in nude mice were clearly visualized at 6 h postinjection of the antisense probe but not the sense control probe. However, liposome did not increase the radioactivity accumulation of probes in tumors for either antisense or sense probe (p > 0.05). Radioactivity counts per minute versus time profiles for (99m) Tc-hTERT ASON were biphasic, indicative of a three-compartment model. The pharmacokinetics parameters of half-life of distribution (T1/2α ), half-life of elimination (T1/2β ), total apparent volume of distribution (Vd), and total rate of clearance were 2.04 ± 0.48 min, 24 ± 4.8 min, 109.83 ± 17.20 mL, and 3.19 ± 0.17 mL/min, respectively. The acute toxicity study results showed the safe application of (99m) Tc-hTERT ASON in vivo. This study provides further evidences that (99m) Tc-hTERT ASON should be developed as a safe, potential molecular image-guided diagnostic agent.

Can Carrier-Mediated Delivery System Promote the Development of Antisense Imaging?

“…In addition, there was no significant difference in radioactivity accumulation between naked ASON and carrier-mediated ASON. These results demonstrated that Lipofectamine and Xfect TM transfection reagent could deliver the ASON into cells in vitro efficiently but not be effective in vivo, which was in accordance with a recent research [16].…”

“…In the present study, the cell accumulation of radiolabeled ASON probes increased significantly (pG0.05) after binding with transfection reagents. The increase in cellular uptake following binding with the carriers was in accordance with the previous studies [16,22]. Furthermore, The CLSM imaging showed that the fluorescence intensity in transfection groups (Lipo-ASON and Xfect-ASON) was clearly higher than that in controls…”

“…The ASON designed to conjugate with the mRNA of hTERT would reduce the expression of hTERT gene based on the complementary base-pairing mechanism [16,24]. To verify our results from the functional assay which showed that the cellular uptake rate of ASON was improved by transfection, we performed the RT-PCR and Western blot for the quantification of target mRNA and protein.…”

“…Pakunlu et al [14] demonstrated that PEGylated liposomes could be successfully applied for the cytoplasmic and nuclear delivery of ASON in vitro and in vivo. Recent reports have shown that cationic liposome Lipofectamine 2000 had been used in the studies of molecular imaging [15,16]. Nanoparticles were another drug carriers developed for the delivery of ASON, which could also be used for imaging in vivo [17,18].…”

Radiopharmaceuticals as probes to characterize tumour tissue

“…While telomerase per se could be targeted for imaging, this activity has not been reported in the field of PET. Liu et al have reported a SPECT probe for detecting human telomerase reverse transcriptase (hTERT), the major component of telomerase activity, using antisense oligonucleotides ( 99m TchTERT ASON) [114]. Though higher tracer accumulation was observed in vivo in MCF7 xenografts compared to labelled control sense oligonucleotides, image quality was compromised due to high background.…”