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Updated: May 12, 2026
Semi-quantitative Detection of RNA-dependent RNA Polymerase Activity of Human Telomerase Reverse Transcriptase Protein
Published on: June 12, 2018
[In-vivo tumor imaging by radiolabeled RNA probe targeting telomerase]
Rong-fu Wang1, Lei Kang, Xiao-jie Xu
1Department of Nuclear Medicine, Peking University First Hospital, Beijing 100034, China. rongfu_wang2003@yahoo.com.cn
Objective:
To explore the value of telomerase targeted radiolabeled small interference RNA (siRNA) in tumor imaging in vivo.
Methods:
Human telomerase reverse transcriptase (hTERT)-targeted and human gene non-targeted siRNAs were chemically synthesized. Through the conjugation with the chelator N-hydroxysuccinimidyl derivative of S-acetylmercaptoacetyltriglycine (NHS-MAG3), the siRNAs were radiolabeled with technetium-99m ((99m)Tc). HE staining and immunohistochemical staining were used to identify their pathological characteristics. 7.4 MBq of (99m)Tc-siRNAs were injected via the tail vein of hepatocarcinoma bearing mice. At 0.5, 1, 3, and 6 h post injection, the mice were laid on a face-up detector and imaged by single-photon emission computed tomography (SPECT), respectively. The ratio of radioactive counts in tumor to that in the contralateral equivalent region was calculated by drawing regions of interest (ROI) at each time point. After the administration of 7.4 MBq of (99m)Tc-siRNAs, the biodistribution (%ID/g) of tumors and blood was measured at the end of 2, 4 and 6 h. Statistical comparisons of the variables were performed by t-test.
Results:
The labeling efficiency reached 73.4% ± 3.0%. After purification, the radiochemical purity was no less than 92% and the specific activity was up to 25.9 GBq/μmol. HE staining showed pathological mitotic figure in the nucleus of the tumor cells. hTERT immunohistochemical staining showed deep brown dyed spots in the cell nucleus. hTERT-targeted (99m)Tc-siRNA administrated xenografts showed tumor images clearly after the administration, especially at 6 h. In contrast, (99m)Tc-control-siRNA showed no tumor image. The ratios of uptake in tumor to that in contralateral region of hTERT-targeted siRNA increased from 2.68 ± 0.21 to 5.86 ± 0.30 at 6 h, whereas those of control siRNA decreased from 1.55 ± 0.16 to 1.28 ± 0.12 (P<0.01). The biodistribution of tumors in the hTERT-targeted mice increased from 0.71 ± 0.14 to 0.97 ± 0.15 at 6 h, whereas that in the control mice decreased.
Conclusion:
(99m)Tc radiolabeled telomerase-targeted siRNA probe allows for noninvasive visualization of tumor telomerase in vivo.
Insights
Technetium-99m labeled telomerase-targeted small interference RNA (siRNA) successfully visualized tumors in vivo. This novel radiotracer enables noninvasive imaging of tumor telomerase activity.
Area of Science:
- Molecular Imaging
- Oncology
- Biotechnology
Background:
- Telomerase is a key enzyme in tumor development and progression.
- Targeting telomerase offers a potential strategy for cancer diagnosis and therapy.
- Developing effective imaging probes for telomerase is crucial for in vivo tumor detection.
Purpose of the Study:
- To evaluate the efficacy of technetium-99m ((99m)Tc) radiolabeled telomerase-targeted small interference RNA (siRNA) for in vivo tumor imaging.
- To assess the specificity and sensitivity of the (99m)Tc-siRNA probe in detecting tumors.
- To explore the potential of this probe for noninvasive visualization of telomerase activity in cancer.
Main Methods:
- Synthesis and radiolabeling of human telomerase reverse transcriptase (hTERT)-targeted and control siRNAs with (99m)Tc.
- In vivo SPECT imaging of hepatocarcinoma-bearing mice after intravenous injection of the radiolabeled siRNAs.
- Quantification of tumor uptake and biodistribution using regions of interest (ROI) analysis and ex vivo measurements.
- Histological analysis (HE staining and immunohistochemistry) to confirm tumor characteristics and hTERT expression.
Main Results:
- High labeling efficiency (>73%) and radiochemical purity (>92%) were achieved for the (99m)Tc-siRNA probes.
- hTERT-targeted (99m)Tc-siRNA demonstrated clear tumor imaging, particularly at 6 hours post-injection.
- Tumor-to-contralateral region ratios significantly increased for targeted siRNA (from 2.68 to 5.86, P<0.01), unlike control siRNA.
- Biodistribution studies confirmed increased tumor accumulation of the targeted siRNA over time.
Conclusions:
- Technetium-99m radiolabeled telomerase-targeted siRNA serves as a viable probe for noninvasive in vivo tumor imaging.
- The probe allows for visualization of tumor telomerase activity, offering potential for early cancer detection and monitoring.
- This approach holds promise for advancing molecular imaging in oncology.
