title: [In-vivo tumor imaging by radiolabeled RNA probe targeting telomerase].
abstract: 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.
  
  
  CONCLUSIONS
  (99m)Tc radiolabeled telomerase-targeted siRNA probe allows for noninvasive visualization of tumor telomerase in vivo.
authors.affiliation: Department of Nuclear Medicine, Peking University First Hospital, Beijing 100034, China. rongfu_wang2003@yahoo.com.cn
authors.forename: Rong-fu
authors.initials: RF
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Kang
authors.forename: Xiao-jie
authors.initials: XJ
authors.lastname: Xu
authors.forename: Ping
authors.initials: P
authors.lastname: Yan
authors.forename: Chun-li
authors.initials: CL
authors.lastname: Zhang
authors.forename: Meng
authors.initials: M
authors.lastname: Liu
mesh_terms: D000818:Animals; D005260:Female; D007553:Isotope Labeling; D008114:Liver Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D057054:Molecular Imaging; D016376:Oligonucleotides, Antisense; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism* / Q000493:pharmacokinetics; D011877:Radionuclide Imaging; D017263:Technetium Tc 99m Mertiatide / Q000493:pharmacokinetics; D019098:Telomerase / Q000037:antagonists & inhibitors / Q000235:genetics*
chemical_list: D016376:Oligonucleotides, Antisense; D034741:RNA, Small Interfering; D017263:Technetium Tc 99m Mertiatide; C509186:TERT protein, human; D019098:Telomerase