title: The biological characterization of (99m)Tc-BnAO-NI as a SPECT probe for imaging hypoxia in a sarcoma-bearing mouse model.
abstract: OBJECTIVE
  Tumor growth beyond the region where vascular oxygen can reach creates a hypoxic domain. In this study, BnAO, a ligand that had been labeled with (99m)Tc-pertechnetate for hypoxia imaging, was conjugated with 2-nitroimidazole to give 3,3,10,10-tetramethyl-1-(2-nitro-1H-imidazo-1-y1)-4,9-diazadodecane-2,11- dionedioxime (BnAO-NI) as a potential ligand for hypoxia detection. Pentoxifylline is a peripheral vasodilator and has been used as a radiosensitizer in tumor radiotherapy. (99m)Tc-BnAO-NI/SPECT was applied to noninvasively assess the pharmacological effect of pentoxifylline in reducing tumor hypoxia in vivo.
  
  
  METHODS
  BnAO-NI was synthesized and formulated with methylene diphosphonate (MDP), stannous chloride and carbonate buffer to afford kits. After mixing with (99m)Tc-pertechnetate, (99m)Tc-BnAO-NI injection can be readily prepared. The partition coefficient, radiochemical purity and in vitro stability were determined. Cellular uptake of radiotracers in KHT cells under hypoxia was conducted in a CO(2) incubator at 37°C under hypoxia or normoxia. A biodistribution study after intravenous injection of (99m)Tc-BnAO-NI in KHT sarcoma-implanted C3H mice was performed. The effect of pentoxifylline (100 mg/kg) on reducing tumor hypoxia was also studied.
  
  
  RESULTS
  The radiochemical purity (RCP) of the (99m)Tc-BnAO-NI preparation was greater than 96% and stable at ambient temperature for 24h (RCP>90%). The accumulation of (99m)Tc-BnAO-NI and (99m)Tc-BnAO in KHT cells under hypoxia were 3.57 and 4.13-fold higher than those under normoxic environment, indicating unambiguous oxygen-dependent uptakes of these two probes. The distribution of (99m)Tc-BnAO-NI in KHT sarcoma-bearing mice revealed rapid clearance from the blood circulation. The tumor uptake peaked at 2h post-injection (0.32 ± 0.05%ID/g) with tumor-to-blood and tumor-to-muscle ratios of 10.32 and 3.96, respectively. The effect of pentoxifylline on the tumor blood perfusion was obvious. The tumor-to-muscle ratios at 2h post-injection of (99m)Tc-BnAO-NI with and without pentoxifylline pretreatment were 1.67 ± 0.38 and 2.59 ± 0.25, respectively (p = 0.025, n = 3).
  
  
  CONCLUSIONS
  This study demonstrates that (99m)Tc-BnAO-NI is a hypoxia-sensitive radio probe for monitoring hypoxic regions in a malignant neoplasm. However, (99m)Tc-BnAO-NI, though with higher lipophilicity than (99m)Tc-BnAO, did not achieve better specific accumulation in hypoxic tissues. (99m)Tc-BnAO-NI/SPECT could be applied in clinics to noninvasively evaluate the feasibility of using pentoxifylline as a radiosensitizer by reducing tumor hypoxia in vivo.
authors.affiliation: Institute of Biomedical imaging and Radiological Sciences, National Yang-Ming University, Taiwan.
authors.forename: Chien-Chung
authors.initials: CC
authors.lastname: Hsia
authors.forename: Fu-Lei
authors.initials: FL
authors.lastname: Huang
authors.forename: Guang-Uei
authors.initials: GU
authors.lastname: Hung
authors.forename: Lie-Hang
authors.initials: LH
authors.lastname: Shen
authors.forename: Chuan-Lin
authors.initials: CL
authors.lastname: Chen
authors.forename: Hsin-Ell
authors.initials: HE
authors.lastname: Wang
mesh_terms: D000818:Animals; D000860:Hypoxia / Q000000981:diagnostic imaging*; D051379:Mice; D008809:Mice, Inbred C3H; D015609:Organotechnetium Compounds; D012513:Sarcoma, Experimental / Q000000981:diagnostic imaging*; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D015609:Organotechnetium Compounds